Three-Component Ion-Exchange Equilibrium and Breakthrough Curve Analysis for the Treatment of F−- and NO3− Contaminated Groundwater Using Anion-Exchange Resin

The design of an anion exchange column and its operating conditions for the removal of fluoride ions (F−) and nitrate ions (NO3−) from the groundwater contaminated with these ions was investigated through laboratory-scale experiments and a mass transfer model for breakthrough curve analysis. Using a strong base anion exchange resin, breakthrough curves were obtained under various binary mixture conditions of chloride (Cl−), NO3−, F−, and hydroxide ions (OH−). A mass transfer model was developed to determine the ion exchange capacity and mass transport coefficient from a breakthrough curve obtained in the binary system. Based on the relationships between ion compositions in the solution and resin phases at equilibrium observed in various binary systems, the selectivity coefficients, KClOH, KFOH, and KNO3OH were determined to be 7.0, 1.65, and 9.5, respectively. Using these selectivity coefficients, the ternary ion exchange equilibrium among Cl−, NO3−, and F− was formulated. The mass transport model was then extended to the ternary system by incorporating the formulated ternary equilibrium relationship. A breakthrough curve obtained for the mixture of F− and NO3− ions using Cl− - form resin was analyzed with the model extended to the ternary system, demonstrating its validity. The concentration profiles of F−, NO3−, and Cl− in the solution and resin phases along the column during operation were also analyzed in detail using the model. Finally, the developed model was applied to the design of an anion exchange column for producing drinking water by removing F− and NO3− from groundwater under conditions representative of typical Indian household usage.