Computer Science
Scientific paper
Dec 1988
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1988gecoa..52.2795c&link_type=abstract
Geochimica et Cosmochimica Acta, vol. 52, Issue 12, pp.2795-2807
Computer Science
17
Scientific paper
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 2 O--HCl and D 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 2 O--HCl solutions ( pH = 1.7) are 33% more rapid than in D 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.
Arnold George W.
Casey William H.
Westrich Henry R.
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