Phosphorus Migration During Direct Reduction of Coal Composite High-Phosphorus Iron Ore Pellets

Abstract

This study investigated the direct reduction process and phosphorus migration features of high-phosphorus iron ores using simulated experiments. Results show that iron oxide was successfully reduced, and a Fe-Si-Al slag formed in carbon-bearing pellets at 1473 K (1200 °C). Fluorapatite then began to decompose into Ca3(PO4)2 and CaF2. As the reaction continued, Ca3(PO4)2 and Fe-Si-Al slag reacted quickly with each other to generate CaAl2Si2O8 and P2, while CaF2 turned into SiF4 gas in the presence of high SiO2. A small amount remained in the slag phase and formed CaAl2Si2O8. Further analysis detailed the migration process of the phosphorus into iron phases, as well as the relationship between carburization and phosphorus absorption in the iron phases. As carbon content in the iron phase increased, the austenite grain boundary melted and formed a large quantity of liquid iron which quickly absorbed the phosphorus. Based on the results of simulation and analysis, this paper proposed a method which reduced the absorption of P by the metallic iron formed and reduced P content in metallic iron during direct reduction.