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gold oxides are typically insoluble in water and are used as pigments, but they also have applications in metallurgy where they provide reflective and conductive properties. These compounds are also used in nanotechnology for electrodes and light weight structural components.

Achieving a satisfactory recovery of precious metals from refractory ores requires a pretreatment process to overcome refractoriness and render the encapsulated gold accessible for leaching [1,2]. Roasting, pressure oxidation, bio-oxidation, alkaline and alkali sulfide leaching, and ultrafine grinding are commonly employed as such processes, but they have limited effectiveness.

The present study explores the use of reductively reduced graphene (rGO) in such a pretreatment to enhance the performance of hematite-based redox gold extractions, and in particular to promote dissolution of [AuCl4] ions in aqueous solution. The extraction behavior of rGO in such systems is investigated using X-ray photoelectron spectroscopy, a quantitative method that provides important information on the composition and structure of thin oxide layers.

rGO was prepared by chemical reduction of commercial, mass-produced GO with ascorbic acid. The resulting rGO was then dissolved in solutions of increasing concentrations of gold ions, and the extraction efficiency was assessed. The results demonstrated that reductive adsorption of gold ions onto rGO was the dominant mechanism responsible for the observed enhancement in extraction performance, and that the extraction kinetics were proportional to the amount of rGO added to the solution.

The gold concentration in the leachate was measured by ICP-OES and the extraction efficiency, R (%), was calculated as follows: R = Co Ce V m (R = 3.6 mg rGO 20 mL of final gold solution with C 100 +- 20 ppm) (where Co is the initial concentration of gold in the leachate, Ce is its concentration after filtration and m is the mass of dry rGO used). pH was varied between 2-11 by addition of HCl or NaOH to measure the influence of the reducing agent on the gold extractability.