Selective recovery of nanoscale copper particles from mobile phone waste printed circuit boards through acid leaching and low temperature electrowinning

Abstract

Waste printed circuit boards were collected and shredded by a shredder in the current work. Shredded boards were treated by NaOH solution to remove or loosen up the polymer coating painted on the boards. As copper was the target element in this experiment two step leaching process was adopted. In the first step, low concentration HNO₃ treatment was done to leach the solders and other metals except copper and second step leaching was done by H₂O₂ added HCl solution for copper leaching. Copper was reclaimed as nanoparticles by electrowinning using this copper-pregnant leach liquor as the electrolyte. Concentration of various elements in the leach liquors of two step leaching process was determined. Different techniques such as particle size analysis, electron microscopy, diffraction and Rietveld refinement were applied to characterize copper nanoparticles. The final copper rich solution found a concentration of copper 29,437.5 ppm with the presence of few other elements. Reclaimed copper particles were approximately 200 to 300 nm revealed by micrographs while having the average crystallite size of 76 nm determined by Rietveld refinement. The presence of metastable cuprous oxide phase was found from the diffraction analysis and the elemental copper phase percentage was 65. Microscopy also confirmed that vacuum drying of the copper particles reduced oxygen contamination from 30 to 6%.

Keywords: Copper recovery; Low temperature electrowinning; Nanoscale particles; PCB, E-Waste.

Fig. 1

Process Flow Diagram for Selective Copper Recovery from Mobile Phone PCBs.

Fig. 2

Representation of process effectiveness for Cu recovery.

Fig. 3

Particle size analysis of sample-1 (a) and sample-2 (b).

Fig. 4

SEM Micrographs of copper particles without stirring and temperature (Sample-1) (a) and with stirring and temperature (Sample-2) (b), at 50k magnifications.

Fig. 5

Macro Scale EDX of Sample-1 (a) and Sample-2 (b).

Fig. 6

XRD analysis of (a) sample-1 (without temperature and stirring), and (b) sample-2 (with temperature and stirring).

Fig. 7

Presentation of achieved accuracy during Rietveld refinement: a, b for sample-1 and c, d for sample − 2.