Environmental impact of waste-derived geopolymer composites: heavy metal leaching and risk assessment

Geopolymers are a relatively new type of material that can be produced from waste. They may contain hazardous compounds, such as heavy metals, which pose environmental risks if released. This study presents the results of heavy metal release from molded geopolymer composites over time and evaluates the leaching mechanisms of various elements. The study also assesses the potential ecological risk of these materials, highlighting the innovative and complex nature of the research program. The geopolymer composites were produced from silica fly ash (CFA) and waste glass powder (GP), with their composition further modified using graphene and nanosilica. The study investigated materials with innovative compositions that could effectively replace traditional Portland cement-based concrete, whose production significantly contributes to carbon emissions. Leachability was assessed using the tank test method. Among the ten metals analyzed, the geopolymer composites released Ba, Cr, Mo, and Sb. The study demonstrated that the leaching process was primarily controlled by dissolution and diffusion; however, for Ba and Mo, depletion of available ions for leaching was also observed. The potential Ecological Risk Index (PERI) ranged from 21.4 to 34.5 depending on the geopolymer composition. The ecological risk analysis indicated no environmental threat from the geopolymer composites.