Process optimization for bio-beneficiation of a chromite concentrate by a Cr(VI) reducing native microbe (Bacillus sp.)

The chromite concentrate generated during processing of a typical Indian chromite ore contained Cr(VI) in the range 10 to 43 mg kg− 1. Therefore, an attempt has been made for the bio-reduction of Cr(VI) using a highly tolerant Bacillus sp. isolated from chromite mine overburden to avoid the problems associated with the use of inorganic and organic reductants. Process was optimized on bench scale while varying pH, pulp density and temperature in absence/presence of media. Almost complete reduction of Cr(VI) in the chromite concentrate was achieved in ~ 12 min of incubation under the optimized conditions of pH ~ 7.0, 35 °C temperature and 60% pulp density with the Bacillus sp. (3.55 × 107 cells mL− 1). The samples (before and after bioreduction) were characterized using XRD and SEM–EDS to derive inference for reduction of chromium(VI).