Effect of Reduction Degree on Characteristics of Slag Formed by Melting Hydrogen‐Reduced DRI and Partitions of P and V between Slag and Metal

Abstract

Self‐fluxing hematite pellets are reduced by hydrogen to different degrees. The reduced pellets are melted in closed MgO crucibles at 1873 K to study the effect of reduction degree on the characteristics of slag formed. The results reveal that the phosphorus content in the metallic phase can be brought down to 130 ppm merely by the self‐fluxing slag, even though the slag weighs only about 8% of the metal. It shows a great potential in reducing the amount of slag formers in the steelmaking process. The slag compositions obtained by melting the reduced pellets are used to prepare small synthetic slag samples for identifying the phases after melting. The use of the small samples is to ensure efficient quenching. Microscopic examination reveals that all the self‐fluxing slags contain mainly three phases, namely, magnesiowüstite, spinel, and a liquid phase. Most of vanadium is found to be in the spinel and magnesiowüstite phases. The liquid phase only contains 1–2 wt% V2O3. Decreased FeO content of the slag increases the vanadium oxide contents in the spinel and magnesiowüstite phases. The fact that vanadium concentrates in the solid oxide phases provides essential information for sustainable extraction of vanadium from the steelmaking slag.

Some Aspects of the Melting and Dephosphorization Mechanism of Hydrogen‐DRI

“…Vickerfält et al investigated the phosphorus content in the metal phase after melting (1800 s) of H‐DRI with a reduction degree of 95% and 99% without carbon additions. [ 10 ] To extend the time interval, the same experimental procedure as Vickerfält et al was carried out for one sample, B6 (900 s). The present results have been depicted alongside relevant experimental data from Vickerfält et.al, in Figure 10 .…”

“…[6][7][8][9] While many studies on the equilibrium phosphorus partition between slag and liquid iron relevant to the autogenous slag of H-DRI and EAF slags have been conducted, the dephosphorization mechanism of H-DRI itself is hardly studied. [10][11][12][13][14][15][16] As DRI carries a significant amount of gangue which with external slag additions eventually forms a top slag, the actual dephosphorization mechanism is not obvious and…”

“…[17][18][19][20][21] The FeO content in the autogenous slag of NG-DRI is thereby set by the carbon content and the reduction degree while being solely dependent on the degree of reduction for H-DRI. [10] When the autogenous slag joins the preexisting top slag, the resulting top slag chemistry is gradually modified. A top slag rich in FeO leads to some serious difficulties with regard to refractory wear, foaming performance, etc., and needs to be addressed.…”

The Melting Mechanism of Hydrogen Direct Reduced Iron in Liquid Slag

“…It is evident by examining Figure 5b that phases not native to the autogenous slag of the H‐DRI are found in the center. [ 19 ] In particular, an alumina containing spinel phase was found. Considering that the slag bath was at the spinel saturation boundary by design, the spinel phase will precipitate as the slag temperature decreases.…”