Bioleaching Of Heavy Metal Co From Spent Lithium Ion Batteries Using Thiobacillus Ferrooxidans And Its Mechanism Study

High metal contents are contained in the spent lithium ion batteries, such as Co andLi, and toxic chemical compounds of LiCoO2and LiPF6are also included, thesechemical material have a potential hazard to the environment. Thus, recycling the spentlithium ion batteries has positive effect to solve the problem of environment pollutionand energy shortage. Many researches have been reported in the cross area ofenvironment and metallurgy, compared with tradition treatment, bioleaching process ofspent lithium ion batteries shows obvious adventage, but many key scientific andtechnical problem has not been solved, and the core problem are attributed to lackingknowledge of bioleaching mechanism and kinetics, so low bioleaching efficiency hasnot been solved. Thus, research on the bioleaching mechanism to improve bioleachingefficiency and metal leaching percentage has scientific significance and practicalsignificance.This paper was mainly focused on three aspects to discuss the bioleaching processof spent lithium ion batteries, which included bioleaching conditions, bioleachingmechanism and metal ion catalysis.1. Original strains were collected from sludge, isolated with pour plate method, andmade physiological morphological characteristics identification to the isolated strain.Systematic studies the different bioleaching conditions （pH, leaching time, temperature,particle size and solid-liquid ratio）. Experimental results showed that the morphologiccharacteristics of the isolated strains were that: Length0～2.0μm, diameter0.3～0.5μm,short rods shape, so that can be identified as the Thiobaccilus ferrooxidans. During thebioleaching processes, inoculating quantity and LiCoO₂particle size have no effect onthe bioleaching rate, leaching efficiencies were improved as the constant temperaturevibrator speed up, highest cobalt leached percentage of48.7%in the solution wasachieved when the temperature was35℃, bacteria growth would be inhibited as thetemperature keeping arising, when sulfur was the only energy sources for the bioleahingprocess, the leached Co was only4.6%, but when Fe2and S+Fe²+as the energy sources,the leached Co were47.5%and48.2%, respectively. So that using the only resource ofFe2+is enough. When the initial Fe²+concentration was too low, enough energy couldnot be provided for bacteria growth. However, high Fe²+concentration was alsodisadvantage to the bioleaching efficiency due to low level of solution Eh, so best concentration was45g/L. the more quantity of LiCoO₂was added into the process, themore total leached Co, when solid/liquid ratio was more than3%, leached Co would notbe increased, but reduced oppositely.2. The indirect and direct mechanism was operated by the method of dialysis bag,Electrochemical theory and technology were also adapted to study the electrochemicalbehaviour and mechanism during the bioleaching process, the adsorption mechanismduring the bioleahing process were studied by the method of coomassie brilliant blue.Experimental results showed that the leached Co in the presence and absence of dialysisbag were both47.6%, these results indicated that the indirect mechanism plays leadingrole in this process. Adsorption results showed that the function of strains adsorbed tothe surface make no sense to the bioleaching rate, also indicated that the indirectmechanism was response for this process, pitting corrosion result showed that the opencircuit potential was0.34V in the absence of bacteria, but0.32V in the presence ofbacteria, it indicated that the corrosion rate was accelerated in the presence of bacteria.The results of cyclic voltammetry curves showed that the corrosion current wasincreased with the potential when the potential was more than0.581V, and highestcurrent was achieved at the potential of1.172V. Besides, the corrosion current withbacteria was much more than which without bacteria. Anodic polarization curve showedthat corrosion potential was0.420V, initiating passive potential was0.776V, passivepotential was0.802V. The results of anodic polarization curve under different scanningrates indicated that leaching rate was under control of electrochemical reaction andspread procedure. Tafel curve indicated the addition of bacteria in the bioleachingprocess was benefit to anode reaction, and inhibit the cathodic reaction.3. Catalytic process using copper, silver and bismuth to accelerate leaching rate of spentlithium ion batteries was discussed in this section. The solution pH, Eh during thebioleaching process and the bacteria concentration during the bioleaching process weredetermined to illustrate the relationship with bioleaching efficiency. Beside, XRD, EDSand SEM analysis were followed to certify the catalytic mechanism. Experimentalresults showed that best catalytic effect was achieved when the addition of copper ionconcentration was0.75g/L, the corresponding cobalt leaching percentage was99.9%atthe6th day. However, the leaching percentage was only43.1%without copper addition.EDX, XRD and SEM analyses also indicated that the copper ion added in thebioleaching process increased enhancement of cobalt dissolution, and the catalyticmechanism was through a cationic interchange reaction, which could be explained asthat the surface of LiCoO₂was replaced by the formation of CuCo₂O₄, and then CuCo₂O₄was dissolved by Fe³+. These results indicate that the cobalt dissolution can beenhanced by the addition of copper ion. Similarly, best catalytic silver effect was0.02g/L, the cobalt leaching percentage reached99.4%at the5th day, the bioleachingrate was accelerated obviously compared with copper ion. However, the cobalt leachingpercentage was80.4%when using bismuth as catalytic ion, although the catalyticmechanism was similarly, catalytic effect was not inferior to copper and silver ion.