<p>Lead-zinc tailings are typically stored in tailings ponds or stockpiles. Over extended periods, weathering and seepage in these storage sites can lead to the release of potentially toxic metals. Alkali-activated solidification/stabilization presents a viable method for reducing contaminant mobility and enhancing the safe reuse potential of lead-zinc tailings. In this study, two alkaline activator systems were employed to stabilize the lead-zinc tailings. Activator A comprised a sodium silicate solution and NaOH, while Activator B comprised S95-grade ground granulated blast-furnace slag and NaOH. The effects of cement content, activator dosage, and water content on compressive strength and leaching behavior were examined. XRD and SEM-EDS analyses were conducted to investigate the reaction products, microstructure, and elemental distribution of the solidified products. The study results show that both activator systems decreased Zn, Mn, and Cd leaching concentrations under the tested conditions. Based on the XRD, SEM-EDS, and leaching results, the reduced heavy metal mobility in SP-B can be primarily attributed to gel formation, physical encapsulation, and chemical retention. The gel-like products formed during hydration and alkali activation enveloped and bonded the fine metal–bearing particles, thereby reducing their direct contact with the leaching solution. The alkaline environment and slag-derived Ca-, Si-, and Al-bearing species likely facilitated adsorption, surface complexation, precipitation, and gel-associated retention. Overall, Activator B demonstrated superior environmental stabilization performance compared to Activator A under the tested conditions and holds potential for the safe reuse of lead-zinc tailings in conventional backfill and non-structural infill applications.</p>