2020 Trinh Selective Copper Recovery by Acid Leaching from Printed Circuit Board Waste Sludge

The most challenging issue associated with recycling the sludge generated from printed circuit boards (PCBs) is the separation of copper (Cu) from iron (Fe), using multi-stage leaching, or adding oxidizing and precipitating agents. Herein we investigated simple acid leaching to effectively extract copper and limit iron dissolution. Selective copper leaching was achieved with all the acids studied, including HCl, HNO3, and H2SO4. The lower concentration of acid solutions resulted in a larger difference in leachabilities between Cu and Fe. Among three leachates, the H2SO4 solution performed effectively on the selective leaching of Cu and Fe. Adjusting the pulp density to 4% and the H2SO4 concentration at ~0.2 M, accomplished ~95% Cu leaching and reduced the Fe extraction to less than 5%. Kinetic studies revealed that Cu leaching followed the ash diffusion-controlled mechanism. Activation energy (Ea) of 9.8 kJ/mol was determined for the first 10 min of leaching. Further, leaching up to 60 min corresponded to a mixed control model, increasing the Ea to 20.9 kJ/mol. The change in the control model with regard to the two leaching stages can be attributed to the Cu hydroxide and metal phases present in the original sample. A simple, economically attractive H2SO4 acid leaching process was demonstrated, recovering Cu efficiently and selectively from PCBs waste sludge under moderate conditions.