Research On The Treatment Of Copper And Cobalt In Waste Lithium Batteries By Bioelectrochemical Coupling System

Waste lithium-ion batteries are rich in copper and cobalt resources.However,the recovery rate of heavy metal resources in used lithium-ion batteries is low in China,and some of the used lithium-ion batteries are still not effectively recovered.In this case,the environment is polluted and a large amount of metal resources are wasted.If we can effectively recycle this part of the metal resources,it will bring huge environmental and economic benefits.The MFC-MEC bioelectrochemical coupling system is a bioelectr-ochemical system（BES）.It is a biological system that uses microorganisms as a catalyst to convert chemical energy into electrical energy.This method can efficiently treat a variety of wastewaters,and is characterized by cleanliness,no pollution,low energy consumption and low cost.In this study,the bio-coupling system was used to recover copper and cobalt in waste lithium-ion batteries.The main research is as follows:1.The experiment built an MFC device.In the MFC device,Cu（II）was used as a cathode electron acceptor.The effects of anode substrate type,effective volume,pole distance,anode electrode material,anode pH,cathode pH and external resistance on MFC production performance and cathode copper recovery were investigated.The optimal experimental conditions were selected by comparative experiments.The results showed that the optimal conditions for the experiment were sodium acetate as the anode substrate,the pH of the anolyte was adjusted to 4,and the graphite plate was used as the anode electrode material.The effective volume was adjusted to 500 mL,and the pole pitch was reduced.The battery catholyte has a pH of 2.5 and the external resistance is reduced to200Ω.The MFC power density was up to 20702.5 mW/m²,the cathode Cu（II）removal rate was up to 99.78%,the cathode efficiency could reach 79.04%,and the copper elemental specific yield was up to 3.12 gCu/gCOD.After the reaction,yellow-brown particles were clearly observed on the cathode of the battery,and the elemental copper was detected by XRD.2.Experiment with lithium cobaltate as the MFC cathode electron acceptor.The effects of stirring,carbon felt area,catholyte pH,catholyte type,concentration,and amount of lithium cobalt oxide adsorbed by titanium wire and carbon felt on MFC production and cathode Co（II）leaching were investigated.The results showed that it was not necessary to add a stirring device to the MFC,the carbon felt area was 5 x 5 cm,and the pH of the catholyte was lowered.And 1 g/L CuSO₄ was used as the battery cathode liquid,and the titanium wire was appropriately wound.When the amount of lithium cobaltate on the cathode carbon felt was 0.15 g,the MFC had better battery performance and Co（II）leaching effect.The MFC anode coulombic efficiency was 76.3%,the maximum voltage was 1.05 V,the maximum power density was 2376.2 mW/m²,and the Co（II）leaching rate was up to 44.84%.The concentration of Co（II）in the catholyte was detected to be up to 54 mg/L.3.The experiment constructed the MFC-MEC coupling device.The effects of MEC cathode electrode material,catholyte pH,catholyte concentration,volume ratio of anode inoculated sludge and organic substrate,reactor effective volume and electrode spacing on the recovery of copper and cobalt by MFC-MEC coupling system were studied experimentally.The results showed that MEC used carbon paper as the cathode electrode material,the concentration of cathode cobalt chloride solution was 5 g/L,the pH of the solution was adjusted to 3,and the volume ratio of the anode anode inoculated sludge to the organic substrate was 1:3.At the same time,when the effective volume of the reactor was reduced to 100 mL,the coupling system performance was better when the electrode spacing was increased,and the copper and cobalt had better recovery effect.The highest removal rates of Cu（II）and Co（II）were 99.63%and 97.38%.At the same time,the connection mode and stacking coupling system of the system were also studied.As a result,when the resistors were connected in series,the cathode efficiency of MFC and MEC in the coupling system was higher at 32.67%and 11.03%.When the cathode electron acceptors in the two MFCs were different from Cu（II）and LiCoO₂,the removal rate of copper ions by MFC in the coupled system reached 99.92%.The leaching rate of Co（II）at the MFC cathode was 72.28%,the concentration of Co（II）in the solution was261.1 mg/L,the removal rate of Co（II）by MEC was 92.09%,and the yield of cobalt was1.004 gCo/gCOD.4.The MFC-MEC coupling system was built in the experiment,and the optimal parameter conditions determined in the previous experiments were applied to the study of copper and cobalt in the waste lithium ion battery.The results showed that the battery performance was better when the effective volume of the MFC was less than 300 mL.When the effective volume of MFC was 500mL,the effect of copper recovery and Co（II）leaching was better.The Co（II）leaching rate was 32.42%,the Co（II）concentration was58.56 mg/L,and the copper elemental yield was 1.223 gCu/gCOD.The cathode product contains were CoSO₄,Co（OH）₂ and Cu elemental,indicating that the Co（III）reduction reaction and the Cu（II）reduction reaction occur in the MFC cathode.For the influence of MEC,MFC’s power generation performance has a greater impact on it.When the electrical properties of MFC were better,the MEC cathode has better effect on Co（II）treatment,the cathode efficiency was 56.12%,the Co（II）removal rate was 54.52%,and the cobalt elemental yield was 0.861 gCo/gCOD.There is a black powder on the surface of the carbon paper electrode.Under the electron microscope,the surface of the carbon paper has round loose particles.The product contained a substance of Co in XRD.The electrical performance of MFC₁ and MFC₂ in the stacked MFC-MEC coupling system was relatively stable.The removal rate of cobalt ion and the yield of elemental mass in MEC were higher than that of one MFC-driven MEC.The removal rate of Co（II）and the yield of elemental mass were 54.52%and 0.861 gCo/gCOD.For the reaction of the MEC cathode,a higher power supply is beneficial to the MEC cathode reduction reaction.