A novel method to recover NaCl from molten salt chlorination residue and recycle NaCl back into molten salt chlorination process in TiCl4 production: Based on phase diagrams analysis

Abstract

TiCl₄ is the significant intermediate to produce high-end titanium materials. Molten salt chlorination is the main way to produce TiCl₄ in China. However, there is a large amount of molten salt chlorination residue (MSCR) produced during this process. The complex residue is difficult to be treated, causing serious environmental problems. To reduce environmental pollution associated with MSCR and recycle NaCl in the molten salt chlorination process, a novel process of phase transition to recover gaseous NaCl from MSCR was proposed. CaCl₂ and MgCl₂ are the dominant impurities to hinder the recovery of NaCl. Thus, the influence mechanism of CaCl₂ and MgCl₂ and improvements in the recovery of NaCl were systematically investigated in this work, including the thermodynamic phase diagrams analyses, the effects of additive of Na₂SiO₃ and temperature. As a result, sodium magnesium silicate and sodium calcium silicate were prohibited to generate and the recovery efficiency of NaCl was promoted along with the increasing activity of NaCl. The recovery efficiency of NaCl is 94.36 % and the content of NaCl in the gaseous product is 99.96 % at 1200℃ when n(CaCl₂+MgCl₂): n(Na₂SiO₃) = 1:1. This method successfully realizes the harmless treatment of MSCR and the recovery of sodium chloride.