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Electrochemistry of pyrite and other sulfides in acid oxygen pressure leaching Bailey, Leonard Keith

Abstract

The oxygen pressure leaching of pyrite has been studied in sulfuric and perchloric acid using an oxygen-18 tracer technique. The results are consistent with an entirely electrochemical mechanism. The leaching potential of a pyrite pulp has been measured as 0.699V SHET*(110°C, 1M H2S04, 176 psi 02) and potentiostatic experiments at that potential have yielded the same reaction product ratios as observed in oxygen pressure leaching. The ratio of sulfate to elemental sulfur produced during pyrite leaching has been found to be a function of the leaching mixed potential. The yield of sulfate is increased with increasing potential until all the mineral sulfur is converted to the sulfate form at potentials above 1.0V. A mechanistic model of pyrite leaching has been advanced, which includes the electrochemical formation of a protective sulfur film as its basis. The theory has been supported by polarization studies in combination with Eh-pH diagrams. Chalcopyrite leaching has been studied using the same 0¹⁸ technique. Again the results are consistent with an electrochemical mechanism. The ratio of the sulfate to elemental sulfur in the reaction products has been observed to increase with higher oxygen pressures. The mixed potential of leaching is also increased at higher pressure indicating that the same type of mechanism observed in the pyrite work is operational for chalcopyrite. Molybdenite leaching has also been discussed in terms of the electrochemical model derived for pyrite with good results, and the mechanism therefore appears to have applications in many, if not most, sulfide systems.

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