Recycling Cobalt From Spent Li-ion Batteries By Electrolytic Stripping And Biomass Acid Leaching Method

To some key problems, this paper puts forward a process of electrolytic stripping and biomass acid leaching cobalt. It is realized the battery powder and Al foil stripping and part of the cobalt leaching when electrolytic stripping-leaching using citric and sulfuric as electrolyte, cathod with Al foil as cathod, platinum electrode as anode. Collecting the leaching residue, use oat straw powder as the reducing agent and sulfuric acid to leach the cobalt. The new process avoids the subsequent problem of separating Al and Co when aluminum foil dissolves by acid leaching process, which implements the resource recycling of Al, and uses oat straw powder as the reducing agent instead of hydrogen peroxide, which makes the process simple and economic security.Dynamics of electrolytic acid leaching is studied, during the preliminary time (5-30min) it conforms to shrinking core model and the apparent activation energy is7.32kJ/mol, and during the last period (75-180min) it conforms to internal diffusion control model and the apparent activation energy is17.05kJ/mol. Through a large number of experiments, it is found that the positive battery powder is peeled off from the aluminum foil in20-30min due to the dissolution of alumina film and hydrogen bubble blows, since then, cobalt leaching rate and current efficiency is gradually reduced. The optimal experimental condations of electrolytic stripping is when the sulfuric acid concentration is20-30g/L, the citric acid concentration is36g/L, and the current density is200A/m, the positive powder is separated from aluminum foil after electrolytic stripping for30min, and the cobalt leaching rate is about40%, current efficiency is40%-50%and aluminum loss is just about2%.This paper uses sulfuric acid with biomass oat straw powder insteading of hydrogen peroxide as a reducing agent to leach cobalt from the electrolytic leaching residual. When controlled the liquid-solid ratio of10, the straw powder dosage of0.7g to1.0g battery powder, the sulfuric acid concentration of2mol/L, temperature of90℃, the size of straw powder particle of60-100mesh, the cobalt leaching rate is over99%. This paper designs the triple acid leaching process in order to reduce COD and make full use of the unreacted acid, and the cobalt concentration increases to around50g/L and COD concentration decreases to1.5g/L. Dynamics research is analyzed the process of biomass pickling, and it is controlled by shrinking core model during the early time (0-20min) and controlled by chemical reaction during the last period (30-150min). Through FT-IR detects the slag powder before and after dealt with acid boiled, the oat straw powder is rich in lignin, xylose, cellulose and hemicellulose etc reduction agent, insteading of hydrogen peroxide to reduction leaching cobalt.The cobalt in the leach liquor is precipitated by oxalate. When controlled the pH value about1-2, temperature50-60℃,[C2O42-]/[Co2+] ratio around1.05-1.1, reaction1h, the sedimentation rate of cobalt is92%-95%, and the production of cobalt oxalate is qualified by analyzing. The cobalt oxalate is used for preparation of battery cathode material with good battery performance through XRD analysis.