Elemental sulfur amendment decreases bio-available Cr-VI in soils impacted by leather tanneries

Long-term disposal of tannery wastes contributed to elevated accumulations of Cr-VI in soils in Shuitou (China). This thesis investigated the reduction of toxic Cr-VI to less-harmful Cr-III using elemental S (S~) in the presence of microorganisms from Cr-contaminated soil. Total Cr in soil varied from 1,822 to 35,168 mg kg\u207b~ and 99% was present as Cr-III species. Fe-rich minerals such as hematite and goethite seemed to concentrate and isolate Cr from redox processes as revealed by the chemical and synchrontron-based micro X-ray fluorescence and diffraction analyses. Amendment with 4.0 mg g\u207b~ S~ decreased the bioavailable Cr-VI below the 0.4 mg kg\u207b~ limit for Cr-VI toxicity in soils. Treatment with S~+Na-acetate+, the addition of non-sterilized soil decreased the Cr-VI in K\u2082CrO\u2084 solution from ~10.8 to 0.28 L\u207b~ and highlighted the role of microorganisms in Cr-VI reduction. This thesis concluded that S~ amendment minimized the Cr-VI toxicity through biologically-mediated redox processes.