Copper leaching from ultrasonically treated milled waste printed circuit boards: investigation of parameters optimization and kinetics

Waste printed circuit boards (WPCBs) encompass abundant metals (gold, silver, and copper), along with other harmful
materials including brominated epoxy resins, plastics, and heavy metals (lead, mercury, and cadmium). Direct burning and
landfilling of WPCBs may cause severe health issues and impair the environment. Therefore, sustainable treatment of WPCBs
is necessary to recover valuable metals and remove hazardous materials before disposal. The present work investigates the
separation of copper-rich metallic fractions from the WPCBs by the combination of hammer milling and ultrasonic irradiation.
Initially, discarded mobile phone PCBs are pre-processed and shortened into 1 × 1 cm2.
Downscaled WPCBs are fed
into the hammer mill to obtain the fine ground powder. The Powdered WPCBs are further processed through ultrasonic
treatment to acquire metal-rich fraction. XRD, SEM–EDS, and ICP/AAS analysis revealed that the current technique can
efficiently separate the metal-rich fraction without using toxic solvents. Results show the enhancement of copper fraction from
42.73 to 87 wt. % after ultrasonic treatment of WPCBs ground powder. Further, nitric acid leaching has been implemented
to metal-rich fractions, and the parameters have been optimized for copper leaching with the assistance of response surface
methodology (RSM) of the design of experiments (DOE). Quantitative dissolution (98.96%) of copper occurred using 3.5 M
nitric acid within 3 h at 30 °C with 50 GPL pulp density and 500 rpm agitation speed. Finally, the kinetics of the leaching
process were studied to conform the kinetics model. Moreover, the activation energy for diffusion (19.075 kJ/mole) and
reaction kinetics model (13.29 kJ/mole) has also been calculated. The low energy consumption due to room temperature
pre-treatment and effective leaching ensures the industrial feasibility of the proposed process.