Biosorption of aquatic cadmium(II) by unmodified rice straw

Cadmium is the most common toxic metal threatening safe rice supply. Rice straw has the potential to remove Cd from large-scale effluent contaminated by heavy metals since it exhibited a short biosorption equilibrium time of 5 min, high biosorption capacity (13.9 mg g(-1)) and high removal efficiency at a pH range of 2.0-6.0. The main Cd biosorption mechanism was Cd2+ ion exchange with K+, Na+, Mg2+ and Ca2+, together with chelation with functional groups such as C=C, C-O, O-H and carboxylic acids. When 0.5% (w/v) rice straw was exposed to 50 mg mL(-1) CdSO4 solution with shaking at 150 r min(-1) for 3 h, about 80% of the aquatic Cd was absorbed and the Cd content in rice straw reached 8-10 mg g(-1), suggesting that the metal-enriched rice straw could become high quality bio-ore by virtue of the industrial mining grade of its metal content and easy metal recovery. (C) 2012 Elsevier Ltd. All rights reserved.