Amany A. El-Kheshen

The growing demand for sustainable and environmentally friendly materials has accelerated interest in the valorization of industrial wastes within the framework of the circular economy. In this study, porous wollastonite-based ceramics were successfully fabricated using cement kiln bypass dust (CKD) and waste glass cullet as low-cost and sustainable secondary raw materials. The proposed approach aims to mitigate environmental pollution, reduce landfill disposal, conserve natural resources, and promote the recycling of industrial by-products into value-added ceramic products. Different batch compositions containing varying proportions of CKD and glass cullet were prepared, compacted, and subsequently sintered under controlled conditions to induce crystallization. The crystallization behavior and phase development were characterized by X-ray diffraction (XRD), while the microstructural features were examined using scanning electron microscopy (SEM). Physical and dielectric properties, including bulk density, open porosity, dielectric constant (ε′), dielectric loss (ε″), and electrical conductivity (σ), were also evaluated. The results confirmed the successful formation of parawollastonite as the predominant crystalline phase, accompanied by a relatively homogeneous porous microstructure. The prepared ceramics exhibited high open porosity values ranging from 52.55 to 63.63% and low bulk densities between 1.050 and 1.318 g cm⁻³, making them suitable for lightweight construction and insulation applications. Dielectric measurements performed over the frequency range of 50 Hz–8 MHz revealed that both dielectric constant (ε′) and dielectric loss (ε″) decreased with increasing frequency. At 50 Hz, ε′ and ε″ ranged from 8.44–9.39 and 0.709–0.733, respectively. The electrical conductivity values (~10⁻² μS cm⁻¹) at low frequencies indicated insulating behavior, whereas poor-to-fair semiconducting characteristics were observed at higher frequencies. The incorporation of large amounts of recycled CKD and waste glass significantly reduced dependence on virgin raw materials while providing a sustainable route for waste utilization. Consequently, this work demonstrated an environmentally responsible and economically viable strategy for producing porous wollastonite-based ceramics with potential applications in both the construction and electrical sectors, thereby contributing to resource efficiency, waste valorization, carbon-emission reduction, and sustainable industrial development.

The use of solid waste such as ceramic sludge, ceramic rollers, and magnesite was studied to obtain cheap refractory ceramics at temperatures of 1300 °C based on XRF, XRD SEM, EDX, bending strength, and dielectric properties. The prepared samples were examined. The results showed that the significant crystalline phases formed were mullite, spinel, and corundum. They also showed that mullite hindered the formation of cordierite and enhanced spinel formation. With increased cordierite content, the microstructure varied from fine grained to coarse grained. Bending strength increased with increasing mullite content and bulk density, ranging from 10.80 to 13.50 MPa. Bulk density increased with the increase in mullite content and sintering temperature and ranged from 1.99 to 1.94 g/cm³, while the percentage of porosity and water absorption decreased and ranged from 29.40 to 38.83, respectively. To examine the effect of the produced phases on the dielectric characteristics, the permittivity (ε′), dielectric loss (ε″), and AC conductivity (σ_ac) were measured in the frequency range of 10⁻¹ Hz to 10⁶ Hz. As the concentration of cordierite increased, there was a noticeable drop in ε′ from 35.6 to 8.2 and σ_ac from 10⁻⁸ s/cm to around 10⁻¹¹ s/cm and high values of resistivity from 10⁸ cm/s to about 10¹⁰ cm/s, suggesting that this material might be an excellent insulator.