Recycle of lead-zinc tailings in blended cement: mechanical property and stabilization/solidification of heavy metals

Recycle of lead-zinc tailings in blended cement: mechanical property and stabilization/solidification of heavy metals | 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 Recycle of lead-zinc tailings in blended cement: mechanical property and stabilization/solidification of heavy metals Zhongtao Luo, Changbo Tang, Yuandong Mu, Xiaohai Liu This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-1571072/v1 This work is licensed under a CC BY 4.0 License Status: Posted Version 1 posted You are reading this latest preprint version Abstract Due to the increasing output and toxicity of heavy metals, the pollution problems of lead-zinc tailings (LZTs) need to be solved urgently. This paper investigated the properties and heavy metal stabilization/solidification of blended cement containing different replacement ratios of ground LZTs. The compressive strength, hydration products, chemically bound water content and microstructure of specimens were analyzed by XRD, FTIR, TG-DSC and SEM tests. The results showed that the addition of LZTs reduced the compressive strength of blended cement. 10% cement replacement by LZTs can be considered as the optimum for blended cement uses. With the increase of LZTs dosage, Ca(OH) 2 content was significantly reduced and the formation of ettringite was promoted. Leaching tests revealed that the leaching concentration of Pb and Zn was much lower than threshold limit. EDS analysis indicated that hydration products (primarily C-S-H gel) played an important role in the stabilization/solidification of heavy metals by means of physical adsorption and encapsulation. This research provides a guidance for the resource utilization of LZTs. lead-zinc tailings blended cement mechanical property stabilization/solidification heavy metal leaching concentration Figures Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 Figure 6 Figure 7 Figure 8 Figure 9 1. Introduction With the development of global industrialization, mining industry has produced a large number of solid wastes such as tailings, which brought a series of environmental pollution and safety problems (Behera et al. 2020 , Liu et al. 2018a ). Tailings are by-products from ore processing (Wang et al. 2017 ). In China, lead-zinc tailings (LZTs) are defined as hazardous solid wastes because of the high-content heavy metals, and the output increase rapidly in recent years. The hazards of LZTs are multiple (Onuaguluchi &Eren 2012 , Yao et al. 2019 ). First of all, the tailing dams are prone to collapse which cause a series of disasters. LZTs from collapsed dams can cover vegetation, clog rivers and, in severe cases, rush into residential areas, causing significant loss of lives (Ince 2019 ). And then, the open-air LZTs often occupy a large area of land, which is not good for the increasingly tense land resources (Han et al. 2017 ). These LZTs usually contain a large amount of heavy metal ions, which are harmful to nearby plants and groundwater (Tao et al. 2019 ). Researchers have proposed many treatment methods to solve the pollution of tailings (Qiu et al. 2020 , Saedi et al. 2020 ). The cement paste backfill (CPB) technology can consume a lot of tailings and avoid the collapse of mines after mining (Qi &Fourie 2019 ). S.K. Behera et al. investigated the use of paste backfill technology in lead-zinc underground mines. The results showed that 5%-8% replacement with cement could meet the required uniaxial compressive strength of 1.1MPa after curing 28 days (Behera et al. 2020 ). While when high sulfide tailings were applied in cemented paste backfill, the strength of composite material decreased obviously due to sulfide erosion (Dong et al. 2019 ). Besides, efficient technologies are also developed to reduce heavy metal toxicity in LZTs. For example, Felipe Saavedra-Mella et al. reported that phosphate treatment could reduce phytotoxicity of heavy metals in LZTs (Saavedra-Mella et al. 2019 ). Dense Medium Separation (DMS) is also a clean technique to recover heavy metals from LZTs (Khalil et al. 2019 ). Although tailings are solid wastes, it can become a reuse resource after proper treatment. Usually, tailings can be used as a mixed material in the production of cement, mortar and concrete (Gou et al. 2019 ). Xinpeng Wang et al. developed Ultra-High Performance Concrete (UHPC) by adding LZTs. They found that the compressive strength and workability of UHPC decreased with the incorporation of LZTs (Wang et al. 2018a ). Wissem Gallala et al. investigated the mechanical and radiation shielding properties of cement mortars containing LZTs. The results showed that LZTs improved the flexural strength of mortars and these mortars behaved effective radiation protection (Gallala et al. 2021 ). Most previous studies have explained the effect of LZTs on cementitious materials from macro perspective. Few literatures focus on micro-analysis, and the pretreatment of LZTs is extremely important such as changing particle size. Moreover, the heavy metal leaching toxicity of LZTs restricts its recycling. Therefore, the solidification of heavy metals is worth considering. It is well known that cement itself is a commonly used carrier in Stabilization/Solidification (S/S) technology for the disposal of solid toxic wastes (Chen et al. 2009 ). The hydration products of cement can stabilize heavy metal ions through precipitation, physical adsorption, and ion substitution to reduce the leaching toxicity (Wang et al. 2018b ). In this paper, LZTs with different particle size were used to prepare blended cement, and the mechanical properties, hydration properties and microstructure of blended cement was investigated. At the same time, the stabilization/solidification of heavy metals in LZTs was discussed to evaluate the environmental safety of blended cement. 2. Materials And Methods 2.1 Materials Ordinary Portland cement (OPC) of grade 42.5 and LZTs were used as raw materials in this experiment. OPC was produced by Tianrui Cement Group Co., Ltd, Zhengzhou, China, and LZTs were obtained from Zhongjin Lingnan Mining Industry in Guangxi, China. The chemical compositions were determined by X-ray fluorescence (XRF, S4 PIONEER, BRUKER, Germany) and shown in Table 1 . The phase compositions of LZTs were identified by X-ray Diffraction (XRD) test. As shown in Fig. 1 , the main mineral phases of LZTs were dolomite, pyrite and barite. Table 1 Chemical compositions of OPC and LZTs (wt.%) Chemical compositions OPC LZTs SiO 2 17.12 3.50 Al 2 O 3 5.54 1.40 Fe 2 O 3 4.73 9.18 CaO 61.40 24.19 MgO 3.74 13.50 K 2 O 1.33 0.36 SO 3 3.37 14.63 TiO 2 0.26 0.07 Na 2 O 0.16 - BaO - 13.86 PbO - 0.49 ZnO - 0.68 LOI 2.35 18.14 2.2 Methods 2.2.1 Paste preparation Before preparing paste mixture, LZTs were pretreated to obtain fine tailing powder. Firstly, LZTs were dried thoroughly in oven at 60℃. And then, two different particle size powders were prepared by being ground for 15 and 30 min in a SM φ500×500 type ball mill, separately. The particle size distributions of two type powders and OPC are shown in Fig. 2 . The particle size distributions of two type LZTs powders both showed bimodal curves, while cement showed monomodal curve. The median particle diameters (D 50 ) value of OPC and ground LZTs were 47.10 µm, 16.90 µm and 8.49 µm, respectively. It was found that two different particle size powders were finer than cement and this tendency was more obvious with the prolongation of grinding time. As a kind of solid waste produced by metal mining operations, LZTs contain certain heavy metals such as Pb and Zn. Therefore, leaching tests of LZTs were conducted according to toxicity characteristic leaching procedure (TCLP) (US 1992 ), and then the leaching concentration of heavy metal was determined by ICP test. The results are shown in Table 2 . Table 2 The leaching concentration of heavy metals in LZTs Heavy metals Leaching concentration (mg/L) Limits (mg/L) 15 min 30 min Pb 19.40 26.00 5.00 Zn 63.00 76.50 100.00 The two different particle size tailing powders were added into the mixture paste at the dosage of 0%, 10%, 20%, 30%, and 50%. The w/b ratio was 0.42 to obtain good workability. The mix proportions of the specimens were shown in Table 3 . Each mixture paste was poured into the mold with size of 40 mm×40 mm×40 mm. All the samples were demolded after 24 hours, and then the cubes were curing at a constant temperature and humidity curing room where the relative temperature was 20 ± 1°C and the relative humidity was not less than 95%. Table 3 The mix proportions of each sample Mixture name Grinding time of LZTs (min) LZTs (% by mass) W/B Control 0 0.42 T15-10 15 10 T15-20 20 T15-30 30 T15-50 50 T30-10 30 10 T30-20 20 T30-30 30 T30-50 50 2.2.2 Analysis methods The compressive strength of all samples was determined at the curing time of 3, 7, and 28 days. After that, small particles and pieces were selected from the inside of the broken samples. These particles and pieces were soaked in absolute ethanol to ensure that the hydration was terminated. Pieces were used for scanning electron microscope with energy dispersive spectrometry (SEM-EDS) test. Small particles were further crushed. Part of the particles below 9.5 mm were used for toxicity leaching test. The rest samples stopped hydration were ground to pass a 200-mesh standard sieve and dried to constant weight at 60 ℃. These powders were used for X-ray Diffraction (XRD) test, Fourier Transform Infrared Spectroscopy (FTIR) and thermogravimetric and differential scanning calorimetry (TG-DSC) test. For each specific experiment, SEM-EDS was performed by a focused ion beam scanning electron microscope (Auriga, Zeiss, Germany). XRD was conducted by D8 VENTURE (Bruker, Germany) with Cu Kα radiation at 40 kV and 40 mA and the 2θ value ranging from 5° to 80°. FTIR was recorded using a TENSOR II spectrometer (Bruker, Germany) across the range from 4000 − 400 cm − 1 . The scanning rate was 10°/min. TG-DSC was measured with the temperature range from 30 to 1000℃ by using TA449F3 thermal analysis system (NETZSCH, Germany). The leaching concentration of heavy metal was tested after TCLP by using Shimadzu Multitype ICP Emission Spectrometera (ICP-OES, ICPE-9820, Japan). 3. Results And Discussion 3.1 Compressive strength The compressive strength development of samples at a certain curing time is shown in Fig. 3 . The dosage of LZTs affected the compressive strength. The 10% LZTs content of different particle sizes slightly weakened the compressive strength of samples in the early or later stage. At the age of 3 days, compared to the control sample, the compressive strength of T15-10 and T30-10 samples decreased by 7.76% and 2.84%, and it was only decreased by 1.90% and 2.06% at 28 days. However, with the increase of LZTs content, the compressive strength decreased significantly. At the age of 3 days, the compressive strength of T15-50 and T30-50 decreased to 12.56 MPa and 14.23 MPa, respectively. The compressive strength of T30-50 even decreased by 70.90% at 28 days. Therefore, the addition of LZTs reduced the compressive strength of mixtures regardless of the difference in the particle size of the tailings or the extension of curing time. With the same LZTs content, the 3 days compressive strength of T15-30 decreased to 25.51 MPa, and this was lower than that of T30-30 (26.49 MPa), while the 28 days compressive strength of T15-30 decreased to 36.49 MPa, and this was higher than that of T30-30 (34.08 MPa). This difference also existed in other samples. It could be seen that the early compressive strength increased as the grinding time increased from 15 min to 30 min. Conversely, longer grinding time hindered the development of later compressive strength. Based on the above analysis, the substitute content of LZT should not exceed 10% in blended cement, and it is beneficial to the development of later compressive strength when the grinding time of LZT is 15min. 3.2 Leaching tests Table 2 showed that the heavy metal leaching concentration of LZTs exceeded the standard limits, indicating that LZTs was harmful to environmental. In order to evaluate the environmental safety of blended cement containing LZTs, toxicity leaching test was carried out when samples cured for 28 days. The leaching concentration of heavy metal lead and zinc was compared with the national standard. The results are shown in Table 4 . Overall, the leaching concentration of Pb and Zn was far below the standard limits. The leaching concentration of Pb was 0 for all samples, indicating that the composite had a strong solidification effect on Pb. This was primarily attributed to physical adsorption of C-S-H gel for its microporous structure and high surface area (Niu et al. 2018 ). Furthermore, Pb was encapsuled physically due to high density of C-S-H gel with the extension of curing age (Wang et al. 2018b ). The solidification of Zn was attributed to physical adsorption and encapsulation by C-S-H gel, and there also formed double hydroxides CaZn 2 (OH) 6 ·2H 2 O) in alkaline environment (Cao et al. 2019 ). From Table 4 , the leaching concentration of Zn increased slightly with the increase of LZTs content. On one hand, the decreasing proportion of cement led to the decrease of these hydration products, and the solidification ability of Zn was weakened correspondingly. On the other hand, the leaching concentration of heavy metals was closely related to the content of LZTs. Moreover, the leaching concentration of Zn was significantly higher than that of Pb from the original LZTs, and hydration products generally had a threshold for the solidification of heavy metals. Therefore, excessive heavy metals could still be leached. Even so, the highest leaching concentration of Zn was only 0.56 mg/L, which was far below the standard limits. With the extension of grinding time, the leaching concentration of Zn also increased gradually. Because prolonging grinding time would result in an increasing leaching concentration of Zn. Moreover, hydration products also decreased with the addition of LZTs grinding for 30 min. This could be seen in the next analysis of chemically bound water directly. Even so, the composites containing LZTs still achieved high efficiency solidification of heavy metals and it ensured that LZTs was used in a harmless way as a supplementary cementitious material. Table 4 Leaching concentration of heavy metals of blended cement (mg/L) Samples T15-10 T15-20 T15-30 T15-40 T15-50 Limits Pb 0 0 0 0 0 5 Zn 0 0 0 0.01 0.01 100 Samples T30-10 T30-20 T30-30 T30-40 T30-50 Limits Pb 0 0 0 0 0 5 Zn 0.01 0.01 0.06 0.28 0.56 100 3.3 XRD analysis As shown in Fig. 4 , hydration products in the mixtures were affected by the addition of LZTs. The XRD pattern of control sample mainly included the diffraction peaks of Ca(OH) 2 , ettringite, clinker dicalcium silicate and tricalcium silicate. The diffraction peaks of dolomite, barite and pyrite appeared after the incorporation of LZTs and began to intensify with the increase of LZTs content. With the increase of LZTs content, the characteristic peak of Ca(OH) 2 became weak gradually. The intensity decrease was very obvious when the LZTs content was higher than 20%. The decrease of cement content led to the reduction of Ca(OH) 2 content. Besides, the consumption by the pozzolanic reaction of tailings could be another reason for the decrease of Ca(OH) 2 content (Liu et al. 2020 ). In addition, the characteristic peak (at 2θ = 9.09°) of ettringite increased with the addition of LZTs especially at the curing age of 3 days. Under the same LZTs content, grinding time for 30 min promoted the formation of ettringite more efficiently which could be beneficial to the improvement of compressive strength [17]. It is consistent with the results in Fig. 3 that compressive strength was improved when the grinding time of LZTs increased from 15 min to 30 min at 3 days. Similarly, at the later hydration stage (28 days), when the LZTs content was 50%, the ettringite diffraction peak intensity of T30-50 was significantly stronger than that of T15-50. This also resulted in higher compressive strength of T30-50 than T15-50. 3.4 FTIR analysis The FTIR absorption spectra of raw LZTs, pure cement paste, and blended cement paste are shown in Fig. 5 . Pure cement paste and blended cement paste performed similar FTIR spectra at the curing age of 28 days. Based on the related literatures, band at 3642 cm − 1 was due to the stretching vibration of Ca-OH in Ca(OH) 2 (Liu et al. 2018b ); bands at around 3433 cm − 1 and 1658 cm − 1 were related to the stretching vibration and bending vibration of Al-OH in ettringite, respectively (Jose et al. 2020 , Ylmen et al. 2009 ); band at 1124 cm − 1 was assigned to the stretching vibration of S-O by the formation of ettringite (Jose et al. 2020 , Qian et al. 2008 ); band at 974 cm − 1 was due to Si–O stretching vibration which indicated that C-S-H gels were formed in these samples (Ren et al. 2017 , Ylmen et al. 2009 , Zak &Deja 2015 ). In addition, the bands at 1473 cm − 1 and 1416 cm − 1 could be associated with the asymmetric stretching vibration of C-O in CO 3 2− due to the carbonization in the air during the curing process (Duran et al. 2016 , Xia et al. 2019 , Yildirim Ozen &Moroydor Derun 2019 , Zhang et al. 2020 ). According to the changes of vibration peaks from above FTIR spectra, it could be concluded that the disappearance of absorption bands confirmed the dissolution of minerals in LZTs. For raw LZTs, characteristic FTIR absorption bands displayed at 2522 cm − 1 , 1814 cm − 1 were attributed to the vibrations of dolomite (Igisu et al. 2014 , Ji et al. 2009 ); band at about 422 cm − 1 was connected with S-S stretching vibrations presented in pyrite (Ye et al. 2017 ). These Bands disappeared in blended cement which represented the destruction of dolomite and pyrite. In addition, the weakness of other vibration bands also supported this conclusion. Based on this analysis, heavy metals were likely to be released from LZTs like Pb and Zn. In terms of hydration products, the vibration bands position of hydration products of blended cement had no shift compared with pure cement, which also indicated that LZTs behaved low activity. The difference was that the vibration band at 974 cm − 1 of C-S-H gel became broad with the increase of tailings content. Because the presence of heavy metals affected the polymerization of C-S-H gel (Xia et al. 2019 , Zak &Deja 2015 ). Accordingly, heavy metals were solidified in C-S-H gel, which was consistent with later EDS analysis. 3.5 Chemically bound water analysis The chemically bound water content of the blended cement was obtained from the weight loss between 60°C and 1000°C (Park &Choi 2021 ). Grinding hardened cement paste was passed a 200-mesh standard sieve, and then, the powder was dried at 60 ℃ to make sure it reached a constant weight, after that, the crucible containing powder sample was placed in a muffle furnace and burned at 1000 ℃ for 3 hours. The chemically bound water content was calculated according to Eq. (1) and Eq. (2): $$\begin{array}{c}{W}_{B}=\frac{{m}_{1}-{m}_{2}}{{m}_{2}}-\frac{{W}_{T,C}}{1-{W}_{T,C}}\#\left(1\right)\end{array}$$ $$\begin{array}{c}{W}_{T,C}={f}_{T}\times {LOI}_{T}+{f}_{C}\times {LOI}_{C}\#\left(2\right)\end{array}$$ Where \({W}_{B}\) is the chemically bound water content; \({m}_{1}\) and \({m}_{2}\) are the sample weight before and after burning at 1000 ℃; \({f}_{T}\) and \({f}_{C}\) are the mass fractions of LZTs and cement, respectively; \({LOI}_{T}\) and \({LOI}_{C}\) are the loss on ignition of LZTs and cement, respectively. Chemically bound water refers to non-evaporable water in the hydration products. The content of chemically bound water represents the total hydration products quantity and it reflects the hydration degree of composite cementitious system (Liao et al. 2020 , Sun et al. 2020 ). From Fig. 6 , as the curing age increased from 3 days to 28 days, the amount of chemically bound water in each sample increased significantly. Because the hydration of the composite system was more sufficient with the extension of curing age. With the incorporation of LZTs, the chemically bond water content decresed correspondingly at any curing age. The reason was that cement was the main source of hydration products in the composite system. When the replacement ratio of LZTs increased, the cement content decreased, resulting in a decrease of hydration products as well as lower chemically bond water than pure cement paste. This was also an important reason for the decrease of compressive strength. Besides, the grinding time also caused the difference in the amount of chemically bound water. The chemically bond water of samples were higher when LZTs ground for 30 min at early curing age (3 days). But the chemically bond water decreased with the extension of LZTs grinding time at 28 days. 3.6 TG-DSC analysis The TG-DSC curve of each sample is shown in Fig. 7 . According to these curves, it could be found that all these curves behaved similar characteristics described as follows. The endothermic peak between 400 ℃ and 500 ℃ was caused by the dehydration of Ca(OH) 2 . The endothermic peak between 700 ℃ and 800 ℃ was mainly due to the dehydration of CaCO 3 which was a product due to the carbonization of Ca(OH) 2 in control samples. But in addition to carbonized products, this part of weight loss also included the decomposition of carbonate in dolomite when LZTs were added. As an important hydration product of cement, the content of Ca(OH) 2 can indirectly evaluate the degree of hydration. The content of Ca(OH) 2 is obtained by the weight loss between 400 ℃ and 500 ℃ according to the TG curves, and the decomposition reaction of Ca(OH) 2 is as follows: Ca(OH) 2 →CaO + H 2 O The content of Ca(OH) 2 is calculated by Eq. (3) and the results are shown in Fig. 8 . $$\begin{array}{c}{W}_{CH}=\frac{74}{18}{WL}_{H}\#\left(3\right)\end{array}$$ Wherein, \({W}_{CH}\) is the content of Ca(OH) 2 and \({WL}_{H}\) is the weight loss between 400 ℃ and 500 ℃. From Fig. 8 , the content of Ca(OH) 2 decreased with the addition of LZTs at the curing age of 3 days and 28 days except sample T30-10. The main reason was that the LZTs replaced a considerable part of cement, resulting in the decrease of Ca(OH) 2 . In the high pH value during cement hydration process, the heavy metal released from LZTs could co-precipitate with Ca(OH) 2 as double hydroxides like CaZn 2 (OH) 6 ·2H 2 O easily, which also lead to the decrease of Ca(OH) 2 (Chen et al. 2007 ). 3.7 SEM-EDS analysis The microstructure is beneficial to the analysis of hydration products types and distribution in hardened paste, and it is closely related to the compressive strength development. The SEM-EDS photographs of pure cement paste and blended cement paste containing LZTs are shown in Fig. 9 . In pure cement paste, a large amount of fibriform and spherical C-S-H gel grew radially at the curing time of 3 days. These C-S-H gel formed the basic network structure. The lamelliform Ca(OH) 2 were obviously stacked and distributed in layers. In addition, there were needle-like crystals ettringite interspersed in the C-S-H gel. Figure 9 (b) and (c) were the SEM photographs of blended cement paste at the curing time of 3 days. The total hydration products were significantly reduced in these two samples. Tailing particles scattered at the interface of hydration products or wrapped in the network structure of the gel. There were more ettringite crystals with the addition of LZTs compared with Fig. 9 (a). These crystals filled the gaps and pores in the C-S-H gel, which made positive contribution to the compressive strength (Dong et al. 2019 ), and this is consistent with the XRD analysis results. Even so, the addition of LZTs not only reduced total hydration products, but also brought more pores, and these factors resulted in the samples exhibiting lower compressive strength. Figure 9 (d) shows the photograph of pure cement paste at the curing time of 28 days. With the extension of curing age, the continuous growing gel established contact each other which made paste denser. While in the samples containing LZTs corresponding to Fig. 9 (f) and (h), although hydration products increased compared with early stage, a part of tailing particles were still exposed on the surface of hydration products. Moreover, there was no obvious change on the surface of these tailing particles, which indicated that in the later hydration period, the pozzolanic effect of tailings was still weak. This led to fragile connection between tailings and hydration products and reduction in compressive strength. In order to explore the solidification behavior of heavy metals in blended cement, energy-dispersive X-ray diffraction (EDS) analyses were conducted to determine the elemental compositions of hydration products. From the results of EDS at spot 1, the Ca/Si ratio of C-S-H gel in pure cement paste was about 0.93, and no heavy metal elements were detected. As for samples containing LZTs, the Ca/Si ratio increased to 2.12 and 1.72 at spot 2 and spot 3, respectively. The higher Ca/Si ratio was probably due to the increasing dissolved content of Ca 2+ and the relatively weak dissolution rate of Si 4+ (Liu et al. 2020 ). Moreover, there existed visible peaks of Pb and Zn in elemental distributions of EDS at both spot 2 and spot 3. This indicated that heavy metals were absorbed by C-S-H gel. Obviously, heavy metals hardly leached duo to the dense network structure and high specific surface area of C-S-H gel (Qian et al. 2008 ). In addition, due to the existence of competition mechanism between different kinds of heavy metals (Cao et al. 2019 ), Pb was more easily absorbed by C-S-H gel than Zn. It could be seen from EDS results that the content of Pb at spot 2 and spot 3 was higher than that of Zn, which also caused higher concentration of Zn than that of Pb in the leaching tests. 4. Conclusions In this study, lead-zinc tailings with different grinding time were used as an alternative admixture to prepare blended cement. The hydration properties and environmental safety of blended cement containing lead-zinc tailings were investigated. Based on the analysis of various aspects, the main conclusions are as follows: The addition of LZTs reduced the compressive strength of blended cement. The substitute content of LZT should not exceed 10% in blended cement, and it is beneficial to the development of later compressive strength when the grinding time of LZT is 15min. The leaching concentration of Pb and Zn was far below the standard limits. And the leaching tests indicated that the S/S technology is feasible to using LZTs as a supplementary cementitious material in a harmless way. According to the analysis of XRD, chemically bound water tests, TG-DSC and SEM, the degree of hydration of blended cement decreased with the addition of LZTs. The content of Ca(OH) 2 also reduced due to the decreasing proportion of cement. Less hydration products and more pores resulted in the blended cement exhibiting lower compressive strength. FTIR and EDS results indicated that the hydration products C-S-H gel had a good stabilization/solidification effect on heavy metals due to its physical adsorption and encapsulation. Declarations Ethical Approval The manuscript has not been submitted to more than one journal for simultaneous consideration. The submitted work is original and has not been published elsewhere in any form or language (partially or in full). Consent to Participate All authors consent to participate in the manuscript. Consent to Publish All authors consent to publish the manuscript. Authors Contributions All authors contributed to the study conception and design. Material preparation, data collection and analysis were performed by Zhongtao Luo, Yuandong Mu, Xiaohai Liu. The first draft of the manuscript was written by Changbo Tang, and all authors commented on previous versions of the manuscript. All authors read and approved the final manuscript. Funding This work was supported by the National Natural Science Foundation of China (52074245). Competing Interests The authors have no relevant financial or non-financial interests to disclose. Availability of data and materials No dataset was generated or analyzed during this study. References Behera SK, Ghosh CN, Mishra DP, Singh P, Mishra K, Buragohain J, Mandal PK (2020) : Strength development and microstructural investigation of lead-zinc mill tailings based paste backfill with fly ash as alternative binder.Cement and Concrete Composites109 Cao X, Wang W, Ma R, Sun S, Lin J (2019) Solidification/stabilization of Pb 2+ and Zn 2+ in the sludge incineration residue-based magnesium potassium phosphate cement: Physical and chemical mechanisms and competition between coexisting ions. 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J Hazard Mater 349:262–271 Niu MD, Li GX, Wang Y, Li QQ, Han LL, Song ZP (2018) Comparative study of immobilization and mechanical properties of sulfoaluminate cement and ordinary Portland cement with different heavy metals. Constr Build Mater 193:332–343 Onuaguluchi O, Eren Ö (2012) Recycling of copper tailings as an additive in cement mortars. Constr Build Mater 37:723–727 Park B, Choi YC (2021) : Hydration and pore-structure characteristics of high-volume fly ash cement pastes.Constr Build Mater278 Qi C, Fourie A (2019) : Cemented paste backfill for mineral tailings management: Review and future perspectives.Minerals Engineering144 Qian GR, Shi J, Cao YL, Xu YF, Chui PC (2008) Properties of MSW fly ash-calcium sulfoaluminate cement matrix and stabilization/solidification on heavy metals. J Hazard Mater 152:196–203 Qiu J, Guo Z, Yang L, Jiang H, Zhao Y (2020) : Effect of tailings fineness on flow, strength, ultrasonic and microstructure characteristics of cemented paste backfill.Constr Build Mater263 Ren XH, Zhang WS, Ye JY (2017) FTIR study on the polymorphic structure of tricalcium silicate. Cem Concrete Res 99:129–136 Saavedra-Mella F, Liu Y, Southam G, Huang L (2019) Phosphate treatment alleviated acute phytotoxicity of heavy metals in sulfidic Pb-Zn mine tailings. Environ Pollut 250:676–685 Saedi A, Jamshidi-Zanjani A, Darban AK (2020) A review on different methods of activating tailings to improve their cementitious property as cemented paste and reusability. J Environ Manage 270:110881 Sun J, Zhang Z, Hou G (2020) Utilization of fly ash microsphere powder as a mineral admixture of cement: Effects on early hydration and microstructure at different curing temperatures. Powder Technol 375:262–270 Tao M, Zhang X, Wang S, Cao W, Jiang Y (2019) : Life cycle assessment on lead–zinc ore mining and beneficiation in China.Journal of Cleaner Production237 US (1992) : Toxicity characteristic leaching procedure, TCLP 1311, EPA 1311 of US (1992) Wang L, Ji B, Hu Y, Liu R, Sun W (2017) A review on in situ phytoremediation of mine tailings. Chemosphere 184:594–600 Wang XP, Yu R, Shui ZH, Zhao ZM, Song QL, Yang B, Fan DQ (2018a) Development of a novel cleaner construction product: Ultra-high performance concrete incorporating lead-zinc tailings. J Clean Prod 196:172–182 Wang YS, Dai JG, Wang L, Tsang DCW, Poon CS (2018b) Influence of lead on stabilization/solidification by ordinary Portland cement and magnesium phosphate cement. Chemosphere 190:90–96 Xia M, Muhammad F, Zeng L, Li S, Huang X, Jiao B, Shiau Y, Li D (2019) Solidification/stabilization of lead-zinc smelting slag in composite based geopolymer. J Clean Prod 209:1206–1215 Yao G, Liu Q, Wang J, Wu P, Lyu X (2019) Effect of mechanical grinding on pozzolanic activity and hydration properties of siliceous gold ore tailings. J Clean Prod 217:12–21 Ye M, Li G, Yan P, Ren J, Zheng L, Han D, Sun S, Huang S, Zhong Y (2017) Removal of metals from lead-zinc mine tailings using bioleaching and followed by sulfide precipitation. Chemosphere 185:1189–1196 Yildirim Ozen M, Moroydor Derun E (2019) A comparative study: Effects of different nanoparticles on the properties of gold mine tailings containing cement mortars. Constr Build Mater 202:396–405 Ylmen R, Jaglid U, Steenari BM, Panas I (2009) Early hydration and setting of Portland cement monitored by IR, SEM and Vicat techniques. Cem Concrete Res 39:433–439 Zak R, Deja J (2015) Spectroscopy study of Zn, Cd, Pb and Cr ions immobilization on C-S-H phase. Spectrochim Acta A Mol Biomol Spectrosc 134:614–620 Zhang P, Muhammad F, Yu L, Xia M, Lin H, Huang X, Jiao B, Shiau Y, Li D (2020) : Self-cementation solidification of heavy metals in lead-zinc smelting slag through alkali-activated materials.Constr Build Mater249 Cite Share Download PDF Status: Posted Version 1 posted You are reading this latest preprint version Research Square lets you share your work early, gain feedback from the community, and start making changes to your manuscript prior to peer review in a journal. As a division of Research Square Company, we’re committed to making research communication faster, fairer, and more useful. We do this by developing innovative software and high quality services for the global research community. Our growing team is made up of researchers and industry professionals working together to solve the most critical problems facing scientific publishing. Also discoverable on Platform About Our Team In Review Editorial Policies Advisory Board Help Center Resources Author Services Accessibility API Access RSS feed Manage Cookie Preferences © Research Square 2026 | ISSN 2693-5015 (online) Privacy Policy Terms of Service Do Not Sell My Personal Information {"props":{"pageProps":{"initialData":{"identity":"rs-1571072","acceptedTermsAndConditions":true,"allowDirectSubmit":true,"archivedVersions":[],"articleType":"Research Article","associatedPublications":[],"authors":[{"id":107324901,"identity":"54ef77ac-ac1d-472a-ad4c-569d74c5e1bb","order_by":0,"name":"Zhongtao Luo","email":"","orcid":"","institution":"Zhengzhou University","correspondingAuthor":false,"submittingAuthor":false,"prefix":"","firstName":"Zhongtao","middleName":"","lastName":"Luo","suffix":""},{"id":107324902,"identity":"dfc7e09a-7d23-4763-b49b-3706dcafa5cb","order_by":1,"name":"Changbo Tang","email":"data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAZAAAAAyAQMAAABI0h/eAAAABlBMVEX///8AAABVwtN+AAAACXBIWXMAAA7EAAAOxAGVKw4bAAAA20lEQVRIiWNgGAWjYBACfvbmAwc+VEjw8MsfPkCcFsmeY4kHZ5yxkJOcwZZAnBaDGznGh3lbKowNbvAYEOmyAzkGh3kbJBIbbvd8vPGGwU5Ot4GADsaGYwUH5+6QSGycc3az5RyGZGOzAwS0MDM2bzjw9oxEYjND7jZpHoYDidsIaWFjZjA4wNsmkdjGkPOMOC08bCwGB4FajHkkctiI0yLBw5YADGQJOQmeY8aWcwyI8Iv9/ceHP3yoqOOxP9788MabCjs5glrQrCQ2apC0kKpjFIyCUTAKRgQAAFVvSLfzJKVjAAAAAElFTkSuQmCC","orcid":"https://orcid.org/0000-0001-8089-5905","institution":"Zhengzhou University","correspondingAuthor":true,"submittingAuthor":false,"prefix":"","firstName":"Changbo","middleName":"","lastName":"Tang","suffix":""},{"id":107324903,"identity":"2e3afa41-e33c-4e88-86c8-50286ed58215","order_by":2,"name":"Yuandong Mu","email":"","orcid":"","institution":"Zhengzhou University","correspondingAuthor":false,"submittingAuthor":false,"prefix":"","firstName":"Yuandong","middleName":"","lastName":"Mu","suffix":""},{"id":107324904,"identity":"31e5fbd0-8fa7-4e40-933f-14e3bd8282e3","order_by":3,"name":"Xiaohai Liu","email":"","orcid":"https://orcid.org/0000-0002-8357-109X","institution":"Zhengzhou University","correspondingAuthor":false,"submittingAuthor":false,"prefix":"","firstName":"Xiaohai","middleName":"","lastName":"Liu","suffix":""}],"badges":[],"createdAt":"2022-04-19 04:45:33","currentVersionCode":1,"declarations":"","doi":"10.21203/rs.3.rs-1571072/v1","doiUrl":"https://doi.org/10.21203/rs.3.rs-1571072/v1","draftVersion":[],"editorialEvents":[],"editorialNote":"","failedWorkflow":false,"files":[{"id":21920747,"identity":"7537f12c-4bb4-4cb2-ac03-17acf1a86e2c","added_by":"auto","created_at":"2022-05-26 15:19:27","extension":"png","order_by":1,"title":"Figure 1","display":"","copyAsset":false,"role":"figure","size":59963,"visible":true,"origin":"","legend":"\u003cp\u003eXRD patterns of LZTs\u003c/p\u003e\u003cp\u003e\u003cbr\u003e\u003c/p\u003e","description":"","filename":"floatimage1.png","url":"https://assets-eu.researchsquare.com/files/rs-1571072/v1/c992b1d2544dec9f6d47c485.png"},{"id":21921017,"identity":"3842dd6f-a297-4136-b95a-dcf235835372","added_by":"auto","created_at":"2022-05-26 15:24:26","extension":"png","order_by":2,"title":"Figure 2","display":"","copyAsset":false,"role":"figure","size":212460,"visible":true,"origin":"","legend":"\u003cp\u003eParticle size distribution of OPC and LZTs with different grinding time\u003c/p\u003e","description":"","filename":"floatimage2.png","url":"https://assets-eu.researchsquare.com/files/rs-1571072/v1/ed07a86ad2ee7a7ffb326da8.png"},{"id":21920749,"identity":"4591c6e7-8fc6-4f9d-a099-ce38c7687348","added_by":"auto","created_at":"2022-05-26 15:19:27","extension":"png","order_by":3,"title":"Figure 3","display":"","copyAsset":false,"role":"figure","size":1208023,"visible":true,"origin":"","legend":"\u003cp\u003eCompressive strength of samples containing LZTs ground for 15 min (a) and 30 min (b)\u003c/p\u003e\u003cp\u003e\u003cbr\u003e\u003c/p\u003e","description":"","filename":"floatimage3.png","url":"https://assets-eu.researchsquare.com/files/rs-1571072/v1/c27b472116f3bad92448eb61.png"},{"id":21920746,"identity":"3b9d2dbb-c451-456f-94f7-6a43171a547e","added_by":"auto","created_at":"2022-05-26 15:19:27","extension":"png","order_by":4,"title":"Figure 4","display":"","copyAsset":false,"role":"figure","size":2374453,"visible":true,"origin":"","legend":"\u003cp\u003eThe XRD patterns of samples with the addition of LZTs ground for 15 min (a for 3 days, b for 28 days) and 30 min (c for 3 days, d for 28 days)\u003c/p\u003e\u003cp\u003e\u003cbr\u003e\u003c/p\u003e","description":"","filename":"floatimage4.png","url":"https://assets-eu.researchsquare.com/files/rs-1571072/v1/f9f93451451712ae8ff52f7c.png"},{"id":21921434,"identity":"a1a05fec-14ee-4c8f-bb12-abf32b1b3aca","added_by":"auto","created_at":"2022-05-26 15:29:26","extension":"png","order_by":5,"title":"Figure 5","display":"","copyAsset":false,"role":"figure","size":1427270,"visible":true,"origin":"","legend":"\u003cp\u003eFTIR spectra of raw LZTs, pure cement paste, and blended cement paste at curing age of 28 days\u003c/p\u003e\u003cp\u003e\u003cbr\u003e\u003c/p\u003e","description":"","filename":"floatimage5.png","url":"https://assets-eu.researchsquare.com/files/rs-1571072/v1/70072805713ebeea917544be.png"},{"id":21920742,"identity":"a718977d-1555-47e6-a4f6-c632b635880c","added_by":"auto","created_at":"2022-05-26 15:19:26","extension":"png","order_by":6,"title":"Figure 6","display":"","copyAsset":false,"role":"figure","size":78511,"visible":true,"origin":"","legend":"\u003cp\u003eChemically bond water of samples containing LZTs\u003c/p\u003e","description":"","filename":"floatimage6.png","url":"https://assets-eu.researchsquare.com/files/rs-1571072/v1/5255dc5e51c45f24aaefd89f.png"},{"id":21921435,"identity":"bcbe53d9-a92b-4e12-a1c7-7b73b84bf678","added_by":"auto","created_at":"2022-05-26 15:29:27","extension":"png","order_by":7,"title":"Figure 7","display":"","copyAsset":false,"role":"figure","size":2421041,"visible":true,"origin":"","legend":"\u003cp\u003eThe TG-DSC curves of samples with the addition of LZTs ground for 15min (a for 3 days, b for 28 days) and 30min (c for 3 days, d for 28 days)\u003c/p\u003e\u003cp\u003e\u003cbr\u003e\u003c/p\u003e","description":"","filename":"floatimage7.png","url":"https://assets-eu.researchsquare.com/files/rs-1571072/v1/f0417c3adf6fd373769d592e.png"},{"id":21920744,"identity":"3d1b6a72-3023-4d4c-94ab-083a9abb361f","added_by":"auto","created_at":"2022-05-26 15:19:26","extension":"png","order_by":8,"title":"Figure 8","display":"","copyAsset":false,"role":"figure","size":130528,"visible":true,"origin":"","legend":"\u003cp\u003eThe content of Ca(OH)\u003csub\u003e2 \u003c/sub\u003eof blended cement containing LZTs\u003c/p\u003e","description":"","filename":"floatimage8.png","url":"https://assets-eu.researchsquare.com/files/rs-1571072/v1/f3c9265f80a576059d86eb96.png"},{"id":21921020,"identity":"a5cb22d5-dc3e-43ee-a125-ea35f86671bb","added_by":"auto","created_at":"2022-05-26 15:24:27","extension":"png","order_by":9,"title":"Figure 9","display":"","copyAsset":false,"role":"figure","size":2315474,"visible":true,"origin":"","legend":"\u003cp\u003eSEM-EDS of (a) pure cement, (b) T15-30, (c) T30-30 at 3 days, (d)-(e) pure cement, (f)-(g) T15-30, (h)-(i) T30-30 at 28 days\u003c/p\u003e\u003cp\u003e\u003cbr\u003e\u003c/p\u003e","description":"","filename":"floatimage9.png","url":"https://assets-eu.researchsquare.com/files/rs-1571072/v1/333ebfb63450d95c770f8e0b.png"},{"id":27131289,"identity":"8a5fbf5a-cc46-4dfa-b3fe-2911c4b75025","added_by":"auto","created_at":"2022-09-29 12:09:46","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":6062685,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-1571072/v1/312e4c02-df0b-457a-8d0d-ec01e18e09a3.pdf"}],"financialInterests":"","formattedTitle":"Recycle of lead-zinc tailings in blended cement: mechanical property and stabilization/solidification of heavy metals","fulltext":[{"header":"1. Introduction","content":"\u003cp\u003eWith the development of global industrialization, mining industry has produced a large number of solid wastes such as tailings, which brought a series of environmental pollution and safety problems (Behera et al. \u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e2020\u003c/span\u003e, Liu et al. \u003cspan citationid=\"CR16\" class=\"CitationRef\"\u003e2018a\u003c/span\u003e). Tailings are by-products from ore processing (Wang et al. \u003cspan citationid=\"CR31\" class=\"CitationRef\"\u003e2017\u003c/span\u003e). In China, lead-zinc tailings (LZTs) are defined as hazardous solid wastes because of the high-content heavy metals, and the output increase rapidly in recent years.\u003c/p\u003e \u003cp\u003eThe hazards of LZTs are multiple (Onuaguluchi \u0026amp;Eren \u003cspan citationid=\"CR20\" class=\"CitationRef\"\u003e2012\u003c/span\u003e, Yao et al. \u003cspan citationid=\"CR35\" class=\"CitationRef\"\u003e2019\u003c/span\u003e). First of all, the tailing dams are prone to collapse which cause a series of disasters. LZTs from collapsed dams can cover vegetation, clog rivers and, in severe cases, rush into residential areas, causing significant loss of lives (Ince \u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e2019\u003c/span\u003e). And then, the open-air LZTs often occupy a large area of land, which is not good for the increasingly tense land resources (Han et al. \u003cspan citationid=\"CR9\" class=\"CitationRef\"\u003e2017\u003c/span\u003e). These LZTs usually contain a large amount of heavy metal ions, which are harmful to nearby plants and groundwater (Tao et al. \u003cspan citationid=\"CR29\" class=\"CitationRef\"\u003e2019\u003c/span\u003e).\u003c/p\u003e \u003cp\u003eResearchers have proposed many treatment methods to solve the pollution of tailings (Qiu et al. \u003cspan citationid=\"CR24\" class=\"CitationRef\"\u003e2020\u003c/span\u003e, Saedi et al. \u003cspan citationid=\"CR27\" class=\"CitationRef\"\u003e2020\u003c/span\u003e). The cement paste backfill (CPB) technology can consume a lot of tailings and avoid the collapse of mines after mining (Qi \u0026amp;Fourie \u003cspan citationid=\"CR22\" class=\"CitationRef\"\u003e2019\u003c/span\u003e). S.K. Behera et al. investigated the use of paste backfill technology in lead-zinc underground mines. The results showed that 5%-8% replacement with cement could meet the required uniaxial compressive strength of 1.1MPa after curing 28 days (Behera et al. \u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e2020\u003c/span\u003e). While when high sulfide tailings were applied in cemented paste backfill, the strength of composite material decreased obviously due to sulfide erosion (Dong et al. \u003cspan citationid=\"CR5\" class=\"CitationRef\"\u003e2019\u003c/span\u003e). Besides, efficient technologies are also developed to reduce heavy metal toxicity in LZTs. For example, Felipe Saavedra-Mella et al. reported that phosphate treatment could reduce phytotoxicity of heavy metals in LZTs (Saavedra-Mella et al. \u003cspan citationid=\"CR26\" class=\"CitationRef\"\u003e2019\u003c/span\u003e). Dense Medium Separation (DMS) is also a clean technique to recover heavy metals from LZTs (Khalil et al. \u003cspan citationid=\"CR14\" class=\"CitationRef\"\u003e2019\u003c/span\u003e).\u003c/p\u003e \u003cp\u003eAlthough tailings are solid wastes, it can become a reuse resource after proper treatment. Usually, tailings can be used as a mixed material in the production of cement, mortar and concrete (Gou et al. \u003cspan citationid=\"CR8\" class=\"CitationRef\"\u003e2019\u003c/span\u003e). Xinpeng Wang et al. developed Ultra-High Performance Concrete (UHPC) by adding LZTs. They found that the compressive strength and workability of UHPC decreased with the incorporation of LZTs (Wang et al. \u003cspan citationid=\"CR32\" class=\"CitationRef\"\u003e2018a\u003c/span\u003e). Wissem Gallala et al. investigated the mechanical and radiation shielding properties of cement mortars containing LZTs. The results showed that LZTs improved the flexural strength of mortars and these mortars behaved effective radiation protection (Gallala et al. \u003cspan citationid=\"CR7\" class=\"CitationRef\"\u003e2021\u003c/span\u003e).\u003c/p\u003e \u003cp\u003eMost previous studies have explained the effect of LZTs on cementitious materials from macro perspective. Few literatures focus on micro-analysis, and the pretreatment of LZTs is extremely important such as changing particle size. Moreover, the heavy metal leaching toxicity of LZTs restricts its recycling. Therefore, the solidification of heavy metals is worth considering. It is well known that cement itself is a commonly used carrier in Stabilization/Solidification (S/S) technology for the disposal of solid toxic wastes (Chen et al. \u003cspan citationid=\"CR4\" class=\"CitationRef\"\u003e2009\u003c/span\u003e). The hydration products of cement can stabilize heavy metal ions through precipitation, physical adsorption, and ion substitution to reduce the leaching toxicity (Wang et al. \u003cspan citationid=\"CR33\" class=\"CitationRef\"\u003e2018b\u003c/span\u003e).\u003c/p\u003e \u003cp\u003eIn this paper, LZTs with different particle size were used to prepare blended cement, and the mechanical properties, hydration properties and microstructure of blended cement was investigated. At the same time, the stabilization/solidification of heavy metals in LZTs was discussed to evaluate the environmental safety of blended cement.\u003c/p\u003e"},{"header":"2. Materials And Methods","content":"\u003cdiv id=\"Sec3\" class=\"Section2\"\u003e \u003ch2\u003e2.1 Materials\u003c/h2\u003e \u003cp\u003eOrdinary Portland cement (OPC) of grade 42.5 and LZTs were used as raw materials in this experiment. OPC was produced by Tianrui Cement Group Co., Ltd, Zhengzhou, China, and LZTs were obtained from Zhongjin Lingnan Mining Industry in Guangxi, China. The chemical compositions were determined by X-ray fluorescence (XRF, S4 PIONEER, BRUKER, Germany) and shown in Table\u0026nbsp;\u003cspan refid=\"Tab1\" class=\"InternalRef\"\u003e1\u003c/span\u003e. The phase compositions of LZTs were identified by X-ray Diffraction (XRD) test. As shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003e, the main mineral phases of LZTs were dolomite, pyrite and barite.\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\u003eChemical compositions of OPC and LZTs (wt.%)\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\u003eChemical compositions\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c2\"\u003e \u003cp\u003eOPC\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c3\"\u003e \u003cp\u003eLZTs\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003c/thead\u003e \u003ctbody\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eSiO\u003csub\u003e2\u003c/sub\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e17.12\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e3.50\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eAl\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e5.54\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e1.40\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eFe\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e4.73\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e9.18\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eCaO\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e61.40\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e24.19\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eMgO\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e3.74\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e13.50\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eK\u003csub\u003e2\u003c/sub\u003eO\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e1.33\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e0.36\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eSO\u003csub\u003e3\u003c/sub\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e3.37\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e14.63\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eTiO\u003csub\u003e2\u003c/sub\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e0.26\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e0.07\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eNa\u003csub\u003e2\u003c/sub\u003eO\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e0.16\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e-\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eBaO\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e-\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e13.86\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003ePbO\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e-\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e0.49\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eZnO\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e-\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e0.68\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eLOI\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e2.35\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e18.14\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\u003e \u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec4\" class=\"Section2\"\u003e \u003ch2\u003e2.2 Methods\u003c/h2\u003e \u003cdiv id=\"Sec5\" class=\"Section3\"\u003e \u003ch2\u003e2.2.1 Paste preparation\u003c/h2\u003e \u003cp\u003eBefore preparing paste mixture, LZTs were pretreated to obtain fine tailing powder. Firstly, LZTs were dried thoroughly in oven at 60℃. And then, two different particle size powders were prepared by being ground for 15 and 30 min in a SM φ500\u0026times;500 type ball mill, separately. The particle size distributions of two type powders and OPC are shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003e. The particle size distributions of two type LZTs powders both showed bimodal curves, while cement showed monomodal curve. The median particle diameters (D\u003csub\u003e50\u003c/sub\u003e) value of OPC and ground LZTs were 47.10 \u0026micro;m, 16.90 \u0026micro;m and 8.49 \u0026micro;m, respectively. It was found that two different particle size powders were finer than cement and this tendency was more obvious with the prolongation of grinding time.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eAs a kind of solid waste produced by metal mining operations, LZTs contain certain heavy metals such as Pb and Zn. Therefore, leaching tests of LZTs were conducted according to toxicity characteristic leaching procedure (TCLP) (US \u003cspan citationid=\"CR30\" class=\"CitationRef\"\u003e1992\u003c/span\u003e), and then the leaching concentration of heavy metal was determined by ICP test. The results are shown in Table\u0026nbsp;\u003cspan refid=\"Tab2\" class=\"InternalRef\"\u003e2\u003c/span\u003e.\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\u003eThe leaching concentration of heavy metals in LZTs\u003c/p\u003e \u003c/div\u003e \u003c/caption\u003e \u003ccolgroup cols=\"4\"\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c4\" colnum=\"4\"\u003e\u003c/div\u003e \u003cthead\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c1\" morerows=\"1\" rowspan=\"2\"\u003e \u003cp\u003eHeavy metals\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colspan=\"2\" nameend=\"c3\" namest=\"c2\"\u003e \u003cp\u003eLeaching concentration (mg/L)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c4\" morerows=\"1\" rowspan=\"2\"\u003e \u003cp\u003eLimits (mg/L)\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c2\"\u003e \u003cp\u003e15 min\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c3\"\u003e \u003cp\u003e30 min\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003c/thead\u003e \u003ctbody\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003ePb\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e19.40\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e26.00\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e5.00\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eZn\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e63.00\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e76.50\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e100.00\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\u003eThe two different particle size tailing powders were added into the mixture paste at the dosage of 0%, 10%, 20%, 30%, and 50%. The w/b ratio was 0.42 to obtain good workability. The mix proportions of the specimens were shown in Table\u0026nbsp;\u003cspan refid=\"Tab3\" class=\"InternalRef\"\u003e3\u003c/span\u003e. Each mixture paste was poured into the mold with size of 40 mm\u0026times;40 mm\u0026times;40 mm. All the samples were demolded after 24 hours, and then the cubes were curing at a constant temperature and humidity curing room where the relative temperature was 20\u0026thinsp;\u0026plusmn;\u0026thinsp;1\u0026deg;C and the relative humidity was not less than 95%.\u003c/p\u003e \u003cp\u003e \u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab3\" border=\"1\"\u003e \u003ccaption language=\"En\"\u003e \u003cdiv class=\"CaptionNumber\"\u003eTable 3\u003c/div\u003e \u003cdiv class=\"CaptionContent\"\u003e \u003cp\u003eThe mix proportions of each sample\u003c/p\u003e \u003c/div\u003e \u003c/caption\u003e \u003ccolgroup cols=\"4\"\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c4\" colnum=\"4\"\u003e\u003c/div\u003e \u003cthead\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c1\"\u003e \u003cp\u003eMixture name\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c2\"\u003e \u003cp\u003eGrinding time of LZTs (min)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c3\"\u003e \u003cp\u003eLZTs (% by mass)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c4\"\u003e \u003cp\u003eW/B\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003c/thead\u003e \u003ctbody\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eControl\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e0\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\" morerows=\"8\" rowspan=\"9\"\u003e \u003cp\u003e0.42\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eT15-10\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\" morerows=\"3\" rowspan=\"4\"\u003e \u003cp\u003e15\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e10\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eT15-20\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e20\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eT15-30\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e30\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eT15-50\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e50\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eT30-10\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\" morerows=\"3\" rowspan=\"4\"\u003e \u003cp\u003e30\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e10\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eT30-20\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e20\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eT30-30\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e30\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eT30-50\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e50\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 \u003cdiv id=\"Sec6\" class=\"Section3\"\u003e \u003ch2\u003e2.2.2 Analysis methods\u003c/h2\u003e \u003cp\u003eThe compressive strength of all samples was determined at the curing time of 3, 7, and 28 days. After that, small particles and pieces were selected from the inside of the broken samples. These particles and pieces were soaked in absolute ethanol to ensure that the hydration was terminated. Pieces were used for scanning electron microscope with energy dispersive spectrometry (SEM-EDS) test. Small particles were further crushed. Part of the particles below 9.5 mm were used for toxicity leaching test. The rest samples stopped hydration were ground to pass a 200-mesh standard sieve and dried to constant weight at 60 ℃. These powders were used for X-ray Diffraction (XRD) test, Fourier Transform Infrared Spectroscopy (FTIR) and thermogravimetric and differential scanning calorimetry (TG-DSC) test.\u003c/p\u003e \u003cp\u003eFor each specific experiment, SEM-EDS was performed by a focused ion beam scanning electron microscope (Auriga, Zeiss, Germany). XRD was conducted by D8 VENTURE (Bruker, Germany) with Cu Kα radiation at 40 kV and 40 mA and the 2θ value ranging from 5\u0026deg; to 80\u0026deg;. FTIR was recorded using a TENSOR II spectrometer (Bruker, Germany) across the range from 4000\u0026thinsp;\u0026minus;\u0026thinsp;400 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e. The scanning rate was 10\u0026deg;/min. TG-DSC was measured with the temperature range from 30 to 1000℃ by using TA449F3 thermal analysis system (NETZSCH, Germany). The leaching concentration of heavy metal was tested after TCLP by using Shimadzu Multitype ICP Emission Spectrometera (ICP-OES, ICPE-9820, Japan).\u003c/p\u003e \u003c/div\u003e \u003c/div\u003e"},{"header":"3. Results And Discussion","content":"\u003cdiv id=\"Sec8\" class=\"Section2\"\u003e \u003ch2\u003e3.1 Compressive strength\u003c/h2\u003e \u003cp\u003eThe compressive strength development of samples at a certain curing time is shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003e.\u003c/p\u003e \u003cp\u003eThe dosage of LZTs affected the compressive strength. The 10% LZTs content of different particle sizes slightly weakened the compressive strength of samples in the early or later stage. At the age of 3 days, compared to the control sample, the compressive strength of T15-10 and T30-10 samples decreased by 7.76% and 2.84%, and it was only decreased by 1.90% and 2.06% at 28 days. However, with the increase of LZTs content, the compressive strength decreased significantly. At the age of 3 days, the compressive strength of T15-50 and T30-50 decreased to 12.56 MPa and 14.23 MPa, respectively. The compressive strength of T30-50 even decreased by 70.90% at 28 days. Therefore, the addition of LZTs reduced the compressive strength of mixtures regardless of the difference in the particle size of the tailings or the extension of curing time.\u003c/p\u003e \u003cp\u003eWith the same LZTs content, the 3 days compressive strength of T15-30 decreased to 25.51 MPa, and this was lower than that of T30-30 (26.49 MPa), while the 28 days compressive strength of T15-30 decreased to 36.49 MPa, and this was higher than that of T30-30 (34.08 MPa). This difference also existed in other samples. It could be seen that the early compressive strength increased as the grinding time increased from 15 min to 30 min. Conversely, longer grinding time hindered the development of later compressive strength.\u003c/p\u003e \u003cp\u003eBased on the above analysis, the substitute content of LZT should not exceed 10% in blended cement, and it is beneficial to the development of later compressive strength when the grinding time of LZT is 15min.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec9\" class=\"Section2\"\u003e \u003ch2\u003e3.2 Leaching tests\u003c/h2\u003e \u003cp\u003eTable\u0026nbsp;\u003cspan refid=\"Tab2\" class=\"InternalRef\"\u003e2\u003c/span\u003e showed that the heavy metal leaching concentration of LZTs exceeded the standard limits, indicating that LZTs was harmful to environmental. In order to evaluate the environmental safety of blended cement containing LZTs, toxicity leaching test was carried out when samples cured for 28 days. The leaching concentration of heavy metal lead and zinc was compared with the national standard. The results are shown in Table\u0026nbsp;\u003cspan refid=\"Tab4\" class=\"InternalRef\"\u003e4\u003c/span\u003e. Overall, the leaching concentration of Pb and Zn was far below the standard limits. The leaching concentration of Pb was 0 for all samples, indicating that the composite had a strong solidification effect on Pb. This was primarily attributed to physical adsorption of C-S-H gel for its microporous structure and high surface area (Niu et al. \u003cspan citationid=\"CR19\" class=\"CitationRef\"\u003e2018\u003c/span\u003e). Furthermore, Pb was encapsuled physically due to high density of C-S-H gel with the extension of curing age (Wang et al. \u003cspan citationid=\"CR33\" class=\"CitationRef\"\u003e2018b\u003c/span\u003e).\u003c/p\u003e \u003cp\u003eThe solidification of Zn was attributed to physical adsorption and encapsulation by C-S-H gel, and there also formed double hydroxides CaZn\u003csub\u003e2\u003c/sub\u003e(OH)\u003csub\u003e6\u003c/sub\u003e\u0026middot;2H\u003csub\u003e2\u003c/sub\u003eO) in alkaline environment (Cao et al. \u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e2019\u003c/span\u003e). From Table\u0026nbsp;\u003cspan refid=\"Tab4\" class=\"InternalRef\"\u003e4\u003c/span\u003e, the leaching concentration of Zn increased slightly with the increase of LZTs content. On one hand, the decreasing proportion of cement led to the decrease of these hydration products, and the solidification ability of Zn was weakened correspondingly. On the other hand, the leaching concentration of heavy metals was closely related to the content of LZTs. Moreover, the leaching concentration of Zn was significantly higher than that of Pb from the original LZTs, and hydration products generally had a threshold for the solidification of heavy metals. Therefore, excessive heavy metals could still be leached. Even so, the highest leaching concentration of Zn was only 0.56 mg/L, which was far below the standard limits.\u003c/p\u003e \u003cp\u003eWith the extension of grinding time, the leaching concentration of Zn also increased gradually. Because prolonging grinding time would result in an increasing leaching concentration of Zn. Moreover, hydration products also decreased with the addition of LZTs grinding for 30 min. This could be seen in the next analysis of chemically bound water directly. Even so, the composites containing LZTs still achieved high efficiency solidification of heavy metals and it ensured that LZTs was used in a harmless way as a supplementary cementitious material.\u003c/p\u003e \u003cp\u003e \u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab4\" border=\"1\"\u003e \u003ccaption language=\"En\"\u003e \u003cdiv class=\"CaptionNumber\"\u003eTable 4\u003c/div\u003e \u003cdiv class=\"CaptionContent\"\u003e \u003cp\u003eLeaching concentration of heavy metals of blended cement (mg/L)\u003c/p\u003e \u003c/div\u003e \u003c/caption\u003e \u003ccolgroup cols=\"7\"\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 \u003cdiv align=\"left\" class=\"colspec\" colname=\"c7\" colnum=\"7\"\u003e\u003c/div\u003e \u003cthead\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c1\"\u003e \u003cp\u003eSamples\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c2\"\u003e \u003cp\u003eT15-10\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c3\"\u003e \u003cp\u003eT15-20\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c4\"\u003e \u003cp\u003eT15-30\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c5\"\u003e \u003cp\u003eT15-40\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c6\"\u003e \u003cp\u003eT15-50\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c7\"\u003e \u003cp\u003eLimits\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003c/thead\u003e \u003ctbody\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003ePb\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e0\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e0\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e0\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e0\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e0\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e \u003cp\u003e5\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eZn\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e0\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e0\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e0\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e0.01\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e0.01\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e \u003cp\u003e100\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eSamples\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eT30-10\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003eT30-20\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003eT30-30\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003eT30-40\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003eT30-50\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e \u003cp\u003eLimits\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003ePb\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e0\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e0\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e0\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e0\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e0\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e \u003cp\u003e5\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eZn\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e0.01\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e0.01\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e0.06\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e0.28\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e0.56\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e \u003cp\u003e100\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 \u003cdiv id=\"Sec10\" class=\"Section2\"\u003e \u003ch2\u003e3.3 XRD analysis\u003c/h2\u003e \u003cp\u003eAs shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003e, hydration products in the mixtures were affected by the addition of LZTs. The XRD pattern of control sample mainly included the diffraction peaks of Ca(OH)\u003csub\u003e2\u003c/sub\u003e, ettringite, clinker dicalcium silicate and tricalcium silicate. The diffraction peaks of dolomite, barite and pyrite appeared after the incorporation of LZTs and began to intensify with the increase of LZTs content. With the increase of LZTs content, the characteristic peak of Ca(OH)\u003csub\u003e2\u003c/sub\u003e became weak gradually. The intensity decrease was very obvious when the LZTs content was higher than 20%. The decrease of cement content led to the reduction of Ca(OH)\u003csub\u003e2\u003c/sub\u003e content. Besides, the consumption by the pozzolanic reaction of tailings could be another reason for the decrease of Ca(OH)\u003csub\u003e2\u003c/sub\u003e content (Liu et al. \u003cspan citationid=\"CR17\" class=\"CitationRef\"\u003e2020\u003c/span\u003e).\u003c/p\u003e \u003cp\u003eIn addition, the characteristic peak (at 2θ\u0026thinsp;=\u0026thinsp;9.09\u0026deg;) of ettringite increased with the addition of LZTs especially at the curing age of 3 days. Under the same LZTs content, grinding time for 30 min promoted the formation of ettringite more efficiently which could be beneficial to the improvement of compressive strength [17]. It is consistent with the results in Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003e that compressive strength was improved when the grinding time of LZTs increased from 15 min to 30 min at 3 days. Similarly, at the later hydration stage (28 days), when the LZTs content was 50%, the ettringite diffraction peak intensity of T30-50 was significantly stronger than that of T15-50. This also resulted in higher compressive strength of T30-50 than T15-50.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec11\" class=\"Section2\"\u003e \u003ch2\u003e3.4 FTIR analysis\u003c/h2\u003e \u003cp\u003eThe FTIR absorption spectra of raw LZTs, pure cement paste, and blended cement paste are shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003e.\u003c/p\u003e \u003cp\u003ePure cement paste and blended cement paste performed similar FTIR spectra at the curing age of 28 days. Based on the related literatures, band at 3642 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e was due to the stretching vibration of Ca-OH in Ca(OH)\u003csub\u003e2\u003c/sub\u003e (Liu et al. \u003cspan citationid=\"CR18\" class=\"CitationRef\"\u003e2018b\u003c/span\u003e); bands at around 3433 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e and 1658 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e were related to the stretching vibration and bending vibration of Al-OH in ettringite, respectively (Jose et al. \u003cspan citationid=\"CR13\" class=\"CitationRef\"\u003e2020\u003c/span\u003e, Ylmen et al. \u003cspan citationid=\"CR38\" class=\"CitationRef\"\u003e2009\u003c/span\u003e); band at 1124 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e was assigned to the stretching vibration of S-O by the formation of ettringite (Jose et al. \u003cspan citationid=\"CR13\" class=\"CitationRef\"\u003e2020\u003c/span\u003e, Qian et al. \u003cspan citationid=\"CR23\" class=\"CitationRef\"\u003e2008\u003c/span\u003e); band at 974 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e was due to Si\u0026ndash;O stretching vibration which indicated that C-S-H gels were formed in these samples (Ren et al. \u003cspan citationid=\"CR25\" class=\"CitationRef\"\u003e2017\u003c/span\u003e, Ylmen et al. \u003cspan citationid=\"CR38\" class=\"CitationRef\"\u003e2009\u003c/span\u003e, Zak \u0026amp;Deja \u003cspan citationid=\"CR39\" class=\"CitationRef\"\u003e2015\u003c/span\u003e). In addition, the bands at 1473 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e and 1416 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e could be associated with the asymmetric stretching vibration of C-O in CO\u003csub\u003e3\u003c/sub\u003e\u003csup\u003e2\u0026minus;\u003c/sup\u003e due to the carbonization in the air during the curing process (Duran et al. \u003cspan citationid=\"CR6\" class=\"CitationRef\"\u003e2016\u003c/span\u003e, Xia et al. \u003cspan citationid=\"CR34\" class=\"CitationRef\"\u003e2019\u003c/span\u003e, Yildirim Ozen \u0026amp;Moroydor Derun \u003cspan citationid=\"CR37\" class=\"CitationRef\"\u003e2019\u003c/span\u003e, Zhang et al. \u003cspan citationid=\"CR40\" class=\"CitationRef\"\u003e2020\u003c/span\u003e).\u003c/p\u003e \u003cp\u003eAccording to the changes of vibration peaks from above FTIR spectra, it could be concluded that the disappearance of absorption bands confirmed the dissolution of minerals in LZTs. For raw LZTs, characteristic FTIR absorption bands displayed at 2522 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e, 1814 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e were attributed to the vibrations of dolomite (Igisu et al. \u003cspan citationid=\"CR10\" class=\"CitationRef\"\u003e2014\u003c/span\u003e, Ji et al. \u003cspan citationid=\"CR12\" class=\"CitationRef\"\u003e2009\u003c/span\u003e); band at about 422 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e was connected with S-S stretching vibrations presented in pyrite (Ye et al. \u003cspan citationid=\"CR36\" class=\"CitationRef\"\u003e2017\u003c/span\u003e). These Bands disappeared in blended cement which represented the destruction of dolomite and pyrite. In addition, the weakness of other vibration bands also supported this conclusion. Based on this analysis, heavy metals were likely to be released from LZTs like Pb and Zn. In terms of hydration products, the vibration bands position of hydration products of blended cement had no shift compared with pure cement, which also indicated that LZTs behaved low activity. The difference was that the vibration band at 974 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e of C-S-H gel became broad with the increase of tailings content. Because the presence of heavy metals affected the polymerization of C-S-H gel (Xia et al. \u003cspan citationid=\"CR34\" class=\"CitationRef\"\u003e2019\u003c/span\u003e, Zak \u0026amp;Deja \u003cspan citationid=\"CR39\" class=\"CitationRef\"\u003e2015\u003c/span\u003e). Accordingly, heavy metals were solidified in C-S-H gel, which was consistent with later EDS analysis.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec12\" class=\"Section2\"\u003e \u003ch2\u003e3.5 Chemically bound water analysis\u003c/h2\u003e \u003cp\u003eThe chemically bound water content of the blended cement was obtained from the weight loss between 60\u0026deg;C and 1000\u0026deg;C (Park \u0026amp;Choi \u003cspan citationid=\"CR21\" class=\"CitationRef\"\u003e2021\u003c/span\u003e). Grinding hardened cement paste was passed a 200-mesh standard sieve, and then, the powder was dried at 60 ℃ to make sure it reached a constant weight, after that, the crucible containing powder sample was placed in a muffle furnace and burned at 1000 ℃ for 3 hours. The chemically bound water content was calculated according to Eq.\u0026nbsp;(1) and Eq.\u0026nbsp;(2):\u003cdiv id=\"Equa\" class=\"Equation\"\u003e\u003cdiv format=\"TEX\" class=\"mathdisplay\" id=\"FileID_Equa\" name=\"EquationSource\"\u003e\n$$\\begin{array}{c}{W}_{B}=\\frac{{m}_{1}-{m}_{2}}{{m}_{2}}-\\frac{{W}_{T,C}}{1-{W}_{T,C}}\\#\\left(1\\right)\\end{array}$$\u003c/div\u003e\u003c/div\u003e\u003cdiv id=\"Equb\" class=\"Equation\"\u003e\u003cdiv format=\"TEX\" class=\"mathdisplay\" id=\"FileID_Equb\" name=\"EquationSource\"\u003e\n$$\\begin{array}{c}{W}_{T,C}={f}_{T}\\times {LOI}_{T}+{f}_{C}\\times {LOI}_{C}\\#\\left(2\\right)\\end{array}$$\u003c/div\u003e\u003c/div\u003e\u003c/p\u003e \u003cp\u003eWhere \u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\({W}_{B}\\)\u003c/span\u003e\u003c/span\u003e is the chemically bound water content; \u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\({m}_{1}\\)\u003c/span\u003e\u003c/span\u003e and \u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\({m}_{2}\\)\u003c/span\u003e\u003c/span\u003e are the sample weight before and after burning at 1000 ℃; \u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\({f}_{T}\\)\u003c/span\u003e\u003c/span\u003e and \u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\({f}_{C}\\)\u003c/span\u003e\u003c/span\u003e are the mass fractions of LZTs and cement, respectively; \u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\({LOI}_{T}\\)\u003c/span\u003e\u003c/span\u003e and \u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\({LOI}_{C}\\)\u003c/span\u003e\u003c/span\u003e are the loss on ignition of LZTs and cement, respectively.\u003c/p\u003e \u003cp\u003eChemically bound water refers to non-evaporable water in the hydration products. The content of chemically bound water represents the total hydration products quantity and it reflects the hydration degree of composite cementitious system (Liao et al. \u003cspan citationid=\"CR15\" class=\"CitationRef\"\u003e2020\u003c/span\u003e, Sun et al. \u003cspan citationid=\"CR28\" class=\"CitationRef\"\u003e2020\u003c/span\u003e). From Fig.\u0026nbsp;\u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e6\u003c/span\u003e, as the curing age increased from 3 days to 28 days, the amount of chemically bound water in each sample increased significantly. Because the hydration of the composite system was more sufficient with the extension of curing age. With the incorporation of LZTs, the chemically bond water content decresed correspondingly at any curing age. The reason was that cement was the main source of hydration products in the composite system. When the replacement ratio of LZTs increased, the cement content decreased, resulting in a decrease of hydration products as well as lower chemically bond water than pure cement paste. This was also an important reason for the decrease of compressive strength. Besides, the grinding time also caused the difference in the amount of chemically bound water. The chemically bond water of samples were higher when LZTs ground for 30 min at early curing age (3 days). But the chemically bond water decreased with the extension of LZTs grinding time at 28 days.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec13\" class=\"Section2\"\u003e \u003ch2\u003e3.6 TG-DSC analysis\u003c/h2\u003e \u003cp\u003eThe TG-DSC curve of each sample is shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig7\" class=\"InternalRef\"\u003e7\u003c/span\u003e. According to these curves, it could be found that all these curves behaved similar characteristics described as follows. The endothermic peak between 400 ℃ and 500 ℃ was caused by the dehydration of Ca(OH)\u003csub\u003e2\u003c/sub\u003e. The endothermic peak between 700 ℃ and 800 ℃ was mainly due to the dehydration of CaCO\u003csub\u003e3\u003c/sub\u003e which was a product due to the carbonization of Ca(OH)\u003csub\u003e2\u003c/sub\u003e in control samples. But in addition to carbonized products, this part of weight loss also included the decomposition of carbonate in dolomite when LZTs were added.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eAs an important hydration product of cement, the content of Ca(OH)\u003csub\u003e2\u003c/sub\u003e can indirectly evaluate the degree of hydration. The content of Ca(OH)\u003csub\u003e2\u003c/sub\u003e is obtained by the weight loss between 400 ℃ and 500 ℃ according to the TG curves, and the decomposition reaction of Ca(OH)\u003csub\u003e2\u003c/sub\u003e is as follows:\u003c/p\u003e \u003cp\u003eCa(OH)\u003csub\u003e2\u003c/sub\u003e\u0026rarr;CaO\u0026thinsp;+\u0026thinsp;H\u003csub\u003e2\u003c/sub\u003eO\u003c/p\u003e \u003cp\u003eThe content of Ca(OH)\u003csub\u003e2\u003c/sub\u003e is calculated by Eq.\u0026nbsp;(3) and the results are shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig8\" class=\"InternalRef\"\u003e8\u003c/span\u003e.\u003cdiv id=\"Equc\" class=\"Equation\"\u003e\u003cdiv format=\"TEX\" class=\"mathdisplay\" id=\"FileID_Equc\" name=\"EquationSource\"\u003e\n$$\\begin{array}{c}{W}_{CH}=\\frac{74}{18}{WL}_{H}\\#\\left(3\\right)\\end{array}$$\u003c/div\u003e\u003c/div\u003e\u003c/p\u003e \u003cp\u003eWherein, \u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\({W}_{CH}\\)\u003c/span\u003e\u003c/span\u003e is the content of Ca(OH)\u003csub\u003e2\u003c/sub\u003e and \u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\({WL}_{H}\\)\u003c/span\u003e\u003c/span\u003e is the weight loss between 400 ℃ and 500 ℃.\u003c/p\u003e \u003cp\u003eFrom Fig.\u0026nbsp;\u003cspan refid=\"Fig8\" class=\"InternalRef\"\u003e8\u003c/span\u003e, the content of Ca(OH)\u003csub\u003e2\u003c/sub\u003e decreased with the addition of LZTs at the curing age of 3 days and 28 days except sample T30-10. The main reason was that the LZTs replaced a considerable part of cement, resulting in the decrease of Ca(OH)\u003csub\u003e2\u003c/sub\u003e. In the high pH value during cement hydration process, the heavy metal released from LZTs could co-precipitate with Ca(OH)\u003csub\u003e2\u003c/sub\u003e as double hydroxides like CaZn\u003csub\u003e2\u003c/sub\u003e(OH)\u003csub\u003e6\u003c/sub\u003e\u0026middot;2H\u003csub\u003e2\u003c/sub\u003eO easily, which also lead to the decrease of Ca(OH)\u003csub\u003e2\u003c/sub\u003e (Chen et al. \u003cspan citationid=\"CR3\" class=\"CitationRef\"\u003e2007\u003c/span\u003e).\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec14\" class=\"Section2\"\u003e \u003ch2\u003e3.7 SEM-EDS analysis\u003c/h2\u003e \u003cp\u003eThe microstructure is beneficial to the analysis of hydration products types and distribution in hardened paste, and it is closely related to the compressive strength development. The SEM-EDS photographs of pure cement paste and blended cement paste containing LZTs are shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig9\" class=\"InternalRef\"\u003e9\u003c/span\u003e.\u003c/p\u003e \u003cp\u003eIn pure cement paste, a large amount of fibriform and spherical C-S-H gel grew radially at the curing time of 3 days. These C-S-H gel formed the basic network structure. The lamelliform Ca(OH)\u003csub\u003e2\u003c/sub\u003e were obviously stacked and distributed in layers. In addition, there were needle-like crystals ettringite interspersed in the C-S-H gel.\u003c/p\u003e \u003cp\u003eFigure\u0026nbsp;\u003cspan refid=\"Fig9\" class=\"InternalRef\"\u003e9\u003c/span\u003e (b) and (c) were the SEM photographs of blended cement paste at the curing time of 3 days. The total hydration products were significantly reduced in these two samples. Tailing particles scattered at the interface of hydration products or wrapped in the network structure of the gel. There were more ettringite crystals with the addition of LZTs compared with Fig.\u0026nbsp;\u003cspan refid=\"Fig9\" class=\"InternalRef\"\u003e9\u003c/span\u003e (a). These crystals filled the gaps and pores in the C-S-H gel, which made positive contribution to the compressive strength (Dong et al. \u003cspan citationid=\"CR5\" class=\"CitationRef\"\u003e2019\u003c/span\u003e), and this is consistent with the XRD analysis results. Even so, the addition of LZTs not only reduced total hydration products, but also brought more pores, and these factors resulted in the samples exhibiting lower compressive strength.\u003c/p\u003e \u003cp\u003eFigure\u0026nbsp;\u003cspan refid=\"Fig9\" class=\"InternalRef\"\u003e9\u003c/span\u003e (d) shows the photograph of pure cement paste at the curing time of 28 days. With the extension of curing age, the continuous growing gel established contact each other which made paste denser. While in the samples containing LZTs corresponding to Fig.\u0026nbsp;\u003cspan refid=\"Fig9\" class=\"InternalRef\"\u003e9\u003c/span\u003e (f) and (h), although hydration products increased compared with early stage, a part of tailing particles were still exposed on the surface of hydration products. Moreover, there was no obvious change on the surface of these tailing particles, which indicated that in the later hydration period, the pozzolanic effect of tailings was still weak. This led to fragile connection between tailings and hydration products and reduction in compressive strength.\u003c/p\u003e \u003cp\u003eIn order to explore the solidification behavior of heavy metals in blended cement, energy-dispersive X-ray diffraction (EDS) analyses were conducted to determine the elemental compositions of hydration products.\u003c/p\u003e \u003cp\u003eFrom the results of EDS at spot 1, the Ca/Si ratio of C-S-H gel in pure cement paste was about 0.93, and no heavy metal elements were detected. As for samples containing LZTs, the Ca/Si ratio increased to 2.12 and 1.72 at spot 2 and spot 3, respectively. The higher Ca/Si ratio was probably due to the increasing dissolved content of Ca\u003csup\u003e2+\u003c/sup\u003e and the relatively weak dissolution rate of Si\u003csup\u003e4+\u003c/sup\u003e (Liu et al. \u003cspan citationid=\"CR17\" class=\"CitationRef\"\u003e2020\u003c/span\u003e). Moreover, there existed visible peaks of Pb and Zn in elemental distributions of EDS at both spot 2 and spot 3. This indicated that heavy metals were absorbed by C-S-H gel. Obviously, heavy metals hardly leached duo to the dense network structure and high specific surface area of C-S-H gel (Qian et al. \u003cspan citationid=\"CR23\" class=\"CitationRef\"\u003e2008\u003c/span\u003e). In addition, due to the existence of competition mechanism between different kinds of heavy metals (Cao et al. \u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e2019\u003c/span\u003e), Pb was more easily absorbed by C-S-H gel than Zn. It could be seen from EDS results that the content of Pb at spot 2 and spot 3 was higher than that of Zn, which also caused higher concentration of Zn than that of Pb in the leaching tests.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003c/div\u003e"},{"header":"4. Conclusions","content":"\u003cp\u003eIn this study, lead-zinc tailings with different grinding time were used as an alternative admixture to prepare blended cement. The hydration properties and environmental safety of blended cement containing lead-zinc tailings were investigated. Based on the analysis of various aspects, the main conclusions are as follows:\u003c/p\u003e \u003cp\u003e \u003col\u003e \u003cspan\u003e \u003cli\u003e \u003cp\u003eThe addition of LZTs reduced the compressive strength of blended cement. The substitute content of LZT should not exceed 10% in blended cement, and it is beneficial to the development of later compressive strength when the grinding time of LZT is 15min.\u003c/p\u003e \u003c/li\u003e \u003c/span\u003e \u003cspan\u003e \u003cli\u003e \u003cp\u003eThe leaching concentration of Pb and Zn was far below the standard limits. And the leaching tests indicated that the S/S technology is feasible to using LZTs as a supplementary cementitious material in a harmless way.\u003c/p\u003e \u003c/li\u003e \u003c/span\u003e \u003cspan\u003e \u003cli\u003e \u003cp\u003eAccording to the analysis of XRD, chemically bound water tests, TG-DSC and SEM, the degree of hydration of blended cement decreased with the addition of LZTs. The content of Ca(OH)\u003csub\u003e2\u003c/sub\u003e also reduced due to the decreasing proportion of cement. Less hydration products and more pores resulted in the blended cement exhibiting lower compressive strength.\u003c/p\u003e \u003c/li\u003e \u003c/span\u003e \u003cspan\u003e \u003cli\u003e \u003cp\u003eFTIR and EDS results indicated that the hydration products C-S-H gel had a good stabilization/solidification effect on heavy metals due to its physical adsorption and encapsulation.\u003c/p\u003e \u003c/li\u003e \u003c/span\u003e \u003c/ol\u003e \u003c/p\u003e"},{"header":"Declarations","content":"\u003ch2\u003eEthical Approval\u003c/h2\u003e\n\u003cp\u003eThe manuscript has not been submitted to more than one journal for simultaneous consideration.\u003c/p\u003e\n\u003cp\u003eThe submitted work is original and has not been published elsewhere in any form or language (partially or in full).\u003c/p\u003e\n\u003ch2\u003eConsent to Participate\u003c/h2\u003e\n\u003cp\u003eAll authors consent to participate in the manuscript.\u003c/p\u003e\n\u003ch2\u003eConsent to Publish\u003c/h2\u003e\n\u003cp\u003eAll authors consent to publish the manuscript.\u003c/p\u003e\n\u003ch2\u003eAuthors Contributions\u003c/h2\u003e\n\u003cp\u003eAll authors contributed to the study conception and design. Material preparation, data collection and analysis were performed by Zhongtao Luo, Yuandong Mu, Xiaohai Liu. The first draft of the manuscript was written by Changbo Tang, and all authors commented on previous versions of the manuscript. All authors read and approved the final manuscript.\u003c/p\u003e\n\u003ch2\u003eFunding\u003c/h2\u003e\n\u003cp\u003eThis work was supported by the National Natural Science Foundation of China (52074245).\u003c/p\u003e\n\u003ch2\u003eCompeting Interests\u003c/h2\u003e\n\u003cp\u003eThe authors have no relevant financial or non-financial interests to disclose.\u003c/p\u003e\n\u003ch2\u003eAvailability of data and materials\u003c/h2\u003e\n\u003cp\u003eNo dataset was generated or analyzed during this study.\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\u003cli\u003e\u003cspan\u003eBehera SK, Ghosh CN, Mishra DP, Singh P, Mishra K, Buragohain J, Mandal PK (2020) : Strength development and microstructural investigation of lead-zinc mill tailings based paste backfill with fly ash as alternative binder.Cement and Concrete Composites109\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eCao X, Wang W, Ma R, Sun S, Lin J (2019) Solidification/stabilization of Pb\u003csup\u003e2+\u003c/sup\u003e and Zn\u003csup\u003e2+\u003c/sup\u003ein the sludge incineration residue-based magnesium potassium phosphate cement: Physical and chemical mechanisms and competition between coexisting ions. 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Constr Build Mater 202:396\u0026ndash;405\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eYlmen R, Jaglid U, Steenari BM, Panas I (2009) Early hydration and setting of Portland cement monitored by IR, SEM and Vicat techniques. Cem Concrete Res 39:433\u0026ndash;439\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eZak R, Deja J (2015) Spectroscopy study of Zn, Cd, Pb and Cr ions immobilization on C-S-H phase. Spectrochim Acta A Mol Biomol Spectrosc 134:614\u0026ndash;620\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eZhang P, Muhammad F, Yu L, Xia M, Lin H, Huang X, Jiao B, Shiau Y, Li D (2020) : Self-cementation solidification of heavy metals in lead-zinc smelting slag through alkali-activated materials.Constr Build Mater249\u003c/span\u003e\u003c/li\u003e\u003c/ol\u003e"}],"fulltextSource":"","fullText":"","funders":[],"hasAdminPriorityOnWorkflow":false,"hasManuscriptDocX":true,"hasOptedInToPreprint":true,"hasPassedJournalQc":"","hasAnyPriority":false,"hideJournal":true,"highlight":"","institution":"","isAcceptedByJournal":false,"isAuthorSuppliedPdf":false,"isDeskRejected":"","isHiddenFromSearch":false,"isInQc":false,"isInWorkflow":false,"isPdf":false,"isPdfUpToDate":true,"isWithdrawnOrRetracted":false,"journal":{"display":true,"email":"[email protected]","identity":"researchsquare","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":true,"externalIdentity":"","sideBox":"","snPcode":"","submissionUrl":"/submission","title":"Research Square","twitterHandle":"researchsquare","acdcEnabled":true,"dfaEnabled":false,"editorialSystem":"","reportingPortfolio":"","inReviewEnabled":false,"inReviewRevisionsEnabled":true},"keywords":"lead-zinc tailings, blended cement, mechanical property, stabilization/solidification, heavy metal, leaching concentration","lastPublishedDoi":"10.21203/rs.3.rs-1571072/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-1571072/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003cp\u003eDue to the increasing output and toxicity of heavy metals, the pollution problems of lead-zinc tailings (LZTs) need to be solved urgently. This paper investigated the properties and heavy metal stabilization/solidification of blended cement containing different replacement ratios of ground LZTs. The compressive strength, hydration products, chemically bound water content and microstructure of specimens were analyzed by XRD, FTIR, TG-DSC and SEM tests. The results showed that the addition of LZTs reduced the compressive strength of blended cement. 10% cement replacement by LZTs can be considered as the optimum for blended cement uses. With the increase of LZTs dosage, Ca(OH)\u003csub\u003e2\u003c/sub\u003e content was significantly reduced and the formation of ettringite was promoted. Leaching tests revealed that the leaching concentration of Pb and Zn was much lower than threshold limit. EDS analysis indicated that hydration products (primarily C-S-H gel) played an important role in the stabilization/solidification of heavy metals by means of physical adsorption and encapsulation. This research provides a guidance for the resource utilization of LZTs.\u003c/p\u003e","manuscriptTitle":"Recycle of lead-zinc tailings in blended cement: mechanical property and stabilization/solidification of heavy metals","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2022-05-26 15:19:25","doi":"10.21203/rs.3.rs-1571072/v1","editorialEvents":[{"type":"communityComments","content":0}],"status":"published","journal":{"display":true,"email":"[email protected]","identity":"researchsquare","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":true,"externalIdentity":"","sideBox":"","snPcode":"","submissionUrl":"/submission","title":"Research Square","twitterHandle":"researchsquare","acdcEnabled":true,"dfaEnabled":false,"editorialSystem":"","reportingPortfolio":"","inReviewEnabled":false,"inReviewRevisionsEnabled":true}}],"origin":"","ownerIdentity":"968b7e7a-2d7e-4a91-a9cd-a4c160592272","owner":[],"postedDate":"May 26th, 2022","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"posted","subjectAreas":[],"tags":[],"updatedAt":"2022-09-29T12:09:38+00:00","versionOfRecord":[],"versionCreatedAt":"2022-05-26 15:19:25","video":"","vorDoi":"","vorDoiUrl":"","workflowStages":[]},"version":"v1","identity":"rs-1571072","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-1571072","identity":"rs-1571072","version":["v1"]},"buildId":"-HB7Z8yhvgn0wM9Nzuekk","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}