Isothermal reduction of powdery 2CaO·Fe2O3 and CaO·Fe2O3 under H2 atmosphere

Injection of natural gas into the tuyere raceway of a blast furnace (BF) can effectively decrease the use of coke, as well as reduce CO2 emission. Therefore, the reduction behaviour of sinters, which account for 60% of the raw materials charged into the BF process under H2, is important for natural gas utilisation. This study used thermogravimetric analysis under H2 atmosphere to investigate the reduction kinetics of dicalcium ferrite (2CaO·Fe2O3, C2F) and calcium ferrite (CaO·Fe2O3, CF), which are the dominant components in fluxed sinters. Results indicated that CF reduction has a larger maximum reduction degree and a higher reaction constant than C2F. The apparent activation energy of CF is also larger than that of C2F, thereby illustrating that C2F reduction proceeds more easily than CF. X-ray diffraction measurements indicated that C2F is reduced to CaO and Fe in a single step, whereas CF is reduced with four steps in the following order: CaO·FeO·Fe2O3, CaO·3FeO·Fe2O3, C2F and Fe. Sharp and ln-ln methods revealed that C2F reduction is described by 2D Avrami-Erofeev (A-E) equation and that of CF is expressed by 2D A-E equation but tends slightly to 3D A-E equation in the late stage. A-E equations were verified to be consistent with the experimental reduction degree data of C2F and CF. A kinetics model that links reduction routes to model functions was proposed to describe the powder reduction of C2F and CF. Comparisons of the reduction behaviours of C2F or CF by H2 and CO implied that the reduction rate rises and activation energy declines during the reduction of samples by H2.