Characterisation of the sintering behaviour of Waelz slag from electric arc furnace (EAF) dust recycling for use in the clay ceramics industry

Waelz slag is an industrial by-product from the recovery of electric arc furnace (EAF) dust which is mainly sent to landfills. Despite the different chemical and mineralogical compositions of Waelz slag compared to traditional clays, previous experiments have demonstrated its potential use as a clay substitute in ceramic processes. Indeed, clayey products containing Waelz slag could improve mechanical and environmental performance, fixing most of the metallic species and moreover decreasing the release of some potential pollutants during firing. However, a deeper understanding of the complex phase transformations during its thermal treatment and the connection of this behaviour with the end properties is desirable in order to explain the role that is played by the Waelz slag and its potential contribution to the ceramic process. For this purpose, in the present study, the chemical, mineralogical, thermal and environmental behaviour of both (i) unfired powdered samples, and (ii) pressed specimen of Waelz slag fired up to different temperatures within the typical range of clay based ceramic production, has been studied. The effect of the heating temperature on the end properties of the fired samples has been assessed. In general, an increase of the firing temperature promotes sintering and densification of the products and decreases the open porosity and water absorption which also contributes to the fixation of heavy metals. On the contrary, an increase in the leaching of Pb, Cr and Mo from the fired specimens is observed. This can be attributed to the creation of Fe and Ca molybdates and chromates that are weakly retained in the alkali matrix. On the other side, at temperature above 950 °C a weight gain related to the emission of evolved gases is observed. In conclusion, the firing temperature of the ceramic process is a key parameter that affects not only the technical properties but also strongly affects the leaching behaviour and the process emissions.The authors gratefully acknowledge the financial support for this research by the BEFESA STEEL R&D, S.L.U. Company, Erandio, Biscay (España) and the framework of the Spanish Ministry of Science and Innovation Project (CTM 2009-11303 TECNO).Peer reviewe

Effect of foundry waste content on technological properties of ceramic bricks

4 pages, 2 figures, 2 tables.-- En: 1st Spanish National Conference on Advances in Materials Recycling and Eco – Energy Madrid, 12-13 November 2009.-- Editors: F. A. López, F. Puertas, F. J. Alguacil and A. Guerrero.A change from linear to cyclical production processes, as proposed by Industrial Ecology, is investigated in this paper. The feasibility of introducing Waelz slag (Ferrosita®) into a ceramic manufacturing process had been assessed in previous studies. In this work, the influence of incorporating Waelz slag and a Waelz slag/Moulding sand mix into a clayey matrix has been evaluated through the analysis of the physical and mechanical properties of fired bodies. A mathematical model has been developed in order to optimize the Waelz slag content in the clay mixture. The results demonstrate that the introduction of Waelz slag or slag/sand mix may improve the physical and mechanical properties of resulting ceramic bodies.The authors gratefully acknowledge financial support for this research by the BEFESA ZINC ASER S.A. Company, Asua, Vizcaya.Peer reviewe