Influence of temperature regime on nickel kinetics in two alluvial soils from arid region

Abstract EN

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 (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.