Separation of arsenopyrite/loellingite and pyrite through bio-flotation by selective attachment of Leptospirillum ferrooxidans

Abstract

The use of bacteria and their metabolites in lieu of chemicals in sulfide ore beneficiation holds promise for lessening the environmental damage caused by the minerals processing. In this study, the attachment of Leptospirillum ferrooxidans (L. ferrooxidans) to arsenopyrite/loellingite and pyrite was investigated through scanning electron microscopy (SEM). The effects of selective attachment, bacterial growth conditions, and extracellular polymeric substances (EPS) were investigated through bio-flotation. X-ray photoelectron spectroscopy (XPS) was utilised to determine the existence of surface species aiding in the separation. The results show L. ferrooxidans exhibits selective attachment to pyrite between 2 h and 72 h exposure via an indirect contact mechanism. Separation of pyrite from arsenopyrite/loellingite was achieved by exposing the minerals for 8 h with an L. ferrooxidans culture grown on HH media in the absence of a PIPX collector, for 10 h with an L. ferrooxidans culture grown on arsenopyrite in the absence of a PIPX collector, and for 10 h with an L. ferrooxidans culture grown on HH media in the presence of a PIPX collector. The results produced 52.2, 74.1, and 66.4 % recovery of pyrite, respectively. However, EPS supernatant extracted from L. ferrooxidans grown on pyrite, conditioned for 10 h in the presence of a PIPX collector, provided the best separation efficiency through the selective depression of arsenopyrite, resulting in 92.9 % pyrite recovery. Hydrophilic complex carbon structures, along with more arsenic oxides and a large amount of attached water, selectively attach to arsenopyrite exposed to EPS within 10 h, thereby depressing its floatability and ensuring a successful separation with a PIPX collector.