RECYCLING OF PRECIOUS METALS FROM WASTE PRINTED CIRCUIT BOARDS VIA A COMBINATION OF PYRO AND HYDROMETALLURGICAL PROCESSES
Electronic waste (e-waste) has emerged as a critical issue in our technologically advanced society due to the escalating rise of electronic devices, necessitating the development of innovative recycling techniques. Printed Circuit Boards (PCBs) are among the most complex components of e-waste, consisting of a diverse mix of metals, polymers, and ceramics. Recycling PCBs is crucial for managing hazardous waste and recovering valuable materials, as they contain higher concentrations of precious metals than other electronic waste. Hydrometallurgical and pyrometallurgical processes are widely employed to recover metallic components from waste PCBs. Typically, mechanical separation is the initial step, followed by leaching and chemical separation to further isolate and process the metals. The primary goal of this project was to extract precious metals (Au and Pd) from waste PCBs through various chemical reagents. First, transition metals, including Cu, Fe, Pb, Ni, Sn, and Zn, were effectively dissolved via HNO3 with a high recovery rate of 99 wt% to facilitate the extraction of precious metals. Ag and Pt were also successfully dissolved with a recovery rate of >95 wt% in the first stage of leaching. Subsequently, thiourea was applied, and various parameters (including temperature, concentrations of ferric ions, sulfuric media, and thiourea) were systematically evaluated as a second leaching stage. The recovery rates for Au and Pd were 52 wt% and 99 wt%, respectively. Following this, the study examined the influence of pre-processing thermal treatment on metal recovery. Then, instead of thiourea, thiosulfate was used, and various parameters were studied, including ammonia concentration, Cu (II) concentration, temperature, and solid-to-liquid ratio. In addition to these two reagents, glycine and sodium bromide were tested as sustainable alternatives for metal dissolution; however, they yielded lower recovery rates than thiosulfate and thiourea. Finally, after applying HNO3 to dissolve transition metals in the first stage of the leaching process, hydroxide precipitation using sodium hydroxide (NaOH) was employed to remove all heavy metals from the wastewater solutions, achieving a high recovery rate. Overall, this research underscores the importance of sustainability in e-waste recycling by prioritizing the use of eco-friendly reagents and promoting the circular economy.
E-waste Recycling, Waste Printed Circuit Boards (WPCBs), Precious Metals, Hydrometallurgical Processes
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