Transformation of boehmite into 2:1 type layered aluminosilicates with different layer charges under hydrothermal conditions

In this study, beidellite, paragonite and other 2:1 type layered aluminosilicates with high layer charges (2:1 type LA-HLC) were synthesized under hydrothermal conditions by using boehmite as a precursor. The concentrations of dissolved Al from boehmite precursor had important effects on the mineral components of the hydrothermal products and the layer charge density of the resultant minerals. A combination of 2:1 type LA-HLC, paragonite, and minor beidellite formed at a relatively high concentration of dissolved Al, while beidellite with a small amount of 2:1 type LA-HLC was produced at a low concentration of dissolved Al. The resultant 2:1 type LA-HLC exhibited poor swelling ability when treated with ethylene glycol. A solid-state transformation mechanism was proposed for the transformation based on the HRTEM images and EDS analyses, which showed that lattice fringes representing (001) faces of 2:1 type layered aluminosilicates (2:1 type LA) were parallel to the (020) direction of boehmite. The successful transformation of boehmite into 2:1 type LA provides insights to well understand the formation of 2:1 type LA in geological processes and offer a facile preparation approach for the synthesis of 2:1 type LA with different layer charges. •Boehmite could be transformed into 2:1 type layered aluminosilicates under hydrothermal conditions.•2:1 type layered aluminosilicates with high layer charges exhibited poorly swelling ability after ethylene glycol treatment.•Layer charges of 2:1 type layered aluminosilicates were estimated based upon the 29Si NMR spectra results.•Dissolved Al from boehmite had effects on the layer charge density of 2:1 type layered aluminosilicates.