Upcycling Superfine Tailings via a Waste-Based Geopolymer: Leaching Behavior, Electrochemical Response, and Pore Evolution under Semidynamic Chloride and Sulfate Erosion

This study discusses the impacts of semidynamic chloride and sulfate erosion on superfine tailings upcycled by a waste-based geopolymer. Unlike previous studies focusing mainly on dynamic leaching or the development/application of geopolymers, this work links ionic release, solution electrochemistry, and pore-structure evolution under the erosion conditions. Results indicate that sulfate erosion caused stronger As/Zn release than chloride erosion, whereas higher geopolymer dosage improved the buffering capacity of tailings and reduced the cumulative leaching of Ca, Si, and Mg ions, which are essential for encapsulating As/Zn pollutants. Electrochemical analyses reveal the stabilized tailings’ buffering capacity in simulated seawater, with elevated pH values in chloride and sulfate environments preventing polymer degradation. Sulfate- and chloride-bearing environments suppressed the development of coarse pores relative to water erosion (characteristic pore diameter reaching 7.46 μm), which is reflected in the best strength performance after chloride erosion (2.37 MPa) of the tailings stabilized with 8% geopolymer dosage. The observed pore microstructural and elemental compositions indicate that chloride/sulfate ions may participate in geopolymerization and generate stable minerals/products related to them (possibly Friedel’s salt and ettringite), which then fill the larger pores. Health risk calculations and benchmark comparisons indicate that the leachate-associated risks remained low within the tested conditions ((non)carcinogenic risks (∼10 –7 –10 –9 ) on health). This study demonstrates that MGF-stabilized tailings are a promising sustainable geotechnical infrastructure solution that supports circular economy goals through waste valorization.