Leaching Studies for Copper and Solder Alloy Recovery from Shredded Particles of Waste Printed Circuit Boards
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INTRODUCTION
DUE to the ever-increasing generation of electrical and electronic wastes (E-wastes) and the depletion of high grade metallic resources, recycling of E-wastes is very important. The printed circuit boards (PCB) contain large amounts of solder alloy (Sn/Zn/Cu) and quantities of Au, Ag, and Pt. Conventional pyrometallurgical methods for recycling of the metallic content of E-wastes result in the production of environmental pollution.[1] The low energy consumption and environmental load characteristic of the hydrometallurgical based route has garnered significant research interest.[2,3] Pre-treatment is one of the key processes for the PCB recycling. It includes mechanical treatment (in order to shred it into pieces); utilizing hammer mills.[4] followed by separation of metals and non-metals, using the same techniques that is used in the mineral dressing (e.g., screening magnetic, eddy current, and density separation techniques).[5] Leaching process, as one of the most important parts of hydrometallurgical treatment, is used to convert the MARYAM KAVOUSI, ANAHITA SATTARI, ESKANDAR KESHAVARZ ALAMDARI, and DAVOUD HAGHSHENAS FATMEHSARI are with the Department of Mining and Metallurgical Engineering, Amirkabir University of Technology, Tehran, Iran. Contact e-mail: [email protected] Manuscript submitted June, 2, 2016.
METALLURGICAL AND MATERIALS TRANSACTIONS B
solid metallic compound to soluble species (cations or anions) by using different acidic/basic solutions. Sulfuric acid,[6] hydrochloric acid,[7,8] and nitric acid[9,10] have been conventionally employed for the dissolution of metallic content of WPCBs,[6–8,11,12] studying leaching copper from PCB in sulfuric acid solution using hydrogen peroxide as an oxidant, and it was found that sulfuric acid, due to its low cost and high efficiency, is a very suitable chemical leaching system for Cu dissolution. In spite of these advantages, it had low selectivity for separation of metals. Also Barakat[13] studied leaching of PCBs using a 3 pct H2SO4 solution at 318 K (45 C) for 1 hour and found that the lead and tin remained un-dissolved in residue. Yazici and Deveci[7] stated that cupric chloride leaching of PCBs has some advantages such as fast kinetics at low temperature and atmospheric pressure, low toxicity, and no iron contamination. But limitations of this system include poor quality of copper product and unconventional electro winning of copper. Jha et al.[14] showed that 95.79 pct of tin was leached out from solder material, using 5.5 M HCl at 363 K (90 C) in 165 minutes, but lead dissolution was found negligible for each set of experiment. Therefore, lead precipitated as chlor plumbic acid {H2[PbCl4]}.[15] Based on Dhawan et al.[16] studies, nitric acid, compared to hydrochloric and sulfuric acids, in the process of metals leaching from waste PBCs, is more effective. Nitric acid is a strong oxidizing reagent for lead dissolution, because of its selectivity, but tin in
solder also reacts with HNO3 and forms precipitate of SnO2 which may prevent the leach
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