Influence of solution pH on the properties of biogenic jarosite produced from ferrous ion bio-oxidation in a bioreactor

Precipitation process of ferric ions from bio-oxidation of ferrous ions is influenced by pH and solution chemistry. Accumulation of iron precipitate may reduce extraction efficiency in bioleach operations. Firstly, this study investigates the impact of pH on the properties of iron precipitate generated in a continuous stirred bioreactor at three pH levels (1.7, 1.9, and 2.2). Characterization of precipitates was performed and identified predominantly as potassium jarosite using Brunauer-Emmett-Teller (BET), thermogravimetric analysis (TGA), X-ray diffraction (XRD), Fourier transform infrared (FTIR), X-ray photoelectron spectroscopy (XPS), and scanning electron microscope/energy dispersive spectroscopy (SEM/EDS). Results showed properties of the formed jarosites altered in response to the influent solution pH, with a major effect on the surface area. Secondly, results showed that pseudo-order-kinetic model can accurately describe the sorption performance of the biogenic jarosite with respect to copper uptake. Monomolecular adsorption capacities (qm) at 303 K were 17.12 and 13.32 mg/g for jarosite generated at pH 2.2 and 1.7, respectively. The sorption thermodynamic data showed the process was endothermic and nonspontaneous. Activation energy in this investigation was calculated to be 21.01 and 23.39 kJ/mol for jarosite produced at pH 2.2 and 1.7, respectively, implying that the rate-limiting step is chemically controlled for both adsorption processes. Results of this study may provide some insights into the management of iron precipitation in biohydrometallurgical processes.