Woodward, GL, Peacock, CL orcid.org/0000-0003-3754-9294, Otero-Fariña, A et al. (3 more authors) (2018) A universal uptake mechanism for cobalt(II) on soil constituents: ferrihydrite, kaolinite, humic acid, and organo-mineral composites. Geochimica et Cosmochimica Acta, 238. pp. 270-291. ISSN 0016-7037
Abstract
Cobalt is a waste product in many industrial processes and its most common radioactive isotope – ⁶⁰Co – is a by-product of nuclear reactors. To better understand the mobility and fate of Co in natural and contaminated environments we investigated Co sorption behaviour to the common soil and sediment constituents ferrihydrite, kaolinite, humic acid (HA), and ferrihydrite-HA and kaolinite-HA organo-mineral composites using sorption batch experiments, synchrotron X-ray absorption spectroscopy (EXAFS), and scanning transmission electron microscopy (STEM). We measured the sorption of Co to the end-member mineral and organic phases and the composites as a function of pH, ionic strength and Co concentration, and also for the composites as a function of organic carbon concentration, with composites made containing a wide range of organic carbon contents. We then determined the molecular mechanisms of Co sorption to the end-member phases and the composites, and used this information to develop molecularly constrained thermodynamic surface complexation models to quantify Co sorption. Sorption to the ferrihydrite-HA and kaolinite-HA organo-mineral composites was found to be intermediate to both of the end-member phases, displaying enhanced sorption respective to the mineral end-member phase at mid-low pH. EXAFS analysis shows that there is a universal sorption mechanism accounting for Co sorption to the end-member mineral and organic phases and the organo-mineral composites at mid-high pH, in which Co sorbs to these phases via inner-sphere bidentate binuclear surface complexes. At mid-low pH, sorption to all the phases except ferrihydrite is the result of outer-sphere complexation. Our new molecularly constrained thermodynamic surface complexation models for Co sorption to ferrihydrite, kaolinite, HA, and ferrihydrite-HA and kaolinite-HA organo-mineral composites, show that Co sorption to the composites cannot be modelled assuming linear additivity of Co sorption to the end-member phases.
Metadata
Item Type: | Article |
---|---|
Authors/Creators: |
|
Copyright, Publisher and Additional Information: | © 2018 The Authors. Published by Elsevier Ltd. This is an open access article under the terms of the Creative Commons Attribution License (CC-BY 4.0), which permits unrestricted use, distribution and reproduction in any medium, provided the original work is properly cited. To view a copy of this license, visit http://creativecommons.org/licenses/by/4.0/. |
Keywords: | Cobalt; Sorption; EXAFS; TEM; Iron (hydr)oxides; Kaolinite; Humic acid; Composites; Surface complexation model |
Dates: |
|
Institution: | The University of Leeds |
Academic Units: | The University of Leeds > Faculty of Engineering & Physical Sciences (Leeds) > School of Chemical & Process Engineering (Leeds) The University of Leeds > Faculty of Environment (Leeds) > School of Earth and Environment (Leeds) > Earth Surface Science Institute (ESSI) (Leeds) |
Funding Information: | Funder Grant number EPSRC EP/M028143/1 |
Depositing User: | Symplectic Publications |
Date Deposited: | 29 Jun 2018 10:06 |
Last Modified: | 13 Aug 2018 09:17 |
Status: | Published |
Publisher: | Elsevier |
Identification Number: | 10.1016/j.gca.2018.06.035 |
Open Archives Initiative ID (OAI ID): | oai:eprints.whiterose.ac.uk:132775 |