Natural zeolites in ceramic tiles: prospects and limits

Low-cost zeolitic rocks are promising substitutes for feldspathic fluxes in ceramic bodies, since their fusibility, scarce hardness and high CEC should improve grinding and sintering. Five large-scale Italian deposits with different mineralogy were characterised and used in porcelain stoneware bodies. Their behaviour during grinding, pressing, drying and firing was appraised in laboratory and compared with zeolite-free bodies. Zeolites increased the slip viscosity during wet grinding, causing a coarser grain size distribution and consequently some drawbacks in both unfired and fired tiles. Overcoming this hindrance by dry grinding of zeolitites, the technological behaviour of zeolite-bearing tiles appear to be similar to current porcelain stoneware, though with larger firing shrinkage and residual closed porosity.