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

Reprocessing tailings for gold recovery is generating new low-grade refractory secondary tailings. Unlocking trapped within these potentially holds additional economic value. In this study, the use of supercritical carbon dioxide (scCO2) at 100 bar and 40 °C extraction from such a sample (0.27 g Au/t) was investigated. The research identified screened following ligands as suitable extractants 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) hexafluoroacetylacetone (HFA). Results screening experiments showed that all presence tri-n-butyl phosphate-nitric acid adduct (TBP-HNO3) oxidant exceeded 50% after 18 h, with highest offered by [Hbet][TF2N] (82% 24 h). A comparative where no scCO2 present, distinct advantage extraction.