Characterization of nanoprecipitates formed from the forced hydrolysis of bioleach liquors under different pH conditions

In this study, Acidianus spp., a thermophilic archae which can oxidize sulphide minerals was used to produce ferric sulphate solutions from pyrite. The ferric sulphate solutions were aged through a forced hydrolysis process at different pH conditions to yield a variety of iron oxide and basic sulphate precipitates which were subsequently characterized by X-ray diffractometer (XRD), scanning electron microscope (SEM) and Branauer–Emmett–Teller (BET) analysis. The results showed that potassium jarosite was formed as the main phase when ageing was done under acidic conditions. Various other iron oxides and oxyhydroxides were precipitated when ageing was done under neutral to basic pH conditions. For example, maghemite was precipitated as the main phase at a pH of 6–7, and magnetite was the main phase from a pH of 7–9. The spherical globular aggregates of magnetite nanoparticles formed were of high purity and had a surface area of 20.77 m2/g. Hematite nanoparticles were then produced via an oxidative transformation of the precursor magnetite nanoparticles at 600 °C. Since various precipitates were formed under different pH conditions, this knowledge can be used to control the solubility of the ferric ion in bioleaching and other industrial systems where iron removal is problematic.