Formation of passivation film during pyrrhotite bioleached by pure L. ferriphilum and mixed culture of L. ferriphilum and A. caldus

Abstract

Bioleaching and electrochemical experiments were conducted to evaluate pyrrhotite dissolution in the presence of pure L. ferriphilum and mixed culture of L. ferriphilum and A. caldus. The results indicate that the pyrrhotite oxidation behavior is the preferential dissolution of iron accompanied with the massive formation of sulfur in the presence of L. ferriphilum, which significantly hinders the leaching efficiency. Comparatively, the leaching rate of pyrrhotite distinctly increases by 68% in the mixed culture of L. ferriphilum and A. caldus at the 3rd day. But, the accumulated ferric ions and high pH value produced by bioleaching process can give rise to the rapid formation of jarosite, which is the primary passivation film blocking continuous iron extraction during bioleaching by the mixed culture. The addition of A. caldus during leaching by L. ferriphilum can accelerate the oxidation rate of pyrrhotite, but not change the electrochemical oxidation mechanisms of pyrrhotite. XRD and SEM/EDS analyses as well as electrochemical study confirm the above conclusions.

Keywords

pyrrhotite / passivation film / bioleaching / moderately thermophilic microorganisms / electrochemistry

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