Effects of inoculum sources from different depths and oxygen concentration on bioleaching and microbial community assembly in mine waste dump.

Acid mine drainage (AMD) from mine waste dumps poses a long-term environmental threat. Microbial spatial heterogeneity and functional responses to oxygen concentration within dumps are key factors influencing AMD generation. In this study, column leaching tests were conducted using microbial communities collected from depths of 10.0 m and 27.3 m in a dump. Initial community analysis indicated that the microbial community from the deeper transition zone possessed higher diversity and was dominated by multiple iron-oxidizing bacteria. In contrast, the shallow community structure was relatively simple, mainly composed of a single iron-oxidizing bacterium and iron-reducing bacteria. Heavy metal release was severely inhibited under unaerated and sterile conditions, with leachate pH increasing to 6.3 and 7.3, respectively. Conversely, a strongly oxidizing (i.e., ORP > 550 mV) and acidic environment was maintained by continuous aeration, promoting Cu2 + and Zn2+ release from sulfides. During the first 45 days of leaching, a strongly acidic environment (i.e., pH ≈ 2.7) was maintained by the transition-zone microbial community via acid production, which favored the formation of jarosite. By contrast, a moderately acidic environment (i.e., 3.0 < pH < 3.4) was maintained by the shallow community, which favored the formation of schwertmannite. Under the same aeration frequency, the initial microbial communities from different depths evolved into similar structures dominated by Leptospirillum (with relative abundances of 18.71% and 33.75%, respectively). Furthermore, RDA results identified DO, ORP, and pH as the key drivers of community assembly (RDA1 [39.4%]).