Separation of pentlandite and pyrrhotite through bio-flotation by selective attachment of Leptospirillum ferrooxidans

The beneficiation of sulfide ore using bacteria and their metabolites shows promise for reducing the use of chemicals during froth flotation. The role of growth conditions in the efficiency of bio-flotation is required prior to trialling larger scale experiments. In this study, scanning electron microscopy (SEM) was used to investigate the selective attachment of Leptospirillum ferrooxidans, L.f, to pentlandite and pyrrhotite. Bio-flotation tests were used to investigate the impact of bacterial growth conditions on extracellular polymeric substances (EPS) effectiveness as a depressant. The surface speciation resulting from exposure to EPS extracted from Po and PN rich cultures was investigated using X-ray photoelectron spectroscopy (XPS). The results show L.f exhibits selective attachment to pyrrhotite between 2 h and 168 h exposure via both indirect contact and non-contact mechanisms. Separation of pyrrhotite from pentlandite was achieved by exposing the minerals to L.f culture grown on pyrrhotite for 72 h in the absence of a PIPX collector and for 48 h in the presence of a PIPX collector. The results produced 45.2 and 94.4 % recovery of pyrrhotite, respectively. However, EPS supernatant extracted from L.f grown on pentlandite, conditioned for 72 h in the presence of a PIPX collector, provided the best separation efficiency through the selective depression of pentlandite, resulting in 95.8 % pyrrhotite recovery. Within 72 h, pentlandite exposed to EPS has hydrophilic complex carbon structures, significantly high concentrations of chemisorbed, physiosorbed water, and small concentrations of hydrophobic elemental sulfur at the surface. The EPS acts as a depressant decreasing pentlandite’s floatability and ensuring a successful separation with a PIPX collector.