*Article* **Use of Arc Furnace Slag and Ceramic Sludge for the Production of Lightweight and Highly Porous Ceramic Materials**

**Gamal A. Khater 1,\*, Bassem S. Nabawy 2, Amany A. El-Kheshen 1, Manal Abdel-Baki Abdel Latif <sup>1</sup> and Mohammad M. Farag <sup>1</sup>**

<sup>1</sup> Glass Research Department, National Research Centre, Cairo 12622, Egypt;

aelkheshen1@yahoo.com (A.A.E.-K.); manalbaki@yahoo.com (M.A.-B.A.L.); mmfaragnrc@gmail.com (M.M.F.)

<sup>2</sup> Geophysical Sciences Department, National Research Centre, Cairo 12622, Egypt; bsnabawy@yahoo.co.uk

**\*** Correspondence: j.khater@yahoo.com

**Abstract:** The utility of recycling some intensive industries' waste materials for producing cellular porous ceramic is the leading aim of this study. To achieve this purpose, ceramic samples were prepared utilizing both arc furnace slag (AFS) and ceramic sludge, without any addition of pure chemicals, at 1100 ◦C. A series of nine samples was prepared via increasing AFS percentage over sludge percentage by 10 wt.% intervals, reaching 10 wt.% sludge and 90 wt.% AFS contents in the ninth and last batch. The oxide constituents of waste materials were analyzed using XRF. All synthesized samples were investigated using XRD to detect the precipitated minerals. The developed phases were β-wollastonite, quartz, gehlenite, parawollastonite and fayalite. The formed crystalline phases were changed depending on the CaO/SiO2 ratio in the batch composition. Sample morphology was investigated via scanning electron microscope to identify the porosity of the prepared ceramics. Porosity, density and electrical properties were measured; it was found that all these properties were dependent on the composition of starting materials and formed phases. When increasing CaO and Al2O3 contents, porosity values increased, while increases in MgO and Fe2O3 caused a decrease in porosity and increases in dielectric constant and electric conductivity. Sintering of selected samples at different temperatures caused formation of two polymorphic structures of wollastonite, either βwollastonite (unstable) or parawollastonite (stable). β-wollastonite transformed into parawollastonite at elevated temperatures. When increasing the sintering temperature to 1150 ◦C, a small amount of fayalite phase (Fe2SiO4) was formed. It was noticed that the dielectric measurements of the selected sintered samples at 1100 ◦C were lower than those recorded when sintering temperatures were 1050 ◦C or 1150 ◦C.

**Keywords:** industrial wastes; arc furnace slag; ceramic sludge; β-wollastonite; parawollastonite; porous ceramics
