Stability of AuCl2− from 25 to 1000 °C at Pressures to 5000 bar and Consequences for Hydrothermal Gold Mobilization
Stability of AuCl2− from 25 to 1000 °C at Pressures to 5000 bar and Consequences for Hydrothermal Gold Mobilization
复制标题
AuCl2− 在 5000 bar 压力下从 25 到 1000 °C 的稳定性以及热液金流动的后果
作者：
A. Zotov;N. Kuzmin;V. Reukov;B. Tagirov
金以AuCl 2 −的形式在高温含氯热液中迁移。该配合物的稳定性已被广泛研究，但在300-500 °C的温度范围内，现有的实验数据之间仍然存在相当大的分歧。为了解决这个问题，我们在450 °C和500至1500 bar（1 bar = 105 Pa）的压力下测量了金在HCl/NaCl流体（NaCl浓度为0.1至3 mol·（kg·H2O）−1）中的溶解度。在对比氧化还原条件下使用分批高压釜方法进行实验：在还原实验中，将氢气加入高压釜中，并且在氧化实验中，通过含水SO2/SO 3缓冲液控制氧化还原状态。在还原系统中进行实验后，测量高压釜中的氢气压力。金的溶解度常数，Au（cr）+ HCl°（aq）+ Cl− = AuCl 2 − + 0.5 H2°（aq），对于实验的T-P参数，确定为log Ks° = −4.77 ± 0.07（500 bar）、−5.11 ± 0.08（1000 bar）和−5.43 ± 0.09（1500 bar）。这些数据与文献中25 ~ 1000 °C温度范围内的数值一起拟合为简单方程log Ks° = 4.302 − 7304 <$T（K）−1 − 4.77 <$log d（w）+ 11080 <$（log d（w））<$T（K）−1 − 6.94 × 106 <$（log d（w））T（K）−2，其中d（w）是纯水的密度。该方程可以与用于活度系数的扩展的Debye-Huckel方程一起使用，以计算在压力高达5000巴、流体氯度至少高达30重量%时的金溶解度。讨论了天然含氯流体中金的形态。
Gold is transported in high-temperature chloride-bearing hydrothermal fluids in the form of AuCl2−. The stability of this complex has been extensively studied, but there is still considerable disagreement between available experimental data on the temperature region 300–500 °C. To solve this problem, we measured the solubility of gold in HCl/NaCl fluids (NaCl concentration varied from 0.1 to 3 mol·(kg·H2O)−1) at 450 °C and pressures from 500 to 1500 bar (1 bar = 105 Pa). The experiments were performed using a batch autoclave method at contrasting redox conditions: in reduced experiments hydrogen was added to the autoclave, and in oxidized experiments the redox state was controlled by the aqueous SO2/SO3 buffer. Hydrogen pressure in the autoclaves was measured after the experiments in the reduced system. The gold solubility constant, Au(cr) + HCl°(aq) + Cl− = AuCl2− + 0.5 H2°(aq), was determined for the experimental T-P parameters as log Ks° = −4.77 ± 0.07 (500 bar), −5.11 ± 0.08 (1000 bar), and −5.43 ± 0.09 (1500 bar). These data, together with values from the literature for temperatures from 25 to 1000 °C, were fitted to the simple equation log Ks° = 4.302 − 7304∙T(K)−1 − 4.77∙log d(w) + 11080∙(log d(w))∙T(K)−1 − 6.94 × 106∙(log d(w)) T(K)−2, where d(w) is the pure water density. This equation can be used together with the extended Debye–Huckel equation for activity coefficients to calculate gold solubility at pressures up to 5000 bar at fluid chlorinities at least up to 30 wt %. The speciation of gold in natural chloride-bearing fluids is discussed.