Mechanism-Guided Molten Salt Engineering via First-Principles Molecular Dynamics for Efficient Titanium Extraction and Waste Salt Mitigation

Abstract Efficient chlorination of low-grade titanium slag demands a molten salt capable of withstanding the sustained enrichment of Mg/Ca chloride impurities without compromising transport properties. NaCl is widely regarded as an ideal molten salt medium. However, the atomic-level role of NaCl in modulating the Mg/Ca–Cl ionic network and governing Cl– mobility and melt viscosity remains unclear, thereby critically limiting the rational design of melt compositions for optimized titanium extraction. Here, first-principles molecular dynamics simulations were employed to reveal the structure-transport relationship in NaCl–MgCl2–CaCl2 molten salts with varying NaCl contents. Increasing NaCl content facilitated the dissociation of highly coordinated Mg- and Ca-centered clusters, weakened the connectivity of extended ionic networks, and increased the fraction of free Cl– ions. These structural changes promoted ionic mobility, resulting in enhanced diffusion and reduced shear viscosity. Considering shear viscosity, salt consumption, and density, an optimal composition window of 65–70 mol % NaCl was proposed. Chlorination experiments under the optimized molten salt conditions exhibited stable operation and achieved a high titanium extraction efficiency of 97.5%, validating the simulation-guided composition design. These findings reveal the atomic-scale mechanism governing structure-transport coupling in multicomponent chloride melts and provide a rational basis for molten salt design in low-grade titanium slag chlorination.