Reaction process and mechanism analysis for CaS generation in the process of reductive decomposition of CaSO3 with coal

• Little is studied at present about the decomposition of CaSO3.
• High purity of CaS is successfully synthesized from CaSO3.
• Gas composition in the decomposition process is analyzed.
• The reaction mechanism of CaS generation has been analyzed.

In this study, using coal as a reducer, the thermal decomposition of CaSO3 to produce CaS was carried out at different conditions. The mineralogical composition and microstructure of the as-obtained CaS were analyzed by scanning electron microscopy (SEM) and X-ray diffraction (XRD). Results revealed that single-phase CaS was detected in the product under optimum conditions and the optimal synthesis conditions of CaS were as follows: molar ratio of C and CaSO3 (C/S ratio)=2.5, reaction temperature 1173 K, reaction time 1.5 h and coal particle size 100 mesh. Under the optimum conditions, the purity and yield of CaS are up to 99.15% and 96.52% respectively, which indicated that the decomposition was almost complete and the as-synthesized CaS can be recycled to be a raw material in chemical industry. Meanwhile, thermodynamic calculation showed that the reaction for CaS generation was very complex and CaS was generated mainly through solid–solid reaction and gas–solid reaction.