Particle size dependent performance of recycled lithium tailings as supplementary cementitious materials

Different from lithium slag, lithium tailings exhibit low hydration activity and cannot achieve high-performance modification merely through mechanical grinding, yet the fundamental reason for this limitation has not been clearly established. This study addresses this question through systematic investigation of lithium tailings on the mechanical performance, microstructure, and environmental safety of cement mortar. Multi-scale characterizations, including ICP-MS, XRF, SEM-EDS, XRD, MIP, IC, and PSD, were employed to clarify the microstructural properties of lithium tailings, while compressive strength and chloride electric flux tests were conducted to evaluate the macroscopic performance. The results show that replacing 30% cement with untreated lithium tailings reduces the mortar fluidity ratio and 28-day compressive strength ratio to 82.3% and 59.5%, respectively. Ten minutes of mechanical grinding effectively optimizes particle morphology and fineness, increasing the fluidity and strength ratios to 95.1% and 73.3%. However, the chloride electric flux remains approximately 7500 C for all tailings mortars, substantially higher than that of plain cement of 4022 C. The inherent porous structure of lithium tailings significantly increases the porosity of hardened paste from 18.48% for plain cement paste to 26.15% for raw lithium tailings paste and 24.06% for ground lithium tailings paste. Environmental assessment verifies that the heavy metal leaching levels of lithium tailings and tailings-modified mortar are within the regulatory limits. It is concluded that properly ground lithium tailings can serve as an inert filler SCM for general engineering applications, whereas their intrinsic porous structure imposes a fundamental limitation on chloride penetration resistance that cannot be eliminated by mechanical grinding alone.