Kinetics of Adsorption of Pb~(2+) onto Small River Sediment

The batch experiments of adsorption of Pb~(2+) onto small river sediments were conducted.The kinetics of the sorption process was analyzed.The results showed that the equilibrium time of adsorption increased with the increasing of sediment mass in solution,while both adsorbed Pb~(2+) on per unit of sediment and Pb~(2+) concentration in the solution after equilibrium decreased.More than 95% of Pb~(2+) in solution was removed when sediment contents larger than 0.6(g·L~(-1)).Both pseudo-first-order and pseudo-second-order kinetics were tested and it was found that the latter gave a better explanation of the adsorption process.The equilibrium adsorption capacities calculated from the pseudo-second-order model could represent the true value.There was no significant correlation between initial adsorption rate of Pb~(2+) and the amount of sediment in solution.However,the pseudo-second-order rate constant increased in the solution with more adsorbent,namely chemical adsorption controlled the process.Elovich equation could explain the mechanism of sorption in the solution with higher contents of sediment;nevertheless,the process of low concentration of adsorbent adsorbing Pb~(2+) disagreed well with Elovich equation.In terms of adsorption rate in the sorption,intra-particle diffusion dominated in the more sediment solution.On the other hand,multi-linearity was presented for the adsorption rate in less adsorbent solution.The first,sharper portion represented adsorption on the external surface.The second portion indicated Pb~(2+) diffused gradually into the interior of particles and intra-particle diffusion controlled.