No abstract

The hydrothermally prepared hexagonal tungsten bronze (HTB) phase displays promising distribution coefficients (. ' ) 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 ·]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 .,1752'8&7,21 )LJXUH Hexagonal Tungsten Bronze (+7%) (left) and pyrochlore (3<52) structures (right) viewed down the Fcrystallographic axis.