Extraction and recovery of Co²⁺ ions from spent lithium-ion batteries using hierarchical mesosponge γ-Al₂O₃ monolith extractors

As visual extraction, detection, and recovery of Co²⁺ ions from spent lithium-ion batteries (SLIBs) via a one-step process becomes a new attractive, simple route for the management of urban electronic waste (e-waste), it will in turn lead ideally to the exploitation of accumulated e-waste and protection of the green environment. The Co²⁺ ion-capture system was achieved by selectively binding with synthesized chelating agents, namely, (E)-4-[(2-mercaptophenyl)diazenyl]-2-nitrosonaphthalen-1-ol (MPDN) and (E)-5-[(1,3,4-thiadiazol-2-yl)diazenyl]benzene-1,3-diol (TDDB), at controlled pH. The dense arrangement of MPDN and TDDB into microscopic, mesospongy γ-Al₂O₃ monoliths enabled the design of a solid/sponge Co²⁺ ion extractor (IE) from the SLIB leach liquor. Our recycling process of Co²⁺ ions from SLIBs showed evidence of (i) Co²⁺ ion waste management, (ii) low-cost collection/recovery of Co²⁺ ions, (iii) sensitive and selective extraction of ultra-trace Co²⁺ ion, and (iv) reduction of e-waste volume through multiple reusability or recyclability. Furthermore, our sponge IE design with large surface area-to-volume ratios, macro/mesopores, and grooves along the micrometric, hierarchical monolith structures results in a facile, naked eye monitoring of ultra-trace Co²⁺ ion collection/binding to a detection limit of approximately 3.05 × 10⁻⁸ M during multifunction extraction steps from SLIBs. Our results also showed evidence of the extraction of Co²⁺ ions (196 mg g⁻¹) from SLIBs by a one-step process. This finding provides a basis for the control of multifunction processes (i.e., extraction, detection, and recovery) and the high performance needed for selective extraction and recovery of Co²⁺ ions from SLIBs in a one-step process.