**1. Introduction**

The growth of industrial waste materials has become a significant public and ecological problem due to enlarged populations and rising industrialization. Solid waste handling is one of the most critical environmental issues in many developing countries. Solid waste is the byproduct of human activities such as the construction, utilization, and sharing of various resources in the world. Many studies have considered various aspects such as technology, innovation, recycling of solid waste management in growing and urbanized countries [1–4].

These wastes present many severe problems related to storage, shipping, and atmosphere or environmental pollution. The use of industrial waste in the fabrication of concrete, building materials, and cement is essential for hindering environmental pollution, lowering production expenses, and saving energy consumption. Thus, developing many technologies for recycling such waste is of great importance [5].

**Citation:** Khater, G.A.; Nabawy, B.S.; El-Kheshen, A.A.; Abdel Latif, M.A.-B.; Farag, M.M. Use of Arc Furnace Slag and Ceramic Sludge for the Production of Lightweight and Highly Porous Ceramic Materials. *Materials* **2022**, *15*, 1112. https://doi.org/10.3390/ma15031112

Academic Editor: A. Javier Sanchez-Herencia

Received: 17 December 2021 Accepted: 21 January 2022 Published: 31 January 2022

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**Copyright:** © 2022 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (https:// creativecommons.org/licenses/by/ 4.0/).

Among all industries, metallurgical industries are significantly costly to operate. Their byproducts are also the most abundant industrial wastes. The many kinds of waste products, such as junk, slags, and refractory wastes, make them a major waste-producing industry. Research by Mukhamedzhanova et al. [6] showed that the addition of accurate quantities of modifiers to metallurgical wastes could allow for the fabrication of many kinds of building materials.

Ferrous slag is a main waste byproduct obtained from iron and steel making. Various investigations have considered the use of iron slag as an economical raw material [7–9]. Many countries are interested in manufacturing construction materials via iron slag recycling. In Italy, 25–40 wt.% iron slag was added to clay to synthesize wall tiles. In South Africa, iron slag was used (up to 75 wt.%) in batches to obtain floor tiles with a water absorption ability of approximately 0.2 wt.% and bending strength of 43.8 MPa [10–12].

Arc furnace slag (AFS) is a byproduct of the steelmaking procedure, resulting from the use of electric arc furnaces, which account for more than 40% of the global steel production. AFS is created after melting and preliminary acid refining of liquid steel. It is a rocky and non-rugged material that can be crushed for use as aggregate in concrete batches [13–15].

A basic assumption is that AFS has an excellent prospect for use as a raw material in ceramic production on account of its aluminosilicate content and the matching of alkali and alkaline earth ingredients via their fluxing function in a prepared frit outline. These qualities can assist in the technical procedures of established processing. Ceramic wall and floor tiles are good candidates for producing controlled porosity bodies. Therefore, it is greatly successful to manufacture such ceramics through recycling of industrial byproducts [16].

Earlier researchers found that blast furnace slag was primarily anticipated to be an additive in Portland cement [17]. This was because of its pozzolanic and cementitious properties. By comparison, AFS does not have these features, and instead has higher iron content [18]. Pioro et al. [19] recommended that metallurgical slag be used to generate construction materials such as ceramic tiles. A complete combination of clays and AFS results in a balanced composition where the most wanted superior properties of tiles may be obtained by forming anorthite and wollastonite phases [20]. Wollastonite, also known as calcium silicate (CaSiO3), has been broadly studied due to its enormous applications in ceramics, dental inserts, structural design, and building, where it is used as a floor material as an alternative to granite and natural marble [21,22]. The most interesting character of this material is its ability to produce both curved and flat sheets [23].

Many efforts were made in earlier studies to build ceramic tiles employing 30–40 wt.% of AFS [18]. Teo et al. [16] established that the use of 40 wt.% AFS was capable of producing excellent mechanical properties in ceramic tiles [24].

The most widespread waste material produced from ceramic manufacturing is ceramic sludge. Several familiar artificial ceramics include wall tiles, floor tiles, sanitary ware, domestic ceramics, and traditional pottery. They are frequently created utilizing natural materials including clay and minerals. Ceramic wastes are classified into two groups according to the raw materials used [25]. The first group is wastes created by structural ceramic industries employing only red pastes for creating blocks, bricks, and roof tiles. The second category is fired ceramic wastes, which are formed in production of stoneware ceramic (floor and wall tiles and sanitary ware). Studies have revealed that during ceramic manufacturing, approximately 30% of the matter is wasted [26,27], and presently these wastes are not constructively reused, which causes much pollution to the environment. This indicates the need for research into pioneering methods of reusing ceramic wastes [28,29]. Ceramic sludge typically has high contents of SiO2 and Al2O3 oxides [30].

The recycling of ceramic sludge and electric arc furnace slag to produce ceramic tile material depends on the reaction between the SiO2 and Al2O3 of the ceramic sludge and the CaO of AFS, enhancing the properties of ceramic tile by developing calcium-aluminatesilicate crystals, such as anorthite and wollastonite. Therefore, it is a prominent way to cancel out the negative effect of iron oxide content in AFS on the densification process. This recycling process has many advantages in terms of cleaning the environment, storing energy, and using sustainable virgin materials [31].

The main goal of this study is to advance the use of two industrial wastes, arc furnace slag and ceramic sludge, for production of lightweight and porous ceramic materials that can be used for environmentally friendly construction. To fulfill this goal, ceramic samples containing parawollastonite, β-wollastonite and gehlenite minerals were prepared at different sintering temperatures. Microstructural, morphological, electrical, and some physical properties of those samples were studied.

#### **2. Experimental Techniques**
