Investigation of leaching kinetics of valuable metals in spent lithium-ion battery cathode material in oxalic acid solution

Lithium-ion batteries are a type of rechargeable battery used in almost every field today. The structure of a lithium-ion battery consists of an anode, cathode, electrolyte, binder, and plastic. The anode typically consists of graphite coated on copper foil, while the cathode material consists of metal oxides coated on aluminum foil. The electrochemical properties of the batteries are determined by the type of metal oxide used, and lithium-ion batteries are named according to the type of metal oxide used. If the cathode material consists of nickel, manganese, and cobalt oxide, it is called NMC; if it consists of lithium iron phosphate, it is called LFP; if it consists of cobalt oxide, it is called LCO. In the lithium battery industry, which contains many metals and has high supply-demand, recycling and recovery of metals are of high environmental and economic importance. In this thesis, after discharging and mechanically opening end-of-life mobile phone batteries, the aluminum foil on which the cathode powder is located was dissolved, and cathode powder was obtained. In the leaching experiments conducted with cathode powder, the effects of oxalic acid concentration, temperature, cathode powder particle size, stirring speed, solid-liquid ratio, and leaching time on the dissolution of lithium, cobalt, nickel, and manganese and the kinetics of the leaching reactions were investigated. The characterization of the obtained samples was performed using XRD, ICP-OES, and SEM-EDS analysis methods. Lithium in the solution increases proportionally with oxalic acid concentration and temperature. Increasing the stirring speed from 200 rpm to 250 rpm created a 4% increase. While the increase in particle size had an inverse effect on dissolution, this difference did not create a significant impact. As the solid-liquid ratio increased, the dissolution amount of all metals decreased. Cobalt and nickel showed similar dissolution and precipitation behavior depending on the changing leaching parameters. The amount of dissolved cobalt and nickel increased with the increase in oxalic acid concentration. However, the dissolved cobalt and nickel formed cobalt oxalate and nickel oxalate compounds. The formed oxalate layer caused the leaching reactions to slow down and stop. It was determined that oxalate formation occurred more slowly at low temperatures and rapidly at high temperatures. Manganese also showed similar behavior to cobalt and nickel, forming manganese oxalate compounds. However, the high oxalic acid concentrations used in the leaching experiments caused the dissolution of manganese oxalate compounds. Therefore, the amount of manganese in the leach solution was higher than that of nickel and cobalt. The data obtained from the leaching experiments showed that the most suitable kinetic model for the leaching of lithium was the Shrinking Core Model. The kinetic equation was derived.