SEM and EDS observations of carrollite bioleaching with a mixed culture of acidophilic bacteria

•Copper and cobalt are brought in solution from pure carrollite during bioleaching.•Copper and cobalt dissolution is accompanied by enrichment in sulphur.•Bacteria of specific genus leave different pitting patterns on carrollite grains.•Bacteria-generated EPS form ferric iron rich spots and develop local reactive sites.•Carrollite dissolution is governed by cooperative bioleaching.

Bioleaching of high purity carrollite minerals with mesophilic bacteria was carried out and monitored by observations in scanning electron microscopy (SEM) and elemental X-ray microanalysis (EDS) to provide evidence of the interaction pattern between carrollite and microorganisms. A bacterial consortium involving three different acidophilic chemolithotrophs was adopted. The evolution of the surface topography, inside alteration effects and elemental composition of the mineral with leaching time was followed. It could be postulated that bacterial adhesion takes place on the mineral surface, resulting in the formation of dissolution pits of various shapes and continues by boring elongated channels deep inside the mineral grains. Enhanced concentration of ferric iron and sulphur could be assumed in vicinity of the zones where mineralized polymer substances are precipitated. It could be inferred that carrollite dissolution is governed by cooperative bioleaching involving oxidation induced by bacteria attached to the surface and ferric iron re-oxidized by planktonic bacteria in suspension.