Exfoliation of coarse printed circuit boards using dimethylacetamide: Production of copper concentrates

Abstract

Conventional hydrometallurgy-based e-waste value recovery technique employs milled printed circuit boards (PCBs) to facilitate the reaction between the metal fraction and leaching reagents. The current work investigates value recovery using coarse PCBs (1 cm × 1 cm). Thus, organic swelling pre-treatment using dimethylacetamide is employed to produce swollen and delaminated PCBs. The adopted experimental conditions were 160 °C, solid: liquid ratio of 1:10, 150 rpm and organic swelling time (15-75 min). The field emission scanning electron microscope (FESEM) images explicitly illustrated the noticeable cracks propagation over time at different sites within the multi-layered structure of PCBs. This resulted in various delaminated PCB components (i.e. halved PCBs, compound unit, copper-glass fibre cloth laminate, copper foil and glass fibre cloth), though the delamination extent varies with time. Copper (Cu) content analysis performed on the delaminated PCB components indicated that a copper concentrate with high Cu contents could be obtained (inner Cu foil: 83.39 %; outer Cu: 88.57 %) by performing organic swelling for coarse PCBs. The swollen particles can be subjected to a less energy-intensive mechanical method to yield embedded copper foils, and it is feasible due to the pre-weakened PCBs after undergoing organic swelling. Since the removal of the electronic components is a prerequisite in organic swelling, hindrances that occurred during delamination were also identified in this work. The presence of the through-hole pins in PCBs in one such condition potentially slows down the organic swelling. The results of this work could be employed to develop alternative PCBs-based value recovery flowsheets to extract the encapsulated inner copper avoiding comminution, which is energy intensive.