Speciation and thermodynamic properties of zinc in sulfur-rich hydrothermal fluids: Insights from ab initio molecular dynamics simulations and X-ray absorption spectroscopy
Speciation and thermodynamic properties of zinc in sulfur-rich hydrothermal fluids: Insights from ab initio molecular dynamics simulations and X-ray absorption spectroscopy
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DOI：
10.1016/j.gca.2016.01.031
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发表时间：
2016-04
影响因子：
5
通讯作者：
Y. Mei;B. Etschmann;Weihua Liu;D. Sherman;D. Testemale;J. Brugger
中科院分区：
文献类型：
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作者：
Y. Mei;B. Etschmann;Weihua Liu;D. Sherman;D. Testemale;J. Brugger
氯和硫是成矿流体中参与金属络合作用的主要元素。Zn（II）-Cl络合物的性质和热力学性质已经通过先前的实验和理论研究进行了研究，并且现在已经在高温（600 °C）下得到了很好的建立。相比之下，在含硫流体中二硫化物络合物对锌形态的作用仍然知之甚少，更好地了解Zn（II）-HS络合作用对于模拟岩浆和变质流体中锌的迁移以及优化硫化矿的湿法冶金加工是必要的。我们进行了初始分子动力学（MD）模拟来计算Zn（II）-HS络合物的形态从环境到热液-岩浆条件（25-600 °C，高达2000 bar）。这些理论计算通过在200-500 °C和600-1000 bar下对富HS−溶液中的Zn（II）进行X射线吸收光谱（XAS）测量得到补充。从头算MD模拟和原位XAS数据预测的形态和几何性质非常吻合。当从室温加热到250 °C时，富HS−溶液中的Zn（II）形态显示出从六重八面体六水合配合物[Zn（H2O）6]2+到四重四面体[Zn（HS）n（H2O）4−n]2− n配合物（n= 1-4）的转变。从头算MD模拟还显示，在温度> 250 °C时，三重三角平面[Zn（HS）3]−配合物变得越来越稳定，在富硫溶液中占主导地位;相反，氯配合物在25-500 °C时显示四面体几何形状，而三角平面ZnCl 3 −在温度> 500 °C时占主导地位。采用热力学积分方法计算了Zn（II）-HS配合物在200、350和600 °C下的稳定常数。从这项研究中产生的稳定常数预测，锌可以通过HS−在高温下在还原，中性到碱性溶液中运输，而氯化锌络合物在酸性流体中占主导地位。
Chlorine and sulfur are the main elements involved in the complexing of metals in ore-forming fluids. The nature and thermodynamic properties of the Zn(II)–Cl complexes have been investigated by previous experimental and theoretical studies and are now well established up to high temperatures (600 °C). In contrast, the role of bisulfide complexes for zinc speciation in sulfur-bearing fluids remains poorly known, and a better understanding of Zn(II)–HS complexation is required for modeling zinc transport in magmatic and metamorphic fluids and for optimizing the hydrometallurgical processing of sulfide ores.We have conductedab initiomolecular dynamics (MD) simulations to calculate the speciation of Zn(II)–HS complexes from ambient to hydrothermal-magmatic conditions (25–600 °C, up to 2000 bar). These theoretical calculations were complemented by X-ray absorption spectroscopy (XAS) measurements of Zn(II) in HS−-rich solutions at 200–500 °C and 600–1000 bar. The speciation and geometrical properties predicted by theab initioMD simulations and thein situXAS data are in excellent agreement. Upon heating from room temperature to 250 °C, Zn(II) speciation in HS−-rich solutions shows a transition from the sixfold octahedral hexaaquo complex [Zn(H2O)6]2+to fourfold tetrahedral [Zn(HS)n(H2O)4−n]2−ncomplexes (n= 1–4).Ab initioMD simulations also show that at temperatures > 250 °C, the threefold trigonal-planar [Zn(HS)3]−complex becomes increasingly stable, and predominates in S-rich solutions; in contrast, chloro-complexes display a tetrahedral geometry at 25–500 °C, while trigonal planar ZnCl3−predominates at temperatures > 500 °C. The stability constants of Zn(II)–HS complexes were calculated by thermodynamic integration of constrainedab initioMD simulations at 200, 350 and 600 °C. The stability constants generated from this study predict that zinc can be transported by HS−at high temperature in reduced, neutral to alkaline solutions, while Zn chloride complexes dominate in acidic fluids.