Removal of chromium (VI) from aqueous solutions on a carbon sorbent chemically prepared from flax shive via the reaction with sulphuric acid

Abstract
A carbon-like sorbent has been prepared from flax shive via sulphuric acid treatment. The ability of the prepared sorbent to remove Cr (VI) from aqueous solutions was investigated by following the influence of various parameters such as contact time, pH, metal ion concentration, temperature and sorbent status (wet and dry). Equilibrium data followed a second order rate expression at pH 4.5 while it followed a first order rate equation at pH 1.5. Sorption studies showed a maximum uptake in the pH range (2.6 - 2.4) on the wet sorbent and in the pH range (2.4 - 2.2) on the dry sorbent for 100 and 220 mg/l of Cr (VI) respectively. At lower pH values, complete reduction of Cr (VI) to Cr (III) was found with low sorption while at higher pH values sorption decreased. An increase in the solution pH was observed during the sorption reaction indicating proton involvement in the sorption /reduction process. Equilibrium data, at pH 3, fit the Langmuir equation. Temperature studies showed a large increase in the Cr (VI) sorption capacity with temperature increase. These studies have shown that that carbon product can work as an efficient sorbent as well as a reducing agent for Cr (VI).