Surface alteration of realgar by Acidithiobacillus ferrooxidans in bioleaching systems

Abstract:

[Objective] Surface alteration of realgar by Acidithiobacillus ferrooxidans BY-3 were investigated in this work. The fundamental knowledge derived from this study should provide an experimental and theoretical foundation for further investigation into the biotechnological applications in realgar extraction. [Methods] The bioleaching experiment was divided into four groups (each containing 100 mL of 9K medium without ferrous iron and 0.500 g of realgar): the first group had no additions; the second group had 4.469 g of FeSO4·7H2O added; the third group had 0.100 g of sulfur added; and the fourth group had 4.469 g of FeSO4·7H2O and 0.100 g of sulfur added. A. ferrooxidans BY-3 were used throughout the bioleaching experiments. Before and after bioleaching on the surface alteration and chemical properties of realgar were characterized by scanning electron microscopy (SEM), energy-dispersive spectroscopy (EDS), X-ray diffraction (XRD), Raman spectroscopy and inductively coupled plasma atomic emission spectroscope (ICP-AES). [Results] All of bioleaching systems shown that A. ferrooxidans BY-3 cells were attached to the surface of the realgar particles. The results suggested that A. ferrooxidans BY-3 cells must be essentially attached so that the direct action occurs. Bioleaching systems in the presence of ferrous iron indicated that surface alteration of realgar was discernible change, whereas bioleaching systems with sulfur was the other way round. Compared to the other three bioleaching systems, there was a higher ratio of As/S by A. ferrooxidans in the medium with ferrous iron as the only substrate. In addition, the mineral composition found in the solid residues after bioleaching comprised jarosite, sulfur, hematite, gothite and magnetit, whereas As2O3 and pararealgar were not observed. [Conclusion] A. ferrooxidans has plays an important role in the alteration of realgar. The effect of ferrous irons could enhance the alteration of realgar by A. ferrooxidans BY-3, while sulfur plays a negative role in the bioleaching of realgar. This study shown that bioleaching technology can effectively solve the problems which oxidation and photochemistry of realgar due to the traditional preparation and the storage of realgar.