Decomposition mechanism of pentlandite during electrochemical bio-oxidation process.

Bioleaching has been applied to the extraction of Ni from sulphide ores, and several pilot heap leaching projects have been established. Electrochemical measurements were carried out to investigate the pentlandite decomposition mechanism using a powder micro-electrode with and without the presence of Acidithiobacillus ferrooxidans on the powder electrode surface. At a low potential of -0.2V vs SCE the pentlandite was transformed to an intermediate phase such as Fe(4.5-y)Ni(4.5-x)S(8-z) when Fe and Ni ions were released from the mineral lattice. Changing the potential from -0.2 to 0.2V resulted in the formation of unstable violarite and FeNi2S4 together with the formation of elemental S on the mineral surface. At higher potentials the unstable intermediate phases were completely decomposed and at 0.7 V the released ferrous ions were oxidised to ferric ions. The presence of Acidithiobacillus ferrooxidans resulted in an increase in the oxidation peak current and a negative shift in the initial peak potential. The bacteria also contributed to the removal of S from the mineral surface.
Bioleaching has been applied to the extraction of Ni from sulphide ores, and several pilot heap leaching projects have been established. Electrochemical measurements were carried out to investigate the pentlandite decomposition mechanism using a powder micro-electrode with and without the presence of Acidithiobacillus ferrooxidans on the powder electrode surface. At a low potential of -0.2V vs SCE the pentlandite was transformed to an intermediate phase such as Fe(4.5-y)Ni(4.5-x)S(8-z) when Fe and Ni ions were released from the mineral lattice. Changing the potential from -0.2 to 0.2V resulted in the formation of unstable violarite and FeNi2S4 together with the formation of elemental S on the mineral surface. At higher potentials the unstable intermediate phases were completely decomposed and at 0.7 V the released ferrous ions were oxidised to ferric ions. The presence of Acidithiobacillus ferrooxidans resulted in an increase in the oxidation peak current and a negative shift in the initial peak potential. The bacteria also contributed to the removal of S from the mineral surface.