Remediation of Cr(VI) from chromium slag by biocementation

[Display omitted] •Microbially induced calcite precipitation to immobilize Cr(VI) from chromium slag.•Biocementation/bio-consolidation of Cr(VI) from chromium slag.•Incorporation of Cr(VI) into CaCO3 to form a strong complex.•Cr(VI) mobility was significantly decreased in the exchangeable fraction.•Cr(VI) concentrations in the leachate decreased significantly after biocementation. Here we demonstrate a calcifying ureolytic bacterium Bacillus sp. CS8 for the bioremediation of chromate (Cr(VI)) from chromium slag based on microbially induced calcite precipitation (MICP). A consolidated structure like bricks was prepared from chromium slags using bacterial cells, and five stage Cr(VI) sequential extraction was carried out to know their distribution pattern. Cr(VI) mobility was found to significantly be decreased in the exchangeable fraction of Cr slag and subsequently, the Cr(VI) concentration was markedly increased in carbonated fraction after bioremediation. It was found that such Cr slag bricks developed high compressive strength with low permeability. Further, leaching behavior of Cr(VI) in the Cr slag was studied by column tests and remarkable decrease in Cr(VI) concentration was noticed after bioremediation. Cr slags from columns were characterized by SEM–EDS confirming MICP process in bioremediation. The incorporation of Cr(VI) into the calcite surface forms a strong complex that leads to obstruction in Cr(VI) release into the environment. As China is facing chromium slag accidents at the regular time intervals, the technology discussed in the present study promises to provide effective and economical treatment of such sites across the country, however, it can be used globally.