Selective copper recovery from ammoniacal waste streams using a systematic biosorption process

Cu–NH₃ bearing effluents arise from electroplating and metal extraction industries, requiring innovative and sustainable Cu recovery technologies to reduce their adverse environmental impact. CO₃²⁻ and Zn are often co-occurring, and thus, selective Cu recovery from these complex liquid streams is required for economic viability. This study assessed 23 sustainable biosorbents classified as tannin-rich, lignin-rich, chitosan/chitin, dead biomass, macroalgae or biochar for their Cu adsorption capacity and selectivity in a complex NH₃-bearing bioleachate. Under a preliminary screen with 12 mM Cu in 1 M ammoniacal solution, most biosorbents showed optimal Cu adsorption at pH 11, with pinecone remarkably showing high removal efficiencies (up to 68%) at all tested pH values. Further refinements on select biosorbents with pH, contact time, and presence of NH₃, Zn and CO₃²⁻ showed again that pinecone has a high maximum adsorption capacity (1.07 mmol g⁻¹), worked over pH 5–12 and was Cu-selective with 3.97 selectivity quotient (K_Cu/Zn). Importantly, pinecone performance was maintained in a real Cu/NH₃/Zn/CO₃²⁻ bioleachate, with 69.4% Cu removal efficiency. Unlike synthetic adsorbents, pinecones require no pre-treatment, which together with its abundance, selectivity, and efficiency without the need for prior NH₃ removal, makes it a competitive and sustainable Cu biosorbent for complex Cu–NH₃ bearing streams. Overall, this study demonstrated the potential of integrating bioleaching and biosorption as a clean Cu recovery technology utilizing only sustainable resources (i.e., bio-lixiviant and biosorbents). This presents a closed-loop approach to Cu extraction and recovery from wastes, thus effectively addressing elemental sustainability.