RECOVERY OF GOLD FROM PYRITE (FeS_2) BY AQUEOUS CHLORINATION I. OXIDATION RATES OF GOLD AND PYRITE IN AQUEOUS CHLORINE SOLUTIONS

摘要

Results are presented of the selective dissolution of gold from iron pyrite (FeS_2), using chlorine (pH < 3) or chloric(I) acid (HOCl, 3 < pH < 7.5) as the oxidant in aqueous chloride media. This could offer an alternative to aerated alkaline cyanide, the industrial use of which is causing increasing environmental concerns. Selective dissolution of gold was predicted thermodynamically to be achievable in the pH range of ca. 3 to 6, below which pyrite would also dissolve, rather than be passivated by Fe(Ⅲ) (hydrous) oxide, and above which gold would be passivated by Au(OH)_3. At pH 2, gold and pyrite dissolution occurred at a significant fraction of their rate limited by Cl_2 (aq) mass transport, and with similar potentials, so that galvanic interaction effects were predicted to be small. The rate of pyrite oxidation decreased fourfold from pH 2 to 4 and by a similar factor from pH 4 to 6. The ratios of gold to pyrite oxidation rates increased from 4.4 to 8 to 29 on increasing the pH from 2 to 4 to 6. The relative oxidant consumptions also changed dramatically as the pH was raised, with 47 % of the oxidant dissolving gold at pH 2 and 92 % at pH 6, but higher HOCl concentrations at pH 6 were required to achieve the same gold dissolution rates as at pH 4.