Isolation of radioactive strontium from natural samples: separation of strontium from alkaline and alkaline earth elements by means of mixed solvent anion exchange

This paper presents the results of studies which led to the procedures for the chromatographic separation of radioactive strontium from alkaline. earth-alkaline and other elements in natural samples, on columns filled with strong base anion exchangers using alcoholic solutions of nitric acid as eluents. It has been shown that potassium, caesium, calcium, barium, yttrium and strontium can be adsorbed on strong base anion exchangers of the DOWEX and AMBERLITE type, which contain the quaternary ammonium group with nitrate as counter-ion, from solutions of nitric acid in alcohol. Adsorption strength increases in the order methanol<ethanol<propanol for each individual cation, and in the order K<Cs<Ca<Y<Sr<Ba series for individual alcohol. Potassium and caesium are not adsorbed on the exchangers from 0.25 M HNO3 in methanol, while they are adsorbed from ethanol and propanol. The adsorption strength is influenced by the polarity of alcohol, by the concentration of nitrate and by pH. The strength with which strontium adsorbs on the exchangers increases in the interval from 0 to 0.25 M NH4NO3 in methanol, after which it starts to decrease. Strontium adsorbs to the exchangers from the alcoholic solution of ammonium nitrate twice as strongly as from the alcoholic solution of nitric acid, while a fraction of water in pure alcohol exceeding 10% prevents adsorption. In the mixture of alcohol and nitric acid, the adsorption strength for calcium and strontium increases with the increase of the volume fraction of alcohol with a lower dielectric constant. The rate and strength of adsorption of ions on the exchanger also increase in the series 0.25 M HNO3 in methanol <0.25 M HNO3 in ethanol <0.25 M HNO3 in 1-propanol for each individual ion, as well as in the Ca<Sr<Ba series for each individual alcohol. Adsorption rates of each individual ion on both exchangers are roughly equal. Strontium can be separated from other elements, with the exception of yttrium, on the columns filled with AMBERLITE CG-400 and DOWEX AG 1x8 exchangers with 0.25 M HNO3 in methanol, 0.25 M HNO3 in ethanol and 0.25 M HNO3 in propanol. Separation is also possible from alcohol mixtures. Strontium separation is most difficult from calcium, while the efficiency of separation increases with a decrease of the polarity of the used alcohol or alcohol mixture. The first group elements of the periodic table are not separated from each other in this way, while the elements of the second group are separated from each other with 0.25 M HNO3 in methanol. Similarly, the first group elements can be completely separated from the second group elements with 0.25 M HNO3 in 2-propanol. (C) 1999 Elsevier Science B.V. All rights reserved.