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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 (Ka) ranged between 5.21 - 5.34 for Soil 1 (S1) and 5.32 - 6.23 kcal mol-1 for Soil 2 (S2), 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 (∆G°) were negative values (ranging between - 0.234 and - 0.411 in S1 and from - 0.357 to - 0.436 in S2 cal mol-1), meaning decrease in ∆G values with increasing the temperature. For Ni2+ desorption (∆Gd),  The free energy of activation values was higher than those for Ni2+ adsorption (∆Ga), 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 (∆H) parameter numerical values were exothermic and showed a greater binding of Ni2+ ions in S2 than in S1 according to the distinction between external surfaces to interlayer surfaces charge ratio. The enthalpy of activation (∆H) values in both soils were - 2.127 and - 0.497 cal mol-1 in S1 and S2 respectively, proposing the heat energy needed to overcome the Ni2+ desorption in S2 as compared to S1.

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