Solubility of Native Gold in H-O-S Fluids at 100-400 deg C and High H_2S Content

摘要

Reaction of MgS, water, and air in sealed gold capsules at 100 to 400°C and 0.15 GPa is used to generate an aqueous fluid with very high (20.6 In) H2S content and to remobilize significant quantities of native gold as gold sulfides. A combination of X-ray photoelectron and Auger electron spectroscopy (XPS, AES), analytical scanning-electron microscopy (SEM-EDX), electron-micro- probe analysis (EPMA), and calculated ~olutioll properties shows that the gold sulfides precipitated during quenching and later perforation of the cap~ules repre- sent native gold dissolved as Au(I)-bisulfide under the experimental conditions. The equilibrium con~tant (logK) for the reaction: Au(s) + H2S(aq) + HS- = Au(HSh- + I/2H2(g) ranges from -3.96 :t: 0.40 at 115°C to -1.06 :t: 0.32 at 400°C; it i~ in good agreement with literature values for 25°C and 300-350°C, and varies inversely with ab~olute temperature 71-~IP1/(2.303R) = -2644 :t: 33K; r = 1.00). The maximum solubility of native gold in this study (29.4 g/kg at 200°C) i~ signifi- cantly greater than that from published studie~ on Au(I)-bisulfides and may stimulate interest in developing bisulfides as gold-complexing agents in gold extraction technology.