A DETAILED INVESTIGATION OF PHOSPHORUS REMOVAL IN SOIL AND SLAG MEDIA

Kinetic studies on phosphorus (P as orthophosphate) sorption onto a sa ndy loam soil hom North Sydney, Australia, and a slag (waste products from the BHP steel industry, Australia) revealed that more than 90% of the P was adsorbed within 70 and 12 hours for the soil and slag respe ctively. The pH of the P solution played a critical role in the rate o f P removal. Removal was at a minimum at pH 2. Dominant removal mechan ism of P at pH less than 8 was physical sorption, while it was chemica l precipitation at pH greater than 10. Adsorptive capacity of the slag was 225 and 53 times of that of the soil for the static and dynamic s ystems respectively. Breakthrough curves obtained from the column expe riments are S-shaped and more spreaded with the decrease of influent P concentration. Simulated results from an equilibrium sorption model ( ESM) and Freundlich isotherm constants did not always match the corres ponding experimental breakthrough data. Mobility of P is restricted by the adsorbent due to its high sorption capacity of P.