Dynamic redox potential measurement for determining the ferric leach kinetics of pyrite

• Published in: Minerals engineering Vol. 10; no. 11; pp. 1279 - 1290
• Main Authors: May, N., Ralph, D.E., Hansford, G.S.
• Format: Journal Article
• Language: English
• Published: Oxford Elsevier Ltd 01.11.1997; Elsevier Science
• Subjects: Applied sciences; bioleaching; Exact sciences and technology; Hydrometallurgy; Metals. Metallurgy; Production of metals; Production of non ferrous metals. Process materials; redox reactions; Sulphide ores; Sulphide ores; redox reactions; bioleaching; Iron III; Pyrite; Ore treatment; Lixiviation; Bacterial leaching; Experimental study; Reaction rate; Leaching; Hydrometallurgy; Sulfide ore
• ISSN: 0892-6875; 1872-9444
• DOI: 10.1016/S0892-6875(97)00114-3

The bioleaching of pyrite has been found to occur via an indirect mechansim. Ferric iron leaches the pyrite, and is reduced to ferrous iron. Bacteria such as Thiobacillus ferrooxidans oxidise the ferrous iron to ferric iron, thus maintaining a high redox potential. The effect of the redox potential on the ferric leach rate was investigated by developing an experimental technique where dynamic redox potential measurements were used to study the kinetics of the sub process. The ferric leach rate of pyrite was found to be of the order of 3 × 10 −7 moles pyrite per mole pyrite per second, which is of the same order of magnitude as rates reported for the bioleaching of pyrite over similar ranges of redox potential. The rate decreased as the redox potential decreased, in what appeared to be a Butler-Volmer-like manner. This, along with the observation that there was no significant effect of the total iron concentration, suggested the likelihood of an electrochemical mechanism being operative, with charge transfer at the pyrite surface being rate limiting.