Strength Enhancement of Saline Sludge Through Steel Slag Carbonation Stabilization

The carbonation stabilization method combines the advantages of high efficiency, low carbon emissions, and low alkalinity, making it a green technology with broad application potential for soft soil stabilization. However, in the practice of carbonation stabilization of saline sludge, the impact of soluble salts on the carbonation stabilization system remains poorly understood. This study investigated the mechanical properties and microstructural mineral evolution of sulfate ion (SO42−) and chloride ion (Cl−) contaminated saline sludge after steel slag carbonation stabilization. The results indicate that the accumulation of Cl− can lead to a significant deterioration in mechanical properties. We hypothesize that this strength reduction is not driven by the formation of chloride-containing expansive Friedel’s salt; instead, it may arise from the hygroscopic nature of chloride salts, which reduces matrix permeability, hinders CO2 gas diffusion within the matrix and lowers carbonation efficiency. Notably, XRD and TG-DTG analyses identified no sulfate- or chloride-bearing crystalline phases (e.g., ettringite or Friedel’s salt). We attribute this phase absence to carbonation reactions competing for Ca(OH)2 in the stabilized soil’s pore solution, thereby suppressing the crystallization of expansive salt compounds. These findings collectively demonstrate minimal chemical reactivity between the steel slag carbonation system and soluble salts, revealing an intrinsic resistance of carbonated steel slag to salt-induced deterioration.