Removal of fluoride ions from solution by chelating resin with imino-diacetate functionality

We present the first reported study of imino-diacetate ion exchange resins which have been exchanged with aluminium ions which may offer an improved means of selectively removing fluoride ions from solution. Fluoride in water resources remains a significant problem worldwide often preventing or restricting beneficial use. This study undertook kinetics, equilibrium, and column tests to determine the effectiveness of Lanxess TP208 resin for fluoride removal over a range of solution fluoride concentrations and pH. Fluoride uptake was significantly influenced by both solution fluoride ion concentration and pH. Equilibrium studies suggested the maximum loading of fluoride ions was 1.3, 12.4, and 60.7 g F/kg resin for fluoride concentrations of ca. 10, 100 and 1000 mg/L, respectively at a solution pH of 6-7.5. Decreasing the solution pH to ca. 5.5 by addition of sulphuric acid resulted in a 27% increase in maximum fluoride loading to 15.7 g F/kg TP208 resin at a solution fluoride concentration of 100 mg/L. Significantly, the sorption process did not release chloride ions or any other detectable anions into solution. Sodium ions were removed from solution stoichiometrically with fluoride. Column studies confirmed the impact of fluoride concentration upon resin performance and suggested that multiple pathways may facilitate fluoride uptake. Future studies should focus on understanding whether imino-diacetate chelating resins exchanged with alternate metal (III) species (e.g. La, Ce, Fe) can effectively remove fluoride ions, the impact of competing ions on resin performance and how to regenerate sodium fluoride loaded resins.