Thiol functionalized activated carbon for gold thiosulfate recovery, an analysis of the interactions between gold and sulfur functions

• Published in: Carbon (New York) Vol. 204; pp. 254 - 267
• Main Authors: de la Torre-Miranda, Nathalie, Reilly, Laoise, Eloy, Pierre, Poleunis, Claude, Hermans, Sophie
• Format: Journal Article
• Language: English
• Published: Elsevier Ltd 01.02.2023
• Subjects: Activated carbon functionalization; Adsorption; Elution; Gold thiosulfate; Mechanism; Thiol functions; Gold thiosulfate; Thiol functions; Elution; Adsorption; Activated carbon functionalization; Mechanism
• ISSN: 0008-6223; 1873-3891
• DOI: 10.1016/j.carbon.2022.12.061

Cyanide salts are currently used as leaching agents in gold extraction processes despite their toxicity. Thiosulfate is a greener choice, but its employment is constrained by the difficulty at recovering gold thiosulfate from the leachate using activated carbon, which in contrast, works well for gold-cyanide adsorption. Aiming to solve this problem, activated carbon has been covalently functionalized with thiol groups (-SH) through a peptide bond formation with cysteamine, as thiol-carrier molecule. The functionalized carbon accomplishes up to 100% Au recovery (with 2 and 25 ppm Au solution) in 8 h contact and its performance seems independent on the solution's pH. In-depth solid characterization techniques (XPS, TOF-SIMS, FTIR, PXRD, TEM, N₂ physisorption, elemental analysis) have been used to unravel the interactions between Au thiosulfate and thiol functions and two different gold adsorption mechanisms have been demonstrated: under acid conditions, the formation of Au1+- S chains has been proven. Under basic conditions, Au⁰ species have been detected in addition to Au1+- S chains. Elution of the gold loaded samples has been accomplished at a 71% level using Na₂S₂O₃ and NH₄OH as eluents. [Display omitted] •Active carbon is covalently functionalized with thiol groups.•The S-rich carbon recovers up to 100% of Au thiosulfate in 8 h contact.•Au1+-S chains formation is proven as adsorption mechanism in acid conditions.•Under basic conditions, Au⁰ species are evidenced in addition to Au1+-S chains.•Elution is accomplished up to 71% using Na₂S₂O₃ and NH₄OH.