Cs~+ and Sr~(2+) Ion-Exchange Properties of Microporous Tungstates

摘要

The hydrothermally prepared hexagonal tungsten bronze (HTB) phase displays promising distribution coefficients (K_D) for both Cs~+ (2-100 ppm) and Sr~(2+) (0.5-60 ppm) in acidic (1M HNO3) radioactive waste simulants. The development of an inorganic ion-exchanger that displays such selectivity has previously eluded researchers in this field. The selectivity for Cs~+ and Sr~(2+) can be modulated by isomorphous substitution of molybdenum into the tungstate framework, and is optimum for material of nominal composition, Na_(0.2)Mo_(0.03)W_(0.97)O_3·zH_2O (Mo-HTB). Both the parent HTB and Mo-HTB phases display fast ion-exchange kinetics for Cs~+ and Sr~(2+) and cation exchange capacities ca. 50% that of the theoretical capacities of 0.9 and 0.45 mmol.g~(-1), respectively. The Mo-HTB adsorbent has a modest tolerance to alkali metal ions such as Na~+ and K~+ in acidic solutions with total Cs~+ and Sr~(2+) uptake dropping by 66% as the concentration of Na~+ increases from 9 mmol.L~(-1) to 1200 mmol L~(-1).