Energy efficient production of glass-ceramics using photovoltaic (P/V) glass and lignite fly ash Vasiliki Savvilotidou a , Anna Kritikaki b , Antonios Stratakis b , Konstantinos Komnitsas b , Evangelos Gidarakos a,⇑ a School of Environmental Engineering, Technical University of Crete, Politechnioupolis, Chania 73100, Greece b School of Mineral Resources Engineering, Technical University of Crete, Politechnioupolis, Chania 73100, Greece article info Article history: Received 19 November 2018 Revised 4 April 2019 Accepted 8 April 2019 Keywords: Waste P/V glass Lignite fly ash Sintering Mechanical properties Physical properties abstract This study investigates an innovative approach for the valorization of specific wastes generated from the energy sector and the production of glass-ceramics. The wastes used were photovoltaic (P/V) glass, pro- duced from the renewable energy sector, and lignite fly ash, produced from the conventional energy sec- tor. The process first involved the production of glass after melting specific mixtures of wastes, namely (i) 70% P/V glass and 30% lignite fly ash, and (ii) 80% P/V glass and 20% lignite fly ash, at 1200 °C for 1 h as revealed by the use of a heating microscope. The results indicated that the P/V glass, as a sodium- potassium-rich inorganic waste, reduces energy requirements of the melting process. The produced glass was then used for the production of glass-ceramics. Dense and homogeneous glass-ceramics, exhibiting high chemical stability and no toxicity, were produced after controlled thermal treatment of glass at 800 °C. The mechanical (compressive strength, Vickers hardness) and physical (open porosity, bulk den- sity and water absorption) properties of the produced glass-ceramics were evaluated. X-ray diffraction (XRD) and Energy Dispersive X-ray fluorescence (ED-XRF) were used for the characterization of the raw materials and the produced glass-ceramics. Scanning electron microscopy (SEM) provided further insights on the microstructure of the final products. The properties of the produced glass-ceramics, namely water absorption and compressive strength, render them suitable for applications in the con- struction industry. The waste valorization approach followed in this study is in line with the principles of circular economy. Ó 2019 Published by Elsevier Ltd. 1. Introduction As a result of industrialization and population growth, the vol- ume of produced inorganic wastes and by-products, such as fly ashes, slags and sludges, steadily increases (Karamberi et al., 2007). Valorization techniques, including waste conversion into glass and glass-ceramics, are explored in order to control the potential release of contaminants or/and to fabricate products with tailored properties (Wu et al., 2015; Leroy et al., 2001). Sintered glass-ceramic composites are considered for the immobilization of toxic metals, metalloids or radioactive elements present in a wide range of wastes, such as bottom and fly ashes, municipal solid waste (MSW) ashes, industrial residues, nuclear waste (McCloy and Goel, 2017), zeolitized volcanoclastic deposits rich in Cs and Sr (Cappelletti et al., 2011), volcanic ashes (Vu et al., 2011), slags and sludges (Erol et al., 2009). ‘‘Glass-ceramics are inorganic, non-metallic materials prepared by controlled crystallization of glasses via different processing methods. They contain at least one type of functional crystalline phase and a residual glass. The volume fraction crystallized may vary from ppm to almost 100%”(Deubener et al., 2018). Depending on the number of nuclei and their dispersion, heterogeneous nucleation (i.e. uncontrolled crystallization or otherwise devitrification) may occur either on the surface or the substrate of glass, reducing its mechanical strength (Deubener et al., 2018; Paul, 1982; Shelby, 2007). In heterogeneous nucleation, nuclei are formed on the sur- face of a foreign substrate mainly due to contact with container material, impurity particles, exposure to atmosphere, etc. (Deubener et al., 2018). In material science, functional glass- ceramics can be used in (i) the building industry (Wu et al., 2015) for architectural and decorative applications (e.g. floors, roofs), (ii) the medical sector as biomaterials (e.g dental filling and bone replacement materials), (iii) the metallurgical and optical https://doi.org/10.1016/j.wasman.2019.04.022 0956-053X/Ó 2019 Published by Elsevier Ltd. ⇑ Corresponding author. E-mail addresses: vsavvilotidou@hotmail.com (V. Savvilotidou), akritik@mred. tuc.gr (A. Kritikaki), astratak@mred.tuc.gr (A. Stratakis), komni@mred.tuc.gr (K. Komnitsas), gidarako@mred.tuc.gr (E. Gidarakos). Waste Management 90 (2019) 46–58 Contents lists available at ScienceDirect Waste Management journal homepage: www.elsevier.com/locate/wasman