Biomass Hydrothermal Reduction Enables Direct Copper Recovery from Wastewater

Abstract Recovering copper (Cu) from strongly acidic copper wastewater (SACW) is essential for resource sustainability and environmental preservation, but conventional technologies bear high economic costs and generate secondary pollution. Here, we demonstrate a biomass waste-mediated hydrothermal reduction process that simultaneously removes and recovers Cu as metallic Cu from SACW. The process operates under mild conditions (180 °C, 7 h) and achieves over 99% removal of Cu(II) across a wide concentration range, directly reducing Cu(II) to metallic Cu(0) without incorporation into hydrochar. Notably, the liquid products from biomass hydrothermal treatment, particularly 2-furoic acid, served as electron donors for Cu(II) reduction, with its C2/C3 atoms potentially providing electron transfer channels that drive the stepwise reduction of Cu(II) to Cu(0). In a 5 L pilot test with two types of industrial wastewater, the technology achieved >99% Cu(II) removal (residual <0.5 mg/L) and recovered metallic Cu with a purity of 99.9% after simple calcination. Life-cycle assessment and technoeconomic analysis highlight superior economic and environmental benefits when treating high-concentration copper-containing wastewater, establishing a sustainable, generalized hydrothermal reduction platform for efficient Cu recovery from industrial wastewaters. This work establishes a chemistry-driven paradigm for sustainable wastewater treatment, enabling efficient circular recovery of high-value resources from acidic metal-containing wastewaters.