Regeneration of Spent Resin Columns
Selective ion exchange is one of the preferred treatment technologies for removing low to trace levels of perchlorate (ClO4-) 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 ClO4- for Type I strong-base anion-exchange resins makes regeneration with conventional NaCl brine extremely difficult and costly for practical applications. The Oak Ridge National Laboratory recently developed a novel methodology to regenerate this type of resins loaded with ClO4-. Tetrachloroferrate (FeCl4-) anions, formed in a solution of ferric chloride and hydrochloric acid (i.e., FeCl3 and HCl), were found to effectively displace ClO4- 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 ~2 - 3 bed volumes of the regenerant solution in a column. There was no significant deterioration of the resin’s performance with respect to ClO4- removal after repeated loading and regeneration cycles. The new methodology offers a cost-effective means to regenerate ClO4--loaded resins with improved regeneration efficiency, recovery, and waste minimization in comparison with conventional brine regeneration techniques. Additionally, a new methodology was also developed to completely destroy perchlorate in the FeCl3-HCl regenerant solution; the regenerant can thus be recycled, and practically no secondary wastes are produced.