Incorporation of Waelz Slag into Commercial Ceramic Bricks: A Practical Example of Industrial Ecology

Abstract

The recovery of electric arc furnace (EAF) dust generates large amounts of an industrial byproduct called Waelz slag. This residue, consisting primarily of iron oxide contaminated with other metal oxides (including zinc and lead), is usually disposed of in landfill sites at a high economic and environmental cost. This paper investigates an alternative based on industrial ecology principles, which involves the incorporation of Waelz slag into clay ceramic construction bricks. For the purpose of this work, Waelz slag and raw materials employed in the manufacture of ceramic bricks (natural clays, wood pulp) were characterized. Subsequently, a series of brick specimens were manufactured according to commercial mixes and using industrial equipment and procedures. Similar specimens were also produced replacing 20−30 wt % of the clay with Waelz slag. The resulting products were analyzed for their physical (bulk density, water absorption, open porosity), mechanical (modulus of rupture), and chemical properties (soluble salts content) in order to evaluate compliance with quality standards for construction materials. The environmental consequences of incorporating slag into ceramic products were also investigated at three stages of their life cycle: release of potentially toxic species during their use (NEN 7345), leaching of heavy metals after disposal in landfill sites (EN 12457 1 and 2), and emission of atmospheric pollutants during the firing process. The experimental results demonstrate that incorporation of Waelz slag does not deteriorate the physical, mechanical, and chemical properties of the resulting products. The leaching of species during its useful lives show compliance with threshold values established according to the Dutch Building Materials Decree (DBMD), and Waelz slag containing bricks fall into the category of nonhazardous waste landfill, just like conventional bricks used at this work. Emissions of CO2 and NOx were reduced versus the emissions of halogenated gases and SO2, which were favored due to the thermal decomposition of S, Cl, and F contained in the waste material.