The extraction of Cs-137 and Sr-89 from waste simulants using pillared montmorillonite
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abstract
Two samples of a silica-pillared montmorillonite produced using 3-aminopropyltrimethoxy silane and an alumina-pillared montmorillonite were evaluated for the removal of 137Cs and 89Sr from a simulated nuclear waste solution and a simulated groundwater, and the results were compared to the parent montmorillonite and two zeolites, AW500 (chabazite) and clinoptilolite. The parent and pillared clays were characterized using x-ray powder diffraction and surface area analysis by nitrogen adsorption/desorption studies. The pillared clays exhibited d-spacings of between 17.43 and 18.32 after calcination, and surface areas ranging from 71.3 to 264.4 m2.g-1. Both of the silica-pillared clays and the alumina-pillared clay exhibited excellent Kds for 137Cs from simulated groundwater with values of 23650, 23260 and 144 570 mL/g, respectively. These were far better than the Kds obtained by clinoptilolite and AW500 which had Kds of only 14 560 and 9650 mL/g, respectively. None of the pillared clays showed a high selectivity for 89Sr from groundwater or 137Cs from simulated alkaline tank waste. They did, however, show a slight selectivity for 89Sr in the simulated Hanford tank wastes, but this is thought to be due to precipitation mechanism rather than to ion exchange.
