Ferric sulphate leaching of metals from waste printed circuit boards

• Leaching of Cu, Ni, Ag and Pd from WPCBs in acidic Fe(III) sulphate solutions is reported.
• T°C, [Fe(III)] and [H2SO4] are all significant parameters as confirmed by data analysis.
• Leaching kinetics of copper is consistent with shrinking particle model (Ea = 18.3 kJ/mol).
• Air/O2/H2O2 supply is required for regeneration of Fe(III) and effective leaching of metals.
• Addition of Cl− improves extraction of metals, Ag and Pd in particular.

Leaching of copper and other metals (i.e., Ni, Ag and Pd) from waste printed circuit boards (WPCBs) in acidic ferric sulphate solutions was studied. The effects of concentration of H2SO4 (0.05–1 M), Fe(III) (0.05–0.5 M) and temperature (20–80 °C) on the extent and kinetics of extraction of metals were investigated using response surface methodology. Under the suitable conditions, high extractions of copper (i.e., ≥ 98%) were readily achieved over a leaching period of 120 min. The kinetic data derived from the shrinking particle model for copper were used as the response for the analysis of data. All the leaching parameters were statistically significant within an order of temperature > [Fe(III)] > [H2SO4] and increasing their levels had positive influence on the leaching kinetics. The activation energy for extraction of copper was found to be 18.3 kJ/mol. In addition to copper, nickel extractions were also high (i.e., up to 92.5% over 120 min) whilst silver and palladium extractions were limited to ≤ 21.4% and ≤ 69.4%, respectively. Further tests indicated that increasing the solids ratio from 1% to 15% w/v had a deleterious influence on the leaching of metals apparently due to limited availability and rapid depletion of Fe(III) at high solids ratios. The supply of air/oxygen (2 L/min) or H2O2 (585 mg/L) for in-situ regeneration of Fe(III) improved the leaching of copper by ≈ 35% over 180 min, with oxygen being the most effective. This indicates the requirement for the continual regeneration of Fe(III) in the leaching medium. The addition of chloride (25.6–116.5 g/L Cl−) was found to promote the leaching of metals, particularly silver and palladium with their almost complete extraction (≥ 99% Ag/Pd) over 120 min. These findings suggest that acidic ferric sulphate solutions can be suitably used as a potent lixiviant system for the extraction of metals from WEEE.