Selection of a suitable ligand for the supercritical extraction of gold from a low-grade refractory tailing

• Published in: The Journal of supercritical fluids Vol. 179; p. 105415
• Main Authors: van Dyk, L.D., Mawire, G., Potgieter, J.H., Dworzanowski, M.
• Format: Journal Article
• Language: English
• Published: Elsevier B.V 01.01.2022
• Subjects: Gold; Ligands; Low-grade tailings; Silicates; Supercritical CO2; Gold; Ligands; Silicates; Supercritical CO2; Low-grade tailings
• ISSN: 0896-8446; 1872-8162
• DOI: 10.1016/j.supflu.2021.105415

Reprocessing tailings for gold recovery is generating new low-grade refractory secondary tailings. Unlocking gold trapped within these secondary tailings potentially holds additional economic value. In this study, the use of supercritical carbon dioxide (scCO2) at 100 bar and 40 °C for gold extraction from such a secondary gold tailings sample (0.27 g Au/t) was investigated. The research identified and screened the following ligands as suitable extractants for gold in scCO2: 3-(trifluoromethyl)-phenyl-thiourea (TPT), 1,1,1-trifluoro-2,4-pentanedione (TFA), betaine bis(trifluoromethylsulfonyl)imide ([Hbet][TF2N]), 4-methyl-4H-1,2,4-triazole-3-thiol (MHTT) and hexafluoroacetylacetone (HFA). Results from screening experiments showed that extraction of gold for all ligands in the presence of a tri-n-butyl phosphate-nitric acid adduct (TBP-HNO3) as oxidant exceeded 50% after 18 h, with the highest extraction offered by [Hbet][TF2N] (82% after 24 h). A comparative study, where no scCO2 was present, showed that the presence of scCO2 offered a distinct advantage in extraction. [Display omitted] •Supercritical carbon dioxide extraction of gold from reprocessed gold tailings.•Extraction of gold for all ligands was higher than 50% after 18 h.•Gold was extracted from its zero valent state.•The presence of scCO2 offered a distinct advantage in extraction.