Pyrometallurgy coupling bioleaching for recycling of waste printed circuit boards

The pyrometallurgy coupling indirect bioleaching strategy is proposed for the recycling of WPCBs to avoid the disadvantages of time-consuming, low processing power, and relatively low efficiency of conventional bioleaching. The results show that under the pulp density of 2.5% (w/v), the low content (0.26 wt.%) of Ni in the raw WPCBs is completely extracted by indirect bioleaching, while the release rate of a high content (24.52 wt.%) of Cu is only 46.9%. However, the calcination pretreatment significantly improves Cu release by indirect bioleaching, and 100% Cu extraction is attained from the 600 °C-treated WPCBs at the high pulp density of 5.0% due to the formation of tractable CuO. Conversely, the release of Ni is inhibited by calcination evidently, and the indirect bioleaching efficiency of Ni declines from 34.9% to 10.1% when the pulp density lifts from 2.5% to 10.0% because of the formation of NiO with lower kinetics of acid-dissolution. On the other hand, due to the complete removal of Cu and the formation of insoluble NiO, the toxicity and environmental risk analysis indicates that the bioleaching residue of the 600 °C-treated WPCBs at the pulp density of 5.0% is completely detoxified and can be reused as non-hazardous materials safely, while the combination of the calcination and indirect bioleaching significantly reduces the environmental risk associated with the WPCBs. These findings provide the theoretical basis for a perfect combined process of pyrometallurgy and bioleaching for tackling the WPCBs from a technological perspective.