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As more and more Mn bearing iron ores are used to decrease steel cost and deal with the problem of hearth deposition, slag regime change and hearth refractory erosion in blast furnace become more often. To address these problems, it is urgent to clarify the effects of MnO upon the ironmaking production. Herein, the viscosities of slags with different MnO contents were measured for the first time, and the influence mechanism of MnO was analysed by infrared spectrum. The wetting behaviours between slags with different MnO contents and alumina-carbon refractory were investigated. The results showed that meltability temperature and viscosity decrease simultaneously with the increasing MnO content from 0 to 2.0 wt-%. Infrared spectrum analysis also proved that the existence of Mn 2þ , Ca 2þ and Mg 2þ makes the Si-O bonds peak moving towards high frequency and the asymmetry of Si-O bond increasing, leading to the decrease in viscosity decreasing. In addition, the characteristic temperatures for wetting reaction increased by ,408C with the increasing MnO content from 0 to 3 wt-% (basicity¼1.18). The characteristic temperatures decreased by nearly 508C with the basicity of slag increasing from 1.0 to 1.3 (MnO ¼ 1 wt-%). Therefore, the increasing MnO content in slag accelerates the erosion rate of BF hearth lining and then decreases the campaign life of blast furnace.

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Alkali metals are one of the important factors promoting the degradation of coke in blast furnace. Previous studies usually focused on the properties of coke affected, respectively, by K and Na separately, while K and Na will simultaneously affect coke performance in the actual production of blast furnace. Through simulating the actual situation where coke is affected by K and Na vapours simultaneously in blast furnace, the evolution of coke structure and thermal properties (CRI, CSR) after alkalisation with different proportions of K and Na vapours are revealed in this study. Results showed that coke structure was broken when the proportion of alkali vapours reached 3%, and coke fine formation rate increased with the increase of K vapour, indicating that K vapour caused a great damage to coke structure; CRI of coke reached the highest and CSR the lowest when K/Na ratio was 3/7. It was observed with SEM/energy dispersive spectrometer that K and Na existed in both mineral matters and carbon matrix; nepheline, generated when coke reacted with alkaline (K, Na) vapours, was determined by XRD. The content of K and Na in nepheline is dependent on the ratio of alkaline (K, Na).

The circulation and accumulation of harmful elements in the blast furnace leads to a decrease in gas utilisation and an increase in heat consumption, which can cause the increase of coke ratio. In this paper, the effect of harmful elements on the coke ratio was quantitatively studied using the Rist diagram. The results show that the effect degree of each harmful element on the coke ratio varies. The influence orders of accumulation times and loads of harmful elements on the coke ratio are Na > K>Zn and Zn > Na > K, respectively. The increase of heat consumption has more effect on the coke ratio than the decrease of gas utilisation. The total increase of coke ratio by the effect of K, Na and Zn is 14.2, 35.8 and 9.3 kg/tHM, respectively, of which the effect of heat consumption accounts for 55.9, 60.9, 60.9%, respectively.