Zeolites as ceramic raw materials: chabazite-rich tuff as potential substitute for feldspars in porcelain stoneware tiles production

The request of white-firing clay materials used in ceramic tile production has been steadily increasing, driven by the ongoing shift toward porcelain stoneware bodies. However, the global sourcing of raw materials has been significantly impacted by current geopolitical dynamics, necessitating a reevaluation of the traditional European supply chain. This context has highlighted the urgent need to explore Italian raw materials for porcelain stoneware manufacturing. In this framework, zeolite-containing waste (ZT), generated during the extraction and processing of tuff from two active quarries in Sorano (Tuscany, Italy), was investigated. The study aimed to characterize ZT and assess its potential as a replacement for feldspars in porcelain stoneware formulations. The collected samples underwent to physical and chemical characterization and the most promising material, particularly for its lower bloating tendency, was selected based on its thermal stability. Two different amounts (10 and 20 wt%) were evaluated against a standard porcelain stoneware composition. The tile production process was replicated at laboratory scale and the resulting samples were evaluated for technological properties throughout the process. The addition of ZT resulted in a slight reduction in both green and dry bulk densities, without compromising mechanical performance. All the studied batches show a maximum in linear shrinkage and bulk density at 1200 °C, reaching the standard requirement for water absorption and mechanical properties. Batch containing 20 wt% of ZT achieved the desired properties at a lower firing temperature (1180 °C), leading to energy savings in the sintering process. Based on these findings, ZT appears to be a good alternative to feldspars within the tested range, offering promising prospects for industrial-scale application.