An overview of using solid wastes for pigment industry

This work reports the use of wastes (Al-rich anodizing sludge, Cr/Ni galvanizing sludge, foundry sand, tionite and marble sawing mud) to formulate distinct inorganic pigment structures that were synthesized by the solid state reaction method. One of the tested formulations is a novel pigment based on hibonite (CaO·6Al2O3), that was found a suitable hosting structure to accommodate cobalt or nickel chromophore ions in tetrahedral coordination, then giving strong blue or turquoise hues, respectively. The use of Cr as chromophore was tested in three distinct pigment structures: (i) red-wine Cr–CaSnSiO5 and brown Cr–CaTiSiO5; (ii) Cr–CaTiO3; (iii) and Cr–TiO2. Developed phases were determined, and the colouring mechanisms of the chromophore species were defined based on diffuse reflectance data. Then, the pigments were added to a standard transparent glaze, and the hues which developed were estimated from L*a*b* colorimetric measurements under the oxygen partial pressure in the atmosphere, to define stable workability window.