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A B S T R A C TIn this study, Acidianus spp., a thermophilic archae which can oxidize sulphide minerals was used toproduce ferric sulphate solutions from pyrite. The ferric sulphate solutions were aged through a forcedhydrolysis process at different pH conditions to yield a variety of iron oxide and basic sulphateprecipitates which were subsequently characterized by X-ray diffractometer (XRD), scanning electronmicroscope (SEM) and Branauer?Emmett?Teller (BET) analysis. The results showed that potassiumjarosite was formed as the main phase when ageing was done under acidic conditions. Various other ironoxides and oxyhydroxides were precipitated when ageing was done under neutral to basic pHconditions. For example, maghemite was precipitated as the main phase at a pH of 6?7, and magnetitewas the main phase from a pH of 7?9. The spherical globular aggregates of magnetite nanoparticlesformed were of high purity and had a surface area of 20.77 m2/g. Hematite nanoparticles were thenproduced via an oxidative transformation of the precursor magnetite nanoparticles at 600 8C. Sincevarious precipitates were formed under different pH conditions, this knowledge can be used to controlthe solubility of the ferric ion in bioleaching and other industrial systems where iron removal isproblematic. 2013 The Korean Society of Industrial and Engineering Chemistry. Published by Elsevier B.V. All rightsreserved