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

Sahar M. Ismail ,Sherine M. Shehata and Alaa M. Zaghloul

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.

Keywords: Alluvial soils, Thermodynamics, Kinetics, Nickel.