Surface properties of pyrite in the course of bioleaching by pure culture of Acidithiobacillus ferrooxidans and a mixed culture of Acidithiobacillus ferrooxidans and Acidithiobacillus thiooxidans

Both Acidithiobacillus ferrooxidans and Acidithiobacillus thiooxidans attached to pyrite rapidly, reaching the adsorption equilibrium in 20–25 min. Furthermore, the adsorption content of substrate-grown bacteria was larger than that of solution-grown ones. Zeta potential studies revealed that isoelectric points (IEP) of pyrite shifted to lower pH after interacting with bacteria.Iron solubilisation by the mixed culture was faster than that for the A. ferrooxidans. There was no close relation between iron recovery and fineness. Circular, square and elongated etch pits were visible by scanning electron microscopy (SEM). Moreover, jarosite in the leaching of 3%(w/v) pulp density was detected by Fourier transform infrared spectroscopy(FTIR) and X-ray diffraction(XRD), though the pH of the solutions declined to below 1.00. S was not detected in the leaching residues. Furthermore, the contact angles showed there was no S produced. These results point to a thiosulfate mechanism in pyrite bioleaching, where the thiosulfate leads to sulphate without S formation.

Research Highlights
► There is no sulfur detected on the pyrite surface in pyrite bioleaching.
► Circular, square and elongated erosion pits appeared on pyrite surface.
► The mixed culture shows superior to the pure culture in the initial stage.
► Jarosite formed in the solution, even the pH was lower than 1.0.
► Higher fineness does not correspond to higher recovery rate.