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

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 HNO 3 ) 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·z H 2 O (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 .

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