Evaluation of NaCl-KCl-Al2S3 Molten Salts by Raman Spectroscopy and Quantum Chemical Calculations

The complex ions in NaCl-KCl-Al2S3 molten salts at temperatures of 923–1003 K were investigated via Raman spectroscopy and quantum chemistry calculations. The results showed the presence of Al2S3Cl–, AlSCl32–, and AlSCl2– in the molten salts. Besides that, there are two types of dissolution reactions for Al2S3: one is the reaction with Cl–, generating AlSCl32– and AlSCl2–, and the other is the reaction with Cl–, forming Al2S3Cl–. Once the temperature increases, the reaction between Al2S3Cl– and Cl– occurs, promoting the formation of AlSCl32– and AlSCl2–. Meanwhile, the reaction between AlSCl2– and Cl– occurs with the formation of AlSCl32–. With the increase in Al2S3 content, Al2S3 participates in the reaction with Cl–, producing Al2S3Cl–, which also leads to the formation of AlSCl2– and AlSCl32–. Meanwhile, the reaction of Al2S3Cl– with Cl– results in the generation of AlSCl32– and AlSCl2–. The non-bridging S atom in Al2S3Cl– and the S atoms in AlSCl32– and AlSCl2– are the easiest to be attacked by electrophilic molecules. In turn, the Al atom bonded to one Cl atom and two S atoms in Al2S3Cl– and the Al atoms in AlSCl32– and AlSCl2– are the primary sites reacting with nucleophilic molecules.