Extraction of microamounts of europium and americium by a phenyltrifluoromethyl sulfone (FS 13) solution of hydrogen dicarbollylcobaltate
(H+B−) in the presence of N,N′-diethyl-N,N′-diphenyl-2,6-dipicolinamide (EtPhDPA, L) has been investigated. The equilibrium data have been explained assuming that the
species HL+, HL2+, ML23+, ML33+ and ML43+ (M3+ = Eu3+, Am3+) are extracted into the organic phase. The values of extraction and stability constants of the cationic complexes in FS 13
saturated with water have been determined. It was found that the stability constants of the corresponding complexes EuLn3+ and AmLn3+, where n = 2, 3, 4 and L is EtPhDPA, in water-saturated FS 13 are comparable.