Incorporation of the ash from cellulignin into vitrified ceramic tiles

The incorporation of the ash from cellulignin, a catalytic biofuel, into a clay/feldspar body was investigated. The cellulignin was obtained by acidic prehydrolysis and was then burnt in boilers leaving behind the ash as a solid residue. Characterization tests of the ash employed X-ray diffraction, particle size distribution, mercury porosimetry, chemical analysis, thermal analysis and high-resolution scanning electron microscopy. The ash/clay/feldspar compositions were fired at 1200 °C and the linear shrinkage, water absorption and flexural strength were determined. Solution and leaching tests were conducted to evaluate the environmental safety of the final ceramics. The results showed that the ash is mainly composed of quartz with partially nanometric particle size, high surface area and high content of alkaline and alkaline earth oxides. These are advantages for a potential use of this ash as a flux. The partial replacement of feldspar by ash promoted a better vitrification decreasing the open porosity and increasing the mechanical strength. Heavy metals present in the ash became inert after the firing stage.