The liberation of refractory precious metals associated with PbSO 4 /BaSO 4 by carbonation and comprehensive recovery in copper anode slime refinery

The liberation of refractory precious metals associated with PbSO 4 /BaSO 4 by carbonation and comprehensive recovery in copper anode slime refinery | Research Square window.SnipcartSettings = { analytics: { enabled: false } }; (function() { var accessVector = localStorage.getItem('access_vector') || ''; window.dataLayer = window.dataLayer || []; if (accessVector) { window.dataLayer.push({ user: { profile: { profileInfo: { snid: accessVector } } } }); } })(); (function(w,d,s,l,i){w[l]=w[l]||[];w[l].push({'gtm.start':new Date().getTime(),event:'gtm.js'});var f=d.getElementsByTagName(s)[0],j=d.createElement(s),dl=l!='dataLayer'?'&l='+l:'';j.async=true;j.src='https://www.googletagmanager.com/gtm.js?id='+i+dl;f.parentNode.insertBefore(j,f);})(window,document,'script','dataLayer','GTM-K279D39R'); Browse Preprints In Review Journals COVID-19 Preprints AJE Video Bytes Research Tools Research Promotion AJE Professional Editing AJE Rubriq About Preprint Platform In Review Editorial Policies Our Team Advisory Board Help Center Sign In Submit a Preprint Cite Share Download PDF Article The liberation of refractory precious metals associated with PbSO 4 /BaSO 4 by carbonation and comprehensive recovery in copper anode slime refinery Zhizhong Liu, Xinhuang Yu, Shuchen Qin, Yuanhao Ren, Rui Ning, and 2 more This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-8390297/v1 This work is licensed under a CC BY 4.0 License Status: Posted Version 1 posted You are reading this latest preprint version Abstract In copper anode slime hydrometallurgical plant, Au and Ag are recovered by perchloric leaching and ammonia leaching, stepwisely and respectively. However, their recovery is incomplete with a significant amount of refractory Au/Ag remaining in ammonia leaching residue, encapsulated by PbSO 4 and BaSO 4 . These gold and silver can only be released by the removal of PbSO 4 /BaSO 4 , which can be realized by Na 2 CO 3 carbonation and the subsequent HCl leaching. In this work, a process flowsheet has been designed to recover Au/Ag in ammonia leaching residue and individual PbSO 4 and BaSO 4 products were also obtained with extra value. The cost of this process can be greatly reduced by Na 2 CO 3 recycling between the two-stage Ba carbonation and one-stage Pb carbonation with freezing crystallization of Na 2 CO 3 . Physical sciences/Chemistry Earth and environmental sciences/Environmental sciences Copper anode slime Ammonia leaching residue Carbonation PbSO4 BaSO4 Figures Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 Figure 6 Introduction Globally, the demand for precious metals, specifically gold (Au), silver (Ag), platinum (Pt), palladium (Pd), and other platinum group metals (PGM) is growing in recent decades. Copper anode slime is an important resources of precious metals 1 – 3 . Several semi-hydrometallurgical flowsheets have been developed to process copper anode slime 4 – 6 , one of which stepwisely consists of sulfuric acid roasting with vaporization of Se 4,7–9 and subsequent leaching of Cu, perchloric acid leaching of Au/PGM/Te 10 , and ammonia leaching of Ag 11 . There are still various valuable metals, including the refractory precious metals and Sn/Sb/Bi/Pb/Ba, remaining in ammonia leaching residue. The remaining precious metals are primarily encapsulated in PbSO 4 /BaSO 4 , thus it is necessary to dissolve these two types of sulfates in order to fully recover precious metals in ammonia leaching residue. At present, ammonia leaching residue is mainly treated by returning to coppper smelting plant. Smelting has the advantage of high recovery of precious metals. However, most of Sn/Ba and part of Sb/Bi/Pb will be lost in the smelting slag. Herein, we proposed a flowsheet (Fig. 1 ) for comprehensive recovering valuable metals from ammonia leaching residue. The core is to effectively remove Pb and Ba, unlock the encapsulation of Au/Ag by PbSO 4 and BaSO 4 , greatly improve the recovery of Au and Ag, and obtain Au/Ag products, Pb products, Ba products, Bi products and Sb/Sn products step by step, so as to realize the comprehensive recovery of valuable metals in ammonia leaching residue. Moreover, it has to connect with the existing mainstream in hydrometallurgical precious metal plant, without any complicated equipment. This flowsheet adopts the carbonation conversion of PbSO 4 /BaSO 4 to PbCO 3 /BaCO 3 , which are both soluble by hydrochloric acid leaching. Specifically, PbSO 4 is transformed into PbCO 3 by using the crystallization mother liquor of the solution after barium conversion, and then it is heated and leached by HCl. Lead enters the solution as PbCl 2 . The solubility of PbCl 2 is slightly small, and even smaller at lower temperature; therefore, it is leached by hydrochloric acid with high liquid-solid ratio, and the solution is heated to increase its solubility. Then, PbSO 4 is precipitated by H 2 SO 4 , and HCl is regenerated for recycling. Thereafter, BaSO 4 is converted to BaCO 3 with a large Na 2 CO 3 /Na 2 SO 4 ratio. After conversion, relatively pure Na 2 CO 3 is obtained by crystallization and recycled, and the mother liquor is recycled for Pb carbonation. Hydrochloric acid with small liquid-solid ratio is used to leach the conversion slag because BaCl 2 has a greater solubility, and H 2 SO 4 is also used to precipitate BaSO 4 , and HCl is regenerated for recycling to realize Ba removal. Afterwards, Bi is leached by H 2 SO 4 +NaCl 12,13 , and BiOCl was obtained by neutralizing and precipitating using Na 2 CO 3 /Na 2 SO 4 mixture solution after Pb carbonation. The residue after removing Pb and Ba is mainly SnO 2 -Sb 2 O 4 enrichment, and Au/Ag are also enriched. The Au/Ag extraction can be achieved by NaClO 3 +HCl+NaCl oxidative leaching 14 , which is then incorporated into the existing Au/Ag process in the main stream of the plant. After leaching precious metals, if the value of Sb/Sn is high, a small rotary kiln can be used for weak reduction roasting to convert Sb 2 O 4 into Sb 2 O 3 which enters the dust 15 , achieving Sb/Sn separation. In this work, the effects of Na 2 CO 3 /Na 2 SO 4 ratioon carbonation of Pb/Ba and the recyling of Na 2 CO 3 by freezing crystallization were especially investigated in this work. The change in the mineralogy of sample in the flowsheet was studied using XRD and chemical phase analysis techniques. Materials and Methods The ammonia leaching residue produced by Copper Anode Slime plant of Daye Nonferrous Enterprise, as shown in Fig. 2, was used in this work as feed. The composition for the elements of interest is shown in Table 1, the chemical phase analysis of Pb/Ba is shown in Table 2, and the XRD analysis is shown in Fig. 3. It can be seen that the ammonia leaching residue contains a significant amount of BaSO 4 and (Pb,Ba)SO 4 . The gold and silver are encapsulated by these sulfates, which is difficult to achieve effective leaching. It is necessary to break the encapsulation by dissolution of BaSO 4 and (Pb,Ba)SO 4 and recover Au/Ag and Pb/Ba. In addition, Sb and Bi also have certain comprehensive recovery value. While, the Sn content is relatively low, so its separation and recovery will not be considered at the moment of research. Table 1 Elemental analysis of ammonia leaching residue（%） Pb Ba As Bi Sb Sn 31.95 22.43 1.13 3.75 4.09 0.95 Table 2 Chemical phase analysis of Pb/Ba in ammonia leaching residue（%） Ba Silicate Sulfate Carbonate Total Ba 2.291 23.8 0.019 26.11 Pb Sulfide Oxide Sulfate Co-sulfate with Ba Total Pb 3.06 25.41 0.33 1.81 30.61 The elemental content in the samples was determined by ICP-OES (Inductively Coupled Plasma Optical Emission Spectrometry, Thermo Fisher Scientific Inc., US). For solid, samples were dissolved using a specific volume of aqua regia (prepared with ultrapure nitric acid and hydrochloric acid in a 1:3 volume ratio), evaporated to dryness, diluted to a constant volume with 5% nitric acid, and finally subjected to ICP analysis to determine the concentration of metal ions in the solution. The content of Na 2 CO 3 and Na 2 SO 4 was determined by titration. A small amount of solid crystallite was dissolved into 50ml water, which was titrated with 0.1M HCl solution until the solution turns from red to colorless using phenolphthalein as an indicator. During this process, Na 2 CO 3 in the solution is neutralized to NaHCO 3 . Then add methyl orange as indicator, continue to titrate with 0.1M HCl solution until the solution changes from yellow to orange, indicating that NaHCO 3 in the solution is completely neutralized to H 2 CO 3 , and record the amount of hydrochloric acid. If the amounts of hydrochloric acid used in the two processes are equal, the average value shall be taken to calculate the content of sodium carbonate. After boiling the remaining solution for 1min, add a concentrated barium chloride solution, shake and wait for the upper solution to become clear before adding another drop of barium chloride solution. If there is precipitation, repeat the above steps until there is no precipitation. Filter and dry the barium sulfate precipitation and weigh it to calculate the sodium sulfate content. Reactions The Pb in ammonia leaching residue mainly exists in the form of PbO and PbSO 4 . The removal of Pb from ammonia leaching residue relies on the difference in solubility product between PbSO 4 and PbCO 3 : at 25℃, the solubility product of PbSO 4 is 1.6×10 -8 , and the solubility product of PbCO 3 is 7.4×10 -14 , realizing the transformation from PbSO 4 to PbCO 3 . The main reactions are as follows: PbSO 4 + Na 2 CO 3 = Na 2 SO 4 + PbCO 3 The concentration of Na 2 SO 4 in the Pb carbonation solution will become higher after several cycles of accumulation, which will finally deteriorate the carbonation effect. Moreover, Na 2 SO 4 will block the pipeline in the industrial production during cooling, so the part of the solution after carbonation must sent to freezing crystallization, generating Na 2 SO 4 ¡10H 2 O product. The Pb in carbonation residue mainly exists in the form of PbCO 3 which can be leached into the solution by HCl. PbCO 3 + 2HCl = PbCl 2 + H2O +CO 2 The Pb removal residue is then sent for Ba removal; while PbSO 4 is precipitated by adding H 2 SO 4 in the leaching solution of PbCl 2 , and the regenerated HCl is returned to leach PbCO 3 . Main reactions: PbCl 2 + H 2 SO 4 = PbSO 4 ↓ + 2HCl The Ba mainly exists in the form of BaSO 4 in the Pb removal residue. The core of barium carbonation process is the solubility product balance of [Ba 2+ ][SO 4 2- ]/[Ba 2+ ][CO 3 2- ]: Although the solubility product of BaSO 4 is 1.08×10 -10 and that of BaCO 3 is 8.1×10 -9 at 25 ℃, if solid BaSO 4 and concentrated Na 2 CO 3 solution are boiled together, BaSO 4 can be converted to BaCO 3 . That is to control the high concentration of carbonate ions so that [Ba 2+ ][CO 3 2- ] is greater than the solubility product of BaCO 3 , so that barium carbonate can be precipitated, while [Ba 2+ ][SO 4 2- ] is reduced to less than the solubility product of BaSO 4 , so that more BaSO 4 can be dissolved. The transformation from BaSO 4 to BaCO 3 was realized by controlling the leaching conditions. BaSO 4 + Na 2 CO 3 ⇋BaCO 3 +Na 2 SO 4 The Ba in carbonation residue is mainly BaCO 3 , and Ba in BaCO 3 is leached into solution by HCl. BaCO 3 + 2HCl = BaCl 2 + H 2 O +CO 2 The Ba removal residue obtained by leaching is sent for the Au/Ag recovery; while the H 2 SO 4 was added to BaCl 2 leaching solution to precipitate BaSO 4 , and regenerated HCl returns to leach BaCO 3 . Main reactions: BaCl 2 + H 2 SO 4 = BaSO 4 ↓ + 2HCl Results and discussion 4.1 PbSO 4 carbonation and leaching First, exploratory tests were carried out for PbSO 4 removal by carbonation, and the effects of different concentration of Na 2 CO 3 in the solution on lead leaching rate were studied, as shown in Table 3. The Pb carbonation was carried out at 80 ℃ for 1h with liquid-solid ratio of 3/1. After filtration and washing, the carbonation residue was leached by hydrochloric acid at 80 ℃ for 1h. The final pH of leaching was controlled at pH 1 with liquid-solid ratio of leaching of 30/1 to ensure a complete PbCl 2 dissolution. Maintaining at high temperature was attempted during filtration to avoid precipitation of PbCl 2 . Table 3 Test results for PbSO 4 carbonation and leaching Test No. Feed solid, g Feed solution Leaching residue, g Pb in leaching residue Pb leaching rate 1 50 80g/L Na 2 CO 3 27.43 21.78% 54.67% 2 50 100g/L Na 2 CO 3 28.79 21.13% 53.84% 3 50 40g/L Na 2 CO 3 25.92 7.01% 86.21% 4 50 40g/L Na 2 CO 3 +300g/L Na 2 SO 4 27.72 8.95% 81.19% 5 50 100g/L Na 2 CO 3 +300g/L Na 2 SO 4 23.91 4.02% 92.71% 6 50 150g/L Na 2 CO 3 +300g/L Na 2 SO 4 22.72 3.23% 94.43% 7 50 0 32.46 17.54% 56.80% It can be seen from Table 3 that the amount of Na 2 CO 3 used in the first two tests is sufficient, but the Pb leaching rate is still low, primarily because the solution temperature drops during filtration and PbCl 2 precipitates. The content of BaSO 4 in the HCl leaching residue is high, and it is easy to settle down. Therefore, from test No. 3, settlement was allowed for 5min to preserve the heat, the supernatant was decanted prior to filtration. It can be seen that only 40g/L Na 2 CO 3 can achieve 86.21% of lead leaching rate. In test No. 6, no Na 2 CO 3 was used, but the leaching rate also reached 56.80%. It is preliminarily considered that the PbO accounts for 56.80% of total Pb in the ammonia leaching residue. It can be seen that the leaching rate of lead in test No. 5 and No. 6 can reach 92.71% and 94.43% respectively, and it is difficult to increase the leaching rate by further increasing the dosage of sodium carbonate. Combined with XRD in Figure 3, it can be inferred that a small portion of Pb is wrapped by BaSO 4 or forms Pb-Ba sulfate complex salt. This portion of Pb can only be released after BaSO 4 leaching. Therefore, the final BaSO 4 product will contain a small amount of PbSO 4 . Next, in order to design a two-stage lead carbonation conversion process, it is necessary to specify the concentration ratio of Na 2 CO 3 and Na 2 SO 4 in the solution when only part of the lead is carbonated. Under the conditions of 100g/L Na 2 CO 3 +300g/L Na 2 SO 4 , liquid-solid ratio of 1/1, conversion temperature of 80 ℃ and conversion time of 1h, the lead conversion is incomplete according to the calculation and test results, so the concentration limit of lead conversion can be explored. Finally, the solution after lead carbonation conversion has 47.7g/L Na 2 CO 3 +327g/L Na 2 SO 4 measured by titration. That is to say, if the ratio of Na 2 CO 3 /Na 2 SO 4 is lower than 47.7g/L/327g/L, lead conversion can not be carried out. According to the limit concentration of Pb carbonation conversion, it is assumed that the concentration after lead conversion is 60 g/L Na 2 CO 3 +327 g/L Na 2 SO 4 . Through calculation, using 76.68 g/L Na 2 CO 3 +302.65 g/L Na 2 SO 4 , 80% PbSO 4 is converted to PbCO 3 in the 1 st stage, while avoiding BaSO 4 in the ammonia leaching residue from being carbonated. In the 2 nd stage, 80.85 g/L Na 2 CO 3 +297.07 g/L Na 2 SO 4 was used to convert the remaining PbSO 4 into PbCO 3 . The Pb removal residue obtained after hydrochloric acid leaching contained 3.06% Pb and its leaching rate was 94.80%. The measured concentration of the solution after the 1 st stage Pb carbonation is 60.95 g/L Na 2 CO 3 +325 g/L Na 2 SO 4 , which is basically consistent with the design estimate. This shows that the two-stage countercurrent Pb carbonation process is feasible. 4.2 BaSO 4 carbonation and leaching In order to carry out the test work for barium removal, a large quantity of Pb removal residue were prepared based on 4kg of ammonia leaching residue. In this work, 150g/L Na 2 CO 3 +300g/l Na 2 SO 4 solution was added to this batch of ammonia leaching residue with a liquid-solid ratio of 3:1 and reacted at 80 ℃ for 1h for carbonation conversion. After washing the carbonation residue, water with a liquid-solid ratio of 30:1 was added, and hydrochloric acid was added to adjust the pH to 1.0. After reacting at 80 ℃ for 1h, filtration and drying, 1818g of Pb removal residue was obtained, and its main chemical composition is shown in Table 4. The XRD analysis results are shown in Figure 4. Table 4 Elemental analysis of Pb removal residue（%） Ba Pb As Sb Sn 36.26 5.85 0.46 6.64 1.57 Taking 50g of Pb removal residue as feed for each Ba removal test, and the liquid-solid ratio of 5:1 was applied for barium carbonation, with the carbonation conversion temperature at 95 ℃. After carbonation conversion for 1h, water was added with the liquid-solid ratio of 5:1 after the conversion residue was washed, and hydrochloric acid was used to adjust the pH to 1.0, and then reacted at 80 ℃ for 1h to obtain Ba removal residue. Test results of one-stage Ba carbonation and leaching is shown in Table 5. Table 5 Test results of one-stage Ba carbonation and leaching Test No. Feed, g Feed solution Residue, g Ba in residue Ba leaching rate 1 50.00 200 g/L Na 2 CO 3 31.11 35.65% 38.83% 2 50.00 250 g/L Na 2 CO 3 28.22 30.60% 52.37% 3 50.00 300 g/L Na 2 CO 3 25.41 24.62% 65.49% 4 50.00 350 g/L Na 2 CO 3 25.20 24.00% 66.64% 5 50.00 400 g/L Na 2 CO 3 29.87 29.33% 51.68% 6 50.00 450 g/L Na 2 CO 3 31.09 29.55% 49.33% It can be seen that the Ba removal residue obtained by using only one-stage carbonation conversion process still contains a large amount of barium, and the leaching rate is not high (up to 70%), and the excessive amount of Na 2 CO 3 will reduce the leaching rate of barium. Therefore, in order to completely convert to BaCO 3 , two-stage barium conversion process can be implemented. First of all, the conversion limit was tested. Under the conditions of liquid-solid ratio of 1:1, 95 ℃ and 1h, 350 g/L Na 2 CO 3 +30 g/L Na 2 SO 4 as feed solution were used for conversion. The conversion solution after Ba carbonation was determined to have 325 g/L Na 2 CO 3 +46.88 g/L Na 2 SO 4 by titration. That is to say, if the mass ratio of Na 2 CO 3 /Na 2 SO 4 in the solution is lower than 325/46.88, the carbonation will no longer occur. Based on the one-stage test and barium conversion limit, 50g of Pb removal residue as feed was taken for two-stage carbonation conversion test. The liquid-solid ratio varied, and the reactions were carried out at 95℃ for 1h. No washing operation was applied between the two stages. After filtering and washing, the conversion residue was added with water with the liquid-solid ratio of 5:1, and hydrochloric acid was added to adjust the pH to 1.0. After reaction at 80 ℃ for 1h, the Ba removal residue was obtained and the test results are shown in Table 6. Table 6 Two-stage Ba carbonation and leaching test results Test No. Feed, g 1 st stage feed solution 2 nd stage feed solution Residue, g Ba in residue Ba leaching rate 1 50.00 401.75 g/L Na 2 CO 3 +8.96 g/L Na 2 SO 4 408.44 g/L Na 2 CO 3 22.35 9.04% 81.34% 2 50.00 353 g/L Na 2 CO 3 +9.38 g/L Na 2 SO 4 360 g/L Na 2 CO 3 14.62 2.18% 98.24% 3 50.00 356.74 g/L Na 2 CO 3 +13 g/L Na 2 SO 4 363.74 g/LNa 2 CO 3 +3.64 g/L Na 2 SO 4 12.13 5.20% 96.52% By calculation, 80% of the BaSO 4 is converted to BaCO 3 using 401.75 g/L Na 2 CO 3 +8.96 g/L Na 2 SO 4 at the first stage and 408.44 g/L Na 2 CO 3 at the second stage to convert the remaining BaSO 4. The liquid-solid ratio was 5/1 at both stages, but the final barium leaching rate is only 81.34%. It should be caused by the high concentration of Na 2 CO 3 , almost reaching its solubility. In order to solve this problem, the liquid-solid ratio was increased to 8/1, and the two-stage barium carbonation conversion test was recalculated, as shown in Table 6. The barium leaching rate has reached 98.24% for test No. 2. Considering the subsequent sodium carbonate crystallization product may contain ~1% sodium sulfate impurities, the test No. 3 was carried out. The concentration of Na 2 SO 4 in the two stages of barium conversion was 13 g/L and 3.64 g/L respectively, and the barium leaching rate could still reach 96.52%. The composition of Ba removal residue is shown in Table 7 for the test No. 2 in Table 6. It is seen that Ba content was reduced to only 2.18%, while Pb content in Ba removal residue was 6.23%. The Pb in the form of PbS cannot be easily converted because no oxidative was added. The Bi/Sb in Ba removal residue was enriched to 23.70% and 22.99%, respectively, which is saleable after Au/Ag recovery. According to XRD analysis in Fig. 5, there is only BiOCl and small amount of BaSO 4 detected in the residue. Table 7 Elemental analysis of Ba removal residue（%） Ba Pb Bi Te Sb Sn 2.18 6.23 23.70 0.48 22.99 5.54 4.3 Na 2 SO 4 /Na 2 CO 3 crystallization and recycling Na 2 SO 4 crystallization In this section, 100 ml solution with 60 g/L Na 2 CO 3 + 325 g/L Na 2 SO 4 was used to simulate the solution after Pb carbonation. The test results for sodium sulfate crystallization are shown in Table 8. Table 8 Test results for Na 2 CO 3 freezing crystallization Freezing temperature 1 st stage freezing 2 nd stage freezing Crystallite dry weight, g Content of Na 2 CO 3 0℃ 1h / 30.37 3.28% 10℃ 1h / 29.29 5.18% 10℃ 1h 1h 24.86 1.27% After freezing at 10℃for 1 h, the crystalline product was added with 25% water for recrystallization. The crystalline Na 2 SO 4 product with 1.27% Na 2 CO 3 was obtained with Na 2 SO 4 recovery reached 75.52%. The obtained crystallization mother liquor still contains enough Na 2 CO 3 concentration (71.55 g/L) for lead conversion, so it can be returned to the lead carbonation conversion section for recycling. Na 2 CO 3 crystallization The solution after the first stage of Ba carbonation conversion was sent for freezing crystallization of sodium carbonate. The obtained Na 2 CO 3 crystallite is returned to the first stage for barium conversion, and the obtained crystallization mother liquor with Na 2 SO 4 pollution is still useful for the Pb carbonation operation. In this section, 100 ml solution with 325 g/L Na 2 CO 3 +40 g/L Na 2 SO 4 was used to simulate the solution after first stage of Ba carbonation. The results for sodium carbonate freezing crystallization test are shown in Table 9. As shown in Fig. 6, the Na 2 CO 3 crystallite usually has a particle size of 1~2mm. The dry weight of the crystallite was obtained by heating up to 160℃ to remove all H 2 O in crystallite. Table 9 Test results for Na 2 CO 3 freezing crystallization Freezing temperature 1 st stage freezing 2 nd stage freezing Crystallite dry weight, g Content of Na 2 SO 4 0℃ 2h / 29.28 6.56% Without washing 10℃ 2h / 27.57 7.30% Without washing 10℃ 2h / 22.77 4.64% With washing 10℃ 2h 2h 20.64 2.30% Without washing 10℃ 2h 2h 19.62 1.25% With washing 15℃ 2h 2h 15.04 0.46% With washing 15℃ 2h / 20.10 1.41% With washing It can be seen that even though difference of Na 2 CO 3 and Na 2 SO 4 concentrations is large in the simulated solution, it is still difficult to crystallize pure Na 2 CO 3 from the solution. By using only one stage crystallization, the content of Na 2 SO 4 as impurity in the obtained Na 2 CO 3 crystallite is as high as 4.64%, which may be due to the entrainment of mother liquor or the production of Na 2 CO 3 -Na 2 SO 4 double salt during crystallization. Therefore, several experiments were carried out by washing, recrystallization, prolonging crystallization time and increasing crystallization temperature. Although these methods will reduce the mass of final crystallite, qualified Na 2 CO 3 products with Na 2 SO 4 content of 1.25%, 1.41% and 0.46% were obtained. Selection of these various products will be determined by the flowsheet design. The obtained crystallization mother liquor still contains 140 g/L Na 2 CO 3 , and the washing solution also contains 100 g/L Na 2 CO 3 , which can be returned for Pb carbonation. 4.4 Flowsheet design and cyclic test Cyclic test for Pb removal Compared to Ba carbonation, Pb carbonation is relatively easy. One-stage conversion can achieve good Pb carbonation. Therefore, the process route of one-stage Pb carbonation + Pb leaching by HCl + freezing crystallization of Na 2 SO 4 after carbonation + return of crystallization mother liquor to carbonation was adopted for laboratory cyclic test. In this test, 100g of ammonia leaching residue as feed was reacted with 300 mL carbonation solution (80.85 g/L Na 2 CO 3 +291 g/L Na 2 SO 4 ) which was initially synthesized. After the carbonation reaction at 80℃ for 1h, 15% of the filtrate was used for crystallization and washing water filter the solid-liquid separation, and filter the washing water as the next washing water for recycling. The liquid after lead conversion, and the crystallization mother liquid was added with the remaining liquid after lead conversion and added with 50.62g water+6.64g Na 2 CO 3 as the liquid before lead conversion. 40g of the obtained lead conversion wet residue was used for acid leaching of lead. Table 10 Cyclic test results for Pb removal by carbonation and leaching Carbonation solution Na 2 SO 4 crystallite, g Wet weight after carbonation, g HCl leaching Feed, g Residue, g 1 st cycle 80.95 g/L Na 2 CO 3 291g/L Na 2 SO 4 （synthesized） 9.82 113.24 40 16.31 2 nd cycle 77.91 g/L Na 2 CO 3 244.22g/L Na 2 SO 4 （measured） 7.12 113.79 40 16.59 3 rd cycle 77.38 g/L Na 2 CO 3 188.98g/L Na 2 SO 4 （measured） 4.59 114.54 40 17.38 The test results are shown in Table 10. It can be seen that the conversion basically reached the end point, and the sodium carbonate concentration remained basically unchanged. Although the concentration of sodium sulfate continues to decrease, the concentration of sodium sulfate will not affect the conversion of lead. The main reason for the decrease is that the washing water takes away more sodium sulfate, and with the increase of washing water circulation times, the amount of free sulfate in the conversion slag also increases synchronously, which is easy to cause lead sulfate precipitation during acid leaching and reduce the lead leaching rate. It is considered that the washing water is not recycled Cyclic test for Ba removal Although the conversion of barium in the above two-stage Ba carbonation test with liquid-solid ratio of 8/1 was relatively complete, the analysis found that the solution after 2 nd stage barium carbonation contained 30g/l Na 2 SO 4 , which could not meet the requirement of returning to the first stage carbonation (13 g/l Na 2 SO 4 was designed). The main reason for the deviation is that some bismuth may also participate in the carbonation, but it cannot be leached by hydrochloric acid at pH 1 and exists in the Ba removal residue in the form of BiOCl. Therefore, the liquid-solid ratio of 12/1 was applied in the 1 st stage, and liquid-solid ratio of 6/1 was applied in the 2 nd stage of cyclic test. This design enables the washing water of the 2 nd stage carbonation to be returned to the 1 st stage, avoiding waste of Na 2 CO 3 in the washing water with a better water balance. In fact, it is necessary to wash the 2 nd stage carbonation residue, otherwise the residual Na 2 SO 4 entrapped in the residue will precipitate barium during hydrochloric acid leaching, affecting the efficiency of barium removal. The test results are shown in Table 11. In the cyclic test, 100g of Pb removal residue was taken and added with 1200mL 1 st stage barium conversion solution (356 g/L Na 2 CO 3 +6 g/L Na 2 SO 4 ). After barium carbonation reaction at 80 ℃ for 1h, the carbonation residue without washing was added with 600 mL of the 2 nd stage barium carbonation solution (360 g/L Na 2 CO 3 ). After the 2 nd stage barium carbonation reaction at 80 ℃ for 1h, the solid-liquid separation is performed and washed with 600 ml of water. The obtained filtrate was combined with the washing water, and 198.48g Na 2 CO 3 and 3.33 g Na 2 SO 4 were added as the first stage barium conversion solution for the next cycle test. The obtained Ba carbonation residue was leached with hydrochloric acid under the above conditions to evaluate the leaching rate. Table 11 Cyclic test results for Pb removal by carbonation and leaching 1 st stage carbonation solution 2 nd stage carbonation solution Wet weight after carbonation, g HCl leaching residue, g 1 st cycle 356 g/L Na 2 CO 3 6 g/L Na 2 SO 4 （synthesized） 360 g/L Na 2 CO 3 133.09 28.37 2 nd cycle 356.03 g/L Na 2 CO 3 5.58g/L Na 2 SO 4 （measured） 360 g/L Na 2 CO 3 132.53 28.53 3 rd cycle 357.73 g/L Na 2 CO 3 5.65g/L Na 2 SO 4 （measured） 360 g/L Na 2 CO 3 131.78 28.04 Recovery of Au/Ag After the removal of Pb and Ba, Au/Ag can be exposed, which are simultaneously leached by HCl, NaClO 3 and NaCl. The main reactions are as follows: 2Au + 8HCl + NaClO 3 = 2HAuCl 4 + NaCl + 3H 2 O 6Ag + 6HCl + NaClO 3 + 11NaCl = 6Na 2 [AgCl 3 ] + 3H 2 O This chlorination leaching was carried out with a liquid-solid ratio of 5:1 at 80 ℃ for 3h. The leaching solution contains 35g/L HCl + 200g/L NaCl + 3g/L NaClO 3 . After reaction and filtration, the filtrate shows obvious golden yellow. As shown in table 12, It can be seen that leaching of Au is quite good, but Ag is hardly leached, and ammonia leaching is required separately for Ag. Table 12 Test results for Au/Ag recovery Ba removal residue Au leaching residue Au g/t Ag % Au g/t Ag % Au leaching rate Ag leaching rate 1240.09 2.10 24.02 1.94 98.33% 20.36% Flowsheet design for Na 2 CO 3 recycling The measured concentration after the 1 st stage Ba carbonation conversion is 328.6 g/L Na 2 CO 3 +41.83 g/L Na 2 SO 4 , corresponding to the limit ratio of barium conversion. 250 ml of the 1 st stage barium conversion solution was taken to crystallize at 15 ℃ for 2 hours to obtain 39.94g of crystalline product. According to titration analysis, the crystalline product contains 1.46% Na 2 SO 4 , and the rest is Na 2 CO 3 , which is enough to return to the the 1 st stage Ba carbonation conversion, while the 2 nd stage barium conversion solution is all prepared with fresh sodium carbonate (360 g/L Na 2 CO 3 ). In addition, 105 ml of crystallization mother liquor (140.72 g/L Na 2 CO 3 +53.18 g/L Na 2 SO 4 ) and 110 ml of crystallization washing water were obtained (100.67 g/L Na 2 CO 3 +30.16 g/L Na 2 SO 4 ). Based on calculation, both the amount of water and the amount of Na 2 CO 3 are fully enough for Pb carbonation conversion. It can be considered that the crystallization mother liquor and washing liquor are combined and returned to lead conversion, and the solution after lead conversion will not be recycled, so as to simplify the process flowsheet. Because there is still a certain amount of Na 2 CO 3 left in the solution after lead conversion, it can be used as a neutralizer for the leaching solution of bismuth leaching with hydrochloric acid, and further consume the residual Na 2 CO 3 until bismuth is completely precipitated. The solution after bismuth precipitation contains only Na 2 SO 4 and a small amount of NaCl. The Na 2 SO 4 in this solution can then be removed by freeze crystallization with water and NaCl recycled to bismuth leaching. There are 1100 mL of the solution after the 1 st stage of barium carbonation, 462 mL of the Na 2 CO 3 crystallization mother liquor and 484 mL of the Na 2 CO 3 crystallization washing liquor can be obtained from the same scale of test (100g of Pb removal residue as feed for Ba removal operation). After combining them, 946 mL of the solution can be obtained, and the concentration is 121.20 g/L Na 2 CO 3 +41.40 g/L Na 2 SO 4 . The mass will be reduced to half after Pb removal, so the corresponding Pb removal feed (ammonia leaching residue) is 200g. If all the solutions obtained after Na 2 CO 3 crystallization are used for lead conversion, the liquid-solid ratio is about 4.75/1, and both the amount of water and sodium carbonate are sufficient for lead conversion. A lead carbonation and leaching test was conducted, and the results are shown in Table 13. Table 13 Test results for Pb removal using recycled Na 2 CO 3 bearing solution Na 2 CO 3 121.20 g/L Na 2 SO 4 41.40 g/L L/S 4.75/1 Carbonation time 1h Carbonation temperature 80℃ Pb leaching rate 95.10% Precipitation of BaSO 4 The measured barium content of hydrochloric acid leaching solution was 62.63 g/L. In precipitation test work, 50 ml of the leaching solution was taken with the addition of 1mL sulfuric acid, and reacted at room temperature for 0.5h. After precipitation of BaSO 4 , the solution contains 7.64g/l Ba. Titration using barium chloride solution detected that it does not contain sulfate. In this process, the hydrochloric acid is regenerated, while maintaining a certain residual BaCl 2 concentration to avoid the sulfate from being brought into the carbonation stage with the regenerated hydrochloric acid. After barium leaching with regenerated hydrochloric acid, sulfuric acid equivalent to the amount of barium in the carbonation residue can be added each time to precipitate BaSO 4 . Conclusion In copper anode slime hydrometallurgical plant, Au/Ag recovery is incomplete with a significant amount of Au/Ag remaining in ammonia leaching residue, encapsulated by PbSO 4 and BaSO 4 . These gold and silver can be released by removal of PbSO 4 /BaSO 4 , which is realized by Na 2 CO 3 carbonation and HCl leaching. The process flowsheet stepwisely includes Pb removal, Ba removal, and Au/Ag leaching. Precipitation using sulfuric acid was adopted to obtain PbSO 4 and BaSO 4 products from their corresponding HCl leaching solution. In particular, barium conversion was realized by two-stage Ba carbonation. The solution after the second stage are returned to the first stage of barium conversion, and the crystalline sodium carbonate after barium conversion in the first stage is returned to the first stage, and the crystallized mother liquor and crystalline washing water are combined and returned for Pb conversion. The chloroauric acid solution and silver ammonia solution were incorporated into their main stream in the copper anode slime plant, respectively. The whole process does not introduce waste water, and the material consumption is mainly sodium carbonate, sulfuric acid, a small amount of hydrochloric acid, sodium chloride and sodium chlorate and ammonia necessary for gold and silver separation. Declarations Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper. Competing interests The author(s) declare no competing interests. Author Contribution Zhizhong Liu: Writing - Review & Editing, Supervision, Project administration, Formal analysis, Investigation. Xinhuang Yu: Data Curation, Validation, Writing - Original Draft, Visualization. Shuchen Qin: Data Curation, Validation, Visualization. Yuanhao Ren: Data Curation, Validation. Rui Ning: Supervision, Project administration. Bao Guo: Conceptualization, Methodology,Supervision, Project administration, Writing - Review & Editing. Kaixi Jiang: Conceptualization, Methodology,Supervision, Project administration. All authors reviewed the manuscript. Data Availability Data will be made available on request. The data sets generated and analyzed during the current study are available from Bao Guo ( [email protected] ) upon reasonable request. References Li, D., Guo, X., Xu, Z., Tian, Q. & Feng, Q. Leaching behavior of metals from copper anode slime using an alkali fusion-leaching process. Hydrometallurgy 157 , 9-12 (2015). Li, D., Guo, X., Xu, Z., Xu, R. & Feng, Q. Metal values separation from residue generated in alkali fusion-leaching of copper anode slime. Hydrometallurgy 165 , 290-294 (2016). Xiao, L. et al. An environmentally friendly process to selectively recover silver from copper anode slime. J. Clean. Prod. 187 , 708-716 (2018). Chen, A. et al. Recovery of silver and gold from copper anode slimes. JOM 67 (2), 493-502 (2015). Ding, Y., Zhang, S., Liu, B. & Li, B. Integrated process for recycling copper anode slime from electronic waste smelting. J. Clean. Prod. 165 , 48-56 (2017). SEISKO, S. et al. Pressure leaching of decopperized copper electrorefining anode slimes in strong acid solution. Physicochem. Probl. Mineral Pro. 53 (1), 465-474 (2017). Chiu, T., Horng, J. & Hoh, Y. Kinetic studies on selenious acid reduction at higher se(iv) concentration. Hydrometallurgy 7 (1), 135-146 (1981). Hoffmann, J. E. Recovering selenium and tellurium from copper refinery slimes. JOM 41 (7), 33-38 (1989). Hyvärinen, O., Lindroos, L. & Yllö, E. Recovering selenium from copper refinery slimes. JOM 41 (7), 42-43 (1989). Ximing, L., Jiajun, K., Xinhui, M. & Bin, L. Chlorine leaching of gold-bearing sulphide concentrate and its calcine. Hydrometallurgy 29 (1), 205-215 (1992). Sansotta, S. & Zahn, D. Solvation structure and dynamics of ag+ in aqueous ammonia solutions: a molecular simulation study. The Journal of Chemical Physics 147 (11) (2017). Ha, T. K., Kwon, B. H., Park, K. S. & Mohapatra, D. Selective leaching and recovery of bismuth as bi2o3 from copper smelter converter dust. Sep. Purif. Technol. 142 , 116-122 (2015). Ke, J., Qiu, R. & Chen, C. Recovery of metal values from copper smelter flue dust. Hydrometallurgy 12 (2), 217-224 (1984). He, Y. & Xu, Z. Recycling gold and copper from waste printed circuit boards using chlorination process. RSC Adv. 5 (12), 8957-8964 (2015). Liu, W. et al. Investigation into oxygen-enriched bottom-blown stibnite and direct reduction. Metallurgical and Materials Transactions B 45 (4), 1281-1290 (2014). Additional Declarations No competing interests reported. Cite Share Download PDF Status: Posted Version 1 posted You are reading this latest preprint version Research Square lets you share your work early, gain feedback from the community, and start making changes to your manuscript prior to peer review in a journal. As a division of Research Square Company, we’re committed to making research communication faster, fairer, and more useful. We do this by developing innovative software and high quality services for the global research community. Our growing team is made up of researchers and industry professionals working together to solve the most critical problems facing scientific publishing. Also discoverable on Platform About Our Team In Review Editorial Policies Advisory Board Help Center Resources Author Services Accessibility API Access RSS feed Manage Cookie Preferences © Research Square 2026 | ISSN 2693-5015 (online) Privacy Policy Terms of Service Do Not Sell My Personal Information {"props":{"pageProps":{"initialData":{"identity":"rs-8390297","acceptedTermsAndConditions":true,"allowDirectSubmit":true,"archivedVersions":[],"articleType":"Article","associatedPublications":[],"authors":[{"id":588665355,"identity":"5b621d3d-cbc7-41db-9727-3a88254da608","order_by":0,"name":"Zhizhong Liu","email":"","orcid":"","institution":"Daye Nonferrous Metals Co., Ltd.","correspondingAuthor":false,"prefix":"","firstName":"Zhizhong","middleName":"","lastName":"Liu","suffix":""},{"id":588665356,"identity":"a23f4c20-005e-43ec-a13b-e89a6b8bb419","order_by":1,"name":"Xinhuang Yu","email":"","orcid":"","institution":"Fuzhou University","correspondingAuthor":false,"prefix":"","firstName":"Xinhuang","middleName":"","lastName":"Yu","suffix":""},{"id":588665357,"identity":"0e6b6dbb-1afd-44ec-b648-7d7ea09369a8","order_by":2,"name":"Shuchen Qin","email":"","orcid":"","institution":"Beijing General Research Institute of Mining and Metallurgy","correspondingAuthor":false,"prefix":"","firstName":"Shuchen","middleName":"","lastName":"Qin","suffix":""},{"id":588665358,"identity":"88930054-67dd-47e8-aba8-965b4820fce3","order_by":3,"name":"Yuanhao Ren","email":"","orcid":"","institution":"Daye Nonferrous Metals Co., Ltd.","correspondingAuthor":false,"prefix":"","firstName":"Yuanhao","middleName":"","lastName":"Ren","suffix":""},{"id":588665359,"identity":"a1b9cad7-31cb-4d50-ba29-dd2d116e91a8","order_by":4,"name":"Rui Ning","email":"","orcid":"","institution":"Daye Nonferrous Metals Co., Ltd.","correspondingAuthor":false,"prefix":"","firstName":"Rui","middleName":"","lastName":"Ning","suffix":""},{"id":588665360,"identity":"5b52fc83-4abe-41b5-88bc-2b54672e5218","order_by":5,"name":"Bao Guo","email":"data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAZAAAAAyAQMAAABI0h/eAAAABlBMVEX///8AAABVwtN+AAAACXBIWXMAAA7EAAAOxAGVKw4bAAAAwElEQVRIiWNgGAWjYHACNiC24QczeUjQkibZQKqWwyRokY9IPvbgR8V5CfkZCYwP3rYxyJsT0mJ4Iy3dsOfMbQnGGQnMhnPbGAx3NhDSMiPHTIK37XYds0QCmzRvG0OCwQEitEj+bTsnwSaRwP6bKC3yEjlmQMMPSPAAbWEmSosBz7N0Y5kzyRISPA+bJeeckzDcQNCW9uRjD99U2EkAGQc/vCmzkSdsC0IBYwOQkCCgHmRLA2E1o2AUjIJRMNIBAIgIOWoiWSn7AAAAAElFTkSuQmCC","orcid":"","institution":"Fuzhou University","correspondingAuthor":true,"prefix":"","firstName":"Bao","middleName":"","lastName":"Guo","suffix":""},{"id":588665361,"identity":"57a6daec-7cce-4772-9c50-50d3d95cac52","order_by":6,"name":"Kaixi Jiang","email":"","orcid":"","institution":"Fuzhou University","correspondingAuthor":false,"prefix":"","firstName":"Kaixi","middleName":"","lastName":"Jiang","suffix":""}],"badges":[],"createdAt":"2025-12-18 02:53:25","currentVersionCode":1,"declarations":"","doi":"10.21203/rs.3.rs-8390297/v1","doiUrl":"https://doi.org/10.21203/rs.3.rs-8390297/v1","draftVersion":[],"editorialEvents":[],"editorialNote":"","failedWorkflow":false,"files":[{"id":102541523,"identity":"dfc1230a-df0a-4352-b4cd-71fc8100cd2d","added_by":"auto","created_at":"2026-02-12 19:12:29","extension":"png","order_by":1,"title":"Figure 1","display":"","copyAsset":false,"role":"figure","size":32436,"visible":true,"origin":"","legend":"\u003cp\u003eFlowsheet of Pb/Ba removal for ammonia leaching residue\u003c/p\u003e","description":"","filename":"floatimage1.png","url":"https://assets-eu.researchsquare.com/files/rs-8390297/v1/00ba85cc9a0271d0cf9fa131.png"},{"id":102746594,"identity":"80b45590-79eb-4f4b-be63-88d55e5cb76f","added_by":"auto","created_at":"2026-02-16 08:58:28","extension":"jpeg","order_by":2,"title":"Figure 2","display":"","copyAsset":false,"role":"figure","size":160617,"visible":true,"origin":"","legend":"\u003cp\u003eAmmonia leaching residue\u003c/p\u003e","description":"","filename":"floatimage2.jpeg","url":"https://assets-eu.researchsquare.com/files/rs-8390297/v1/8f59f7649f00a4711233b5ab.jpeg"},{"id":102746599,"identity":"bac08b26-7833-45d4-b4be-1411dfb21b29","added_by":"auto","created_at":"2026-02-16 08:58:32","extension":"png","order_by":3,"title":"Figure 3","display":"","copyAsset":false,"role":"figure","size":33093,"visible":true,"origin":"","legend":"\u003cp\u003eXRD pattern of ammonia leaching residue\u003c/p\u003e","description":"","filename":"floatimage3.png","url":"https://assets-eu.researchsquare.com/files/rs-8390297/v1/bd5f262a7eac3ee84e146dc1.png"},{"id":102541525,"identity":"a3803b0a-7791-47b7-8bad-20fdcff803d3","added_by":"auto","created_at":"2026-02-12 19:12:29","extension":"png","order_by":4,"title":"Figure 4","display":"","copyAsset":false,"role":"figure","size":27000,"visible":true,"origin":"","legend":"\u003cp\u003eXRD pattern of Pb removal residue\u003c/p\u003e","description":"","filename":"floatimage4.png","url":"https://assets-eu.researchsquare.com/files/rs-8390297/v1/3a4e3ed029249df6bdcb1680.png"},{"id":102746882,"identity":"0def8f5a-d2a2-4378-a40d-6e7f65ae09b4","added_by":"auto","created_at":"2026-02-16 09:02:34","extension":"png","order_by":5,"title":"Figure 5","display":"","copyAsset":false,"role":"figure","size":30404,"visible":true,"origin":"","legend":"\u003cp\u003eXRD pattern of Ba removal residue\u003c/p\u003e","description":"","filename":"floatimage5.png","url":"https://assets-eu.researchsquare.com/files/rs-8390297/v1/2533c7a47f2f40b2244d1bd8.png"},{"id":102541528,"identity":"ade6e288-0a39-4d26-a63d-999428ff649e","added_by":"auto","created_at":"2026-02-12 19:12:29","extension":"jpeg","order_by":6,"title":"Figure 6","display":"","copyAsset":false,"role":"figure","size":206009,"visible":true,"origin":"","legend":"\u003cp\u003eNa\u003csub\u003e2\u003c/sub\u003eCO\u003csub\u003e3 \u003c/sub\u003ecrystallite with 1~2mm size\u003c/p\u003e","description":"","filename":"floatimage6.jpeg","url":"https://assets-eu.researchsquare.com/files/rs-8390297/v1/abd13f5468ec9886eb818d51.jpeg"},{"id":103056311,"identity":"a7301d8c-386a-4b30-a2f9-d9fec0d513f5","added_by":"auto","created_at":"2026-02-20 09:05:53","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":1744164,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-8390297/v1/64b9efb2-91dd-4034-9740-d0c098371528.pdf"}],"financialInterests":"No competing interests reported.","formattedTitle":"The liberation of refractory precious metals associated with PbSO 4 /BaSO 4 by carbonation and comprehensive recovery in copper anode slime refinery","fulltext":[{"header":"Introduction","content":"\u003cp\u003eGlobally, the demand for precious metals, specifically gold (Au), silver (Ag), platinum (Pt), palladium (Pd), and other platinum group metals (PGM) is growing in recent decades. Copper anode slime is an important resources of precious metals\u003csup\u003e\u003cspan additionalcitationids=\"CR2\" citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR3\" class=\"CitationRef\"\u003e3\u003c/span\u003e\u003c/sup\u003e. Several semi-hydrometallurgical flowsheets have been developed to process copper anode slime\u003csup\u003e\u003cspan additionalcitationids=\"CR5\" citationid=\"CR4\" class=\"CitationRef\"\u003e4\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR6\" class=\"CitationRef\"\u003e6\u003c/span\u003e\u003c/sup\u003e, one of which stepwisely consists of sulfuric acid roasting with vaporization of Se\u003csup\u003e4,7\u0026ndash;9\u003c/sup\u003e and subsequent leaching of Cu, perchloric acid leaching of Au/PGM/Te\u003csup\u003e10\u003c/sup\u003e, and ammonia leaching of Ag\u003csup\u003e11\u003c/sup\u003e. There are still various valuable metals, including the refractory precious metals and Sn/Sb/Bi/Pb/Ba, remaining in ammonia leaching residue. The remaining precious metals are primarily encapsulated in PbSO\u003csub\u003e4\u003c/sub\u003e/BaSO\u003csub\u003e4\u003c/sub\u003e, thus it is necessary to dissolve these two types of sulfates in order to fully recover precious metals in ammonia leaching residue.\u003c/p\u003e \u003cp\u003eAt present, ammonia leaching residue is mainly treated by returning to coppper smelting plant. Smelting has the advantage of high recovery of precious metals. However, most of Sn/Ba and part of Sb/Bi/Pb will be lost in the smelting slag. Herein, we proposed a flowsheet (Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003e) for comprehensive recovering valuable metals from ammonia leaching residue. The core is to effectively remove Pb and Ba, unlock the encapsulation of Au/Ag by PbSO\u003csub\u003e4\u003c/sub\u003e and BaSO\u003csub\u003e4\u003c/sub\u003e, greatly improve the recovery of Au and Ag, and obtain Au/Ag products, Pb products, Ba products, Bi products and Sb/Sn products step by step, so as to realize the comprehensive recovery of valuable metals in ammonia leaching residue. Moreover, it has to connect with the existing mainstream in hydrometallurgical precious metal plant, without any complicated equipment.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eThis flowsheet adopts the carbonation conversion of PbSO\u003csub\u003e4\u003c/sub\u003e/BaSO\u003csub\u003e4\u003c/sub\u003e to PbCO\u003csub\u003e3\u003c/sub\u003e/BaCO\u003csub\u003e3\u003c/sub\u003e, which are both soluble by hydrochloric acid leaching. Specifically, PbSO\u003csub\u003e4\u003c/sub\u003e is transformed into PbCO\u003csub\u003e3\u003c/sub\u003e by using the crystallization mother liquor of the solution after barium conversion, and then it is heated and leached by HCl. Lead enters the solution as PbCl\u003csub\u003e2\u003c/sub\u003e. The solubility of PbCl\u003csub\u003e2\u003c/sub\u003e is slightly small, and even smaller at lower temperature; therefore, it is leached by hydrochloric acid with high liquid-solid ratio, and the solution is heated to increase its solubility. Then, PbSO\u003csub\u003e4\u003c/sub\u003e is precipitated by H\u003csub\u003e2\u003c/sub\u003eSO\u003csub\u003e4\u003c/sub\u003e, and HCl is regenerated for recycling.\u003c/p\u003e \u003cp\u003eThereafter, BaSO\u003csub\u003e4\u003c/sub\u003e is converted to BaCO\u003csub\u003e3\u003c/sub\u003e with a large Na\u003csub\u003e2\u003c/sub\u003eCO\u003csub\u003e3\u003c/sub\u003e/Na\u003csub\u003e2\u003c/sub\u003eSO\u003csub\u003e4\u003c/sub\u003e ratio. After conversion, relatively pure Na\u003csub\u003e2\u003c/sub\u003eCO\u003csub\u003e3\u003c/sub\u003e is obtained by crystallization and recycled, and the mother liquor is recycled for Pb carbonation. Hydrochloric acid with small liquid-solid ratio is used to leach the conversion slag because BaCl\u003csub\u003e2\u003c/sub\u003e has a greater solubility, and H\u003csub\u003e2\u003c/sub\u003eSO\u003csub\u003e4\u003c/sub\u003e is also used to precipitate BaSO\u003csub\u003e4\u003c/sub\u003e, and HCl is regenerated for recycling to realize Ba removal. Afterwards, Bi is leached by H\u003csub\u003e2\u003c/sub\u003eSO\u003csub\u003e4\u003c/sub\u003e+NaCl\u003csup\u003e12,13\u003c/sup\u003e, and BiOCl was obtained by neutralizing and precipitating using Na\u003csub\u003e2\u003c/sub\u003eCO\u003csub\u003e3\u003c/sub\u003e/Na\u003csub\u003e2\u003c/sub\u003eSO\u003csub\u003e4\u003c/sub\u003e mixture solution after Pb carbonation. The residue after removing Pb and Ba is mainly SnO\u003csub\u003e2\u003c/sub\u003e-Sb\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e enrichment, and Au/Ag are also enriched. The Au/Ag extraction can be achieved by NaClO\u003csub\u003e3\u003c/sub\u003e+HCl+NaCl oxidative leaching\u003csup\u003e\u003cspan citationid=\"CR14\" class=\"CitationRef\"\u003e14\u003c/span\u003e\u003c/sup\u003e, which is then incorporated into the existing Au/Ag process in the main stream of the plant. After leaching precious metals, if the value of Sb/Sn is high, a small rotary kiln can be used for weak reduction roasting to convert Sb\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e into Sb\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e which enters the dust\u003csup\u003e\u003cspan citationid=\"CR15\" class=\"CitationRef\"\u003e15\u003c/span\u003e\u003c/sup\u003e, achieving Sb/Sn separation.\u003c/p\u003e \u003cp\u003eIn this work, the effects of Na\u003csub\u003e2\u003c/sub\u003eCO\u003csub\u003e3\u003c/sub\u003e/Na\u003csub\u003e2\u003c/sub\u003eSO\u003csub\u003e4\u003c/sub\u003e ratioon carbonation of Pb/Ba and the recyling of Na\u003csub\u003e2\u003c/sub\u003eCO\u003csub\u003e3\u003c/sub\u003e by freezing crystallization were especially investigated in this work. The change in the mineralogy of sample in the flowsheet was studied using XRD and chemical phase analysis techniques.\u003c/p\u003e"},{"header":"Materials and Methods","content":"\u003cp\u003eThe ammonia leaching residue produced by Copper Anode Slime plant of Daye Nonferrous Enterprise, as shown in Fig. 2, was used in this work as feed. The composition for the elements of interest is shown in Table 1, the chemical phase analysis of Pb/Ba is shown in Table 2, and the XRD analysis is shown in Fig. 3. It can be seen that the ammonia leaching residue contains a significant amount of BaSO\u003csub\u003e4\u0026nbsp;\u003c/sub\u003eand (Pb,Ba)SO\u003csub\u003e4\u003c/sub\u003e. The gold and silver are encapsulated by these sulfates, which is difficult to achieve effective leaching. It is necessary to break the encapsulation by dissolution of BaSO\u003csub\u003e4\u0026nbsp;\u003c/sub\u003eand (Pb,Ba)SO\u003csub\u003e4\u0026nbsp;\u003c/sub\u003eand recover Au/Ag and Pb/Ba. In addition, Sb and Bi also have certain comprehensive recovery value. While, the Sn content is relatively low, so its separation and recovery will not be considered at the moment of research.\u003c/p\u003e\n\u003cp\u003eTable 1 Elemental analysis of ammonia leaching residue（%）\u003c/p\u003e\n\u003cdiv align=\"\"\u003e\n \u003ctable border=\"1\" cellspacing=\"0\" cellpadding=\"0\"\u003e\n \u003ctbody\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 94px;\"\u003e\n \u003cp\u003ePb\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 94px;\"\u003e\n \u003cp\u003eBa\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 94px;\"\u003e\n \u003cp\u003eAs\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 94px;\"\u003e\n \u003cp\u003eBi\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 94px;\"\u003e\n \u003cp\u003eSb\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 94px;\"\u003e\n \u003cp\u003eSn\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 94px;\"\u003e\n \u003cp\u003e31.95\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 94px;\"\u003e\n \u003cp\u003e22.43\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 94px;\"\u003e\n \u003cp\u003e1.13\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 94px;\"\u003e\n \u003cp\u003e3.75\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 94px;\"\u003e\n \u003cp\u003e4.09\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 94px;\"\u003e\n \u003cp\u003e0.95\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003c/tbody\u003e\n \u003c/table\u003e\n\u003c/div\u003e\n\u003cp\u003e\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eTable 2 Chemical phase analysis of Pb/Ba in ammonia leaching residue（%）\u003c/p\u003e\n\u003ctable border=\"1\" cellspacing=\"0\" cellpadding=\"0\"\u003e\n \u003ctbody\u003e\n \u003ctr\u003e\n \u003ctd rowspan=\"2\" valign=\"top\" style=\"width: 109px;\"\u003e\n \u003cp\u003eBa\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd colspan=\"2\" valign=\"top\" style=\"width: 171px;\"\u003e\n \u003cp\u003eSilicate\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 123px;\"\u003e\n \u003cp\u003eSulfate\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 144px;\"\u003e\n \u003cp\u003eCarbonate\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 109px;\"\u003e\n \u003cp\u003eTotal Ba\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd colspan=\"2\" valign=\"top\" style=\"width: 171px;\"\u003e\n \u003cp\u003e2.291\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 123px;\"\u003e\n \u003cp\u003e23.8\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 144px;\"\u003e\n \u003cp\u003e0.019\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 109px;\"\u003e\n \u003cp\u003e26.11\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd rowspan=\"2\" valign=\"top\" style=\"width: 109px;\"\u003e\n \u003cp\u003ePb\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 83px;\"\u003e\n \u003cp\u003eSulfide\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 88px;\"\u003e\n \u003cp\u003eOxide\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 123px;\"\u003e\n \u003cp\u003eSulfate\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 144px;\"\u003e\n \u003cp\u003eCo-sulfate with Ba\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 109px;\"\u003e\n \u003cp\u003eTotal Pb\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" style=\"width: 83px;\"\u003e\n \u003cp\u003e3.06\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 88px;\"\u003e\n \u003cp\u003e25.41\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 123px;\"\u003e\n \u003cp\u003e0.33\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 144px;\"\u003e\n \u003cp\u003e1.81\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 109px;\"\u003e\n \u003cp\u003e30.61\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003c/tbody\u003e\n\u003c/table\u003e\n\u003cp\u003eThe elemental content in the samples was determined by ICP-OES (Inductively Coupled Plasma Optical Emission Spectrometry, Thermo Fisher Scientific Inc., US). For solid, samples were dissolved using a specific volume of aqua regia (prepared with ultrapure nitric acid and hydrochloric acid in a 1:3 volume ratio), evaporated to dryness, diluted to a constant volume with 5% nitric acid, and finally subjected to ICP analysis to determine the concentration of metal ions in the solution.\u003c/p\u003e\n\u003cp\u003eThe content of Na\u003csub\u003e2\u003c/sub\u003eCO\u003csub\u003e3\u003c/sub\u003e and Na\u003csub\u003e2\u003c/sub\u003eSO\u003csub\u003e4\u003c/sub\u003e was determined by titration. A small amount of solid crystallite was dissolved into 50ml water, which was titrated with 0.1M HCl solution until the solution turns from red to colorless using phenolphthalein as an indicator. During this process, Na\u003csub\u003e2\u003c/sub\u003eCO\u003csub\u003e3\u003c/sub\u003e in the solution is neutralized to NaHCO\u003csub\u003e3\u003c/sub\u003e. Then add methyl orange as indicator, continue to titrate with 0.1M HCl solution until the solution changes from yellow to orange, indicating that NaHCO\u003csub\u003e3\u003c/sub\u003e in the solution is completely neutralized to H\u003csub\u003e2\u003c/sub\u003eCO\u003csub\u003e3\u003c/sub\u003e, and record the amount of hydrochloric acid. If the amounts of hydrochloric acid used in the two processes are equal, the average value shall be taken to calculate the content of sodium carbonate. After boiling the remaining solution for 1min, add a concentrated barium chloride solution, shake and wait for the upper solution to become clear before adding another drop of barium chloride solution. If there is precipitation, repeat the above steps until there is no precipitation. Filter and dry the barium sulfate precipitation and weigh it to calculate the sodium sulfate content.\u0026nbsp;\u003c/p\u003e\n\u003ch2\u003eReactions\u0026nbsp;\u003c/h2\u003e\n\u003cp\u003eThe Pb in\u0026nbsp;ammonia leaching residue\u0026nbsp;mainly exists in the form of PbO and PbSO\u003csub\u003e4\u003c/sub\u003e. The removal of Pb from\u0026nbsp;ammonia leaching residue\u0026nbsp;relies on the difference in solubility product between PbSO\u003csub\u003e4\u003c/sub\u003e and PbCO\u003csub\u003e3\u003c/sub\u003e: at 25℃, the solubility product of PbSO\u003csub\u003e4\u003c/sub\u003e is 1.6\u0026times;10\u003csup\u003e-8\u003c/sup\u003e, and the solubility product of PbCO\u003csub\u003e3\u003c/sub\u003e is 7.4\u0026times;10\u003csup\u003e-14\u003c/sup\u003e, realizing the transformation from PbSO\u003csub\u003e4\u003c/sub\u003e to PbCO\u003csub\u003e3\u003c/sub\u003e. The main reactions are as follows:\u003c/p\u003e\n\u003cp\u003ePbSO\u003csub\u003e4\u003c/sub\u003e + Na\u003csub\u003e2\u003c/sub\u003eCO\u003csub\u003e3\u003c/sub\u003e = Na\u003csub\u003e2\u003c/sub\u003eSO\u003csub\u003e4\u003c/sub\u003e + PbCO\u003csub\u003e3\u003c/sub\u003e\u003c/p\u003e\n\u003cp\u003eThe concentration of Na\u003csub\u003e2\u003c/sub\u003eSO\u003csub\u003e4\u003c/sub\u003e in the Pb carbonation solution will become higher after several cycles of accumulation, which will finally deteriorate the carbonation effect. Moreover, Na\u003csub\u003e2\u003c/sub\u003eSO\u003csub\u003e4\u003c/sub\u003e will block the pipeline in the industrial production during cooling, so the part of the solution after carbonation must sent to freezing crystallization, generating Na\u003csub\u003e2\u003c/sub\u003eSO\u003csub\u003e4\u003c/sub\u003e\u0026iexcl;10H\u003csub\u003e2\u003c/sub\u003eO product.\u003c/p\u003e\n\u003cp\u003eThe Pb in carbonation residue mainly exists in the form of PbCO\u003csub\u003e3\u003c/sub\u003e which can be leached into the solution by HCl.\u003c/p\u003e\n\u003cp\u003ePbCO\u003csub\u003e3\u003c/sub\u003e + 2HCl = PbCl\u003csub\u003e2\u003c/sub\u003e + H2O +CO\u003csub\u003e2\u003c/sub\u003e\u003c/p\u003e\n\u003cp\u003eThe Pb removal residue is then sent for Ba removal; while PbSO\u003csub\u003e4\u003c/sub\u003e is precipitated by adding H\u003csub\u003e2\u003c/sub\u003eSO\u003csub\u003e4\u003c/sub\u003e in the leaching solution of PbCl\u003csub\u003e2\u003c/sub\u003e, and the regenerated HCl is returned to leach PbCO\u003csub\u003e3\u003c/sub\u003e. Main reactions:\u003c/p\u003e\n\u003cp\u003ePbCl\u003csub\u003e2\u0026nbsp;\u003c/sub\u003e+ H\u003csub\u003e2\u003c/sub\u003eSO\u003csub\u003e4\u003c/sub\u003e = PbSO\u003csub\u003e4\u003c/sub\u003e\u0026darr; + 2HCl\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eThe Ba mainly exists in the form of BaSO\u003csub\u003e4\u003c/sub\u003e in the Pb removal residue. The core of barium carbonation process is the solubility product balance of [Ba\u003csup\u003e2+\u003c/sup\u003e][SO\u003csub\u003e4\u003c/sub\u003e\u003csup\u003e2-\u003c/sup\u003e]/[Ba\u003csup\u003e2+\u003c/sup\u003e][CO\u003csub\u003e3\u003c/sub\u003e\u003csup\u003e2-\u003c/sup\u003e]: Although the solubility product of BaSO\u003csub\u003e4\u003c/sub\u003e is 1.08\u0026times;10\u003csup\u003e-10\u003c/sup\u003e and that of BaCO\u003csub\u003e3\u003c/sub\u003e is 8.1\u0026times;10\u003csup\u003e-9\u003c/sup\u003e at 25 ℃, if solid BaSO\u003csub\u003e4\u003c/sub\u003e\u0026nbsp; and concentrated Na\u003csub\u003e2\u003c/sub\u003eCO\u003csub\u003e3\u003c/sub\u003e solution are boiled together, BaSO\u003csub\u003e4\u003c/sub\u003e can be converted to BaCO\u003csub\u003e3\u003c/sub\u003e. That is to control the high concentration of carbonate ions so that [Ba\u003csup\u003e2+\u003c/sup\u003e][CO\u003csub\u003e3\u003c/sub\u003e\u003csup\u003e2-\u003c/sup\u003e] is greater than the solubility product of BaCO\u003csub\u003e3\u003c/sub\u003e, so that barium carbonate can be precipitated, while [Ba\u003csup\u003e2+\u003c/sup\u003e][SO\u003csub\u003e4\u003c/sub\u003e\u003csup\u003e2-\u003c/sup\u003e] is reduced to less than the solubility product of BaSO\u003csub\u003e4\u003c/sub\u003e, so that more BaSO\u003csub\u003e4\u003c/sub\u003e can be dissolved. The transformation from BaSO\u003csub\u003e4\u003c/sub\u003e to BaCO\u003csub\u003e3\u003c/sub\u003e was realized by controlling the leaching conditions.\u003c/p\u003e\n\u003cp\u003eBaSO\u003csub\u003e4\u003c/sub\u003e + Na\u003csub\u003e2\u003c/sub\u003eCO\u003csub\u003e3\u003c/sub\u003e ⇋BaCO\u003csub\u003e3\u003c/sub\u003e +Na\u003csub\u003e2\u003c/sub\u003eSO\u003csub\u003e4\u003c/sub\u003e\u003c/p\u003e\n\u003cp\u003eThe Ba in carbonation residue is mainly BaCO\u003csub\u003e3\u003c/sub\u003e, and Ba in BaCO\u003csub\u003e3\u003c/sub\u003e is leached into solution by HCl.\u003c/p\u003e\n\u003cp\u003eBaCO\u003csub\u003e3\u0026nbsp;\u003c/sub\u003e+ 2HCl = BaCl\u003csub\u003e2\u0026nbsp;\u003c/sub\u003e+ H\u003csub\u003e2\u003c/sub\u003eO +CO\u003csub\u003e2\u003c/sub\u003e\u003c/p\u003e\n\u003cp\u003eThe Ba removal residue obtained by leaching is sent for the Au/Ag recovery; while the H\u003csub\u003e2\u003c/sub\u003eSO\u003csub\u003e4\u003c/sub\u003e was added to BaCl\u003csub\u003e2\u003c/sub\u003e leaching solution to precipitate BaSO\u003csub\u003e4\u003c/sub\u003e, and regenerated HCl returns to leach BaCO\u003csub\u003e3\u003c/sub\u003e. Main reactions:\u003c/p\u003e\n\u003cp\u003eBaCl\u003csub\u003e2\u003c/sub\u003e + H\u003csub\u003e2\u003c/sub\u003eSO\u003csub\u003e4\u003c/sub\u003e = BaSO\u003csub\u003e4\u003c/sub\u003e\u0026darr; + 2HCl\u003c/p\u003e"},{"header":"Results and discussion","content":"\u003cp\u003e\u003cstrong\u003e4.1 PbSO\u003csub\u003e4\u003c/sub\u003e carbonation and leaching\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eFirst, exploratory tests were carried out for PbSO\u003csub\u003e4\u003c/sub\u003e removal by carbonation, and the effects of different concentration of Na\u003csub\u003e2\u003c/sub\u003eCO\u003csub\u003e3\u003c/sub\u003e in the solution on lead leaching rate were studied, as shown in Table 3. The Pb carbonation was carried out at 80 ℃ for 1h with liquid-solid ratio of 3/1. After filtration and washing, the carbonation residue was leached by hydrochloric acid at 80 ℃ for 1h. The final pH of leaching was controlled at pH 1 with liquid-solid ratio of leaching of 30/1 to ensure a complete PbCl\u003csub\u003e2\u0026nbsp;\u003c/sub\u003edissolution. Maintaining at high temperature was attempted during filtration to avoid precipitation of PbCl\u003csub\u003e2\u003c/sub\u003e.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eTable 3 Test results for PbSO\u003csub\u003e4\u003c/sub\u003e carbonation and leaching\u003c/p\u003e\n\u003ctable border=\"1\" cellspacing=\"0\" cellpadding=\"0\" width=\"99%\"\u003e\n \u003ctbody\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 12px;\"\u003e\n \u003cp\u003eTest No.\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 16px;\"\u003e\n \u003cp\u003eFeed solid, g\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 21px;\"\u003e\n \u003cp\u003eFeed solution\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 14px;\"\u003e\n \u003cp\u003eLeaching residue, g\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 16px;\"\u003e\n \u003cp\u003ePb in leaching residue\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 18px;\"\u003e\n \u003cp\u003ePb leaching rate\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 12px;\"\u003e\n \u003cp\u003e1\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 16px;\"\u003e\n \u003cp\u003e50\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 21px;\"\u003e\n \u003cp\u003e80g/L Na\u003csub\u003e2\u003c/sub\u003eCO\u003csub\u003e3\u003c/sub\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 98px;\"\u003e\n \u003cp\u003e27.43\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 110px;\"\u003e\n \u003cp\u003e21.78%\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 119px;\"\u003e\n \u003cp\u003e54.67%\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 12px;\"\u003e\n \u003cp\u003e2\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 16px;\"\u003e\n \u003cp\u003e50\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 21px;\"\u003e\n \u003cp\u003e100g/L Na\u003csub\u003e2\u003c/sub\u003eCO\u003csub\u003e3\u003c/sub\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 14px;\"\u003e\n \u003cp\u003e28.79\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 16px;\"\u003e\n \u003cp\u003e21.13%\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 18px;\"\u003e\n \u003cp\u003e53.84%\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 12px;\"\u003e\n \u003cp\u003e3\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 16px;\"\u003e\n \u003cp\u003e50\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 21px;\"\u003e\n \u003cp\u003e40g/L Na\u003csub\u003e2\u003c/sub\u003eCO\u003csub\u003e3\u003c/sub\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 14px;\"\u003e\n \u003cp\u003e25.92\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 16px;\"\u003e\n \u003cp\u003e7.01%\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 18px;\"\u003e\n \u003cp\u003e86.21%\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 12px;\"\u003e\n \u003cp\u003e4\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 16px;\"\u003e\n \u003cp\u003e50\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 21px;\"\u003e\n \u003cp\u003e40g/L Na\u003csub\u003e2\u003c/sub\u003eCO\u003csub\u003e3\u003c/sub\u003e\u003c/p\u003e\n \u003cp\u003e+300g/L Na\u003csub\u003e2\u003c/sub\u003eSO\u003csub\u003e4\u003c/sub\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 14px;\"\u003e\n \u003cp\u003e27.72\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 16px;\"\u003e\n \u003cp\u003e8.95%\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 18px;\"\u003e\n \u003cp\u003e81.19%\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 12px;\"\u003e\n \u003cp\u003e5\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 16px;\"\u003e\n \u003cp\u003e50\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 21px;\"\u003e\n \u003cp\u003e100g/L Na\u003csub\u003e2\u003c/sub\u003eCO\u003csub\u003e3\u003c/sub\u003e\u003c/p\u003e\n \u003cp\u003e+300g/L Na\u003csub\u003e2\u003c/sub\u003eSO\u003csub\u003e4\u003c/sub\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 14px;\"\u003e\n \u003cp\u003e23.91\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 16px;\"\u003e\n \u003cp\u003e4.02%\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 18px;\"\u003e\n \u003cp\u003e92.71%\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 12px;\"\u003e\n \u003cp\u003e6\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 16px;\"\u003e\n \u003cp\u003e50\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 21px;\"\u003e\n \u003cp\u003e150g/L Na\u003csub\u003e2\u003c/sub\u003eCO\u003csub\u003e3\u003c/sub\u003e\u003c/p\u003e\n \u003cp\u003e+300g/L Na\u003csub\u003e2\u003c/sub\u003eSO\u003csub\u003e4\u003c/sub\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 14px;\"\u003e\n \u003cp\u003e22.72\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 16px;\"\u003e\n \u003cp\u003e3.23%\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 18px;\"\u003e\n \u003cp\u003e94.43%\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 12px;\"\u003e\n \u003cp\u003e7\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 16px;\"\u003e\n \u003cp\u003e50\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 21px;\"\u003e\n \u003cp\u003e0\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 14px;\"\u003e\n \u003cp\u003e32.46\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 16px;\"\u003e\n \u003cp\u003e17.54%\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 18px;\"\u003e\n \u003cp\u003e56.80%\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003c/tbody\u003e\n\u003c/table\u003e\n\u003cp\u003eIt can be seen from Table 3 that the amount of Na\u003csub\u003e2\u003c/sub\u003eCO\u003csub\u003e3\u003c/sub\u003e used in the first two tests is sufficient, but the Pb leaching rate is still low, primarily because the solution temperature drops during filtration and PbCl\u003csub\u003e2\u0026nbsp;\u003c/sub\u003eprecipitates. The content of BaSO\u003csub\u003e4\u003c/sub\u003e in the HCl leaching residue is high, and it is easy to settle down. Therefore, from test No. 3, settlement was allowed for 5min to preserve the heat, the supernatant was decanted prior to filtration. It can be seen that only 40g/L Na\u003csub\u003e2\u003c/sub\u003eCO\u003csub\u003e3\u003c/sub\u003e can achieve 86.21% of lead leaching rate. In test No. 6, no Na\u003csub\u003e2\u003c/sub\u003eCO\u003csub\u003e3\u003c/sub\u003e was used, but the leaching rate also reached 56.80%. It is preliminarily considered that the PbO accounts for 56.80% of total Pb in the ammonia leaching residue.\u003c/p\u003e\n\u003cp\u003eIt can be seen that the leaching rate of lead in test No. 5 and No. 6 can reach 92.71% and 94.43% respectively, and it is difficult to increase the leaching rate by further increasing the dosage of sodium carbonate. Combined with XRD in Figure 3, it can be inferred that a small portion of Pb is wrapped by BaSO\u003csub\u003e4\u003c/sub\u003e or forms Pb-Ba sulfate complex salt. This portion of Pb can only be released after BaSO\u003csub\u003e4\u003c/sub\u003e leaching. Therefore, the final BaSO\u003csub\u003e4\u003c/sub\u003e product will contain a small amount of PbSO\u003csub\u003e4\u003c/sub\u003e.\u003c/p\u003e\n\u003cp\u003eNext, in order to design a two-stage lead carbonation conversion process, it is necessary to specify the concentration ratio of Na\u003csub\u003e2\u003c/sub\u003eCO\u003csub\u003e3\u003c/sub\u003e and Na\u003csub\u003e2\u003c/sub\u003eSO\u003csub\u003e4\u003c/sub\u003e in the solution when only part of the lead is carbonated. Under the conditions of 100g/L Na\u003csub\u003e2\u003c/sub\u003eCO\u003csub\u003e3\u003c/sub\u003e+300g/L Na\u003csub\u003e2\u003c/sub\u003eSO\u003csub\u003e4\u003c/sub\u003e, liquid-solid ratio of 1/1, conversion temperature of 80 ℃ and conversion time of 1h, the lead conversion is incomplete according to the calculation and test results, so the concentration limit of lead conversion can be explored. Finally, the solution after lead carbonation conversion has 47.7g/L Na\u003csub\u003e2\u003c/sub\u003eCO\u003csub\u003e3\u003c/sub\u003e+327g/L Na\u003csub\u003e2\u003c/sub\u003eSO\u003csub\u003e4\u003c/sub\u003e measured by titration. That is to say, if the ratio of Na\u003csub\u003e2\u003c/sub\u003eCO\u003csub\u003e3\u003c/sub\u003e/Na\u003csub\u003e2\u003c/sub\u003eSO\u003csub\u003e4\u003c/sub\u003e is lower than 47.7g/L/327g/L, lead conversion can not be carried out.\u003c/p\u003e\n\u003cp\u003eAccording to the limit concentration of Pb carbonation conversion, it is assumed that the concentration after lead conversion is 60 g/L Na\u003csub\u003e2\u003c/sub\u003eCO\u003csub\u003e3\u003c/sub\u003e+327 g/L Na\u003csub\u003e2\u003c/sub\u003eSO\u003csub\u003e4\u003c/sub\u003e. Through calculation, using 76.68 g/L Na\u003csub\u003e2\u003c/sub\u003eCO\u003csub\u003e3\u003c/sub\u003e+302.65 g/L Na\u003csub\u003e2\u003c/sub\u003eSO\u003csub\u003e4\u003c/sub\u003e, 80% PbSO\u003csub\u003e4\u003c/sub\u003e is converted to PbCO\u003csub\u003e3\u0026nbsp;\u003c/sub\u003ein the 1\u003csup\u003est\u003c/sup\u003e stage, while avoiding BaSO\u003csub\u003e4\u003c/sub\u003e in the ammonia leaching residue from being carbonated. In the 2\u003csup\u003end\u003c/sup\u003e stage, 80.85 g/L Na\u003csub\u003e2\u003c/sub\u003eCO\u003csub\u003e3\u003c/sub\u003e+297.07 g/L Na\u003csub\u003e2\u003c/sub\u003eSO\u003csub\u003e4\u0026nbsp;\u003c/sub\u003ewas used to convert the remaining PbSO\u003csub\u003e4\u003c/sub\u003e into PbCO\u003csub\u003e3\u003c/sub\u003e. The Pb removal residue obtained after hydrochloric acid leaching contained 3.06% Pb and its leaching rate was 94.80%. The measured concentration of the solution after the 1\u003csup\u003est\u003c/sup\u003e stage Pb carbonation is 60.95 g/L Na\u003csub\u003e2\u003c/sub\u003eCO\u003csub\u003e3\u003c/sub\u003e+325 g/L Na\u003csub\u003e2\u003c/sub\u003eSO\u003csub\u003e4\u003c/sub\u003e, which is basically consistent with the design estimate. This shows that the two-stage countercurrent Pb carbonation process is feasible.\u003c/p\u003e\n\u003cp id=\"_Toc195622538\"\u003e\u003cstrong\u003e4.2 BaSO\u003csub\u003e4\u003c/sub\u003e carbonation and leaching\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eIn order to carry out the test work for barium removal, a large quantity of Pb removal residue were prepared based on 4kg of ammonia leaching residue. In this work, 150g/L\u0026nbsp;Na\u003csub\u003e2\u003c/sub\u003eCO\u003csub\u003e3\u003c/sub\u003e+300g/l\u0026nbsp;Na\u003csub\u003e2\u003c/sub\u003eSO\u003csub\u003e4\u003c/sub\u003e solution was added to this batch of ammonia leaching residue with a liquid-solid ratio of 3:1 and reacted at 80 ℃ for 1h for carbonation conversion. After washing the carbonation residue, water with a liquid-solid ratio of 30:1 was added, and hydrochloric acid was added to adjust the pH to 1.0. After reacting at 80 ℃ for 1h, filtration and drying, 1818g of Pb removal residue was obtained, and its main chemical composition is shown in Table 4. The XRD analysis results are shown in Figure 4.\u003c/p\u003e\n\u003cp\u003eTable 4 Elemental analysis of Pb removal residue（%）\u003c/p\u003e\n\u003cdiv align=\"\"\u003e\n \u003ctable border=\"1\" cellspacing=\"0\" cellpadding=\"0\"\u003e\n \u003ctbody\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 109px;\"\u003e\n \u003cp\u003eBa\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 109px;\"\u003e\n \u003cp\u003ePb\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 109px;\"\u003e\n \u003cp\u003eAs\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 110px;\"\u003e\n \u003cp\u003eSb\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 110px;\"\u003e\n \u003cp\u003eSn\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 109px;\"\u003e\n \u003cp\u003e36.26\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 109px;\"\u003e\n \u003cp\u003e5.85\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 109px;\"\u003e\n \u003cp\u003e0.46\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 110px;\"\u003e\n \u003cp\u003e6.64\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 110px;\"\u003e\n \u003cp\u003e1.57\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003c/tbody\u003e\n \u003c/table\u003e\n\u003c/div\u003e\n\u003cp\u003eTaking 50g of Pb removal residue as feed for each Ba removal test, and the liquid-solid ratio of 5:1 was applied for barium carbonation, with the carbonation conversion temperature at 95 ℃. After carbonation conversion for 1h, water was added with the liquid-solid ratio of 5:1 after the conversion residue was washed, and hydrochloric acid was used to adjust the pH to 1.0, and then reacted at 80 ℃ for 1h to obtain Ba removal residue. Test results of one-stage Ba carbonation and leaching is shown in Table 5.\u003c/p\u003e\n\u003cp\u003eTable 5 Test results of one-stage Ba carbonation and leaching\u003c/p\u003e\n\u003ctable border=\"1\" cellspacing=\"0\" cellpadding=\"0\"\u003e\n \u003ctbody\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 96px;\"\u003e\n \u003cp\u003eTest No.\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 92px;\"\u003e\n \u003cp\u003eFeed, g\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 121px;\"\u003e\n \u003cp\u003eFeed solution\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 106px;\"\u003e\n \u003cp\u003eResidue, g\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 113px;\"\u003e\n \u003cp\u003eBa in residue\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 129px;\"\u003e\n \u003cp\u003eBa leaching rate\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 96px;\"\u003e\n \u003cp\u003e1\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 92px;\"\u003e\n \u003cp\u003e50.00\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 121px;\"\u003e\n \u003cp\u003e200 g/L\u0026nbsp;Na\u003csub\u003e2\u003c/sub\u003eCO\u003csub\u003e3\u003c/sub\u003e\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 106px;\"\u003e\n \u003cp\u003e31.11\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 113px;\"\u003e\n \u003cp\u003e35.65%\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 129px;\"\u003e\n \u003cp\u003e38.83%\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 96px;\"\u003e\n \u003cp\u003e2\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 92px;\"\u003e\n \u003cp\u003e50.00\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 121px;\"\u003e\n \u003cp\u003e250 g/L\u0026nbsp;Na\u003csub\u003e2\u003c/sub\u003eCO\u003csub\u003e3\u003c/sub\u003e\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 106px;\"\u003e\n \u003cp\u003e28.22\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 113px;\"\u003e\n \u003cp\u003e30.60%\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 129px;\"\u003e\n \u003cp\u003e52.37%\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 96px;\"\u003e\n \u003cp\u003e3\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 92px;\"\u003e\n \u003cp\u003e50.00\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 121px;\"\u003e\n \u003cp\u003e300 g/L\u0026nbsp;Na\u003csub\u003e2\u003c/sub\u003eCO\u003csub\u003e3\u003c/sub\u003e\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 106px;\"\u003e\n \u003cp\u003e25.41\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 113px;\"\u003e\n \u003cp\u003e24.62%\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 129px;\"\u003e\n \u003cp\u003e65.49%\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 96px;\"\u003e\n \u003cp\u003e4\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 92px;\"\u003e\n \u003cp\u003e50.00\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 121px;\"\u003e\n \u003cp\u003e350 g/L\u0026nbsp;Na\u003csub\u003e2\u003c/sub\u003eCO\u003csub\u003e3\u003c/sub\u003e\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 106px;\"\u003e\n \u003cp\u003e25.20\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 113px;\"\u003e\n \u003cp\u003e24.00%\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 129px;\"\u003e\n \u003cp\u003e66.64%\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 96px;\"\u003e\n \u003cp\u003e5\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 92px;\"\u003e\n \u003cp\u003e50.00\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 121px;\"\u003e\n \u003cp\u003e400 g/L\u0026nbsp;Na\u003csub\u003e2\u003c/sub\u003eCO\u003csub\u003e3\u003c/sub\u003e\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 106px;\"\u003e\n \u003cp\u003e29.87\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 113px;\"\u003e\n \u003cp\u003e29.33%\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 129px;\"\u003e\n \u003cp\u003e51.68%\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 96px;\"\u003e\n \u003cp\u003e6\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 92px;\"\u003e\n \u003cp\u003e50.00\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 121px;\"\u003e\n \u003cp\u003e450 g/L\u0026nbsp;Na\u003csub\u003e2\u003c/sub\u003eCO\u003csub\u003e3\u003c/sub\u003e\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 106px;\"\u003e\n \u003cp\u003e31.09\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 113px;\"\u003e\n \u003cp\u003e29.55%\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 129px;\"\u003e\n \u003cp\u003e49.33%\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003c/tbody\u003e\n\u003c/table\u003e\n\u003cp\u003eIt can be seen that the Ba removal residue obtained by using only one-stage carbonation conversion process still contains a large amount of barium, and the leaching rate is not high (up to 70%), and the excessive amount of\u0026nbsp;Na\u003csub\u003e2\u003c/sub\u003eCO\u003csub\u003e3\u003c/sub\u003e will reduce the leaching rate of barium. Therefore, in order to completely convert to BaCO\u003csub\u003e3\u003c/sub\u003e, two-stage barium conversion process can be implemented. First of all, the conversion limit was tested. Under the conditions of liquid-solid ratio of 1:1, 95 ℃ and 1h, 350 g/L Na\u003csub\u003e2\u003c/sub\u003eCO\u003csub\u003e3\u003c/sub\u003e+30 g/L Na\u003csub\u003e2\u003c/sub\u003eSO\u003csub\u003e4\u003c/sub\u003e as feed solution were used for conversion. The conversion solution after Ba carbonation was determined to have 325 g/L Na\u003csub\u003e2\u003c/sub\u003eCO\u003csub\u003e3\u003c/sub\u003e+46.88 g/L Na\u003csub\u003e2\u003c/sub\u003eSO\u003csub\u003e4\u003c/sub\u003e by titration. That is to say, if the mass ratio of Na\u003csub\u003e2\u003c/sub\u003eCO\u003csub\u003e3\u003c/sub\u003e/Na\u003csub\u003e2\u003c/sub\u003eSO\u003csub\u003e4\u003c/sub\u003e in the solution is lower than 325/46.88, the carbonation will no longer occur.\u003c/p\u003e\n\u003cp\u003eBased on the one-stage test and barium conversion limit, 50g of Pb removal residue as feed was taken for two-stage carbonation conversion test. The liquid-solid ratio varied, and the reactions were carried out at 95℃ for 1h. No washing operation was applied between the two stages. After filtering and washing, the conversion residue was added with water with the liquid-solid ratio of 5:1, and hydrochloric acid was added to adjust the pH to 1.0. After reaction at 80 ℃ for 1h, the Ba removal residue was obtained and the test results are shown in Table 6.\u003c/p\u003e\n\u003cp\u003eTable 6 Two-stage Ba carbonation and leaching test results\u003c/p\u003e\n\u003ctable border=\"1\" cellspacing=\"0\" cellpadding=\"0\" width=\"99%\"\u003e\n \u003ctbody\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 6px;\"\u003e\n \u003cp\u003e\u003cstrong\u003eTest No.\u0026nbsp;\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 10px;\"\u003e\n \u003cp\u003e\u003cstrong\u003eFeed, g\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 21px;\"\u003e\n \u003cp\u003e\u003cstrong\u003e1\u003csup\u003est\u003c/sup\u003e stage\u003c/strong\u003e\u003c/p\u003e\n \u003cp\u003e\u003cstrong\u003efeed solution\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 20px;\"\u003e\n \u003cp\u003e\u003cstrong\u003e2\u003csup\u003end\u003c/sup\u003e stage\u003c/strong\u003e\u003c/p\u003e\n \u003cp\u003e\u003cstrong\u003efeed solution\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 10px;\"\u003e\n \u003cp\u003e\u003cstrong\u003eResidue, g\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 13px;\"\u003e\n \u003cp\u003e\u003cstrong\u003eBa in residue\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 15px;\"\u003e\n \u003cp\u003e\u003cstrong\u003eBa leaching rate\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 6px;\"\u003e\n \u003cp\u003e1\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 10px;\"\u003e\n \u003cp\u003e50.00\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 21px;\"\u003e\n \u003cp\u003e401.75\u0026nbsp;g/L Na\u003csub\u003e2\u003c/sub\u003eCO\u003csub\u003e3\u003c/sub\u003e\u003c/p\u003e\n \u003cp\u003e+8.96 g/L Na\u003csub\u003e2\u003c/sub\u003eSO\u003csub\u003e4\u003c/sub\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 20px;\"\u003e\n \u003cp\u003e408.44\u0026nbsp;g/L Na\u003csub\u003e2\u003c/sub\u003eCO\u003csub\u003e3\u003c/sub\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 10px;\"\u003e\n \u003cp\u003e22.35\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 13px;\"\u003e\n \u003cp\u003e9.04%\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 15px;\"\u003e\n \u003cp\u003e81.34%\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 6px;\"\u003e\n \u003cp\u003e2\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 10px;\"\u003e\n \u003cp\u003e50.00\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 21px;\"\u003e\n \u003cp\u003e353\u0026nbsp;g/L Na\u003csub\u003e2\u003c/sub\u003eCO\u003csub\u003e3\u003c/sub\u003e\u003c/p\u003e\n \u003cp\u003e+9.38 g/L Na\u003csub\u003e2\u003c/sub\u003eSO\u003csub\u003e4\u003c/sub\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 20px;\"\u003e\n \u003cp\u003e360\u0026nbsp;g/L Na\u003csub\u003e2\u003c/sub\u003eCO\u003csub\u003e3\u003c/sub\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 10px;\"\u003e\n \u003cp\u003e14.62\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 13px;\"\u003e\n \u003cp\u003e2.18%\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 15px;\"\u003e\n \u003cp\u003e98.24%\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 6px;\"\u003e\n \u003cp\u003e3\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 10px;\"\u003e\n \u003cp\u003e50.00\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 21px;\"\u003e\n \u003cp\u003e356.74\u0026nbsp;g/L Na\u003csub\u003e2\u003c/sub\u003eCO\u003csub\u003e3\u003c/sub\u003e\u003c/p\u003e\n \u003cp\u003e+13 g/L Na\u003csub\u003e2\u003c/sub\u003eSO\u003csub\u003e4\u003c/sub\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 20px;\"\u003e\n \u003cp\u003e363.74\u0026nbsp;g/LNa\u003csub\u003e2\u003c/sub\u003eCO\u003csub\u003e3\u003c/sub\u003e\u003c/p\u003e\n \u003cp\u003e+3.64 g/L Na\u003csub\u003e2\u003c/sub\u003eSO\u003csub\u003e4\u003c/sub\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 10px;\"\u003e\n \u003cp\u003e12.13\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 13px;\"\u003e\n \u003cp\u003e5.20%\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 15px;\"\u003e\n \u003cp\u003e96.52%\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003c/tbody\u003e\n\u003c/table\u003e\n\u003cp\u003eBy calculation, 80% of the BaSO\u003csub\u003e4\u003c/sub\u003e is converted to BaCO\u003csub\u003e3\u003c/sub\u003e using 401.75 g/L Na\u003csub\u003e2\u003c/sub\u003eCO\u003csub\u003e3\u003c/sub\u003e+8.96 g/L Na\u003csub\u003e2\u003c/sub\u003eSO\u003csub\u003e4\u003c/sub\u003e at the first stage and 408.44 g/L Na\u003csub\u003e2\u003c/sub\u003eCO\u003csub\u003e3\u003c/sub\u003e at the second stage to convert the remaining BaSO\u003csub\u003e4.\u003c/sub\u003e The liquid-solid ratio was 5/1 at both stages, but the final barium leaching rate is only 81.34%. It should be caused by the high concentration of Na\u003csub\u003e2\u003c/sub\u003eCO\u003csub\u003e3\u003c/sub\u003e, almost reaching its solubility. In order to solve this problem, the liquid-solid ratio was increased to 8/1, and the two-stage barium carbonation conversion test was recalculated, as shown in Table 6. The barium leaching rate has reached 98.24% for test No. 2. Considering the subsequent sodium carbonate crystallization product may contain ~1% sodium sulfate impurities, the test No. 3 was carried out. The concentration of Na\u003csub\u003e2\u003c/sub\u003eSO\u003csub\u003e4\u003c/sub\u003e in the two stages of barium conversion was 13 g/L and 3.64 g/L respectively, and the barium leaching rate could still reach 96.52%. The composition of Ba removal residue is shown in Table 7 for the test No. 2 in Table 6. It is seen that Ba content was reduced to only 2.18%, while Pb content in Ba removal residue was 6.23%. The Pb in the form of PbS cannot be easily converted because no oxidative was added. The Bi/Sb in Ba removal residue was enriched to 23.70% and 22.99%, respectively, which is saleable after Au/Ag recovery. According to XRD analysis in Fig. 5, there is only BiOCl and small amount of BaSO\u003csub\u003e4\u003c/sub\u003e detected in the residue.\u003c/p\u003e\n\u003cp\u003eTable 7 Elemental analysis of Ba removal residue（%）\u003c/p\u003e\n\u003cdiv align=\"\"\u003e\n \u003ctable border=\"1\" cellspacing=\"0\" cellpadding=\"0\"\u003e\n \u003ctbody\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 82px;\"\u003e\n \u003cp\u003eBa\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 82px;\"\u003e\n \u003cp\u003e\u0026nbsp; \u0026nbsp; \u0026nbsp; Pb\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 82px;\"\u003e\n \u003cp\u003eBi\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 82px;\"\u003e\n \u003cp\u003eTe\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 82px;\"\u003e\n \u003cp\u003eSb\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 82px;\"\u003e\n \u003cp\u003eSn\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 82px;\"\u003e\n \u003cp\u003e2.18\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 82px;\"\u003e\n \u003cp\u003e6.23\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 82px;\"\u003e\n \u003cp\u003e23.70\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 82px;\"\u003e\n \u003cp\u003e0.48\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 82px;\"\u003e\n \u003cp\u003e22.99\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 82px;\"\u003e\n \u003cp\u003e5.54\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003c/tbody\u003e\n \u003c/table\u003e\n\u003c/div\u003e\n\u003cp\u003e\u003cstrong\u003e4.3 Na\u003csub\u003e2\u003c/sub\u003eSO\u003csub\u003e4\u003c/sub\u003e /Na\u003csub\u003e2\u003c/sub\u003eCO\u003csub\u003e3\u003c/sub\u003e crystallization and recycling\u003c/strong\u003e\u003c/p\u003e\n\u003cp id=\"_Toc195622536\"\u003e\u003cstrong\u003eNa\u003csub\u003e2\u003c/sub\u003eSO\u003csub\u003e4\u003c/sub\u003e crystallization\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eIn this section, 100 ml solution with 60 g/L Na\u003csub\u003e2\u003c/sub\u003eCO\u003csub\u003e3\u0026nbsp;\u003c/sub\u003e+ 325 g/L Na\u003csub\u003e2\u003c/sub\u003eSO\u003csub\u003e4\u003c/sub\u003e was used to simulate the solution after Pb carbonation. The test results for sodium sulfate crystallization are shown in Table 8.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eTable 8 Test results for Na\u003csub\u003e2\u003c/sub\u003eCO\u003csub\u003e3\u003c/sub\u003e freezing crystallization\u003c/p\u003e\n\u003cdiv align=\"\"\u003e\n \u003ctable border=\"1\" cellspacing=\"0\" cellpadding=\"0\" width=\"79%\"\u003e\n \u003ctbody\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 17px;\"\u003e\n \u003cp\u003e\u003cstrong\u003eFreezing temperature\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 20px;\"\u003e\n \u003cp\u003e\u003cstrong\u003e1\u003csup\u003est\u003c/sup\u003e stage freezing\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 19px;\"\u003e\n \u003cp\u003e\u003cstrong\u003e2\u003csup\u003end\u0026nbsp;\u003c/sup\u003estage freezing\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 25px;\"\u003e\n \u003cp\u003e\u003cstrong\u003eCrystallite dry weight, g\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 17px;\"\u003e\n \u003cp\u003e\u003cstrong\u003eContent of\u0026nbsp;\u003c/strong\u003e\u003cstrong\u003eNa\u003csub\u003e2\u003c/sub\u003eCO\u003csub\u003e3\u003c/sub\u003e\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 17px;\"\u003e\n \u003cp\u003e0℃\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 20px;\"\u003e\n \u003cp\u003e1h\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 19px;\"\u003e\n \u003cp\u003e/\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 25px;\"\u003e\n \u003cp\u003e30.37\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 17px;\"\u003e\n \u003cp\u003e3.28%\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 17px;\"\u003e\n \u003cp\u003e10℃\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 20px;\"\u003e\n \u003cp\u003e1h\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 19px;\"\u003e\n \u003cp\u003e/\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 25px;\"\u003e\n \u003cp\u003e29.29\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 17px;\"\u003e\n \u003cp\u003e5.18%\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 17px;\"\u003e\n \u003cp\u003e10℃\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 20px;\"\u003e\n \u003cp\u003e1h\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 19px;\"\u003e\n \u003cp\u003e1h\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 25px;\"\u003e\n \u003cp\u003e24.86\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 17px;\"\u003e\n \u003cp\u003e1.27%\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003c/tbody\u003e\n \u003c/table\u003e\n\u003c/div\u003e\n\u003cp\u003eAfter freezing at 10℃for 1 h, the crystalline product was added with 25% water for recrystallization. The crystalline Na\u003csub\u003e2\u003c/sub\u003eSO\u003csub\u003e4\u003c/sub\u003e product with 1.27% Na\u003csub\u003e2\u003c/sub\u003eCO\u003csub\u003e3\u003c/sub\u003e was obtained with Na\u003csub\u003e2\u003c/sub\u003eSO\u003csub\u003e4\u003c/sub\u003e recovery reached 75.52%. The obtained crystallization mother liquor still contains enough Na\u003csub\u003e2\u003c/sub\u003eCO\u003csub\u003e3\u003c/sub\u003e concentration (71.55 g/L) for lead conversion, so it can be returned to the lead carbonation conversion section for recycling.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eNa\u003csub\u003e2\u003c/sub\u003eCO\u003csub\u003e3\u003c/sub\u003e crystallization\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe solution after the first stage of Ba carbonation conversion was sent for freezing crystallization of sodium carbonate. The obtained Na\u003csub\u003e2\u003c/sub\u003eCO\u003csub\u003e3\u0026nbsp;\u003c/sub\u003ecrystallite is returned to the first stage for barium conversion, and the obtained crystallization mother liquor with Na\u003csub\u003e2\u003c/sub\u003eSO\u003csub\u003e4\u003c/sub\u003e pollution is still useful for the Pb carbonation operation.\u003c/p\u003e\n\u003cp\u003eIn this section, 100 ml solution with 325 g/L Na\u003csub\u003e2\u003c/sub\u003eCO\u003csub\u003e3\u003c/sub\u003e+40 g/L Na\u003csub\u003e2\u003c/sub\u003eSO\u003csub\u003e4\u003c/sub\u003e was used to simulate the solution after first stage of Ba carbonation. The results for sodium carbonate freezing crystallization test are shown in Table 9. As shown in Fig. 6, the Na\u003csub\u003e2\u003c/sub\u003eCO\u003csub\u003e3\u0026nbsp;\u003c/sub\u003ecrystallite usually has a particle size of \u0026nbsp;1~2mm. The dry weight of the crystallite was obtained by heating up to 160℃ to remove all H\u003csub\u003e2\u003c/sub\u003eO in crystallite.\u003c/p\u003e\n\u003cp\u003eTable 9 Test results for Na\u003csub\u003e2\u003c/sub\u003eCO\u003csub\u003e3\u003c/sub\u003e freezing crystallization\u003c/p\u003e\n\u003cdiv align=\"\"\u003e\n \u003ctable border=\"1\" cellspacing=\"0\" cellpadding=\"0\"\u003e\n \u003ctbody\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 92px;\"\u003e\n \u003cp\u003e\u003cstrong\u003eFreezing temperature\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 70px;\"\u003e\n \u003cp\u003e\u003cstrong\u003e1\u003csup\u003est\u003c/sup\u003e stage freezing\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 71px;\"\u003e\n \u003cp\u003e\u003cstrong\u003e2\u003csup\u003end\u0026nbsp;\u003c/sup\u003estage freezing\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 108px;\"\u003e\n \u003cp\u003e\u003cstrong\u003eCrystallite dry weight, g\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 90px;\"\u003e\n \u003cp\u003e\u003cstrong\u003eContent of Na\u003csub\u003e2\u003c/sub\u003eSO\u003csub\u003e4\u003c/sub\u003e\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 129px;\"\u003e\n \u003cp\u003e\u003cstrong\u003e\u0026nbsp;\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 92px;\"\u003e\n \u003cp\u003e0℃\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 70px;\"\u003e\n \u003cp\u003e2h\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 71px;\"\u003e\n \u003cp\u003e/\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 108px;\"\u003e\n \u003cp\u003e29.28\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 90px;\"\u003e\n \u003cp\u003e6.56%\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 129px;\"\u003e\n \u003cp\u003eWithout washing\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 92px;\"\u003e\n \u003cp\u003e10℃\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 70px;\"\u003e\n \u003cp\u003e2h\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 71px;\"\u003e\n \u003cp\u003e/\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 108px;\"\u003e\n \u003cp\u003e27.57\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 90px;\"\u003e\n \u003cp\u003e7.30%\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 129px;\"\u003e\n \u003cp\u003eWithout washing\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 92px;\"\u003e\n \u003cp\u003e10℃\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 70px;\"\u003e\n \u003cp\u003e2h\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 71px;\"\u003e\n \u003cp\u003e/\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 108px;\"\u003e\n \u003cp\u003e22.77\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 90px;\"\u003e\n \u003cp\u003e4.64%\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 129px;\"\u003e\n \u003cp\u003eWith washing\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 92px;\"\u003e\n \u003cp\u003e10℃\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 70px;\"\u003e\n \u003cp\u003e2h\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 71px;\"\u003e\n \u003cp\u003e2h\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 108px;\"\u003e\n \u003cp\u003e20.64\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 90px;\"\u003e\n \u003cp\u003e2.30%\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 129px;\"\u003e\n \u003cp\u003eWithout washing\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 92px;\"\u003e\n \u003cp\u003e10℃\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 70px;\"\u003e\n \u003cp\u003e2h\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 71px;\"\u003e\n \u003cp\u003e2h\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 108px;\"\u003e\n \u003cp\u003e19.62\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 90px;\"\u003e\n \u003cp\u003e1.25%\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 129px;\"\u003e\n \u003cp\u003eWith washing\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 92px;\"\u003e\n \u003cp\u003e15℃\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 70px;\"\u003e\n \u003cp\u003e2h\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 71px;\"\u003e\n \u003cp\u003e2h\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 108px;\"\u003e\n \u003cp\u003e15.04\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 90px;\"\u003e\n \u003cp\u003e0.46%\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 129px;\"\u003e\n \u003cp\u003eWith washing\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 92px;\"\u003e\n \u003cp\u003e15℃\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 70px;\"\u003e\n \u003cp\u003e2h\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 71px;\"\u003e\n \u003cp\u003e/\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 108px;\"\u003e\n \u003cp\u003e20.10\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 90px;\"\u003e\n \u003cp\u003e1.41%\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 129px;\"\u003e\n \u003cp\u003eWith washing\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003c/tbody\u003e\n \u003c/table\u003e\n\u003c/div\u003e\n\u003cp\u003eIt can be seen that even though difference of Na\u003csub\u003e2\u003c/sub\u003eCO\u003csub\u003e3\u003c/sub\u003e and Na\u003csub\u003e2\u003c/sub\u003eSO\u003csub\u003e4\u003c/sub\u003e concentrations is large in the simulated solution, it is still difficult to crystallize pure Na\u003csub\u003e2\u003c/sub\u003eCO\u003csub\u003e3\u003c/sub\u003e from the solution. By using only one stage crystallization, the content of Na\u003csub\u003e2\u003c/sub\u003eSO\u003csub\u003e4\u0026nbsp;\u003c/sub\u003eas impurity in the obtained Na\u003csub\u003e2\u003c/sub\u003eCO\u003csub\u003e3\u0026nbsp;\u003c/sub\u003ecrystallite is as high as 4.64%, which may be due to the entrainment of mother liquor or the production of Na\u003csub\u003e2\u003c/sub\u003eCO\u003csub\u003e3\u003c/sub\u003e-Na\u003csub\u003e2\u003c/sub\u003eSO\u003csub\u003e4\u003c/sub\u003e double salt during crystallization. Therefore, several experiments were carried out by washing, recrystallization, prolonging crystallization time and increasing crystallization temperature. Although these methods will reduce the mass of final crystallite, qualified Na\u003csub\u003e2\u003c/sub\u003eCO\u003csub\u003e3\u003c/sub\u003e products with Na\u003csub\u003e2\u003c/sub\u003eSO\u003csub\u003e4\u003c/sub\u003e content of 1.25%, 1.41% and 0.46% were obtained. Selection of these various products will be determined by the flowsheet design. The obtained crystallization mother liquor still contains 140 g/L Na\u003csub\u003e2\u003c/sub\u003eCO\u003csub\u003e3\u003c/sub\u003e, and the washing solution also contains 100 g/L Na\u003csub\u003e2\u003c/sub\u003eCO\u003csub\u003e3\u003c/sub\u003e, which can be returned for Pb carbonation.\u003c/p\u003e\n\u003cp id=\"_Toc195622547\"\u003e\u003cstrong\u003e4.4 Flowsheet design and cyclic test\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eCyclic test for Pb removal\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eCompared to Ba carbonation, Pb carbonation is relatively easy. One-stage conversion can achieve good Pb carbonation. Therefore, the process route of one-stage Pb carbonation + Pb leaching by HCl + freezing crystallization of Na\u003csub\u003e2\u003c/sub\u003eSO\u003csub\u003e4\u003c/sub\u003e after carbonation + return of crystallization mother liquor to carbonation was adopted for laboratory cyclic test. In this test, 100g of ammonia leaching residue as feed was reacted with 300 mL carbonation solution (80.85 g/L Na\u003csub\u003e2\u003c/sub\u003eCO\u003csub\u003e3\u003c/sub\u003e+291 g/L Na\u003csub\u003e2\u003c/sub\u003eSO\u003csub\u003e4\u003c/sub\u003e) which was initially synthesized. After the carbonation reaction at 80℃ for 1h, 15% of the filtrate was used for crystallization and washing water filter the solid-liquid separation, and filter the washing water as the next washing water for recycling. The liquid after lead conversion, and the crystallization mother liquid was added with the remaining liquid after lead conversion and added with 50.62g water+6.64g Na\u003csub\u003e2\u003c/sub\u003eCO\u003csub\u003e3\u003c/sub\u003e as the liquid before lead conversion. 40g of the obtained lead conversion wet residue was used for acid leaching of lead.\u003c/p\u003e\n\u003cp\u003eTable 10 Cyclic test results for Pb removal by carbonation and leaching\u003c/p\u003e\n\u003ctable border=\"1\" cellspacing=\"0\" cellpadding=\"0\"\u003e\n \u003ctbody\u003e\n \u003ctr\u003e\n \u003ctd rowspan=\"2\" style=\"width: 69px;\"\u003e\n \u003cp\u003e\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd rowspan=\"2\" style=\"width: 152px;\"\u003e\n \u003cp\u003e\u003cstrong\u003eCarbonation solution\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd rowspan=\"2\" style=\"width: 92px;\"\u003e\n \u003cp\u003e\u003cstrong\u003eNa\u003csub\u003e2\u003c/sub\u003eSO\u003csub\u003e4\u0026nbsp;\u003c/sub\u003ecrystallite,\u0026nbsp;\u003c/strong\u003e\u003cstrong\u003eg\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd rowspan=\"2\" style=\"width: 138px;\"\u003e\n \u003cp\u003e\u003cstrong\u003eWet weight after\u0026nbsp;\u003c/strong\u003e\u003cstrong\u003ecarbonation,\u0026nbsp;\u003c/strong\u003e\u003cstrong\u003eg\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd colspan=\"2\" style=\"width: 199px;\"\u003e\n \u003cp\u003e\u003cstrong\u003eHCl leaching\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 100px;\"\u003e\n \u003cp\u003e\u003cstrong\u003eFeed, g\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 99px;\"\u003e\n \u003cp\u003e\u003cstrong\u003eResidue, g\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 69px;\"\u003e\n \u003cp\u003e1\u003csup\u003est\u003c/sup\u003e cycle\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 152px;\"\u003e\n \u003cp\u003e80.95\u0026nbsp;g/L Na\u003csub\u003e2\u003c/sub\u003eCO\u003csub\u003e3\u003c/sub\u003e\u003c/p\u003e\n \u003cp\u003e291g/L Na\u003csub\u003e2\u003c/sub\u003eSO\u003csub\u003e4\u003c/sub\u003e（synthesized）\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 92px;\"\u003e\n \u003cp\u003e9.82\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 138px;\"\u003e\n \u003cp\u003e113.24\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 100px;\"\u003e\n \u003cp\u003e40\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 99px;\"\u003e\n \u003cp\u003e16.31\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 69px;\"\u003e\n \u003cp\u003e2\u003csup\u003end\u003c/sup\u003e cycle\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 152px;\"\u003e\n \u003cp\u003e77.91\u0026nbsp;g/L Na\u003csub\u003e2\u003c/sub\u003eCO\u003csub\u003e3\u003c/sub\u003e\u003c/p\u003e\n \u003cp\u003e244.22g/L Na\u003csub\u003e2\u003c/sub\u003eSO\u003csub\u003e4\u003c/sub\u003e（measured）\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 92px;\"\u003e\n \u003cp\u003e7.12\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 138px;\"\u003e\n \u003cp\u003e113.79\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 100px;\"\u003e\n \u003cp\u003e40\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 99px;\"\u003e\n \u003cp\u003e16.59\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 69px;\"\u003e\n \u003cp\u003e3\u003csup\u003erd\u003c/sup\u003e cycle\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 152px;\"\u003e\n \u003cp\u003e77.38\u0026nbsp;g/L Na\u003csub\u003e2\u003c/sub\u003eCO\u003csub\u003e3\u003c/sub\u003e\u003c/p\u003e\n \u003cp\u003e188.98g/L Na\u003csub\u003e2\u003c/sub\u003eSO\u003csub\u003e4\u003c/sub\u003e（measured）\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 92px;\"\u003e\n \u003cp\u003e4.59\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 138px;\"\u003e\n \u003cp\u003e114.54\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 100px;\"\u003e\n \u003cp\u003e40\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 99px;\"\u003e\n \u003cp\u003e17.38\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003c/tbody\u003e\n\u003c/table\u003e\n\u003cp\u003eThe test results are shown in Table 10. It can be seen that the conversion basically reached the end point, and the sodium carbonate concentration remained basically unchanged. Although the concentration of sodium sulfate continues to decrease, the concentration of sodium sulfate will not affect the conversion of lead. The main reason for the decrease is that the washing water takes away more sodium sulfate, and with the increase of washing water circulation times, the amount of free sulfate in the conversion slag also increases synchronously, which is easy to cause lead sulfate precipitation during acid leaching and reduce the lead leaching rate. It is considered that the washing water is not recycled\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eCyclic test for Ba removal\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eAlthough the conversion of barium in the above two-stage Ba carbonation test with liquid-solid ratio of 8/1 was relatively complete, the analysis found that the solution after 2\u003csup\u003end\u003c/sup\u003e stage barium carbonation contained 30g/l Na\u003csub\u003e2\u003c/sub\u003eSO\u003csub\u003e4\u003c/sub\u003e, which could not meet the requirement of returning to the first stage carbonation (13 g/l Na\u003csub\u003e2\u003c/sub\u003eSO\u003csub\u003e4\u003c/sub\u003e was designed). The main reason for the deviation is that some bismuth may also participate in the carbonation, but it cannot be leached by hydrochloric acid at pH 1 and exists in the Ba removal residue in the form of BiOCl. Therefore, the liquid-solid ratio of 12/1 was applied in the 1\u003csup\u003est\u003c/sup\u003e stage, and liquid-solid ratio of 6/1 was applied in the 2\u003csup\u003end\u003c/sup\u003e stage of cyclic test. This design enables the washing water of the 2\u003csup\u003end\u003c/sup\u003e stage carbonation to be returned to the 1\u003csup\u003est\u003c/sup\u003e stage, avoiding waste of Na\u003csub\u003e2\u003c/sub\u003eCO\u003csub\u003e3\u003c/sub\u003e in the washing water with a better water balance. In fact, it is necessary to wash the 2\u003csup\u003end\u003c/sup\u003e stage carbonation residue, otherwise the residual Na\u003csub\u003e2\u003c/sub\u003eSO\u003csub\u003e4\u003c/sub\u003e entrapped in the residue will precipitate barium during hydrochloric acid leaching, affecting the efficiency of barium removal.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eThe test results are shown in Table 11. In the cyclic test, 100g of Pb removal residue was taken and added with 1200mL 1\u003csup\u003est\u0026nbsp;\u003c/sup\u003estage barium conversion solution (356 g/L Na\u003csub\u003e2\u003c/sub\u003eCO\u003csub\u003e3\u003c/sub\u003e+6 g/L Na\u003csub\u003e2\u003c/sub\u003eSO\u003csub\u003e4\u003c/sub\u003e). After barium carbonation reaction at 80 ℃ for 1h, the carbonation residue without washing was added with 600 mL of the 2\u003csup\u003end\u003c/sup\u003e stage barium carbonation solution (360 g/L Na\u003csub\u003e2\u003c/sub\u003eCO\u003csub\u003e3\u003c/sub\u003e). After the 2\u003csup\u003end\u003c/sup\u003e stage barium carbonation reaction at 80 ℃ for 1h, the solid-liquid separation is performed and washed with 600 ml of water. The obtained filtrate was combined with the washing water, and 198.48g Na\u003csub\u003e2\u003c/sub\u003eCO\u003csub\u003e3\u003c/sub\u003e and 3.33 g Na\u003csub\u003e2\u003c/sub\u003eSO\u003csub\u003e4\u0026nbsp;\u003c/sub\u003ewere added as the first stage barium conversion solution for the next cycle test. The obtained Ba carbonation residue was leached with hydrochloric acid under the above conditions to evaluate the leaching rate.\u003c/p\u003e\n\u003cp\u003eTable 11 Cyclic test results for Pb removal by carbonation and leaching\u003c/p\u003e\n\u003ctable border=\"1\" cellspacing=\"0\" cellpadding=\"0\"\u003e\n \u003ctbody\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 69px;\"\u003e\n \u003cp\u003e\u0026nbsp;\u003c/p\u003e\n \u003cp\u003e\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 172px;\"\u003e\n \u003cp\u003e\u003cstrong\u003e1\u003csup\u003est\u003c/sup\u003e stage carbonation solution\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 162px;\"\u003e\n \u003cp\u003e\u003cstrong\u003e2\u003csup\u003end\u003c/sup\u003e stage carbonation solution\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 134px;\"\u003e\n \u003cp\u003e\u003cstrong\u003eWet weight after\u0026nbsp;\u003c/strong\u003e\u003cstrong\u003ecarbonation,\u0026nbsp;\u003c/strong\u003e\u003cstrong\u003eg\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 113px;\"\u003e\n \u003cp\u003e\u003cstrong\u003eHCl leaching residue, g\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 69px;\"\u003e\n \u003cp\u003e1\u003csup\u003est\u003c/sup\u003e cycle\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 172px;\"\u003e\n \u003cp\u003e356 g/L Na\u003csub\u003e2\u003c/sub\u003eCO\u003csub\u003e3\u003c/sub\u003e\u003c/p\u003e\n \u003cp\u003e6 g/L Na\u003csub\u003e2\u003c/sub\u003eSO\u003csub\u003e4\u003c/sub\u003e\u003c/p\u003e\n \u003cp\u003e（synthesized）\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 162px;\"\u003e\n \u003cp\u003e360 g/L Na\u003csub\u003e2\u003c/sub\u003eCO\u003csub\u003e3\u003c/sub\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 134px;\"\u003e\n \u003cp\u003e133.09\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 113px;\"\u003e\n \u003cp\u003e28.37\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 69px;\"\u003e\n \u003cp\u003e2\u003csup\u003end\u003c/sup\u003e cycle\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 172px;\"\u003e\n \u003cp\u003e356.03\u0026nbsp;g/L Na\u003csub\u003e2\u003c/sub\u003eCO\u003csub\u003e3\u003c/sub\u003e\u003c/p\u003e\n \u003cp\u003e5.58g/L Na\u003csub\u003e2\u003c/sub\u003eSO\u003csub\u003e4\u003c/sub\u003e\u003c/p\u003e\n \u003cp\u003e（measured）\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 162px;\"\u003e\n \u003cp\u003e360 g/L Na\u003csub\u003e2\u003c/sub\u003eCO\u003csub\u003e3\u003c/sub\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 134px;\"\u003e\n \u003cp\u003e132.53\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 113px;\"\u003e\n \u003cp\u003e28.53\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 69px;\"\u003e\n \u003cp\u003e3\u003csup\u003erd\u003c/sup\u003e cycle\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 172px;\"\u003e\n \u003cp\u003e357.73\u0026nbsp;g/L Na\u003csub\u003e2\u003c/sub\u003eCO\u003csub\u003e3\u003c/sub\u003e\u003c/p\u003e\n \u003cp\u003e5.65g/L Na\u003csub\u003e2\u003c/sub\u003eSO\u003csub\u003e4\u003c/sub\u003e\u003c/p\u003e\n \u003cp\u003e（measured）\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 162px;\"\u003e\n \u003cp\u003e360 g/L Na\u003csub\u003e2\u003c/sub\u003eCO\u003csub\u003e3\u003c/sub\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 134px;\"\u003e\n \u003cp\u003e131.78\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 113px;\"\u003e\n \u003cp\u003e28.04\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003c/tbody\u003e\n\u003c/table\u003e\n\u003cp\u003e\u003cstrong\u003eRecovery of Au/Ag\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eAfter the removal of Pb and Ba, Au/Ag can be exposed, which are simultaneously leached \u0026nbsp;by HCl, NaClO\u003csub\u003e3\u003c/sub\u003e and NaCl. The main reactions are as follows:\u0026nbsp;\u003c/p\u003e\n\u003cp\u003e2Au + 8HCl + NaClO\u003csub\u003e3\u003c/sub\u003e = 2HAuCl\u003csub\u003e4\u003c/sub\u003e + NaCl + 3H\u003csub\u003e2\u003c/sub\u003eO\u003c/p\u003e\n\u003cp\u003e6Ag +\u0026nbsp;6HCl + NaClO\u003csub\u003e3\u003c/sub\u003e + 11NaCl = 6Na\u003csub\u003e2\u003c/sub\u003e[AgCl\u003csub\u003e3\u003c/sub\u003e] + 3H\u003csub\u003e2\u003c/sub\u003eO\u003c/p\u003e\n\u003cp\u003eThis chlorination leaching was carried out with a liquid-solid ratio of 5:1 at 80 ℃ for 3h. The \u0026nbsp; leaching solution contains 35g/L HCl + 200g/L NaCl + 3g/L NaClO\u003csub\u003e3\u003c/sub\u003e. After reaction and filtration, the filtrate shows obvious golden yellow. As shown in table 12, It can be seen that leaching of Au is quite good, but Ag is hardly leached, and ammonia leaching is required separately\u0026nbsp;for Ag.\u003c/p\u003e\n\u003cp\u003eTable 12 Test results for Au/Ag recovery\u003c/p\u003e\n\u003cdiv align=\"\"\u003e\n \u003ctable border=\"0\" cellspacing=\"0\" cellpadding=\"0\"\u003e\n \u003ctbody\u003e\n \u003ctr\u003e\n \u003ctd colspan=\"2\" style=\"width: 160px;\"\u003e\n \u003cp\u003eBa removal residue\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd colspan=\"4\" style=\"width: 337px;\"\u003e\n \u003cp\u003eAu leaching residue\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 80px;\"\u003e\n \u003cp\u003eAu g/t\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 80px;\"\u003e\n \u003cp\u003eAg %\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 69px;\"\u003e\n \u003cp\u003eAu g/t\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 66px;\"\u003e\n \u003cp\u003eAg %\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 98px;\"\u003e\n \u003cp\u003eAu leaching rate\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 104px;\"\u003e\n \u003cp\u003eAg leaching rate\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 80px;\"\u003e\n \u003cp\u003e1240.09\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 80px;\"\u003e\n \u003cp\u003e2.10\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 69px;\"\u003e\n \u003cp\u003e24.02\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 66px;\"\u003e\n \u003cp\u003e1.94\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 98px;\"\u003e\n \u003cp\u003e98.33%\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 104px;\"\u003e\n \u003cp\u003e20.36%\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003c/tbody\u003e\n \u003c/table\u003e\n\u003c/div\u003e\n\u003cp id=\"_Toc195622552\"\u003eFlowsheet design for Na\u003csub\u003e2\u003c/sub\u003eCO\u003csub\u003e3\u0026nbsp;\u003c/sub\u003erecycling\u003c/p\u003e\n\u003cp\u003eThe measured concentration after the 1\u003csup\u003est\u003c/sup\u003e stage Ba carbonation conversion is 328.6 g/L Na\u003csub\u003e2\u003c/sub\u003eCO\u003csub\u003e3\u003c/sub\u003e+41.83 g/L Na\u003csub\u003e2\u003c/sub\u003eSO\u003csub\u003e4\u003c/sub\u003e, corresponding to the limit ratio of barium conversion. 250 ml of the 1\u003csup\u003est\u0026nbsp;\u003c/sup\u003estage barium conversion solution was taken to crystallize at 15 ℃ for 2 hours to obtain 39.94g of crystalline product. According to titration analysis, the crystalline product contains 1.46% Na\u003csub\u003e2\u003c/sub\u003eSO\u003csub\u003e4\u003c/sub\u003e, and the rest is Na\u003csub\u003e2\u003c/sub\u003eCO\u003csub\u003e3\u003c/sub\u003e, which is enough to return to the the 1\u003csup\u003est\u003c/sup\u003e stage Ba carbonation conversion, while the 2\u003csup\u003end\u003c/sup\u003e stage barium conversion solution is all prepared with fresh sodium carbonate (360 g/L Na\u003csub\u003e2\u003c/sub\u003eCO\u003csub\u003e3\u003c/sub\u003e). In addition, 105 ml of crystallization mother liquor (140.72 g/L Na\u003csub\u003e2\u003c/sub\u003eCO\u003csub\u003e3\u003c/sub\u003e+53.18 g/L Na\u003csub\u003e2\u003c/sub\u003eSO\u003csub\u003e4\u003c/sub\u003e) and 110 ml of crystallization washing water were obtained (100.67 g/L Na\u003csub\u003e2\u003c/sub\u003eCO\u003csub\u003e3\u003c/sub\u003e+30.16 g/L Na\u003csub\u003e2\u003c/sub\u003eSO\u003csub\u003e4\u003c/sub\u003e). Based on calculation, both the amount of water and the amount of Na\u003csub\u003e2\u003c/sub\u003eCO\u003csub\u003e3\u003c/sub\u003e are fully enough for Pb carbonation conversion. It can be considered that the crystallization mother liquor and washing liquor are combined and returned to lead conversion, and the solution after lead conversion will not be recycled, so as to simplify the process flowsheet. Because there is still a certain amount of Na\u003csub\u003e2\u003c/sub\u003eCO\u003csub\u003e3\u003c/sub\u003e left in the solution after lead conversion, it can be used as a neutralizer for the leaching solution of bismuth leaching with hydrochloric acid, and further consume the residual Na\u003csub\u003e2\u003c/sub\u003eCO\u003csub\u003e3\u003c/sub\u003e until bismuth is completely precipitated. The solution after bismuth precipitation contains only Na\u003csub\u003e2\u003c/sub\u003eSO\u003csub\u003e4\u0026nbsp;\u003c/sub\u003eand a small amount of NaCl. The Na\u003csub\u003e2\u003c/sub\u003eSO\u003csub\u003e4\u0026nbsp;\u003c/sub\u003ein this solution can then be removed by freeze crystallization with water and NaCl recycled to bismuth leaching.\u003c/p\u003e\n\u003cp\u003eThere are 1100 mL of the solution after the 1\u003csup\u003est\u003c/sup\u003e stage of barium carbonation, 462 mL of the Na\u003csub\u003e2\u003c/sub\u003eCO\u003csub\u003e3\u0026nbsp;\u003c/sub\u003ecrystallization mother liquor and 484 mL of the\u0026nbsp;Na\u003csub\u003e2\u003c/sub\u003eCO\u003csub\u003e3\u0026nbsp;\u003c/sub\u003ecrystallization washing liquor can be obtained from the same scale of test (100g of Pb removal residue as feed for Ba removal operation). After combining them, 946 mL of the solution can be obtained, and the concentration is 121.20 g/L Na\u003csub\u003e2\u003c/sub\u003eCO\u003csub\u003e3\u003c/sub\u003e+41.40 g/L Na\u003csub\u003e2\u003c/sub\u003eSO\u003csub\u003e4\u003c/sub\u003e. The mass will be reduced to half after Pb removal, so the corresponding Pb removal feed (ammonia leaching residue) is 200g. If all the solutions obtained after\u0026nbsp;Na\u003csub\u003e2\u003c/sub\u003eCO\u003csub\u003e3\u0026nbsp;\u003c/sub\u003ecrystallization are used for lead conversion, the liquid-solid ratio is about 4.75/1, and both the amount of water and sodium carbonate are sufficient for lead conversion. A lead carbonation and leaching test was conducted, and the results are shown in Table 13.\u003c/p\u003e\n\u003cp\u003eTable 13 Test results for Pb removal using recycled\u0026nbsp;Na\u003csub\u003e2\u003c/sub\u003eCO\u003csub\u003e3\u0026nbsp;\u003c/sub\u003ebearing\u0026nbsp;solution\u003c/p\u003e\n\u003cdiv align=\"\"\u003e\n \u003ctable border=\"0\" cellspacing=\"0\" cellpadding=\"0\"\u003e\n \u003ctbody\u003e\n \u003ctr\u003e\n \u003ctd\u003eNa\u003csub\u003e2\u003c/sub\u003eCO\u003csub\u003e3\u003c/sub\u003e\u003cbr\u003e\u003c/td\u003e\n \u003ctd\u003e121.20\u0026nbsp;g/L\u003cbr\u003e\u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd\u003eNa\u003csub\u003e2\u003c/sub\u003eSO\u003csub\u003e4\u003c/sub\u003e\u003cbr\u003e\u003c/td\u003e\n \u003ctd\u003e41.40 g/L\u003cbr\u003e\u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd\u003eL/S\u003cbr\u003e\u003c/td\u003e\n \u003ctd\u003e4.75/1\u003cbr\u003e\u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd\u003eCarbonation time\u003cbr\u003e\u003c/td\u003e\n \u003ctd\u003e1h\u003cbr\u003e\u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd\u003eCarbonation temperature\u003cbr\u003e\u003c/td\u003e\n \u003ctd\u003e80℃\u003cbr\u003e\u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd\u003ePb leaching rate\u003cbr\u003e\u003c/td\u003e\n \u003ctd\u003e95.10%\u003cbr\u003e\u003c/td\u003e\n \u003c/tr\u003e\n \u003c/tbody\u003e\n \u003c/table\u003e\n\u003c/div\u003e\n\u003cp\u003e\u003cstrong\u003ePrecipitation of BaSO\u003csub\u003e4\u003c/sub\u003e\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe measured barium content of hydrochloric acid leaching solution was 62.63 g/L. In precipitation test work, 50 ml of the leaching solution was taken with the addition of 1mL sulfuric acid, and reacted at room temperature for 0.5h. After precipitation of BaSO\u003csub\u003e4\u003c/sub\u003e, the solution contains 7.64g/l Ba. Titration using barium chloride solution detected that it does not contain sulfate. In this process, the hydrochloric acid is regenerated, while maintaining a certain residual BaCl\u003csub\u003e2\u003c/sub\u003e concentration to avoid the sulfate from being brought into the carbonation stage with the regenerated hydrochloric acid. After barium leaching with regenerated hydrochloric acid, sulfuric acid equivalent to the amount of barium in the carbonation residue can be added each time to precipitate BaSO\u003csub\u003e4\u003c/sub\u003e.\u003c/p\u003e"},{"header":"Conclusion","content":"\u003cp\u003eIn copper anode slime hydrometallurgical plant, Au/Ag recovery is incomplete with a significant amount of Au/Ag remaining in ammonia leaching residue, encapsulated by PbSO\u003csub\u003e4\u003c/sub\u003e and BaSO\u003csub\u003e4\u003c/sub\u003e. These gold and silver can be released by removal of PbSO\u003csub\u003e4\u003c/sub\u003e/BaSO\u003csub\u003e4\u003c/sub\u003e, which is realized by Na\u003csub\u003e2\u003c/sub\u003eCO\u003csub\u003e3\u003c/sub\u003e carbonation and HCl leaching. The process flowsheet stepwisely includes Pb removal, Ba removal, and Au/Ag leaching. Precipitation using sulfuric acid was adopted to obtain PbSO\u003csub\u003e4\u003c/sub\u003e and BaSO\u003csub\u003e4\u003c/sub\u003e products from their corresponding HCl leaching solution. In particular, barium conversion was realized by two-stage Ba carbonation. The solution after the second stage are returned to the first stage of barium conversion, and the crystalline sodium carbonate after barium conversion in the first stage is returned to the first stage, and the crystallized mother liquor and crystalline washing water are combined and returned for Pb conversion. The chloroauric acid solution and silver ammonia solution were incorporated into their main stream in the copper anode slime plant, respectively. The whole process does not introduce waste water, and the material consumption is mainly sodium carbonate, sulfuric acid, a small amount of hydrochloric acid, sodium chloride and sodium chlorate and ammonia necessary for gold and silver separation.\u003c/p\u003e"},{"header":"Declarations","content":"\u003cp\u003e \u003ch2\u003eDeclaration of competing interest\u003c/h2\u003e \u003cp\u003eThe authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.\u003c/p\u003e \u003c/p\u003e\u003cp\u003e \u003ch2\u003eCompeting interests\u003c/h2\u003e \u003cp\u003eThe author(s) declare no competing interests.\u003c/p\u003e \u003c/p\u003e\u003ch2\u003eAuthor Contribution\u003c/h2\u003e\u003cp\u003eZhizhong Liu: Writing - Review \u0026amp; Editing, Supervision, Project administration, Formal analysis, Investigation. Xinhuang Yu: Data Curation, Validation, Writing - Original Draft, Visualization. Shuchen Qin: Data Curation, Validation, Visualization. Yuanhao Ren: Data Curation, Validation. Rui Ning: Supervision, Project administration. Bao Guo: Conceptualization, Methodology,Supervision, Project administration, Writing - Review \u0026amp; Editing. Kaixi Jiang: Conceptualization, Methodology,Supervision, Project administration. All authors reviewed the manuscript.\u003c/p\u003e\u003ch2\u003eData Availability\u003c/h2\u003e\u003cp\u003eData will be made available on request. The data sets generated and analyzed during the current study are available from Bao Guo ([email protected]) upon reasonable request.\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\n\u003cli\u003eLi, D., Guo, X., Xu, Z., Tian, Q. \u0026amp; Feng, Q. Leaching behavior of metals from copper anode slime using an alkali fusion-leaching process. \u003cem\u003eHydrometallurgy\u003c/em\u003e \u003cstrong\u003e157\u003c/strong\u003e, 9-12 (2015).\u003c/li\u003e\n\u003cli\u003eLi, D., Guo, X., Xu, Z., Xu, R. \u0026amp; Feng, Q. Metal values separation from residue generated in alkali fusion-leaching of copper anode slime. \u003cem\u003eHydrometallurgy\u003c/em\u003e \u003cstrong\u003e165\u003c/strong\u003e, 290-294 (2016).\u003c/li\u003e\n\u003cli\u003eXiao, L. et al. An environmentally friendly process to selectively recover silver from copper anode slime. \u003cem\u003eJ. Clean. Prod.\u003c/em\u003e \u003cstrong\u003e187\u003c/strong\u003e, 708-716 (2018).\u003c/li\u003e\n\u003cli\u003eChen, A. et al. Recovery of silver and gold from copper anode slimes. \u003cem\u003eJOM\u003c/em\u003e \u003cstrong\u003e67\u003c/strong\u003e(2), 493-502 (2015).\u003c/li\u003e\n\u003cli\u003eDing, Y., Zhang, S., Liu, B. \u0026amp; Li, B. Integrated process for recycling copper anode slime from electronic waste smelting. \u003cem\u003eJ. Clean. Prod.\u003c/em\u003e \u003cstrong\u003e165\u003c/strong\u003e, 48-56 (2017).\u003c/li\u003e\n\u003cli\u003eSEISKO, S. et al. Pressure leaching of decopperized copper electrorefining anode slimes in strong acid solution. \u003cem\u003ePhysicochem. Probl. Mineral Pro.\u003c/em\u003e \u003cstrong\u003e53\u003c/strong\u003e(1), 465-474 (2017).\u003c/li\u003e\n\u003cli\u003eChiu, T., Horng, J. \u0026amp; Hoh, Y. Kinetic studies on selenious acid reduction at higher se(iv) concentration. \u003cem\u003eHydrometallurgy\u003c/em\u003e \u003cstrong\u003e7\u003c/strong\u003e(1), 135-146 (1981).\u003c/li\u003e\n\u003cli\u003eHoffmann, J. E. Recovering selenium and tellurium from copper refinery slimes. \u003cem\u003eJOM\u003c/em\u003e \u003cstrong\u003e41\u003c/strong\u003e(7), 33-38 (1989).\u003c/li\u003e\n\u003cli\u003eHyv\u0026auml;rinen, O., Lindroos, L. \u0026amp; Yll\u0026ouml;, E. Recovering selenium from copper refinery slimes. \u003cem\u003eJOM\u003c/em\u003e \u003cstrong\u003e41\u003c/strong\u003e(7), 42-43 (1989).\u003c/li\u003e\n\u003cli\u003eXiming, L., Jiajun, K., Xinhui, M. \u0026amp; Bin, L. Chlorine leaching of gold-bearing sulphide concentrate and its calcine. \u003cem\u003eHydrometallurgy\u003c/em\u003e \u003cstrong\u003e29\u003c/strong\u003e(1), 205-215 (1992).\u003c/li\u003e\n\u003cli\u003eSansotta, S. \u0026amp; Zahn, D. Solvation structure and dynamics of ag+ in aqueous ammonia solutions: a molecular simulation study. \u003cem\u003eThe Journal of Chemical Physics\u003c/em\u003e \u003cstrong\u003e147\u003c/strong\u003e(11) (2017).\u003c/li\u003e\n\u003cli\u003eHa, T. K., Kwon, B. H., Park, K. S. \u0026amp; Mohapatra, D. Selective leaching and recovery of bismuth as bi2o3 from copper smelter converter dust. \u003cem\u003eSep. Purif. Technol.\u003c/em\u003e \u003cstrong\u003e142\u003c/strong\u003e, 116-122 (2015).\u003c/li\u003e\n\u003cli\u003eKe, J., Qiu, R. \u0026amp; Chen, C. Recovery of metal values from copper smelter flue dust. \u003cem\u003eHydrometallurgy\u003c/em\u003e \u003cstrong\u003e12\u003c/strong\u003e(2), 217-224 (1984).\u003c/li\u003e\n\u003cli\u003eHe, Y. \u0026amp; Xu, Z. Recycling gold and copper from waste printed circuit boards using chlorination process. \u003cem\u003eRSC Adv.\u003c/em\u003e \u003cstrong\u003e5\u003c/strong\u003e(12), 8957-8964 (2015).\u003c/li\u003e\n\u003cli\u003eLiu, W. et al. Investigation into oxygen-enriched bottom-blown stibnite and direct reduction. \u003cem\u003eMetallurgical and Materials Transactions B\u003c/em\u003e \u003cstrong\u003e45\u003c/strong\u003e(4), 1281-1290 (2014). \u003c/li\u003e\n\u003c/ol\u003e"}],"fulltextSource":"","fullText":"","funders":[],"hasAdminPriorityOnWorkflow":false,"hasManuscriptDocX":true,"hasOptedInToPreprint":true,"hasPassedJournalQc":"","hasAnyPriority":false,"hideJournal":true,"highlight":"","institution":"","isAcceptedByJournal":false,"isAuthorSuppliedPdf":false,"isDeskRejected":"","isHiddenFromSearch":false,"isInQc":false,"isInWorkflow":false,"isPdf":false,"isPdfUpToDate":true,"isWithdrawnOrRetracted":false,"journal":{"display":true,"email":"[email protected]","identity":"researchsquare","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":true,"externalIdentity":"","sideBox":"","snPcode":"","submissionUrl":"/submission","title":"Research Square","twitterHandle":"researchsquare","acdcEnabled":true,"dfaEnabled":false,"editorialSystem":"","reportingPortfolio":"","inReviewEnabled":false,"inReviewRevisionsEnabled":true},"keywords":"Copper anode slime, Ammonia leaching residue, Carbonation, PbSO4, BaSO4","lastPublishedDoi":"10.21203/rs.3.rs-8390297/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-8390297/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003cp\u003eIn copper anode slime hydrometallurgical plant, Au and Ag are recovered by perchloric leaching and ammonia leaching, stepwisely and respectively. However, their recovery is incomplete with a significant amount of refractory Au/Ag remaining in ammonia leaching residue, encapsulated by PbSO\u003csub\u003e4\u003c/sub\u003e and BaSO\u003csub\u003e4\u003c/sub\u003e. These gold and silver can only be released by the removal of PbSO\u003csub\u003e4\u003c/sub\u003e/BaSO\u003csub\u003e4\u003c/sub\u003e, which can be realized by Na\u003csub\u003e2\u003c/sub\u003eCO\u003csub\u003e3\u003c/sub\u003e carbonation and the subsequent HCl leaching. In this work, a process flowsheet has been designed to recover Au/Ag in ammonia leaching residue and individual PbSO\u003csub\u003e4\u003c/sub\u003e and BaSO\u003csub\u003e4\u003c/sub\u003e products were also obtained with extra value. The cost of this process can be greatly reduced by Na\u003csub\u003e2\u003c/sub\u003eCO\u003csub\u003e3\u003c/sub\u003e recycling between the two-stage Ba carbonation and one-stage Pb carbonation with freezing crystallization of Na\u003csub\u003e2\u003c/sub\u003eCO\u003csub\u003e3\u003c/sub\u003e.\u003c/p\u003e","manuscriptTitle":"The liberation of refractory precious metals associated with PbSO 4 /BaSO 4 by carbonation and comprehensive recovery in copper anode slime refinery","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2026-02-12 19:12:24","doi":"10.21203/rs.3.rs-8390297/v1","editorialEvents":[{"type":"communityComments","content":0}],"status":"published","journal":{"display":true,"email":"[email protected]","identity":"researchsquare","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":true,"externalIdentity":"","sideBox":"","snPcode":"","submissionUrl":"/submission","title":"Research Square","twitterHandle":"researchsquare","acdcEnabled":true,"dfaEnabled":false,"editorialSystem":"","reportingPortfolio":"","inReviewEnabled":false,"inReviewRevisionsEnabled":true}}],"origin":"","ownerIdentity":"65497aec-0b3d-4ff9-8ee2-c1b382f618b2","owner":[],"postedDate":"February 12th, 2026","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"posted","subjectAreas":[{"id":62627014,"name":"Physical sciences/Chemistry"},{"id":62627015,"name":"Earth and environmental sciences/Environmental sciences"}],"tags":[],"updatedAt":"2026-02-16T06:25:15+00:00","versionOfRecord":[],"versionCreatedAt":"2026-02-12 19:12:24","video":"","vorDoi":"","vorDoiUrl":"","workflowStages":[]},"version":"v1","identity":"rs-8390297","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-8390297","identity":"rs-8390297","version":["v1"]},"buildId":"XKTyCvWXoU3ODBz1xrDgd","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}