Decomposition mechanism of pentlandite during electrochemical bio-oxidation process

Electrochemical measurements were carried out to elucidate decomposition mechanism of pentlandite using modified powder microelectrode with Acidithiobacillus ferrooxidans attached or without on the mineral powder surface. Cyclic voltammetry (CV) results show that at a low potential of about −0.2 V (vs SCE), the pentlandite was transformed to an intermediated phase like Fe4.5-yNi4.5-xS8-z when Fe and Ni ions were evacuated from mineral lattice; when the potential was changed from −0.2 V to 0.2 V, the unstable violarite (Fe3Ni3S4) and FeNi2S4 were formed which was accompanied by element sulfur formed on the mineral surface; when the potential increased over 0.2 V, the unstable intermediated phase decomposed entirely; at a higher potential of 0.7 V, the evacuated ferrous ion was oxidized to ferric ion. The presence of Acidithiobacillus ferrooxidans made the oxidation peak current increase with initial peak potential negatively moving, and the bacteria also contributed to the sulfur removing from mineral surface, which was demonstrated by the reduction characteristic at potential ranging from −0.75 to −0.5 V. Leaching experiments and electrochemical results show that the solution acidity increasing when pH<2 may impede the oxidation process slightly.