Box-Behnken Optimization and Theoretical Study for Copper Recovery from Scrap Laptop Computer Printed Circuit Board by Malonic Acid and Hydrogen Peroxide

Copper (Cu) is a major target in metal recovery during the recycling of scrap printed circuit boards (PCBs). Herein, we report on the optimization of parameters for the leaching of Cu from scrap PCB pieces by malonic acid and hydrogen peroxide (H2O2). Large PCBs obtained from scrap laptop computers were cut into smaller 2 cm by 2 cm pieces and de-epoxidized by NaOH treatment. The average Cu content in each PCB piece was determined by complete solubilization in aqua-regia and found to be (0.84±0.13) mg/g. An optimization study of three parameters including malonic acid concentration, H2O2 concentration, and contact time was carried out through the Box-Behnken design. Analysis of variance data revealed that the linear model was best fitted to the experimental data with R2 = 0.9591 and R2 (adjusted) = 0.8652, but the predictive power of the model was low with R2 (predicted) = 0.2298. The conditions at which the highest leaching efficiency of 51.3% was obtained were a malonic acid concentration of 0.5 M, a H2O2 concentration of 1.0 M, and a contact time of 75 min. The contact time was the most significant individual parameter that influenced the efficiency of Cu leached with a p-value of 0.001. Response surface plots revealed that high leaching efficiencies were observed at high malonic acid and H2O2 concentrations at prolonged contact time. Theoretical calculations show that the malonic acid prefers to coordinate with Cu in a 2:1 malonic acid: Cu ratio.