Kinetics of Cu Adsorption by Selected Variable Charge Soils Under Acidic Conditions

Characteristics of the reaction kinetics of Cu adsorption by three variable charge soils under acidic conditions were investigated by using a home-made dynamic device.Results showed that Cu adsorption could be divided into rapid and slow reactions.The maximal capacity of Cu adsorption calculated from the first order equation was in the order of Latosol Latosolic red soil Red soil,and decreased with in-creasing acidity.The half-time values(t1/2)were 249 min,244 min and 444 min for the pH5.5 treatment of the influent,and 28 min,99 min and 167 min for the pH3.3 treatment of the influent in the Red soil,Latosolic red soil and Latosol,respectively.The b values of the rate con-stant of Elovich and parabolic diffusion equation,by explaining the apparent diffusion rate of ions,were in the sequence of Latosol Latosolic red soil Red soil,and decreased with increasing acidity.The first order kinetics and parabolic diffusion equation were better described than Elovich equation by the comparison of the correlative coefficients.In the processes of Cu adsorption,the pH values of effluent were lower than that of pH5.5 and pH4.3 of the influent in the Latosolic red soil and Red soil,and higher pH3.3 and pH3.8.It showed that the former released H+ and the latter consumed H+.The released H+ could be involved in the hydrolyzation of the Cu ions.The amounts of H+ consumption in the Latosol were bigger than that in the Latosolic red soil and Red soil.At the initial stage,H+ consumption was a rapid reaction,which could in-clude cation exchange,the specific adsorption of SO24-to release OH-for neutralizing H+ in the solution,and surface protonation of soil min-erals,while the dissolution of the minerals was a slow process.