Publication date: 15 May 2014
Source:Journal of Crystal Growth, Volume 394
Author(s): C.H. van der Weijden , R.D. van der Weijden
The role of bicarbonate on the growth rate of calcite in thermo-, chemo- and pH-stated experiments was observed in a foregoing paper by Van der Weijden et al. (1997) [31] . The data are used here to explore especially the effect of bicarbonate on the calcite growth rate in more detail. The experimental range of pH is from 7.6 to 8.9, the initial seed concentrations are 165±12Ω ) are 2.1–4. In the pH-range of 7.6–8.9 the activity ratios of to decrease from 510 to 30. The effect of increasing bicarbonate on R lin (mk lin , which decreases with a factor of 2.8 in the indicated pH-range. The contribution of bicarbonate to R lin is also apparent in plots of R lin versus the free dissolved calcium to carbonate ratios (r ) for a selection of results with Ω =2.7±0.7 in the pH-range from 7.6 to 8.9. Where others found a dependence of R lin with a maximum at r ≈1, symmetrically decreasing on either side of this value, it is shown here that R lin increases at r >1 for higher values of free dissolved bicarbonate, in this case at pH 7.6. In the present paper a kinetic model relating the growth rate (R ) to the activities of and successfully describes the data with associated k -values for both species in a narrow Ω-range. Implicitly, these ion pairs represent the effect of Ca2+, and on the growth rate.
Source:Journal of Crystal Growth, Volume 394
Author(s): C.H. van der Weijden , R.D. van der Weijden