Freundlich sorption parameters for cadmium, copper, nickel, lead, and zinc for different soils: Influence of kinetics

The mobility of heavy metals in the soil-water environment is highly dependent on their adsorption and kinetic behavior with the soil matrix. In this study, the retention of five heavy metals (Cd, Cu, Ni, Pb, and Zn) by ten soils from nine soil series was quantified using kinetic sorption batch methods over a wide range of input concentrations for each heavy metal. Retention results indicated that adsorption isotherms for all heavy metals and soils exhibited nonlinear behavior and also was kinetic. Soils with high organic matter and soils with high pH, due to the presence of carbonates, exhibited strong sorption for all heavy metals. For all ten soils used, adsorption of heavy metals followed the order Pb > Cu > Cd > Zn > Ni. For soils with high pH, adsorption followed the order Pb > Cu > Zn > Cd > Ni where Zn exhibited more affinity than Cd. The influence of time of reaction resulted in increased values of the Freundlich distribution coefficients (K-f) for all soils. This is indicative of increased sorption which varied among soils and heavy metals. With the exception of Cu, the Freundlich parameter b did not change with time for all ten soils. The parameter b was negatively correlated with pH and regression equation for Zn, Cd, and Ni was suitable to predict b vs. pH for 1 and 7 days reaction time. Moreover, b did not change significantly with time which simplifies the predictive capabilities of sorption models for heavy metals with time.