Analysis of the environmental compatibility of the use of porcelain stoneware tiles manufactured with waste incineration bottom ash

In line with circular economy principles and the reduction of primary material exploitation, waste-to-energy (WtE) by-products such as bottom ash (BA) are increasingly being used as raw materials in cement and ceramics manufacturing. However, it is critical to verify that the final product presents not only adequate technical properties but also that it does not pose negative impacts to the environment and human health during its use. This study investigates the environmental compatibility of the use of ceramic porcelain stoneware tiles manufactured with BA as partial replacement of traditional raw materials, with a particular focus on the leaching behavior of the tiles during their use, and also after crushing to simulate their characteristics at their end of life. To evaluate the latter aspect, compliance leaching tests were performed on crushed samples and compared with Italian End-of-Waste (EoW) thresholds for the use of construction and demolition waste as recycled aggregates. Whereas, to assess the environmental compatibility of the tiles during the utilization phase, a methodology based on the application of monolithic leaching tests to intact tiles, and the evaluation of the results through multi-scenario human health risk assessment and the analysis of the main mechanisms governing leaching at different stages, was employed. The results of the study indicate that the analyzed BA-based tiles showed no significant increase in the release of potential contaminants compared to traditional formulations and fully complied with End-of-Waste criteria. The results of the monolith tests used as input for site-specific risk assessment, simulating worst-case scenarios involving the potential contamination of the groundwater, indicated negligible risks to human health for both types of tiles, even considering very conservative assumptions. As for differences in the release mechanisms, tiles containing BA exhibited a shift toward depletion-controlled leaching and some differences in early element release compared to the ones with a traditional formulation.