Valorizing carbonate-rich mining waste in porcelain stoneware production

The increasing demand for raw materials in the ceramic tiles industry requires the exploration of secondary raw materials to mitigate the environmental impact of mining and quarrying, as well as to address waste management challenges. This study evaluates the potential of utilizing extractive waste generated from the washing of carbonate aggregates, taken from a quarry in Emilia-Romagna, Italy, in porcelain stoneware bodies. This waste was thoroughly characterized for its chemical, mineralogical, and thermal properties. It contains a high carbonate content (over 70 wt%) and was incorporated as a partial substitute for the fluxing components due to its low quartz content and limited plasticity. Laboratory scale tests were then performed on a reference batch (B0), two batches with simple substitution of 4 and 8 wt% of the fluxes with extractive waste (WS4 and WS8), and two batches with 4 and 8 wt% extractive waste and different proportions of all of the components (WF4 and WF8). Firing was performed from 1150 degrees C to 1230 degrees C to follow the evolution of the technological properties, phase composition (X-ray powder diffraction and the Rietveld method) and microstructure (SEM). No bottleneck was encountered in the tile-making process, but a delay in the sintering kinetics and a lower densification efficiency (from 2.391 g/cm3 in B0 to 2.206 g/cm3 in WS8) were observed in the fired products. The addition of waste silts induced a variation of the chemical composition of the batches that can lead to the production of porcelain stoneware tiles only with a careful batch design.