  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 (KCu/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.
