Muscovite dissolution kinetics as a function of pH and time at 70°C

Details Muscovite dissolution kinetics as a function of pH and time at 70°C Muscovite dissolution kinetics as a function of pH and time at 70°C

Jul 1989

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1989gecoa..53.1493k&link_type=abstract

Geochimica et Cosmochimica Acta, vol. 53, Issue 7, pp.1493-1501

Physics

12

Scientific paper

The dissolution rate of muscovite at 70°C was determined using a single-pass, flow-through apparatus. Dissolution rate data were obtained at approximately unit pH interval over the pH range 1.4 to 11.8 in 11 separate experiments, each lasting 50 days. The muscovite dissolution rates were defined by the silica, aluminum and/or potassium release rates to solution. Under most pH conditions the dissolution at steady-state was congruent or nearly so. Speciation-solubility calculations made using the geochemical modeling code EQ3NR indicate that the fluids were maintained far from equilibrium with respect to muscovite and undersaturated with respect to possible secondary minerals. Under all pH conditions we initially observe a transiently elevated dissolution rate. The dissolution rate gradually approaches a limiting (steady-state) value, which we interpret as the dissolution rate of the bulk mineral. From pH 1 to approximately pH 5, the limiting rate for muscovite dissolution at 70°C varies negatively with pH, and the rate constant, k , is 10 -14.7 mol/cm 2 · s. Under acidic conditions the dissolution rate is proportional to-0.37 pH. As pH is increased at 70°C, the rate of dissolution becomes essentially pH independent, and k is 10 -16.6 mol/cm 2 · s. At about pH 7 and higher the limiting rate for muscovite dissolution varies positively with hydroxyl ion activity, and the dissolution rate is proportional to +0.22 pH. Under alkaline conditions k is 10 -18.1 mol/cm 2 · s at 70°C.

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