Molecular dynamics simulations of ionic transport, local structures, and physicochemical properties of multi-component NaCl-MgCl₂-CaCl₂-FeCl₂/FeCl₃ molten salt systems

TiCl₄ is a vital intermediate raw material for the production of both metallic titanium and titanium dioxide pigment via the chloride process. The current low-grade titanium feedstock available in China is more suitable for the preparation of TiCl₄ by molten salt chlorination. However, industrial practice reveals that the prolonged presence of FeCl₂ and FeCl₃ in the molten salt deteriorates its chlorination properties, posing significant challenges for efficient titanium production. This study employs large-scale molecular dynamics simulations to address deficiencies in thermodynamic structure data for the multi-component NaCl-MgCl₂-CaCl₂-FeCl₂/FeCl₃ system, particularly focusing on key structural and transport properties, including mean square displacement (MSD) and radial distribution function (RDF), etc. Additionally, the rotation-pendulum and Archimedes methods were utilized to assess the influences of varying FeCl₂/FeCl₃ content on the viscosity and density of the molten salt. The results show that Fe²⁺ and Fe³⁺ ions significantly affect the structure and transport properties of other ions in the molten salt compared to Na⁺ and Ca²⁺. These ions form stronger bonds with Cl⁻, promoting the formation of longer chain structures and the formation of larger ionic clusters. As a result, elevated levels of Fe²⁺ and Fe³⁺ ions correlate positively with increased viscosity, owing to the microstructural changes arising from ion pair interactions. This work may provide a new strategy for extending the operational lifespan of molten salts employed in titanium slag chlorination processes while enhancing its chlorination efficiency, which would be beneficial for facilitating a cleaner and more efficient route for the utilization of titanium resources.