Use of sludge stabilization products for remediation of heavy metal (loid)s-contaminated mine tailings: Physicochemical, biochemical and microbial mechanisms

The sludge stabilization products (hereinafter referred to “Composts”) added in different addition ratios (30 %, 50 % and 80 %) were applied to remediate the heavy metal(loid)s-contaminated mine tailings. Physicochemical, biochemical and microbial characteristics at day 0 and 180 were systematically investigated. The Composts added in different ratios could all remediate the mine tailings in terms of significantly decreased bulk density, increased organic matters, porosity, germination index, pH and DHA activity, as well as obviously declined aqueous extractable Cu, Pb, As, Cd, Hg, Cr, Zn and Ni (p < 0.05). Taken phytotoxicity alleviation and metal (loid)s mobility inhibition into consideration, the 50 % Composts was the most recommended in this study, with the highest reduction (82.9 %∼91.4 %) in aqueous heavy metal (loid)s concentration comparted to the un-amended. The transformation of Cu, Pb, As, Cd and Hg from exchangeable to more stable forms (especially organically-bound form), due to their enhanced complexation with humus through promoted organic matters aromatization, was considered to drive the alleviation of their leaching pollution in mine tailing soil. While the declined aqueous extractable Cr, Zn and Ni were more likely ascribed to the increased pH value. Further, different from fungal communities not sensitive during remediation, the highest porosity and DHA activity by the 50 % Composts amendment benefited the improved archaeal diversity and enriched bacterial family Bacillaceae (capable of heavy metals biomineralization), further significantly (p < 0.05) contributing to the decrease in Cd mobility. Overall, this study highlights the effective role of the Composts in alleviating heavy metal(loid)s pollution in mine tailings and further clarifies the multiple mechanisms including immobilization, pH adjusting and microbial effects.