Thermodynamics of aragonite-strontianite solid solutions: results from stoichiometric solubility at 25 and 76/sup 0/C
Dissolution of synthetic strontianite-aragonite solid solutions was followed analytically to stoichiometric saturation using large solid to solution ratios in CO/sub 2/-H/sub 2/O solution at 25 and 76/sup 0/C. The compositional dependence of the equilibrium constant was calculated from the composition of saturated (stoichiometric) solutions and used to calculate the activities and activity coefficients of CaCO/sub 3/ and SrCO/sub 3/ in the solid Ca/sub (1-x)/Sr/sub x/CO/sub 3/ at 25 and 76/sup 0/C. The results show that the solid-solution is not regular by unsymmetrical. The experimental results indicate the Henry's law coefficients of SrCO/sub 3/ in aragonites containing 0 to 6 mole percent SrCO/sub 3/ are approximately 91 +/- and 23 +/- 1 at 25 and 76/sup 0/C, respectively, and for strontianites the Henry's law coefficients and applicable compositional ranges are approximately 7.3 +/- 0.3 (0.84 less than or equal to x less than or equal to 1.00) and 3.3 +/- 0.5 (0.50 less than or equal to x less than or equal to 1.00) at 25 and 76/sup 0/C, respectively. Marine aragonites are neither at equilibrium nor stoichiometric saturation with surface sea water. The experimentally observed distribution coefficient of Sr in aragonite is 12 times larger than the calculated equilibrium value (0.095) at 25/sup 0/C. Naturally occurring strontianites contain large amounts of calcium primarily because Ca/Sr ratios in natural waters are typically large. Neither equilibrium no stoichiometric saturation is observed at 76/sup 0/C during laboratory recrystallization of strontianite-aragonite solid solutions even after apparent 100 percent conversion to a narrow secondary composition of demonstration of a nearly constant composition system for periods of 300 hours.
- Research Organization:
- Geological Survey, Reston, VA (USA)
- OSTI ID:
- 6938694
- Journal Information:
- Geochim. Cosmochim. Acta; (United States), Journal Name: Geochim. Cosmochim. Acta; (United States) Vol. 51:6; ISSN GCACA
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
580400* -- Geochemistry-- (-1989)
ALKALINE EARTH METAL COMPOUNDS
ALKALINE EARTH METALS
ARAGONITE
CALCIUM
CALCIUM CARBONATES
CALCIUM COMPOUNDS
CARBON COMPOUNDS
CARBONATE MINERALS
CARBONATES
CHEMICAL COMPOSITION
CHEMISTRY
CONCENTRATION RATIO
DISPERSIONS
DISSOLUTION
ELEMENTS
EQUATIONS
EQUATIONS OF STATE
EQUILIBRIUM
GEOCHEMISTRY
METALS
MINERALS
MIXTURES
OXYGEN COMPOUNDS
PHYSICAL PROPERTIES
SATURATION
SOLID SOLUTIONS
SOLUBILITY
SOLUTIONS
STOICHIOMETRY
STRONTIUM
STRONTIUM COMPOUNDS
THERMODYNAMIC PROPERTIES
THERMODYNAMICS