Complexation of thorium with phosphate

Journal article, 2011

Using liquid-liquid extraction and the AKUFVE-technique developed by the Nuclear Chemistry Department at Chalmers University of Technology, Sweden, the complex formation equilibria of hydrogen phosphate (HPO 4 2- ) with thorium have been studied at different temperatures (15, 25 and 35 °C), varying pH (7, 8 and 8.7) and in 1 M (Na, H)ClO 4 . Evaluation of the acquired solvent extraction data indicated the formation of the ThHPO 4 2+ , Th(HPO 4 ) 2 (aq) and Th(HPO 4 ) 3 2- complexes. For Th(HPO 4 ) 2 (aq) and Th(HPO 4 ) 3 2- , the logarithm of the stability constants obtained at 25 °C were 17.0 ±3.5 and 23.7 ±0.2, respectively. Only an estimate of the stability of ThHPO 4 2+ could be obtained. Enthalpies and entropies of the complex formation reactions have been determined: Th(HPO 4 ) 2 (aq) (ΔH = 698 ± 27kJmol -1 , ΔS = 2669±91 Jmol -1 K -1 ) and Th(HPO 4 ) 3 2- (ΔH = 499 ±4kJmol -1 , ΔS = 2137 ± 12 Jmol -1 K -1 ). © by Oldenbourg Wissenschaftsverlag, München.