Kinetic and isotherm modeling of lead(II) sorption onto some waste plant materials

Peepul leaves were identified as the most potent Pb(II) sorbent (q(max) = 127.34 mg g(-1)), followed in decreasing order by banana peels (72.79 mg g(-1)), peanut hulls (69.75 mg g(-1)), coir fibers (52.03 mg g(-1)), rice stem (49.57 mg g(-1)). teak saw dust (40.70 mg g(-1)), discarded tea leaves (35.89 mg g(-1)), mango leaves (31.54 mg g(-1)), rice husk (31.13 mg g(-1)) and grass clippings (29.05 mg g(-1)). The tested plant materials sorbed Pb(II) optimally at pH 4 or 5, but peepul leaves showed substantial sorption even at lower pH values. Kinetics of Pb(11) sorption by the selected biomass types, excepting peepul leaves. was very fast with >90% sorption occurring within 10 min. The kinetic data of Pb(II) sorption are in good agreement with both pseudo-first-order and -second-order reaction models. However, external diffusion, rather than infra-particle diffusion, seems to be the major mechanism of Pb(II) sorption by the tested plant materials. The isotherm data of Pb(II) biosorption more significantly fitted to Langmuir (r(2) = 0.96-0.99) than to Freundlich (r(2) = 0.88-0.97) model. (C) 2008 Elsevier B.V. All rights reserved.