Acid-enhanced limestone defluoridation in column reactor using oxalic acid |
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| Authors: | Suresh K Nath Robin K Dutta |
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| Institution: | 1. Department of Radiology and Advanced Imaging Research Center, University of Texas Southwestern Medical Center, Dallas, TX;2. Department of Radiology, University of Texas Southwestern Medical Center, Dallas, TX;3. Department of Urology, University of Texas Southwestern Medical Center, Dallas, TX;4. Department of Pathology, University of Texas Southwestern Medical Center, Dallas, TX;1. Department of Chemistry, Fuzhou University, Fuzhou, Fujian 350108, China;2. State Key Laboratory of Structural Chemistry, Fujian Institute of Research on the Structure of Matter, Chinese Academy of Sciences, Fuzhou, Fujian 350002, China;1. Physics Department, Faculty of Science, Qassim University Buraydah 51452, Saudi Arabia;2. Physics Department, Faculty of Science, Al-Azhar University, Assuit 71452, Egypt;3. Qassim university, Agricultural College, P.O. Box 6622, Buraydah 51452, Saudi Arabia;1. School of Chemical and Biological Engineering, Seoul National University, Seoul 151-742, Republic of Korea;2. Department of Chemical Engineering, Soongsil University, Seoul 156-743 Republic of Korea;3. Department of Chemical and Biomolecular Engineering, University of Illinois, Urbana, IL 61801, USA |
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| Abstract: | Acid enhanced limestone defluoridation of water has been studied in a crushed limestone column reactor using oxalic acid (OA). The defluoridation has been studied with varying initial fluoride concentrations of 5, 10, 15 and 20 mg/L and acid concentrations of 0.01, 0.05 and 0.1 M. The fluoride removal was found to increase with increase in the concentration of the acid, removing fluoride up to 95% with 0.1 M OA. The observed good fluoride removal has been attributed to a combination of two mechanisms of fluoride removal, viz., precipitation of calcium fluoride and adsorption of fluoride ions on limestone surfaces. While the removal by precipitation remains same on repeated use of the same limestone column, the adsorption is more with the fresh limestone and decreases gradually on repeated use of the same limestone column. The precipitate has been characterized using various analytical tools, viz., X-ray diffraction, IR spectroscopy, thermogravimetric analysis, scanning electron microscopy combined with energy dispersive X-ray spectroscopy and X-ray photoelectron spectroscopy. The Ca2+ ions, formed due to dissolution of limestone by the acid, precipitate calcium fluoride along with precipitation of calcium oxalate. A good fluoride removal ability, low residual oxalate, acceptable final pH, low-cost and simplicity of the process make the present acid-enhanced limestone defluoridation process with OA a potential method for defluoridation of groundwater. |
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