Heavy metal removal from coal fly ash under alkaline conditions by indigenous bacteria isolated from a coal ash dumpsite

Bioleaching is a process that uses microorganisms to remove heavy metals from waste materials, such as fly ash, electronic waste, low-grade ores, mine tailings, and spent catalysts.This study explored indigenous bacteria from contaminated environments to identify promising candidates for heavy metal bioleaching and investigate the underlying mechanisms.The bacteria were identified at the genomic level to determine their species, and bioleaching experiments were conducted to evaluate the effect of pulp density on heavy metal removal from fly ash using two bacterial species.The bioleaching efficiency, bacterial population, and other parameters were measured to analyze the bioleaching mechanisms.The results identified the bacterial isolates as Bacillus toyonensis and Bacillus tropicus.The addition of 5% (w/v) fly ash yielded the highest bioleaching efficiency for copper, zinc, chromium, and nickel.Among the two, Bacillus toyonensis showed the highest efficiency, with 63.62% for copper, 79.38% for zinc, 60.42% for chromium, and 52.26% for nickel.The bioleaching process occurred in an alkaline medium, with the pH shifting from neutral to alkaline during the experiment.In conclusion, the two Bacillus species effectively bioleached heavy metals from fly ash through biosorption, complexolysis, and redoxolysis mechanisms, similar to those found in other heterotrophic and autotrophic bacteria.However, it is important to note that bioleaching in this study took place in an alkaline medium, excluding acidolysis and complexolysis mechanisms that involve organic acids.