SELECTIVE REMOVAL OF STRONTIUM AND CESIUM FROM SIMULATED WASTE SOLUTION WITH TITANATE ION EXCHANGERS IN A FILTER CARTRIDGE CONFIGURATION (2011)

This report describes experimental results for the selective removal of strontium and cesium from simulated waste solutions using monosodium titanate (MST) and crystalline silicotitanate (CST)-laden filter cartridges. Four types of ion exchange cartridge media (CST and MST designed by both 3M and POROX{reg_sign}) were evaluated. In these proof-of-principle tests effective uptake of both Sr-85 and Cs-137 was observed. However, the experiments were not performed long enough to determine the saturation levels or breakthrough curve for each filter cartridge. POREX{reg_sign} MST cartridges, which by design were based on co-sintering of the active titanates with polyethylene particles, seem to perform as well as the 3M-designed MST cartridges (impregnated filter membrane design) in the uptake of strontium. At low salt simulant conditions (0.29 M Na{sup +}), the instantaneous decontamination factor (D{sub F}) for Sr-85 with the 3M-design MST cartridge measured 26, representing the removal of 96% of the Sr-85. On the other hand, the Sr-85 instantaneous D{sub F} with the POREX{reg_sign} design MST cartridge measured 40 or 98% removal of the Sr-85. Strontium removal with the 3M-design MST and CST cartridges placed in series filter arrangement produced an instantaneous decontamination factor of 41 or 97.6% removal compared to an instantaneous decontamination factor of 368 or 99.7% removal of the strontium with the POREX{reg_sign} MST and CST cartridge design placed in series. At high salt simulant conditions (5.6 M Na{sup +}), strontium removal with 3M-designed MST cartridge only and with 3M-designed MST and CST cartridges operated in a series configuration were identical. The instantaneous decontamination factor and the strontium removal efficiency, under the above configuration, averaged 8.6 and 88%, respectively. There were no POREX{reg_sign} cartridge experiments using the higher ionic strength simulant solution. At low salt simulant conditions, the uptake of Cs-137 with POREX{reg_sign} CST cartridge out performed the 3M-designed CST cartridges. The POREX{reg_sign} CST cartridge, with a Cs-137 instantaneous decontamination factor of 55 and a Cs-137 removal efficiency of 98% does meet the Cs-137 decontamination goals in the low salt simulant liquor. The Cs-137 removal with 3M-designed CST cartridge produced a decontamination factor of 2 or 49% removal efficiency. The Cs-137 performance graph for the 3M-designed CST cartridge showed an early cessation in the uptake of cesium-137. This behavior was not observed with the POREX{reg_sign} CST cartridges. No Cs-137 uptake tests were performed with the POREX{reg_sign} CST cartridges at high salt simulant conditions. The 3M-designed CST cartridges, with an instantaneous Cs-137 decontamination factor of less than 3 and a Cs-137 removal efficiency of less than 50% failed to meet the Cs-137 decontamination goals in both the low and high salt simulant liquors. This poor performance in the uptake of Cs-137 by the 3M CST cartridges may be attributed to fabrication flaws for the 3M-designed CST cartridges. The reduced number of CST membrane wraps per cartridge during the cartridge design phase, from 3-whole wraps to about 1.5, may have contributed to Cs-137 laden simulant channeling/by-pass which led to the poor performance in terms of Cs-137 sorption characteristics for the 3M designed CST cartridges. The grinding of CST ion exchange materials, to reduce the particle size distribution and thus enhance their easy incorporation into the filter membranes and the co-sintering of MST with polyethylene particles, did not adversely affect the sorption kinetics of both CST and MST in the uptake of Cs-137 and Sr-85, respectively. In general, the POREX{reg_sign} based cartridges showed more resistance to simulant flow through the filter cartridges as evidenced by higher pressure differences across the cartridges. Based on these findings they conclude that incorporating MST and CST sorbents into filter membranes represent a promising method for the semi-continuous removal of radioisotopes of strontium and cesium from waste solutions.