Kinetics of phosphorus sorption by goethite and kaolinite-goethite (k-g) system

Reactions between phosphate (PO4) and soils or soil components is quick at first. It then becomes slower and continues for long time without reaching any true equilibrium. Many kinetic equations have been used either to deduce the mechanisms or simply to summarise results of this continued removal of PO4 from solution. In this study five kinetic models, those of first-order, Elovich, Parabolic Diffusion, Modified Freundlich, and a new kinetic equation, were evaluated to describe the rate of PO4 sorption from synthetic goethite and kaolinite-goethite (k-g) system into 0.01M calcium chloride (CaCl2) solutions of 0.0403 to 0.4435 mmol P L-1. The rate of PO4 sorption is a dynamic factor that regulates PO4 continuous supply and was found initially rapid but gradually declined with time. Comparison of coefficients of determination (r) indicates that Modified Freundlich and the New kinetic models were found better for PO4 sorption by goethite, while Modified Freundlich, New kinetic and Parabolic Diffusion models were found even better for kaolinite-goethite (k-g) system.