Hydration and Crystallization Behavior of MgO in Cold-Bonded Pellets Containing Basic Oxygen Furnace Dust
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INTRODUCTION
IN the metallurgical steelmaking processes of the contemporary world, basic oxygen furnace (BOF) steelmaking is the overriding technique and approximately 70 pct of steel is made from it. In the BOF steelmaking process, 10 to 30 kg of industrial dust can be produced per ton of steel. At present, the dust content generated annually in the world is as high as 30 million tons or more.[1,2] BOF dust collected by the dry flue gas cleaning system[3] contains more than 50 pct of total iron (TFe) and a certain amount of alkaline earth oxides, such as MgO and CaO, which has high secondary utilization value. Currently, BOF dust is primarily used as a sintering raw material to return to blast furnaces for ironmaking and recovering Fe resources,[4] while the particle size of the BOF dust is tiny (average particle size is less than 70
XIANG LI, PING TANG, XUEQIN ZHU, PENGPENG QIN, and GUANGHUA WEN are with the College of Materials Science and Engineering, Chongqing University, Chongqing, 400044 P.R. China and also with the Chongqing Key Laboratory of VanadiumTitanium Metallurgy and New Materials, Chongqing University, Chongqing, 400044 P.R. China. Contact email: [email protected] Manuscript submitted November 11, 2019.
METALLURGICAL AND MATERIALS TRANSACTIONS B
lm), which affects the gas permeability for sintering.[5] Meanwhile, due to the fine particle size of BOF dust, a large amount of fugitive dust generated in the transportation process seriously pollutes the environment. Therefore, it is also difficult to apply to other fields. In steel plants, plenty of unrecovered BOF dust is piled in the open air, which causes resource waste. Fine dust particles are scattered in the atmosphere, causing environmental pollution, which is harmful to human health after being inhaled. Consequently, it is significant to explore a reasonable utilization route for such a large number of harmful BOF dust. BOF dust can be prepared into cold-bonded pellets with a certain strength by agglomerating and pelletizing, and it can be returned to BOF nearby[6] as fluxing medium, oxidant, and iron raw material in the steelmaking process for recycling. It is an exclusive economical and environmentally friendly technique to recycle large quantities of BOF dust. Since the cold-bonded pellets need to withstand certain impacts and pressures during stacking, drying, and transporting, the binders must be added during preparation to increase the pellet strength.[7] Nevertheless, there are various issues with the binders currently used in the pellets. (1) Organic binders[8,9] are expensive. The pellet moisture made with such binders is uncontrollable. The pellet needs to be fired to satisfy the moisture and strength requirement, which will lead to secondary pollution and energy invested. (2) Commonly used inorganic binders, such as
bentonite (Al2(Si4O10)(OH)2),[10] sodium silicate (Na2OÆnSiO2),[11] and Portland cement (nCaOÆSiO2),[12] all contain SiO2, which affects BOF alkaline conditions. They are also necessary to enhance the pellet strength by firing, r
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