Abstract
The effect of Mg 2+ on the kinetics of calcite crystal growth was investigated using calcite-seeded solutions with a pH-stat system. Five different solution compositions with the same degree of supersaturation with respect to calcite but different CO 3 2−/Ca 2+ molar ratios were employed in this study. In the presence of Mg 2+, calcite crystal growth rates showed a linear decrease with increasing Mg 2+ concentration for the five different solutions employed. By normalizing the crystal growth rate in the presence of Mg 2+ to that in the absence of Mg 2+, the rate reductions in the five solutions converge to a single line when plotted against the molar ratio of Mg 2+/Ca 2+. The widely used “empirical degree of supersaturation model” and the simple “Langmuir adsorption model” cannot explain the observed effects of the Mg 2+/Ca 2+ ratio on the inhibition of calcite crystal growth. Instead, a competitive Langmuir adsorption model involving Ca 2+ and Mg 2+ was shown to better fit the experimental data.
Published Version
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