Dynamic Migration Process and Mechanism of Phosphorus Permeating into Metallic Iron with Carburizing in Coal-based Direct Reduction

Abstract

Coal-based direct reduction is one of the most important methods of high phosphorus iron ore dephosphorization. Recently, extensive work has been performed on the dephosphorization of high phosphorus iron ore using coalbased direct reduction. Sun et al. 1) used the process of direct reduction-magnetic separation to treat high phosphorus iron ore to achieve direct reduction iron (DRI). During the reduction process, phosphorus was reduced from fluorapatite and partially migrated into the metallic iron phase. Yin et al. 2)proposed a reduction process combined with microwave and magnetic separation, which improved the iron yield but did not reduce the phosphorus content of the iron. Li 3) was also able to obtain DRI with a high phosphorus content of 0.3%. In summary, it is difficult to reduce the phosphorus content of iron, because phosphorus can enter into iron easily; therefore, many scientists have focused on perfecting a dephosphorizing mechanism of direct reduction. 4,5) However, knowledge of the phosphorus distribution behavior and of the mechanism of metallic iron in the carbothermal reduction process has not been understood well.Nobuhiro Maruoka 6,7) investigated the phosphorus distribution behavior of solid iron and the effects of slag composition and oxygen partial pressure on the equilibrium of phosphorus between solid iron and molten slag. However, the phosphorus distribution behavior during the reduction The uneven distribution of phosphorus in direct reduction iron (DRI) was found in a carbothermal reduction experiment at 1 200°C. The results showed that phosphorus creates reticular distribution in DRI, and its content is high where carbon distributes intensively. The microstructure of eroded iron at room temperature was observed, and it was found that phosphorus is distributed mainly in the ledeburite and rarely in the ferrite or cementite. Ultimately, the process of the phosphorus migration with carburization into DRI was revealed: First, the austenite grain boundary melts and absorbs significant amounts of phosphorus while carburizing; meanwhile, the internal austenite remains solid, and the process of phosphorus entering into austenite is blocked, then, the austenite melted completely, therefore, the processes of carburizing and absorption of phosphorus occurred rapidly and phosphorus was mainly absorption at this stage. Based on these studies, low phosphorus DRI can be obtained by lowering the temperature and reducing the reducing agent, which preventing melted of DRI and inhibiting the absorption of phosphorus. Dynamic Migration Process and Mechanism of PhosphorusKEY WORDS: coal-based; direct reduction iron; phosphorus; migration mechanism; dephosphorization method.process remains unclear, and it is difficult to analyze the phosphorus content of the metal dispersed in the gangue phase.Current research mainly concentrated on the result of dephosphorization by direct reduction, [8][9][10] while few studies have focused on the dynamic changes and migration mechanism of phosphorus in DRI. Clarifyin...

Phosphorus-Containing Mineral Evolution and Thermodynamics of Phosphorus Vaporization during Carbothermal Reduction of High-Phosphorus Iron Ore

“…The migration of phosphorus in high-phosphorus iron ore was studied in the authors' laboratory. It was discovered that approximately 15-30% of the phosphorus was volatilized as a gas [19]. The purpose of this study was to define the phosphorus gasification and to determine the thermodynamic principles of fluorapatite dephosphorization through vaporization during the carbothermal reduction of high-phosphorous iron ore.…”

Research on Reaction Mechanism of Vacuum Carbon Thermal Reduction and Dephosphorization in High Phosphate Iron Ore

“…At this time, it was easy to ignore the effect of the large amount of reduced metallic iron on the reduction reaction. Some research [26][27][28] considered that iron did not participate in the reaction, and the fluoroapatite reacted only with the fixed carbon and gangue. The reduced phosphorus was volatilized in the form of gas phase such as P 2 or PO.…”

“…In order to have a better knowledge of the dephosphorization behavior of high-phosphorus iron ore, many separation methods have been proposed. The research methods of separation were classified into the following types: physical method [11][12][13], chemical method [14][15][16][17] magnetization roasting-magnetic separation method [18][19][20][21][22], and coal-based direct reduction method [23][24][25][26][27][28]. Among these reported separation methods, the coal-based direct reduction method has better characteristics such as simplicity of the process, a convenient and easy operation, and being economical and environmentally friendly.…”

“…Reduced iron with a content of 90% and less than 0.1% phosphorus could be obtained by this method. Our group had also completed the basic research on the new process of separation of iron and phosphorus from high-phosphorous iron ore based on a RHF and obtained low-P nuggets, which could be directly used as raw material for steel-making [26][27][28]. Therefore, numerous researchers now agree that the phosphorus of high-phosphorus iron ore can be effectively removed by the coal-based direct reduction method.…”

Gasification and Migration of Phosphorus from High-phosphorus Iron Ore during Carbothermal Reduction

“…China and Europe have 4-5 billion tons and more than 14 billion tons of iron reserves, respectively. [1][2][3][4] Corresponding resources have also been reported in the United States and Egypt. 5) On account of the high content of phosphorus in the iron ore, which adversely affects the quality of pig iron and steel, phosphorus and iron combine to form Fe 3 P, thereby forming a binary eutectic Fe 3 P-Fe with iron and causing steel to exhibit a "cold and brittle" phenomenon; this phenomenon limits the use of the Highphosphorus iron ore in industry.…”