![]() ![]() A similar process was used in the present study to remove the chemical coating. 21 used sodium hydroxide to remove the chemical coating. Therefore, it is necessary to find an alternative process for removing the chemical coatings from PCBs without loss of metals. The reasons for these losses include the insufficient liberation of metals due to their intimate association with plastics, the generation of fines during size reduction and the inefficiency of separation processes for metal recovery from fine fractions 1. One important liability of physical separation processes is a significant loss of valuable metals. At present, a mechanical–physical method is widely employed to treat waste PCBs and separate the metal and nonmetal 3, 20. Therefore, it is necessary to first remove as much of the chemical coating as possible. This makes metal recovery complicated because the chemical coating inhibits the contact between a lixiviant and the metal. The metals present on the PCB are covered by a chemical coating 3, 20, 21. In the present study, various process parameters were optimized for metal recovery. Then, the PCBs were subjected to an acid leaching process for metal recovery. In the proposed process, the waste PCBs were pre-treated to remove the chemical coating present. In this study, we propose an efficient hydrometallurgical process using large pieces of PCBs rather than pulverized PCBs to simplify the overall recycling (metallic as well as nonmetallic fraction) process. If complete metal recovery can be achieved from large pieces of PCBs, then the remaining board (nonmetallic part) can be easily recycled, which would be difficult if pulverized PCBs were used. The effect of the above-mentioned leaching reagents on the PCB pieces during the hydrometallurgical recycling process has also not been reported. However, little is known about the use of large pieces of PCBs for the recovery of metals. Most of the above-mentioned reports used powdered/pulverized waste PCBs for metal recovery. Reagents such as cyanide 16, halide 17, thiosulfate 18 and thiourea 19 have also been commonly used for the recovery of precious metals. Several studies have reported the use of nitric acid (HNO 3), HCl, sulfuric acid (H 2SO 4) and aqua regia for the recovery of metals from waste PCBs 1, 13, 14, 15. Hydrometallurgical processes involve the dissolution of metals in alkaline or acid medium. These attributes make the hydrometallurgical process a potential alternative for the treatment of waste EEE 1, 7, 12. These processes are relatively suitable for small-scale applications. Compared with pyrometallurgical processes, hydrometallurgical processes offer a relatively low capital cost, reduced environmental impact and high metal recoveries. The formation of dioxins and furans is unavoidable due to the use of halogenated flame retardants, which presents environmental problems thus, off-gas treatment is a prerequisite 1, 11. ![]() These processes are energy intensive and high-cost and require high-grade (rich in copper and precious metals) feeds. These treatments lead to the production of hazardous gases that must be removed from the air with flue gas cleaning systems. Pyrometallurgical processes require heating the waste EEE at high temperatures to recover valuable metals. Several methods based on pyrometallurgy 8, 9 and hydrometallurgy 1, 10 are currently used for the recovery of metals from waste PCBs. ![]() Recycling waste PCBs is useful for not only resource recovery but also protecting the environment 7. These waste PCBs can be a rich secondary source of valuable metals. Therefore, one special target for waste EEE recycling is PCBs. ![]() The metal content of waste PCBs can be as high as 40% 6 and such metals typically include Cu, Sn, Pb, Cd, Cr, Zn, Ni and Mn 1. Technological advancements in EEE have shortened their life span, thus causing a huge tonnage of waste PCBs to be produced, which presents a new environmental challenge 3, 4, 5. Printed circuit boards (PCBs) are essential components of almost all waste EEE 3. A variety of equipment is classified as EEE 2. The production of electric and electronic equipment (EEE) is rapidly increasing due to the revolution of informatics technology 1. ![]()
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