New sorbents for the hydrometallurgical recovery of gold from electric and electronic wastes

This study examines the adsorption performance of functionalized electrospun fibers (EFs) and an amine-loaded metal–organic framework (UiO-66-NH2) for gold recovery, testing model acidic solutions simulating Waste Electrical and Electronic Equipment (WEEE) hydrometallurgical leachates. Dithioester-functionalized EFs and UiO-66-NH2 were selected for their stability in the acidic environment, the affinity for gold via thiol and amine groups, and the potential formation of gold nanoparticles through surface reduction. Experiments reveal that EFs exhibited excellent stability, easy separation, and high adsorption capacities, overcoming 100 mg/g in various operating conditions, even at a dissolved gold concentration below 20 mg/L. DTE provides a clear improvement of the adsorption capacity (around 27 mg/g for the plain EFs in contrast to 32–34 mg/g for the DTE-loaded fibers at 1 M HCl and 20 mg/g Au as initial concentration), dependent on the solution acidity and quickly approaching saturation, also at low gold concentration, testifying to the strong affinities between gold, amine, and thiol groups. Copper ions had a synergistic effect on gold uptake, enhancing adsorption and precipitation phenomena, and EFs exploited their best performance in highly acidic conditions (around 71 mg/g for the plain EFs in contrast to 96–104 mg/g for the DTE-loaded fibers at 1 M HCl and 20 mg/g Au as initial concentration), making them suitable for hydrometallurgical treatments. In contrast, UiO-66-NH2 was more effective at solution pH = 2 and showed competitive adsorption between gold and copper, reducing its efficiency. Sodium ions had a mild competitive effect, but DTE-functionalized EFs maintained high selectivity toward gold. Spent EFs analysis further confirmed their potential for selective gold recovery, suggesting promising applications in refining WEEE leachates and in using gold-loaded sorbent as a functional material, useful, for example, to produce waste-derived catalysts.