Gold Dissolution in Dry Salt Melts in the Presence of SiO 2 as a Function of Р(O 2 )

The solubility of gold was measured in dry NaCl salt melt at 860°С in closed systems with SiO 2 (silica glass). The reactions do not occur in a closed system without oxidizer. Reaction of SiO 2 with salt in the presence of an oxidizer (KClO 4 ) results in the formation of water-soluble sodium silicates (a mixture of meta-, ortho-, and pyrosilicates). Gold mobilization by a salt melt is limited by the diffusion of Na in SiO 2 . In a closed system with the addition of a strong oxidizer (dry KClO 4 salt), the solubility of gold increase with increasing amount of KClO 4 and the saturation level is estimated to be ~3 wt % Au. For ampoule configurations used in our experiments, 5.5 g of gold dissolved per 1 g of KClO 4 . Only cheap, non-toxic reagents were used in our model experiments on gold dissolution in a salt melt, which did not require elevated pressures. The solubility of 30 g Au per 1 kg NaCl will eliminate geochemical problems associated with the compact leaching of gold ores using cyanide.