KINETICS OF ZINC SORPTION BY SOME CALCAREOUS SOILS OF IRAN

The kinetics of Zn sorption by ten calcareous soils of Iran were measured and fitted to several equations (zero-, first-, second-, third-order, parabolic diffusion, simple Elovich, and exponential equations). Two initial concentrations of zinc i.e.20 and 80 mg Zn I^-1 were used and observations were carried out for 100 hours. The time required to reach the near equilibrium state was about 24 hours, by which time most of the Zn in solution had been sorbed. Zero-order, first-, second-, and third-order equations did not adequately describe zinc sorption kinetics. Both simple Elovich and exponential equations did adequately describe the data. Regression analysis indicated that the total CaCO₃, active CaCO₃, clay content, and specific surface area were closely related to the coefficients of these two equations. The magnitude coefficients of the equations were positively related to these soil properties. Thus, Zn sorption kinetics can be predicted from data collected during routine soil evaluation.