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 00:00:00 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-
• Journal Information: Geol. Soc. Am., Abstr. Programs; (United States), Vol. 17; Conference: 98. annual meeting of the Geological Society of America, Orlando, FL, USA, 28-31 Oct 1985
• Country of Publication: United States
• Language: English

Related Subjects

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