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.