Solvent Extraction of Gold from Alkaline Cyanide Solution with a Tri‐n‐octylamine/Tri‐n‐butyl phosphate/n‐heptane Synergistic System

Abstract

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 (ϕ _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 ϕ _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 − logϕ _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.

Keywords:

• Solvent extraction
• KAu(CN)₂
• tri‐n‐octylamine
• stripping
• aggregations

Acknowledgements

The authors acknowledge the financial support of the National Natural Science Foundation of China. Many thanks are given to Professor Weijin Zhou and Xiangyun Wang of Peking University for their kind help and meaningful discussions. Special thanks are given to Miss Lingtian Tang of Peking University for her help during the whole experiment.