ZINC ADSORPTION BY 2 ALKALINE SOILS

Zinc adsorption by two alkaline solids, Mormon clay loam and Willows clay, both deficient in zinc for rice culture, was examined over a wide range of zinc solution concentrations. At zinc equilibrium concentrations (0.1 ppm zinc for Willows clay and 0.23 ppm for Mormon clay loam), zinc adsorption at 25°C can be described by either the Langmuir or the Freundlich adsorption isotherm. The exponent of concentration of the Freundlich equation is about 1.0. At higher zinc concentrations, however, zinc adsorption can be described only by the Freundlich equation, with the exponent of concentration being 0.31. Zinc adsorption by Mormon clay loam and Willows clay is an endothermic reaction. The rate of zinc adsorption can be described by multiple-order kinetic equation. The activation energy of adsorption is 43.1 kilocalories per mole for Mormon clay loam and 31.4 kilocalories per mole for Willws clay. Because of the high activation energy, the adsorption is considered to be chemisorption rather than due to the electrostatic attraction forces between zinc ions and the surfaces of colloidal particles. The greater stability of adsorbed zinc may result from dehydration during the aging of zinc on the surface of clay minerals. © 1979 The Williams & Wilkins Co.