Stabilizing feldspar powder from lithium extraction byproducts using microbial-induced calcium carbonate precipitation (MICP) as road subgrade material

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To promote the sustainable use of feldspar powder, a by-product of lithium extraction, as road subgrade material, this study employed microbial-induced calcium carbonate precipitation (MICP) to improve its engineering performance. Two curing methods, direct mixing and periodic grouting with , were compared under different cementation-solution concentrations. Dry density, unconfined compressive strength, shear strength, XRD, and SEM were used to evaluate macroscopic performance and solidification mechanisms. Periodic grouting exhibited superior densification and stabilisation, achieving a calcium carbonate content of 18.7% after eight grouting cycles using a 1.0 mol/L solution. At this content, the treated feldspar powder reached a dry density of 2.02 g/cm3, an unconfined compressive strength of 787.8 kPa, and a cohesion of 163.76 kPa. Microstructural analyses showed that MICP promoted mineral transformation and biogenic calcite precipitation, which filled interparticle pores and formed cementing bridges between particles, thereby enhancing compactness and strength. These findings demonstrate the feasibility of MICP-treated feldspar powder for road subgrade applications and provide a sustainable pathway for valorising lithium-industry waste.