Optimization of Geopolymers for Sustainable Management of Mine Tailings: Impact on Mechanical, Microstructural, and Toxicological Properties

This study investigates the use of geopolymer technology as an alternative for the management of mine tailings, which is a serious environmental problem in mining areas, including the Arequipa region of Peru. In this study, the mixture of stabilized mine tailings with different percentages of binders (i.e., metakaolin and pumice) and their impact on the mechanical, microstructural, and toxicological properties of the synthesized geopolymers were analyzed. The ratios of mine tailings to binder material varied between 100/0 and 0/100. The activation was carried out with an alkaline solution of sodium hydroxide (10 M) and sodium silicate (modulus 2.5). Specimens were fabricated as 50 mm cubes, and the seven mix designs were evaluated in triplicate. The evaluations included compressive strength at 7, 14, 28, and 56 days of curing, chemical analysis by Fourier Transform Infrared Spectroscopy (FT-IR), microstructural characterization by X-ray diffraction (XRD) and Scanning Electron Microscopy (SEM/EDS), thermal behavior by thermogravimetry and differential thermal analysis (TGA/DTA) between 40 °C and 1000 °C, and toxicological tests by the Toxicity Characteristic Leaching Procedure (TCLP, EPA 1311) to determine the efficiency of immobilization of toxic metals. The results demonstrate significant improvements in compressive strength for the F50 specimens compared to A0, with increases of approximately 300%, 270%, and 461% observed at 7, 28, and 56 days of curing, respectively, with microstructural stability with an average pore size of 7.21 μm, and efficiency in the immobilization of heavy metals in geopolymers with 30% or 40% binder (60%–70% mine tailings). The leachate concentrations of As, Cd, Pb, and Hg were below the established thresholds, indicating that the stabilized mine tailings can be classified as “non-hazardous materials”. Geopolymers with 30% to 50% binder showed strength development with microstructural stability and efficiency in the immobilization of heavy metals, complying with current regulations. Therefore, these geopolymers are suitable for various applications and in different environmental conditions.