Experimentally reversed portlandite and brucite solubilities in pure H/sub 2/O from 300 to 600/degree/C and 1 to 3 Kbar

Conference · Tue Jan 01 04:00:00 EST 1985 · Geol. Soc. Am., Abstr. Programs; (United States)

OSTI ID:5811024

Walther, J V

In the portlandite runs the molality of Ca decreases with increasing pressure at constant temperature. For instance, at 2 Kbar log molalities at 300, 400, 500 and 600/degree/C give values of -2.34, -2.71, -3.18 and -4.18, respectively. At 500/degree/C, pressures of 1, 2 and 3 Kbar yield values of -4.40, -3.18 and -2.65. Distribution of species in solution can be calculated with the aid of data from Helgeson and co-workers assuming Ca/sup ++/ is the dominant Ca species. These calculated Ca concentrations are within /plus minus/0.2 log units of experimental values in most cases. Although the computed pH's are close to 2 units greater than neutral, the solutions apparently contained no significant Ca(OH)/sup +/ or Ca(OH)/sub 2(aq)/. Concentrations of Mg in the brucite runs show a sigmoidal behavior at 2 Kbar as a function of temperature with log molalities of Mg of -4.00, -4.28, -4.14, and -4.60 at 350, 450, 550, and 600/degree/C, respectively. Values at 1 Kbar are lower and decrease monotonically from 350/degree/C to 550/degree/C. Based on available thermodynamic data for Mg/sup ++/ it appears that either Mg(OH)/sup +/ or Mg(OH)/sub 2(aq)/ is the dominant Mg species in solution. The solubility behavior at 2 Kbar is similar to corundum where a neutral aqueous complex is proposed, suggesting that Mg(OH)/sub 2(aq)/ is the dominant species in the 2 Kbar runs. These investigations aid in defining the minimum extent of mass transfer of Ca and Mg during geological processes. Coupled with association constants of chloride complexes solubilities of Ca- and Mg-bearing minerals in dilute chloride solutions can be calculated. Additionally, the portlandite solubilities give a basis for interpreting calcite solubilities in H/sub 2/O-CO/sub 2/ mixtures.

• Research Organization: Northwestern Univ., Evanston, IL (USA)
• OSTI ID: 5811024
• Report Number(s): CONF-8510489-
• Conference Information: Journal Name: Geol. Soc. Am., Abstr. Programs; (United States) Journal Volume: 17
• Country of Publication: United States
• Language: English

Related Subjects

58 GEOSCIENCES
580400* -- Geochemistry-- (-1989)
ALKALINE EARTH METAL COMPOUNDS
CALCIUM COMPOUNDS
CALCIUM HYDROXIDES
CHEMISTRY
GEOCHEMISTRY
HYDROGEN COMPOUNDS
HYDROXIDES
KINETICS
MAGNESIUM COMPOUNDS
MAGNESIUM HYDROXIDES
OXYGEN COMPOUNDS
PH VALUE
PRESSURE EFFECTS
REACTION KINETICS
SOLUBILITY
TEMPERATURE EFFECTS
THERMODYNAMICS