05 August 2008

SCIENCE: Utilization of Electric Arc Furnace Dust as Raw Material for the Production

Article in Journal of Environmental Science and Health, Part A, (2006) 41:9, 1943-1954 by Constantine Sikalidis and Manassis Mitrakas, Department of Chemical Engineering, Aristotle University of Thessaloniki, Thessaloniki, Greece.

... Following the EAF process, dust is generating and is usually collected by evacuation into a baghouse. In accordance with the increase of steel production by EAF process, the Electric Arc Furnace Dust (EAFD) production is also constantly increasing. The specific dust portion per ton of crude steel in the electric steel process is about 10 to 15 kilos,[2] or approximately 1.5% of the scrap steel charged to the EAF. This dust contains most of the zinc, lead, cadmium and halides contained in the charge.[3–5] Table 1 shows the worldwide occurrence of EAFD and moreover the output forecast for the year 2007.[2] Consequently, the administration of millions of tons of dust becomes increasingly difficult the greater their bulk. ...

EAFD is classified as an environmentally hazardous waste in most regions of the world, mainly because of its relatively high levels of Pb, Cd and Cr and in general because of its chemical and physical properties.[2,4] Most of the currently developed and commercialised processes are predominantly applied to the recycling of EAFD and to a lesser extent, to its inactivation prior to permanent disposal in landfills.[2,3] Currently, about 55% of EAFD is processed by high temperature metal recovery processes, mainly for Zn and Pb recovery. ...

RESULTS AND DISCUSSION

The chemical analyses of clayey material and EAFD samples are given in Tables 2 and 3, respectively. Clayey material is typical for such applications. Main elements in EAFD were found to be Fe and Zn, which is common in EAFD.[8] The sum of their oxides almost exceeds the 50 wt% of the dust. The toxic metal which presented the highest concentration, ranging between 64 mg kg‾1 and 104 x 10³ mg kg‾1 (Table 3), was Pb.

Among the other toxic metals, Cu and Cr showed one order of magnitude lower concentration than Pb (27-32 x 10² mg kg‾1 and 14-37 x 10³ mg kg‾1, respectively). Furthermore, Cd and Ba presented two orders of magnitude lower concentration than Pb (43-60 x 10 mg kg‾1 and 25-61 x 10 mg kg‾1, respectively). The extremely low concentration of Hg does not create considerable environmental problems. Main phases identified within EAFD (Fig. 1) were, Fe3O4, ZnO, Mn3O4 and PbO.[9] This suggests that EAFD could be used as raw material for the production of ceramics. The particles’ size of EAFD (>125 μm 0.4%; <125>100 μm 0.7%; <100>63 μm 9% <63>50 μm 28.4%; <50>) is similar to the one (100% <>

... The disposal to the environment of EAFD presents serious problems due to the extremely high leachability mainly because of Pb and secondly of Se and Sb presence. In addition, due to high concentrations of Cl- and SO4 2-, environmental restrictions arise (compare column 3 and 4 of Table 5). The results of leaching experiments (Table 5) indicate that hazardous elements in EAFD can be stabilized completely within a sintered ceramic body being strong enough to be used in bricks production. The concentrations of heavy metals and soluble salts in the leachates of ceramic specimens, were found to be extremely low (compare columns 3 and 6 of Table 5), fulfilling even the EU standards for potable water. ...

CONCLUSIONS

EAFD studied presents certain but not big differences from other EAFD formed in other similar steel plants. Main problem for the environmental disposal of this dust is the high leachability mainly of Pb but also of Se and Sb. By mixing of EAFD and clayey material and following the conventional forming process of ceramic plastic mass extrusion, followed by drying and firing, the heavy metals of the dust can be stabilized in the glassy phase resulting to a sintered ceramic body, having enough strength to be used as brick or other similar ceramic products. Leaching experiments support the utilization of EAFD as raw material in the production of ceramic bricks. The product obtained was found to be environmentally accepted resulting also in profitable economics. On the contrary, the addition of EAFD in dolomite-concrete products might result to not environmentally accepted products due to Pb leachability. Further research is needed concerning the presuppositions under which the leachability, especially of Pb introduced by EAFD addition in dolomite-concrete products can be reduced.

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