Fe2+ oxidation rate drastically affect the formation and phase of secondary iron hydroxysulfate mineral occurred in acid mine drainage

During the processes of secondary iron hydroxysulfate mineral formation, Fe2+ ion was oxidized by the following three methods: (1) biooxidation treatment by Acidithiobacillus ferrooxidans (A. ferrooxidans); (2) rapid abiotic oxidation of Fe2+ with H2O2 (rapid oxidation treatment); (3) slow abiotic oxidation of Fe2+ with H2O2 (slow oxidation treatment). X-ray diffraction (XRD) patterns, element composition, precipitate weight and total Fe removal efficiency were analyzed. The XRD patterns and element composition of precipitates synthesized through the biooxidation and the slow oxidation treatments well coincide with those of potassium jarosite, while precipitates formed at the initial stage of incubation in the rapid oxidation treatment showed a similar XRD pattern to schwertmannite. With the ongoing incubation, XRD patterns and element composition of the precipitates that occurred in the rapid oxidation treatment were gradually close to those in the biooxidation and the slow oxidation treatments. Due to the inhibition of A. ferrooxidans itself and its extracellular polymeric substances (EPS) in aggregation of precipitates, the amount of precipitates and soluble Fe removal efficiency were lower in the biooxidation treatment than in the slow oxidation treatment. Therefore, it is concluded that Fe2+ oxidation rate can greatly affect the mineral phase of precipitates, and slow oxidation of Fe2+ is helpful in improving jarosite formation.

► Slow oxidation of Fe2+ is helpful in jarosite formation.
► The already-formed schwertmannite can be gradually transformed to jarosite.
► Precipitates formation can be inhibited probably by EPS from A. ferrooxidans.