The mining industry generates a notable amount of mine tailings (MTs). Disposal of MTs creates environmental impacts such as air pollution and the release of heavy metals into surface and underground water. The European Union (EU)-funded project “Integrated mineral technologies for more sustainable raw material supply” (ITERAMS) includes an effort to produce eco-friendly backfill materials to enhance operation and mine safety and covers for surface deposits of tailings based on geopolymerization technology. This paper investigates the effects of activator concentration, curing temperature and time on alkali-activated materials based on low-alumina MTs from the Cu/Ni mine in Northern Finland. Alkaline activators containing sodium silicate solution (Na₂SiO₃) at different concentrations were used and two different curing temperatures, 40 °C and 60 °C, for periods of 7, 14, and 28 days were considered. Scanning electron microscopy/energy-dispersive X-ray spectroscopy (SEM/EDS) and X-ray diffraction (XRD) were performed to investigate the structure, morphology and phase compositions of the alkali-activated products. The effect of curing temperature and alkaline solutions on mechanical strength and water absorption were investigated. The results indicate that the alkalinity and curing temperature affect the mechanical and microstructural properties of the compositions of alkali-activated MTs. The 30 wt% Na₂SiO₃ addition enables the alkali activated MT to improve the compressive strength with a highest value of 6.44 and 15.70 MPa after 28 days of curing at 40 °C and 60 °C, respectively. The results of this study deliver useful information for recycling and utilization of MTs as sustainable material through the alkali activation. Graphic Abstract

The interconnectedness of Earth’s ecological and social systems means that changes in one area invariably affect others. Human activities continue to push the planet beyond safe thresholds, threatening both environmental stability and human well-being. Despite decades of discourse, a universally recognized and operational definition of sustainability remains elusive. While frameworks such as the Sustainable Development Goals, Planetary Boundaries, and Decent Living Standards have advanced the conversation, none fully captures the complexities of socio-ecological interdependencies or provides actionable guidance. This paper outlines the historical and conceptual context of sustainability, including the shift from the Holocene to the Anthropocene, and critically reviews key frameworks such as the Millennium Development Goals, Sustainable Development Goals, Planetary Boundaries, Doughnut Economy, and Decent Living Standards. It identifies key gaps, including the misalignment between biophysical thresholds and social goals, lack of regional specificity, and missing mechanisms for translating global objectives into just and implementable policies. Building on this analysis, this paper proposes a more precise definition of sustainability: any action that accelerates planetary overshoot or impedes the achievement of a decent life must be considered unsustainable. By advancing this integrative definition, this paper seeks to inform academic discourse and support the development of more equitable and operational sustainability strategies, particularly in the context of the Sustainable Development Goals. In doing so, it offers conceptual guidance to address persistent gaps in the SDG framework, with specific relevance to targets such as SDG 8 (Decent Work and Economic Growth).