Abstract
A mixed culture of A. ferrooxidans and A. thiooxidans isolated from a coal gangue dump was used to bioleach coal gangue in a column reactor to investigate the leaching of elements. The changes of metal ions (Fe, Mn and Cr) and sulfate in the leaching solution, elemental composition, mineral components and sulfur speciation of the coal gangue before and after bioleaching were analyzed by atomic absorption, anion chromatography, XRF, XRD and XPS. The results show that the mixed culture could promote the release of metal ions in coal gangue, with a leaching concentration of Fe > Mn > Cr. EC and Eh have significantly increased with the increase of metal ion concentrations in the leaching solution. XRF analyses show that the contents of Fe, Mn and S decreased in coal gangue after bioleaching. XRD results suggest that the bioleaching has impacts on minerals in coal gangue, particularly the Fe-containing components. XPS analyses show that sulfur speciation in the raw gangue samples was associated with sulfate, dibenzothiophene and pyrite sulfur. After continuous leaching by the mixed culture, the total sulfur, pyrite sulfur and sulfate sulfur in coal gangue decreased from 2.06% to 1.18%, 0.66% to 0.14% and 1.02% to 0.52%. The desulfurization rates of the pyrite and sulfate were 78.79% and 49.02 %. It is concluded that the mixed culture of these two microorganisms could effectively leach metals from coal gangue coupling with the oxidation of sulfide to sulfate. This study has provided fundamental information as a potential application in the recovery of valuable metals from coal gangue or environmental remediation related to gangue in the future.
Highlights
Bacterial cells were collected at the late exponential phase
The variations of pH, D8, Eh and electronic conductivity (EC) of the leaching solutions presented in Figure analyzed by XRD
ESCAincrease can be associated with the release of exchangeable alkali ions and soluble oxides
Summary
Coal mining and processing have generated massive coal gangue and accumulated as gangue dumps. The leaching, weathering and biological catalysis of coal gangue can release metals and sulfur into the environment. The formation of acid mine drainage (AMD) from oxidation of pyrites and other sulfur-bearing minerals in coal gangue causes serious environmental pollution to the air, surface water and surrounding soil [1,2]. There has been concerns over the pollution caused by coal gangue dumps. The number of reports related to environmental pollution and risk assessment of sulfur and metals has increased in the past thirty years [3,4]. Coal gangue contains valuable elements and minerals, which can be used as a potential resource for recovery
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