Adsorption/Desorption Kinetics of Zn in Soils: Influence of Phosphate

Transport of heavy metals such as zinc in soils may be affected by several rate limiting processes including kinetic sorption and release. Batch kinetic experiments were carried out to evaluate sorption and desorption of Zn for soils having distinctly different properties. A second objective was to test the hypothesis that phosphate additions to soils increases zinc adsorption. Sorption isotherms exhibited strong nonlinearity as well as kinetic behavior. Distinct differences in the amount of Zn sorbed among the different soils where highest sorption was observed for the neutral Webster soil. In contrast Windsor and Olivier (acidic) soils exhibited lower sorption capacities where Windsor soil showed least sorption. The influence of P on increased Zn sorption was clearly manifested in the isotherms where similar trends were observed for the two acidic and neutral soils. Distinct discrepancies between adsorption and successive desorption isotherms indicate considerable hysteresis for Zn release the extent of which varied among the three soils. For the two acidic soils Zn released ranged from 50%∼60% of that sorbed whereas for the neutral soil only 10%∼15% of sorbed Zn was released over time.