Beneficiation of industrial wastes, such as mine tailings (MTs), through development of alternative eco-friendly geopolymer binders for construction composites offers a twofold environmental benefit, as it reduces the demand for cement and it increases the sustainability of industrial processes by creating a value-added product from an industrial byproduct. While MTs have the requisite composition for use as a geopolymer precursor, they are often low-reactive. This study explored the effect of Class C Fly Ash (FAc) on the geopolymerization of low-reactive gold MTs. A 10 M sodium hydroxide (NaOH) solution was used as the alkaline activator with four different concentrations of FAc (5, 10, 15 and 20 wt.%). The results indicated that the combination of FAc with the low-reactive gold MTs improved the physicochemical stability of the final geopolymerized samples, with a 95–120% increase in compressive strength, compared to the geopolymer samples of only low-reactive gold MTs. Although some of the strength improvement could be attributed to geopolymerization of the FAc itself, the presence of the FAc also improved the reactivity of the MTs, increasing the geopolymer production of the MTs. This study documents the positive effects of the FAc on gold MTs with low-calcium content and their conversion into sustainable inorganic composite geopolymers for the construction field.

This work presented the production and incorporation of calcium-hydrolyzed nano-solutions at three concentrations (1, 2, and 3 wt.%) in alkali-activated gold mine tailings (MTs) from Arequipa, Perú. As the primary activator solution, a sodium hydroxide (NaOH) solution at 10 M was used. Calcium-hydrolyzed nanoparticles with a particle size of 10 nm were localized inside self-assembled molecular spherical systems (micelles) with diameters of less than 80 nm that were well-dispersed in aqueous solutions and acted as secondary activator, and also as additional calcium resource for alkali-activated materials (AAMs) based on low-calcium gold MTs. High-resolution transmission electron microscopy/energy-dispersive X-ray spectroscopy (HR-TEM/EDS) analyses were carried out to characterize the morphology, size, and structure of the calcium-hydrolyzed nanoparticles. Fourier transform infrared (FTIR) analyses were then used to understand the chemical bonding interactions in the calcium-hydrolyzed nanoparticles and in the AAMs. Scanning electron microscopy/energy-dispersive X-ray spectroscopy (SEM/EDS) and quantitative X-ray diffraction (QXRD) were performed to study the structural, chemical, and phase compositions of the AAMs; uniaxial compressive tests evaluated the compressive strength of the reaction AAMs; and nitrogen adsorption–desorption analyses measured porosity changes in the AAMs at the nanostructure level. The results indicated that the main cementing product generated was amorphous binder gel with low quantities of nanostructured C-S-H and C-A-S-H phases. The surplus production of this amorphous binder gel produced denser AAMs at the micro-level and nano-level (macroporous systems). In addition, each increase in the concentration of calcium-hydrolyzed nano-solution had a direct/proportional effect on the mechanical properties of the AAM samples. AAM with 3 wt.% calcium-hydrolyzed nano-solution had the highest compressive strength, with a value of 15.16 MPa, which represented an increase of 62% compared with the original system without nanoparticles that were aged under the same conditions at 70 °C for seven days. These results provided useful information about the positive effect of calcium-hydrolyzed nanoparticles on gold MTs and their conversion into sustainable building materials through alkali activation.

The stability of tailings dams is governed predominantly by the physical properties and geotechnical behavior of their primary construction material—tailings. Consequently, a systematic understanding of these characteristics is of great significance for the rational design and long-term stable operation of tailings dams. This review focuses on the physical properties and geotechnical behavior observed in different types of tailings. In terms of physical properties, the particle size distribution exhibits a pronounced hydraulic classification characteristic within the impoundment, consisting predominantly of silt-sized particles and displaying an overall trend toward finer gradation. The mineralogical and chemical composition is dominated by quartz, hematite, and silicates. However, significant spatial variability exists both between different tailings types and across distinct zones within the same tailings pond. Regarding geotechnical behavior, the permeability of tailings is governed by a fines content threshold: below this threshold, permeability decreases with increasing fines content, while beyond it, the permeability stabilizes. When studying consolidation and compression behavior using slurry specimens, the compression curves exhibit nonlinear characteristics, primarily described by the modified Gibson theory. The shear behavior of tailings is significantly influenced by confining pressure, drainage conditions, anisotropy and stress paths. The presence of transitional behavior leads to the critical state line determined based on a single sampling method erroneously assessing the dilation/cosntraction characteristics of in situ tailings, thereby affecting the assessment of liquefaction risk. Future research should focus on the seepage, consolidation and shear properties of clayey fine-grained tailings and unsaturated tailings, and aim to elucidate the key controlling factors of transitional behavior to enhance the reliability of tailings dam stability assessments.