Regeneration of perchlorate (CIO₄^-)-loaded anion exchange resins by a novel tetrachloroferrate (FeCl₄^-) displacement technique

Selective ion exchange is one of the preferred treatment technologies for removing low levels of perchlorate (CIO₄^-) from contaminated water because of its high efficiency and minimal impact on water quality through the addition or removal of chemicals and nutrients. However, the exceptionally high affinity of CIO₄^- for type I anion-exchange resins makes regeneration with conventional NaCl brine extremely difficult and costly for practical applications. The present study entails the development of a novel regeneration methodology applicable to highly selective anion-exchange resins. Tetrachloroferrate (FeCl₄^-) anions, formed in a solution of ferric chloride and hydrochloric acid (e.g., 1 M FeCl₃ and 4 M HCl), were found to effectively displace CIO₄^- anions that were sorbed on the resin. A mass-balance analysis indicated that a nearly 100% recovery of ion-exchange sites was achieved by washing with as little as ∼5 bed volumes of the regenerant solution in a column flow-through experiment. There was no significant deterioration of the resin's performance with respect to CIO₄^- removal after repeated loading and regeneration cycles. Thus, the new methodology may offer a cost-effective means to regenerate CIO₄^- -loaded resins with improved regeneration efficiency, recovery, and waste minimization in comparison with conventional brine regeneration techniques.