PHOSPHATE SORPTION BY HEMATITE AND KAOLINITE-HEMATITE (K-H) SYSTEM ASDESCRIBED BY ISOTHERMS

The sorption of phosphate (P) by synthetic hematite and kaolinite-hema tite (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 d ifferent initial phosphate (P) concentrations (40-444 mmol kg(-1)).The experimental data were fitted to Langmuir, Freundlich, Temkin, Gouy C hapman, and Sposito isotherms. Each model was found to describe sorpti on data with comparable success, with the two surface Langmuir for hem atite and Freundlich for kaolinite-hematite models being slightly supe rior. The amount of P sorbed increased as initial P concentration incr eased and pH values decreased. The amount of P sorbed by kaolinite-hem atite (k-h) system is always less than that of hematite.