Zinc Sorption in Some Calcareous Soils of North-West Iran

Sorption is one of the most important chemical processes which affect zinc (Zn) behavior in the soil. In this study, the effects of soil properties on Zn adsorption were studied in 25 soil samples from the North-West of Iran in batch system as a function of initial Zn concentration (0-0.49 mM). Results indicated that cation exchange capacity (CEC), calcium carbonate equivalent (CCE), and soil pH were primarily responsible for retaining of Zn in all the soil samples. Eighty percent variability in the adsorption maxima (гmax) of Zn was attributed to silt, CEC, and soil pH. CEC positively influenced гmax of Zn, while the reduction of pH and silt content of the soils increased гmax capacity of Zn. Langmuir equation (R2=0.99; RMSE=0.22) proved more effective in describing Zn adsorption in soils as compared with Freundlich isotherm (R2=0.93; RMSE=0.59). The гmax of Zn in these 25 soils ranged from 2.62 to 15.56 mmol kg-1. Langmuir 2-surface isotherm showed that the Zn binding strength in the high energy surface (K1L) was about 4.2 times greater than on the low-energy surface (K2L) while гmax of Zn in the low energy surface was about 1.6 times greater than on the high energy surface of adsorption sites of soils. Regression model as a function of soil Langmuir equation parameters and soil physicochemical properties to predict Zn availability demonstrated the utility of Langmuir parameters.