Slag, blast furnace and obtaining characteristics
Author: Ana Maria
Author: Ana Maria
The process for the production of pig iron and slag from blast occurs in a blast furnace to temperature of 1650 C (HOGAN, Meusel, SPELLMAN, 2001), where the iron ore, fluxes (limestone or dolomite) and fuel or reducing (coke or coal) are introduced in order to effect the separation of iron impurities or jeans, or promote reduo1 their oxides (LITTLE; Setepla, 1999). The slag formed by the merger of the impurities of iron ore (gangue) with the flux and ash coke. Through the flux can withdraw from the gangue and obtain a sufficiently liquid slag, which allows for both the reactions with the metal and control quality. The species most commonly used chemicals and fluxes are CaO, MgO, CaF2, and in some cases, an acid flux, such as SiO2 (GEYER, Dal Molin; Vilela, 1995; Waelkens, CARMINE, 1985). For its insolubility and lower density, the molten slag floats on the iron, and then can be conducted by canals to the courtyard of cooling air, or granulators (GEYER; Dal Molin, Vilela, 1995; Waelkens, CARMINE, 1985).
When the slag, while leaving the blast furnace, is conducted to the granulator and cooled suddenly by jets of water under high pressure, we obtain the slag granulated blast furnace. A size obtained is similar to that of river sand, with a porous structure, rough texture and unit weight around 1000 kg / m (Aldasoro, 1985; GEYER, Dal Molin;
Vilela, 1995; HOGAN, Meusel, SPELLMAN, 2001). The sudden cooling of the slag prevents the atoms to organize themselves into crystalline structure. Thus, the glassy solid formed has a higher level of energy to retain the energy of crystallization, becoming a predominantly amorphous material with latent hydraulic activity (DRON, 1984 apud Silva, 1998). When dried and ground, we obtain slag granulated blast furnace ground, which has characteristics of cementitious material. The main characteristics that influence the reactivity of the slag of blast furnace are: the degree vitrification (glass content), fineness, and chemical and mineralogical composition (SAMET; CHAABOUNI, 2004 and Taylor, 1992). The glass fraction must represent at least two thirds of the slag furnace for meeting the requirements of reactivity (PAL; MUKHERJEE, PATHAK, 2003), knowing that only the glass has sufficient solubility to participate in the reactions hydration (COELHO, 2002, JOHN, 1995). Hydraulics slag also depends on its reactivity (COELHO, 2002). For its time, the reactivity depends on the temperature of the molten slag in the blast furnace and cooling conditions, factors that modify the physiological coordination and energy connection slag. The fineness is of great influence on the activity and the hydro slag, because a greater fineness increases the activity of the slag (MUKHERJEE, 2004). The rate of hydration of slag without activator is slower than that of cement Portland. Data show that between 8% and 16% slag to moisturize the age of 3 days, and between 30% and 37%, approximately, before 28 days. After 150 days, occurs hydration of anhydrous slag grains without activators (RAJAOKARIVONY - ANDRIAMBOLONA et al.1990 apud Silva, 1998), and electrochemical measurements (potential corrosion, corrosion rate) may have high coefficients of variation (JUNG, YOON; SOHN, 2003). Particles larger than 45 ?m are difficult to hydrate and the largest
that 75 micron never completely hydrate (MEHTA Monteiro, 1994). The chemical composition of slag blast furnace contains between 95% and 96% of the total oxide CaO, SiO2, Al2O3 and MgO, which are the same that comprise the Portland clinker, but in different proportions. May still exist in smaller quantities FeO, MnO, sulfur, among others (MEHTA Monteiro, 1994). The content of these oxides can vary in composition slag, depending on the composition of raw materials and process.About the Author:
Ana Maria is Civil Engineer and expert in Concrete. Visit
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