Dissolution of silica from montmorillonite: effect of solution chemistry |
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| Authors: | RW Lahann HE Roberson |
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| Institution: | Department of Geological Sciences and Environmental Studies, State University of New York at Binghamton, Binghamton, NY 13901, U.S.A. |
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| Abstract: | The rate of silica removal from two montmorillonites (Chambers and Polkville) has been measured as a function of time, temperature, solution composition, and exchange ion on the clay. Silica removal rate increased with temperature from 200 to 350°C, decreased with time, and could be approximated initially by a parabolic rate law. Solution composition influenced silica removal rate by determining the exchange population of the clay; silica removal is most rapid when K-exchange ions are present. Thus increasing the concentration of K+ accelerated silica removal, whereas increasing the concentration of Na+, Ca2+, and Mg2+ inhibited silica removal. Activation energies for silica removal range from 5 to 10 kcal/mol. The largest values are associated with the largest concentrations of inhibitor ions in solution. Activation energies of this magnitude suggest that the rate-limiting step for silica removal is transport through a hydrated, expanded interlayer space. Application of experimental results to diagenesis in moderately to deeply buried sediments suggests that K+ uptake by montmorillonite may precede and accelerate illite formation. |
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