Recycling of bottom ash from biomass combustion in porcelain stoneware tiles: Effects on technological properties, phase evolution and microstructure

This work aims to evaluate the use of bottom biomass ash as an alternative raw material in porcelain stoneware bodies. For this purpose, ash coming from a biomass thermoelectric power plant in Emilia-Romagna (Italy) was selected and its chemical, mineralogical and thermal properties determined. Data indicated its technological role as a flux, so it was introduced in a porcelain stoneware batch in partial replacement of feldspars and experimented at laboratory scale. A bottleneck, relative to the rheological behavior of the slips, was overcome by a slight deflocculant increase. The powder compacts were fired from 1000° to 1220 °C in order to follow the evolution of the technological properties, phase composition (XRPD-Rietveld) and microstructure (SEM). The introduction of ash allowed to lower the firing temperature by 20 °C, while keeping the technological properties comparable with those of the benchmark. Moreover, the mineralogical and microstructural data revealed different sintering kinetics.