Kalidoss Jayasankar

Although several techniques have been developed to extract copper from waste printed circuit boards (PCBs), there remain several challenges regarding energy consumption, local area contamination and environmental damage. A novel technique has been developed for extracting copper foils from waste PCBs based on low temperature pyrolysis followed by exfoliation to overcome these issues. The standard pretreatment steps of removing electronic components from PCBs and mechanical processing/size-reduction/powdering, etc., were minimized in this study. Several unsorted ‘as received’ PCBs were heat treated in the temperature range 750–850 °C for 5–20 min. in an argon atmosphere. Brittle dark chars and other residues on the heat-treated specimens were scrapped off to separate copper foils and other residuals. Most of the electronic components mounted on PCBs had dropped off during the heat treatment. Good-quality copper foils were recovered in all cases; the purity of copper was in excess of 85 wt.%. Key impurities present were Pb, Sn and Zn with typical concentrations less than 4 wt.%. Key features of the technique include minimizing energy intensive pre-treatment processes and waste handling, low pyrolysis temperatures and short heating times. This energy-efficient approach has the potential to enhance resource recovery while reducing the loss of materials, local area contamination and pollution near e-waste processing facilities.

Primary and secondary mill scales (MSs) are waste products produced by the surface oxidation of steel during the hot (800 to 1200 °C) rolling process in downstream steelmaking. While the primary MS is comprised of FeO, Fe₃O₄, and Fe₂O₃ in a range of proportions, the secondary MS primarily contain red ferric oxide (Fe₂O₃) (red MS). We report a novel route for extracting iron from red MS and transforming it into ferro-aluminium alloys using carbothermic reduction in the presence of alumina. The red MS powder was blended with high-purity alumina (Al₂O₃) and synthetic graphite (C) in a range of proportions. The carbothermic reduction of red MS-Al₂O₃-C blends was carried out at 1450 °C and 1550 °C under an argon atmosphere for 30 min and then furnace-cooled. The red MS was completely reduced to iron at these temperatures with reduced iron distributed around the matrix as small droplets. However, the addition of alumina unexpectedly resulted in a significant increase in the number and sizes of iron droplets generated, much higher reactivity, and the formation of ferrous alloys. A small amount of alumina reduction into metallic aluminium was also observed at 1450 °C. There is an urgent need to identify the true potential of industrial waste and the materials within it. This study showed that red MS is a valuable material source that could be transformed into ferro-aluminium alloys. These alloys find application in a range of industrial sectors such as construction, automotive, infrastructure, etc.

Thermal plasma systems are used to recover essential elements from sophisticated end-of-life (EOL) electronic components. The photovoltaic (PV) industry has undergone rapid development, resulting in an increasing quantity of silicon (Si)-based solid waste (SIBS), and is considered the most difficult waste to handle for recycling. In this study, we have implemented a novel pathway for transforming solar waste panels (containing 35% Si) and compact disk s (CDs containing 20% carbon) into an advanced hybrid material by high-temperature carbothermal reduction (around 1600 $^{\circ}$ C–1700 $^{\circ}$ C) using sustainable thermal plasma arc technology. The benefit of the thermal plasma technique is that it is an environmentally friendly, single-step process that is scalable compared to other carbothermic methods and chemical routes. The pure phases of Si and silicon carbide (SiC) were confirmed using Fourier transform infrared spectroscopy (FT-IR), X-ray diffraction (XRD), Raman spectroscopy, and X-ray photoelectron spectroscopy (XPS). This study also involved the development of an Al-Si-SiC metal matrix composite (MMC) by gravity casting, using a combination of Silicon carbide (SiC), Silicon (Si), and Aluminium alloy (Al). Hardness is remarkably improved from 56 to 76 Brinell hardness number (BHN) compared to existing Al alloy. The thermal conductivity of the composite showed remarkable improvement, 126 W/m $\cdot$ K, compared with the existing Al alloy. This innovative approach of using solar waste as resources is an alternative for materials synthesis of silicon carbide and also reduces the dependency on traditional raw materials.