Dry stacking of stabilized gold tailings: Mechanical and leaching performance of alkali-activated systems

The stabilization of gold tailings (GT) presents both geotechnical and environmental challenges due to their high moisture content, low strength, and heavy-metal content. Recent studies have independently examined the mechanical and leaching behavior of stabilized GT, highlighting the need for more comprehensive research investigating these behaviors in combination, particularly with alternative binders. This study evaluates a one-part alkali-activated binder (AAB) as an alternative to ordinary Portland cement (OPC), focusing on mechanical performance, microstructure, and leaching analysis. The AAB consisted of ground granulated blast furnace slag activated with sodium hydroxide and sodium silicate. GT specimens were stabilized with different binder contents, degrees of compaction, and curing times, and then subjected to unconfined compressive strength (UCS), scanning electron microscopy/energy-dispersive X-ray spectroscopy (SEM/EDX), and leaching tests. AAB-stabilized specimens achieved higher strength at shorter curing times (UCS=8.55 MPa) than OPC-stabilized specimens at longer curing times (UCS=6.92 MPa). Microstructural analysis indicated the formation of a dense matrix of CASH gels, thereby increasing strength and stiffness. Leaching tests showed reductions of several metals, including Mn, Zn, and Cd, with Mn leaching reduced by up to 99.9%. However, AAB stabilization substantially increased arsenic (As) leaching under alkaline conditions, particularly with higher binder contents and longer curing periods. As concentrations increased from 0.014 mg/L in untreated GT to up to 2.1838 mg/L in the most highly cemented AAB treatment, exceeding the toxicity limit. Overall, AABs effectively enhance the geotechnical properties of GT for dry stacking applications. However, their high alkalinity may mobilize oxyanions such as arsenate. These findings highlight the need to integrate mechanical and environmental assessments when designing stabilization strategies for hazardous tailings.