Integration of cascaded aeration and neutralization for the treatment of acid mine drainage: Insights into the formation of jarosite

Abstract Acid mine drainage (AMD) treatment has become a major environmental issue confronting the global mining industry. For treating AMD economically and efficiently, a novel AMD passive treatment system consisting of cascaded aeration based biomineralization process driven by Acidithiobacillus ferrooxidans (A. ferrooxidans) LX5 followed by lime neutralization was developed. Compositions and structures of precipitates were measured through a scanning electron microscope equipped with an energy-dispersive X-ray spectrometry (SEM-EDS) and X-ray powder diffraction (XRD). Results showed that the biogenic Fe-minerals, with 1–1.5 μm diameter and 17.5 m2/g specific surface area, belonged to jarosite expressed as KFe3(SO4)2(OH)6 with Fe/S molar ratios between 1.61 and 1.68. The density and Fe2+ bio-oxidation rate of A. ferrooxidans LX5 immobilized on the surface of jarosite (namely immobilized cells) were approximately 8.3 × 108 cells/g and 7.3 mmol L−1 h−1, which were approximately 10 and 2.2 times higher than those of cultivating A. ferrooxidans LX5 solution used as the control (namely suspension cells). The constructed water-dropping system could supply sufficient oxygen for the Fe2+ bio-oxidation. The initial Fe2+ in the AMD was completely oxidized into Fe3+ and 41.8% of total Fe was removed during biomineralization. In addition, it was found that 34% of Zn2+, 21% of Cd2+, 42.7% of Cr3+, and 23.8% of Cu2+ were removed by co-precipitation or adsorption to jarosite simultaneously. With this novel treatment system, the amounts of lime addition required for AMD neutralization and toxic solid waste production were drastically decreased by about 70 wt% and 81.3 wt%, respectively, in comparison to the control (without biomineralization). These results show water-dropping aeration and A. ferrooxidans LX5 play a significant role in the Fe2+ bio-oxidation and removal of metal ions, and the integration of cascaded aeration and neutralization is a possibility for cost-effective treatment of highly acid and toxic metal-loaded AMD.