Influence of CaO and SiO2 on the Reducibility of W^|^uuml;stite Using H2 and CO Gas

Abstract

CaO-(0-20 mass%) and SiO2-containing (0-30 mass%) wüstite ('FeO') compacts were isothermally reduced at 1 273 K under CO and H2 gas. Prior to reduction, the phase of dicalcium ferrite (Ca2Fe2O5) and fayalite (Fe2SiO4) was equilibrated with 'FeO' at 1 273 K under 50%CO/50%CO2 and identified using X-ray diffraction and scanning electron microscopy. The rate of reduction for CaO-containing 'FeO' compacts under both H2 and CO increased up to the vicinity of 2.5 mass% CaO, and then decreased with higher CaO dependent on the formation of an intermediate phase of dicalcium ferrite. For SiO2-containing 'FeO', the rate decreased with SiO2 additions. When the dense fayalite is present reduction using CO was limited, while considerable reduction was observed using H2. The reduction was affected by three distinct reduction mechanisms of interfacial chemical reaction, gaseous mass transport, solid state diffusion of oxygen or a combination of these individual mechanisms termed the mixed control. The contribution of each mechanism with the content of CaO or SiO2 affecting the reduction behavior was determined. The compact porosity increased when CaO was added to approximately 2.5 mass% and subsequently decreased with higher CaO, but continuously decreased with SiO2 additions. The ratio of the effective diffusivity (De) to molecular interdiffusivity (D) was highest at the vicinity of 2.5 mass% CaO and thus the maximum reduction rate was obtained when the porosity was highest.

Reduction Behavior of Dolomite-Fluxed Magnetite: Coke Composite Pellets at 1573 K (1300 °C)

“…It was reported that the flux materials such as CaO and SiO 2 have influence on the reducibility of FeO affecting the interfacial chemical reaction, gaseous mass transport, and solid state diffusion of oxygen. [13] Likewise, fluxed dolomite in the present study is considered to have changed the degree of reduction of magnetite. The major components of dolomite are CaO and MgO as indicated in Table III.…”

“…As Kim et al reported, CaO contents increases the reduction rate of wu¨stite by forming calcium ferrite, while SiO 2 decreases the reduction rate by forming stable fayalite compounds. [13] Thus, increased basicity in MD10 samples resulted in the faster reduction of wu¨stite as described in Eq. [7].…”

“…These basic oxides were reported to have positive effect of iron oxide reduction by facilitating gas mass transfer due to the increase of micro porosities. [13] The reduction can be divided into three distinct stages according to the change of slopes. Similar to previous studies, [14] Stage 1 is the incubation period required for initial heating of pellet after insertion into the hot zone and subsequent nucleation events.…”

“…[12] Other researchers investigated the influence of CaO and SiO 2 on the reducibility of wu¨stite in terms of the formation of intermediate phases such as dicalcium ferrite or falyaite. [13] Porosity change associated with agglomerate's microstructure has the largest influence on reducibility of iron oxide accordingly. [13] Carbon composite pellets during heating takes advantage of the higher energy efficiency due to the proximity of reactants and the exothermic heat generated within the pellet as the carbon oxidizes internally.…”

“…[13] Porosity change associated with agglomerate's microstructure has the largest influence on reducibility of iron oxide accordingly. [13] Carbon composite pellets during heating takes advantage of the higher energy efficiency due to the proximity of reactants and the exothermic heat generated within the pellet as the carbon oxidizes internally. The present authors have also studied the effect of minerals on the reduction of carbon composite pellets in terms of the reducibility and physical property.…”