Selective recovery of copper contained in waste PCBs from cellphones with impurity inhibition in the citrate-phosphate system

Abstract

A technique to selectively recover copper contained in waste PCBs from cellphones, based on leaching and electrowinning processes, is presented. Sodium citrate (Cit, Na3C6H5O7) solutions and hydrogen peroxide (H2O2) were employed as eco-friendly and low toxicity reagents. Ammonium phosphate ((NH4)3PO4) was proposed as a chemical inhibitor to avoid other base-metal co-dissolution, which could accumulate in the leaching solutions and contaminate the final product. Selective leaching assures the attainment of clean solutions appropriate for electrolytic treatment, followed by reuse. The material used for testing was a coarse fraction (particle size >500 μm and metal composition >50%) of waste PCBs (EWPCB) from cellphones. Thermodynamic analyses for the M-Cit-PO43− system was used to determine possible experimental leaching conditions and the pH effect was evaluated during the leaching-electrowinning-recirculation cycle. With a controlled pH at ambient temperature (25 °C), it was possible to selectively leach high concentrations of copper (>30 g/L copper), with fresh and recycled solutions, while suppressing most metal impurities. Despite impurity extraction, product purity was scarcely affected, obtaining deposits with elevated copper contents (≈99.7%). This methodology guarantees a selective process, which is useful in the treatment of multi-metallic waste.