Study on properties and hydration mechanism of green alkali-activation lithium slag composite cementitious materials

Abstract

Lithium is widely used in smart electronic devices and new energy vehicles owing to its low density and high chemical activity. Lithium slag (LS) is a byproduct of the smelting of lithium from lithium pyroxene or lithium mica. The effective treatment of LS is crucial for ecosystem protection. In this study, a method is developed to prepare green alkali-activated LS composite cementitious backfill materials (ALSCs) using calcium carbide slag (CCS). The effects of the CCS content, LS content, and water-cement ratio on the rheological behavior and mechanical properties of the ALSCs are analyzed. The mineral composition, bonding structure, micromorphology, and pore structure characteristics of ALSCs were clarified using acoustic emission monitoring (AE), X-ray diffraction (XRD), Fourier-transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM) with energy dispersive spectroscopy (EDS), and molecular dynamics (MD) simulation techniques. The results indicate that the optimal LS and CCS contents are 12 % and 10 %, respectively. The ALSCs exhibited excellent mechanical properties, with their compressive strength and fluidity reaching 17.64 MPa and 243 mm, respectively. The cumulative acoustic emission (AE) energy increased with the compressive strength. The clustering of the cumulative energy curves became more significant and exhibited a stepped-up tendency. The primary hydration products were C-A-H, C-S-H, and C-A-S-H. The synergistic hydration coupling of the solid waste improved the densification of the hydration products and refined the pore structure and late strength. Thus, ALSCs can replace cement as a cementitious material for downhole filling to thereby reducing filling costs and promote the utilization of solid waste resources.