Other
Scientific paper
Aug 1979
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1979gecoa..43.1223f&link_type=abstract
Geochimica et Cosmochimica Acta, vol. 43, Issue 8, pp.1223-1239
Other
10
Scientific paper
Speciation of aqueous magnesium in the system MgO-SiO 2 -H 2 O-HCl in supercritical aqueous fluids has been investigated using standard rapid-quench hydrothermal techniques and a modification of the Ag + AgCl buffer method ( and , 1973. Am. J. Sci . 267 , 268-286). A concentric double-capsule charge was utilized. The outer gold capsule contained the assemblage talc + quartz + Ag + AgCl + H 2 O - MgCl 2 fluid; the inner platinum capsule, Ag + AgCl + H 2 O - HCl fluid. During the experiments, f H 2 and thus f HCl equilibrated between the two capsules. After quenching, measurement of the chloride concentration in the fluid in the inner capsule and total magnesium in the fluid in the outer capsule defines the concentrations of HCl and Mg that coexist with talc + quartz in the outer capsule. Changes in the measured molality of HCl as a function of the total magnesium concentration at constant P and T were used to identify the predominant species of magnesium in the hydrothermal fluid. Experimental results showed that at 2000 bar, MgCl° 2 is the predominant species above 550°C and Mg 2+ , below 400°C. Data at intermediate temperatures when combined with the dissociation constant for HCl were used to obtain the dissociation constant for MgCl° 2 . The results of these experiments were combined with results from experiments using Ag + AgCl in conjunction with the oxygen buffer, hematite-magnetite, to obtain the equilibrium constant for the reaction from which the difference in Gibbs free energy of MgCl° 2 and HC1° was obtained as a function of temperature at 1000, 1500 and 2000 bar pressure, Solubility constants for brucite. forsterite, chrysotile, and talc were calculated.
Frantz John D.
Popp Robert K.
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