Characterization of Synthetic Na-Beidellite

J. Theo Kloprogge1, J. Ben H. Jansen1 and John W. Geus2
1 Institute of Earth Sciences, Department of Geochemistry, University of Utrecht Budapestlaan 4, P.O. Box 80.021, 3508 TA Utrecht, The Netherlands
2 Analytical Chemical Laboratory, Department of Inorganic Chemistry, University of Utrecht Croesestraat 77a, 3522 AD Utrecht, The Netherlands

Abstract: Na-beidellite, a member of the smectite group, was grown hydrothermally from a gel of composition 0.35Na2O·2.35Al2O3·7.3SiO2 in NaOH solutions at a pH between 7.5 and 13.5, a pressure of 1 kbar, and a temperature of 350°C. The synthetic Na-beidellite was characterized by means of scanning electron microscopy, X-ray powder diffraction, infrared spectroscopy, electron microprobe, inductively coupled plasma-atomic emission spectroscopy, and thermogravimetric analysis. The unit-cell parameters of the orthorhombic cell are: a = 5.18, b = 8.96, and c = 12.54 Å. The cation-exchange capacity was determined to be 70 meq/100 g. A maximum of 40 wt. % water was present and reversibly lost by heating to about 55°C. The loss of water caused a decrease of the basal spacing to 9.98 Å. At temperatures ≥600°C, the Na-beidellite started to dehydroxylate, reaching its maximum in the range 600°–630°C. At 1100°C the remaining solid recrystallized to Al6Si2O13 (mullite) and SiO2 (cristobalite).

Key Words: Beidellite • Cation-exchange capacity • Scanning electron microscopy • Synthesis • Thermal analysis • X-ray powder diffraction

Clays and Clay Minerals; August 1990 v. 38; no. 4; p. 409-414; DOI: 10.1346/CCMN.1990.0380410
© 1990, The Clay Minerals Society
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