Application of Brazilian kaolinite clay as adsorbent to removal of U(VI) from aqueous solution: Kinetic and thermodynamic of cation-basic interactions

The compound N¹-[3-(trimethoxysilyl)propyl]diethylenetriamine was anchored onto Amazon kaolinite surface by heterogeneous route. The modified and natural kaolinite samples were characterized by transmission electron microscopy, scanning electron microscopic, X-ray diffraction, and nuclear magnetic nuclei of ²⁹Si and ¹³C. The well-defined peaks obtained in the ¹³C NMR spectrum in the 5.0-62.1 ppm region confirmed the attachment of organic functional groups as pendant chains bonded into the porous clay. The ability of these materials to remove U(VI) from aqueous solution was followed by a series of adsorption isotherms adjusted to a Sips equation at room temperature and pH 4.0. The kinetic parameters analyzed by the Lagergren and Elovich models gave a good fit for a pseudo-second order reaction with k₂ values 16.0 and 25.1 mmol g⁻¹ min⁻¹ ranges for natural and modified kaolinite clays, respectively. The energetic effects caused by metal ion adsorption were determined through calorimetric titrations.