A novel approach for treating acid mine drainage by forming schwertmannite driven by a combination of biooxidation and electroreduction before lime neutralization.

Acid mine drainage (AMD) contains abundant iron, sulfates, and various metal ions, and it causes environmental pollution. The traditional AMD lime neutralization forms a layer of iron hydroxide and gypsum on the surface of the lime particles, preventing continuous reaction and leading to excessive lime addition and neutralized sludge production. In this study, an approach for treating AMD using a cyclic process of biooxidation and electroreduction before lime neutralization was proposed, in which the Fe2+ in AMD was oxidized to Fe3+ and induced to form schwertmannite through Acidithiobacillus ferrooxidans. The remaining Fe3+ was reduced to Fe2+ using an electric field. After three biooxidation and two electroreduction cycles, 98.2% of Fe and 62.4% of SO42- in AMD precipitated as schwertmannite (Fe8O8(OH)5.16(SO4)1.37). The yield of schwertmannite reached 33.98 g/LAMD, with a high specific surface area of 112.59 m2/g. The lime dosage and sludge yield of the treated AMD in the subsequent neutralization stage (pH = 7.00) decreased by 85.0% and 74.5%, respectively, than those of raw AMD. The pilot test results showed that the integrated treatment of biooxidation-electroreduction cyclic mineralization and lime neutralization has practical applications.