Colloid formation in groundwater: effect of phosphate,manganese, silicate and dissolved organic matter on the dynamic heterogeneous oxidation of ferrous iron |
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| Institution: | 1. Department of Physics, Faculty of Science, Suez University, Suez, Egypt;2. Physics Department, Faculty of Science, King Abdulaziz University, Jeddah, Saudi Arabia;3. Physics Department, Faculty of Science, Zagazig University, Egypt;4. Materials Science Lab (1), Physics Department, Faculty of Science, Cairo University, Giza, Egypt;5. Ultrasonic Laboratory, National Institute of Standards, Giza, Egypt;6. Science and Technology Center of Excellence (STCE), Ministry of Military Production, Cairo, Egypt;7. Materials Science and Nanotechnology Department, Faculty of Postgraduate Studies for Advanced Science, Beni-Suef University, Egypt;8. Department of Mechanical and Aerospace Engineering, University of California, Irvine, CA, USA;1. School of Civil and Resources Engineering, University of Science and Technology Beijing, Beijing, 100083, China;2. Key Laboratory of High-Efficient Mining and Safety of Metal Mines, Ministry of Education, Beijing, 100083, China;1. Institut de Minéralogie et de Physique des Matériaux et de Cosmochimie (IMPMC), UMR CNRS 7590, UR IRD 206, Université Pierre et Marie Curie (UPMC), Campus Jussieu, 75252 Paris Cedex 05, France;2. CEREGE, UMR 6635 CNRS/Aix-Marseille Université, Europôle de l''Arbois, 13545 Aix-en-Provence, France;4. Centre IRD Noumea, 101 Promenade Roger Laroque, BP A5, 98848 Noumea Cedex, New Caledonia;5. Stanford Synchrotron Radiation Lightsource (SSRL), 2575 Sand Hill Road, Menlo Park, CA 94025, USA;6. Observatoire des Sciences de l’Univers de Grenoble, BP 53, 38041 Grenoble Cedex 9, France;7. European Synchrotron Radiation Facility (ESRF), FAME Beamline, French CRG, BP 220, F-38043 Grenoble Cedex, France;8. Sincrotrone Trieste (ELETTRA), Area Science Park, Strada Statale, 34012 Basovizza, Trieste, Italy;1. KIT INE, Postfach 3640, 76021 Karlsruhe, Germany;2. Paul Scherrer Institut, 5232 Villigen PSI, Switzerland;3. Australian Nuclear Science and Technology Organisation, Kirrawee DC, NSW 2232, Australia;4. Eberhard Karls Unversität Tübingen, Center for Applied Geoscience (ZAG), Hölderlinstrasse 12, 72074 Tübingen, Germany;1. Key Laboratory of Arable Land Conservation (Middle and Lower Reaches of Yangtse River), Ministry of Agriculture, College of Resources and Environment, Huazhong Agricultural University, Wuhan 430070, China;2. Department of Ecosystem Science and Management, University of Wyoming, Laramie, WY 82071, United States;3. Laboratory of Physical Chemistry and Colloid Science, Wageningen University, Dreijenplein 6, 6703 HB Wageningen, Netherlands |
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| Abstract: | Subsurface aeration is the in situ oxidation of Fe from groundwater that is used to make drinking water potable. When subsurface aeration is applied to an anaerobic groundwater system with pH>7, Fe(II) is oxidised heterogeneously. The heterogeneous oxidation of Fe(II) can result in the in situ formation of Fe colloids. To study this, the effect of substances commonly found in groundwater (e.g. PO4, Mn, silicate and fulvic acid) on the heterogeneous oxidation process was measured. The heterogeneous oxidation of Fe(II) becomes retarded when PO4, Mn, silicate or fulvic acid is present in the groundwater in addition to Fe(II). Phosphate and fulvic acid retarded the oxidation process most. The heterogeneous oxidation was described using a model with a homogeneous (k1) and an autocatalytic oxidation rate constant (k′2). From the modelling it followed that the homogeneous oxidation rate constant was not affected or even slightly elevated whereas the autocatalytic oxidation rate constant decreased remarkably by the addition of PO4, Mn, silicate or fulvic acid. From speciation calculations it followed that the decreased availability of the Fe(II) species can only explain a small part of the retarded autocatalytic oxidation process. Therefore exploratory calculations were performed to gain insight into whether the adsorption of PO4 or fulvic acid could explain the retarded autocatalytic oxidation. These calculations showed that the adsorption of fulvic acid could explain the retarded autocatalytic oxidation process. In contrast the adsorption of PO4 only partly explained the retarded autocatalytic oxidation process. In terms of colloid formation this study shows that the heterogeneous oxidation of Fe(II) in presence of PO4, Mn, silicate or fulvic acid leads to the formation of Fe colloids. |
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