A green route to sustainable alkali-activated materials by heat and chemical activation of lithium slag

Lithium slag (LS) is a potential new resource for fabricating alkali-activated materials, however, few works have reported the utilization of LS in alkaline activation area. Herein, the mineral composition of LS was evaluated by Rietveld quantitative analysis and the mechanical properties of alkali-activated LS (AALS) were systematically investigated. Based on the above studies, a method of heat incorporating with chemical activation was carried out to further improve the reaction activity of LS. The results indicated that pre-heating facilitated the improvement of reaction activity of LS and the active amorphous constituents in LS dramatically increased from 17.3 wt% to 50.7 wt% after heat activation at 700 °C. Furthermore, we also found that more active constituents in LS enhanced the rate and degree of reaction and resulted in the increase of mechanical strength of AALS. The compressive strength of specimens (aged for 1d) increased from 12.8 MPa to 47.7 MPa because a denser microstructure was observed in specimens prepared by heat-activated LS resource. In addition, the mechanism of heat activation for LS was also investigated by thermogravimetric analysis (TGA) and in-situ X-ray diffraction (XRD) at different temperature step. The results illustrated that the defective crystals in LS tended to transform into glassy phases between 300 and 800 °C. And the transformation was more significant as the temperature rising.