Effect of physical properties of liquid phase by MD simulation on NaCl separation behavior during the phase transition of molten salt chloride slag.

Molten salt chlorination process in the titanium industry is difficult to apply on a large scale because of producing a large amount of environmentally polluting molten salt chloride slag. The phase transition method is an effective novel method to achieve the separation of the impurity components and recovery of NaCl from the molten salt chloride slag, which is mainly composed of ternary mixed molten salt NaCl-MgCl-CaCl. This study investigated how the physical properties of the liquid phase influence the separation behavior of NaCl during the phase transition of chloride salt slag. Molecular dynamics simulations were used to study the physical properties of the liquid phase of molten salt chloride slag with NaSiO additive, including radial distribution function, ion self-diffusion coefficient, density and viscosity. The ternary mixed molten salt NaCl-MgCl-CaCl system with oppositely charged ion pairs exhibits a more stable coordination structure, with the interaction strengths following the order Mg-Cl > Ca-Cl > Na-Cl. The recovery of NaCl at different temperatures was investigated by phase transition method using NaSiO additive. The additive of NaSiO leads to a decrease in the ionic self-diffusion coefficients, density and viscosity of the mixed molten salt. The determination coefficients R for the fitted models of density/viscosity (mixed molten salt with NaSiO) and NaCl recovery during the phase transition of molten salt chloride slag were 0.9626 and 0.9073, respectively. The regression equation describing the relationship between density and NaCl recovery showed better agreement. The experimental results provide a reliable validation of the calculated results. These research results provide important insights to solve the pollution problem of molten salt chloride slag.