Electrochemical oscillation during copper recovery from waste printed circuit boards by slurry electrolysis: Generation mechanism and process characteristics

Slurry electrolysis can be used to recover copper from waste printed circuit boards (WPCBs), but electrochemical oscillations during recovery increase the power consumption. Therefore, copper(II) chloride was selected as a simulated electrolyte to study electrochemical oscillations during the recovery of copper from WPCBs by slurry electrolysis. The results showed that a cuprous chloride passivation film formed on the cathode and induced decaying, bottom-up electrochemical oscillations whose amplitude and frequency were affected by several factors. Among them, the current intensity, initial pH, and sodium chloride concentration inhibited the electrochemical oscillations. Under a copper(II) chloride concentration of 0.2 mol/L, a current of 0.03 A, an electrode spacing of 2 cm, an initial pH of 4, and no NaCl, the maximum amplitude and frequency of the oscillations were 0.43 V and 0.42 Hz, respectively. Phase space reconstruction showed that the potential oscillations of the system evolved between the near-linear equilibrium region and the periodic oscillation region. By appropriately increasing the current intensity, electrode spacing, copper(II) chloride concentration, and NaCl concentration, and reducing the initial pH reduced the system's power consumption by 3.6%. However, the system's average power significantly increased upon increasing the current intensity and electrode spacing. This work provides theoretical support for recovering valuable metals from WPCBs with reduced energy consumption by controlling process conditions.