Solvent extraction of gold from alkaline cyanide solution with a tri-n-octylamine/tri-n-butyl phosphate/n-heptane synergistic system

Solvent extraction of KAu(CN)(2) from alkaline cyanide solution by using the pre-acidified tertiary amine, tri-n-octylamine(TOA) as extractant with the addition of tri-n-butyl phosphate (TBP) as a synergist has been studied. The influence of several variables such as the molar ratio of TOA to KAu(CN)(2) (n(r)), the volume percentage of TBP (phi(TBP)), the phase ratio of the organic phase to the aqueous phase and the pH value of the aqueous phase were investigated. The results indicated that, at a certain pH range, while phi(TBP) is above 20%(v/v) and n(r) is bigger than 1, the organic phase can extract gold from the aqueous phase completely. The relationship between the extraction percentage of gold (E) against n(r) and the logD - log phi(TBP) plot indicate that the stoichiometry of the extracted species is a 1:1:3 complex, namely, [TOA (.) H+] (.) [Au(CN)(2)(-)](.)3TBP. Dynamic laser scattering (DLS) method reveals that the organic phase tends to self-assemble to form aggregations when the concentration of gold in the organic phase reaches a certain limiting value. The stripping of the loading organic phase by NaOH and inorganic salts, such as NH4SCN, NaClO4 and potassium halides, has also been investigated.