Abstract
Recent advances in the electronics sector and the short life-span of electronic products have triggered an exponential increase in the generation of electronic waste (E-waste). Effective recycling of E-waste has thus become a serious solid waste management challenge. E-waste management technologies include pyrometallurgy, hydrometallurgy, and bioleaching. Determining the metal content of an E-waste sample is critical in evaluating the efficiency of a metal recovery method in E-waste recycling. However, E-waste is complex and of diverse origins. The lack of a standard digestion method for E-waste has resulted in difficulty in comparing the efficiencies of different metal recovery processes. In this study, several solid digestion protocols including American Society for Testing and Materials (ASTM)-D6357-11, United States Environment Protection Agency Solid Waste (US EPA SW) 846 Method 3050b, ultrasound-assisted, and microwave digestion methods were compared to determine the metal content (Ag, Al, Au, Cu, Fe, Ni, Pb, Pd, Sn, and Zn) of electronic scrap materials (ESM) obtained from two different sources. The highest metal recovery (mg/g of ESM) was obtained using ASTM D6357-11 for most of the metals, which remained mainly bound to silicate fractions, while a microwave-assisted digestion protocol (MWD-2) was more effective in solubilizing Al, Pb, and Sn. The study highlights the need for a judicious selection of digestion protocol, and proposes steps for selecting an effective acid digestion method for ESM.
Highlights
Rapid industrialization and urbanization have resulted in an exponential increase in the generation of hazardous industrial and municipal solid wastes (MSW) including electronic wastes (E-wastes), fly ash, spent catalyst, and battery wastes [1,2,3]
The current study evaluates the recovery efficiency of several digestion protocols to determine the metal content in E-wastes, using electronic scrap material (ESM) from printed circuit boards (PCBs) as an example
Scanning Electron Microscopy (SEM) micrographs of electronic scrap materials (ESM) samples as-received from the two sources
Summary
Rapid industrialization and urbanization have resulted in an exponential increase in the generation of hazardous industrial and municipal solid wastes (MSW) including electronic wastes (E-wastes), fly ash, spent catalyst, and battery wastes [1,2,3]. 2.2 billion tonnes annually by 2025 [4] These solid wastes generally contain mixtures of hazardous chemicals including polymers and heavy metals (such as cadmium, mercury, and lead) [1,5]. Rapid technological advancement has resulted in the growing consumption of heavy metals (for instance copper, nickel, zinc, chromium, iron, etc.) in various industries such as automobile, electronics, steel, chemical, and even medicine fields [8] Such increasing demand has caused massive depletion of natural ore reserves, making it extremely crucial to search for alternative sources of these metals. An acid digestion reaction of a solid waste depends on the following factors: the acid used and its concentration, reaction time, external driving forces (heat, ultrasound, agitation, microwave, etc.), reaction conditions (temperature, solid-liquid ratio, etc.), and the chemical form of the metals present in the solid waste matrix [32]. Method D 6357-11, US EPA (United States Environmental Protection Agency) methods, as well as ultrasound-assisted and microwave digestion methods
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