Abstract
The microbially mediated recovery of valuable metals contained in mining waste presents an economical alternative to conventional hydrometallurgical processes. In order to investigate the effect of bacterial adaptation and biological oxidation on bioleaching, the microbially mediated bioleaching of a pyrrhotite sample from mine waste, with indigenous bacteria existing in acid mine drainage, was studied. The indigenous bacteria were sub-cultured repeatedly for iron adaptation, and Acidithiobacillus ferrooxidans was identified as the dominant member of the microbial consortium. The point of zero charge (PZC) of pyrrhotite sampled from mine waste was determined as 3.0. The performance of bioleaching by contact and non-contact biological oxidation was compared by conducting bioleaching under different initial pH (pHini) conditions (2.8 and 3.2). Negatively charged bacteria could be attached onto the pyrrhotite, which has a positive surface charge at lower pHini (2.8) than the PZC (3.0). Bacteria attachment and corrosion pits on the surface of the pyrrhotite residues were observed at pHini of 2.8. Under bacteria-adapted conditions, the leaching concentration of Fe (44.2 mg/L) at pHini of 2.8 was 2.1 times greater than that (21.3 mg/L) at pHini of 3.2. Under non-adapted bacteria conditions, the extent of Fe leaching was not significantly different between the pHini of 2.8 and 3.2. This could be attributed to the fact that the adapted bacteria could more easily attach onto the pyrrhotite surfaces at pHini 2.8, allowing contact biological oxidation during the bioleaching experiments. We demonstrate here that the bioleaching of pyrrhotite could increase Fe recovery through bacterial adaptation and contact biological oxidation.
Highlights
Bioleaching is a technique used to recover valuable metals from sulfide minerals
Ever since it became a known fact that acidophilic bacteria can survive in a strongly acidic environment [1], bioleaching has been widely used for the recovery of valuable metals from slime or low-grade ore minerals and the removal of heavy metals from polluted soils
Various bioleaching experiments characterized by bio-adaptation and bio-oxidation were carried out using a pyrrhotite sample obtained from an abandoned mine and indigenous bacteria (A. ferrooxidans) inhabiting the acid mine drainage in order to enhance the recovery of valuable metal from mine waste
Summary
Bioleaching is a technique used to recover valuable metals from sulfide minerals. Ever since it became a known fact that acidophilic bacteria can survive in a strongly acidic environment [1], bioleaching has been widely used for the recovery of valuable metals from slime or low-grade ore minerals and the removal of heavy metals from polluted soils. Various studies using the bioleaching technique to recover valuable metals (Fe, Cu, Pb, Zn, etc.) from sulfide minerals including chalcopyrite [2], arsenopyrite [3,4], molybdenite [5,6], galena [7,8,9], and sphalerite [9,10] have been reported. Indigenous acidophilic bacteria have been already used for the recovery of Cu, Au, and U in slime [11,12,13]
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