Recovering iron and sulfate in the form of mineral from acid mine drainage by a bacteria-driven cyclic biomineralization system

Abstract

Acid mine drainage (AMD) is recognized as a challenge encountered by mining industries globally. Cyclic mineralization method, namely Fe2+ oxidation/mineralization–residual Fe3+ reduction–resultant Fe2+ oxidation/mineralization, could precipitate Fe and SO42− present in AMD into iron hydroxysulfate minerals and greatly improve the efficiency of subsequent lime neutralization, but the current Fe0-mediated reduction approach increased the mineralization cycles. This study constructed a bacteria-driven biomineralization system based on the reactions of Acidithiobacillus ferrooxidans-mediated Fe2+ oxidation and Acidiphilium multivorum-controlled Fe3+ reduction, and utilized water-dropping aeration and biofilm technology to satisfy the requirement of practical application. The resultant biofilms showed stable activity for Fe conversion: the efficiency of Fe2+-oxidation, Fe-precipitation, and Fe3+-reduction maintained at 98%, 32%, and 87%, respectively. Dissolved oxygen for Fe-oxidizing bacteria growth was continuously replenished by water-dropping aeration (4.2–7.2 mg/L), and the added organic carbon was mainly metabolized by Fe-reducing bacteria. About 89% Fe and 60% SO42− were precipitated into jarosite mineral after five biomineralization cycles. Fe was removed via forming secondary mineral precipitates, while SO42− was coprecipitated into mineral within the initial three biomineralization cycles, and then mainly precipitated with Ca2+ afterwards. Fe concentration in AMD was proven to directly correlate with subsequent lime neutralization efficiency. Biomineralization for five cycles drastically reduced the amount of required lime and neutralized sludge by 75% and 77%, respectively. The results in this study provided theoretical guidance for practical AMD treatment based on biomineralization technology.