With the continued growth in lithium ion batteries (LIBs) usage in recent years, the recycling of spent LIBs has become more urgent due to the increased demand for critical metals and growing environmental pressures. Although a wide range of investigations has been undertaken, the majority have focused on treatment of manually dismantled batteries that do not represent large-scale industrial practice. In the present work, industrially processed LIB waste was treated hydrometallurgically via reductive acid leaching and purification steps that allowed for the subsequent recovery of valuable metals.
Acid leaching of industrial LIB waste containing both active materials and metallic components was compared with waste that contained only fine powders of cathode materials. Results revealed that metallic components present in LIB waste could act as reductants that increased Li and Co acid dissolution whereas, Cu was found in both the leaching solution (~60%) and leach residue (~40%). In order to improve the total recovery of valuable metals, ascorbic acid (C6H8O6) and large-size overflow fractions that contained 16 wt% Al, 12 wt% Cu, 8.4 wt% Co, and 1.4 wt% Li were investigated as additives. With ascorbic acid, selective extraction of Li and Co (> 99%) vs. Cu (0.1%) could be achieved, resulting in a Cu-rich leach residue (~12 wt% Cu). Addition of large-size overflow fractions, increased Co and Li dissolution to > 99% as the attached Li and Co in these fractions was also simultaneously recovered.
The multi-metal pregnant leaching solution (PLS) produced was subsequently purified prior to Mn and Li recovery. High-purity MnO2 was obtained by oxidative precipitation with a stoichiometric amount of KMnO4 following the Mn separation from other elements - particularly Fe and Co - by solvent extraction and selective stripping. Co/Ni was then recovered via a solvent extraction-electrowinning process that resulted in a Li-rich raffinate. Recovery of Li2CO3 following evaporation was investigated, but due to LiNaSO4 crystal formation high losses occur. In comparison, Li recovery as high purity Li3PO4 was more efficient, as 92% was recovered under optimal conditions. Nevertheless, the residual waste solution after Li recovery has high Na+ and SO42- levels that pose a challenge to disposal.
Consequently, a novel method that utilizes nickel-metal hydride (NiMH) waste into the LIB recycling system that results in the synergistic leaching of LIB and NiMH was explored. The PLS produced underwent rare earth elements (REEs) recovery by double sulfate precipitation, followed by Co, Ni, and Li. The resultant sulfate waste solution containing Na+, Li+, SO42- and OH-, was used to produce Na2SO4 and NaOH that can be utilized for REE recovery. Through this process, savings of up to 1.8 t of reducing additive (35% H2O2) and 0.8 t of precipitant (Na2SO4) were expected. Moreover, issues related to the disposal of Li-bearing leftover waste solution were solved.
|Publication status||Published - 2020|
|MoE publication type||G5 Doctoral dissertation (article)|
- spent lithium-ion battery, hydrometallurgy, recycling, metal circular economy