Rice bran carbon: An alternative to commercial activated carbon for the removal of hexavalent chromium from aqueous solution

Abstract

Rice bran carbon (RBC) prepared from rice bran (an agricultural waste) was successfully utilized for the removal of hexavalent chromium from aqueous solution. The potentiality of RBC was tested and compared with commercial activated carbon (CAC), and it was found that RBC removed 95% of hexavalent chromium at pH 2, 1000 μM Cr(VI) concentration, temperature 30 °C, and adsorbent dose of 2 g/L. The maximum uptake of total chromium obtained by applying the Langmuir isotherm model was 138.88 mg/g for RBC, which was found comparable to that obtained by utilizing CAC (116.28 mg/g) at 40 °C. The removal of Cr(VI) was found maximum at a proton to chromium ratio of 10 and chromium to carbon ratio of 0.052, and these ratios were found to be applicable over a range of Cr(VI) concentrations. The removal of Cr(VI), at low pH (< 2.0), was not only due to sorption of Cr(VI) but also because of reduction of Cr(VI) into less toxic Cr(III), which was also adsorbed on the surface of the sorbent. The rate of reduction removal of Cr(VI) followed pseudo-first order kinetics, whereas the sorption of total chromium followed pseudosecond order kinetics for both the types of activated carbons.