HR: 1330h
AN: B12C-0792    [PDF]
TI: Interaction of Magnesium and Inorganic Carbon Species with the Dissolving Calcite Surface
AU: Amonette, J E
EM: jim.amonette@pnl.gov
AF: Pacific Northwest National Laboratory, Chemical Sciences Division P. O. Box 999, K8-96, Richland, WA 99352 United States
AU: * Arvidson, R S
EM: rsa4046@ruf.rice.edu
AF: Rice University, Dept. of Earth Science - MS 126 P.O. Box 1892, Houston, TX 77251-1892 United States
AU: Collier, M
EM: spaceman@rice.edu
AF: Rice University, Dept. of Earth Science - MS 126 P.O. Box 1892, Houston, TX 77251-1892 United States
AU: Davis, K J
EM: kjdavis@rice.edu
AF: Rice University, Dept. of Earth Science - MS 126 P.O. Box 1892, Houston, TX 77251-1892 United States
AU: Vinson, M
EM: mvinson@rice.edu
AF: Rice University, Dept. of Earth Science - MS 126 P.O. Box 1892, Houston, TX 77251-1892 United States
AU: Luttge, A
EM: aluttge@rice.edu
AF: Rice University, Dept. of Earth Science - MS 126 P.O. Box 1892, Houston, TX 77251-1892 United States
AB: Much of the current focus of biomineralization studies involves investigation of the processes by which calcifying organisms orchestrate various nucleation and growth reaction mechanisms to bring about a selective result. These strategies must include the ability to incorporate or exclude impurities, calibrate saturation index, and organize other aspects of interfacial chemistry that in turn control the overall reactivity and behavior of the surface. In nearshore marine or terrestrial environments, the stress imposed by variations in salinity, saturation state, ratios of major and minor solution components, temperature, and other environmental variables may have selected for effective chemical strategies by which calcifiers can maintain skeletal integrity even in marginally saturated or undersaturated conditions. This notion is the motivation for developing an understanding of the mechanistic role of Mg$^{2+}$ and other components in undersaturated solutions, and it is our goal to use these observations to build a general model for the interaction of lattice and impurity components in dissolution reactions. The inhibition imposed by dissolved Mg and inorganic carbon species is selective and complex, but can be understood in terms of changes in etch pit morphology, step speeds, double kink nucleation and single kink propagation rates. By independently varying pH, CO$_2$, and Mg$^{2+}$ concentrations in otherwise simple NaHCO$_3$ solutions, we have used a suite of AFM and scanning interferometry experiments to selectively elucidate the action of dissolved species at specific surface sites. In CO$_2$-free solutions, pH $ > 8$, dissolved Mg generates relatively little inhibition even at concentrations of $\sim \! 1$ mM. In carbonated solutions of fixed alkalinity (pH 8.5 -- 9), inhibition at concentrations of Mg$^{2+}$ less than $\sim 50 \ \mu$M appear to result from attachment at obtuse $(+)$ step edges. Higher total Mg$^{2+}$ concentrations ($\sim \! 1$ mM) appear to retard $(+)$ kink propagation along $(-)$ step edges, resulting in unique etch pit profiles. The change in etch pit morphology may be linked to changes in the relative rates of double kink nucleation versus single kink propagation rates, mediated by competitive adsorption of ion pairs of magnesium with either carbonate or bicarbonate.
DE: 1045 Low-temperature geochemistry
DE: 1050 Marine geochemistry (4835, 4850)
DE: 3947 Surfaces and interfaces
DE: 4835 Inorganic marine chemistry
DE: 5112 Microstructure
SC: Biogeosciences [B]
MN: 2003 Fall Meeting