Synergistic Aqueous Biphasic Systems: A New Paradigm for the One-Pot Hydrometallurgical Recovery of Critical Metals


An acidic aqueous biphasic system (AcABS), in which the inorganic salt component of a traditional aqueous biphasic system (ABS) is replaced by the inorganic acid inherently present in typical hydrometallurgical leachate solution, is shown to selectively separate cobalt from nickel, a separation relevant to the recycling of nickel metal hydride (NiMH) batteries. To overcome the limitation of electrodeposition in the presence of high acid concentration, a mixed ABS- AcABS approach is developed in which HCl is partially substituted by addition of a predictable amount of NaCl. This synergistic ABS-AcABS retains the metal extraction efficiency of AcABS while diminishing the acid concentration required to induce phase separation as well as its distribution to the ionic-liquid-rich phase. Selective deposition of cobalt in the presence of coextracted manganese impurities was achieved in AcABS, ABS, and ABS-AcABSs. The morphology and composition of the obtained deposits as well as the Faradaic efficiency of the process can be altered by varying the NaCl to HCl ratio and water content, resulting in highly tailored cobalt deposits. These results highlight the potential of AcABS-derived systems as a new extraction-separation platform for the integrated hydrometallurgical treatment of critical metals, from leaching to electrodeposition.



subject category

Chemistry; Science & Technology - Other Topics; Engineering


Schaeffer, N; Gras, M; Passos, H; Mogilireddy, V; Mendonca, CMN; Pereira, E; Chainet, E; Billard, I; Coutinho, JAP; Papaiconomou, N

our authors


This work was part of BATRE-ARES Project (ERA-MIN/0001/2015) funded by ADEME and FCT. M.G. would like to acknowledge labex CEMAM and EIT InnoEnergy H2020 for financial support. This work was partly developed within the scope of the Project CICECO-Aveiro Institute of Materials, POCI-01-0145-FEDER-007679 (FCT ref. UID/CTM/50011/2013), financed by national funds through the FCT/MEC and when appropriate cofinanced by FEDER under the PT2020 Partnership Agreement.

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