Due to the high proportion of the steel output produced by oxygen converter, significant quantities of converter sludge (CS) and dedust wastewater (DW) are generated annually as waste materials. This study tries to achieve the co-utilization of converter sludge-containing dedust wastewater (CSDW) in iron ore sintering to save fresh water and emission reduction. Firstly, this study quantitatively characterized the mineralogical characteristics of the CS through X-ray diffraction (XRD-Rietveld) and scanning electron microscope (SEM-EDS). The results indicated that the iron oxides wrapped the metallic Fe, and other impurities such as CaO, MgO and ZnFe2O4 mixed in the way of physical accumulation. The mineral composition of CS was metallic iron (9.2%), wustite (47.5%), calcium carbonate (31.7%), magnesium ferrite (4.8%), and zinc ferrite (6.7%). Influence of CSDW concentration on the granulation performance and sintering indexes was systematically studied through a series of experiments. Research findings showed that the permeability firstly raised from 9.66 to 12.88 JPU and then reduced to 11.94 JPU, and reached the maximum when the CSDW concentration was 40%. Migration behaviors of harmful elements Zn, K, Na, and Cl have been studied based on experiments and thermodynamic calculations. Cl in DW plays an important role in promoting the removal of alkali metals. The catalytic mechanism can be summarized as the reaction of HCl, Cl2 and alkali metal oxides (Na2CO3, K2CO2, NaAlSi2O2, and KAlSi2O2) to form NaCl and KCl. With this technology, the removal rate of ZnO, K2O, and Na2O increased from 23% to 74%, 13% e42%, 1%e34%, respectively. This study aims to propose a new method for the co-utilization of CSDW in iron ore sintering, which would be helpful to save fresh water and reducing emissions in the iron and steel industry.

Introduction

Steel stands as one of the most widely used materials in the world across industries from construction to blacksmithing to sewing. As one of the essential industry, the iron and steel industry is the impact of China’s national economic development (da Silva et al., 2018; Peng et al., 2018; Wang et al., 2017). World steel output reached 1808 million tons in 2018, up 112.7% from 2000, with growth in China contributes most of the rise as its total output share rose to 51.32% from 15.1%. Generally, technologies of steelmaking can be divided into basic oxygen furnace (converter), openhearth steelmaking and electric steelmaking. Fig. 1 gives the proportion of the steel output produced by converter to the total output in some countries in 2017. The statistical results indicate that converter is the most important method to produce steel in the world, especially in China. During the operation of a converter, the high-pressure oxygen blown by lance plays an essential role in controlling the carbon content of the molten steel. Accordingly, a large amount of CO, iron and other semi-metallic elements are generated and enter the wet dust removal system in form of flue gas. Under the treatment of the wet cleaning system, these dust are dispersed in the water to form the suspension liquid. After solidliquid separation, the suspension liquid becomes the converter sludge (CS) with the water content of 30%~40%. It has been reported (Su et al., 2004a; Wu et al., 2012) that as many as 2e3 m3 steelmaking dedust wastewater (DW) and 15e20 kg CS can be obtained for every ton of steel produced.