Extraction of trivalent lanthanide cations by diphenyl phosphinic acid

The distribution of trivalent lanthanides between solutions of diphenyl phosphinic acid, (ϕ)₂PO(OH), in chloroform and aqueous phases containing nitrate ions was investigated radiometrically. The distribution ratio was studied as a function of mineral acid and salt concentrations in the aqueous phase and extractant concentration in the organic phase, for all lanthanides except Pm. The compositions of the extracted complexes were investigated by the usual slope analysis. The results obtained for a given set of conditions indicate that none of the anions present in the aqueous medium are present in the extracted complex species. For these conditions, the distribution ratio D was found to vary as extractant]^2.7 and H⁺]⁻³, where the concentrations refer to the organic and aqueous phases, respectively. It therefore appears that a mixture of complex species is extracted, and the possible structures of these species and a mechanism for the extraction are discussed.