Abstract
Thiosulfate leaching combined with ion-exchange resins is an innovative alternative for gold recovery. According to the properties of activated carbon, it could replace resins in the gold recovery process, improve efficiency, and reduce operating cost. In this research, the adsorption process of gold thiosulfate complex on thiol-modified activated carbon was studied. Thioglycolic acid (ATG) was impregnated in activated carbon, and its adsorption ability was tested with synthetic solutions of gold and sodium thiosulfate (Au 10 mg·L−1, Na2S2O3 0.1 mol·L−1, pH = 10.0). Carbon was characterized by infrared spectroscopy, SEM-EDS, PZC titration, hardness number measures, and proximal analysis. Synthetic solutions were also characterized by UV-vis spectroscopy and cyclic voltammetry. The percentage of volatile material increased from 10.0 to 13.9% due to the impregnation process of ATG. Infrared spectra show characteristic bands of C-H, S-H, and C-S bonds. In the adsorption tests, the ATG-impregnated carbon achieved 91% of gold recovery, while the same amount of ATG in the liquid phase stirred with unmodified activated carbon reached 90% of gold recovery. The 44.9% of gold recovered with activated carbon impregnated with ATG was eluted with sodium cyanide ([NaCN] = 0.2 mol·L−1; [NaOH] = 0.25 mol·L−1; [CH3CH2OH] = 30% V/V; pH = 12.0; t = 24 h). These results suggest the gold transferred from the thiosulfate complex to a new gold thiolate complex.
Highlights
Cyanidation has been the most used technique for the hydrometallurgical gold recovery
It is important to emphasize that the gold a mechanism of exchange of ligands; in Section 2.5., this topic is described in more detail when the mining industry consumes large amounts of activated carbon, despite the fact that it is regenerated proposed mechanism of adsorption is presented
The adsorption of ATG in activated carbon allowed for a recovery of
Summary
Cyanidation has been the most used technique for the hydrometallurgical gold recovery. Molecules 2020, 25, 2902 rate by 20 times, according to the following reactions [2] In this case, ammonia and copper are combined to form a cupric tetra-amine complex, which is a strong oxidizing agent that improves the gold leaching [4,5]. Silica mesoporous gel was prepared through sol–gel synthesis using mercaptosilanes as precursors in order to study its ability to adsorb gold thiosulfate complex It achieved gold recoveries higher than 90% after 24 h of stirring in synthetic solutions of 50 mg·L−1 of gold [17]. The groups attached to the carbon surface constitute active centers susceptible to physical or chemical interactions This property allows for the incorporation of sulfur functionalities capable of interacting with the gold thiosulfate complex and recovering it from leaching solutions [18,19,20,21]. The mechanism of gold recovery for this system was proposed
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