AVS 49th International Symposium
    Electrochemistry and Fluid-Solid Interfaces Monday Sessions
       Session EC+SS-MoA

Paper EC+SS-MoA6
Solution Composition Effects on Calcite Dissolution and Growth Processes

Monday, November 4, 2002, 3:40 pm, Room C-104

Session: Liquid-Solid Interfaces & Nanoscale Electrochemistry
Presenter: A.S. Lea, Pacific Northwest National Laboratory
Authors: A.S. Lea, Pacific Northwest National Laboratory
J.E. Amonette, Pacific Northwest National Laboratory
D.R. Baer, Pacific Northwest National Laboratory
N.G. Colton, Pacific Northwest National Laboratory
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We have examined the influence of a number of solution impurities on step motion and shape of pits during dissolution and growth on the cleavage surface of calcite. Mg@super 2+@, in contrast to the other impurities (Ca@super 2+@, Mn@super 2+@, Sr@super 2+@, Co@super 2+@, Mg@super 2+@, and CO@sub 3@@super 2-@) we have studied, exhibits unique behavior by uniformly enhancing dissolution rather than retarding dissolution. Of the impurities that retard dissolution, Sr@super 2+@ and CO@sub 3@@super 2-@ demonstrate selective sorption to the most sterically accessible step site resulting in a substantial slowing of dissolution of this type of step. Mn@super 2+@ and Co@super 2+@, however, retard dissolution uniformly due to non-selective step sorption. For Mn@super 2+@, Sr@super 2+@, Co@super 2+@, and Ca@super 2+@, little impact on dissolution rate is seen until a threshold concentration is reached, whereupon near complete frustration of dissolution occurs upon further increase in impurity concentration. These results can be explained using a simple terrace-ledge-kink model that incorporates site-blocking and works equally well with metal ion or carbonate ion pair concentrations. This site-blocking model cannot explain the enhanced dissolution behavior of calcite in the presence of Mg@super 2+@. In calcite growth processes, Ca@super 2+@ ions demonstrate preferred kink sorption sites, manifested by the unique pit shape observed during pit fill-in. @FootnoteText@ This work was supported by the Office of Basic Energy Science, Geosciences Research Program, U. S. Department of Energy. The work was conducted in the Environmental Molecular Sciences Laboratory, a U.S. Department of Energy user facility located at Pacific Northwest National Laboratory. .