An alternative to conventional methods for mine tailings disposal is stabilization with alkali-activated binders (AABs), developed from agro-industrial waste. Despite increasing interest in this topic, there is still a lack of studies focusing on the stabilization of iron ore tailings (IOTs) using AABs, particularly those that combine the characterization of cementitious gels with an evaluation of leaching behavior. This study assessed the strength, mineralogy, and leaching performance of IOTs stabilized with AABs formulated from rice husk ash (RHA) and hydrated eggshell lime (HEL), using sodium hydroxide as the alkaline activator. Tests included unconfined compressive strength (UCS), X-ray diffraction (XRD), Fourier-transform infrared spectroscopy (FTIR), and metal leaching analyses. The IOT–AAB mixture with the highest AAB content and dry unit weight achieved an average UCS of 2.14 MPa after 28 days of curing. UCS increased with AAB content, followed by dry unit weight and curing time, the latter showing a non-linear influence. The formation of C–S–H gel was confirmed after 28 days, while N–A–S–H gel was detected as early as 7 days of curing. The cemented IOT–AAB mixtures showed no metal toxicity and effectively encapsulated barium originating from the RHA.

Alkali-activated materials derived from industrial waste are promising alternatives to Portland cement for geotechnical applications. However, their environmental safety under realistic exposure conditions remains poorly understood, particularly due to the limitations of conventional chemical assessments, which may not capture early-stage curing effects, leaching behavior, and associated ecotoxicological risks. This study investigates whether conventional chemical assessment methods are sufficient to evaluate the environmental performance of such materials. An alkali-activated cement produced from photovoltaic module glass and hydrated oyster shell lime was evaluated through an integrated approach combining leaching tests and ecotoxicological assays. Leaching behavior was assessed at curing ages ranging from 7 to 91 days. Ecotoxicological effects were evaluated using extracts obtained from the alkaline cement after 7 days of curing, with zebrafish embryos under both acetic acid‑extracted and water-extracted conditions. Leaching tests showed a progressive reduction in several regulated metals; however, Ba, Cd, Cu, Ni, Pb, and Zn exceeded regulatory thresholds at specific curing ages. All mixtures produced highly alkaline leachates (pH > 13), and non-regulated elements (Ga, In, K, and Li) were also detected. Ecotoxicological assays revealed acute toxicity in acetic acid‑extracted leachates and sublethal effects in water- extracted leachates, including impaired hatching and reduced spontaneous movement. The results demonstrate that reductions in leached concentrations and compliance with conventional chemical criteria do not necessarily correspond to biological safety, highlighting the need to integrate ecotoxicological assays into environmental assessments of sustainable cementitious materials. Graphical Abstract