Synthesis of LDHs from vermiculite

https://doi.org/10.3390/catal7040105

“The environmentally benign synthesis scheme for obtaining Li₄SiO₄ and Mg-Al-CO₃ LDH from the vermiculite mineral is illustrated in Figure 1.The raw vermiculite mineral was first thermally pretreated at 900 °C to produce expanded vermiculite (EXVMT) with a higher specific surface area. The chemical composition of the samples was determined by X-ray fluorescence (XRF) spectroscopy (Panalytical Axios-mAX), which included SiO₂ (40.8 wt %), MgO (21.7 wt %), Al₂O₃ (20.8 wt %), K₂O (6.5 wt %), Fe₂O₃ (5.0 wt %), CaO (2.9 wt %), Na₂O (1.4 wt %), and TiO₂ (0.9 wt %). Then, the obtained EXVMT was leached in acidic solution at 80 °C, by which SiO₂ powder and an acidic wastewater containing Mg²⁺, Al³⁺, and other metals, were formed (Figure 1a). Following this, Li₄SiO₄ could be synthesized using a solid-state method by reacting the above obtained SiO₂ powder with lithium nitrate (Figure 1b), and Mg-Al-CO₃ LDH could be prepared using a co-precipitation method from the above obtained acidic wastewater (Figure 1c). During the whole synthesis procedure, both the obtained SiO₂ and the acidic wastewater were utilized, representing a promising and environmentally benign route for converting vermiculite minerals into high-value added products.”

“Figure 1. Schematic illustration of the synthesis of Li₄SiO₄ and LDH from vermiculite, (a) the vermiculite is treated with acid to obtain a silica and an acidic solution, (b) the synthesis of Li₄SiO₄ from the SiO₂ obtained in step (a), and (c) the synthesis of LDH from the acidic solution obtained in step (a).”