24 covery of cesium is highly dependent on the partic lot lar ferrocyanide used. These predictions were confirmed by the column « NH4NO3 SOLUTIONS HNOz SOLUTIONS ioF LL Zirconium ferrocyanide was an excellent excha. 107 Ka oiol L 10° L I 0 = CESIUM I O=RUBIDIUM =| 10 periments. Zine ferrocyanide was found to be the bh exchange medium for the separation and recovery eesium and rubidium. Using 2 AZ ammonium nitr: or 3 Vf nitric acid, the adsorbed rubidium coulel completely recovered from a zine ferrocyanide ci umn. Cesium could then be eluted from the coli with either 9 VW nitric acid or 9 AJ ammonium nitra’ ] iO | 8 | 6 4 2 0 2 MOLARITY | 4 | 6 } 8 ! 10 Fic. 19—Distribution coefficients for the partition of cesium and rubidium between zirconium ferrocyanide and ammonium nitrate andnitric acid. columns of zirconium ferrocyanide adsorbed greater than 999% of the cesium but a maximum of only 46% of rubidium from the spiked water solutions. The adsorbed rubidium was readily eluted with 6 M nitric acid, but the cesium could be only partially eluted using 9 Mf acid. Zirconium ferrocyanide is therefore the most specific of the exchangers examined for the concentration of cesium, but is of little value for the separation of rubidium because of the low value of Ky for this ion. SUMMARY The ion exchange behavior of several heavy metal ferrocyanides has been investigated. The ferrocya- nides have shown varying degrees of stability in the eluents studied. Zine ferrocyanide and zirconium ferrocyanide were stable in nitrie acid and ammonium nitrate. Copper ferrocyanide was attacked in the ion exchange columns by nitric acid, but was stable in ammonium nitrate. According to the values of Kp for the three ferrocyanides, the separation of rubid- jum from cesium is feasible in each case, but the re- material for the concentration of cesium since to adsorption occurred and the cesium could not eluted effectively. Rubidium, however, was poorly a sorbed by the material and could be readily elut: Likewise, copper ferrocyanide adsorbed cesit strongly, and it could be eluted only with great di culty. Rubidium was effectively adsorbed and sep rated from ceslum on copper ferrocyanide colum using ammonium nitrate as eluent. Zirconium ferrocyanide, because of the high valu of its distribution coefficient Ay and values of t. distribution coefficients for cesium under all conditic: is ideally suited to concentrate fallout "Cs from 5. water. The #*Cs adsorbed on columns of zirconiu ferrocyanide can be counted directly and the conce tration of the radionuclide determined. Other radi nuclides will not interfere since the ferrocyanide specific for the alkali metals and because the activi of other long-lived nuclides such as ##K is known be equal to or less than that of cesium. Similar! copper ferroevanide concentrates cesium and rubi: ium but is of little value in analysis because of t! difficulties encountered in elution of adsorbed speci Cesium and rubidium, on the other hand, can : quantitatively recovered from as well as concentrate by zme ferrocyanide. Zinc ferroeyanide is, therefor an ideal material for the preconcentration of rubi: ium and cesium before analysis. Trace amounts : cesium and rubidium maybe concentrated on colum of this exchanger from large volumes of natural we ters and then determined after removal from the co umn by neutron activation with a minimum | contamination from nuclides other than those of zu or iron. Zine ferrocyanide can also be used to sep: rate these alkali metals from mixtures of other el ments imbiological samples, REFERENCES 1. Gustafson, P. F., Brar, S..8,, and Miuniak, 8S. E. Naéu 211, 843 (1966). 2, Folsom, T, R., Young, D. R., and Sreeknmoran, C. Serip; Institute of Oceanography, unpublished data. 3. Folsom, T. 2., Feldman, C., and Rains, T. C. Science 144 538 (1964).