Solvent extraction of lithium from brines with high magnesium/lithium ratios; Investigation on parameter interactions

Solvent extraction of lithium from brines with high magnesium/lithium ratios; Investigation on parameter interactions | 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 Research Article Solvent extraction of lithium from brines with high magnesium/lithium ratios; Investigation on parameter interactions Anahita Kazemi Kia, Hamid Reza Mortaheb, Mahsa Baghban Salehi, and 1 more This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-4265065/v1 This work is licensed under a CC BY 4.0 License Status: Published Journal Publication published 17 Aug, 2024 Read the published version in Environmental Science and Pollution Research → Version 1 posted 6 You are reading this latest preprint version Abstract Solvent extraction of lithium from brine with a high Mg/Li ratio was investigated. Tributyl phosphate (TBP), ferric chloride (FeCl3), and kerosene were used as the extractant, co-extractant, and diluent, respectively. The mechanism of extraction process was studied by LC-MS, UV-VIS, and FT-IR analyses. Effects of organic to aqueous phase volume ratio (O/A) on the extraction efficiency and separation factor were optimized. The effects of major parameters including Fe/Li molar ratio, hydrochloric acid concentration, and TBP volume percent as well as their interactions on the lithium extraction efficiency were evaluated using central composite design. These major parameters represent interactions within their selected ranges. While the lithium extraction efficiency as the resposense value in the experimental design showed the most sensivity to the acid concentration, the separation factors were more affected by alteration in the TBP volume percent with the fixed optimum values of the other major parameters. The highest one-stage extraction efficiency of 76.3% and Li/Mg separation factor of 304 were obtained at the optimum conditions of Fe/Li= 2.99, HCl=0.01 M, and TBP= 55%. The Mg/Li mass ratio could be significantly reduced from 192 in the feed to 1.5 in the stripping solution. Based on the findings, a schematic diagram of the process including extraction, stripping, and saponification steps was proposed. Solvent extraction Magneseum rich brine Lithium extraction efficiency Separation factor Experimental design Figures Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 Figure 6 Figure 7 Figure 8 Figure 9 Figure 10 Figure 11 Figure 12 Figure 13 Figure 14 Introduction The rapid growth of industries requires an increasing global demand for clean, inexpensive, and sustainable energy resources. According to the new EU regulations, the contribution of green and renewable energy should be increased to about 42% by 2030 to remediate the escalating and critical problem of greenhouse gas emissions (Hatfield-Dodds et al. 2017 ; Trujillo-Baute et al. 2018 ). During the last two decades, the shortage of fossil fuel resources has led to a growth in applying lithium-ion batteries to meet the environmental goals (Diouf et al. 2015; Sterba et al. 2019 ). Lithium is also used in various industries such as electronics (Xie et al. 2021 ; Liu et al. 2019 ), aviation(Kablov et al. 2021 ; Sverdlin et al. 1998 ), sea transportation (Salucci et al. 2023 ), and pharmaceuticals (Zhu et al. 2019 ). The primary resources of lithium including ores and water resources (brines, seawaters, and geothermal waters) as well as the secondary sources such as spent batteries have been considered for lithium production (Talens Peiro et al. 2013; Golmohammadzadeh et al. 2018 ). Lithium distribution in different resources and their interfering impurities are varied significantly (Wesselborg et al. 2021 ). The lithium extraction process depends widely on the source type, lithium concentration, and presence of interfering ions. The exploitable lithium in the pegmatite deposits ranges from about 1.25 to 4% Li 2 O (Bale et al. 1989) while its concentrations in the brines are about 100–2000 mg/L (Zhou et al. 2012 ; Ji et al. 2017 ; Zhang et al. 2019 ). The lithium extraction from brines with relatively moderate concentrations might be feasible in comparison to the extraction from mineral sources as it does not require an extra step of dissolution. Different processes such as chemical precipitation (Zhao et al. 2023 ), adsorption (Romero et al. 2018 ), membrane processes (Su et al. 2020 ), electrochemical methods (Su et al. 2020 ), and solvent extraction (Hano et al. 1992 ; Torkaman et al. 2017 ) can be applied to retrieve lithium. On the other hand, the performance of applied process depends on the type and amount of co-ions including magnesium as a significant impurity, which is widely varied in diferent resources (Su et al. 2020 ). The solvent extraction as a simple process has the advantages such as low energy consumption, low waste generation, and recyclability of extractants. The method has been tested in a pilot scale for lithium extraction (Zhou et al. 2012 ; Su et al. 2020 ; Shi et al. 2020 ; Su et al. 2020 ). In a solvent extraction process, when the feed solution comes into contact with an extracting organic phase, the consituents in the feed solution is distributed between the two phases. Various extractants have been applied to extract lithium by solvent extraction including trioctyl phosphine oxide (TOPO) with co-extractant of HTTA (4, 4, 4-trifluoro-1-(2-thienyl)butane-1,3-dione) (Ji et al. 2016 ), trialkyl phosphine oxide (cyanex923) with co-extractan of LIX54 (a β-diketone derivative) (Pranolo et al. 2015 ), neutral ligand trialkylphosphine oxide (Cyanex 923) along with hydroxyl 1-hydroxyethyl-3-methyl imidazolium bis(trifluoromethylsulfonyl)imide ([OHEMIM][NTf2]) as the co-extractant (Shi et al. 2015 ). Despite their feasible performances, the aforementioned extractants have some disadvantages such as high price, lack of selectivity for lithium over interfering ions so that some pretreatments are required (Ji et al. 2016 ). Alternatively, TBP has been found as a low-cost selective extractant in the lithium extraction (Pranolo et al. 2015 ; Li et al. 2021 ; Ji et al. 2016 ) However, TBP cannot individually form a complex with lithium in the aqueous phase (Li et al. 2021 ). Metal chloride compounds such as CuCl 2 , InCl 3 , SnCl 4 , and FeCl 3 as well as room temperature ionic liquids such as ([C 4 mim][Tf 2 N]), (C 4 mim + ·PF6 − ) (Zhou et al. 2012 ; Li et al. 2021 ; Yang et al. 2019 ; Okamura et al. 2014 ; Shi et al. 2015 ), were utilized as TBP co-extractants. Among these co-extractants, FeCl 3 has shown a promising performance for lithium extraction due to its appropriate selectivity towards lithium (Lum et al. 2012 ; Lum et al. 2013 ). The presence of H + is essential in the extraction using TBP/FeCl 3 to prevent hydrolysis of iron during the process (Wesselborg et al. 2021 ; Lum et al. 2013 ). However, an excessive concentration of H + may decompose the TBP structure and degrades the extraction efficiency. Therefore, managing acid concentration in the solution is crucial as it also causes corrosion problems in the equipments (Yu et al. 2019 ; Shi et al. 2019 ; Ji et al. 2022 ). As a result, in order to optimize the performance of an extraction process containing TBP/FeCl 3 , it is necessary to investigate the effects of major parameters affecting the process as well as their interactions. Many studies have investigated effective parameters in the lithium solvent extraction (Bale et al. 1989; Yu et al. 2019 ; Li et al. 2019 ; Ji et al. 2022 ). However, to our knowledge, no experimental study was reported, in which the interactions of major parameter have been investigated simultaneously. The experimental design with the common response surface methodology (RSM) approach allows investigate not only the effect of adjusting each parameter but also their combined effects on the response value. In the present research, the RSM is applied to evaluate the effects of major parameters of solvent extraction and their interactions on lithium extraction efficiency. The optimized test conditions are then applied to assess their effects on the sepation factor. Finally, stripping and saponification for recovery of extracting phase are performed and a sketch for the whole process is proposed. Experimental Materials Lithium chloride (LiCl), sodium chloride (NaCl), potassium chloride (KCl), magnesium chloride hexahydrate (MgCl 2 .6H 2 O), ferric chloride hexahydrate (FeCl 3 .6H 2 O), and concentrated hydrochloric acid (HCl, 37%) were all purchased from Merck. Tributyl phosphate (TBP, 99%) was obtained from Sigma-Aldrich and used without further purification. Kerosene as the diluent was provided from a domestic provider. Experimental procedure The aqueous samples of synthetic feed with different HCl concnetrations, LiCl as the main source of lithium, NaCl and KCl as the co-ions, and MgCl 2 .6H 2 O as the co-ion as well as the chloride source were prepared. The Fe/Li ratio in the synthetic feed was adjusted by adding FeCl 3 .6H 2 O. The organic phases containing kerosene and TBP were prepared with predetermined volumetric percents. The feed and organic phases were poured in a round-bottom flask and stirred for 10 min using an overhead stirrer (RE 162, IKA, Netherlands, 700 rpm). The different organic to aqueous volume ratios (O/A) (0.25, 0.5, 0.7, 1, 1.3, 1.5, 1.7, and 2) were tested in the primary experiments to determine the optimum ratio for the lithium extraction. The volume of the aqueous phase was fixed while the O/A ratio was adjusted by altering the volume of the organic phase. The two-phase mixture was then poured into a 50-ml decanter funnel. After 30 min, when the equilibrium conditions were reached, the aqueous phase was gently separated from the organic phase. The stripping and saponification of the organic phase were performed to re-extract lithium from the aqueous phase as well as to re-use the extracting organic phase for the next extraction operation with the fresh aqueous feed. In the stripping stage, the organic phase was mixed with an acidic aqueous phase containing 0.3 M HCl and 5 M NaCl in an O/A ratio of 7:1. The organic phase was then saponified using an alkaline solution of 0.05 M NaOH and 5 M NaCl with an O/A ratio of 7:1. The extraction efficiency of each ion, E M , is calculated as follows: \(E\text{M}= \frac{C\text{M}0- C\text{M} }{C\text{M}0} \times 100\) (%) (1) In which, C M0 and C M are the initial and equilibrium concentrations of each co-ion (Na + , K + , Mg 2+ , and Fe 3+ ) in the aqueous phase, respectively. The “Li/M” separation factor, β , is determined by calculation of lithium and co-ions distribution ratios, D M , by the following equations: $$D\text{M}=\frac{C\text{M}0- C\text{M} }{C\text{M} }\times \frac{{V}_{\text{a}\text{q}}}{{V}_{\text{o}\text{r}\text{g}}}$$ 2 $$\beta =\frac{{D}_{\text{L}\text{i}}}{{D}_{\text{M}}}$$ 3 in which, V aq and V org represent the volume of the aqueous and organic phases, respectively. The stripping efficiency, \({E}_{\text{M}}^{{\prime }}\) , is determined by: \({E}_{\text{M}}^{{\prime }}= \frac{{C}_{\text{M}0}^{{\prime }}- {C}_{\text{M}}^{{\prime }} }{{C}_{\text{M}0}^{{\prime }}} \times 100\) (%) (4) \({C}_{\text{M}0}^{{\prime }}\) and \({C}_{\text{M} }^{{\prime }}\) denote the initial and equilibrium concentrations of metal ion in the organic phase. The central composite design (CCD) method was utilized to evaluate each effective parameter individually as well as their simultaneous interactions on the response value. The lithium extraction efficiency, E Li , was set as the response while the molar ratio of Fe/Li (A), the HCl concentration in the aqueous pahse (B), and the volume percent of TBP in the organic phase (C) were set as the independent variables. The two-level factorial design incorporates a CCD (central composite design) which consists of a center point and star points. The purpose is to increase the level of each variable from 2 to 5, while ensuring a normal distribution of data around the mean value. To control for any examiner errors, the number of repeats was set to 5. The distribution of points was arranged to achieve a normal distribution by drawing the number of observations according to the variables. By using a normal distribution, the mean value, variance, or standard error of each variable can be easily determined. The points were set in a rotating arrange i.e. the variances of all points depend only on their distance from the central point of the test, and are independent of the direction or path of variable alteration in the test space (Salehi et al. 2018). The ranges of effective parameters were set as 0.5-3 for the molar ratio of Fe/Li (A), 0-0.5 (M) for the HCl concentration in the aqueous phase (B), and 10–90 (%) for TBP volume percent in the organic phase (C). Table S1 shows the range of parameters and their levels designated by 7DX software (USA, version 7.1.3 Ease-State). The plan of experimental design and the ranges of each parameter are shown Fig. 1 . Characterization Inductivity coupled plasma-atomic emission spectrometry (ICP-AES; spectro arcos, Germany) was used to determine the concentration of cations in the aqueous phase before and after extraction. The formation and presence of ionic species in the organic phase were studied using liquid chromatography-mass spectrometry (LC-Ms, Quattro micro API, HPLC: alliance 2695, USA) analysis. Fourier transform infrared measurement (FT-IR, Perkin Elmer Spectrum 65, USA) was applied to detect the peak shift related to the P = O functional group by formation of the [Li(TBP) 2 ][FeCl 4 ] complex (Li et al. 2021 ). The formation of [FeCl 4 ] − was verified using Ultraviolet Visible Spectrometer (UV-VIS; Perkinelmer, Lambda25, USA) analysis. Result and discussion Mechanism of \({\mathbf{L}\mathbf{i}\mathbf{F}\mathbf{e}\mathbf{C}\mathbf{l}}_{4}.2\mathbf{T}\mathbf{B}\mathbf{P}\) complex formation The mechanism of selective extraction of lithium from the brine is shown in Fig. 2 . In an environment with high chloride concentration, Fe 3+ will react with Cl − to form [FeCl 4 ] − as follows (Su et al. 2020 ): \({\text{F}\text{e}}^{3+}\) (aq) + \({4\text{C}\text{l}}^{-}\) (aq) ↔ \({\text{F}\text{e}\text{C}\text{l}}_{4}^{-}\) (aq) (5) In presense of chloride ions, the various species of FeCl n 3−n are produced. Fe 3+ can be coordinated by water up to the coordination number of 6, which diminishes the electrostatic interactions of Fe-Cl in the produced species. It has been found that the length of Fe-Cl bond is increased from 2.07 Å in FeCl 2 + to 2.22 Å in FeCl 2 (H 2 O) 4 + , from 2.13 Å in FeCl 3 to 2.22 Å in FeCl 3 (H 2 O) 3 , and from 2.22 Å in FeCl 4 − to 2.40 Å in FeCl 4 (H 2 O) 2 − (Sun et al. 2022 ). The hydrogen bonding between chloride ions and the surrounding water molecules weakens the Fe-Cl coordinative interaction (Sun et al. 2022 ). The increase in the FeCl bond length resulted in a decrease in the Fe-Cl bond energy, which induces instability of the FeCl n 3−n complexes in the aqueous phase whereas the FeCl 4 − structure with the the highest length of Fe-Cl bond represents the highest tendency to migrate from the aqueous phase to the organic phase. FeCl 4 − can form a complex with TBP in the organic phase. The produced complex is neutralized by coupling with a metal cation transferred to the organic phase. According to the extraction mechanism, the affinity of complex formation towards metal ions is H + >Li + >Ca + >Mg 2+ >Na + >K + (Zhang et al. 2020 ). The bond length of metal ̶ O (of the TBP structure) and metal ̶̶̶ Cl in the generated complex is in the order of K + >Na + >Li + indicating that the formed Li-contaied complex (Eq. 6) has the highest stability among the mentioned cations (Sun et al. 2022 ; Li et al. 2021 ). \({\text{L}\text{i}}^{+}\) (aq) + \({\text{F}\text{e}\text{C}\text{l}}_{4}^{-}\) (aq) + 2TBP (org) ↔ \({\text{L}\text{i}\text{F}\text{e}\text{C}\text{l}}_{4}.2\text{T}\text{B}\text{P}\) (org) (6) Effect of chloride ion concentration on extraction efficiency It has been found that a small fraction of FeCl n 3−n in the aqueous phase is in the form of FeCl 4 − (Wesselborg et al. 2021 ). However, according to the Le Chatelier principle, the concentration of FeCl 4 − can be balanced by reaction of FeCl 3 and FeCl 2 + in the presence of adequate chloride concentration (Sun et al. 2022 ). Although the excessive concentration of chloride ion does not yield more FeCl 4 − , the low chloride concentration may lead to loss in the iron content, which reduces the extraction efficiency. Therefore, selecting the suitable chloride concentration is important to optimize the process performance. Experiments with different Cl − concentrations were performed to study the effect of chloride concentration on the extraction efficiency through measurement of FeCl 4 − concentration. Ultraviolet Visible Spectrometer (UV-VIS) analysis was used to detect the absorption intensity of the FeCl 4 − . In order to determine the maximum absorption wavelength, the organic phase containing the generated complex was scanned in the wavelength range of 300–800 nm. Three characteristic peaks of FeCl 4 − were identified at 531, 619, and 684 nm (Fig. S1 ). The peak appeared at 684 nm was selected as the representative peak because of the absence of unknown species at the wavelengths of greater than 650 nm (Lum et al. 2013 ; Ji et al. 2022 ; Li et al. 2021 ). Figure 3 shows the absorption intensities observed by UV-VIS for the feed solutions having chloride concentratons of 1, 2, and 6 M. The figure shows that the absorption intensity i.e. FeCl 4 − in the organic phase is increased by increasing the chloride concentration in the aqueous phase. The higher extraction efficiencies for the feeds with higher chloride concentratin in Fig. 3 also show a direct relationship of extraction efficiency with the chloride concentration as a result of formation higher FeCl 4 − species. However, excessive chloride concentration higher than 6 M does not yield higher extraction efficiencies as was explained earlier. As a result, the chloride concentration in the feed solution was fixed at 6 M in the consequent experiments. Figure 4 represents the FT-IR peaks of organic phase before and after the solvent extraction. The figure shows that the peak related to the P = O functional group in the TBP structure shifts from 1280 cm − 1 to 1261 cm − 1 confirming formation of LiFeCl 4 .2TBP in the presence of FeCl 4 − (Su et al. 2020 ). The formation of FeCl 4 − species can also be confirmed by LC-MS analysis. Figures 5 a, b, and c represent the peaks of the organic phase detected in the LC-MS analyses after the solvent extraction with the feed solutions containing 1, 2, and 6 M chloride, respectively. Three peaks at the mass-to-charge ratios of 197, 198, and 200 in the figures are related to the FeCl 4 − species confirming its presence in the organic phase (Lavanant et al. 1998 ; Hellman et al. 2006 ). It is noticeable that the peak intensities in Fig. 5 c, which is related to the extraction from the feed with 6 M chloride concentration is higher than intensities of the corresponded peaks in Figs. 5 a and b indicating the higher concentration of FeCl 4 − in the organic phase by increasing the chloride concentration in the feed phase. The findings of the preceding analyses indicate that the concentration of FeCl 4 − in the form of LiFeCl 4 .2TBP complex is directly related to the chloride concentration. Effect of O/A ratio on extraction efficiency and separation factor The extraction efficiency of each metal ion from the aqueous phase and therefore their separation factors are affected by the volume ratio of organic to aqueous phase (O/A), which is related to the concentration of each reactant in formation of the metal ion complexes. Figure 6 a shows the extraction efficiencies of each metal ion at different O/A ratio. The figure shows that lithium extraction efficiency is increased with a steep slope by increasing O/A ratio up to O/A = 1 while the slope is a slightly lower at higher O/A ratios. The extraction efficiencies of other metal ions (Mg 2+ , Na + , K + ) varies in a nearly constant range. Figure 6 b shows the separation factors obtained in the experiments with different O/A ratios. It can be seen that the highest separation factors of lithium to metals are obtained at O/A = 1. Extraction performance based on experimental design The objective of the CCD experiments was to study the impact of major parameters such as Fe/Li ratio, HCl concentration, and TBP volume percentage on the efficiency of lithium extraction. The optimization process was carried out using DX 7 software to obtain the maximum response. It is noticeable that in all the experiments, the p-values calculated based on the results of the ANOVA table are less than 0.001. This indicates that the presented answers and results are significant and valid. Table 1 displays the parameters determined from the experimental design that yielded the best response for the lithium extraction efficiency within the specified ranges. According to the table, the maximum and minimum levels of Fe/Li molar ratio and HCl concentration should be set for optimum lithium extraction efficiency, respectively, while the TBP volume percent should be considered at its medium level. The lithium extraction efficiency obtained from the experiment with the set parameters agrees with the predicted response value. Table 1 Optimum parameters and response predicted by experimental design and obtained lithium extraction efficiency in experiment Model Target conditions A: Fe/Li (molar ratio) B: HCl (M) TBP (%) Lithium extraction efficiency (%) Predicted A, B, and C: in range Response: maximum 2.99 0.02 55.0 77.0 Actual 76.3 Figure 7 shows the 3D response and interactions of B (acid concentration) and C (TBP volume percent) in three levels (minimum, medium, and maximum) of A (Fe/Li molar ratio = 0.5, 1.75, and 3), respectively. The greatest range of response (lithium extraction efficiency) is observed at the minimum level of B and a wide range of C Fig. 7 c. According to the 3D response, there are reverse trends for TBP v% in the organic phase at low and high acid concentrations. Specifically, increasing the TBP v% at low acid concentration enhances the lithium extraction efficiency, whereas it decreases the extraction efficiency at higher acid concentrations. This trend can be attributed to the competition of H + and Li + to form the complex with TBP. Figures 7 d-f display the correlation between B and C at the minimum, average, and maximum levels of the Fe/Li molar ratio. The point where the “Min” and “Max” curves intersect in each figure confirms the relationship between the two variables of B and C across all three levels of A. Figure 8 shows that although the lithium extraction is in the range of 62–76% for the Fe/Li molar ratio of 0.5 to 3, the separation factors of Li/Mg is increased sharply. Meanwhile, the separation factors of Li/Na and Li/K are varied insignificantly due to lower affinities of these co-ions for complex formation. The figure shows that the highest Li/Mg separation factor is obtained at about Fe/Li molar ratio = 3. Figure 9 displays the 3D response and interactions between two variables, A (Fe/Li molar ratio) and C (TBP v%), on the lithium extraction efficiency at three levels of variable B (acid concentration = 0, 0.25, and 0.50 M). The highest response levels are observed at low acid concentrations and a wide range of A and C parameters (Fig. 9 (a)). However, the lithium extraction efficiencies are significantly reduced at medium and maximum HCl concentrations (shown in Figs. 9 b and c) due to the competition between H + and Li + in the complex formation. To further study the interactions between variables A and C, Figs. 9 d-f represent the lithium extraction efficiency at the minimum, average, and maximum levels of variable B. The intersection of the "Min" and "Max" curves in Fig. 9 e confirms the interaction of A and C within the range of parameters that need to be optimized. As it was found that solvent extraction in the lower acid concentration yields a better performance for lithium extraction, to have a precise examination, the experiments were performed at low acid concentrations (0.02, 0.05, and 0.1 M). Figure 10 shows the lithium extraction efficiencies and the Li/co-ion separation factors. As seen in the figure, the lithium extraction efficiency is slightly decreased by increasing the acid concentration. Meanwhile, the Li/co-ion separation factors remain nearly constant. Higher acid concentrations increase the competition between Li + and H + , resulting in less lithium extraction and a lower Li/Mg separation factor at the constant magnesium concentration. It should be noted that during extraction, the presence of a controlled amount of HCl in the aqueous phase is required to avoid iron hydrolysis. The H + and Li + equilibrium constants are determined by the following equations (Li et al. 2019 ): $$K\text{H}=\frac{{[{\text{H}\text{F}\text{e}\text{C}\text{l}}_{4} .2\text{T}\text{B}\text{P}]}_{\left(\text{o}\text{r}\text{g}\right)}}{{{{{[\text{H}}^{+}]}_{\left(\text{a}\text{q}\right)}[\text{F}\text{e}}^{3+}]}_{\left(\text{a}\text{q}\right)}{[{{\text{C}\text{l}}^{-}]}^{4}}_{\left(\text{a}\text{q}\right)}{{\left[\text{T}\text{B}\text{P}\right]}^{2}}_{\left(\text{o}\text{r}\text{g}\right)}}= \frac{{\text{D}}_{\text{H}}}{{{[\text{F}\text{e}}^{3+}]}_{\left(\text{a}\text{q}\right)}{[{{\text{C}\text{l}}^{-}]}^{4}}_{\left(\text{a}\text{q}\right)}{{\left[\text{T}\text{B}\text{P}\right]}^{2}}_{\left(\text{o}\text{r}\text{g}\right)}}$$ 7 $$K\text{L}\text{i}=\frac{{[{\text{L}\text{i}\text{F}\text{e}\text{C}\text{l}}_{4} .2\text{T}\text{B}\text{P}]}_{\left(\text{o}\text{r}\text{g}\right)}}{{{{{[\text{L}\text{i}}^{+}]}_{\left(\text{a}\text{q}\right)}[\text{F}\text{e}}^{3+}]}_{\left(\text{a}\text{q}\right)}{[{{\text{C}\text{l}}^{-}]}^{4}}_{\left(\text{a}\text{q}\right)}{{\left[\text{T}\text{B}\text{P}\right]}^{2}}_{\left(\text{o}\text{r}\text{g}\right)}}= \frac{{D}_{\text{L}\text{i}}}{{{[\text{F}\text{e}}^{3+}]}_{\left(\text{a}\text{q}\right)}{[{{\text{C}\text{l}}^{-}]}^{4}}_{\left(\text{a}\text{q}\right)}{{\left[\text{T}\text{B}\text{P}\right]}^{2}}_{\left(\text{o}\text{r}\text{g}\right)}}$$ 8 The reported values of equilibrium constants in certain conditions reveal that H + has a more tendency to form complex with TBP than lithium ( K H > 6 K Li ) (Su et al. 2020 ). This fact highlights the impact of H + concentration in the aqueous phase on the extraction performance. The higher sensitivity of response value to the variation in the acid concentration can be confirmed also by observing the perturbation diagram in Fig. S2 that represents a significant shift in the response slope by alterating the acid concentration (B). Figure 11 shows the 3D response and interactions of A (Fe/Li molar ratio) and B (acid concentration) in three levels (minimum, medium, and maximum) of C (TBP v%=10, 50, and 90), respectively. According to Eq. (6), as the TBP concentration increases, the forward reaction succeeds and results in higher lithium extraction efficiencies. Figures 11 d-f depict the impact of the interaction between A and B on the lithium extraction efficiency, at the minimum, medium, and maximum levels of TBP v% (C). It is observed in Fig. 11 d that the intersection of A and B occurs in the Min level of TBP v% within the designated range. The 3D response confirms high lithium extraction efficiencies for high and medium TBP volume percents (Figs. 11 b and c). Moreover, high levels of lithium extraction efficiency are obtained even at low TBP v% for the Fe/Li molar ratio of 1.7-3 (Fig. 11 a). However, as seen in Fig. 12 , a third organic phase is formed beween the aqueous and the main organic phase at the low level of TBP v% (up to about 40 v%) leading to loss in a part of organic phase. The formation of this third phase, which has been also observed in previous studies (Li et al. 2022 ), is attributed to the low solubility of produced complex in kerosene in the presence of low concentration of free TBP (Zhou et al. 2012 ). As shown in Fig. 13 , increasing TBP v% up to 60% significantly increases the lithium extraction efficiency. The slope of increment in the lithium exration efficiency at higher TBP v% is decreased. In presence of excess TBP, the co-ions (in particular magnesium) can take part in complexation reaction with TBP in the organic phase leading to decrease in the separation factors, β Li/co−ions . Stripping and regeneration The lithium recovery from the organic phase can be performed by regenerating the extracting organic phase through stripping and saponification steps. Figure 14 shows a schematic diagram of the whole process consisting extraction, stripping, and saponification steps. In order to evaluate the effect of acid concentration in the stripping step of regeneration process, stripping tests were performed using HCl with different concentrations and NaCl 5M with O/A = 7:1. The results in Table 2 show that as the HCl concentration increases up to 0.3 M, the lithium and magnesium stripping efficiencies are increased. Higher acid concentrations may cause some troubles in the next saponification process (Shi et al. 2019 ). The saponification is performed using fresh NaOH 0.05 M and NaCl 5 M solutions. By performing three subsquenet runs, 73% of the remaining lithium in the stripped organic phase is transferred to the saponificating aqueous phase. It should be noted that a negligible amount of iron loss (about 1%) was detected in the effeluent aqueous phases during stripping and saponification steps so that only a fine adjustment of iron may be required for the recycled organic phase. Table 2 Lithium and magnesium stripping efficiencies in the stripping processes by different acid concentrations HCl conc. (mol/l) Li stripping (%) Mg stripping (%) 0.07 36.0 21.0 0.15 64.0 43.0 0.30 81.6 60.5 Conclusion Solvent extraction of a brine feed with high Mg/Li ratio was performed using TBP and FeCl 3 as the extractant and co-extractant, respectively. The UV-VIS and LC-MS analyses confirmed that a chloride concentration of 6 M is vital to produce adequate FeCl 4 − concentration for taking part in formation \(\) of the complex [LiFeCl 4 .2TBP]. The FT-IR analysis also verified the formation of the complex by detecting the shift in the TBP representative peak. The Fe/Li molar ratio, acid concentration in the feed, and TBP volume percent in the organic phase were seleceted as the main parameters affecting the lithium solvent extraction. The central composite design (CCD) method was used to assess the effect of main parameters as well as their interactions on the lithium extraction efficiencies. By setting the organic to aqueous volume ratio (O/A = 1), the optimal conditions in a single-stage extraction were determined as Fe/Li molar ratios of 2.99, HCl concentrations of 0.02 M, and TBP volume percent of 55% to yield the highest lithium extraction efficiency (77.0%) as it was confirmed by the experiment (76.3%). The results showed that in the whole defined range of Fe/Li molar ratio, the other two major parameters of HCl concentration and TBP v% have interactions in their selected ranges. Meanwhile, the interactions of the other two parameters were observed merely in the medium HCl concentration level and the minimum TBP v% level which are of less importance because of low lithium extraction efficiencies and appearance of a third phase, respectively. While the results of experimental design revealed that the HCl concentration has the most influential effect on the lithium extraction efficiency in the selected range, the complentary experiments with the suggested parameters showed that TBP concentration in the organic phase has the most influential effect on the Li/Mg separation factor whereas its value at the optimum conditions were determined as 304. About 81% of extracted lithium could be recoverd from the organic phase by applying a stripping solution with 0.3 M HCl and phase ratio of 7:1 through a single-stage stripping process. The Mg/Li mass ratio of 192 in the feed could be reduced to 1.5 in the stripping solution. NOMENCLATURE TBP Tributyl phosphate TOPO Trioctyl phosphine oxide HTTA 4, 4, 4-trifluoro-1-(2-thienyl)butane-1,3-dione Cyanex923 Trialkyl phosphine oxide LIX54 A β-diketone derivative [OHEMIM][NTf2] Hydroxyl 1-hydroxyethyl-3-methyl imidazolium bis(trifluoromethylsulfonyl)imide RSM Response surface methodology CCD Central composite design method E M Extraction efficiency of each ion [%] C M0 Initial concentrations of each co-ion [mg/l] C M Equilibrium concentrations of each co-ion [mg/l] D M Distribution ratio of co-ions [-] V aq Volume of the aqueous phase [ml] V org Volume of the organic phases [ml] Stripping efficiency [%] Initial concentrations of metal ion in the organic phase [mg/l] Equilibrium concentrations of metal ion in the organic phase [mg/l] v% Volume percent [%] K H Equilibrium constant of hydrogen [-] K Li Equilibrium constant of lithium [-] O/A Organic phase to aqueous phase volume ratio [-] β Li/M” separation factor [-] Declarations Ethical Approval Not applicable Consent to Participate Not applicable Consent to Publish Not applicable Author Contributions All authors contributed to the study conception and design. Material preparation, data collection and analysis were performed by Anahita Kazemi Kia. The first draft of the manuscript was written by Anahita Kazemi Kia and the corresponding authors edited the draft and commented on previous versions of the manuscript. All authors read and approved the final manuscript. Funding The authors declare that no funds, grants, or other support were received during the preparation of this manuscript. Competing interests The authors have no relevant financial or non-financial interests to disclose. References Bale MD and May AV (1989) Processing of ores to produce tantalum and lithium. Miner Eng 2:299–320. https://doi.org/10.1016/0892-6875(89)90001-0 Diouf B and Pode R (2015) Potential of lithium-ion batteries in renewable energy. Renew. 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Desalination 496:114710. https://doi.org/10.1016/j.desal.2020.114710 Supplementary Files Appendix.docx Highlights.docx Graphicalabstract.png Graphical abstract Cite Share Download PDF Status: Published Journal Publication published 17 Aug, 2024 Read the published version in Environmental Science and Pollution Research → Version 1 posted Editorial decision: Major Revision 21 Jun, 2024 Reviewers agreed at journal 22 May, 2024 Reviewers invited by journal 22 May, 2024 Editor invited by journal 16 May, 2024 Editor assigned by journal 18 Apr, 2024 First submitted to journal 16 Apr, 2024 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. 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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-4265065","acceptedTermsAndConditions":true,"allowDirectSubmit":false,"archivedVersions":[],"articleType":"Research Article","associatedPublications":[],"authors":[{"id":305410388,"identity":"7a50b014-f52c-45bf-b29c-8dfd1490c4b4","order_by":0,"name":"Anahita Kazemi Kia","email":"","orcid":"","institution":"CCERCI: Chemistry and Chemical Engineering Research Center of Iran","correspondingAuthor":false,"prefix":"","firstName":"Anahita","middleName":"Kazemi","lastName":"Kia","suffix":""},{"id":305410389,"identity":"1feaa0d3-45ff-4a32-bdb3-85392df4865b","order_by":1,"name":"Hamid Reza 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1","display":"","copyAsset":false,"role":"figure","size":144231,"visible":true,"origin":"","legend":"\u003cp\u003ePlan of experimental design by CCD method\u003c/p\u003e","description":"","filename":"1.png","url":"https://assets-eu.researchsquare.com/files/rs-4265065/v1/c45e8b9169f397ad8466533e.png"},{"id":57670604,"identity":"8cf6701c-5e4a-4d25-b7d7-12bff6d8896c","added_by":"auto","created_at":"2024-06-04 06:24:23","extension":"png","order_by":2,"title":"Figure 2","display":"","copyAsset":false,"role":"figure","size":194929,"visible":true,"origin":"","legend":"\u003cp\u003eSchematic of solvent extraction mechanism\u003c/p\u003e","description":"","filename":"2.png","url":"https://assets-eu.researchsquare.com/files/rs-4265065/v1/4ed039bd7c93824a9df9c1fb.png"},{"id":57671165,"identity":"f34ff1b1-640d-4bce-ba3f-ae9addcfdefb","added_by":"auto","created_at":"2024-06-04 06:32:23","extension":"png","order_by":3,"title":"Figure 3","display":"","copyAsset":false,"role":"figure","size":40762,"visible":true,"origin":"","legend":"\u003cp\u003eAbsorption intensities by UV-VIS at 684 nm and lithium extractions in different chloride concentrations\u003c/p\u003e","description":"","filename":"3.png","url":"https://assets-eu.researchsquare.com/files/rs-4265065/v1/b1ba6568aa2b8b7a8c95e7c3.png"},{"id":57671668,"identity":"15f41105-a25f-463a-8c91-2bc0b8d0a038","added_by":"auto","created_at":"2024-06-04 06:40:23","extension":"png","order_by":4,"title":"Figure 4","display":"","copyAsset":false,"role":"figure","size":66652,"visible":true,"origin":"","legend":"\u003cp\u003eFT-IR spectra of organic phase before and after solvent extraction\u003c/p\u003e","description":"","filename":"4.png","url":"https://assets-eu.researchsquare.com/files/rs-4265065/v1/06c9f37362dccff93053d23e.png"},{"id":57671163,"identity":"3a9b5b9a-aa1b-4df6-9d9c-0a92633599e0","added_by":"auto","created_at":"2024-06-04 06:32:23","extension":"png","order_by":5,"title":"Figure 5","display":"","copyAsset":false,"role":"figure","size":59819,"visible":true,"origin":"","legend":"\u003cp\u003eMass to charge ratios in LC-MS analyses of organic phase after extraction with the feed phase containing \u003cstrong\u003ea\u003c/strong\u003e 1 m, \u003cstrong\u003eb\u003c/strong\u003e 2 M, and \u003cstrong\u003ec \u003c/strong\u003e6 M chloride concentration\u003c/p\u003e","description":"","filename":"5.png","url":"https://assets-eu.researchsquare.com/files/rs-4265065/v1/92efd73bed9d2c0978a2651b.png"},{"id":57671669,"identity":"8576665c-4cef-4edb-b877-be200c308fca","added_by":"auto","created_at":"2024-06-04 06:40:23","extension":"png","order_by":6,"title":"Figure 6","display":"","copyAsset":false,"role":"figure","size":61485,"visible":true,"origin":"","legend":"\u003cp\u003eEffect of O/A volume ratio on \u003cstrong\u003ea\u003c/strong\u003e extraction efficiency; \u003cstrong\u003eb\u003c/strong\u003e lithium extraction efficiency and lithium/co-ion separation factor ([HCl]=0.02M, [Li\u003csup\u003e+\u003c/sup\u003e]=0.05M, [Mg\u003csup\u003e2+\u003c/sup\u003e]=3.5M, [Na\u003csup\u003e+\u003c/sup\u003e]=0.6M, and [K\u003csup\u003e+\u003c/sup\u003e]=0.02M)\u003c/p\u003e","description":"","filename":"6.png","url":"https://assets-eu.researchsquare.com/files/rs-4265065/v1/da04544125828272c2b85343.png"},{"id":57670620,"identity":"ded7e138-0273-408f-b385-1c7e0f7c9fd4","added_by":"auto","created_at":"2024-06-04 06:24:24","extension":"png","order_by":7,"title":"Figure 7","display":"","copyAsset":false,"role":"figure","size":931930,"visible":true,"origin":"","legend":"\u003cp\u003eResponse surface of extractions in three levels of A (Fe/Li molar ratio); 3D response (\u003cstrong\u003ea\u003c/strong\u003e: Min, \u003cstrong\u003eb\u003c/strong\u003e: Mean, \u003cstrong\u003ec\u003c/strong\u003e: Max), and interactions (\u003cstrong\u003ed\u003c/strong\u003e: Min, \u003cstrong\u003ee\u003c/strong\u003e: Mean, \u003cstrong\u003ef\u003c/strong\u003e: Max) versus independent variables of HCl concentration (B) and TBP volume percent (C)\u003c/p\u003e","description":"","filename":"7.png","url":"https://assets-eu.researchsquare.com/files/rs-4265065/v1/51a2a76815297638bc94924f.png"},{"id":57670616,"identity":"06fbec6a-1959-4b92-809b-15e414ad3937","added_by":"auto","created_at":"2024-06-04 06:24:23","extension":"png","order_by":8,"title":"Figure 8","display":"","copyAsset":false,"role":"figure","size":46429,"visible":true,"origin":"","legend":"\u003cp\u003eEffect of Fe/Li molar ratios on lithium extraction and separation factors of Li/co-ions (TBP v%=55%, [HCl] = 0.02 M, [Li\u003csup\u003e+\u003c/sup\u003e] = 0.05, [Mg\u003csup\u003e2+\u003c/sup\u003e] = 3.5, [Na\u003csup\u003e+\u003c/sup\u003e] = 0.6, and [K\u003csup\u003e+\u003c/sup\u003e] = 0.02, and O/A = 1)\u003c/p\u003e","description":"","filename":"8.png","url":"https://assets-eu.researchsquare.com/files/rs-4265065/v1/ed494e010f6e535d709e044e.png"},{"id":57671168,"identity":"3255d0c3-aafe-4a79-a698-5e1ddcdbc9d6","added_by":"auto","created_at":"2024-06-04 06:32:24","extension":"png","order_by":9,"title":"Figure 9","display":"","copyAsset":false,"role":"figure","size":963237,"visible":true,"origin":"","legend":"\u003cp\u003eResponse surface of extractions in three levels of B (HCl concentration); 3D response\u003cstrong\u003e(a\u003c/strong\u003e: Min, \u003cstrong\u003eb\u003c/strong\u003e: Mean, \u003cstrong\u003ec\u003c/strong\u003e: Max), and interactions (\u003cstrong\u003ed\u003c/strong\u003e: Min, \u003cstrong\u003ee\u003c/strong\u003e: Mean, \u003cstrong\u003ef\u003c/strong\u003e: Max) versus independent variables of Fe/Li molar ratio (A) and TBP volume percent (C)\u003c/p\u003e","description":"","filename":"9.png","url":"https://assets-eu.researchsquare.com/files/rs-4265065/v1/da15f38285467b3b1e2a02e2.png"},{"id":57671166,"identity":"430e01c1-0565-4a3e-9836-0932d072df89","added_by":"auto","created_at":"2024-06-04 06:32:23","extension":"png","order_by":10,"title":"Figure 10","display":"","copyAsset":false,"role":"figure","size":32151,"visible":true,"origin":"","legend":"\u003cp\u003eEffects of acid concentration on lithium extraction and Li/Mg separation factor\u003c/p\u003e","description":"","filename":"10.png","url":"https://assets-eu.researchsquare.com/files/rs-4265065/v1/0055135eb2c5727508c8b823.png"},{"id":57670617,"identity":"e14a17f5-6f4b-476e-96d5-9e92973248a1","added_by":"auto","created_at":"2024-06-04 06:24:24","extension":"png","order_by":11,"title":"Figure 11","display":"","copyAsset":false,"role":"figure","size":936957,"visible":true,"origin":"","legend":"\u003cp\u003eResponse surface of extractions in three levels of C (TBP vol%); 3D response (a: Min, b: Mean, c: Max), and interactions (\u003cstrong\u003ed\u003c/strong\u003e: Min, \u003cstrong\u003ee\u003c/strong\u003e: Mean, \u003cstrong\u003ef\u003c/strong\u003e: Max) versus independent variables of (A) Fe/Li (molar ratio), and (B) HCl concentration (M)\u003c/p\u003e","description":"","filename":"11.png","url":"https://assets-eu.researchsquare.com/files/rs-4265065/v1/a755ea4210997d81feb7102f.png"},{"id":57671167,"identity":"dac1479c-a695-4b5e-977b-3e3407ee5343","added_by":"auto","created_at":"2024-06-04 06:32:24","extension":"png","order_by":12,"title":"Figure 12","display":"","copyAsset":false,"role":"figure","size":344472,"visible":true,"origin":"","legend":"\u003cp\u003ePhase behaviors by extraction with different TBP v%; \u003cstrong\u003ea\u003c/strong\u003e 55.0 v%, \u003cstrong\u003eb\u003c/strong\u003e 26.2 v%\u003c/p\u003e","description":"","filename":"12.png","url":"https://assets-eu.researchsquare.com/files/rs-4265065/v1/a75bc32fca9bec1d7a28d4ff.png"},{"id":57670613,"identity":"400e01b4-9161-4b5e-acdc-65180a9fdbee","added_by":"auto","created_at":"2024-06-04 06:24:23","extension":"png","order_by":13,"title":"Figure 13","display":"","copyAsset":false,"role":"figure","size":56029,"visible":true,"origin":"","legend":"\u003cp\u003eEffects of TBP v% on lithium extraction and separation factors of Li/co-ions ([HCl] = 0.02 M, Fe/Li = 2.99, [Li\u003csup\u003e+\u003c/sup\u003e] = 0.05, [Mg\u003csup\u003e2+\u003c/sup\u003e] = 3.5, [Na\u003csup\u003e+\u003c/sup\u003e] = 0.6, and [K\u003csup\u003e+\u003c/sup\u003e] = 0.02, and O/A = 1)\u003c/p\u003e","description":"","filename":"13.png","url":"https://assets-eu.researchsquare.com/files/rs-4265065/v1/1a1e365bfacee49db78ff440.png"},{"id":57670615,"identity":"d3e60dd1-d16f-437d-a3e4-ad8356317a0b","added_by":"auto","created_at":"2024-06-04 06:24:23","extension":"png","order_by":14,"title":"Figure 14","display":"","copyAsset":false,"role":"figure","size":54698,"visible":true,"origin":"","legend":"\u003cp\u003eShcematic diagram of lihium extraction process\u003c/p\u003e","description":"","filename":"14.png","url":"https://assets-eu.researchsquare.com/files/rs-4265065/v1/baf9b22e51aa5b6b4b7e57fd.png"},{"id":63071422,"identity":"b7caf8b3-7a7b-44d6-ba95-a4f3cc95a620","added_by":"auto","created_at":"2024-08-22 20:07:05","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":5005890,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-4265065/v1/24b3eb2b-a16c-4a04-8323-75e21107098a.pdf"},{"id":57670611,"identity":"c7d7b44a-032c-4a98-8ab1-6d52f8e6227d","added_by":"auto","created_at":"2024-06-04 06:24:23","extension":"docx","order_by":1,"title":"","display":"","copyAsset":false,"role":"supplement","size":377102,"visible":true,"origin":"","legend":"","description":"","filename":"Appendix.docx","url":"https://assets-eu.researchsquare.com/files/rs-4265065/v1/850754d8f7f730ee09f0186c.docx"},{"id":57670610,"identity":"88338e09-c43d-4b07-8908-b190669e1dd5","added_by":"auto","created_at":"2024-06-04 06:24:23","extension":"docx","order_by":2,"title":"","display":"","copyAsset":false,"role":"supplement","size":15366,"visible":true,"origin":"","legend":"","description":"","filename":"Highlights.docx","url":"https://assets-eu.researchsquare.com/files/rs-4265065/v1/c3e4ee2ade9ab1cbcf1491e8.docx"},{"id":57670607,"identity":"435687cc-1608-49bc-9f16-9ef9b174dadc","added_by":"auto","created_at":"2024-06-04 06:24:23","extension":"png","order_by":3,"title":"","display":"","copyAsset":false,"role":"supplement","size":391495,"visible":true,"origin":"","legend":"\u003cp\u003eGraphical abstract\u003c/p\u003e","description":"","filename":"Graphicalabstract.png","url":"https://assets-eu.researchsquare.com/files/rs-4265065/v1/3f4399a67aaba4dda03c3de6.png"}],"financialInterests":"","formattedTitle":"Solvent extraction of lithium from brines with high magnesium/lithium ratios; Investigation on parameter interactions","fulltext":[{"header":"Introduction","content":"\u003cp\u003eThe rapid growth of industries requires an increasing global demand for clean, inexpensive, and sustainable energy resources. According to the new EU regulations, the contribution of green and renewable energy should be increased to about 42% by 2030 to remediate the escalating and critical problem of greenhouse gas emissions (Hatfield-Dodds et al. \u003cspan citationid=\"CR4\" class=\"CitationRef\"\u003e2017\u003c/span\u003e; Trujillo-Baute et al. \u003cspan citationid=\"CR40\" class=\"CitationRef\"\u003e2018\u003c/span\u003e). During the last two decades, the shortage of fossil fuel resources has led to a growth in applying lithium-ion batteries to meet the environmental goals (Diouf et al. 2015; Sterba et al. \u003cspan citationid=\"CR29\" class=\"CitationRef\"\u003e2019\u003c/span\u003e). Lithium is also used in various industries such as electronics (Xie et al. \u003cspan citationid=\"CR44\" class=\"CitationRef\"\u003e2021\u003c/span\u003e; Liu et al. \u003cspan citationid=\"CR17\" class=\"CitationRef\"\u003e2019\u003c/span\u003e), aviation(Kablov et al. \u003cspan citationid=\"CR10\" class=\"CitationRef\"\u003e2021\u003c/span\u003e; Sverdlin et al. \u003cspan citationid=\"CR28\" class=\"CitationRef\"\u003e1998\u003c/span\u003e), sea transportation (Salucci et al. \u003cspan citationid=\"CR30\" class=\"CitationRef\"\u003e2023\u003c/span\u003e), and pharmaceuticals (Zhu et al. \u003cspan citationid=\"CR47\" class=\"CitationRef\"\u003e2019\u003c/span\u003e).\u003c/p\u003e \u003cp\u003eThe primary resources of lithium including ores and water resources (brines, seawaters, and geothermal waters) as well as the secondary sources such as spent batteries have been considered for lithium production (Talens Peiro et al. 2013; Golmohammadzadeh et al. \u003cspan citationid=\"CR3\" class=\"CitationRef\"\u003e2018\u003c/span\u003e). Lithium distribution in different resources and their interfering impurities are varied significantly (Wesselborg et al. \u003cspan citationid=\"CR42\" class=\"CitationRef\"\u003e2021\u003c/span\u003e). The lithium extraction process depends widely on the source type, lithium concentration, and presence of interfering ions. The exploitable lithium in the pegmatite deposits ranges from about 1.25 to 4% Li\u003csub\u003e2\u003c/sub\u003eO (Bale et al. 1989) while its concentrations in the brines are about 100\u0026ndash;2000 mg/L (Zhou et al. \u003cspan citationid=\"CR48\" class=\"CitationRef\"\u003e2012\u003c/span\u003e; Ji et al. \u003cspan citationid=\"CR7\" class=\"CitationRef\"\u003e2017\u003c/span\u003e; Zhang et al. \u003cspan citationid=\"CR49\" class=\"CitationRef\"\u003e2019\u003c/span\u003e). The lithium extraction from brines with relatively moderate concentrations might be feasible in comparison to the extraction from mineral sources as it does not require an extra step of dissolution. Different processes such as chemical precipitation (Zhao et al. \u003cspan citationid=\"CR50\" class=\"CitationRef\"\u003e2023\u003c/span\u003e), adsorption (Romero et al. \u003cspan citationid=\"CR27\" class=\"CitationRef\"\u003e2018\u003c/span\u003e), membrane processes (Su et al. \u003cspan citationid=\"CR32\" class=\"CitationRef\"\u003e2020\u003c/span\u003e), electrochemical methods (Su et al. \u003cspan citationid=\"CR32\" class=\"CitationRef\"\u003e2020\u003c/span\u003e), and solvent extraction (Hano et al. \u003cspan citationid=\"CR5\" class=\"CitationRef\"\u003e1992\u003c/span\u003e; Torkaman et al. \u003cspan citationid=\"CR41\" class=\"CitationRef\"\u003e2017\u003c/span\u003e) can be applied to retrieve lithium. On the other hand, the performance of applied process depends on the type and amount of co-ions including magnesium as a significant impurity, which is widely varied in diferent resources (Su et al. \u003cspan citationid=\"CR32\" class=\"CitationRef\"\u003e2020\u003c/span\u003e).\u003c/p\u003e \u003cp\u003eThe solvent extraction as a simple process has the advantages such as low energy consumption, low waste generation, and recyclability of extractants. The method has been tested in a pilot scale for lithium extraction (Zhou et al. \u003cspan citationid=\"CR48\" class=\"CitationRef\"\u003e2012\u003c/span\u003e; Su et al. \u003cspan citationid=\"CR32\" class=\"CitationRef\"\u003e2020\u003c/span\u003e; Shi et al. \u003cspan citationid=\"CR33\" class=\"CitationRef\"\u003e2020\u003c/span\u003e; Su et al. \u003cspan citationid=\"CR32\" class=\"CitationRef\"\u003e2020\u003c/span\u003e). In a solvent extraction process, when the feed solution comes into contact with an extracting organic phase, the consituents in the feed solution is distributed between the two phases. Various extractants have been applied to extract lithium by solvent extraction including trioctyl phosphine oxide (TOPO) with co-extractant of HTTA (4, 4, 4-trifluoro-1-(2-thienyl)butane-1,3-dione) (Ji et al. \u003cspan citationid=\"CR9\" class=\"CitationRef\"\u003e2016\u003c/span\u003e), trialkyl phosphine oxide (cyanex923) with co-extractan of LIX54 (a β-diketone derivative) (Pranolo et al. \u003cspan citationid=\"CR24\" class=\"CitationRef\"\u003e2015\u003c/span\u003e), neutral ligand trialkylphosphine oxide (Cyanex 923) along with hydroxyl 1-hydroxyethyl-3-methyl imidazolium bis(trifluoromethylsulfonyl)imide ([OHEMIM][NTf2]) as the co-extractant (Shi et al. \u003cspan citationid=\"CR35\" class=\"CitationRef\"\u003e2015\u003c/span\u003e).\u003c/p\u003e \u003cp\u003eDespite their feasible performances, the aforementioned extractants have some disadvantages such as high price, lack of selectivity for lithium over interfering ions so that some pretreatments are required (Ji et al. \u003cspan citationid=\"CR9\" class=\"CitationRef\"\u003e2016\u003c/span\u003e). Alternatively, TBP has been found as a low-cost selective extractant in the lithium extraction (Pranolo et al. \u003cspan citationid=\"CR24\" class=\"CitationRef\"\u003e2015\u003c/span\u003e; Li et al. \u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e2021\u003c/span\u003e; Ji et al. \u003cspan citationid=\"CR9\" class=\"CitationRef\"\u003e2016\u003c/span\u003e) However, TBP cannot individually form a complex with lithium in the aqueous phase (Li et al. \u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e2021\u003c/span\u003e). Metal chloride compounds such as CuCl\u003csub\u003e2\u003c/sub\u003e, InCl\u003csub\u003e3\u003c/sub\u003e, SnCl\u003csub\u003e4\u003c/sub\u003e, and FeCl\u003csub\u003e3\u003c/sub\u003e as well as room temperature ionic liquids such as ([C\u003csub\u003e4\u003c/sub\u003emim][Tf\u003csub\u003e2\u003c/sub\u003eN]), (C\u003csub\u003e4\u003c/sub\u003emim\u003csup\u003e+\u003c/sup\u003e\u0026middot;PF6\u003csup\u003e\u0026minus;\u003c/sup\u003e) (Zhou et al. \u003cspan citationid=\"CR48\" class=\"CitationRef\"\u003e2012\u003c/span\u003e; Li et al. \u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e2021\u003c/span\u003e; Yang et al. \u003cspan citationid=\"CR45\" class=\"CitationRef\"\u003e2019\u003c/span\u003e; Okamura et al. \u003cspan citationid=\"CR23\" class=\"CitationRef\"\u003e2014\u003c/span\u003e; Shi et al. \u003cspan citationid=\"CR35\" class=\"CitationRef\"\u003e2015\u003c/span\u003e), were utilized as TBP co-extractants. Among these co-extractants, FeCl\u003csub\u003e3\u003c/sub\u003e has shown a promising performance for lithium extraction due to its appropriate selectivity towards lithium (Lum et al. \u003cspan citationid=\"CR13\" class=\"CitationRef\"\u003e2012\u003c/span\u003e; Lum et al. \u003cspan citationid=\"CR14\" class=\"CitationRef\"\u003e2013\u003c/span\u003e).\u003c/p\u003e \u003cp\u003eThe presence of H\u003csup\u003e+\u003c/sup\u003e is essential in the extraction using TBP/FeCl\u003csub\u003e3\u003c/sub\u003e to prevent hydrolysis of iron during the process (Wesselborg et al. \u003cspan citationid=\"CR42\" class=\"CitationRef\"\u003e2021\u003c/span\u003e; Lum et al. \u003cspan citationid=\"CR14\" class=\"CitationRef\"\u003e2013\u003c/span\u003e). However, an excessive concentration of H\u003csup\u003e+\u003c/sup\u003e may decompose the TBP structure and degrades the extraction efficiency. Therefore, managing acid concentration in the solution is crucial as it also causes corrosion problems in the equipments (Yu et al. \u003cspan citationid=\"CR46\" class=\"CitationRef\"\u003e2019\u003c/span\u003e; Shi et al. \u003cspan citationid=\"CR36\" class=\"CitationRef\"\u003e2019\u003c/span\u003e; Ji et al. \u003cspan citationid=\"CR8\" class=\"CitationRef\"\u003e2022\u003c/span\u003e).\u003c/p\u003e \u003cp\u003eAs a result, in order to optimize the performance of an extraction process containing TBP/FeCl\u003csub\u003e3\u003c/sub\u003e, it is necessary to investigate the effects of major parameters affecting the process as well as their interactions. Many studies have investigated effective parameters in the lithium solvent extraction (Bale et al. 1989; Yu et al. \u003cspan citationid=\"CR46\" class=\"CitationRef\"\u003e2019\u003c/span\u003e; Li et al. \u003cspan citationid=\"CR16\" class=\"CitationRef\"\u003e2019\u003c/span\u003e; Ji et al. \u003cspan citationid=\"CR8\" class=\"CitationRef\"\u003e2022\u003c/span\u003e). However, to our knowledge, no experimental study was reported, in which the interactions of major parameter have been investigated simultaneously.\u003c/p\u003e \u003cp\u003eThe experimental design with the common response surface methodology (RSM) approach allows investigate not only the effect of adjusting each parameter but also their combined effects on the response value.\u003c/p\u003e \u003cp\u003eIn the present research, the RSM is applied to evaluate the effects of major parameters of solvent extraction and their interactions on lithium extraction efficiency. The optimized test conditions are then applied to assess their effects on the sepation factor. Finally, stripping and saponification for recovery of extracting phase are performed and a sketch for the whole process is proposed.\u003c/p\u003e"},{"header":"Experimental","content":"\u003cdiv id=\"Sec3\" class=\"Section2\"\u003e \u003ch2\u003eMaterials\u003c/h2\u003e \u003cp\u003eLithium chloride (LiCl), sodium chloride (NaCl), potassium chloride (KCl), magnesium chloride hexahydrate (MgCl\u003csub\u003e2\u003c/sub\u003e.6H\u003csub\u003e2\u003c/sub\u003eO), ferric chloride hexahydrate (FeCl\u003csub\u003e3\u003c/sub\u003e.6H\u003csub\u003e2\u003c/sub\u003eO), and concentrated hydrochloric acid (HCl, 37%) were all purchased from Merck. Tributyl phosphate (TBP, 99%) was obtained from Sigma-Aldrich and used without further purification. Kerosene as the diluent was provided from a domestic provider.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec4\" class=\"Section2\"\u003e \u003ch2\u003eExperimental procedure\u003c/h2\u003e \u003cp\u003eThe aqueous samples of synthetic feed with different HCl concnetrations, LiCl as the main source of lithium, NaCl and KCl as the co-ions, and MgCl\u003csub\u003e2\u003c/sub\u003e.6H\u003csub\u003e2\u003c/sub\u003eO as the co-ion as well as the chloride source were prepared. The Fe/Li ratio in the synthetic feed was adjusted by adding FeCl\u003csub\u003e3\u003c/sub\u003e.6H\u003csub\u003e2\u003c/sub\u003eO. The organic phases containing kerosene and TBP were prepared with predetermined volumetric percents.\u003c/p\u003e \u003cp\u003eThe feed and organic phases were poured in a round-bottom flask and stirred for 10 min using an overhead stirrer (RE 162, IKA, Netherlands, 700 rpm). The different organic to aqueous volume ratios (O/A) (0.25, 0.5, 0.7, 1, 1.3, 1.5, 1.7, and 2) were tested in the primary experiments to determine the optimum ratio for the lithium extraction. The volume of the aqueous phase was fixed while the O/A ratio was adjusted by altering the volume of the organic phase. The two-phase mixture was then poured into a 50-ml decanter funnel. After 30 min, when the equilibrium conditions were reached, the aqueous phase was gently separated from the organic phase.\u003c/p\u003e \u003cp\u003eThe stripping and saponification of the organic phase were performed to re-extract lithium from the aqueous phase as well as to re-use the extracting organic phase for the next extraction operation with the fresh aqueous feed. In the stripping stage, the organic phase was mixed with an acidic aqueous phase containing 0.3 M HCl and 5 M NaCl in an O/A ratio of 7:1. The organic phase was then saponified using an alkaline solution of 0.05 M NaOH and 5 M NaCl with an O/A ratio of 7:1.\u003c/p\u003e \u003cp\u003eThe extraction efficiency of each ion, \u003cem\u003eE\u003c/em\u003e\u003csub\u003eM\u003c/sub\u003e, is calculated as follows:\u003c/p\u003e \u003cp\u003e \u003cspan class=\"InlineEquation\"\u003e \u003cspan class=\"mathinline\"\u003e\\(E\\text{M}= \\frac{C\\text{M}0- C\\text{M} }{C\\text{M}0} \\times 100\\)\u003c/span\u003e \u003c/span\u003e (%) (1)\u003c/p\u003e \u003cp\u003eIn which, \u003cem\u003eC\u003c/em\u003e\u003csub\u003eM0\u003c/sub\u003e and \u003cem\u003eC\u003c/em\u003e\u003csub\u003eM\u003c/sub\u003e are the initial and equilibrium concentrations of each co-ion (Na\u003csup\u003e+\u003c/sup\u003e, K\u003csup\u003e+\u003c/sup\u003e, Mg\u003csup\u003e2+\u003c/sup\u003e, and Fe\u003csup\u003e3+\u003c/sup\u003e) in the aqueous phase, respectively. The \u0026ldquo;Li/M\u0026rdquo; separation factor, \u003cem\u003eβ\u003c/em\u003e, is determined by calculation of lithium and co-ions distribution ratios, \u003cem\u003eD\u003c/em\u003e\u003csub\u003eM\u003c/sub\u003e, by the following equations:\u003cdiv id=\"Equ1\" class=\"Equation\"\u003e\u003cdiv format=\"TEX\" class=\"mathdisplay\" id=\"FileID_Equ1\" name=\"EquationSource\"\u003e\n$$D\\text{M}=\\frac{C\\text{M}0- C\\text{M} }{C\\text{M} }\\times \\frac{{V}_{\\text{a}\\text{q}}}{{V}_{\\text{o}\\text{r}\\text{g}}}$$\u003c/div\u003e\u003cdiv class=\"EquationNumber\"\u003e2\u003c/div\u003e\u003c/div\u003e\u003cdiv id=\"Equ2\" class=\"Equation\"\u003e\u003cdiv format=\"TEX\" class=\"mathdisplay\" id=\"FileID_Equ2\" name=\"EquationSource\"\u003e\n$$\\beta =\\frac{{D}_{\\text{L}\\text{i}}}{{D}_{\\text{M}}}$$\u003c/div\u003e\u003cdiv class=\"EquationNumber\"\u003e3\u003c/div\u003e\u003c/div\u003e\u003c/p\u003e \u003cp\u003ein which, \u003cem\u003eV\u003c/em\u003e\u003csub\u003eaq\u003c/sub\u003e and \u003cem\u003eV\u003c/em\u003e\u003csub\u003eorg\u003c/sub\u003e represent the volume of the aqueous and organic phases, respectively.\u003c/p\u003e \u003cp\u003eThe stripping efficiency,\u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\({E}_{\\text{M}}^{{\\prime }}\\)\u003c/span\u003e\u003c/span\u003e, is determined by:\u003c/p\u003e \u003cp\u003e \u003cspan class=\"InlineEquation\"\u003e \u003cspan class=\"mathinline\"\u003e\\({E}_{\\text{M}}^{{\\prime }}= \\frac{{C}_{\\text{M}0}^{{\\prime }}- {C}_{\\text{M}}^{{\\prime }} }{{C}_{\\text{M}0}^{{\\prime }}} \\times 100\\)\u003c/span\u003e \u003c/span\u003e (%) (4)\u003c/p\u003e \u003cp\u003e \u003cspan class=\"InlineEquation\"\u003e \u003cspan class=\"mathinline\"\u003e\\({C}_{\\text{M}0}^{{\\prime }}\\)\u003c/span\u003e \u003c/span\u003e and \u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\({C}_{\\text{M} }^{{\\prime }}\\)\u003c/span\u003e\u003c/span\u003edenote the initial and equilibrium concentrations of metal ion in the organic phase.\u003c/p\u003e \u003cp\u003eThe central composite design (CCD) method was utilized to evaluate each effective parameter individually as well as their simultaneous interactions on the response value. The lithium extraction efficiency, \u003cem\u003eE\u003c/em\u003e\u003csub\u003eLi\u003c/sub\u003e, was set as the response while the molar ratio of Fe/Li (A), the HCl concentration in the aqueous pahse (B), and the volume percent of TBP in the organic phase (C) were set as the independent variables.\u003c/p\u003e \u003cp\u003eThe two-level factorial design incorporates a CCD (central composite design) which consists of a center point and star points. The purpose is to increase the level of each variable from 2 to 5, while ensuring a normal distribution of data around the mean value. To control for any examiner errors, the number of repeats was set to 5. The distribution of points was arranged to achieve a normal distribution by drawing the number of observations according to the variables. By using a normal distribution, the mean value, variance, or standard error of each variable can be easily determined. The points were set in a rotating arrange i.e. the variances of all points depend only on their distance from the central point of the test, and are independent of the direction or path of variable alteration in the test space (Salehi et al. 2018).\u003c/p\u003e \u003cp\u003eThe ranges of effective parameters were set as 0.5-3 for the molar ratio of Fe/Li (A), 0-0.5 (M) for the HCl concentration in the aqueous phase (B), and 10\u0026ndash;90 (%) for TBP volume percent in the organic phase (C). Table \u003cspan refid=\"MOESM1\" class=\"InternalRef\"\u003eS1\u003c/span\u003e shows the range of parameters and their levels designated by 7DX software (USA, version 7.1.3 Ease-State).\u003c/p\u003e \u003cp\u003eThe plan of experimental design and the ranges of each parameter are shown Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003e.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec5\" class=\"Section2\"\u003e \u003ch2\u003eCharacterization\u003c/h2\u003e \u003cp\u003eInductivity coupled plasma-atomic emission spectrometry (ICP-AES; spectro arcos, Germany) was used to determine the concentration of cations in the aqueous phase before and after extraction.\u003c/p\u003e \u003cp\u003eThe formation and presence of ionic species in the organic phase were studied using liquid chromatography-mass spectrometry (LC-Ms, Quattro micro API, HPLC: alliance 2695, USA) analysis.\u003c/p\u003e \u003cp\u003eFourier transform infrared measurement (FT-IR, Perkin Elmer Spectrum 65, USA) was applied to detect the peak shift related to the P\u0026thinsp;=\u0026thinsp;O functional group by formation of the [Li(TBP)\u003csub\u003e2\u003c/sub\u003e][FeCl\u003csub\u003e4\u003c/sub\u003e] complex (Li et al. \u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e2021\u003c/span\u003e). The formation of [FeCl\u003csub\u003e4\u003c/sub\u003e]\u003csup\u003e\u0026minus;\u003c/sup\u003e was verified using Ultraviolet Visible Spectrometer (UV-VIS; Perkinelmer, Lambda25, USA) analysis.\u003c/p\u003e \u003c/div\u003e"},{"header":"Result and discussion","content":"\u003cdiv id=\"Sec7\" class=\"Section2\"\u003e \u003cp\u003eMechanism of \u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\({\\mathbf{L}\\mathbf{i}\\mathbf{F}\\mathbf{e}\\mathbf{C}\\mathbf{l}}_{4}.2\\mathbf{T}\\mathbf{B}\\mathbf{P}\\)\u003c/span\u003e\u003c/span\u003e complex formation\u003c/p\u003e \u003cp\u003eThe mechanism of selective extraction of lithium from the brine is shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003e.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eIn an environment with high chloride concentration, Fe\u003csup\u003e3+\u003c/sup\u003e will react with Cl\u003csup\u003e\u0026minus;\u003c/sup\u003e to form [FeCl\u003csub\u003e4\u003c/sub\u003e]\u003csup\u003e\u0026minus;\u003c/sup\u003e as follows (Su et al. \u003cspan citationid=\"CR32\" class=\"CitationRef\"\u003e2020\u003c/span\u003e):\u003c/p\u003e \u003cp\u003e \u003cspan class=\"InlineEquation\"\u003e \u003cspan class=\"mathinline\"\u003e\\({\\text{F}\\text{e}}^{3+}\\)\u003c/span\u003e \u003c/span\u003e \u003csub\u003e(aq)\u003c/sub\u003e +\u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\({4\\text{C}\\text{l}}^{-}\\)\u003c/span\u003e\u003c/span\u003e\u003csub\u003e(aq)\u003c/sub\u003e \u0026harr; \u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\({\\text{F}\\text{e}\\text{C}\\text{l}}_{4}^{-}\\)\u003c/span\u003e\u003c/span\u003e\u003csub\u003e(aq)\u003c/sub\u003e (5)\u003c/p\u003e \u003cp\u003eIn presense of chloride ions, the various species of FeCl\u003csub\u003en\u003c/sub\u003e\u003csup\u003e3\u0026minus;n\u003c/sup\u003e are produced. Fe\u003csup\u003e3+\u003c/sup\u003e can be coordinated by water up to the coordination number of 6, which diminishes the electrostatic interactions of Fe-Cl in the produced species. It has been found that the length of Fe-Cl bond is increased from 2.07 \u0026Aring; in FeCl\u003csub\u003e2\u003c/sub\u003e\u003csup\u003e+\u003c/sup\u003e to 2.22 \u0026Aring; in FeCl\u003csub\u003e2\u003c/sub\u003e(H\u003csub\u003e2\u003c/sub\u003eO)\u003csub\u003e4\u003c/sub\u003e\u003csup\u003e+\u003c/sup\u003e, from 2.13 \u0026Aring; in FeCl\u003csub\u003e3\u003c/sub\u003e to 2.22 \u0026Aring; in FeCl\u003csub\u003e3\u003c/sub\u003e(H\u003csub\u003e2\u003c/sub\u003eO)\u003csub\u003e3\u003c/sub\u003e, and from 2.22 \u0026Aring; in FeCl\u003csub\u003e4\u003c/sub\u003e\u003csup\u003e\u0026minus;\u003c/sup\u003e to 2.40 \u0026Aring; in FeCl\u003csub\u003e4\u003c/sub\u003e(H\u003csub\u003e2\u003c/sub\u003eO)\u003csub\u003e2\u003c/sub\u003e\u003csup\u003e\u0026minus;\u003c/sup\u003e (Sun et al. \u003cspan citationid=\"CR38\" class=\"CitationRef\"\u003e2022\u003c/span\u003e). The hydrogen bonding between chloride ions and the surrounding water molecules weakens the Fe-Cl coordinative interaction (Sun et al. \u003cspan citationid=\"CR38\" class=\"CitationRef\"\u003e2022\u003c/span\u003e). The increase in the FeCl bond length resulted in a decrease in the Fe-Cl bond energy, which induces instability of the FeCl\u003csub\u003en\u003c/sub\u003e\u003csup\u003e3\u0026minus;n\u003c/sup\u003e complexes in the aqueous phase whereas the FeCl\u003csub\u003e4\u003c/sub\u003e\u003csup\u003e\u0026minus;\u003c/sup\u003e structure with the the highest length of Fe-Cl bond represents the highest tendency to migrate from the aqueous phase to the organic phase.\u003c/p\u003e \u003cp\u003eFeCl\u003csub\u003e4\u003c/sub\u003e\u003csup\u003e\u0026minus;\u003c/sup\u003e can form a complex with TBP in the organic phase. The produced complex is neutralized by coupling with a metal cation transferred to the organic phase. According to the extraction mechanism, the affinity of complex formation towards metal ions is H\u003csup\u003e+\u003c/sup\u003e\u0026gt;Li\u003csup\u003e+\u003c/sup\u003e\u0026gt;Ca\u003csup\u003e+\u003c/sup\u003e\u0026gt;Mg\u003csup\u003e2+\u003c/sup\u003e\u0026gt;Na\u003csup\u003e+\u003c/sup\u003e\u0026gt;K\u003csup\u003e+\u003c/sup\u003e (Zhang et al. \u003cspan citationid=\"CR53\" class=\"CitationRef\"\u003e2020\u003c/span\u003e). The bond length of metal ̶ O (of the TBP structure) and metal ̶̶̶ Cl in the generated complex is in the order of K\u003csup\u003e+\u003c/sup\u003e\u0026gt;Na\u003csup\u003e+\u003c/sup\u003e\u0026gt;Li\u003csup\u003e+\u003c/sup\u003e indicating that the formed Li-contaied complex (Eq.\u0026nbsp;6) has the highest stability among the mentioned cations (Sun et al. \u003cspan citationid=\"CR38\" class=\"CitationRef\"\u003e2022\u003c/span\u003e; Li et al. \u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e2021\u003c/span\u003e).\u003c/p\u003e \u003cp\u003e \u003cspan class=\"InlineEquation\"\u003e \u003cspan class=\"mathinline\"\u003e\\({\\text{L}\\text{i}}^{+}\\)\u003c/span\u003e \u003c/span\u003e \u003csub\u003e(aq)\u003c/sub\u003e + \u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\({\\text{F}\\text{e}\\text{C}\\text{l}}_{4}^{-}\\)\u003c/span\u003e\u003c/span\u003e\u003csub\u003e(aq)\u003c/sub\u003e + 2TBP \u003csub\u003e(org)\u003c/sub\u003e \u0026harr; \u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\({\\text{L}\\text{i}\\text{F}\\text{e}\\text{C}\\text{l}}_{4}.2\\text{T}\\text{B}\\text{P}\\)\u003c/span\u003e\u003c/span\u003e \u003csub\u003e(org)\u003c/sub\u003e (6)\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec8\" class=\"Section2\"\u003e \u003ch2\u003eEffect of chloride ion concentration on extraction efficiency\u003c/h2\u003e \u003cp\u003eIt has been found that a small fraction of FeCl\u003csub\u003en\u003c/sub\u003e\u003csup\u003e3\u0026minus;n\u003c/sup\u003e in the aqueous phase is in the form of FeCl\u003csub\u003e4\u003c/sub\u003e\u003csup\u003e\u0026minus;\u003c/sup\u003e (Wesselborg et al. \u003cspan citationid=\"CR42\" class=\"CitationRef\"\u003e2021\u003c/span\u003e). However, according to the Le Chatelier principle, the concentration of FeCl\u003csub\u003e4\u003c/sub\u003e\u003csup\u003e\u0026minus;\u003c/sup\u003e can be balanced by reaction of FeCl\u003csub\u003e3\u003c/sub\u003e and FeCl\u003csub\u003e2\u003c/sub\u003e\u003csup\u003e+\u003c/sup\u003e in the presence of adequate chloride concentration (Sun et al. \u003cspan citationid=\"CR38\" class=\"CitationRef\"\u003e2022\u003c/span\u003e). Although the excessive concentration of chloride ion does not yield more FeCl\u003csub\u003e4\u003c/sub\u003e\u003csup\u003e\u0026minus;\u003c/sup\u003e, the low chloride concentration may lead to loss in the iron content, which reduces the extraction efficiency. Therefore, selecting the suitable chloride concentration is important to optimize the process performance.\u003c/p\u003e \u003cp\u003eExperiments with different Cl\u003csup\u003e\u0026minus;\u003c/sup\u003e concentrations were performed to study the effect of chloride concentration on the extraction efficiency through measurement of FeCl\u003csub\u003e4\u003c/sub\u003e\u003csup\u003e\u0026minus;\u003c/sup\u003e concentration. Ultraviolet Visible Spectrometer (UV-VIS) analysis was used to detect the absorption intensity of the FeCl\u003csub\u003e4\u003c/sub\u003e\u003csup\u003e\u0026minus;\u003c/sup\u003e. In order to determine the maximum absorption wavelength, the organic phase containing the generated complex was scanned in the wavelength range of 300\u0026ndash;800 nm. Three characteristic peaks of FeCl\u003csub\u003e4\u003c/sub\u003e\u003csup\u003e\u0026minus;\u003c/sup\u003e were identified at 531, 619, and 684 nm (Fig. \u003cspan refid=\"MOESM1\" class=\"InternalRef\"\u003eS1\u003c/span\u003e). The peak appeared at 684 nm was selected as the representative peak because of the absence of unknown species at the wavelengths of greater than 650 nm (Lum et al. \u003cspan citationid=\"CR14\" class=\"CitationRef\"\u003e2013\u003c/span\u003e; Ji et al. \u003cspan citationid=\"CR8\" class=\"CitationRef\"\u003e2022\u003c/span\u003e; Li et al. \u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e2021\u003c/span\u003e). Figure\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e3\u003c/span\u003e shows the absorption intensities observed by UV-VIS for the feed solutions having chloride concentratons of 1, 2, and 6 M. The figure shows that the absorption intensity i.e. FeCl\u003csub\u003e4\u003c/sub\u003e\u003csup\u003e\u0026minus;\u003c/sup\u003e in the organic phase is increased by increasing the chloride concentration in the aqueous phase.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eThe higher extraction efficiencies for the feeds with higher chloride concentratin in Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e3\u003c/span\u003e also show a direct relationship of extraction efficiency with the chloride concentration as a result of formation higher FeCl\u003csub\u003e4\u003c/sub\u003e\u003csup\u003e\u0026minus;\u003c/sup\u003e species. However, excessive chloride concentration higher than 6 M does not yield higher extraction efficiencies as was explained earlier. As a result, the chloride concentration in the feed solution was fixed at 6 M in the consequent experiments.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eFigure\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e4\u003c/span\u003e represents the FT-IR peaks of organic phase before and after the solvent extraction. The figure shows that the peak related to the P\u0026thinsp;=\u0026thinsp;O functional group in the TBP structure shifts from 1280 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e to 1261 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e confirming formation of LiFeCl\u003csub\u003e4\u003c/sub\u003e.2TBP in the presence of FeCl\u003csub\u003e4\u003c/sub\u003e\u003csup\u003e\u0026minus;\u003c/sup\u003e (Su et al. \u003cspan citationid=\"CR32\" class=\"CitationRef\"\u003e2020\u003c/span\u003e).\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eThe formation of FeCl\u003csub\u003e4\u003c/sub\u003e\u003csup\u003e\u0026minus;\u003c/sup\u003e species can also be confirmed by LC-MS analysis. Figures\u0026nbsp;\u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e5\u003c/span\u003ea, b, and c represent the peaks of the organic phase detected in the LC-MS analyses after the solvent extraction with the feed solutions containing 1, 2, and 6 M chloride, respectively. Three peaks at the mass-to-charge ratios of 197, 198, and 200 in the figures are related to the FeCl\u003csub\u003e4\u003c/sub\u003e\u003csup\u003e\u0026minus;\u003c/sup\u003e species confirming its presence in the organic phase (Lavanant et al. \u003cspan citationid=\"CR19\" class=\"CitationRef\"\u003e1998\u003c/span\u003e; Hellman et al. \u003cspan citationid=\"CR6\" class=\"CitationRef\"\u003e2006\u003c/span\u003e). It is noticeable that the peak intensities in Fig.\u0026nbsp;\u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e5\u003c/span\u003ec, which is related to the extraction from the feed with 6 M chloride concentration is higher than intensities of the corresponded peaks in Figs.\u0026nbsp;\u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e5\u003c/span\u003ea and b indicating the higher concentration of FeCl\u003csub\u003e4\u003c/sub\u003e\u003csup\u003e\u0026minus;\u003c/sup\u003e in the organic phase by increasing the chloride concentration in the feed phase.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eThe findings of the preceding analyses indicate that the concentration of FeCl\u003csub\u003e4\u003c/sub\u003e\u003csup\u003e\u0026minus;\u003c/sup\u003e in the form of LiFeCl\u003csub\u003e4\u003c/sub\u003e.2TBP complex is directly related to the chloride concentration.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec9\" class=\"Section2\"\u003e \u003ch2\u003eEffect of O/A ratio on extraction efficiency and separation factor\u003c/h2\u003e \u003cp\u003eThe extraction efficiency of each metal ion from the aqueous phase and therefore their separation factors are affected by the volume ratio of organic to aqueous phase (O/A), which is related to the concentration of each reactant in formation of the metal ion complexes. Figure\u0026nbsp;\u003cspan refid=\"Fig7\" class=\"InternalRef\"\u003e6\u003c/span\u003ea shows the extraction efficiencies of each metal ion at different O/A ratio. The figure shows that lithium extraction efficiency is increased with a steep slope by increasing O/A ratio up to O/A\u0026thinsp;=\u0026thinsp;1 while the slope is a slightly lower at higher O/A ratios. The extraction efficiencies of other metal ions (Mg\u003csup\u003e2+\u003c/sup\u003e, Na\u003csup\u003e+\u003c/sup\u003e, K\u003csup\u003e+\u003c/sup\u003e) varies in a nearly constant range. Figure\u0026nbsp;\u003cspan refid=\"Fig7\" class=\"InternalRef\"\u003e6\u003c/span\u003eb shows the separation factors obtained in the experiments with different O/A ratios. It can be seen that the highest separation factors of lithium to metals are obtained at O/A\u0026thinsp;=\u0026thinsp;1.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec10\" class=\"Section2\"\u003e \u003ch2\u003eExtraction performance based on experimental design\u003c/h2\u003e \u003cp\u003eThe objective of the CCD experiments was to study the impact of major parameters such as Fe/Li ratio, HCl concentration, and TBP volume percentage on the efficiency of lithium extraction. The optimization process was carried out using DX 7 software to obtain the maximum response. It is noticeable that in all the experiments, the p-values calculated based on the results of the ANOVA table are less than 0.001. This indicates that the presented answers and results are significant and valid.\u003c/p\u003e \u003cp\u003eTable\u0026nbsp;\u003cspan refid=\"Tab1\" class=\"InternalRef\"\u003e1\u003c/span\u003e displays the parameters determined from the experimental design that yielded the best response for the lithium extraction efficiency within the specified ranges. According to the table, the maximum and minimum levels of Fe/Li molar ratio and HCl concentration should be set for optimum lithium extraction efficiency, respectively, while the TBP volume percent should be considered at its medium level. The lithium extraction efficiency obtained from the experiment with the set parameters agrees with the predicted response value.\u003c/p\u003e \u003cp\u003e \u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab1\" border=\"1\"\u003e \u003ccaption language=\"En\"\u003e \u003cdiv class=\"CaptionNumber\"\u003eTable 1\u003c/div\u003e \u003cdiv class=\"CaptionContent\"\u003e \u003cp\u003eOptimum parameters and response predicted by experimental design and obtained lithium extraction efficiency in experiment\u003c/p\u003e \u003c/div\u003e \u003c/caption\u003e \u003ccolgroup cols=\"6\"\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c4\" colnum=\"4\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c5\" colnum=\"5\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c6\" colnum=\"6\"\u003e\u003c/div\u003e \u003cthead\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c1\"\u003e \u003cp\u003eModel\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c2\"\u003e \u003cp\u003eTarget conditions\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c3\"\u003e \u003cp\u003eA: Fe/Li\u003c/p\u003e \u003cp\u003e(molar ratio)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c4\"\u003e \u003cp\u003eB: HCl\u003c/p\u003e \u003cp\u003e(M)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c5\"\u003e \u003cp\u003eTBP\u003c/p\u003e \u003cp\u003e(%)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c6\"\u003e \u003cp\u003eLithium extraction efficiency (%)\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003c/thead\u003e \u003ctbody\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003ePredicted\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\" morerows=\"1\" rowspan=\"2\"\u003e \u003cp\u003eA, B, and C: in range\u003c/p\u003e \u003cp\u003eResponse: maximum\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\" morerows=\"1\" rowspan=\"2\"\u003e \u003cp\u003e2.99\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\" morerows=\"1\" rowspan=\"2\"\u003e \u003cp\u003e0.02\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\" morerows=\"1\" rowspan=\"2\"\u003e \u003cp\u003e55.0\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e77.0\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eActual\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e76.3\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003c/tbody\u003e \u003c/colgroup\u003e \u003c/table\u003e\u003c/div\u003e \u003c/p\u003e \u003cp\u003eFigure\u0026nbsp;\u003cspan refid=\"Fig8\" class=\"InternalRef\"\u003e7\u003c/span\u003e shows the 3D response and interactions of B (acid concentration) and C (TBP volume percent) in three levels (minimum, medium, and maximum) of A (Fe/Li molar ratio\u0026thinsp;=\u0026thinsp;0.5, 1.75, and 3), respectively. The greatest range of response (lithium extraction efficiency) is observed at the minimum level of B and a wide range of C Fig.\u0026nbsp;\u003cspan refid=\"Fig8\" class=\"InternalRef\"\u003e7\u003c/span\u003ec. According to the 3D response, there are reverse trends for TBP v% in the organic phase at low and high acid concentrations. Specifically, increasing the TBP v% at low acid concentration enhances the lithium extraction efficiency, whereas it decreases the extraction efficiency at higher acid concentrations. This trend can be attributed to the competition of H\u003csup\u003e+\u003c/sup\u003e and Li\u003csup\u003e+\u003c/sup\u003e to form the complex with TBP.\u003c/p\u003e \u003cp\u003eFigures\u0026nbsp;\u003cspan refid=\"Fig8\" class=\"InternalRef\"\u003e7\u003c/span\u003ed-f display the correlation between B and C at the minimum, average, and maximum levels of the Fe/Li molar ratio. The point where the \u0026ldquo;Min\u0026rdquo; and \u0026ldquo;Max\u0026rdquo; curves intersect in each figure confirms the relationship between the two variables of B and C across all three levels of A.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eFigure\u0026nbsp;\u003cspan refid=\"Fig9\" class=\"InternalRef\"\u003e8\u003c/span\u003e shows that although the lithium extraction is in the range of 62\u0026ndash;76% for the Fe/Li molar ratio of 0.5 to 3, the separation factors of Li/Mg is increased sharply. Meanwhile, the separation factors of Li/Na and Li/K are varied insignificantly due to lower affinities of these co-ions for complex formation. The figure shows that the highest Li/Mg separation factor is obtained at about Fe/Li molar ratio\u0026thinsp;=\u0026thinsp;3.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eFigure\u0026nbsp;\u003cspan refid=\"Fig10\" class=\"InternalRef\"\u003e9\u003c/span\u003e displays the 3D response and interactions between two variables, A (Fe/Li molar ratio) and C (TBP v%), on the lithium extraction efficiency at three levels of variable B (acid concentration\u0026thinsp;=\u0026thinsp;0, 0.25, and 0.50 M). The highest response levels are observed at low acid concentrations and a wide range of A and C parameters (Fig.\u0026nbsp;\u003cspan refid=\"Fig10\" class=\"InternalRef\"\u003e9\u003c/span\u003e(a)). However, the lithium extraction efficiencies are significantly reduced at medium and maximum HCl concentrations (shown in Figs.\u0026nbsp;\u003cspan refid=\"Fig10\" class=\"InternalRef\"\u003e9\u003c/span\u003eb and c) due to the competition between H\u003csup\u003e+\u003c/sup\u003e and Li\u003csup\u003e+\u003c/sup\u003e in the complex formation.\u003c/p\u003e \u003cp\u003eTo further study the interactions between variables A and C, Figs.\u0026nbsp;\u003cspan refid=\"Fig10\" class=\"InternalRef\"\u003e9\u003c/span\u003ed-f represent the lithium extraction efficiency at the minimum, average, and maximum levels of variable B. The intersection of the \"Min\" and \"Max\" curves in Fig.\u0026nbsp;\u003cspan refid=\"Fig10\" class=\"InternalRef\"\u003e9\u003c/span\u003ee confirms the interaction of A and C within the range of parameters that need to be optimized.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eAs it was found that solvent extraction in the lower acid concentration yields a better performance for lithium extraction, to have a precise examination, the experiments were performed at low acid concentrations (0.02, 0.05, and 0.1 M). Figure\u0026nbsp;\u003cspan refid=\"Fig11\" class=\"InternalRef\"\u003e10\u003c/span\u003e shows the lithium extraction efficiencies and the Li/co-ion separation factors. As seen in the figure, the lithium extraction efficiency is slightly decreased by increasing the acid concentration. Meanwhile, the Li/co-ion separation factors remain nearly constant.\u003c/p\u003e \u003cp\u003eHigher acid concentrations increase the competition between Li\u003csup\u003e+\u003c/sup\u003e and H\u003csup\u003e+\u003c/sup\u003e, resulting in less lithium extraction and a lower Li/Mg separation factor at the constant magnesium concentration.\u003c/p\u003e \u003cp\u003eIt should be noted that during extraction, the presence of a controlled amount of HCl in the aqueous phase is required to avoid iron hydrolysis. The H\u003csup\u003e+\u003c/sup\u003e and Li\u003csup\u003e+\u003c/sup\u003e equilibrium constants are determined by the following equations (Li et al. \u003cspan citationid=\"CR16\" class=\"CitationRef\"\u003e2019\u003c/span\u003e):\u003cdiv id=\"Equ3\" class=\"Equation\"\u003e\u003cdiv format=\"TEX\" class=\"mathdisplay\" id=\"FileID_Equ3\" name=\"EquationSource\"\u003e\n$$K\\text{H}=\\frac{{[{\\text{H}\\text{F}\\text{e}\\text{C}\\text{l}}_{4} .2\\text{T}\\text{B}\\text{P}]}_{\\left(\\text{o}\\text{r}\\text{g}\\right)}}{{{{{[\\text{H}}^{+}]}_{\\left(\\text{a}\\text{q}\\right)}[\\text{F}\\text{e}}^{3+}]}_{\\left(\\text{a}\\text{q}\\right)}{[{{\\text{C}\\text{l}}^{-}]}^{4}}_{\\left(\\text{a}\\text{q}\\right)}{{\\left[\\text{T}\\text{B}\\text{P}\\right]}^{2}}_{\\left(\\text{o}\\text{r}\\text{g}\\right)}}= \\frac{{\\text{D}}_{\\text{H}}}{{{[\\text{F}\\text{e}}^{3+}]}_{\\left(\\text{a}\\text{q}\\right)}{[{{\\text{C}\\text{l}}^{-}]}^{4}}_{\\left(\\text{a}\\text{q}\\right)}{{\\left[\\text{T}\\text{B}\\text{P}\\right]}^{2}}_{\\left(\\text{o}\\text{r}\\text{g}\\right)}}$$\u003c/div\u003e\u003cdiv class=\"EquationNumber\"\u003e7\u003c/div\u003e\u003c/div\u003e\u003cdiv id=\"Equ4\" class=\"Equation\"\u003e\u003cdiv format=\"TEX\" class=\"mathdisplay\" id=\"FileID_Equ4\" name=\"EquationSource\"\u003e\n$$K\\text{L}\\text{i}=\\frac{{[{\\text{L}\\text{i}\\text{F}\\text{e}\\text{C}\\text{l}}_{4} .2\\text{T}\\text{B}\\text{P}]}_{\\left(\\text{o}\\text{r}\\text{g}\\right)}}{{{{{[\\text{L}\\text{i}}^{+}]}_{\\left(\\text{a}\\text{q}\\right)}[\\text{F}\\text{e}}^{3+}]}_{\\left(\\text{a}\\text{q}\\right)}{[{{\\text{C}\\text{l}}^{-}]}^{4}}_{\\left(\\text{a}\\text{q}\\right)}{{\\left[\\text{T}\\text{B}\\text{P}\\right]}^{2}}_{\\left(\\text{o}\\text{r}\\text{g}\\right)}}= \\frac{{D}_{\\text{L}\\text{i}}}{{{[\\text{F}\\text{e}}^{3+}]}_{\\left(\\text{a}\\text{q}\\right)}{[{{\\text{C}\\text{l}}^{-}]}^{4}}_{\\left(\\text{a}\\text{q}\\right)}{{\\left[\\text{T}\\text{B}\\text{P}\\right]}^{2}}_{\\left(\\text{o}\\text{r}\\text{g}\\right)}}$$\u003c/div\u003e\u003cdiv class=\"EquationNumber\"\u003e8\u003c/div\u003e\u003c/div\u003e\u003c/p\u003e \u003cp\u003eThe reported values of equilibrium constants in certain conditions reveal that H\u003csup\u003e+\u003c/sup\u003e has a more tendency to form complex with TBP than lithium (\u003cem\u003eK\u003c/em\u003e\u003csub\u003eH\u003c/sub\u003e \u0026gt; 6 \u003cem\u003eK\u003c/em\u003e\u003csub\u003eLi\u003c/sub\u003e) (Su et al. \u003cspan citationid=\"CR32\" class=\"CitationRef\"\u003e2020\u003c/span\u003e). This fact highlights the impact of H\u003csup\u003e+\u003c/sup\u003e concentration in the aqueous phase on the extraction performance.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eThe higher sensitivity of response value to the variation in the acid concentration can be confirmed also by observing the perturbation diagram in Fig. \u003cspan refid=\"MOESM2\" class=\"InternalRef\"\u003eS2\u003c/span\u003e that represents a significant shift in the response slope by alterating the acid concentration (B).\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eFigure\u0026nbsp;\u003cspan refid=\"Fig14\" class=\"InternalRef\"\u003e11\u003c/span\u003e shows the 3D response and interactions of A (Fe/Li molar ratio) and B (acid concentration) in three levels (minimum, medium, and maximum) of C (TBP v%=10, 50, and 90), respectively. According to Eq.\u0026nbsp;(6), as the TBP concentration increases, the forward reaction succeeds and results in higher lithium extraction efficiencies.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eFigures\u0026nbsp;\u003cspan refid=\"Fig14\" class=\"InternalRef\"\u003e11\u003c/span\u003ed-f depict the impact of the interaction between A and B on the lithium extraction efficiency, at the minimum, medium, and maximum levels of TBP v% (C). It is observed in Fig.\u0026nbsp;\u003cspan refid=\"Fig14\" class=\"InternalRef\"\u003e11\u003c/span\u003ed that the intersection of A and B occurs in the Min level of TBP v% within the designated range. The 3D response confirms high lithium extraction efficiencies for high and medium TBP volume percents (Figs.\u0026nbsp;\u003cspan refid=\"Fig14\" class=\"InternalRef\"\u003e11\u003c/span\u003eb and c). Moreover, high levels of lithium extraction efficiency are obtained even at low TBP v% for the Fe/Li molar ratio of 1.7-3 (Fig.\u0026nbsp;\u003cspan refid=\"Fig14\" class=\"InternalRef\"\u003e11\u003c/span\u003ea).\u003c/p\u003e \u003cp\u003eHowever, as seen in Fig.\u0026nbsp;\u003cspan refid=\"Fig16\" class=\"InternalRef\"\u003e12\u003c/span\u003e, a third organic phase is formed beween the aqueous and the main organic phase at the low level of TBP v% (up to about 40 v%) leading to loss in a part of organic phase. The formation of this third phase, which has been also observed in previous studies (Li et al. \u003cspan citationid=\"CR21\" class=\"CitationRef\"\u003e2022\u003c/span\u003e), is attributed to the low solubility of produced complex in kerosene in the presence of low concentration of free TBP (Zhou et al. \u003cspan citationid=\"CR48\" class=\"CitationRef\"\u003e2012\u003c/span\u003e).\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eAs shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig17\" class=\"InternalRef\"\u003e13\u003c/span\u003e, increasing TBP v% up to 60% significantly increases the lithium extraction efficiency. The slope of increment in the lithium exration efficiency at higher TBP v% is decreased. In presence of excess TBP, the co-ions (in particular magnesium) can take part in complexation reaction with TBP in the organic phase leading to decrease in the separation factors, \u003cem\u003eβ\u003c/em\u003e\u003csub\u003eLi/co\u0026minus;ions\u003c/sub\u003e.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec11\" class=\"Section2\"\u003e \u003ch2\u003eStripping and regeneration\u003c/h2\u003e \u003cp\u003eThe lithium recovery from the organic phase can be performed by regenerating the extracting organic phase through stripping and saponification steps. Figure\u0026nbsp;\u003cspan refid=\"Fig18\" class=\"InternalRef\"\u003e14\u003c/span\u003e shows a schematic diagram of the whole process consisting extraction, stripping, and saponification steps.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eIn order to evaluate the effect of acid concentration in the stripping step of regeneration process, stripping tests were performed using HCl with different concentrations and NaCl 5M with O/A\u0026thinsp;=\u0026thinsp;7:1. The results in Table\u0026nbsp;\u003cspan refid=\"Tab2\" class=\"InternalRef\"\u003e2\u003c/span\u003e show that as the HCl concentration increases up to 0.3 M, the lithium and magnesium stripping efficiencies are increased. Higher acid concentrations may cause some troubles in the next saponification process (Shi et al. \u003cspan citationid=\"CR36\" class=\"CitationRef\"\u003e2019\u003c/span\u003e).\u003c/p\u003e \u003cp\u003eThe saponification is performed using fresh NaOH 0.05 M and NaCl 5 M solutions. By performing three subsquenet runs, 73% of the remaining lithium in the stripped organic phase is transferred to the saponificating aqueous phase. It should be noted that a negligible amount of iron loss (about 1%) was detected in the effeluent aqueous phases during stripping and saponification steps so that only a fine adjustment of iron may be required for the recycled organic phase.\u003c/p\u003e \u003cp\u003e \u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab2\" border=\"1\"\u003e \u003ccaption language=\"En\"\u003e \u003cdiv class=\"CaptionNumber\"\u003eTable 2\u003c/div\u003e \u003cdiv class=\"CaptionContent\"\u003e \u003cp\u003eLithium and magnesium stripping efficiencies in the stripping processes by different acid concentrations\u003c/p\u003e \u003c/div\u003e \u003c/caption\u003e \u003ccolgroup cols=\"3\"\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\u003e\u003c/div\u003e \u003cthead\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c1\"\u003e \u003cp\u003eHCl conc. (mol/l)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c2\"\u003e \u003cp\u003eLi stripping (%)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c3\"\u003e \u003cp\u003eMg stripping (%)\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003c/thead\u003e \u003ctbody\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e0.07\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e36.0\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e21.0\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e0.15\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e64.0\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e43.0\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e0.30\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e81.6\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e60.5\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003c/tbody\u003e \u003c/colgroup\u003e \u003c/table\u003e\u003c/div\u003e \u003c/p\u003e \u003c/div\u003e"},{"header":"Conclusion","content":"\u003cp\u003eSolvent extraction of a brine feed with high Mg/Li ratio was performed using TBP and FeCl\u003csub\u003e3\u003c/sub\u003e as the extractant and co-extractant, respectively.\u003c/p\u003e \u003cp\u003eThe UV-VIS and LC-MS analyses confirmed that a chloride concentration of 6 M is vital to produce adequate FeCl\u003csub\u003e4\u003c/sub\u003e\u003csup\u003e\u0026minus;\u003c/sup\u003e concentration for taking part in formation\u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\)\u003c/span\u003e\u003c/span\u003eof the complex [LiFeCl\u003csub\u003e4\u003c/sub\u003e.2TBP]. The FT-IR analysis also verified the formation of the complex by detecting the shift in the TBP representative peak.\u003c/p\u003e \u003cp\u003eThe Fe/Li molar ratio, acid concentration in the feed, and TBP volume percent in the organic phase were seleceted as the main parameters affecting the lithium solvent extraction. The central composite design (CCD) method was used to assess the effect of main parameters as well as their interactions on the lithium extraction efficiencies. By setting the organic to aqueous volume ratio (O/A\u0026thinsp;=\u0026thinsp;1), the optimal conditions in a single-stage extraction were determined as Fe/Li molar ratios of 2.99, HCl concentrations of 0.02 M, and TBP volume percent of 55% to yield the highest lithium extraction efficiency (77.0%) as it was confirmed by the experiment (76.3%).\u003c/p\u003e \u003cp\u003eThe results showed that in the whole defined range of Fe/Li molar ratio, the other two major parameters of HCl concentration and TBP v% have interactions in their selected ranges. Meanwhile, the interactions of the other two parameters were observed merely in the medium HCl concentration level and the minimum TBP v% level which are of less importance because of low lithium extraction efficiencies and appearance of a third phase, respectively.\u003c/p\u003e \u003cp\u003eWhile the results of experimental design revealed that the HCl concentration has the most influential effect on the lithium extraction efficiency in the selected range, the complentary experiments with the suggested parameters showed that TBP concentration in the organic phase has the most influential effect on the Li/Mg separation factor whereas its value at the optimum conditions were determined as 304.\u003c/p\u003e \u003cp\u003eAbout 81% of extracted lithium could be recoverd from the organic phase by applying a stripping solution with 0.3 M HCl and phase ratio of 7:1 through a single-stage stripping process. The Mg/Li mass ratio of 192 in the feed could be reduced to 1.5 in the stripping solution.\u003c/p\u003e"},{"header":"NOMENCLATURE","content":"\u003cp style='margin:0in;text-align:justify;text-indent:0in;line-height:200%;font-size:16px;font-family:\"Times New Roman\",serif;color:black;'\u003e\u003cspan style=\"line-height:200%;color:#1C1917;background:white;\"\u003eTBP \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; Tributyl phosphate\u003c/span\u003e\u003c/p\u003e\n\u003cp style='margin:0in;text-align:justify;text-indent:0in;line-height:200%;font-size:16px;font-family:\"Times New Roman\",serif;color:black;'\u003e\u003cspan style=\"color:windowtext;\"\u003eTOPO \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp;Trioctyl phosphine oxide\u0026nbsp;\u003c/span\u003e\u003c/p\u003e\n\u003cp style='margin:0in;text-align:justify;text-indent:0in;line-height:200%;font-size:16px;font-family:\"Times New Roman\",serif;color:black;'\u003e\u003cspan style=\"color:windowtext;\"\u003eHTTA \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; 4, 4, 4-trifluoro-1-(2-thienyl)butane-1,3-dione\u003c/span\u003e\u003c/p\u003e\n\u003cp style='margin:0in;text-align:justify;text-indent:0in;line-height:200%;font-size:16px;font-family:\"Times New Roman\",serif;color:black;'\u003e\u003cspan style=\"line-height:200%;color:windowtext;\"\u003eCyanex923 \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp;\u0026nbsp;\u003c/span\u003e\u003cspan style=\"color:windowtext;\"\u003eTrialkyl phosphine oxide\u0026nbsp;\u003c/span\u003e\u003c/p\u003e\n\u003cp style='margin:0in;text-align:justify;text-indent:0in;line-height:200%;font-size:16px;font-family:\"Times New Roman\",serif;color:black;'\u003e\u003cspan style=\"line-height:200%;color:windowtext;\"\u003eLIX54 \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp;\u0026nbsp;\u003c/span\u003e\u003cspan style='font-family:\"Georgia\",serif;color:windowtext;'\u003eA \u0026beta;-diketone derivative\u003c/span\u003e\u003c/p\u003e\n\u003cp style='margin:0in;text-align:justify;text-indent:0in;line-height:200%;font-size:16px;font-family:\"Times New Roman\",serif;color:black;'\u003e\u003cspan style=\"line-height:200%;color:windowtext;\"\u003e[OHEMIM][NTf2] Hydroxyl 1-hydroxyethyl-3-methyl imidazolium \u0026nbsp;bis(trifluoromethylsulfonyl)imide\u0026nbsp;\u003c/span\u003e\u003c/p\u003e\n\u003cp style='margin:0in;text-align:justify;text-indent:0in;line-height:200%;font-size:16px;font-family:\"Times New Roman\",serif;color:black;'\u003e\u003cspan style=\"color:windowtext;\"\u003eRSM \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; Response surface methodology\u0026nbsp;\u003c/span\u003e\u003c/p\u003e\n\u003cp style='margin:0in;text-align:justify;text-indent:0in;line-height:200%;font-size:16px;font-family:\"Times New Roman\",serif;color:black;'\u003eCCD \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp;Central composite design method\u003c/p\u003e\n\u003cp style='margin:0in;text-align:justify;text-indent:0in;line-height:200%;font-size:16px;font-family:\"Times New Roman\",serif;color:black;'\u003e\u003cem\u003e\u003cspan style=\"line-height:200%;\"\u003e\u0026nbsp;E\u003c/span\u003e\u003c/em\u003e\u003csub\u003e\u003cspan style=\"line-height:200%;\"\u003eM\u003c/span\u003e\u003c/sub\u003e\u003cspan style=\"line-height:200%;\"\u003e\u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; Extraction efficiency of each ion [%]\u003c/span\u003e\u003c/p\u003e\n\u003cp style='margin:0in;text-align:justify;text-indent:0in;line-height:200%;font-size:16px;font-family:\"Times New Roman\",serif;color:black;'\u003e\u003cem\u003e\u003cspan style=\"color:black;background:white;\"\u003eC\u003c/span\u003e\u003c/em\u003e\u003csub\u003e\u003cspan style=\"color:black;background:white;\"\u003eM0\u003c/span\u003e\u003c/sub\u003e\u003cspan style=\"color:black;background:white;\"\u003e\u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp;Initial concentrations of each co-ion [mg/l]\u003c/span\u003e\u003c/p\u003e\n\u003cp style='margin:0in;text-align:justify;text-indent:0in;line-height:200%;font-size:16px;font-family:\"Times New Roman\",serif;color:black;'\u003e\u003cem\u003e\u003cspan style=\"color:black;background:white;\"\u003eC\u003c/span\u003e\u003c/em\u003e\u003csub\u003e\u003cspan style=\"color:black;background:white;\"\u003eM\u003c/span\u003e\u003c/sub\u003e\u003cspan style=\"color:black;background:white;\"\u003e\u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; Equilibrium concentrations of each co-ion [mg/l]\u003c/span\u003e\u003c/p\u003e\n\u003cp style='margin:0in;text-align:justify;text-indent:0in;line-height:200%;font-size:16px;font-family:\"Times New Roman\",serif;color:black;'\u003e\u003cem\u003e\u003cspan style=\"color:black;background:white;\"\u003eD\u003c/span\u003e\u003c/em\u003e\u003csub\u003e\u003cspan style=\"color:black;background:white;\"\u003eM\u003c/span\u003e\u003c/sub\u003e\u003cspan style=\"color:black;background:white;\"\u003e\u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; Distribution ratio of co-ions [-]\u003c/span\u003e\u003c/p\u003e\n\u003cp style='margin:0in;text-align:justify;text-indent:0in;line-height:200%;font-size:16px;font-family:\"Times New Roman\",serif;color:black;'\u003e\u003cem\u003e\u003cspan style=\"color:black;background:white;\"\u003eV\u003c/span\u003e\u003c/em\u003e\u003csub\u003e\u003cspan style=\"color:black;background:white;\"\u003eaq \u0026nbsp;\u003c/span\u003e\u003c/sub\u003e\u003cspan style=\"color:black;background:white;\"\u003e\u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; Volume of the aqueous phase [ml]\u003c/span\u003e\u003c/p\u003e\n\u003cp style='margin:0in;text-align:justify;text-indent:0in;line-height:200%;font-size:16px;font-family:\"Times New Roman\",serif;color:black;'\u003e\u003cem\u003e\u003cspan style=\"color:black;background:white;\"\u003eV\u003c/span\u003e\u003c/em\u003e\u003csub\u003e\u003cspan style=\"color:black;background:white;\"\u003eorg\u003c/span\u003e\u003c/sub\u003e\u003cspan style=\"color:black;background:white;\"\u003e\u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; Volume of the organic phases [ml]\u003c/span\u003e\u003c/p\u003e\n\u003cp style='margin:0in;text-align:justify;text-indent:0in;line-height:200%;font-size:16px;font-family:\"Times New Roman\",serif;color:black;'\u003e\u003cimg src=\"data:image/png;base64,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\" width=\"39\" height=\"36\"\u003e\u003cspan style=\"color:black;background:white;\"\u003e\u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; Stripping efficiency [%]\u003c/span\u003e\u003c/p\u003e\n\u003cp style='margin:0in;text-align:justify;text-indent:0in;line-height:200%;font-size:16px;font-family:\"Times New Roman\",serif;color:black;'\u003e\u003cimg src=\"data:image/png;base64,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\" width=\"47\" height=\"35\"\u003e\u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; Initial concentrations of metal ion in the organic phase [mg/l]\u003c/p\u003e\n\u003cp style='margin:0in;text-align:justify;text-indent:0in;line-height:200%;font-size:16px;font-family:\"Times New Roman\",serif;color:black;'\u003e\u003cimg src=\"data:image/png;base64,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\" width=\"36\" height=\"32\"\u003e\u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp;Equilibrium concentrations of metal ion in the organic phase [mg/l]\u003c/p\u003e\n\u003cp style='margin:0in;text-align:justify;text-indent:0in;line-height:200%;font-size:16px;font-family:\"Times New Roman\",serif;color:black;'\u003e\u003cspan style=\"line-height:200%;\"\u003ev% \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp;Volume percent [%]\u003c/span\u003e\u003c/p\u003e\n\u003cp style='margin:0in;text-align:justify;text-indent:0in;line-height:200%;font-size:16px;font-family:\"Times New Roman\",serif;color:black;'\u003e\u003cem\u003e\u003cspan style=\"line-height:200%;color:windowtext;\"\u003eK\u003c/span\u003e\u003c/em\u003e\u003csub\u003e\u003cspan style=\"line-height:200%;color:windowtext;\"\u003eH\u003c/span\u003e\u003c/sub\u003e\u003cspan style=\"line-height:200%;color:windowtext;\"\u003e\u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp;Equilibrium constant of hydrogen [-]\u003c/span\u003e\u003c/p\u003e\n\u003cp style='margin:0in;text-align:justify;text-indent:0in;line-height:200%;font-size:16px;font-family:\"Times New Roman\",serif;color:black;'\u003e\u003cem\u003e\u003cspan style=\"line-height:200%;color:windowtext;\"\u003eK\u003c/span\u003e\u003c/em\u003e\u003csub\u003e\u003cspan style=\"line-height:200%;color:windowtext;\"\u003eLi \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp;\u003c/span\u003e\u003c/sub\u003e\u003cspan style=\"line-height:200%;color:windowtext;\"\u003eEquilibrium constant of lithium [-]\u003c/span\u003e\u003c/p\u003e\n\u003cp style='margin:0in;text-align:justify;text-indent:0in;line-height:200%;font-size:16px;font-family:\"Times New Roman\",serif;color:black;'\u003e\u003cspan style=\"line-height:200%;color:windowtext;\"\u003eO/A \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp;Organic phase to\u0026nbsp;\u003c/span\u003e\u003cspan style=\"color:black;background:white;\"\u003eaqueous\u003c/span\u003e\u003cspan style=\"line-height:200%;color:windowtext;\"\u003e\u0026nbsp;phase volume ratio [-]\u003c/span\u003e\u003c/p\u003e\n\u003cp style='margin:0in;text-align:justify;text-indent:0in;line-height:200%;font-size:16px;font-family:\"Times New Roman\",serif;color:black;'\u003e\u003cem\u003e\u003cspan style=\"color:black;background:white;\"\u003e\u0026beta;\u003c/span\u003e\u003c/em\u003e\u003cspan style=\"color:black;background:white;\"\u003e\u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; Li/M\u0026rdquo; separation factor [-]\u003c/span\u003e\u003c/p\u003e"},{"header":"Declarations","content":"\u003cp\u003e\u003cstrong\u003eEthical Approval\u0026nbsp;\u003c/strong\u003eNot applicable\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eConsent to Participate\u003c/strong\u003e Not applicable\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eConsent to Publish\u003c/strong\u003e Not applicable\u003c/p\u003e\n\u003cp\u003e\u003cem\u003e\u003cstrong\u003eAuthor Contributions\u003c/strong\u003e All authors contributed to the study conception and design. Material preparation, data collection and analysis were performed by Anahita Kazemi Kia. The first draft of the manuscript was written by Anahita Kazemi Kia and the corresponding authors edited the draft and commented on previous versions of the manuscript. All authors read and approved the final manuscript.\u003c/em\u003e\u003c/p\u003e\n\u003cp\u003e\u003cem\u003e\u003cstrong\u003eFunding\u003c/strong\u003e\u003c/em\u003e\u003cem\u003e\u0026nbsp;The authors declare that no funds, grants, or other support were received during the preparation of this manuscript.\u003c/em\u003e\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eCompeting interests\u003c/strong\u003e \u003cem\u003eThe authors have no relevant financial or non-financial interests to disclose.\u003c/em\u003e\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\n\u003cli\u003eBale MD and May AV (1989) Processing of ores to produce tantalum and lithium. Miner Eng 2:299\u0026ndash;320. https://doi.org/10.1016/0892-6875(89)90001-0\u003c/li\u003e\n\u003cli\u003eDiouf B and Pode R (2015) Potential of lithium-ion batteries in renewable energy. Renew. Energy 76:375\u0026ndash;380. https://doi.org/10.1016/j.renene.2014.11.058\u003c/li\u003e\n\u003cli\u003eGolmohammadzadeh R, Faraji F, and Rashchi F (2018) Recovery of lithium and cobalt from spent lithium ion batteries (LIBs) using organic acids as leaching reagents: A review. Resour Conserv Recycl 136:418\u0026ndash;435. https://doi.org/10.1016/j.resconrec.2018.04.024\u003c/li\u003e\n\u003cli\u003eHatfield-Dodds S\u003cem\u003e,\u003c/em\u003e Schandl H, Newth D, Obersteiner M, Cai Y, Baynes T, West J, Havlik P (2017) Assessing global resource use and greenhouse emissions to 2050, with ambitious resource efficiency and climate mitigation policies. J Clean Prod 144:403\u0026ndash;414. https://doi.org/10.1016/j.jclepro.2016.12.170\u003c/li\u003e\n\u003cli\u003eHano T, Matsumoto M, Ohtake T, Egashira N, and Hori F (1992) Recovery of lithium from geothermal water by solvent extraction technique. Solvent Extr Ion Exch 10:195\u0026ndash;206. https://doi.org/10.1080/07366299208918100\u003c/li\u003e\n\u003cli\u003eHellman H, Laitinen RS, Kaila L, Jalonen J, Hietapelto V, Jokela J, Sarpola A, Ramo J (2006) Identification of hydrolysis products of FeCl\u003csub\u003e3\u003c/sub\u003e\u0026middot;6H\u003csub\u003e2\u003c/sub\u003eO by ESI-MS. J mass Spectrom\u003cem\u003e \u003c/em\u003e41:1421\u0026ndash;1429. https://doi.org/10.1002/jms.1107\u003c/li\u003e\n\u003cli\u003eJi ZY, Chen QB, Yuan JS, Liu J, Zhao YY, and Feng WX (2017) Preliminary study on recovering lithium from high Mg\u003csup\u003e2+\u003c/sup\u003e/Li\u003csup\u003e+\u003c/sup\u003e ratio brines by electrodialysis. 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Desalination 496:114710. https://doi.org/10.1016/j.desal.2020.114710\u003c/li\u003e\n\u003c/ol\u003e"}],"fulltextSource":"","fullText":"","funders":[],"hasAdminPriorityOnWorkflow":false,"hasManuscriptDocX":true,"hasOptedInToPreprint":true,"hasPassedJournalQc":"","hasAnyPriority":false,"hideJournal":false,"highlight":"","institution":"","isAcceptedByJournal":true,"isAuthorSuppliedPdf":false,"isDeskRejected":"","isHiddenFromSearch":false,"isInQc":false,"isInWorkflow":false,"isPdf":false,"isPdfUpToDate":true,"isWithdrawnOrRetracted":false,"journal":{"display":true,"email":"[email protected]","identity":"environmental-science-and-pollution-research","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"espr","sideBox":"Learn more about [Environmental Science and Pollution Research](https://www.springer.com/journal/11356)","snPcode":"11356","submissionUrl":"https://submission.nature.com/new-submission/11356/3","title":"Environmental Science and Pollution Research","twitterHandle":"","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"em","reportingPortfolio":"Springer Hybrid","inReviewEnabled":true,"inReviewRevisionsEnabled":false},"keywords":"Solvent extraction, Magneseum rich brine, Lithium extraction efficiency, Separation factor, Experimental design","lastPublishedDoi":"10.21203/rs.3.rs-4265065/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-4265065/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"Solvent extraction of lithium from brine with a high Mg/Li ratio was investigated. Tributyl phosphate (TBP), ferric chloride (FeCl3), and kerosene were used as the extractant, co-extractant, and diluent, respectively. The mechanism of extraction process was studied by LC-MS, UV-VIS, and FT-IR analyses. Effects of organic to aqueous phase volume ratio (O/A) on the extraction efficiency and separation factor were optimized. The effects of major parameters including Fe/Li molar ratio, hydrochloric acid concentration, and TBP volume percent as well as their interactions on the lithium extraction efficiency were evaluated using central composite design. These major parameters represent interactions within their selected ranges. While the lithium extraction efficiency as the resposense value in the experimental design showed the most sensivity to the acid concentration, the separation factors were more affected by alteration in the TBP volume percent with the fixed optimum values of the other major parameters. The highest one-stage extraction efficiency of 76.3% and Li/Mg separation factor of 304 were obtained at the optimum conditions of Fe/Li= 2.99, HCl=0.01 M, and TBP= 55%. The Mg/Li mass ratio could be significantly reduced from 192 in the feed to 1.5 in the stripping solution. Based on the findings, a schematic diagram of the process including extraction, stripping, and saponification steps was proposed.","manuscriptTitle":"Solvent extraction of lithium from brines with high magnesium/lithium ratios; Investigation on parameter interactions","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2024-06-04 06:24:18","doi":"10.21203/rs.3.rs-4265065/v1","editorialEvents":[{"type":"communityComments","content":0},{"type":"decision","content":"Major Revision","date":"2024-06-21T11:02:10+00:00","index":"","fulltext":""},{"type":"reviewerAgreed","content":"","date":"2024-05-22T12:11:05+00:00","index":0,"fulltext":""},{"type":"reviewersInvited","content":"","date":"2024-05-22T09:30:34+00:00","index":"","fulltext":""},{"type":"editorInvited","content":"Environmental Science and Pollution Research","date":"2024-05-16T17:08:38+00:00","index":"","fulltext":""},{"type":"editorAssigned","content":"","date":"2024-04-18T05:10:26+00:00","index":"","fulltext":""},{"type":"submitted","content":"Environmental Science and Pollution Research","date":"2024-04-16T09:06:28+00:00","index":"","fulltext":""}],"status":"published","journal":{"display":true,"email":"[email protected]","identity":"environmental-science-and-pollution-research","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"espr","sideBox":"Learn more about [Environmental Science and Pollution Research](https://www.springer.com/journal/11356)","snPcode":"11356","submissionUrl":"https://submission.nature.com/new-submission/11356/3","title":"Environmental Science and Pollution Research","twitterHandle":"","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"em","reportingPortfolio":"Springer Hybrid","inReviewEnabled":true,"inReviewRevisionsEnabled":false}}],"origin":"","ownerIdentity":"e06a0fea-bf88-4760-b085-7d4e2a82acd5","owner":[],"postedDate":"June 4th, 2024","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"published-in-journal","subjectAreas":[],"tags":[],"updatedAt":"2024-08-22T19:39:13+00:00","versionOfRecord":{"articleIdentity":"rs-4265065","link":"https://doi.org/10.1007/s11356-024-34617-8","journal":{"identity":"environmental-science-and-pollution-research","isVorOnly":false,"title":"Environmental Science and Pollution Research"},"publishedOn":"2024-08-17 15:57:44","publishedOnDateReadable":"August 17th, 2024"},"versionCreatedAt":"2024-06-04 06:24:18","video":"","vorDoi":"10.1007/s11356-024-34617-8","vorDoiUrl":"https://doi.org/10.1007/s11356-024-34617-8","workflowStages":[]},"version":"v1","identity":"rs-4265065","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-4265065","identity":"rs-4265065","version":["v1"]},"buildId":"qtupq5eGEP_6zYnWcrvyt","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}