Solvent Extraction of Calcium and Strontium into Nitrobenzene by Using a Synergistic Mixture of Hydrogen Dicarbollylcobaltate and 2,6-(Diphenylphosphino)Pyridine Dioxide

Solvent extraction of microamounts of calcium and strontium by a nitrobenzene solution of hydrogen dicarbollylcobaltate (H+B–) in the presence of 2,6-(diphenylphosphino)pyridine dioxide (DPPPDO, L) has been investigated. The equilibrium data have been explained assuming that the species HL+, HL+ 2, CaL2+ 2, CaL2+ 3, SrL2+ 2, SrL2+ 3 and SrL2+ 4 are extracted into the organic phase. The values of extraction and stability constants of the species in nitrobenzene saturated with water have been determined.