Currently, the most popular LIBs recycling processes are either pyrometallurgical and hydrometallurgical. Although the former is the most used method on an industrial scale, hydrometallurgical has become a promising process due to its recovery rate, high purity of the metals and a lower energy consumption. The main step of the hydrometallurgical process is the leaching, where acid is used as an extracting agent to recover metal from the waste LIBs. Different factors influencing the leaching process are the extracting agent concentration, temperature, solid-liquid ratio, reaction time and reductant agent concentration. Determine the reaction rate and the rate controlling step is essential to optimize leaching parameters and improve the process efficiency.
In this work, a mathematical model is presented with the aim of determine the leaching reaction kinetic of LIBs components, namely, LiCoO2 particles. The model is based on a solid-liquid reaction model, in particular on the shrinking core model, due to the formation of Co3O4 in the outer part of the LiCoO2 particle when is used an inorganic acid as extracting agent in absence of an external reducing agent. In this model, the diffusion of the reactant through the product layer and the chemical reaction at the surface of the unreacted core are defined as the rate controlling step. A series of extraction analyses were carried out and their results were used to adjust the formulated model.
COMSOL Multiphysics 5.5 program was used to adjust the kinetic model with the experimental results, obtaining as result the value of the kinetics and diffusion constant. The implemented model for simulation of the lithium and cobalt leaching from LiCoO2 reproduces the experimental results, predicting the non-equimolar proportion between Li+ and Co2+ and verifying the hypothesis of the Co3O4 layer formation.
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