Recovery of precious metals from ammoniacal thiosulfate solutions by hybrid mesoporous silica: 1-Factors affecting gold adsorption

• Novelty in the application of hybrid mesoporous silica in recovery of gold thiosulfate.
• Detailed study of the chemistry with respect to reagent concentrations in a simulated system.
• Finding the significant factors (concentrations, interfering ions, etc.) in adsorption of the gold.
• High adsorption capacity and selectivity of the adsorbents for gold compound in simulated solutions.
• Attractiveness in real application due to technical and economic material synthesis advantages.

Mesoporous silica materials mainly of type MSU-X functionalized with simple amine and thiol (mercapto-) ligands, have been used to adsorb gold thiosulfate complex from ammoniacal copper-bearing solutions. Variation in major reagent concentrations was investigated for the determination of the appropriate dosages of ammonium, thiosulfate and cupric salts to obtain a high recovery of gold thiosulfate from simulated leach solutions. It was found that ammonium/ammonia concentration and specifically its ratio with respect to that of thiosulfate had determining effects on gold adsorption by functionalized mesoporous silica. The adsorbents performed well in both neutral and alkaline pH provided that the latter was provided by aqueous ammonia solution. There was significant interference with gold adsorption in presence of high concentrations of sodium ions in the solutions. Among the anionic species, chloride was found to cause the largest detrimental effect on gold thiosulfate uptake by the hybrid silica. Adsorption isotherms and kinetics of gold recovery by functional mesoporous silica were investigated. The material showed exceptionally high adsorption capacities reaching above 3 mmol (∼600 mg) gold per gram of amine-bearing adsorbent accompanied by an average maximum of 80% precious metal recovery.