The hydrometallurgical method of copper leaching from scrap electronics is commonly undertaken using pulverized printed circuit boards. Though studies on the use of organic acids like citric and oxalic acids for copper removal are well documented, those on the use of malonic acid are rare. Herein, we report on the investigation of the efficiencies of mixtures of malonic acid and hydrogen peroxide for copper leaching from unpulverized scrap PCB by the Box-Behnken design and the theoretical determination of the most stable copper-malonic acid complex. The average copper content in each unpulverized printed circuit board was found to be (0.84 ± 0.13) mg/g following aqua-regia digestion and atomic absorption spectrophotometry measurement. The conditions at which the highest leaching efficiency of 51.3% was obtained were a malonic acid concentration of 0.5 M, a hydrogen peroxide 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 copper leached with a p-value of 0.001. Theoretical calculations show that malonic acid prefers to coordinate with copper in a 2:1 malonic acid: copper ratio. This study shows that appreciable amounts of copper can be leached from the minimally processed unpulverized printed circuit board.

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.