CHARACTERISTICS OF KINETICS OF Pb~(2+)-H~+ ADSORPTION BY SELECTED VARIABLE CHARGE SOILS UNDER ACIDIC CONDITIONS

Characteristics of the reaction kinetics of Pb adsorption by three variable charge soils under acidic conditions were investigated.Results showed that maximal amounts of Pb adsorption fitted by the first order equation remarkably were the order of LatosolLatosolic red soilRed soil,and decreased with increase in acidity.The half-time values(t1/2)were 231 min,266 min and 182 min for the pH 5.5 treatment of the influent,and 43 min,26 min and 32 min for the pH 3.3 treatment of the influent in the Red soil,Latosolic red soil and Latosol,respectively.The b values of the rate constant of Elovich and parabolic diffusion equation,by explaining the apparent diffusion rate of ions,were in the sequence of LatosolLatosolic red soilRed soil and decreased with increase in acidity.In the processes of Pb adsorption,the pH values of effluent were lower than that of pH 4.3 and pH 5.5 of influent in latosolic red soil and red soil,and higher than that of pH 3.3 and pH 3.8.It showed that the former released H+ and the latter consumed H+.The amounts of H+ consumption in Latosol were bigger than that in Latosolic red soil and Red soil.At the initial stage,H+ consumption was the rapid reaction,which could be cation exchange,and the specific adsorption of SO2-4 to release OH-for neutralizing H+ in the solution,and surface protonation of soil minerals,and then H+ dissolution to minerals was a slow processes.