Surface chemistry of labradorite feldspar reacted with aqueous solutions at pH = 2, 3, and 12
- Sandia National Laboratories, Albuquerque, NM (USA)
The reaction of feldspar with an aqueous solution is examined by complementing dissolution rate measurements with analysis of mineral surface chemistry. Rates of feldspar dissolution were measured in H{sub 2}O-HCl and D{sub 2}O-DCl solutions. These measurements were combined with elastic recoil detection (ERD) analysis of hydrogen isotope concentration, and Rutherford backscattering analysis (RBS) of silicon, aluminum and calcium concentrations near the surface of the mineral. Dissolution rates of labradorite feldspar in H{sub 2}O-HCl solutions (pH = 1.7) are 33% more rapid than in D{sub 2}O-DCl mixtures (pD = 1.7). The depth of penetration and inventory of hydrogen in the feldspar is a strong function of solution pH, temperature, and reaction time. Hydrogen infiltrates the feldspar more extensively from an acidic solution than from a basic solution, and complete isotopic exchange between the hydration layer and water proceeds in time on the order of hours. The hydrolysis of bridging Si-O-Al bonds by reaction with a strongly acidic solution for several hundreds of hours progresses to depths of several hundreds of Angstroms into the mineral. Calcium is also removed from the mineral to this depth during reaction with an acidic solution. The composition of the reacted surface, however, cannot be explained solely on the basis of ion exchange or depolymerization reactions. The data suggest that the silicon-rich surface of feldspar continually repolymerizes during reaction, and that this repolymerization eliminates hydrogen from the hydration layer.
- DOE Contract Number:
- AC04-76DP00789
- OSTI ID:
- 5014080
- Journal Information:
- Geochimica et Cosmochimica Acta; (USA), Journal Name: Geochimica et Cosmochimica Acta; (USA) Vol. 52:12; ISSN GCACA; ISSN 0016-7037
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
580000* -- Geosciences
CHEMICAL ANALYSIS
CHEMICAL BONDS
CHEMICAL REACTION KINETICS
CHEMICAL REACTIONS
CHEMISTRY
CONCENTRATION RATIO
DECOMPOSITION
DISSOLUTION
ELASTIC SCATTERING
FELDSPARS
GEOCHEMISTRY
HYDROCHLORIC ACID
HYDROGEN COMPOUNDS
HYDROGEN ISOTOPES
HYDROLYSIS
INORGANIC ACIDS
ION EXCHANGE
ISOTOPE RATIO
ISOTOPES
ISOTOPIC EXCHANGE
KINETICS
LYSIS
MINERALS
PH VALUE
QUANTITATIVE CHEMICAL ANALYSIS
REACTION KINETICS
RUTHERFORD SCATTERING
SCATTERING
SOLVENTS
SOLVOLYSIS
STRUCTURAL CHEMICAL ANALYSIS
SURFACE PROPERTIES
THERMODYNAMIC ACTIVITY