Chemistry of Phosphate Adsorption in Soil

Abstract

The sorption/dosorption of phosphate in soils and calcite is studied in different electrolyte solutions and at different temperatures. Soil being the adsorbent is analysed for its physico-chemical properties. The various phosphate fractions and the available phosphate are determined and correlated with the soil properties. The Langmuir and Dubinin - Radushkevich adsorption equations are applicable to the equilibrium sorption data. Para meters like adsorption maximum and energy of adsorption are determined the values of which depend upon the cations and anions present in. the soil solution, temperature of the concentration of the electrolyte and physico chemical properties of the soils. Kinetics of phosphate sorption show that the process follows two steps first order kinetics and the data is also found to fit the Elovich type equation. From the rate constants, the activation energy, enthalpy of activation, entropy of activation, free energy of activation and energy of desorption are calculated. Desorption of the added phosphate in different electrolyte solutions is also of the first. order. desorption by the additional increments of resin Amberlite IRA 400 (CI-) is accompanied by the increase in solution concentration of Ca2+ , K+, Na+ and H+, indicating Us. dissolution of some inorganic phosphate compound. Applying the solubility method to the desorption data confirms the presen