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.