Research on the preparation of geopolymer using lepidolite lithium slag and ground granulated blast furnace slag as precursors and its solidification effects on heavy metals

With the acceleration of industrialization and urbanization, the effective treatment and resource utilization of solid waste have become critical research topics. As a bulk solid waste generated during lithium extraction from lithium ores such as spodumene and lepidolite, lithium slag poses significant disposal challenges while showing potential utilization as a geopolymer precursor. However, the preparation of geopolymer with high lepidolite lithium slag (LS) content and its immobilization capacity on heavy metals remain insufficiently understood. Therefore, in this study, through preparing geopolymers with LS and ground granulated blast furnace slag (GGBS) as precursors, the feasibility of high LS content to prepare geopolymers was evaluated, and the solidification effects of geopolymers on three typical heavy metals, including Pb(II), Zn(II), and Cr(III),were investigated. The findings indicate that the geopolymers with appropriate LS and GGBS proportion in precursors have high compressive strength, which reaches a maximum value of 57.2 MPa at 28 d when the LS to GGBS ratio of 3:7. The incorporation of heavy metals delays the geopolymerization process and accordingly brings a significant reduction of the early-aged strength, but the strength reduction gradually weakens over time. The geopolymer demonstrates an excellent heavy metal immobilization ability, with a much higher solidification efficiency up to 99.9 % and very low heavy metal leaching concentrations, and these three heavy metal ions are effectively solidified in stable chemical forms. The main hydrates of the geopolymer are N(C)-A-S-H gels and ettringite, with minimal influence of heavy metals on the phase composition and microstructure. These heavy metals can somewhat improve the pore structure of geopolymers. Moreover, compared with ordinary Portland cement, these geopolymers have lower integrated material cost and carbon emissions. Overall, the geopolymers exhibit favorable mechanical properties, good economic benefits, significant reduced carbon emissions, and excellent heavy metal immobilization, highlighting the potential of lepidolite lithium slag for resource utilization in geopolymer preparation. • High strength geopolymers are prepared using LS and GGBS as precursors with their synergistic effects. • Much higher LS content of over 70 % may cause efflorescence and volume instability of geopolymers. • The geopolymer with LS and GGBS as precursors exhibits excellent solidification capability on heavy metals. • Geopolymers have favorable economic and environmental advantages with lower integrated cost and embodied carbon emissions.