HDEHP-Impregnated Kaolinite for Adsorption of Uranium from Dilute Phosphoric Acid

Impregnation of kaolinite with di(2-ethylhexyl) hydrogen phosphate (HDEHP) improves the uranium adsorption from commercial phosphoric acid. The uranium adsorption was studied as a function of conditions: contact time, solid/liquid ratio, temperature, mechanical stirring speed, and phosphoric acid concentration, and the optimum conditions were determined. The adsorbent was characterized by the X-ray fluorescence and FTIR spectroscopy. The results show that 92% of uranium was adsorbed from commercial phosphoric acid (30% P 2 O 5 ) onto impregnated kaolinite at room temperature after 30-min contact. The adsorption kinetics was analyzed by the pseudo-first- and pseudo-second-order models, with the pseudo-second-order model giving better fit. The thermodynamic functions (Δ H 0 , Δ S 0 , and Δ G 0 ) of the uranium adsorption show that the process is exothermic and spontaneous.