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Factors affecting the dissociation of metal ions from humic substances

Published online by Cambridge University Press:  02 January 2018

Nick Bryan ,
Dominic Jones ,
Rose Keepax ,
Dean Farrelly ,
Liam Abrahamsen ,
Rebecca Beard ,
Nigel Li  and
George Weir
Nick Bryan*
Affiliation:
National Nuclear Laboratory, 5th Floor, Chadwick House, Birchwood, Warrington WA3 6AE, UK
Dominic Jones
Affiliation:
Centre for Radiochemistry Research, School of Chemistry, University of Manchester, Manchester M13 9PL, UK
Rose Keepax
Affiliation:
Centre for Radiochemistry Research, School of Chemistry, University of Manchester, Manchester M13 9PL, UK
Dean Farrelly
Affiliation:
Centre for Radiochemistry Research, School of Chemistry, University of Manchester, Manchester M13 9PL, UK
Liam Abrahamsen
Affiliation:
National Nuclear Laboratory, 5th Floor, Chadwick House, Birchwood, Warrington WA3 6AE, UK
Rebecca Beard
Affiliation:
Centre for Radiochemistry Research, School of Chemistry, University of Manchester, Manchester M13 9PL, UK
Nigel Li
Affiliation:
Centre for Radiochemistry Research, School of Chemistry, University of Manchester, Manchester M13 9PL, UK
George Weir
Affiliation:
National Nuclear Laboratory, 5th Floor, Chadwick House, Birchwood, Warrington WA3 6AE, UK
*
*E-mail: [email protected]
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Abstract

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Previously, it has been suggested that metal ions complexed to humic acid in the environment might show slower dissociation than those added to humic substances in the laboratory, which has serious implications for the transport of radionuclides in the environment. The dissociation of lanthanide and anthropogenic actinide ions from humic substance complexes has been studied as a function of humic concentration and metal ion:humic concentration ratio. The results suggest that the apparently slower kinetics observed for metal ions complexed in the environment are probably due to the large humic concentrations that are used in those studies. Further, there is no evidence that the dissociation rate constant varies at very low metal ion concentrations. Although humic samples size-fractionated by ultrafiltration showed that more metal may be bound non-exchangeably, there was no evidence for different rate constants. Ultrafiltration of Eu(III)/humic acid mixtures did show a shift in Eu from smaller to larger fractions over a period of two days. Therefore, the results suggest that dissociation rate constants determined in the laboratory at metal ion concentrations higher than those expected in the environment may be used in predicting radionuclide mobility, provided that the humic acid concentration is in the range expected at the site.

Keywords

dissociationmetal ionshumic substanceslanthanideactinide
Type
Research Article
Information
Mineralogical Magazine , Volume 79 , Issue 6 , November 2015 , pp. 1397 - 1405
Creative Commons
Creative Common License - CCCreative Common License - BY
Copyright © The Mineralogical Society of Great Britain and Ireland 2015. This is an open access article, distributed under the terms of the Creative Commons Attribution (CC BY) license (http://creativecommons.org/licenses/by/4.0/), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.
Copyright
Copyright © The Mineralogical Society of Great Britain and Ireland 2015

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