Sustainable Materials by Mimicking Natural Weathering

The chemical weathering of silicate rocks is of significance to decipher the interaction between minerals and fluids in lithospheric evolution, and a sufficient utilization of this knowledge is helpful to comprehensively understand the value of mineral weathering in materials synthesis and element cycling. In this study, hydrothermal experiments were carried out to investigate the accelerated transformation between muscovite and kaolinite, two phyllosilicates. Nanokaolinite with a diameter of about 400-500 nm and thickness of about 20-50 nm was synthesized from muscovite under hydrothermal conditions. The XRD result of the starting muscovite precursor showed a (001) d-spacing of 10.13 Å consistent with its 2:1 structure of tetrahedral-octahedral-tetrahedral (TOT) sheets along with the existence of interlayer K+ ions. After muscovite transformation to kaolinite, the characteristic reflection (001) of as-synthesized kaolinite phase was determined to be 7.17 Å. The transformation of muscovite to kaolinite was characterized by several techniques such as X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), high-resolution transmission electron microscopy (HRTEM), and magic-angle-spinning nuclear magnetic resonance spectroscopy (MAS NMR). The transformation mechanism of muscovite to kaolinite is hypothesized as a partial dissolution and localized rearrangement followed by recrystallization. Here, nanokaolinite was prepared rapidly by hydrothermal conversion of muscovite, which served as a precursor. The synthetic nanokaolinite has many potential applications in paper and other coatings because of its ideal size, purity, and morphology, and the released K as niter, KNO3 during the kaolinite synthesis can serve as a K-fertilizer.