Aqueous Speciation of the Actinides with Organic Ligands Relevant to Nuclear Waste

Abstract

The aqueous speciation and hydrolysis of actinides in both the presence and absence of organic ligands has been investigated in the pH range 1 - 13. The speciation and hydrolysis of Th4+, U4+ and UO22+ with H3thme, H3tea, H3bic, H3heidi, H3NTA, H2ADA and H3cit have been investigated using various analytical techniques (1H NMR, 13C NMR, IR, UV-Vis(-nIR) spectroscopy and potentiometric titrations). The PHREEQC interactive software suite was used to predict speciation with the formation constants for various complexes calculated in the Hyperquad software suite.Formation constants of Th4+, U4+ and UO22+ hydroxide species have been calculated showing the formation of polymeric complexes. Experiments showed no complexation of actinides by H3thme and H3tea in aqueous solutions. However, 1:3 (M:L) complexation of Th4+ and U4+ was observed with H3bic along with 1:2 (M:L) complexation of UO22+. A variety of 1:1 and 1:2 (M:L) complexes were observed with H3heidi, H3NTA, H2ADA and H3cit for the actinides. Formation constants for complexes of H3NTA with Th4+ and UO22+, H2ADA with Th4+ and H3cit with UO22+ were calculated in Hyperquad. Studies of Pu3+ with H3heidi showed little complexation but 5Me-HXTAH4 showed 1:3 (M:L) speciation. Complexation of PuO22+ by saldien(Et2N)2H2 and salterpyH2 was shown and a secondary band was observed at ~944 nm after multiple days. The functionalities of organic ligands have been shown to have a profound effect on the (partial) hydrolysis of the actinides.

Date of Award	31 Dec 2014
Original language	English
Awarding Institution	The University of Manchester
Supervisor	Scott Heath (Supervisor)