Based on our best knowledge acquired previously about separation and recovery of Sc_2O_3 from Bayan Obo tailings,the detail thermodynamic analyses of these chemical reactions,possibly occurred during the roasting process among CaCl_2,carbon and Bayan Obo tailings,were discussed. Also,X-ray diffraction( XRD) technique was used to detect the phase transformations during roasting decomposition process. The main chemical reactions,2CaCl_2+ 2SiO_2+ O_2( g) = 2Ca SiO_3+ 2Cl_2( g),CaCl_2+ SiO_2+ H_2O( g) = CaSiO_3...