Study On Bioleaching Of Valuable Metals From Spent Li-ion Batteries And Mechanism Exploration

Swift development of electric vehicle(EV) absolutely produces enormous amounts of spent EV Li-ion batteries(LIBs), hence more studies should be performed to seek cheap, efficient, safe and eco-friendly ways for the recovery of spent EV LIBs. Using a kind of economically effective, safe and environmental processing technology to realize its harmless and recycling is of great significance. Owing to the advantages of smaller acid consumption, lower costs, higher leaching rate, safety and eco-friendly traits, bioleaching technology has caused wide public concern.There are a few studies about the recovery of Li and Co from LiCoO2 at present. In this work, release of valuable Li, Ni、Co and Mn from three typical spent EV LIBs cathode LiFePO4, LiMn2O4 and LiNixCoyMn1-x-yO2 by bioleaching at 1% pulp density was explored for the first time. By changing the experimental conditions we explored the optimization conditions and analyzed the mechanism,which were designed to obtain the basic data for the practical application of bioleaching technology.The results showed the maximum extraction efficiency of Li occurred in the sulfur–Acidithiobacillus thiooxidans system, indicating that Li release was due to acid solution by biogenic H2SO4; whereas the mixed energy source-mixed culture system harvested the highest dissolution yield for Ni、Co and Mn than other systems, suggesting these metals were mobilized by a combined work of Fe2+ reduction and acid dissolution. Moreover, a non-contact mechanism accounted for Li extraction, while a contact mechanism between the cathodes and cells was essential for mobilization of Ni、Co and Mn. Due to the enhancement effect in cell growth, pH adjustment greatly improved bioleaching performance, an average extraction efficiency of 4 valuable metals from the resistant LiNixCoyMn1-x-yO2 reached more than 95%, especially the release efficiencies of Co and Ni rose from 43.5%, 38.3% to 96.1%,97.2%, respectively.Meanwhile, it studied the mechanism that EPS(extracellular polymeric substances) promoted the bioleaching efficiency of spent lithium-ion batteries.It indicated that EPS can greatly improve the bioleaching efficiency at 2% and 4% pulp density.The highest efficiencies were appeared in the ones which added Acidithiobacillus thiooxidans EPS. Under the condition of 2%, the maximum extraction efficiency of Li, Mn, Co and Ni were 99.4%, 99.9%, 99.9%, 89.3% respectively. Compared with the ones without adding EPS, the average growth rate reached 100% for the four metals at 4% pulp density.According to SEM characterization, EPS wrapped in a large number of microorganisms adhering to the surface of the material, promoted adsorption intake of energy substrates and improved microbial’s ability to adapt to adverse living environment. The concentration of H+、Fe2+ and Fe3+ were increased simultaneously,which increased the bacterial growth rate and metal leaching rate. The lowest pH was showed in Acidithiobacillus thiooxidans-EPS system, which conducive to the growth of acidophilus bacteria. The system produced a relatively more Fe2+ to enhance the reduction dissolution of the target element and improved the bioleaching efficiency.