Study On The Metal Separation Process Of Discarded Printed Circuit Boards

Nowadays with the rapid development of science and technology, electronic equipments are frequently upgraded, which leads to a significant increase of waste electric and electronic equipments. Because of the double characteristics with harmfulness and resource of discarded printed circuit boards (PCBs) ,which has high metal content, it is important to develop an economical, effective and environmental friendly technology for recycling metal from PCBs.The composition of the waste PCBs is analyzed. The results show that waste PCBs contain valuable metals which are important for economy and environmental protection to recover. The potential-pH equilibrium diagram for the system of Cu, Zn, Fe, Ni and Sn in water and ammonia were drawn to analyze the process of oxidative ammonia leaching from thermodynamics. The results show that leaching of Cu, Zn, Fe, Ni and Sn can be leached by acid at the appropriate pH range and potential range. The leaching will be enhanced by increasing the amount of acid. Cu, Zn and Ni can be leached with the formation of complex ions at the appropriate pH range and potential range. The leaching will be enhanced by increasing the amount of ammonia and oxygen pressure.Three-stage leaching using HCl-CuCl₂ is studied. The optimal conditions are confirmed.1.0mol/L HCl is used as leachant for the first stage. The extraction of Zn, Fe and Ni is 99.99%, 92.14% and 82.5% respectively. 1.8mol/L HCl is used as leachant for the second stage. The extraction of Sn is 99.94%. The dissolution of Sn is controlled by a surface reaction, and the activation energy of Sn amounts to 42.7kJ/mol. CuCl₂ is used as leachant for the third stage. The extraction of Pb is 99.92%. The dissolution of Pb is controlled by a surface reaction, and the reaction obey the rule of first-order reacting rate. The activation energy of Pb amounts to 44.8kJ/mol.The ammonia/ammonium leaching under oxygen pressure for PCBs was carried out to investigate the extraction behavior of copper, zinc and nickel. The optimal conditions are confirmed. Under optimum leaching conditions 100% Zn, 99.29% Cu and 65.74% Ni were effectively recovered with almost no leaching of Sn, Pb and Fe. The dissolution of Cu is controlled by diffusion, and the activation energy of Cu amounts to 14.68kJ/mol.Homebred extractant LK-C2 is used to separation and recover metals in leaching solution. The extraction of Cu, Fe and Ni is 99.98%, 96.14% and 99.35% respectively. H₂SO₄ is used as stripping extractant. The stripping rate of Cu, Fe and Ni is 97.51%, 99.18% and 98.31%. Cu, Fe, Ni and Zn can be separated by using LK-C2 effectively.Considering the complexity and variety of waste PCBs, different technics flows are given to recover metals from waste PCBs.