The Biological Leaching of Heavy Metals in High-Sulfur Coal Gangue: Environmental Impact Factors and Microbial Succession

Abstract

High-sulfur coal gangue (HSCG) contains high concentrations of polluting pyrite (FeS₂). However, studies on the microbial leaching of pollutants from HSCG and the interactions between microorganisms and mineral components are still limited. In this study, leaching experiments on HSCG was conducted in a mixed microbial community after being domesticated and enriched, to identify the optimal conditions for microbial leaching. The leaching effect of microorganisms on the surface of HSCG particles was evaluated, the functional microorganisms and genes within the microbial community were identified, and the metabolic pathways were also investigated. Results indicated that biological leaching effect reached the optimal with the mineral particle size of 0.15~10 mm at an aeration rate of 0.5 L/min for 3~5 days at 25~30°C. Microorganisms grew on the surface of coal gangue, causing  noticeable bacterial corrosion traces. A significant number of pollutants, including Fe, Al, Mn, and S, were removed from the coal gangue. The leaching residues primarily contained quartz, with minor pyrite and anatase titanium dioxide. Dominant microorganisms included Burkholderiales sp. GJ-E10, Acidithiobacillus ferriphilus, and Acidiferrobacter thiooxydans, which mainly facilitated iron and sulfur oxidation. The abundance of functional genes associated with sulfur, nitrogen, and iron metabolism increased, while functional genes related to carbon fixation generally showed a decreasing trend. In the biological leaching system, the microbial metabolic pathways primarily contributed to enhancing microbial resistance. The study was expected to provide insights into the biological leaching mechanisms of mixed microbial communities through analysis of the microbial leaching conditions for heavy metals in HSCG.

Keywords: High-sulfur coal gangue, Heavy metals, Biological leaching, Optimal conditions, Functional genes, Metabolic pathways