The ceramic tile industry is growing worldwide, and requires annually a huge amount of raw materials, mainly clays, feldspars, and quartz sand. Concerning the European tile industry, a major part of these raw materials is imported from sources outside the European Union. In Italy, before 2022, a third of ball clays (40% of the employed raw materials) was imported from Donetsk basin, in Ukraine. The success of these clays derives from unequaled technological features (e.g. high plasticity, easy sinterability, and light color). These favorable properties arise mainly from their mineralogical composition and grain size distribution. The recent geopolitical upheaval poses serious questions on the supply chains for the ceramic production, stressing how the supply on alternative chain is strategic and vital for the ceramic sector.
The largest industrial district of the Italian tile production is located in the Sassuolo area. Starting from 90’s, the production converted into porcelain stoneware, with a shift from local resources to imported raw materials. However, in the current geopolitical scenario a partial return to local resources, alongside favoring the tendency toward a circular economy, can represent and option to reduce the import reliance.
Regarding the characterization of raw material deposits located near Sassuolo district, the literature data were mainly obtained by qualitative mineralogical analysis coupled with chemical data, which provide a semi-quantitative mineralogical analysis, while and accurate quantitative phase analysis and detailed testing are missing.
In this work, we present the full characterization of two red clays deriving from quarries located near the Sassuolo ceramic district. These red clays are iron-rich (~7% Fe₂O₃), thus comporting well-known issues in the ceramic tiles production. The features of these samples were compared with those of a German ball clay containing rather high levels of iron (~3% Fe₂O₃). The employed analytical techniques are X-ray diffraction with Rietveld analysis, X-ray fluorescence, and thermogravimetric analyses. Moreover, we tested the effects of a partial substitution of Ukrainian ball clay body (used as benchmark) with the most suitable Italian red clay and the German ball clay into a standard batch for porcelain stoneware. The obtained bodies were fully characterized from milling to firing. The amount of the novel raw materials added to the batches were carefully chosen to evaluate the effect of the iron on the technological properties of the semifinished and finished products.
Results demonstrated that the substitution of the classic Ukrainian ball clays with the Italian and German clays do not introduce any bottleneck in the ceramic production. The addition of the German ball clay resulted in a slight increase of the sintering temperature (compared to the benchmark), possibly related to the higher quartz content of this raw material. Conversely, the addition of Italian red clay induced a reduction in the firing temperature (compared to the benchmark), possibly related to the higher content of iron as well as of feldspars. The most significant variations are in the color of the tiles, which results darker (compared to the benchmark) in all the tested bodies, for the presence of iron.