Influence of pH, soil humic/fulvic acid, ionic strength, foreign ions and addition sequences on adsorption of Pb(II) onto GMZ bentonite

This work contributed to the adsorption of Pb(II) onto GMZ bentonite in the absence and presence of soil humic acid (HA)/fulvic acid (FA) using a batch technique. The influences of pH from 2 to 12, ionic strengths from 0.004 M to 0.05 M NaNO3, soil HA/FA concentrations from 1.6 mg/L to 20 mg/L, foreign cations (Li+, Na+, K+), anions (Cl-, NO3-), and addition sequences on the adsorption of Pb(II) onto GMZ bentonite were tested. The adsorption isotherms of Pb(II) were determined at pH 3.6 +/- 0.1 and simulated with the Langmuir, Freundlich, and D-R adsorption models, respectively. The results demonstrated that the adsorption of Pb(II) onto GMZ bentonite increased with increasing pH from 2 to 6. HA was shown to enhance Pb(II) adsorption at low pH, but to reduce Pb(II) adsorption at high pH, whereas FA was shown to decrease Pb(II) adsorption at pH from 2 to 11. The results also demonstrated that the adsorption was strongly dependent on ionic strength and slightly dependent on the concentration of HA/FA. The adsorption of Pb(II) onto GMZ bentonite was dependent on foreign ions in solution. The addition sequences of bentonite/Pb(II)/HA had no effect on the adsorption of Pb(II). (C) 2008 Elsevier B.V. All rights reserved.