Multiscale modeling of Na2WO4–WO3–CoO melt diffusion layer for molecular dynamics combined with finite element analysis

Abstract

In the process of molten salt electrolysis of spent tungsten carbide for the separation of tungsten and cobalt, the nature of the molten salt has a crucial impact on product quality and efficiency. In this study, the microscopic and macroscopic models of the diffusion layer of Na2WO4–WO3–CoO molten salt were developed. The structure, transport properties and electroanalytical behavior of Na2WO4–WO3–CoO molten salt were investigated by combining molecular dynamics and finite element simulation under different CoO and WO3 molar ratios and different applied electric field conditions. The cost of this approach is relatively low compared to experiments. It was found that the addition of CoO hinders the mass transfer and increases the electrochemical impedance. The reason for this is that the addition of CoO leads to an increase in the entropy of the molten salt. The change in external electric field does not affect this law. The calculated results are in general agreement with the available experimental data. In the study of the structure of molten salts, the vacancy volume factor, which is a metric for evaluating the size of the vacancy volume of molten salts, was proposed for the first time. The addition of CoO also affects the microstructure, which can be used to infer changes in the electrodeposition products. Experimental results of electrodeposition support this speculation. This study confirms that a combination of macroscopic and microscopic, molecular dynamics and finite element simulations can theoretically aid the development of molten salt electrolysis processes.