| dc.description.abstract | It is beneficial to recover Cr and Fe as Cr-Fe alloy from the electric arc furnace dust (EAFD) since the dust is abundant in Cr2O3 and Fe2O3. This study investigated a new recovery approach by taking the advantage of thermite reactions between metallic oxides(ie., chromium oxide and iron oxide) and aluminum powder (i.e., prepared from waste, parings and scrap, referred to as aluminum scrap, AS). Sludge from water treatment plant(referred to as WTS), with silicon dioxide (SiO2) as main constituent, was added as a glass-former to facilitate the separation of metal and slag and to improves the resultant quality of the slag.
This study determined the appropriate mix ratio of aluminum to EAFD by experiments based on the stoichiometry of the assumed thermite reactants in the tested wastws and reaction paths. The highest reaction temperature developed reflected the mix of EAFD to aluminum scrap is optimum under the balanced effects of factors such as species, oxidized degree, reaction path, impurities, non-reactive oxides, aluminum stoichiometry, and heat loss from the reactor wall. The results show that a mix ratio of EAFD: AS=3.89:1 is optimum in this study. The alloy retrieved in this case consisted of 86.27%(w/w) Fe-Cr alloy (i.e., 71.77% Fe and 14.50% Cr)., which is to be used as ore iron for producing stainless steel.
In the experiments with 10-40% (w/w) WTS added, the retrieved alloy consisting of Fe-Cr alloy, ranging from 89.27 to 86.77(w/w). The Fe content in the alloy ranged from74.77-75.83%(w/w) Fe, and 14.50-10.94%(w/w), showing that Fe concentration in retrieved alloy increased approximately from 72%(w/w) to 75%(w/w), with the increasing addition of WTS. The increased concentration of Fe in alloy indicates the separation of alloy from slag was enhanced with the addition of WTS.
On the other hand, with the addition of WTS, the retrieved slag became porous, resulting in the increase of absorption, which is supposed to be contributed by the formation of Ca2Al2SiO7 slag.
The reaction kinetics of aluminum- electric arc furnace dust system was analyzed by Kissinger equation:
d[ln(β/Tp2)]/d[1/Tp]= -E/R.
where β: dT / dt , heating rate(K/min)
Tp: peak temperature(K)
E: activation energy(KJ/mole)
R: gas constant(8.314JK-1mole)
Differental scanning calorimetric analysis was conducted at different
Heating rates ranging from 5 to 20 K/min and peak temperature measured as 165 KJ/mole for Al-Fe2O3 system.
The results of this work suggest that to recover Fe and Cr from EAFD and WTS using thermite reactions is a promising technology not only energy conservative but also recycling- beneficial.
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