[Selective recovery of copper, zinc and nickel from printed circuit boards by ammonia leaching under pressure].

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 degrees C for 150 minutes, using 4 mol/L NH4OH and 1 mol/L (NH4)2CO3 as leaching solution, with 700 r/min stirring speed and 0.2 MPa oxygen. With this method, Zn, Cu and Ni could be effectively recovered from printed circuit boards by 100%, more than 99% and more than 64%, respectively. The kinetics of Cu leaching behavior was studied and it was found that the shrinking core model described it well. It was a diffusion control process and the apparent activation energy was 14.68 kJ/mol.