![]() This phenomenon is now known as “urban mining.” In this work, a polyphenols-rich plant extract has been obtained from olive-tree leaves, and its ability to contribute to reducing four metals, namely, Ag, Cu, Cr, and Sn, that are present in scrap PCBs has been studied. Recycling printed circuit boards (PCBs) is becoming a source of precious metals and an alternative to conventional mining. ![]() A comparison of results with liquidus data for similar experiments using Na2O flux showed that B2O3 was more effective in lowering the liquidus. Based on the experimental results, B2O3 may be a suitable fluxing agent to reduce the smelting temperature in the CaO-Al2O3-SiO2-B2O3 quaternary system. Only one sample (C/S = 1.0, 18.8 wt% B2O3) resulted in an increase in the liquidus temperature due to the expansion of the pseudowollastonite phase field at high B2O3 contents. The lowest liquidus temperature was 900 ☌ for slag with initial composition having C/S = 0.6 and 18.8 wt% B2O3 representing a decline of the liquidus by 435 ☌ compared to the undoped slag. Doping with successively higher amounts of B2O3 caused the boundaries of the initial primary phase fields to shift position, generally resulting in a reduction of the liquidus temperature. Depending on temperature and composition, anorthite (CaO.Al2O3.2SiO2), pseudowollastonite (CaO.SiO2), gehlenite (2) and tridymite (SiO2) crystals were observed in equilibrium with the liquid phase at temperatures below the liquidus. The liquidus temperatures of the synthetic slags were determined within an uncertainty of ± 10-20 ☌. Quenched samples were characterised using Scanning Electron Microscopy (SEM) to reveal the equilibrium phase assemblage and Electron Probe Microanalysis (EPMA) to determine the chemistry of individual phases. Fifteen samples with CaO/SiO2 (C/S) ratios of 0.3, 0.6 and 1.0 containing 15.6-19.1 wt% Al2O3 were equilibrated at a range of temperatures close to predicted liquidus phase boundaries within the B2O3-free ternary. The phase equilibria in the CaO-Al2O3-SiO2 ternary system doped with around 5, 10, 15 and 20 wt% B2O3 was studied using a high-temperature equilibration followed by rapid quenching technique. An integrated, definite framework for full resource recovery from waste PCBs was proposed. Sustainable processing routes for converting discarded PCBs into value-added products should also be attempted, as amplified in this review. The futuristic recycling perspective should treat base and precious metal-rich components separately with minimal environmental effect, end product usage, and maximum economic benefit. Electronic components such as monolithic ceramic capacitors, tantalum capacitors, integrated circuits, and central processing units mounted on the PCBs are important due to precious metals' presence. Current recycling techniques at a commercial scale are preferably based on pyrometallurgy (smelting-refining), where electronic waste is only a fraction of the total feed stream. Selective recovery (using solvent extraction, precipitation, polymer inclusion membrane, adsorption, ion exchange) of high purity product from multi-elemental leach solution has recently gained interest and is reviewed. A novel combination of different pre-treatments and hybrid thermal-chemical routes are often reported for improved separation efficiency and performance. Pre-treatments play a decisive and significant role in upgradation and efficient metal extraction. This review critically discusses the systematic and sequential processes adopted for PCB metallic recoveries via physical, pyrometallurgical, hydrometallurgical, and combined technologies. The rapid depletion of natural resources, massive generation of end-of-life PCBs and inherently metal-loaded values inevitably call for recycling and recovery. ![]() Printed circuit boards (PCBs) are an essential and central component of electronic waste.
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