Sustainable bioleaching of heavy metals from coal tailings using Bacillus inaquosorum B.4: Mechanistic insights and environmental implications

Abstract

Coal tailings are byproducts of the coal washing process and pose significant environmental pollution issues due to the release of heavy metal elements. In this study, a sustainable bioleaching method was proposed, and a Bacillus inaquosorum B.4 strain with high Extracellular Polymeric Substances(EPS) production characteristics was isolated through mutagenesis. The importance of EPS in the adsorption of free heavy metals was validated, as EPS-covered (EPS-C) cells exhibited significantly higher removal rates of Cu (71.30 ± 1.10 %), Pb (79.90 ± 1.02 %), and Zn (64.90 ± 1.00 %) compared to EPS-removed (EPS-R) cells. The adsorption kinetics followed pseudo-second-order kinetics models. The significant bioleaching efficiency of this strain for heavy metals Pb, Zn, and Cu in coal tailings was investigated. Through shake flask experiments under conditions of a particle size of 45–74 μm, pH of 7, and a bacterial concentration of 15.00 %, the bioleaching rates of Pb, Zn, and Cu were found to be 91.88 mg/kg、23.21 mg/kg、8.06 mg/kg, respectively. The B.4 strain's mechanism of action was determined using techniques like SEM, XRD, FT-IR, and LA-ICP-MS. It involves absorbing organic compounds, disrupting the lattice structure of heavy metal minerals, and releasing metal ions. These metal ions are then immobilized by forming complexes with functional groups on the bacterial surface. The bioleaching process was primarily subject to a combination of chemical reaction and diffusion control. This research offers a practical bioremediation strategy to manage heavy metals in coal tailings and has important implications for environmental protection and sustainable resource utilization.