Particle-size reduction of dickite by ultrasound treatments: Effect on the structure, shape and particle-size distribution

This paper reports on the effects of ultrasound treatment on dickite from Tragos, Mangualde, in Portugal. Ultrasonic treatment modifies both particle size and morphology. The elongated crystals observed in the sample are broken up, after their treatment, along the cleavage planes 001 and 110, mainly along the largest direction (a axis), into smaller units that retain the typical lamellar morphology of the starting crystals. The decrease in particle size results in a significant increase in the specific surface area (SSA). When compared to the structure of the untreated dickite, X-ray Diffraction (XRD) patterns of the sonicated sample do not reveal appreciable structural modifications. On the contrary, previous results reported for sonicated kaolinite show a progressive decrease of its structural order. The corresponding Fourier Transform Infrared (FTIR) spectra show a decrease of the intensity of the OH stretching bands, which are related to the loss of some OH groups due to prototropic mechanism.