Modulating the carbon chain length of organic phosphine for the selective Au(I) recovery from a copper-ammonia-thiosulfate leaching solution

[Display omitted] •Organic phosphine(III) can be used as an extractant for gold selective recovery from Cu2+-NH3-thiosulfate solutions.•The longer the carbon chain, the better the selectivity of the extractant for Au(I).•Trihexylphosphine (THP) showed good selectivity for Au(I) in gold-leaching solution.•The extraction percentage of low concentration gold ions (6.73 mg/L) in actual gold leaching solution by THP reached 98 %. The selective recovery of gold ions from gold leaching solutions limits the industrial application of the copper-ammonia (Cu2+–NH3)-thiosulfate system. Here, the influence of the carbon chain length of organic phosphines on the selective recovery of gold ions was studied, and an extractant (trihexylphosphine, THP) that is suitable for the selective recovery of gold ions from a Cu2+–NH3-thiosulfate leaching solution was screened. The selectivity of organic phosphines with different carbon chain lengths for gold ions was C8 = C6 > C4 > C3 > C2, and when the number of carbon atoms in a single carbon chain was at least six, the selective recovery of gold ions from the Cu2+–NH3-thiosulfate solution was realized. THP completely recovered low concentration gold ions (6.73 mg/L) in the Cu2+–NH3-thiosulfate gold leaching solution regardless of the pH. The mechanism of gold ion extraction into the organic phase mainly involved ligand exchange between THP and [Au(S2O3)2]3−. Job’s method and density functional theory calculations confirmed that the composition ratio of the complex formed by THP and Au was 2:1 at the practical and theoretical levels, respectively. Finally, Multiwfn and VMD were used to visually predict the possible reaction sites in THP. This study provides an exact method for the selective recovery of gold ions from thiosulfate-based gold leaching solutions, which will promote the development of thiosulfate-based gold leaching systems.