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Abstract
The dissolution of the main metals (Cu, Zn, Sn, Pb and Fe) found in waste printed circuit boards (WPCBs) was investigated by electrochemical corrosion measurements (potentiodynamic polarization and electrochemical impedance spectroscopy (EIS)) in different bromide-based systems that could be used as lixiviants in hydrometallurgical route of metals recovery. The analysis of the corrosion products was carried out by X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS) measurements. All measurements showed that the addition of bromine in the electrolyte favors to great extents the dissolution process of all studied metals as compared to bromine-free electrolytes. In the investigated experimental conditions, the highest dissolution rates of the metals were obtained in acidic KBr solution containing 0.01 mol/L bromine and they decreased in the following order: Zn >> Sn > Pb > Fe > Cu. The XRD and XPS chemical assessment allowed the identification of the dissolution products formed on the metallic surfaces after exposure to the electrolytes. They consisted mainly of oxides in the case of Cu, Zn, Sn and Fe, while the presence of PbBr2 was also noticed on the lead surface. Based on the results of EIS and surface investigations, several models explaining the corrosion behavior of the metals were proposed and discussed. The obtained results demonstrate that all studied metals could be successfully leached using brominated solutions, providing a viable alternative for the selective and efficient recovery of the base metals from WPCBs through a multi-step hydrometallurgical processing route.
Highlights
The hydrometallurgical route is a selective way toward metal recovery from waste printed circuit boards (WPCBs), being easier to control and creating less environmental hazards than the pyrometallurgical approach [1]
In a previous research [18], we investigated the ability of the Br− /Br2 leaching system to remove the exposed metallic parts from different models of computer motherboards (CMB), simultaneous with the electrochemical lixiviants regeneration and the partial electrodeposition of the dissolved metals
The operating parameters were not optimized, the results indicate that CMB could be completely dismantled in about 18 h, with cathodic and anodic mean current efficiencies of 43.6% and
Summary
The hydrometallurgical route is a selective way toward metal recovery from waste printed circuit boards (WPCBs), being easier to control and creating less environmental hazards than the pyrometallurgical approach [1]. Various leaching reagents were used to ensure a fast kinetics of the dissolution process of both noble and base metals: cyanide [2], thiosulfate [3,4], thiourea [5,6], H2 SO4. Low-toxicity and applicability over a wide range of pH values (from acidic to neutral) are important characteristics of the bromide leaching system [16]. Because bromine is an efficient lixiviant, but because elemental bromine is hazardous and extremely difficult to store or transport in safe conditions, it is preferable to be produced in-situ, in the leaching reactor [15,17]
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