Evaluating Ion Exchange for Removing Radium From Groundwater

Abstract

This article, the second in a series, focuses on the results of bench‐ and pilot‐scale studies of ion exchange processes for radium removal from groundwater in Lemont, Ill. Batch and column studies indicated a very high resin selectivity for radium compared with common cations. Exhaustion‐regeneration studies with a variety of resins showed that a standard gel‐type strong‐acid cation exchanger is most suitable for radium removal in cyclic operation. Because the ion exchange softening process, operated to hardness breakthrough (300‐360 bed volumes [BV]), removes radium but does not fully utilize the resin capacity, cyclic runs were made with resins exhausted to radium breakthrough (2,500‐3,000 BV) and regenerated with sodium and calcium salts. But because of the poor radium regenerability of the exhausted resins, simultaneous breakthrough of radium and hardness occurred during the subsequent exhaustion run on the sodium cycle, and high radium leakage was observed on the calcium cycle. A study of factors affecting elution showed that during normal regeneration with 15‐20 lb NaCl/cu ft, only 20‐25 percent of the adsorbed radium was removed. For the Lemont water containing 12 pCi/L of Ra‐226, this left a typical Ra‐226 residual of 14,000 pCi Ra‐226/L resin after regeneration. Use of very high regenerant dosages (up to 20 times stoichiometric) could desorb 75‐90 percent of the adsorbed radium, but such excessive regenerant use, compared with normal dosages of two to three times stoichiometric, would not be economical without incorporation of regenerant‐reuse techniques. The sodium ion exchange softening process (operated to hardness breakthrough without regenerant reuse) continues to be an appropriate technology for the removal of radium.