Alkali activation mechanisms and hydration characteristics of lithium slag for zero-cement binder applications

초록

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 lowcarbon construction materials.

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