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

The effect of different gangue oxides(Al2O3, SiO2 and Fe2O3) on the gasification and migration of phosphorus during the carbothermal reduction of fluorapatite has been investigated. The vaporization of phosphorus during the carbothermal reduction of synthesized model sample demonstrating a high-phosphorus iron ore was analyzed by gas mass spectrometry. Results revealed that the dephosphorization of fluorapatite was promoted by Al2O3 and SiO2 to form CaAl2O4 and CaSiO3, respectively. The promotion effect of SiO2 was larger than that of Al2O3. With the increase in the addition of gangues, the thermodynamic conditions for the reduction of fluorapatite were continuously optimized, thereby accelerating the dephosphorization of fluorapatite. At a C/O (O originated from fluorapatite and Fe2O3) of larger than 1 in molar ratio, P-2 was the the dephosphorization product. Whereas, at a C/O of less than 1, the dephosphorization product turn to PO. With the addition of Fe2O3 to fluorapatite, a large amount of phosphorus was absorbed by liquid iron, resulting in a decrease of the amount of volatilized P-2, leading to the slow increase or decrease in the dephosphorization ratio of the pellets. Phosphorus was absorbed by liquid iron as P-2, whereas PO gas was completely volatilized. Gasification dephosphorization mainly occured from 10 min to 25 min at 1 200 degrees C. These findings leads to a new idea on the dephosphorization of a high-phosphorous iron ore, that is, decreasing the reduction temperature to retard melting of iron and simultaneously adding the additives to promote the dephosphorization of fluorapatite.