Preparation of geopolymers from thermally activated lithium slag: Activity enhancement and microstructure

As an industrial by-product of the lithium extraction process from spodumene, lithium slag (LS) is less reactive, rendering it a chemically infeasible binder. In this study, a thermal activation approach was employed to enhance the reactivity of LS. The underlying mechanisms of LS's thermal activation at various temperatures were thoroughly explored through XRD and ICP. The results indicated that alterations in the aluminosilicate composition of LS occurred during calcination between 500 °C and 900 °C, leading to the transformation of spodumene into amorphous forms. Particularly noteworthy was the initial increase in the LS amorphous phase content with increasing temperature, followed by a subsequent decline. Building upon these findings, a lithium slag geopolymer (LSG) was prepared via alkali activation, using the activated LS as the exclusive precursor. It was observed that elevating the content of active components in LS enhanced the geopolymerization reactions, resulting in an improved mechanical strength of LSG. Remarkably, after 28 days of aging, geopolymer specimens prepared from LS calcined at 700 °C exhibited a compressive strength of 36.0 MPa. Combining these results with FTIR and SEM-EDS analyses, it becomes evident that suitable calcination temperatures empower LS to release a higher quantity of silicon and aluminum ions. These ions play a significant role in the geopolymerization process, leading to the formation of an amorphous sodium (calcium) aluminosilicate hydrate (N(C)-A-S-H) gel. This gel acts as a binder, tightly binding the residual solid particles, and thus forming a denser microstructure.