Phosphate Sorption of Heavy Metal Polluted Soils

Three surface soil samples differing in clay content were treated with manure and Cd or Ni. A soil sample was also collected from a field polluted with industrial effluents and sewer water and was treated with manure only. After six wetting and drying cycles, these 20 treated samples were examined for phosphate sorption. There was increase in phosphate sorption with increase in clay and clay/organic carbon ratio. The sorption decreased with addition of manure, Cd and Ni but Ni was more effective than Cd in reducing P sorption. The negative effect of the combined application of Cd and manure was less than the sum of their individual effects. Similar trend was observed with Ni. The organic matter was less effective in reducing P sorption in already polluted soil as compared to unpolluted ones. An inverse relationship between P sorption maxima and bonding energy constant was observed. Sorption of P was satisfactorily described by Langmuir and Freundlich isotherms.