Cesium phosphotungstic acid

Cesium isotopes can be recovered from fission products by digestion in nitric acid, and after filtration of waste the radioactive cesium phosphotungstate is precipitated using phosphotungstic acid. This technique can be used to prepare radioactive cesium metal or compounds. Various processes for removal of Cs isotopes from radioactive waste have been developed including solvent extraction using macrocycHc polyethers (62) or crown ethers (63) and coprecipitation with sodium tetraphenylboron (64). 

In acylation with acidic ammonium and cesium salts of phosphotungstic acid, direct correlation was found between activity and the number of accessable Br0nsted acid sites.69,70 Moreover, cesium salts were found to be more active, than HY and H-Beta zeolites.70... 

Alkylation of toluene with methanol was carried out on potassium, ammonium, cesium and thallium salts of phosphotungstic acid (MXH3.XPW12O40 M=K NH4, Cs and Tr, x is varied from 0 to 3). The major products obtained are xylenes, tri - and tetra-methylbenzenes. The selectivity of p-xylene was found to be higher than the equilibrium values. The salts with composition M2,5Ho,5PWi204o showed maximum activity and para selectivity. p-Xylene selectivity was evaluated as a function of x. It is seen that para selectivity correlates linearly with the number of strong acid sites with a strength of Ho <-5.6. 

For cesium, the waste packaging process calls for the separation of the cesium from the acid waste, purification to remove metallic contaminants, conversion to anhydrous chloride, and subsequent encapsulation in double-walled metal cans. The cesium currently is separated from the acid waste by phosphotungstic acid precipitation and partially purified... 

Both the approaches were combined together to evaluate the performance of these HPA-loaded membranes with small particles [17] and MEA stabilization techniques to yield a stabiUzed MEA for operation at 120°C and 35% relative humidity (RH). MEAs were prepared using Nafion /phosphotungstic acid composite membranes with phosphotungstic acid (HPW) particle size of 30-50 nm and the HPW additive stabilized by substituting its protons with cesium counter ions. The Nafion in the membrane and electrodes were simultaneously converted to the Cs form by an imi-exchange process. The melt processability of the Nafion in the Cs form permitted the MEA to be heat treated at 200°C and 30 atm, promoting the development of a durable membrane/electrode interface. The prior stabilization of the HPW permitted MEA reprotonation with minimal additive loss which was confirmed by FTIR, TGA, and in situ electrochemical impedance spectroscopy (EIS). 

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