Abstract:
Stability of chromium in the tailing dumps and stockpiles of chromium concentrate at chrome mining fields is
affected by pH, redox potential, and the presence of other metallic species in the waste rocks. It is desirable to
keep chromium in the dump site in the trivalent state since the hexavalent state, Cr(VI), is highly mobile and
carcinogenicity to aquatic life forms and humans, whereas the trivalent state, Cr(III), precipitates easily and is
less toxic than Cr(VI). In this study, microbial remediation with indigenous bacteria was used to reduce Cr(VI)
to Cr(III) in presence of Fe(II)/Fe(III) redox couple in simulated ferrochrome slag.
The consortium of bacterial culture strains were isolated from sand drying beds and dried sludge from the
belt filter press at the Wastewater Treatment Works. Culture achieved 100 % Cr(VI) removal under aerobic
condition for 100 mg/L Cr(VI) in 24 h and 100 % Cr(VI) removal under anaerobic condition for 20 mg/L Cr(VI) in
48 h. Increased Cr(VI) reduction occurred in the presence of Fe(II) which confirmed that Fe(II) served as an
alternative electron donor for Cr(VI) reduction. Complete reduction of 50 mg/L Cr(VI) was achieved within 12 h
using 50 - 100 mg/L Fe(II). Kinetic evaluation in the presence of Fe(III) found that Cr(VI) reduction was noncompetitively
inhibited by the presence of Fe(III).
