Influence of Temperature Regime on Nickel Kinetics in Two Alluvial Soils from Arid Region

The effect of soil temperature on Nickel (Ni²+) adsorption/desorption using a kinetics approach was studied in two Egyptian surface alluvial soil samples (0-30 cm) varying in their clay content and other related properties and collected from El-Menoufya Governorate, Egypt. The kinetics of Ni²+ adsorption, as well as desorption, were determined at three temperature regimes i.e. 5, 28, and 50°C for each soil using the batch technique. The calculated values of energies of activation for adsorption (K_a) ranged between 5.21 - 5.34 for Soil 1 (S_1) and 5.32 - 6.23 kcal mol^-1 for Soil 2 (S_2), respectively. The respective values of Ed were 2.44 - 3.71 and 2.42 - 3.57 kcal mol_-1. Results also showed that the Ed values were greater than the Ea values in both soils; implying further energy has been required to desorb Ni²+ than to release for both soils. Thermodynamic variables have been calculated by Gibbs and Eyring s equations. The free energy of Ni²+ adsorption (ΔG°) were negative values (ranging between -0.234 and - 0.411 in S_1 and from - 0.357 to - 0.436 in S_2 cal mol^-1), meaning decrease in ΔG values with increasing the temperature. For Ni²+ desorption (ΔGd), The free energy of activation values was higher than those for Ni²+ adsorption (ΔGa), suggesting that it is necessary to release Ni²+ more free energy than to adsorb it. The good agreement of calculated AG° from Gibbs theory reaction denoting that the thermodynamic constants could be determined using the kinetic parameters. The enthalpy (ΔH) parameter numerical values were exothermic and showed a greater binding of Ni^2+ ions in S_2 than in S_1 according to the distinction between external surfaces to interlayer surfaces charge ratio. The enthalpy of activation (ΔH) values in both soils were - 2.127 and - 0.497 cal mol^-¹ in S_1 and S_2 respectively, proposing the heat energy needed to overcome the Ni²+ desorption in S_2 as compared to S_1.