The use of blast furnace slag and derived materials in the vitrification of electric arc furnace dust
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I.
INTRODUCTION
T I G H T E R environmental regulations have prompted industry to search for economically feasible, clean methods of treating hazardous waste to make nonleachable products. Electric arc furnace (EAF) dust is a solid waste generated in the purification of the exhaust gases released during the manufacture of steel via the smelting of scrap metal. The EAF dust is hazardous and toxic since it contains soluble oxides of Pb, Cd, As, and Cr which are formed at high temperature above the steel bath and in the off-gas systems of the EAF. After disposal of flue dust in landfills, these soluble oxides find their way into the water table, causing pollution.m Because of the large quantities of dust produced (some 15 kg/t of steel manufacturedt2]), its nonferrous nature, and the present inopportune manner in which it is discarded, better methods of treating this waste are required. Among the possible treatments of solid wastes that contain heavy metals, vitrification has long been regarded as a marketable method of recycling. However, the basic approach up to now has been the incorporation of a relatively low proportion of waste into conventional glass. The currently used process for the vitrification of EAF dust consists essentially of directly melting a mixture of glass forming materials with a small quantity of the dust.t3.41 Raw materials include silica sand, cullet, and, depending upon final use, other metallurgical by-products such as slags, spent refractories, and mill scale. However, since the physicochemical properties of the resulting glass are affected largely by the starting materials selected, the amount of by-product from the smelting of metals that can be added depends upon the use of the final product. In this article, an alternative vitrification method is proposed, based on the
use of blast furnace slag and sol-gel techniques.tS] Leachability and ecotoxicity tests are also performed,
II.
A. Methods and Materials
Granulated blast furnace slag was collected from the AHV plant (Vizcaya, Spain). The slag was ground to a size of less than 60 /xm. Blaine's surface area was determined by the air permeability method, at 3000 cm z kg-'. The EAF dust, formed during the production of carbon steel, was collected from the Azma plant (Madrid, Spain). The mineralogical composition of the EAF flue dust was determined by X-ray diffraction (XRD) as cincite (ZnO), franklinite ( Z n O ' F e 2 0 3 ) , m a g n e t i t e (Fe304) , and hematites (a Fe203) and lesser contents of calcium ferrite (CaO-FezO3) and sodium, potassium, and aluminum silicates.t6~ The particle size was lower than 10/_tin. Gel was produced as described by Alonso et aL,FJ i.e., the dissolution of slag in ethanol (slag/ethanol ratio = 1: 50 g mL -~) and HNO3 (ratio alcohol: acid volume = 2:1) at 40 ~ for 15 minutes. After filtering to remove insoluble material from the sol, gelification was performed in an alTable 1. Composition of Raw Materials (Weight Percent)
Component SiO2 CaO AlzO 3
MgO F%O3 MnO
K20 F.A. LOPEZ, Principal Researcher, A
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