Evaluating Ion Exchange for Removing Radium From Groundwater

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 régénérant dosages (up to 20 times stoichiometric) could desorb 75-90 percent of the adsorbed radium, but such excessive régénérant 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 régénérant reuse) continues to be an appropriate technology for the removal of radium. Este artículo, el segundo de una serie, se enfoca en los resultados de estudios de intercambio de iones en procesos hechos a escala bench y piloto para remover el radio de las aguas subterráneas en Lemont, Ill. Estudios de lotes y columnares indicaron una gran selectibilidad de la resina para el radio comparada con los cationes comunes. Estudios de agotamiento-regeneración con una gran variedad de resinas demostró que el intercambiador estándar de tipo gel de fuertes cationes ácidos es el mejor para remover el radio en una operación cíclica. Debido a que el proceso de ablandamiento de intercambio de iones, operado a una dureza límite (300-360 volúmenes de capa [BV]), remueve el radio pero no utiliza toda la capacidad de la resi