Anion Exchange by Mixed-bed Ion Exchange at Ultralow Concentrations

The effects of the cation-to-anion resin ratio and the amount of resin on anion exchange performance was experimentally studied with mixed-bed columns. Three different amounts of resin and five different cation-to-anion resin ratios were selected, and 10-4 M NaCl solution was used. The experiments were performed in continuous packed bed ion exchange column with commercially available exchange resins. The performance was evaluated with the breakthrough curves obtained. The results showed that the shape of chloride breakthrough curves and the level of leakage depended on the amount of anion exchange resin based on the resin ratio. In addition, the selectivity coefficient for chloride-hydroxide exchange and the diffusion coefficient influenced the steepness and the pattern of breakthrough curves. It was expected that cation exchange rate could be higher than anion exchange rate depending on resin capacities. However, anion exchange rate was higher due to other parameters that influence ion exchange rate, i.e. the shape of breakthrough curve. They were selectivity coefficients, mass-transfer coefficients and diffusion coefficients of ions.