Non-isothermal reduction mechanism and kinetics of high chromium vanadium–titanium magnetite pellets

Non-isothermal reduction kinetics and mechanism of high chromium vanadium–titanium magnetite pellets were studied at 400–1100°C, simulating the lumpy zone of blast furnace conditions. The phase transformation behaviour of valuable elements including Fe, Cr, V and Ti and microstructural changes of reduced pellets were examined by means of X-ray diffraction (XRD) and SEM-EDX. The swelling of reduced pellets was highest at 900°C, while cold crushing strength was highest at 1100°C. Phase transformation behaviour of valuable elements in the lumpy zone is as follows: Fe₂O₃→Fe₃O₄→FeO→Fe; Fe₂Ti₃O₉→Fe₂TiO₄→Fe₅TiO₈→FeTiO₃; V₂O₃→VO; (Fe_0·6Cr_0·4)₂O₃→FeO·Cr₂O₃→Cr₂O₃. By analysing the non-isothermal reduction kinetics of high chromium vanadium–titanium magnetite pellets, based on the evaluation of reaction activation energy calculated according to Coats–Redfern method, gaseous internal diffusion through solid product layer and interfacial chemical reaction are most likely to be the main rate controlling steps in the reduction process.