Using the Equilibrium and Thermodynamic Parameters of Copper Adsorption in some Calcareous Soils

Ten different soil samples from Basrah and Messan governorates of southern Iraqi were used to study the mechanism of copper (Cu) adsorption. Copper was added at 0 , 4 , 8 , 16 and 32 mg Cu kg^-1 soil and two salts (0.01 M CaCl₂ and 0.01 M NaCl) with two temperature (25±1 C° and 45±1 C°). Copper adsorption was tested using isothermal equation parameters of Langmuir, Freundlich and D-R as well as thermodynamic parameters (K°, ΔG°, ΔH° and ΔS°). The results showed that the isotherm equations that give the best description of copper adsorption were in the following order: Langmuir > D-R > Freundlich according to their (R²) values. The value of activity energy (E) which ranges from 8.006 – 15.823 kJ mol^-1 showed that the copper adsorption is an ionic exchange reaction. The value and sign of ΔG° of copper adsorption in the studied soils exhibit that it is a spontaneous process and increases with increasing the temperature. For the positive ΔH° values, Cu at sorption is considered an endothermic reaction and the positive ΔS° indicates the degree of randomness between the solid and liquid phases. There is not any clear effect of soil properties. But there is a general effect of whole soil properties on the calculated parameters. The results also showed that the amount of adsorbed Cu under using 0.01 M CaCl₂ on adsorption sites was lower compared to 0.01 M NaCl