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

Abstract

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, P₂ 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 P₂, leading to the slow increase or decrease in the dephosphorization ratio of the pellets. Phosphorus was absorbed by liquid iron as P₂, whereas PO gas was completely volatilized. Gasification dephosphorization mainly occured from 10 min to 25 min at 1200°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.