Recycling of solid wastes in the synthesis of Co-bearing calcium hexaluminate pigment

Cobalt doped calcium hexaluminate was firstly synthesized using pure reagents; subsequently, the pure reagents were substituted with industrial wastes, the composition of which had been characterized using X-Ray diffraction and X-Ray fluorescence namely, Al-anodising sludge replaced pure aluminium whilst marble cutting rejects and foundry sand were employed as sources of calcite and silica, respectively. As expected, cobalt doped hibonite was the major phase present in calcined powders and displayed an intense blue coloration due to the incorporation of cobalt in tetrahedral positions, as confirmed by transitions from 4A2(F) to the excited 4T1(F) and 4T1(P) states observed from UV–Vis–NIR absorption spectra. The novel waste-derived hibonite pigment showed strong and stable colouring potential when applied in different ceramic supports.