Surfactant gel extraction of gold(III), palladium(II), platinum(II), and lead(II) as thiourea-complexes.

Anionic surfactant solutions of sodium dodecylbenzenesulfonate (SDBS) and sodium dodecylsulfate (SDS) separate into two phases through cooling of the solution and the addition of salts. Thiourea (TU) reacts with many metals to form cationic complexes of [M(TU)(n)](m+); some of them extract into the SDBS phase. The separation was examined for lead and tin in commercially purchased solders. More than 95% lead was extracted into the SDBS phase, while tin remained in the aqueous phase. An abnormal decrease in extractability was observed for the [M(TU)(n)](m+) of noble metal complexes at low metal concentrations. The surfactant phases of SDBS and SDS were confirmed as lamellar structures using small angle X-ray scattering (SAXS), and the stability and rigidity of this structure influenced the extractability of the [Au(TU)(n)](3+) complex. The separation of gold(III) and palladium(II) was examined for the SDS system.