Synthesis of LDHs from vermiculite

“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).”

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