In-situ remediation enlightens a down-to-earth pathway for managing the pyrite ash dumps in Italy: challenges in potentially toxic elements retention and CO2 mitigation

With the unprecedented urbanization in the last decades, massive solid wastes containing potentially toxic elements (PTEs) have been generated and dumped, which can be detrimental to soil health and affect flora and fauna. To minimize the exposure risks, delivering in-situ or ex-situ sustainable management of solid wastes continues to be one of the biggest public health challenges worldwide. Concurrently, in-situ high-performance solidification/stabilization^© (S/S) has been proposed as a remediation strategy to prevent the release of pollutants in the stockpile sites, with ordinary Portland cement (OPC) being conventionally used as a cost-effective binder. However, growing concerns related to the substantial greenhouse gas emissions associated with the OPC production process and the limited PTEs retention capacity of OPC make the application of OPC under scrutiny. In this work, we examined the feasibility of minimizing the use of OPC in the S/S process of pyrite ash, a typical Pb and sulfate-rich solid waste generated in the sulfuric acid production industry. Four alternative binders (CEM/IIIB, calcium aluminate cement, white-steel-slag and ground-granulated blast-furnace slag mixture, and alkaline-activated ground-granulated blast-furnace slag) were tailored as solutions alternative to conventional OPC, with the aim of mitigating the anthropogenic CO₂ emissions and promoting the PTEs retention. The experimental characterization and geochemical modeling of the stabilized products revealed the different interactions between the applied binder scenarios and pyrite ash, which clarifies the roles of hydration products and the binding systems’ microstructures on the Pb and sulfate leachability. Further, we evaluated the cradle-to-gate carbon footprint and cost analysis associated with each binder-pyrite ash system. Overall findings underscore that applying these alternative binders could be pivotal in the envisaged carbon-neutral scenario and offer technical benefits in future field trials if the growth of the cement-free roadmap continues.