title: Effect of anthropogenic organic complexants on the solubility of Ni, Th, U(IV) and U(VI).
abstract: The influence of anthropogenic organic complexants (citrate, EDTA and DTPA from 0.005 to 0.1M) on the solubility of nickel(II), thorium(IV) and uranium (U(IV) and U(VI)) has been studied. Experiments were carried out in 95%-saturated Ca(OH)2 solutions, representing the high pH conditions anticipated in the near field of a cementitious intermediate level radioactive waste repository. Results showed that Ni(II) solubility increased by 2-4 orders of magnitude in the presence of EDTA and DTPA and from 3 to 4 orders of magnitude in the case of citrate. Citrate had the greatest effect on the solubility of Th(IV) and U(IV)/(VI). XRD and SEM analyses indicate that the precipitates are largely amorphous; only in the case of Ni(II), is there some evidence of incipient crystallinity, in the form of Ni(OH)2 (theophrastite). A study of the effect of calcium suggests that U(VI) and Ni(II) may form metal-citrate-OH complexes stabilised by Ca(2+). Thermodynamic modelling underestimates the concentrations in solution in the presence of the ligands for all the elements considered here. Further investigation of the behaviour of organic ligands under hyperalkaline conditions is important because of the use of the thermodynamic constants in preparing the safety case for the geological disposal of radioactive wastes.
authors.affiliation: Department of Chemistry, Loughborough University, LE11 3TU Loughborough, Leicestershire, United Kingdom. Electronic address: m.felipe-sotelo@lboro.ac.uk.
authors.forename: M
authors.initials: M
authors.lastname: Felipe-Sotelo
authors.affiliation: Department of Chemistry, Loughborough University, LE11 3TU Loughborough, Leicestershire, United Kingdom.
authors.forename: M
authors.initials: M
authors.lastname: Edgar
authors.affiliation: MCM Consulting. Täfernstrasse 11, CH 5405 Baden-Dättwil, Switzerland.
authors.forename: T
authors.initials: T
authors.lastname: Beattie
authors.affiliation: Enviras Ltd., LE11 3TU Loughborough, Leicestershire, United Kingdom.
authors.forename: P
authors.initials: P
authors.lastname: Warwick
authors.affiliation: Department of Chemistry, Loughborough University, LE11 3TU Loughborough, Leicestershire, United Kingdom.
authors.forename: N D M
authors.initials: NDM
authors.lastname: Evans
authors.affiliation: Department of Chemistry, Loughborough University, LE11 3TU Loughborough, Leicestershire, United Kingdom.
authors.forename: D
authors.initials: D
authors.lastname: Read
keywords: Anthropogenic ligands; Nickel; Solubility; Thorium; Uranium