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Studies of Adsorption of Pillarized and Organofunctionalized Smectite Clay for Th⁴⁺ Removal

D.J.L. Guerra, E.S. Menonça, R.A.R. Silva, W. Lara

Journal of Ceramic Science and Technology, Vol. 3, No. 1 (2012), pp. 17-28

DOI: 10.4416/JCST2012-00040

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Abstract

A natural smectite clay sample was taken from the Amazon region, Amazonas State, Brazil. Zirconium polyoxycations were inserted into the smectite structure in a pillaring process. The pillarized smectite was organofunctionalized with the compound 3-mercaptopropyltrimethoxysilane. The natural and modified clay samples were used for the adsorption of tetravalent thorium cation from aqueous solution in a batch process. The adsorption process was fitted to equilibrium and kinetic models. The effects of stirring time, adsorbent dosage and pH on the adsorption capacity demonstrated that 90 min is sufficient to reach equilibrium at room temperature at pH 6.0. From the cation/basic center interactions for each smectite at the solid-liquid interface, the equilibrium constant and exothermic thermal effects were calculated with calorimetric methodology. By considering the net interactive number of moles for thorium cation and the equilibrium constant, the enthalpy, (-7.2 ± 0.11 to -7.0 ± 0.11 kJ mol-1) and negative Gibbs free energy, (-22.4 ± 0.1 to -23.1 ± 0.1 kJ mol-1) were calculated. These values enabled determination of the positive entropy, (51.2 ± 0.1 to 54.1 ± 0.1 JK-1mol-1). All liquid/solid interface adsorptions were spontaneous in nature and enthalpically driven.

Keywords

Smectite, adsorption isotherms, thorium, thermodynamic, kinetic

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