Water cleaning sludge as principal component of composites to enhance mechanical properties of ecologically clean red ceramics

Hazardous municipal water cleaning sludge (WCS) was used as the main component for environmentally clean ceramics production in combinations with salts from acid neutralization, glass waste, and clay-sand mixture. The WCS has a high content of Cl, Ba and Br; the glass waste has Pb and Cr; salts from acid neutralization have total content of extremely hazardous elements of 12.57%. The ceramics developed here have flexural resistance strength 2.5 times higher than reference ceramics. The processes of ceramic structure formation were studied by looking at samples sintered at 900°, 950°, 1000°, 1050° and 1100 °C. The samples were studied with X-ray fluorescence (XRF), X-ray Diffraction (XRD), scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), laser micro-mass analysis (LAMMA), and atomic absorption spectroscopy (AAS) methods. It was proved that high values of these properties can be mainly attributed to glass formation and formation of new minerals - Lazurite Na8(Al2SiO4)6(SO4,S)2, Magnetite Fe3O4, Hematite Fe2O3 and Nepheline Na3K(Si0.553Al0.447)8O16. The AAS method showed a very low level of contamination of leachate solutions compared with the requirements of Brazilian environmental standards. The use of water treatment sludge, salts from acid neutralization, and glass waste (GW) can partially decrease the mining of natural materials and the irreversible destruction of nature by quarries.