Sorption characteristics of copper(II) in selected calcareous soils of Iran in relation to soil properties

Abstract

The Langmuir, Freundlich, and Temkin isotherms were fitted to copper (Cu) adsorption data of 20 highly calcareous soils of Fars Province, ranging widely in relevant physical and chemical characteristics. One-gram samples of each soil were equilibrated for 24 h with 30 mL of 0.01 M CaCl2 containing 50 to 500 mg Cu L−1. The amount of Cu retained by soil solids was calculated based on the difference between the initial and equilibrium Cu concentrations. The Cu adsorption data showed a highly significant fit to the Freundlich, Temkin, and linear form of Langmuir adsorption isotherms. The fit to Langmuir and Temkin equations were, however, closer than that of Freundlich. Adsorption maxima (b) calculated from Langmuir isotherm was positively correlated with clay, cation exchange capacity (CEC), and calcium carbonate equivalent (CCE), whereas, Langmuir bonding energy coefficient (K) was related only to clay. Organic matter (OM), clay, and CEC were found to have a significant relationship with Freundlich coefficients (n and k). Temkin coefficients (k1 and k2) were positively correlated to CEC and clay. The distribution coefficient (i.e., maximum buffering capacity) was also highly significantly correlated with CEC and clay. It is concluded that the sites of Cu retention in the calcareous soils are clay, OM, and calcium carbonate.