EXTRACTION OF TRIVALENT AND TETRAVALENT ACTINIDES WITH DIHEXYL N,N-DIETHYLCARBAMOYLMETHYL PHOSPHONATE (DHDECMP) AND TBP FROM NITRIC-ACID SOLUTIONS

Extraction of trivalent (Pu3+, Am3+, actinides and Eu3+, a representative of lanthanides) and tetravalent (Np4+ and Pu4+) actinides has been studied with dihexyl N,N-di-ethylcarbamoylmethyl phosphonate (DHDECMP) in combination with TBP in benzene from 2M nitric acid. The stoichiometries of the species extracted were found to be M(NO3)3 . (3 - n) TBP . n DHDECMP (for trivalent ions) and M(NO3)4 . (2 - n) TBP . n DHDECMP (for tetravalent ions) by the slope ratio method. The extraction constants evaluated (from the distribution data) indicate that for tetravalent ions (with solvation number two) the extraction constant increases when TBP (Kh = 0.17) molecules are successively replaced by more basic DHDECMP (Kh = 0.34) molecules. However, for trivalent ions (with solvation number three) when TBP molecules are totally replaced by DHDECMP molecules stereochemical factors appear and instead of increase, a substantial decrease in extraction constants is observed for Eu3+ and Am3+, a lesser decrease being observed for Pu3+ (larger ion).