PRODUCTION OF HIGH-PURITY GD-153 .2. REMOVAL OF SAMARIUM, TERBIUM, AND MICROAMOUNTS OF EUROPIUM FROM GADOLINIUM BY EXTRACTION CHROMATOGRAPHY

Extraction and extraction-chromatographic behavior of Sm, Eu, Gd, and Tb in the system di-2-ethylhexyl hydrogen phosphate (DEHP)-decane-nitr ic acid has been studied at various concentrations of nitric acid and lanthanide in aqueous phase. The optimal range of nitric acid concentr ations for extraction-chromatographic separation of samarium, europium , gadolinium, and terbium has been determined. The influence of gadoli nium concentration on distribution of europium and terbium has been ex amined. At gadolinium content in solution below 50% of the dynamic exc hange capacity of the column, the gadolinium distribution coefficient slightly decreases with increasing gadolinium concentration in the ini tial solution, the distribution factors of the impurity lanthanides re maining virtually unchanged. With further increase in gadolinium conte nt in the initial solution, the gadolinium distribution factor drastic ally decreases, and ''tails'' are formed at the expense of increasing fraction of the extracted complex form GdA(3). These data allowed a co nclusion that composition of extracted complexes is different for Sm, Eu, Gd, and Tb. Conditions proposed for extraction-chromatographic pur ification of gadolinium in the system DEHP-decane-nitric acid provide for removal of impurity lanthanides (samarium, terbium, and microamoun ts of europium) with the purification factors greater than 100 (Sm, Tb ) and about 2 (Eu) at the column charge of up to 50%.