Migration behavior of alkali metals in an iron ore sintering process with the substitution of biomass for coke breeze

Iron ore sintering is a process in which iron ore powder, flux, iron-bearing dust, solid fuel (such as coke powder), and return fines are mixed in a certain proportion, granulated, and then processed into agglomerates by high-temperature generated by solid-fuel combustion, which is an important process prior to blast furnace ironmaking. The iron ore sintering process is an important emitter of atmospheric particles in which alkali metal elements in a sinter bed contribute to the formation of fine particles during combustion, aggravating particulate emissions. Using biomass materials such as charcoal to replace coke in the sintering process can significantly alleviate the emission of both greenhouse gases and pollutants. However, owing to the high content of alkali metals in biomass and their poor combustion characteristics, alkali-metal-related problems inevitably arise. In this study, a small sintering experiment was conducted in a volatilization condensation test facility and analyses were performed based on data obtained by X-ray fluorescence spectroscopy, scanning electron microscopy energy dispersive spectrometer, and inductively coupled plasma-atomic emission spectrometry followed by thermodynamic simulation. The purpose of these analyses was to investigate the laws associated with alkali metal migration and enrichment, removal rate of alkali metal elements, and influence of technological measures on removal process in iron ore sintering using charcoal and coke as fuel with iron-bearing dust added. The results show that K is easier to remove than Na, and the alkali compounds volatilized into a flue gas mainly contain KCl with small amount of NaCl. With the same fuel mass fraction the removal rate of alkali metal in the sintering process using charcoal as fuel is less than that using coke. As the alkali metal compounds in the downstream flue gas migrate, they collide with the raw material particles because of the inertial effect. In addition, owing to the low temperature of the raw materials in the low bed, alkali metal compounds tend to condense and deposit on the particles’ surface. During the sintering process, a large number of alkali metal compounds discharged into the waste gas are trapped and absorbed by the low bed, and the alkali metal chloride accumulated in the low bed promotes the removal of chloride from the alkali metal. With the addition of CaCl₂, the removal rate of K and Na when using charcoal as fuel is higher than that using coke. Accordingly, the content of K and Na in sintering products with charcoal as fuel is lower than that using coke. The use of biomass as fuel in iron ore sintering in combination with chlorine removal process is feasible and has good prospects.