Facies-Specific NaOH-Activated Gold Tailings from Senegal for Non-Load-Bearing Masonry Units: Mix Design, Strength and Leaching Performance

The distinct oxidized and sulfidic facies of Sabodala gold mine tailings (Senegal), characterised by near-neutral drainage, are evaluated as potential secondary raw materials for non-load-bearing masonry in West Africa. This study evaluates NaOH-activated tailings as alkali-activated binders, examining mechanical performance, water absorption, leaching behavior, preliminary durability and curing energy demand. Both facies were activated with NaOH solutions of varying molarity and solution-to-solids ratio, with minor additions (~3 wt%) of Portland cement or hydrated lime and curing temperatures up to 210˚C. NaOH molarity emerged as the primary strength driver, while solution fraction defined facies-specific optima at ~21 wt% (oxidized) and ~18 wt% (sulfidic). Within this window, under 210˚C/4 h curing, 28-day compressive strengths reached 12 - 20 MPa with 24 h water absorption of 10% - 15%. Product leachates for As, Cd, Cr, Cu, Ni, Pb and Zn remained low and within indicative construction product limits. Accelerated wet-dry and sulfate exposure tests showed strength retention generally above ~80%, though these represent short-term screening rather than full service-life assessment. The consistent flexural-compressive strength relationship (ft ~ 0.26 - 0.27 fc) enables compression-based quality control. Overall, this work establishes practical, facies-specific mixture windows for NaOH-activated Sabodala tailings as secondary mineral resources, guiding the development of lower-energy curing schedules and supporting future standardization of tailings-based masonry units and mine-tailings management strategies.