Dissolution rates of prehnite, epidote, and albite

Journal Article · Fri Nov 01 00:00:00 EST 1991 · Geochimica et Cosmochimica Acta; (United States)

OSTI ID:5201175

Rosemary, N M ^[1]

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1. Stanford Univ., CA (United States)

Dissolution rates of prehnite and epidote in aqueous solutions were measured in the temperature range 25 to 90C, and as a function of pH. The dissolution rate of albite was measured at pH 1.4 at temperatures between 25 and 90C. Batch experiments using low ionic strength pH buffers in constant temperature water batch or ovens provided data on cumulative element release as a function of time. Steady state Si, Ca, Na, and Al release data obtained from these experiments were used to obtain limiting dissolution rates, where the term limiting rate denotes dissolution of a bulk mineral under conditions where it is far from equilibrium with the fluid. At 90C and at pH 1.4 to 6, prehnite and epidote dissolution rates decrease and are proportional to approximately {minus}0.3 pH for prehnite and {minus}0.2 pH for epidote. Above pH 6, prehnite dissolution becomes pH independent, by epidote dissolution increases with rates that are proportional to between +0.3 and +0.6 pH. Prehnite and epidote dissolution is linear and stoichiometric at low pH. At pH greater than 7, both minerals initially display preferential release of Si and Al relative to Ca; however, with increasing reaction dissolution becomes stoichiometric. This suggests that a Ca-enriched layer forms but reaches a steady state thickness which does not impede subsequent linear stoichiometric release. At pH 1.4, the limiting dissolution rate for albite is linear and stoichiometric. At pH 1.4, the activation energies are 18.12 {plus minus} 0.81 kcal mol{sup {minus}1} for prehnite, 19.76 {plus minus} 1.2 kcal mol{sup {minus}1} for epidote and 17.07 {plus minus} 1.6 kcal mol{sup {minus}1} for albite. At pH 6.5, the activation energy for prehnite dissolution is 20.73 {plus minus} 3.2 kcal mol{sup {minus}1}.

• OSTI ID: 5201175
• Journal Information: Geochimica et Cosmochimica Acta; (United States), Vol. 55:11; ISSN 0016-7037
• Country of Publication: United States
• Language: English

Related Subjects

58 GEOSCIENCES
ALBITE
CHEMICAL REACTION KINETICS
DISSOLUTION
CALCIUM HYDROXIDES
EPIDOTES
HYDROTHERMAL SYSTEMS
ROCK-FLUID INTERACTIONS
GEOCHEMISTRY
HYDROTHERMAL ALTERATION
PH VALUE
SOLUBILITY
STOICHIOMETRY
ALKALINE EARTH METAL COMPOUNDS
ALUMINIUM COMPOUNDS
ALUMINIUM SILICATES
CALCIUM COMPOUNDS
CALCIUM SILICATES
CHEMISTRY
FELDSPARS
GEOTHERMAL SYSTEMS
HYDROGEN COMPOUNDS
HYDROXIDES
IRON COMPOUNDS
IRON SILICATES
KINETICS
MINERALS
OXYGEN COMPOUNDS
REACTION KINETICS
SILICATE MINERALS
SILICATES
SILICON COMPOUNDS
TRANSITION ELEMENT COMPOUNDS
580000* - Geosciences