Ammoniacal leaching process for the selective recovery of value metals from waste lithium-ion batteries

The recovery of valuable metals in spent lithium-ion batteries (LIBs) is not only environmentally sustainable but also economically advantageous. In this research, ammoniacal leaching process was adopted to selectively extract valuable metals from the mixed types of cathode active materials. By employing the ammonium sulphite as the reductant, while the ammonia and ammonium carbonate are used to provide NH3 to complex metal elements. The Eh-pH diagrams were used to study the extraction behaviour of Co, Li, Ni and Mn during ammoniacal leaching, and the Co, Ni can be leached out as the complexes ([Ni(NH3)n]2+, [Co(NH3)m]2+), while the Li was leached out as metallic ion. Manganese is first leached out as [Mn(NH3)β]2+ and then precipitated as (NH4)2Mn(SO3)2·H2O and (NH4)2Mn(SO4)3 when an excess of ammonium sulphites added to the solution. A detailed understanding of the ammoniacal selective leaching process is carried out by investigating the effects of factors such as reaction temperature (50-90 ℃), leaching time (2-6 h), agitation intensity (400-900 rpm) and solid-to-liquid ratio (10-50 g/L). The experiment of response surface methodology shows that significant interactions exist between ammonium sulphite and ammonium carbonate, ammonium sulphite and ammonia according to the leaching efficiency of Co. Under the optimum conditions, Co, Li, Ni, Mn and Al can be leached out with the efficiencies of 84.56%, 90.31%, 64.13%, 4.53% and 1.72%, respectively. The results proved the possibility of selective leaching. Summarily, this research is potentially beneficial for the design of a selective recycling technique.