Reduction of iron(III) minerals by natural organic matter in groundwater |
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| Institution: | 1. Groundwater Protection and Restoration Group, Department of Civil and Structural Engineering, University of Sheffield, Sheffield S1 3JD UK;1. Departamento de Medicina, Universitat Internacional de Catalunya, Barcelona, España;2. Servei de Responsabilitat Professional, Colegio de Médicos de Barcelona, Consejo de Colegios de Médicos de Cataluña, Barcelona, España;3. Institut de Medicina Legal i Ciències Forenses de Catalunya, Barcelona, España;4. Unidad de Medicina Legal, Departamento de Salud Pública, Universidad de Barcelona, Barcelona, España;1. Unidad de Investigación en Cuidados de Salud (Investén-isciii), Instituto de Salud Carlos III, Madrid, España;2. Hospital Universitario Vall d’Hebron, Universidad Autónoma de Barcelona, Barcelona, España;1. Department of Chemistry, Adekunle Ajasin University, Akungba Akoko, Nigeria;2. School of Chemical Engineering, Universiti Sains Malaysia, Penang, Malaysia |
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| Abstract: | Construction of the entrance tunnel to the Äspö Hard Rock Laboratory, a prototype repository in Sweden for research into the geological disposal of spent nuclear fuel, has resulted in increased transport of organic carbon from the surface into the groundwater. This increased input of organic matter has induced accelerated oxidation of organic carbon associated with reduction of iron(III) minerals as the terminal electron acceptor in microbial respiration. Hydrochemical modeling of major solute ions at the site indicates an apparent first-order decay constant for organic carbon of 3.7 ± 2.6/yr. This rapid turnover is not accompanied by an equivalent mobilization of ferrous iron. Thermodynamic calculation of iron mineral solubility suggests that ferrous clay minerals may form in hydraulically transmissive fractures. The conditional potentials for the oxidation–reduction of such phases coincide with measured redox potentials at the site. The calculated potential is sufficiently low so that such phases would provide reducing capacity against future intrusion of O2 into the groundwater, thus buffering a repository against oxic corrosion of the engineered barriers. |
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