Behaviour of reduction-sorption of chromium(VI) from an aqueous solution on a modified sorbent from rice husk

A carbonaceous sorbent produced from rice husk via sulphuric acid treatment was used to remove Cr(VI) from aqueous solutions varying contact time, pH, Cr(VI) concentration and sorbent status (wet and dry). Cr(VI) was removed from the aqueous solution via reduction to Cr(III) and sorption. Reduction and sorption processes were investigated in terms of kinetics and equilibrium. The rate of reduction removal of Cr(VI) at pH 2 followed a pseudo first-order model while the rate of sorption of total chromium followed pseudo second-order model. Chromium sorption was highly dependent on the initial pH value with reduction taking place in solution with pH up to 7 showing sorption maxima in the pH range 1.8-2.8 for concentration range 100-500 mg/l with an increase in the equilibrium pH. Carbon dioxide evolved from the sorption media was determined. Reduction-sorption mechanism was investigated via physicochemical tests including cation exchange capacity, base neutralization and sorbent acidity in addition to FTIR studies for sorbent samples before and after sorption reaction.