Self-driven MFC-MEC Coupled System For Efficient Cobalt Recovery From LiCoO₂

Cobalt element as a form of LiCoO2is extensively present in spent lithium ion batteries With the exponential growth on demand of lithium ion batteries, cobalt recovery from these wastes is thus promising in view of both environmental and economic perspectives. While conventional pyrometallurgical, hydrometallurgical, biometallurgical as well as electrochemical processes have been proposed to recover cobalt, the great energy consumption, high cost and serious second pollution urge a turn to environmental friendly and cost-effective strategies. Bioelectrochemical systems (BESs) including microbial fuel cells (MFC) and microbial electrolysis cells (MEC), are regarded as a new sustainable and effective strategy for treatment of these wastes. While MFC-MEC coupled system has been used for hydrogen production, and MFC and MEC have been separately used for LiCoO2leaching, no literatures were reported using self-driven MFC-MEC coupled system for cobalt complete recovery.In this study, particles of LiCoC2were used as an electron acceptor in the cathodes of MFC, which powered MEC using Co(II) as a final electron acceptors. Pure cobalt was thus completely recovered from this self-driven system, in which no external power was input while organic wastes were utilized in the anodes of both MFC and MEC, and solid wastes of LiCoO2and the subsequent Co(II) were respectively reduced on the cathodes of MFC and MEC.1) Under conditions of NaCl0.0mg/L, pH2.0, solid/liquid ratio10.0g/L, initial oxygen3.00mg/L, working volume25mL in MFC and NaCl0.0mg/L, pH=6.0, Co(II)50mg/L, initial oxygen3.00mg/L, working volume25mL in MEC, release of cobalt in the cathodes of MFC reached2.11±0.02mg·L-1·h-1and Co(II) reduction rate in the cathodes of MEC exhibited2.49±0.04mg·L-1·h-1. An apparent diminish in size of LiCoO2particles on the cathodes of MFC was observed using scanned electron microscopy (SEM), and pure cobalt on the cathodes of MEC was confirmed by X-Ray Diffraction(XRD). 2) The addition of NaCl (100mM) increased both cobalt leaching (102%) and Co(II) reduction (40%) whereas100mM NaCl in the cathodes of MEC increased cobalt leaching (74%) but decreased Co(II) reduction (53%).3) Decrease of pH to1.0in the cathodes of MFC increased both cobalt leaching (7.65times) and Co(II) reduction (86%) while decrease of pH to3.0in the cathodes of MEC had no apparent effect on cobalt leaching but decreased Co(II) reduction (33%).4) A decrease in oxygen concentration (1.00mg/L) in the cathodes of MFC was in favour of cobalt leaching6.24±0.18mg·L-1·h-1and a decrease in oxygen concentration (1.00mg/L) in the cathodes of MFC was in favour of Co(II) reduction3.39±0.06mg·L-1·h-1.5) An increase in solid/liquid ratio from0.2g/L to1.0g/L in the cathodes of MFC enhanced cobalt leaching(10%) and Co(II) reduetion(44%).6) A in working volume (13mL) in the cathodes of MFC benefited to both cobalt leaching (96%) and Co(II) reduction (34%) whereas a decrease in working volume (13mL) in the cathodes of MEC improved cobalt leaching (15%)but was detrimental to Co(II) reduction (55%).7) Two MFC in series or parallel led to an increase in cobalt leaching (65%,25%) and Co(II) reduction (64%,21%).8) Under an optimal condition of NaCl0.0mM, pH=1.0, solid/liquid ratio1.0g/L, initial oxygen1.00mg/L, working volume13mL in MFC and NaCl0.0mg/L, pH6.0Co(II)50mg/L, initial oxygen1.00mg/L, working volume13mL in MEC, a cobalt leaching rate of46.31±0.80mg·L-1·h-1with a yield of2.53±0.12g LiCoO2g COD-1, and a Co(II) reduction rate of7.06±0.14mg·L-1·h-1with a yield of0.81±0.02g Co g COD-1were reached. This study provides a new process for complete recovery of cobalt and recycle of spent lithium ion batteries.