The Effect of Dry Grinding on Antigorite from Mulhacen, Spain

A. Drief and F. Nieto
Departamento de Mineralogía y Petrología, Instituto Andaluz de Ciencias de la Tierra, Universidad de Granada-C.S.I.C., Av. Fuentenueva s/n, 18002 Granada, Spain

Abstract: Alteration of the crystal structure of Mulhacén antigorite caused by dry, vibration grinding was investigated by X-ray diffraction (XRD), infrared spectroscopy (IR), thermal analyses (TG), grain-size distribution, and transmission and analytical electron microscopy (TEM, AEM). Grinding for 1 min reduces particles to a size ideal for IR and TG. With prolonged grinding, XRD and electron diffraction patterns showed that the crystal structure was affected mainly along the c axis, causing a partial loss of crystallinity. TG analyses revealed that vibration grinding modified mineral dehydration, accelerating the dehydroxylation process and transforming the structural OH to adsorbed water in the resulting matrix. IR spectra and AEM showed that grinding affected the tetrahedral sheet to a lesser extent than the octahedral sheet. Partial release of Mg by preferential destruction of the octahedral sheet after 10 min grinding produced an increase in the Si/Mg ratio in semi-crystalline particles, whereas the amorphous material product after 120 min showed the same composition as the initial antigorite. TEM and grain-size distribution results revealed that grinding led to a general decrease in particle size at the beginning of the experiment followed by the agglomeration of ultrafine particles as grinding proceeded.

Key Words: Antigorite • Crystallinity • Dehydroxylation • Dry Grinding • IR Spectra • Serpentine • Thermal Analysis

Clays and Clay Minerals; August 1999 v. 47; no. 4; p. 417-424; DOI: 10.1346/CCMN.1999.0470404
© 1999, The Clay Minerals Society
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