Analysis of the development and effects of a combined treatment system for acid mine drainage via bio-oxidation and carbonate rock neutralization

Abstract

Acid mine drainage (AMD) has a low pH and a high concentration of sulfates and heavy metals and its untreated discharge contributes to environmental pollution. Traditional bio-oxidation is less effective in removing Fe³⁺ and few studies have reported passive treatment using biological oxidation. Here, based on the biofilm formation on the surface of an elastic filler by iron-oxidizing bacteria, we proposed a novel treatment system for AMD involving a combination of bio-oxidation and addition of carbonate rocks prior to the neutralization phase. The results showed that the Fe²⁺ oxidation efficiency and total iron (TFe) removal efficiency reached 40.18–55.00% and 5.86–17.39% (during Fe²⁺ oxidation without carbonate rocks) as well as 39.09–52.64% and 25.09–47.33% (during Fe²⁺ oxidation with carbonate rocks), respectively. The corresponding values for the control group (single carbonate neutralization) were 24.22–34.73% and 12.31–30.14%, respectively. The X-ray diffractometry and scanning electron microscopy results showed that carbonate rock addition in the oxidation section regulated the acidic environment and provided favorable conditions for schwertmannite formation. Additionally, schwertmannite provided ideal attachment conditions for bacteria. High-throughput sequencing revealed that Acidithiobacillus and Leptospirillum dominated the biological oxidation stage, accounting for more than 75% of bacteria. This demonstrated that Acidithiobacillus and Leptospirillum could co-exist in passive processing systems as the dominating flora. The results can be used as a basic data reference for the development of a process and method for the combined treatment of AMD by biological oxidation and carbonate rock neutralization.