Understanding the Relationship Between Structure and Thermophysical Properties of CaO-SiO 2 -MgO-Al 2 O 3 Molten Slags
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I.
INTRODUCTION
RECENTLY, with continuous mining and consumption, the ores rich in irons are gradually diminishing, and low-degree iron ores have been increasingly used in the iron and steel sector. The degradation in iron ores results in the variation in the chemical compositions of blast furnace slags (BFSs),[1,2] and as a typical result, the Al2O3 content in BFSs has increased, which causes changes in the BFS macroscopic properties such as viscosity and crystallization behaviors. Conventionally, hot BFSs at ~1823 K (1550 C) are water quenched, and then the slags obtained in a glassy state are further utilized as raw materials in cement manufacturing.[3-5] However, using the water-quenching method, the thermal heat in hot slags has generally been wasted, and recently, various dry granulation methods YONGQI SUN and HAO WANG are with the Department of Energy and Resources Engineering, College of Engineering, University, Beijing 100871 People’s Republic of China. ZUOTAI ZHANG is with the School of Environmental Science and Engineering, South University of Science and Technology of China, Shenzhen 518055, People’s Republic of China and also with Key Laboratory of Municipal Solid Waste Recycling Technology and Management of Shenzhen City, Shenzhen 518055, People’s Republic of China. Contact e-mail: [email protected] Manuscript submitted June 14, 2017.
METALLURGICAL AND MATERIALS TRANSACTIONS B
such as rotary cup atomizer[6] and spinning disk atomizer[7] have been developed to recover the waste heat in slags. The main objectives of these methods are to break the liquid slags into small droplets to resist the crystallization of slags and thus facilitate transformation into a glassy state. The variation in Al2O3 content can change the crystallization behaviors of the BFS including crystalline phases and crystallization ability and thus change the difficulties of slag heat recovery. In previous studies,[8,9] it was found that the crystallization ability of a BFS first decreased and then increased with increasing Al2O3 content, as demonstrated by a varying critical cooling rate. Generally, the macroscopic properties of slags are directly related to the microscopic structures. As an amphoteric oxide, the role of Al2O3 in a BFS is complicated and unclear, especially from the viewpoints of crystallization control and heat recovery from the slags; thus, the present study was motivated. Herein a basic quaternary CaO-SiO2-MgO-Al2O3 (CSMA) system was prepared, and the structural variations and their relationship with thermophysical properties were investigated. The aforementioned four types of oxides are in fact the main compositions of a BFS.[3,4] Generally, there are two aspects involved in understanding the relationship between the structures of molten slags and their crystallization behaviors. First, crystals are formed from liquid slags, i.e., with decreasing temperature, the crystals are precipitated gradually.
Thus, the crystallization behaviors of slags should be determined by the microscopic structures of the slags
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