Phosphate sorption by hematite and kaolinite-hematite (k-h) system as described by isotherms

The sorption of phosphate (P) by synthetic hematite and kaolinite-hematite (k-h) system was investigated under conditions of varying pH (4.0, 5.0, 6.0, 7.0, 8.0, and 9.0) and equilibrating solution composition. Sorption experiments were carried out in background solution of six different initial phosphate (P) concentrations (40-444 mmol kg(-1)).The experimental data were fitted to Langmuir, Freundlich, Temkin, Gouy Chapman, and Sposito isotherms. Each model was found to describe sorption data with comparable success, with the two surface Langmuir for hematite and Freundlich for kaolinite-hematite models being slightly superior. The amount of P sorbed increased as initial P concentration increased and pH values decreased. The amount of P sorbed by kaolinite-hematite (k-h) system is always less than that of hematite.