SCIENCE: Chemical, physical, structural and morphological characterization of the electric arc furnace dust

Article in Journal of Hazardous Materials B136 (2006) 953–960 by Janaina G.M.S. Machado, Feliciane Andrade Brehm, Carlos Alberto Mendes Moraes, Carlos Alberto dos Santos, Antonio Cezar Faria Vilela , Joao Batista Marimon da Cunha, Laboratorio de Siderurgia/LASID, Universidade Federal do Rio Grande do Sul, UFRGS/PPGEM Centro de Tecnologia, Porto Alegre, RS, Brazil ans other Institutes.

Abstract

Electric arc furnace dust (EAFD) is a hazardous industrial waste generated in the collection of particulate material during steelmaking process via electric arc furnace. Important elements to the industry such as, Fe and Zn are the main ones in EAFD. Due to their presence, it becomes very important to know how these elements are combined before studying new technologies for its processing. The aim of this work was to carry out a chemical, physical, structural and morphological characterization of the EAFD. The investigation was carried out by using granulometry analysis, chemical analysis, scanning electron microscopy (SEM), energy dispersive spectroscopy via SEM (EDS), X-ray mapping analysis via SEM, X-ray diffraction (XRD) and M¨ossbauer spectroscopy. By XRD the following phases were detected: ZnFe2O4, Fe3O4, MgFe2O4, FeCr2O 4, Ca0.15Fe2.85O4, MgO, Mn3O4, SiO2 and ZnO. On the other hand, the phases detected by M¨ossbauer spectroscopy were: ZnFe2O4, Fe3O4, Ca0.15Fe2.85O4 and FeCr2O4. Magnesium ferrite (MgFe2O4), observed in the XRD pattern as overlapped peaks, was not identified in theM¨ossbauer spectroscopy analysis.

Extracts

Electric arc furnace dust (EAFD) is a solid waste generated during the steelmaking process. It is classified according to NBR 10005 [1] as dangerous solid waste-class I, because the elements Pb & Cd leach in water exceeding the maximum limits permitted by the NBR 10004 [2,3]. The State Foundation for Environmental Protection of Rio Grande do Sul – FEPAM – requires that this waste must be stored in an appropriate place protected from rain. Due to the great amount generated, 12–14 kg of dust per ton of steel, an evaluation of the steel recycling alternatives is necessary.

When galvanized scrap is used in the EAF, most of the zinc from the steel scrap ends up in the dust and fume due to its very low solubility in molten steel and slag, and, especially, because zinc vapor pressure is higher than iron vapor pressure at steelmaking temperature. Vapor zinc is carried out the furnace with other gaseous or particulate compounds generated during steelmaking reactions, generating compounds like ZnO and ZnFe2O4. According to Leclerc [5], when some zinc particles are in contact with iron particles at high temperatures in an oxidizing atmosphere, zinc ferrite formation will occur in the furnace and in the evacuation system. The problem is that zinc does not comes out alone, other elements evaporate and are collected in the dedusting system originating the EAFD. ...

3. Results and discussion
3.1. Granulometric analysis

The granulometric distribution analysis of the EAFD is shown in Fig. 2. The mean particle diameter of EAFD determined by laser granulometer was 1.88µm. It can be seen from Fig. 2 that the EAFD has a heterogeneous distribution of particle size, where 60% have size between 0.90 and 4.30µm. Such an irregular granulometric distribution is in agreement with that published by Mantovani et al. [9]. Probably, this is due to the agglomerated state of the particles because this material is well known to have fine granulometry.

Xia and Pickles [10] also pointed out that the particles in EAFD tend to exist as aggregates consisting of very fine individual particles. Most of the individual particles were lower than 1µm. Takano et al. [6] determined in two different types of EAFD that almost 90% of the particles are lower than 10 µm.

Menad et al. [11] analyzed the particle size distribution of EAFD with two screen sizes (i.e., 500 and 15µm). They observed that the dust is very fine; more than 70% of particles are lower than 15 µm. They also observed that the metals are more concentrated in the fine fraction of the waste. 3.2. Chemical characterization The result of the chemical analysis of EAFD is presented in Table 1. ...

4. Conclusions

• The mean particle diameter of EAFD was 1.88 µm. The EAFD has a heterogeneous distribution of particles, where 60% have size between 0.90 and 4.30 µm;

• Fe and Zn are present in the EAFD with 49.96 and 9.24%, respectively;

• XRD technique detected in the EAFD the following phases: ZnFe2O4, Fe3O4, MgFe2O4, FeCr2O4, Mn3O4, MgO, SiO2, Ca0.15Fe2.85O4 and ZnO. However, except for SiO2 and ZnO, the signals from all the phases exhibit overlapping. Because of such overlapping the presence of these phases cannot be unequivocally assured;

• The ferrous oxide phases detected by M¨ossbauer spectroscopy were: ZnFe2O4, Fe3 O4, Ca0.15Fe2.85O4 and FeCr2O4; ...

In conclusion, the characterization of a solid waste using many techniques increase the reliability in the results and also give more conditions to decide about the best feasible recycling method.