China Nonferrous Metallurgy

In view of the lack of systematic thermodynamic analysis and thermal analysis of calcium roasting of vanadium slag, thermogravimetric analysis (TG) and differential scanning calorimetric analysis (DSC) were conducted on the roasting process of vanadium slag mixed with CaCO₃ or CaO. The phase transformation mechanisms during roasting process were analyzed, and the main conclusions were drawn as follows. It is feasible to produce calcium metavanadate, calcium pyrovanadate and calcium orthovanadate in the range of 350-960℃ during calcified roasting of vanadium slag. The calcination process of vanadium slag is mainly composed of four reaction stages which are interconnected or overlapping, namely, metal Fe oxidation stage, iron olivine oxidation and decomposition stage, spinel oxidation and decomposition stage of vanadate formation stage, silica-calcium reaction and pyroxene decomposition stage. The control temperature of phase transformation in the roasting process is: the oxidation of metal iron in the range of 350-700℃, the oxidation and decomposition of iron olivine in the range of 500-750℃, the oxidation and decomposition of spinel in the range of 500-900℃ and the decomposition temperature of silica-calcium reaction and pyroxene is generally above 900℃. These results can provide theoretical support for temperature control in production site.