| Nowadays with the rapid development of science and technology, electronic equipments are frequently upgraded, which led to a significant increase of waste electric and electronic equipments. Because of the double characteristics with harmfulness and resource of discarded printed circuit board (PCB) as one of the most typical waste electric and electronic equipments which is rich in metals, it isimperative to develop an economical, effective and environmental friendly technology for recycling metals from PCBs.In this paper, the potential-pH equilibrium diagrams for the system of copper,zinc, nickel in water and ammonia were drawn to analyze the process of oxidative ammonia leaching on thermodynamics. The results show that leaching of copper, zinc and nickel can be achieved 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. The order of leaching is zinc, copper and nickel in turn.The ammonia/ammonium leaching process using oxygen as oxidant in autoclave was studied to extract copper, zinc and nickel from printed circuit board. Parameters such as leaching time, concentration of leaching reagents, stirring speed, oxygen pressure and temperature were optimized. The best results were achieved when the leaching was carried out at 55 for 150 minutes, using 4 mol/L NH4OH and 1 mol/L (NH4)2CO3 as leaching solution, with 700r/min stirring speed and 0.2MPa oxygen. With this method, Zn, Cu and Ni could be effectively recovered from printed circuit boards by 100%, more than 99% and more than 65%, respectively.The kinetics of Cu leaching behavior was studied and it was found that the shrinking core model described it well. The model enabled the determination of theoxygen reaction order of 0.5 and the activation energy of 14.68kJ/mol, which is likely to be a consequence of diffusion. Fitting by diffusion model had made a further validation. |
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