From high-volume industrial waste to new ceramic material: The case of red gypsum muds in the TiO2 industry

The present study aims to apply the principles of circular economy, using special inorganic waste (in particular, red gypsum muds from a TiO2 plant in Tuscany, Italy) to produce ceramic materials for the construction and building industries. Red gypsum (RG) muds produced during more than 10 years of industrial processing were chemically and mineralogically characterized by X-ray fluorescence spectrometry (XRF), X-ray powder diffraction (XRPD), scanning electron microscopy with energy dispersive X-ray spectrometer (SEM/EDS), and thermal analyses (TA). The analyses testify that RG waste production is chemically and mineralogically constant over time, and therefore suitable to be used as a secondary raw material in industrial ceramic production. Ceramic specimens have been realized using an extremely high amount of the RG waste (up to 70%) and characterized using the same chemical-mineralogical techniques, revealing that anhydrite, pyroxene, and Fe/Ti oxides are the main crystalline phases, embedded in a glassy compact matrix. Overall results indicate that the production of ceramic materials could represent a definitive and sustainable solution for the problematic management of the large volumes of RG waste deriving from TiO2 plants.