The recovery of precious metals from waste printed circuit boards (PCBs) is an effective recycling process. This paper presents a promising hydrometallurgical process to recover precious metals from waste PCBs. To simplify the metal leaching process, large pieces of PCBs were used instead of a pulverized sample. The chemical coating present on the PCBs was removed by sodium hydroxide (NaOH) treatment prior to the hydrometallurgical treatment. Among the leaching reagents examined, hydrochloric acid (HCl) showed great potential for the recovery of metals. The HCl-mediated leaching of waste PCBs was investigated over a range of conditions. Increasing the acid concentration decreased the time required for complete metal recovery. The shaking speed showed a pronounced positive effect on metal recovery, but the temperature showed an insignificant effect. The results showed that 1 M HCl recovered all of the metals from 4 cm × 4 cm PCBs at room temperature and 150 rpm shaking speed in 22 h.

An efficient and rapid metal leaching process for solubilisation of heavy and precious metals from waste printed circuit board (PCB) powder was investigated. The PCB powder was first treated with 0.1 M sodium hydroxide (NaOH) solution to remove the chemical coating. An incubation time of 8 h and 150 rpm shaking speed were found to be optimum for the removal of the chemical coating from the PCB powder (1 g). The NaOH treated PCB powder was further subjected for metal leaching using an Aspergillus niger (A. niger) culture supernatant and hydrogen peroxide (H₂O₂). 100% solubilisation of all the metals was observed. The shaking speed showed insignificant effect on metal solubilisation. The 3.18% H₂O₂ concentration was found to be optimum for metal solubilisation. An increase in temperature (80 °C) reduced the time required for metal solubilisation. Optimization of all these parameters considerably decreased the leaching period to 2 h.