Abstract: Performance deterioration due to sulfate attack is a major problem facing the durability of concrete structures. To improve the mechanical properties and durability of concrete, this study prepared RHA-L concrete by incorporating rice husk ash (RHA) and lithium slag (LS). The performance changes and damage mechanisms of RHA-L concrete immersed in a 5% Na₂SO₄ solution for 150 days were investigated. XRD, SEM, and MIP were used to characterize the pore structure and micro-morphology of the concrete during the erosion process, and a lifespan prediction model was established based on the deterioration of concrete strength. The results indicate that sulfate attack exhibits a two-stage characteristic: in the first 90 days, the formation of ettringite and gypsum fills the pores, resulting in a decrease in porosity and an increase in compressive strength and dynamic elastic modulus by 8.2% and 5.35%, respectively. After 90 days, the accumulation of expansion stress from the erosion products leads to a 65.9% increase in porosity and a 10.26% decrease in dynamic elastic modulus, significantly reducing mechanical properties. Microstructural analysis shows that the initial filling effect of ettringite and gypsum optimizes the pore structure, while their excessive accumulation in the later stage causes micro-crack propagation and the dissociation of C-S-H gel, resulting in mechanical property deterioration. Based on the kinetic equation of strength degradation and the established degradation pattern, a lifespan prediction model for RHA-L concrete in sulfate environments was developed, and the prediction results meet engineering design requirements.