Nitric acid pressure leaching of limonitic laterite ores: Regeneration of HNO3 and simultaneous synthesis of fibrous CaSO4·2H2O by-products
来源期刊:中南大学学报(英文版)2020年第11期
论文作者:马保中 王成彦 邵爽 王昕 张文娟 陈永强
文章页码:3249 - 3258
Key words:limonitic laterite ores; Ca(NO3)2 solution; HNO3 regeneration; CaSO4·2H2O by-products; solubility
Abstract: An innovative technology, nitric acid pressure leaching of limonitic laterite ores, was proposed by our research team. The HNO3 regeneration is considerable significance for the improvement of the proposed technology and its commercial application, but it has not been systematically investigated. Herein, regenerating HNO3 from Ca(NO3)2 solution with low-cost H2SO4, and simultaneous synthesis of fibrous CaSO4·2H2O by-products were studied. As a theoretical basis, the solubility of CaSO4·2H2O in HNO3 medium is studied. It is concluded that the solubility of CaSO4·2H2O increases with increasing temperature or increasing HNO3 concentration, which has considerable guiding significance for the subsequent experimental research and analysis. Then, the effects of various factors on the residual Ca2+ concentration of filtrate, the regenerated HNO3 concentration and the morphology of synthesized products are investigated using ICP-AES and SEM. And the effect mechanism is also analyzed. The results indicate the regenerated HNO3 concentration reaches 116 g/L with the residual Ca2+ concentration being 9.7 g/L at the optimum conditions. Moreover, fibrous CaSO4·2H2O by-products with high aspect ratios (length, 406.32 μm; diameter, 14.71 μm; aspect ratio, 27.62) can be simultaneously synthesized.
Cite this article as: SHAO Shuang, MA Bao-zhong, WANG Xin, ZHANG Wen-juan, CHEN Yong-qiang, WANG Cheng-yan. Nitric acid pressure leaching of limonitic laterite ores: Regeneration of HNO3 and simultaneous synthesis of fibrous CaSO4·2H2O by-products [J]. Journal of Central South University, 2020, 27(11): 3249-3258. DOI: https://doi.org/10.1007/s11771-020-4463-2.
J. Cent. South Univ. (2020) 27: 3249-3258
DOI: https://doi.org/10.1007/s11771-020-4463-2
SHAO Shuang(邵爽)1, 2, MA Bao-zhong(马保中)1, 2, 3, WANG Xin(王昕)2,
ZHANG Wen-juan(张文娟)1, 2, 3, CHEN Yong-qiang(陈永强)1, 2, 3, WANG Cheng-yan(王成彦)1, 2, 3
1. State Key Laboratory of Advanced Metallurgy, University of Science and Technology Beijing,Beijing 100083, China;
2. School of Metallurgical and Ecological Engineering, University of Science and Technology Beijing,Beijing 100083, China;
3. Beijing Key Laboratory of Green Recycling and Extraction of Metals, Beijing 100083, China
Central South University Press and Springer-Verlag GmbH Germany, part of Springer Nature 2020
Abstract: An innovative technology, nitric acid pressure leaching of limonitic laterite ores, was proposed by our research team. The HNO3 regeneration is considerable significance for the improvement of the proposed technology and its commercial application, but it has not been systematically investigated. Herein, regenerating HNO3 from Ca(NO3)2 solution with low-cost H2SO4, and simultaneous synthesis of fibrous CaSO4·2H2O by-products were studied. As a theoretical basis, the solubility of CaSO4·2H2O in HNO3 medium is studied. It is concluded that the solubility of CaSO4·2H2O increases with increasing temperature or increasing HNO3 concentration, which has considerable guiding significance for the subsequent experimental research and analysis. Then, the effects of various factors on the residual Ca2+ concentration of filtrate, the regenerated HNO3 concentration and the morphology of synthesized products are investigated using ICP-AES and SEM. And the effect mechanism is also analyzed. The results indicate the regenerated HNO3 concentration reaches 116 g/L with the residual Ca2+ concentration being 9.7 g/L at the optimum conditions. Moreover, fibrous CaSO4·2H2O by-products with high aspect ratios (length, 406.32 μm; diameter, 14.71 μm; aspect ratio, 27.62) can be simultaneously synthesized.
Key words: limonitic laterite ores; Ca(NO3)2 solution; HNO3 regeneration; CaSO4·2H2O by-products; solubility
Cite this article as: SHAO Shuang, MA Bao-zhong, WANG Xin, ZHANG Wen-juan, CHEN Yong-qiang, WANG Cheng-yan. Nitric acid pressure leaching of limonitic laterite ores: Regeneration of HNO3 and simultaneous synthesis of fibrous CaSO4·2H2O by-products [J]. Journal of Central South University, 2020, 27(11): 3249-3258. DOI: https://doi.org/10.1007/s11771-020-4463-2.
1 Introduction
At present, high pressure acid leaching and reducing roasting–atmospheric acid leaching are mainly applied to treat limonitic laterite ores [1, 2]. Ni/Co recovery is achieved by precipitation, and chelating ion exchange resins with high selectivity [3]. Nitric acid is a widely used leaching agent with strong oxidizability, which can sufficiently oxidize the divalent iron to hematite while dissolving valuable metals [4, 5]. So, nitric acid was selected and developed to treat limonitic laterite ores by our research team [4, 5]. And a series of laboratory tests and pilot-scale tests were completed and some exciting results were achieved. The technical route of the HNO3 pressure leaching for limonitic laterite ores treatment is shown in Figure 1 [4, 5]. After selective pressure leaching limonitic laterite ores with HNO3, the leach iron residue is separated and applied to iron making. Subsequently, Fe/Al, Ni/Co, and Mg dissolved in the leach liquor are successively precipitated in the form of hydroxides by adding CaO and controlling the pH value. As a result, a large amount of Ca(NO3)2 solution is produced.
Figure 1 A technical route of nitric acid pressure leaching for limonitic laterite ores treatment
Given that HNO3 is usually expensive, regenerating HNO3 from Ca(NO3)2 solution is undoubtedly the key step of the proposed technology commercial application. Herein, a method for regeneration of HNO3 from Ca(NO3)2 solution with low-cost H2SO4 was proposed (marked in Figure 1). Our previous studies [4-6] indicated that HNO3 is easily regenerated by mixing Ca(NO3)2 solution and H2SO4 solution (Eq. (1)), and fibrous calcium sulfate by-products can be simultaneously synthesized. Regeneration of HNO3 with H2SO4 and simultaneous synthesis of fibrous calcium sulfate by-products, will undoubtedly reduce the production cost. However, the effects of reaction conditions on the regenerated HNO3 concentration and the morphology of synthesized calcium sulfate have not been systematically studied.
Ca(NO3)2+H2SO4+2H2O=2HNO3+CaSO4·2H2O(↓) (1)
Calcium sulfate whiskers have been widely applied as reinforcing materials in papermaking and building due to its excellent performance (high strength, non-toxicity, superior workability, good compatibility, etc.) and overwhelming economic advantage [7-15]. The performance of calcium sulfate whiskers is mainly affected by their morphology and size (especially the aspect ratio) [11]. The aspect ratio is one of the most important evaluation criteria of calcium sulfate whiskers [8]. And the calcium sulfate whiskers with high aspect ratio in particular are marketable.
Generally, the synthesis processes of calcium sulfate whiskers include hydrothermal method [16, 17], salt-solution method [18-21] and atmospheric acidification method [22-25]. Calcium sulfate whiskers are synthesized in mixed medium of regenerated HNO3 and residual H2SO4 in this study, which belongs to the scope of atmospheric acidification method. Atmospheric acidification method has milder reaction condition (atmospheric pressure and the temperature of lower than 90 °C) than hydrothermal method and takes less time than salt-solution method [22, 26]. Thus, it costs less and is more efficient. MAO et al [24, 25] prepared calcium sulfate whiskers in aqueous HCl solutions and investigated the effects of metal ions and additives on the morphology and size of products. EL MOUSSAOUITI et al [23] explored the crystallization of calcium sulfate in concentrated H3PO4 solutions. It is noted that there is a paucity of information available on the synthesis of calcium sulfate whiskers in mixed acid medium of HNO3 and H2SO4.
The low sulfur content of regenerated HNO3 used for cyclic leaching will facilitate the production of high-grade leach iron residue. The residual sulfur content in regenerated HNO3 can be indirectly monitored by investigating the residual Ca2+ concentration. So, low residual Ca2+ concentration is an important indicator in regenerated HNO3. The residual Ca2+ concentration is essentially the solubility of calcium sulfate in mixed acid medium. At present, the solubilities of calcium sulfate in H2O and H2SO4 have been widely measured [27, 28], but its solubility in HNO3 medium is rarely conducted. The solubility of calcium sulfate in different media is mainly affected by temperature and solution composition [29–32]. In this study, the solubility measurement of CaSO4·2H2O in HNO3 medium was first carried out to provide a theoretical basis for the subsequent experimental research and analysis. Subsequently, the influences of several factors, such as reaction temperature, solution addition sequence, and dilution volume ratio of H2SO4, on the residual Ca2+ concentration of filtrate, the regenerated HNO3 concentration and the morphology of calcium sulfate whiskers were systematically investigated to determine the optimum conditions. And the effect mechanism was also analyzed.
2 Experimental
2.1 Materials
Analytically grade Ca(NO3)2·4H2O (purity≥ 99.0%), CaSO4·2H2O (purity≥99.0%), H2SO4 (purity, 95.0%-98.0%) and HNO3 (purity, 65.0%- 68.0%) were purchased from Sinopharm Chemical Reagent Co., Ltd. In this study, all chemicals were used directly without any further purification. And deionized water was used to prepare solution.
2.2 Procedures
2.2.1 Solubility measurement
First, HNO3 solutions with predetermined concentrations (50, 100, 150 g/L) were prepared and placed in a thermostatic shaking bath (THZ-82A, Jiangsu Changzhou Ronghua Instrument Manufacture Co., Ltd) with a speed of 200 r/min at corresponding temperatures (30, 50, 70, 80, 90 °C). Then a small amount of CaSO4·2H2O was added to the HNO3 solutions per 12 h until the solid phase was no longer dissolved. The mixed products were then continually shaken for 24 h to ensure that the equilibrium state was achieved. Finally, the samples were placed for 48 h so that the supernatant became clear. Sampling of the supernatant using a glass pipette preheated to the sampling temperature and sampling of the equilibrating solid phase were for further analysis.
2.2.2 HNO3 regeneration and fibrous CaSO4·2H2O by-products synthesis
In a typical synthesis procedure, 100 mL Ca(NO3)2 solution with a Ca2+ concentration of 60 g/L was prepared and added into a beaker. Theoretical amount (calculated according to the molar ratio of SO42- and Ca2+) of H2SO4 solution was diluted through mixing H2SO4 and deionized water with volume ratios of 1:4-1:12 mL/mL and was added into another beaker. The two prepared solutions were first preheated to 15-90 °C, and subsequently one solution was dropwise added into another solution at a rate of 10 mL/min using a constant flow pump. The mixture was treated at a stirring rate of 200 r/min for 30 min. The products were filtered and rinsed with 50 mL deionized water. Finally, solid products were dried at 70 °C in a vacuum oven for 8 h.
2.3 Characterizations
The concentration of residual Ca2+ was analyzed by inductively-coupled plasma–atomic emission spectroscopy (ICP-AES, Optima 5300DV, Perkin Elmer). The concentration of regenerated HNO3 was calculated using the concentration of residual Ca2+ according to Eq. (2). The solid phases were characterized by X-ray powder diffraction (XRD, Rigaku D/MAX-rA diffractometer) using Cu Kα radiation. The morphology of products was characterized by scanning electron microscopy (SEM, HITACHI S-3500 N/INCA Oxford, Japan).
(2)
where c (g/L) is the concentration of regenerated HNO3; c0 (g/L) and c1 (g/L) are the Ca2+ concentrations before and after the reaction, respectively; V0 (L) and V1 (L) are the solution volumes before and after the reaction, respectively; M1 is the relative molecular mass of HNO3; M2 is the relative atomic mass of Ca.
3 Results and discussions
3.1 Solubility of CaSO4·2H2O in HNO3 medium
As a theoretical basis, the solubility of CaSO4·2H2O in HNO3 medium is first studied. In the process of regenerating HNO3 with H2SO4, it is inevitable that a small amount of H2SO4 remains in solution without reaction. Assuming that all of the added H2SO4 (theoretical amount) does not convert to HNO3, the maximum concentration of unreacted H2SO4 is less than 1.5 mol/L. The solubilities of calcium sulfate in H2O and 1.5 mol/L H2SO4 have been measured [27, 28], and they are also analyzed for comparison with the solubility of CaSO4·2H2O in HNO3 medium.
In H2O medium [28], the solubility of CaSO4 first has a slight increase with increasing temperature, and then gradually decreases when the temperature is above 50 °C. In general, the solubility of CaSO4 is very small in H2O medium. In 1.5 mol/L H2SO4 medium [28], the solubility of CaSO4 increases with increasing temperature, and its value is less than 11 g/L CaSO4 (equivalent to 14 g/L CaSO4·2H2O) when the temperature increases to 90 °C. As shown in Figure 2, the solubility of CaSO4·2H2O in HNO3 medium increases with increasing temperature, and the increase is more pronounced when the temperature exceeds 70 °C, especially. Moreover, the solubility of CaSO4·2H2O increases not only with increasing temperature but also with increasing HNO3 concentration. Based on the above discussion, lowering the reaction temperature is preferable to ensure a lower residual Ca2+ concentration when the HNO3 concentration is fixed, which may have considerable guiding significance for the subsequent experimental research and analysis.
Figure 2 Solubility curves of CaSO4·2H2O in HNO3 medium
Through comparing the solubility data between 1.5 mol/L H2SO4 and different concentration HNO3, it clearly indicates that the solubility of CaSO4·2H2O in HNO3 medium is much higher than that in H2SO4 medium. In the studies, at least 60% of H2SO4 can convert to HNO3. Thus, the residual H2SO4 concentration in the solution will actually be less than 0.6 mol/L, which will have a negligible effect on the solubility of CaSO4·2H2O compared with regenerated HNO3. In other words, regenerated HNO3 has much more dominant effect on the solubility of CaSO4·2H2O compared with residual H2SO4 in multi-component acid medium. Consequently, the effect of regenerated HNO3 on CaSO4·2H2O solubility will be emphatically discussed in this article.
It should be ensured that no phase transformation occurs during the solubility measurement. Thus, XRD analysis of the equilibrating solid phase was performed as shown in Figure 3. The XRD results show that all equilibrating solid phases in different HNO3 concentrations at 90 °C are still single-phase CaSO4·2H2O. This indicates that 90 °C has not reached the phase transition temperature of CaSO4·2H2O to CaSO4·0.5H2O, and the equilibrating solid phase is CaSO4·2H2O below 90 °C. In other words, it can be concluded that CaSO4·2H2O is the most stable phase when the temperature is below 90 °C in HNO3 medium.
Figure 3 XRD patterns of equilibrating solid phase at 90 °C
3.2 HNO3 regeneration and fibrous CaSO4·2H2O by-products synthesis
3.2.1 Effect of reaction temperature
According to Figure 2, temperature is a key effect factor for residual Ca2+ concentration. Therefore, under the conditions of adding H2SO4 solution into Ca(NO3)2 solution and 1:4 mL/mL H2SO4 dilution volume ratio, the variations in the residual Ca2+ concentration and regenerated HNO3 concentration with reaction temperature were investigated as shown in Figure 4(a). It is observed the concentration of regenerated HNO3 decreases gradually with increasing reaction temperature, which will lead to a lower solubility of CaSO4·2H2O according to Figure 2. However, the residual Ca2+ concentration remains basically unchanged as the temperature increases from 15 to 50 °C, and then increases obviously when the temperature is over 50 °C. This can be attributed to the fact that temperature has more dominant effect on the solubility of CaSO4·2H2O compared with the regenerated HNO3 concentration.
Figure 4 Effects of parameters on residual Ca2+ concentration and regenerated HNO3 concentration:
Figure 5 shows the morphology of calcium sulfate synthesized at different reaction temperatures under the condition of adding H2SO4 solution into Ca(NO3)2 solution. The calcium sulfate synthesized at 50 °C is composed of tiny particles and irregular sheets. Further increasing temperature to 70 °C, the flaky products decrease obviously and the needle-like products increase significantly. With the increase of reaction temperature, the crystallinity and aspect ratio of calcium sulfate whiskers increase obviously. These findings suggest that reaction temperature has a significant effect on the crystallization of calcium sulfate, which is consistent with the results of obtained by SONG et al [15]. It is noted that the solubility of calcium sulfate increasing results in the supersaturation decreasing. Crystal growth rate is faster than nucleation rate at low supersaturation during crystallization process. This is why the crystal morphology of calcium sulfate becomes better with increasing temperature.
In general, in order to ensure a lower residual Ca2+ concentration and a higher regenerated HNO3 concentration, 50 °C was selected as the optimum reaction temperature under the condition of adding H2SO4 solution into Ca(NO3)2 solution.
The effect of reaction temperature on the residual Ca2+ concentration and regenerated HNO3 concentration is shown in Figure 4(b) under the conditions of adding Ca(NO3)2 solution into H2SO4 solution and 1:4 mL/mL H2SO4 dilution volume ratio. The residual Ca2+ concentration increases obviously with increasing reaction temperature, and the increase is more pronounced when the reaction temperature exceeds 70 °C, which is completely matched with the variation trend of CaSO4·2H2O solubility with temperature (Figure 2). The concentration of regenerated HNO3 drops sharply when the temperature exceeds 50 °C. As shown in Figure 4(b), the concentration of regenerated HNO3 reaches 116 g/L at 50 °C, while only 90 g/L at 80 °C.
Under the condition of adding Ca(NO3)2 solution into H2SO4 solution, the SEM images of calcium sulfate synthesized at different reaction temperatures are shown in Figure 6. It can be observed that the length of calcium sulfate whiskers synthesized at 50 °C reaches to 406.32 μm. Further increasing temperature leads to the synthesis of good crystallinity and high aspect ratios whiskers. And the products with the best crystal morphology and uniform size are synthesized at 80 °C. The viscosity of solution decreases with the increase of temperature, which contributes to the formation of whiskers with uniform size [15]. When the reaction temperature continues increasing to 90 °C, the length of whiskers is obviously shorter than 80 °C. This might be attributed to the vigorous movement of Ca2+ and SO42- in the solution at high temperature. The vigorous movement of ions may interrupt the ordered arrangement of atoms, which is not conducive to the axial growth of crystals.
Figure 5 SEM images of calcium sulfate synthesized at different reaction temperatures (adding H2SO4 solution into Ca(NO3)2 solution):
Figure 6 SEM images of calcium sulfate synthesized at different reaction temperatures (adding Ca(NO3)2 solution to H2SO4 solution):
For comprehensive consideration of the regenerated HNO3 concentration and products morphology, 50 °C was selected as the optimum reaction temperature under the condition of adding Ca(NO3)2 solution into H2SO4 solution.
3.2.2 Effect of solution addition sequence
As shown in Figure 5, the calcium sulfate crystals mainly are platelet-like at 50 °C and good crystallinity whiskers can be synthesized by increasing temperature to 80 °C under the condition of adding H2SO4 solution into Ca(NO3)2 solution. While under the condition of adding Ca(NO3)2 solution into H2SO4 solution (Figure 6), needle-like whiskers have been successfully prepared at 50 °C and the length of calcium sulfate whiskers reaches to 406.32 μm. The above discussions suggest that calcium sulfate whiskers can be synthesized at lower temperature under the condition of adding Ca(NO3)2 solution into H2SO4 solution.
At the identical reaction temperature, a comparison between Figures 5 and 6 clearly shows that the products synthesized under the condition of adding Ca(NO3)2 solution into H2SO4 solution has a fewer flake structure, more uniform morphology, larger aspect ratios and better crystallinity. Obviously, the crystallization of calcium sulfate whiskers can occur in high acid environment under the condition of adding Ca(NO3)2 solution into H2SO4 solution. In the crystallization process, the solubility of CaSO4·2H2O is greater due to the high acid environment and high temperature resulting from the exothermic phenomenon of H2SO4. It can be inferred that the supersaturation is smaller at this time. And lower supersaturation is conducive to crystal growth. In addition, a comparison between Figure 4(a) and Figure 4(b) clearly shows that the solution addition sequence has little effect on the concentration of residual Ca2+ and regenerated HNO3.
Therefore, on the premise that the concentration of regenerated HNO3 is not affected, adding Ca(NO3)2 solution into H2SO4 solution was selected as the optimum solution addition sequence to obtain higher quality calcium sulfate by- products.
3.2.3 Effect of H2SO4 dilution volume ratio
The experiments were carried out by adding Ca(NO3)2 solution into H2SO4 solution at 50 °C, and the effect of H2SO4 dilution volume ratio (1:4-1:12 mL/mL) on the residual Ca2+ concentration and regenerated HNO3 concentration is shown in Figure 4(c). It can be seen from Figure 4(c) that the regenerated HNO3 concentration decreases linearly with increasing the dilution volume ratio of H2SO4, which is caused by a large increase in the solution volume. The residual Ca2+ concentration decreases with increasing the dilution volume ratio of H2SO4. This is partly due to the reduced CaSO4·2H2O solubility in low concentration of regenerated HNO3 solution, and partly due to the increased solution volume. In short, lower H2SO4 dilution volume ratio should be promoted to ensure a higher concentration of regenerated HNO3.
The influence of H2SO4 dilution volume ratio on the morphology of calcium sulfate is shown in Figures 6(a) and Figure 7. Calcium sulfate whiskers can be synthesized at different H2SO4 dilution volume ratios. However, a comparison between Figures 6(a) and Figure 7 clearly showed that the diameter of whiskers becomes wider and the aspect ratio decreases obviously with increasing the dilution volume ratio of H2SO4. Thus, lower H2SO4 dilution volume ratio is more beneficial to the synthesis of whiskers. Hence, 1:4 mL/mL was selected as the optimum dilution volume ratio of H2SO4.
Figure 7 SEM images of calcium sulfate synthesized at different dilution volume ratios of H2SO4:
According to the single-factor experimental results, the optimum conditions for regenerating HNO3 and synthesizing calcium sulfate whiskers are 50 °C, solution addition sequence of adding Ca(NO3)2 solution into H2SO4 solution, H2SO4 dilution volume ratio of 1:4 mL/mL. The morphology of the products synthesized at the optimum conditions is shown in Figure 6(a) and fibrous calcium sulfate (length, 406.32 μm; diameter, 14.71 μm; aspect ratio, 27.62) is synthesized. The corresponding XRD result is shown in Figure 8, which indicates that the synthesized product is CaSO4·2H2O. In summary, HNO3 with a concentration of 116 g/L (the residual Ca2+ being 9.7 g/L) can be regenerated and CaSO4·2H2O whiskers with good crystallinity and high aspect ratios can be efficiently synthesized, simultaneously.
Figure 8 XRD pattern of product synthesized at optimum conditions
It is worth noting that HNO3 can be regenerated and recycled for leaching in this study. Meanwhile, fibrous CaSO4·2H2O by-products can be simultaneously synthesized, and the synthesis process is simple and easy to operate. Through the content of this study, the process of nitric acid pressure leaching limonitic laterite ores is further improved. HNO3 recycling and the synthesis of fibrous CaSO4·2H2O by-products undoubtedly reduce the production cost. These make this technology beneficial to realize commercial application.
4 Conclusions
This study aimed to improve the HNO3 regeneration step in the process of nitric acid pressure leaching of limonitic laterite ores. Conclusions can be drawn as follows:
1) The solubility of CaSO4·2H2O in HNO3 medium increases with increasing temperature or increasing HNO3 concentration.
2) The optimum conditions for the HNO3 regeneration and whiskers synthesis are 50 °C, adding Ca(NO3)2 solution into H2SO4 solution and 1:4 mL/mL H2SO4 dilution volume ratio. Under these conditions, HNO3 with a concentration of 116 g/L (the residual Ca2+ is 9.7 g/L) can be regenerated, and fibrous CaSO4·2H2O by-products with high aspect ratios (length, 406.32 μm; diameter, 14.71 μm; aspect ratio, 27.62) can be simultaneously synthesized.
3) The regenerated HNO3 concentration decreases gradually and the residual Ca2+ concentration increases obviously with increasing reaction temperature. Therefore, low temperature is preferable for the HNO3 regeneration.
Contributors
The overarching research goals were developed by WANG Cheng-yan and MA Bao-zhong. SHAO Shuang performed the experiments and collected the data. WANG Xin and ZHANG Wen-juan analyzed the measured data and the calculated results. The research activity planning and execution were managed by CHEN Yong-qiang. The initial draft of the manuscript was written by SHAO Shuang. MA Bao-zhong and WANG Cheng-yan reviewed and edited the manuscript.
Conflict of interest
SHAO Shuang, MA Bao-zhong, WANG Xin, ZHANG Wen-juan, CHEN Yong-qiang, and WANG Cheng-yan declare that they have no conflict of interest.
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(Edited by YANG Hua)
中文导读
褐铁型红土镍矿硝酸加压浸出:再生HNO3并同步制备CaSO4·2H2O副产物
摘要:HNO3再生对于褐铁型红土镍矿硝酸加压浸出技术的完善和工业应用意义重大。本文采用低成本的H2SO4从Ca(NO3)2溶液中再生HNO3,并同步制备CaSO4·2H2O副产物。作为理论基础,测定了CaSO4·2H2O在HNO3介质中的溶解度。结果表明,CaSO4·2H2O的溶解度随着温度的升高或HNO3浓度的增大而不断增大,这对后续的实验研究和结果分析具有指导意义。借助电感耦合等离子体原子发射光谱分析和扫描电子显微镜等检测手段考察了各因素对滤液残留Ca2+浓度、再生HNO3浓度和产物形貌的影响,并分析了其影响机理。结果表明,在最优条件下,再生HNO3浓度达116 g/L,滤液残留Ca2+浓度为9.7 g/L,同步制备的CaSO4·2H2O副产物具备高纵横比(长406.32 μm;直径14.71 μm;纵横比27.62)。
关键词:褐铁型红土镍矿;Ca(NO3)2溶液;HNO3再生;CaSO4·2H2O副产物;溶解度
Foundation item: Project(2182040) supported by the Beijing Natural Science Foundation, China; Projects(51674026, 51974025, U1802253) supported by the National Natural Science Foundation of China; Project(FRF-TT-19-001) supported by the Fundamental Research Funds for the Central Universities, China
Received date: 2020-02-24; Accepted date: 2020-08-02
Corresponding author: MA Bao-zhong, PhD, Professor; Tel: +86-10-62333170; E-mail: bzhma_ustb@yeah.net; ORCID: https://orcid. org/0000-0003-3907-9097; WANG Cheng-yan, PhD, Professor; Tel: +86-10-62332271; E-mail: chywang@yeah. net; ORCID: https://orcid.org/0000-0003-3982-6208