Function and mechanism of assistant reducers in iron recovery by the direct reduction in tunnel kilns of hematite

Iron enrichment from refractory low-grade hematite was studied by using the method of direct reduction roasting in a tunnel kiln and magnetic separation. This study focused on the function and the mechanism of the assistant reducer NCP. Under the conditions of coal as the reducer with a mass fraction of 20%, CCO and NCP as the assistant reducers with mass fractions of 15% and 5% respectively, and roasting at 1 200℃ for 8 h, a concentrate of the Fe grade of 92. 61% with the Fe recovery of 92. 38% can be produced. The mechanisms of NCP were also investigated by X-ray diffraction and scanning electron microscopy. It is shown that NCP can react with quartz in the raw ore and generate natrosilite and albite, which can destroy the structure of the raw ore and induce a reaction between reducing gas and hematite to create Fe.