Reaction mechanism during hydrothermal alteration of K-feldspar under alkaline conditions and nanostructures of the producted tobermorite

K-feldspar alteration in alkaline fluid generally generates layered aluminosilicate and other minerals. Previous studies mainly focused on the reaction mechanism and alteration products, however, little is known on the mechanisms of alteration and the secondary products at nano-scale. We studied the alternation mechanism of K-feldspar under extreme alkaline conditions (190 degrees C, 24h, initial pH = 12. 4) and the microstructure of tobermorite as one of the alternation products. Characterizations of X-ray powder diffraction, scanning electron microscopy and energy dispersive spectroscopy reveal that the secondary phases resulting from alternation of K-feldspar are mainly a mixture of tobermorite, hydrogrossular and calcite. Novel nanometer-scale measurements by high resolution analytical transmission electron microscope reveal the formation of an alteration rim of porous amorphous material nanometer thick at the interface of the K-feldspar and secondary phase, and the interface shows spatial and structural discontinuity. Coupled interfacial dissolution reprecipitation (CIDR) explains the sharp interface and the formation of the amorphous layer. The nanostructure measurements of the fibrous tobermorite crystals in the alteration products show that the pore diameter of tobermorite has a range of 0 - 160nm, and the average pore diameter is about 40nm. The nano pores and nano channels in tobermorite may promote the solubility of ions and gases and affect the chemical balance of the surrounding fluid. This provides an important basis for the application of layered aluminosilicate as natural and industrial adsorption materials and catalysts.