The crystal growth of smectite: A study based on the change in crystal-chemistry and morphology of saponites with synthesis time

Smectites are 2:1 type swelling clay minerals widely distributed in the Earth’s crust. The unique structures and properties endow them with various applications in many fields. However, their growth process and mechanism are still not completely understood. In this study, we tried to understand this growth process and pattern from the perspective of crystal-chemistry and morphology. Smectites were synthesized by hydrothermal treatment of starting materials at 220°C under autogenous pressure from 0.25 to 30 days. The starting materials were obtained from mixtures of Mg- and Ni- smectite precursors synthesized at 150°C for 1 day with identical molar weight. The starting materials, as well as further synthesized samples, are identified as smectite, saponite type, by X-ray diffraction analysis (XRD), and Fourier-transform infrared (FTIR) spectroscopy. The FTIR spectra of the starting material exhibited the vMg3OH and vNi3OH bands only. After the hydrothermal treatment (220°C) of the starting materials, the vM...