article · Waste Management
Growing volumes of electronic waste contain valuable precious metals like gold, creating a strong need for cost-effective and sustainable recovery methods that reduce the demand for primary mining. An activated carbon material derived from biomass and treated with sulphuric acid has been evaluated for capturing gold from simulated electronic waste liquids. The material achieved a high maximum gold uptake of over 1679 milligrams per gram, demonstrating rapid adsorption within approximately five hours. The process showed strong selectivity for gold complexes, driven by stable coordination and the chemical reduction of gold ions into metallic gold on the material surface. Furthermore, the captured gold was successfully recovered and the carbon adsorbent regenerated using an acidic thiourea solution, indicating good potential for reuse in recycling streams.
Electronic waste represents a rich source of gold, yet extracting it typically relies on harsh, expensive processes. Using activated carbon made from biomass provides a low-cost, sustainable alternative to harvest precious metals from discarded technology, helping turn harmful waste streams into secondary resources and easing the environmental burden of conventional metal mining.
This technology could enable e-waste recyclers and resource recovery operators to selectively capture gold from complex hydrometallurgical processing solutions. The research is currently early-stage, having been tested on simulated waste streams at laboratory scale, though the demonstrated regeneration of the adsorbent indicates useful operational potential.
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The surging affluent in society, concomitant with increasing global demand for electrical and electronic devices, has led to a sharp rise in e-waste generation. E-wastes contain significant amounts of precious metals, such as gold, which can be recovered and reused, thus reducing the environmental impact of mining new metals. Selective recovery using sustainable and cost-effective materials and methods is therefore vital. This study undertook a detailed evaluation of low-cost biomass-derived activated carbon (AC) for selective recovery of Au from simulated e-waste streams. Utilizing high-performance synthesized H<sub>2</sub>SO<sub>4</sub>-AC, the adsorption mechanisms were explicated through a combination of characterization techniques, i.e., FE-SEM, BET, TGA, XRD, FTIR, XPS, and DFT simulations to conceptualize the atomic and molecular level interactions. Optimization of coordination geometries between model H<sub>2</sub>SO<sub>4</sub>-AC and anionic complexes revealed the most stable coordination for AuCl<sub>4</sub><sup>-</sup> (binding energy, E<sub>b</sub> = -4064.15 eV). The Au selectivity was further enhanced by reduction of Au(III) to Au(0), as determined by XRD and XPS. The adsorption reaction was relatively fast (∼5h), and maximum Au uptake reached 1679.74 ± 37.66 mg/g (among highest), achieved through adsorption isotherm experiments. Furthermore, a mixture of 0.5 M thiourea/1 M HCl could effectively elute the loaded Au and regenerate the spent AC. This study presents radical attempts to examine in detail, the synergistic effects of H<sub>2</sub>SO<sub>4</sub> activation on biomass-derived ACs for selective recovery of Au from complex mixtures. The paper therefore describes a novel approach for the selective recovery of Au from e-wastes using multifunctional biomass-derived H<sub>2</sub>SO<sub>4</sub>-AC.
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DOI: 10.1016/j.wasman.2024.02.002
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