EXTRACTION OF ACTINIDES AND NITRIC-ACID FROM SOLUTIONS IN HEAVY-WATER

An interest in study of extraction of metals from solutions in heavy w ater is stimulated by development of nuclear transmutation technologie s. Theoretical analysis of this problem shows that substitution of com mon water by heavy water should increase extraction of metals by neutr al extractants and amines. Namely, the isotope effect should be positi ve, i.e., the ratio between distribution coefficients of metal in syst ems with heavy water and common water should be greater than unity (be ta > 1). In contrast, in extraction of relatively bulky cations by org anophosphorus acids via cation-exchange mechanism the negative isotope effect (beta < 1) is expected. These theoretical predictions were con firmed experimentally. In fact, the extraction of americium nitrate an d uranyl nitrate by tributyl phosphate, and americium nitrate by trioc tylamine in the presence of unextractable salting-out agent is charact erized by positive isotope effect (beta > 1). The isotope effect is al so positive (beta = 1.8) in extraction of nitric acid with a 30% solut ion of TBP in n-dodecane. In extraction of uranyl nitrate with TBP in the presence of nitric acid (HNO3, DNO3) the sign of the isotope effec t changes from positive to negative with increasing nitric acid conten t owing to stronger replacing ability of deuteronitric acid with respe ct to uranyl nitrate. In accordance with theoretical prediction, extra ction of americium with di(2-ethylhexyl) hydrogen phosphate is charact erized by a negative isotope effect.