Study On Recovery Of Cobalt From Spent Lithium-ion Batteries

Disposal of spent lithium-ion batteries(LIBs) has becoming more and more important with the growth of production and use of LIBs. Recycling treatment has attracted more and more attentions. Compared to other methods of treatment, recycling can not only resolves environmental problems, but also slows the lack of resource effectively by recovering and reusing of valued metals from LIBs.On the basis of analyzing and comparing pyrometallurgical, hydrometallurgical and some other related recycling techniques for spent LIBs, the paper proposed a hydrometallurgical process combining leach and salting out. The process included two main steps, the first step is leaching of LiCoO₂ cathode from LIBs in acid solution, and then cobalt can be dissolved;the second step is salting out, it can makes separation and recovery of cobaltous from other ions in the leachate. Compared to organic solvent extraction, salting out which is adopted in the paper for the first time is an economic and green environmental technique. It has many advantages such as cheap raw materials, simple flow sheet, low energy consuming, nonpolluting, and so on.Leaching of LiCoO₂ cathode in hydrochloric acid was carried out through orthogonal test. In the test, some factors affecting the leaching rate of cobalt were analyzed. These factors included concentration of hydrochloric acid(C), temperature of leaching (T), time of leaching (t), ratio of solid and liquor(S/L). The highest leaching ratio of Co was 94.99% under the best condition of C=3molL^-1, T=60℃, t=60min, and S/L=10g·L^-1.Because chlorine produced during the leaching in hydrochloric acid can caused deterioration of environment and damaged to human bodies, sulfuric acid was chosen to replace hydrochloric acid. Adding 1.5% hydrogen peroxide(volume fraction) to sulfuric acid solution, the leaching ratio in this solution system was nearly the same with that in hydrochloric acid system. In the sulfuric acid solution without reducing agent, ultrasonic was used to strengthen the effect of leaching. It was found to be that the effect of ultrasonic was decided by the concentration of sulfuric acid solution: the effect of ultrasonic was obviously good when the concentration of sulfuric acid solution is lower than 1.0 mol·L^-1;but when the concentration of sulfuric acidsolution is higher than 1.0 molL"1, the effect of ultrasonic can be ignored, because ultrasonic can not or can only produced little H2O2 with decreasing of free H2O.Salting out was based on the model of solvation, it can separated and recovered Co2+ from other ions in the leachate. According to the model, whether Co2+ can be salted out or not is determined by solvation energy, the solvation energy of Co2+ in the solution reduced with the increasing of saturation. The saturation of solution can be adjusted by adding ammonium sulphate and ethanol, and then Co2+ can be salted out as (NH4)2Co(SC>4)2. The efficiency of salting out was affected by the consumption of (NH4)2SO4 and ethanol. When the volume ratio of leachate and (NtL^SC^ saturated solution and ethanol was 2:1:3, the total efficiency of Co2+ was more than 92%. According to the difference of solvation energy, Co2+ and Al3+ in the leachate can be separated by graded salting out. The greatest mass fraction of (NH4)2Co(SO4)2 in the graded production can reached up to 94%, (NH4) A1(SC>4)2 was the other phase of the production.