Abstract
Using in situ atomic force microscopy, the growth rates of the obtuse and acute step
orientations on the calcite surface were measured at two saturation indices as a
function of the aqueous calcium-to-carbonate ratio and aqueous strontium concentration.
The amount of strontium required to inhibit growth was found to correlate with the
aqueous calcium concentration, but did not correlate with carbonate. This suggests that
strontium inhibits attachment of calcium ions to the reactive sites on the calcite surface.
Strontium/calcium cation exchange selectivity coefficients for those sites, Kex, of 1.09 ±
0.09 and 1.44 ± 0.19 are estimated for the obtuse and acute step orientations,
respectively. The implication of this finding is that to avoid poisoning calcite growth, the
concentration of calcium should be higher than the quotient of the strontium
concentration and Kex, regardless of saturation state. Additionally, analytical models of
nucleation and propagation of steps are expanded from previous work to capture growth
rates of these steps at multiple saturation indices and the effect of strontium. This work
will have broader implications for naturally occurring or engineered calcite growth, such
as to sequester subsurface strontium contamination.
