Mobilisation of Iron from rocks in a fractured aquifer: Lithological and geochemical controls |
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| Institution: | 1. College of Agriculture, Plant and Soil Sciences, University of Kentucky, Lexington, KY, USA;2. College of Engineering, Civil Engineering, University of Kentucky, Lexington, KY, USA;1. Centre for Systems Biology, University of Birmingham, UK;2. Centre for Computational Biology & Institute of Microbiology and Infection & School of Biosciences, University of Birmingham, Edgbaston, Birmingham B15 2TT, UK;3. Geotechnical and Hydrogeological Engineering Research Group, Federation University Australia, Victoria, Australia;4. Department of Biotechnology, Faculty of Applied Sciences, Delft University of Technology, The Netherlands;5. Department of Environmental Microbiology, UFZ – Helmholtz Centre for Environmental Research, 04318 Leipzig, Germany |
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| Abstract: | Iron mobilisation from aquifer rocks in an important fractured aquifer system in South Africa is resulting in clogging of boreholes by Fe oxide minerals. Leach experiments using natural waters were conducted to determine the effects of redox conditions, pH lithology and presence of organic acids on the rate and extent of Fe dissolution from aquifer rocks, with the aim of clarifying the association of Fe clogging with geological formations that show Fe staining on weathering. The results indicate that the greatest amount of Fe (>30 mmol/kg rock) is leached from arenaceous rocks with low total Fe contents (49.0–75.0 mmol/kg) under anoxic conditions. Rocks with the highest Fe contents (>800 mmol/kg) generated low concentrations of Fe (<10 mmol/kg) even under favourable conditions of 0 mg/L DO and pH 3. The extent of Fe dissolution from the rocks was found to be most strongly dependent on the redox conditions, and the form of Fe present in the rock, with ascorbate-extracted amorphous Fe being the most mobile. The rate of dissolution is affected by pH and the presence of natural organic acids in the leachate. However, the effect of organic acids was only noticeable on arenaceous rocks. |
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