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.
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