Combining mineral and clay-based wastes to produce porcelain-like ceramics: An exploratory study

The present work was aimed at producing waste-only ceramics with higher added value, while finding a viable end-use, other than landfilling, for wastes from extraction and beneficiation of mineral resources. Based on their fluxing character and plasticity, four non-hazardous industrial wastes were selected and characterized: one clay mining tail, the sludge from potable water treatment and two sludges from gneiss and varvite cutting processes. Using the phase diagram of the SiO2–Al2O3–K2O system, four mixtures located within the wastes-defined polygon were formulated, uniaxially pressed and fired for 40 min at 900–1150 °C. The results obtained for the properties of fired samples show that water absorption values below 10% (ceramic tiles) and 3% (porcelain tiles) were reached upon firing at 1100 and 1150 °C, respectively, without firing warpage. Density values were also within the usual range but flexural strength, although adequate for common application, is lower than usual (at least 3 MPa). In terms of industrial production, although process adjustments are still required (green processing, firing cycle) the obtained results demonstrate that porcelain-like ceramic tiles can be manufactured using only the selected wastes as raw materials, suggesting that, for the composition range investigated, firing temperatures should be ~ 1100 °C and a fast-firing type processing might be feasible.