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  • 1 Fachbereich Anorganische Chemie und Kernchemie der Technischen Hochschule Darmstadt 6100 Darmstadt (FRG)
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The principles of selective separations by recrystallization are explained and formulae for the calculation of decontamination factors are presented. Experiments with strontium sulfate and radioactive strontium ions demonstrate the validity of the theoretical considerations. Similar or higher decontamination factors are found than those calculated for a uniform distribution of the radioactive strontium ions between crystals and solution. The high values are explained by assuming a recrystallization mechanism which consists of dissolution and redeposition of crystal layers. The half-times of recrystallization increase sharply with Sr2+ or SO 42− concentration in the solution. In nitric acid solutions as well as in mixtures containing nitrates and nitric acid the solubility of strontium sulfate is rather high, accordingly the decontamination factors are low under these conditions and furthermore the recrystallization half-times are long.