Calcite Growth Rates As a Function of Aqueous Calcium-to-Carbonate Ratio, Saturation Index, and Inhibitor Concentration: Insight into the Mechanism of Reaction and Poisoning by Strontium

Abstract

Using in situ atomic force microscopy, the growth rates of the obtuse and acute step orientations on the {101̅ 4} 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, suggesting that strontium inhibits attachment of calcium ions to reactive sites on the calcite surface. Strontium/ calcium cation exchange selectivity coefficients, K ex , are estimated at 1.09 ± 0.09 and 1.44 ± 0.19 for reactive sites on the obtuse and acute step orientations, respectively. The implication of this work is that, to avoid poisoning calcite growth, the concentration of calcium should be higher than the quotient of the strontium concentration and K ex , regardless of the saturation index. Previous analytical models of nucleation of kink sites on steps are expanded to include growth rates at multiple saturation indices and the effect of strontium. The rate constants for calcium attachment are found to be similar for the two step orientations, but those of carbonate vary significantly. This work will have implications for natural or engineered calcite growth, such as to sequester subsurface strontium contamination.

Kinetics and mechanisms of cadmium carbonate heteroepitaxial growth at the calcite (101¯4) surface

“…4a, providing Fig 4b. This is consistent with the observation, previously reported in the literature for calcite growth, that the calcite step velocities and, more generally, the calcite growth rate decrease as the calcium-to-carbonate ratio increases (Nehrke et al, 2007;Larsen et al, 2010;Stack and Grantham, 2010;Bracco et al, 2012;Gebrehiwet et al, 2012). Additionally, the growth of 2D nuclei takes place at [Cd 2+ ] 0 P 0.025 mM (Fig.…”

Growth Rate and Morphology of a Single Calcium Carbonate Crystal on Polysulfone Film Measured with Time Lapse Raman Micro Spectroscopy

“…The growth rate depends on solution parameters, such as: the supersaturation index (SI), the ionic strength (I), the pH and the [Ca 2+ ]/[CO 3 2-] ratio [8,[32][33][34][35]. Table 1 compares the results from this study with results from the literature [33][34][35].…”

“…These studies have revealed a dependence of growth kinetics upon parameters such as pH, supersaturation ratio, ionic strength or temperature [2][3][4]. Atomic Force Microscopy (AFM) has been extensively used to study mechanisms and growth rates of single crystals from solution [5][6][7], including calcite crystals [1,[8][9][10][11][12][13][14]. The high resolution of AFM can visualize monomolecular steps on atomically flat crystal surfaces.…”

Precipitation in Pores: A Geochemical Frontier

“…A fi nal example metal contaminant is strontium-90, which is found sometimes as a legacy waste from nuclear weapons production (Riley et al 1992). Due to the similar chemical behavior and size of strontium and calcium, strontium incorporates into the calcite (CaCO 3 ) crystal lattice (Wasylenki et al 2005;Bracco et al 2012). If one could therefore induce precipitation of a strontium-rich calcite, the contaminant would be trapped as a solid phase and immobilized.…”

“…Due to the relatively small difference in rate constants in these systems, the range of solution conditions over which this might exist is limited but this may not always be true. In fact, mineral growth kinetics measurements such as these may actually refl ect this condition already since possible transport limits are often poorly controlled or verifi ed; in Bracco et al (2012), the step velocity was measured as a function of fl ow rate under one condition, but not under all calcium-to-carbonate ratios so the rate constant for carbonate quoted above may refl ect a partial transport control over carbonate attachment.…”