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Solvent extraction of micro-amounts of Eu3+ and Am3+ from water into nitrobenzene by means of a mixture of hydrogen dicarbollylcobaltate (H+B-) and tetraisopropyl[oxybis(2,1-ethanediyliminocarbonyl)]-bisphosphoramidate (L) was studied. The equilibrium data were explained assuming that the species HL+, ML2 3+ and ML3 3+ (M3+ = Eu3+ or Am3+) are extracted into the organic phase. Extraction and stability constants of the cationic complex species in nitrobenzene saturated with water were determined and discussed. From the experimental results, it is obvious that this effective ligand L for the Eu3+ and Am3+ could be considered as a potential extraction agent for nuclear waste treatment.

Extraction of micro-amounts of europium by a nitrobenzene solution of hydrogen dicarbollylcobaltate (H+B-) in the presence of N,N'-dimethyl- -N,N'-diphenyl-2,6-dipicolinamide (MePhDPA, L) was investigated. The equilibrium data were explained assuming that the species HL+, + HL2 , 3+ EuL2 and 3+ EuL3 are extracted into the organic phase. The values of the extraction and stability constants of the species in nitrobenzene saturated with water were determined.

From extraction experiments and y -activity measurements, the exchange extraction constant corresponding to the equilibrium Ba 2+ (aq) + SrL 2 2+ (nb) ⇄ BaL 2 2+ (nb) + Sr 2+ (aq) occurring in the two-phase water-nitrobenzene system (L = benzo-15-crown-5; aq = aqueous phase, nb = nitrobenzene phase) was evaluated as log K ex (Ba 2+ , SrL 2 2+ ) = 0.3 ± 0.1. Furthermore, the stability constant of the benzo-15-crown-5 -barium complex in nitrobenzene saturated with water was calculated for the temperature of 25 °C: log β ng (BaL 2 2+ ) = 13.3±0.1.

General relations among thermodynamic parameters characterizing chemical equilibria including species ?2?+, HA, H+ and A- in both phases of a two-phase water-nitrobenzene extraction system have been derived. From the extraction measurements, the equilibrium distribution constant of electroneutral 1-(2-thiazolylazo)-2-naphthol (TAN, HA) between the nitrobenzene and aqueous phases has been determined: log ATD(HA) = 3.90?0.02. By using this value and further known constants and applying the mentioned relations, the following values of dissociation constants of TAN in nitrobenzene saturated with water have been calculated for a temperature of 25?C: pKdnb(H2A+) = -log Kdnb(H2A+) = 4.9 and pKdnb(HA) = -log Kdnb(HA) = 16.5.