Volumen II - SAM

These raw materials were initially characterized in terms of their chemical composition by X-ray
fluorescence and energy dispersion.
Ceramic body compositions were then prepared by distinct incorporations of 0, 5, 10, 15 and 20 wt. % of
waste into the different clays. These were prepared by mixing the proper raw materials in a pan mill during
30 minutes. The plasticity of the compositions was evaluated by the Atterberg method, determining the
plastic limit and plastic index. Cylindrical specimens with 20.3 mm in diameter and 8.5 mm in thickness
were obtained by uniaxial press molding at 18 MPa, dried at 110 o C for 24h and then fired at 850 o C in a
laboratory furnace. The heating rate for the firing procedure was 3 o C/minute with one hour soaking at the
maximum temperature. Cooling occurred by natural convection inside the furnace after it was turned off. The
specimens were tested for water absorption, diametral shrinkage and diametrical compression. Seven
specimens were tested for each condition of waste incorporation, which allowed a statistical analysis given
by average and standard deviation (error bar) for the value of each technical property.
3. RESULTS AND DISCUSSION
According to the literature [3] the chemical composition of EAFD depends on several factor, such as, the
quality of the processed steel scrap, the type of steel being produced, technological requirements, operating
conditions and the degree of return of the dust into the process. Reference data [3] imply that the prevailing
elements in EAFD display the following concentrations: Fe 10-45%, Zn 2-46%, Pb 0.40-15.14%, Cr 0.2-
11%, Cd 0.01-0.30%, Mn 1-5%, Cu < 3%, Si l-5%, Ca 1-25%, Mg 1-12%, Al 0.1-1.5%, C 0.11-2.36%, S
1.5-2.5%, Na 0.5-1.8%, K 0.35-2.30%.
Table 1 shows the chemical composition of the clay materials. Table 2 shows elemental composition of the
waste, which is predominantly composed of Fe, Na and Zn compounds. With the only exception of Na, the
other determinations are in accordance with those above-mentioned. As mention in the introduction of this
work, several complex phases may be present in the EAFD. However, magnetite and zincite seems to be the
most common phases associated with Fe and Zn, respectively. The high amount of Na in the chemical
composition of the EAFD could be a consequence of either salt or soda lime glass contamination in the
waste.
The clays have significant differences. The Aclay has higher amount of SiO2 and lower amount of Al2O3 in
comparison with the Bclay. The amount of alkaline oxides in the Aclay is also higher. These characteristics
are due to the different mineralogical constitution found on both clays. The Aclay has a predominance of
illite and montmorillonite as clayminerals. By contrast, the Brazilian clay, Bclay, has as its main claymineral
the kaolinite.
Table 1. Chemical composition of the clays (wt.%).
Oxides Aclay Bclay
SiO2 63.28 42.85
Al2O3 18.72 30.84
Fe2O3 8.29 7.96
TiO2 0.82 1.33
CaO 1.06 -
MgO 3.01 -
K2O 4.82 1.19
LoI 15.63
Table 2. Elemental composition of EAFD
Element Si Fe Ca Mg K Na Zn Mn S Cl C O
wt% 1.47 25.53 2.36 2.16 1.83 11.57 7.31 1.78 1.10 0.68 11.73 32.48
Fig. 1 presents an extrusion prognostic using the plasticity of the ceramic body compositions [14]. This
prognostic is mainly related to the workability and productivity of the green pieces. It can be observed that
both clays are located outside the limit of the acceptable region. However, while the Aclay has low
plasticity, the Bclay, displays excessive plasticity. This result is associated with the different mineralogical
constitution of the clays. This figure also reveals that the incorporation of 20 wt.% of EAFD decreases the
1518