The Characteristics of the Phase Transition of Air-Quenched Ladle Furnace Slag
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https://doi.org/10.1007/s11837-020-04464-2 2020 The Minerals, Metals & Materials Society
PYROMETALLURGICAL PROCESSING OF SECONDARY RESOURCES
The Characteristics of the Phase Transition of Air-Quenched Ladle Furnace Slag JIHUI ZHAO,1,2 YIREN WANG,1,5 KUIZHEN FANG,3 YE ZHENG,4 and DONGMIN WANG3 1.—School of Civil Engineering, Sun Yat-Sen University, Guangzhou, China. 2.—Southern Marine Science and Engineering Guangdong Laboratory, Zhuhai, China. 3.—School of Chemical and Environmental Engineering, China University of Mining and Technology, Beijing, China. 4.—Department of Civil Engineering, McGill University, Montreal, Canada. 5.—e-mail: [email protected]
The application of ladle furnace slag (LFS) as a cementitious material is limited due to its low cementitious activity and volume stability. This study incorporated air quenching to optimize the crystalline states and types of LFS, and investigated the characteristics of phase transition considering apparent morphology and mineral compositions. Compared to slow-cooled LFS, airquenched LFS mainly comprises spherical vitreous particles with loose porous structures, ranging from 0.5 mm to 10 mm. Its mineral composition include C12A7, C2S, C3A, C3S, and small amounts of free CaO and free MgO. Air quenching transforms C12A7 into an amorphous state and allows C2S to form metastable b-C2S crystal structures, improving the cementitious activity. In addition, the air quenching reduces the size of free MgO from 20–45 lm to 2– 3.5 lm, which is about an order of magnitude reduction, thereby improving the volume stability. Furthermore, air quenching destroys the high-polymerization structure of the six-coordinated Al, transforming it into a low-polymerization state.
INTRODUCTION The ladle arc refining furnace (LF) has been widely used as a major out-of-furnace refining technique due to its simple equipment, low investment cost, convenient operation, and good refining effect.1,2 Ladle furnace slag (LFS) is the steel slag generated during the LF refining process.3 According to statistics, producing 1 ton of refining molten steel generates 20–50 kg of refining slag,4 which means that, at a rough estimation, China produces approximately 10 million tons of slag residue. However, at present, only a small amount of LFS can be recycled as metallurgical return materials (such as flux and slag material).5,6 Most of the remaining LFS is disposed of and mixed with other wastes, such as converter steel slag and electric arc furnace oxidation slag, which have low re-
(Received July 15, 2020; accepted October 23, 2020)
utilization rates, leading to land occupation and environmental contamination.7–9 Therefore, it is necessary to conduct a comprehensive study on the utilization of LFS. The chemical and mineral composition of LFS is different from those of common industrial wastes, such as fly ash, blast furnace slag, converter steel slag, etc. The chemical composition of oxides mainly contains calcium oxide, alumina oxide, and other oxides (e.g., over-burned free MgO and free Ca
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