Reductive sorption of Cr(VI) from aqueous solution on dehydrated date palm leaflets

A carbonaceous sorbent produced from date palm leaflets via sulfuric acid treatment was tested for the removal of Cr(VI) from aqueous solutions varying contact time, initial pH and Cr(VI) concentration. Cr(VI) was removed via reduction to Cr(III) and sorption. Chromium sorption depends mainly on the initial pH with Cr(VI) reduction accompanied by a rise in the equilibrium pH, showing sorption maxima in the pH range 1.8-2.8 for concentration range 100- 500 mg/l. A shift in sorption maxima to lower initial pH values was observed with the rise in initial Cr(VI) concentration. Sorption data at low pH values did not fit the Langmuir equation. Kinetic studies were carried out at initial pH 2.0, 2.8 and 4.0 for initial Cr(VI) concentration of 100 mg/l for which optimum sorption was observed at initial pH 2.8. Cr(VI) removal follows a pseudo first order kinetic model at pH 2 but follows pseudo second order model at initial pH 2.8 and 4.0. Chromium sorption followed well pseudo second order kinetic model at the pH studied. Cr(VI) reduction to Cr(III) was accompanied by oxidation of the sorbent surface showing an increase in surface functionality. Mechanism of reduction and sorption is discussed.