High-Performance Composite Aerogels with CaSO₄ Whisker and Nanofiller Synthesized from Lepidolite Lithium Slag

According to the chemical composition and structure properties of lepidolite lithium slag (i.e., LS), reinforcing materials were prepared to improve the mechanical properties and flame retardancy of poly(vinyl alcohol) (PVA)/montmorillonite (MMT) aerogels. Specifically, calcium sulfate anhydrous whiskers (CSAW) were synthesized from LS rich in CaO and SO3 (i.e., LS-B), and nanofillers were obtained from LS rich in Al2O3 and SiO2 (i.e., LS-A). A densified columnar-honeycomb structure of composite aerogels was obtained by adding the above CSAW and nano LS-A. The results show that the mechanical properties were improved remarkably, and the peaks of heat release rate, smoke production rate, and total smoke production were decreased significantly with the combined addition of CSAW and nano LS-A. The strength was increased by about 160%, and the modules were increased by about 130%. The fire safety was also promoted significantly, i.e., the peak of heat release rate was 128.37 kW·m–2, and the smoke production rate was cut down about 3.0 times. The enhancing mechanism of the combined effect from CSAW and nano LS-A on mechanical properties and flame retardancy should be due to the columnar-honeycomb structure formed by CSAW and PVA/MMT and the filling effect of nano LS-A. The proportion of LS utilized in the composite aerogels was achieved by more than 40%. The composite aerogel can be potentially applied in flame retardant fields. This study is of great significance for the high value and comprehensive utilization of LS. It also provides an idea for improving the mechanical properties and flame retardancy of PVA/MMT aerogels in the future.