JWSS - Journal of Water and Soil Science

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As apparent Zn recovery in mineral soils (saturated and unsaturated) is nill, the precise assessment of processes responsible for Zn retention in these soils is of great importance. A laboratory study was conducted to characterize Zn adsorption in eight lowland calcareous soils. The fit of sorption data was evaluated by Freundlich and Langmuir isotherms. In this study, 2-g soil samples were equilibrated for 24 hours with 40 mL 0.0lM CaCl₂ solution containing 5 to 500 mg Zn L^-1. The amount of Zn adsorbed was calculated based on the difference between the initial and equilibrium Zn concentrations.

Zinc adsorption data were fitted to a linear form of Freundlich equation. However the Langmuir isotherm was divided into two distinct linear portions, representing two different types of adsorption sites. The Langmuir K₁ was higher and adsorption maxima (b₁) was lower in part I (corresponding to lower Zn concentration) than in part II (corresponding to higher Zn concentration). Thus, it seems that in parts I and II, sites are more important for their high adsorption energy and adsorption capacity, respectively. Langmuir adsorption maxima (b₂) was positively correlated with clay content, CCE and P concentration and negatively correlated with CEC.

Keywords: Freundlich isotherms, Langmuir isotherms, Adsorption maxima, Calcium carbonate equilibrium, Cation exchange capacity.

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