Kinetics of phosphate sorption by goethite‐ and bentonite‐goethite (b‐g) system

Abstract

The study of phosphate (PO₄) fixation due to reactions which occur to the surface of soil minerals has been limited by a lack of evidence on which a structural model may be based. A structural model should attempt at least to describe the coordination on the absorbed PO₄ ^3‐ ion, that is, to indenfity the immediate neighbour atoms or ions in contact with it. 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 kinetics models 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 bentonite‐goethite (b‐g) system into 0.01 M calcium chloride (CaCl₂) solutions of 0.0403–0.4435 mmol P L^‐1. The rate of PO₄ sorption is a dynamic factor that regulates the continuous supply of PO₄and was found initially to be rabid but gradually declined with time. The adsorption of PO₄ per gram of goethite was faster and greater than the adsorbed amount of PO₄per gram of bentonite‐goethite system. Comparison of the coefficients of determination (r) indicates that Elovich, Freundlich, and the new kinetic models provided better fits for phosphate sorption by goethite while First order, Parabolic, and Freundlich were found to be the best for bentonite goethite (b‐g) system.

Notes

Postal address of the corresponding author: A. Dimirkou, 14 Thermopillon St. 15344 Pallini, Attiki, Greece.