A novel approach for treating acid mine drainage through forming schwertmannite driven by a mixed culture of Acidiphilium multivorum and Acidithiobacillus ferrooxidans prior to lime neutralization.

As the predominant treatment approach of acid mine drainage (AMD), lime neutralization often exhibits inefficiencies since the abundance of iron and sulfate in AMD usually form iron hydroxide and gypsum precipitate coatings on the surface of lime. In this study, a novel approach of biomineralization prior to lime neutralization for treating AMD was proposed, in which iron and sulfate were biologically precipitated as schwertmannite through iron biological reduction-oxidation driven by a culture mixed with Acidiphilium multivorum JZ-6 and Acidithiobacillus ferrooxidans LX5. It was found that only five cycles of iron reduction by A. multivorum JZ-6 followed by iron oxidation by A. ferrooxidans LX5 could remove completely iron and nearly 40% of sulfate in AMD, while non-ferrous metals (Al, Mn, Cu, Ni, and Zn) were hardly removed. Consequently, the amounts of lime required and sludge generated in the subsequent lime neutralization process were reduced by 56% and 68%, respectively. As a result, the content of non-ferrous metals in the sludge was increased by 3.2 folds. The level of Al was increased surprisingly to 19% (wt/wt), a level similar to the commercially valuable bauxite. The novel process of biomineralization prior to lime neutralization provides a sustainable way for AMD treatment.