Alkali Activation Mechanisms and Hydration Characteristics of Lithium Slag for Zero-Cement Binder Applications

Lithium slag powder (LSP), a byproduct of lithium extraction from spodumene ore, is a potential sustainable cementitious binder. However, its alkali-activation behavior remains insufficiently understood. This study investigates the reactivity, hydration mechanisms, and mechanical performance of alkali-activated LSP and compares those LSP properties with those of fly ash (FA) and ground granulated blast-furnace slag (GGBS). Leaching tests using NaOH and Ca(OH) 2 solutions with different molarities were conducted to quantify Si, Al, and Ca. The reaction residues were characterized using X-ray diffraction, scanning electron microscopy-energy dispersive X-ray spectroscopy, and Fourier-transform infrared spectroscopy. The results showed that LSP exhibited high Si and Al dissolution, even at low NaOH concentrations, indicating its highly reactive aluminosilicate structure. In Ca(OH) 2 environments, initial dissolution of Si is followed by its rapid consumption through C–(A)–S–H and sulfate-bearing hydrate formation, accompanied by AFt-to-AFm transformation and carbonation. Isothermal calorimetry revealed that increasing the Ca(OH) 2 content accelerated the hydration kinetics and enhanced the cumulative heat release. Mortar tests demonstrated that alkali-activated LSP achieved a competitive long-term compressive strength, reaching 38 MPa at 28 days for optimal Ca(OH) 2 content, which provided a balance between reaction kinetics and matrix stability. These findings confirm the feasibility of using lithium slag as a zero-cement binder and provide insights into the reaction mechanisms of low-carbon construction materials.