Novel solvent system for metal ion separation: Improved solvent extractionof strontium(II) and lead(II) as dicyclohexano-18-crown-6 complexes

As a part of our study of hazardous metal ion separations, the extraction o f Sr2+ and Pb2+ from solutions containing nitric acid and various nitrate s alts has been investigated. High partition ratios (D-Sr > 100-10) were obse rved using comparatively low (10-50 mM) concentrations of dicyclohexano-18- crown-6 in a group of nitrile solvents with relatively high dielectric cons tants (adiponitrile, glutaronitrile, succinonitrile, malononitrile; epsilon = 30-60) Which are able to participate in coalescence extraction. Equilibr ia in the solvent extraction system were characterized, with Sr(II) and Pb( II) occurring in the organic phase primarily as partially dissociated ion p airs. A dramatic increase of extraction efficiency over traditional systems is achieved because of the formation of solvated cationic complexes in the organic phase.