Release of water and gases from halite crystals
Zimmermann, Jean Louis; Moretto, Robert
European Journal of Mineralogy Volume 8 Number 2 (1996), p. 413 - 422
published: Apr 26, 1996
manuscript accepted: Dec 6, 1995
manuscript received: May 29, 1995
ArtNo. ESP147050802021, Price: 29.00 €
Abstract Qualitative and quantitative analyses of fluids, by thermogravimetry and by coupled manometrymass spectrometry, were carried out on clear halite crystals with few macroscopic inclusions (1 mm) and on cloudy halite crystals with many small inclusions (less than 30 μm) of the Bresse evaporitic basin (France). Water is the most abundant fluid in the two types of halite and there is up to five times more water in cloudy halite (0.2-0.5 wt%). Carbon dioxide and hydrogen contents are much lower: CO2/H2O < 0.01 and H2/H2O < 0.005. Organic compounds, with CH4, are always present (< 0.05% H2O), and are twice as abundant in cloudy samples. There are also traces of nitrogen and, in some samples, hydrogen sulphide and sulphur dioxide. The release histograms and the kinetics characteristics of the release of each fluid in the clear and cloudy halites were determined by an incremental heating study, from 80 to 460 °C. Nitrogen is released below 240 °C and is probably of atmospheric origin. About 90% of the water is expelled from 280 to 420 °C, corresponding to the decrepitation of inclusions. Likewise, CO2 liberation occurs mainly between these temperatures, but above 420 °C an additional part comes from carbonate dissociation through heating. Hydrogen, whose content is less than 0.5% that of H2O, is extracted continuously from 200 to 460 °C, with a single activation energy of 30kcal/mol; more than 60% of its extraction occurs above 360 °C. Most of the hydrogen originates from dissociation of organic matter present in the halite crystals and from water reduction during heating.