Study on the Effect of Different Addition Ratios of Red Mud and Iron Oxide Scale on Phosphorus Removal Behavior in Molten Iron

This study aims to utilize red mud with high alumina and iron oxide content from aluminum plants as raw material to achieve high‐value utilization of red mud. The effect of different ratios of red mud and iron oxide scale on phosphorus removal efficiency was investigated through laboratory experiments combined with characterization techniques such as XRD, scanning electron microscope‐energy dispersive spectrometer (SEM‐EDS), infrared spectroscopy, and Raman spectroscopy. Through dephosphorization experiments, it was found that the highest dephosphorization rate of 66% was achieved when the mass ratio of the two substances was 2:3. When the red mud content exceeds 20%, the phosphorus removal rate decreases due to reduced alkalinity and the Al/P competition effect. By introducing its high content of Al 2 O 3 and Fe 2 O 3 and high basicity characteristics into the converter phosphorus removal system, the slag system performance can be optimized to partially replace traditional lime or dolomite flux agents and reduce raw material costs. XRD and SEM‐EDS analysis of the dephosphorization slag revealed that its primary phase consists of an nC 2 S‐C 3 P solid solution and uniformly distributed spherical Ca 3 (PO 4 ) 2 particles. Raman and infrared analysis results indicate that at a 20% red mud content, the siloxane network primarily consists of moderately to weakly polymerized Q 0 (Si) and Q 1 (Si) structures. At this point, the OP bond vibration peak exhibits maximum intensity. As the proportion of red mud increases, the intensity of this vibration peak decreases. Enhanced SiOAl bending vibrations indicate that Al 3+ incorporation into the silicon/phosphorus oxygen network weakens the Q 0 (P) peak, leading to reduced phosphorus fixation. This indicates a competitive relationship between Al and P. Excessive Al in the slag reduces the migration of P into the slag, thereby decreasing the phosphorus removal rate of molten iron. Q 1 (P) and Q 2 (P) exhibit relatively low relative intensity and small variation. Multiple spectroscopic characterization analyses confirm that phosphorus in the slag is primarily incorporated into low‐polymerization phosphate structural units, indicating that phosphorus in the slag mainly exists as low‐polymerization phosphate. This oligomeric form significantly enhances phosphorus's migration activity, making it more readily immobilized by Ca 2+ to form a stable phase. This study provides theoretical basis and technical reference for the green, high‐value utilization of red mud in converter steelmaking processes.