OXIDATION OF PYRITE IN NITRIC ACID SOLUTIONS: RELATION TO TREATMENT OF REFRACTORY GOLD ORES

摘要

Nitric acid processes for the pre-oxidation of gold-bearing sulfides have been the focus of considerable development efforts in the last ten years. Pyritic sulfur oxidizes independently to S~0 and to SO_4~(2-). The formation of elemental sulfur must be avoided because the sulfur can complicate the pre-oxidation and subsequent cyanidation steps. Oxidation of pyrite in nitric acid solutions has been studied by linear potential sweep voltammetry and the results compared with those of leach tests. Voltammetry showed the proportion of S~0 and SO_4~(2-) formed to depend on the potential, varying from about 70 % at 0.82 V, to negligible at 1.5 V vs. SHE, but to be independent of temperature in the range 26 - 80℃. Leach tests also showed sulfur formation to be independent of temperature. Good correlation was obtained between pyrite oxidation rates derived from voltammetry and those obtained in the laboratory reactor. Thus, voltammetry can be used to predict leaching characteristics.