『Abstract
Steady state Iceland-spar calcite dissolution rates were measured
at 25℃ in aqueous solutions containing 0.1 M NaCl and up to 0.05
M dissolved bicarbonate at pH from 7.9 to 9.1 in the presence
of 13 distinct dissolved organic ligands in mixed-flow reactors.
The organic ligands considered in this study include those most
likely to be present in either (1) aquifers at the conditions
pertinent to CO2 sequestration or (2) soil/early
diagenetic environments: acetate, phthalate, citrate, EDTA4-,
succinate, D-glucosaminate, L-glutamate,
D-gluconate, 2,4-dihydroxybenzoate, 3,4-dihydroxybenzoate,
fumarate, malonate, and gallate. Results show that the presence
of <0.05 mol/kg of these organic anions changes calcite dissolution
rates by less than a factor of 2.5 with the exception of citrate
and EDTA4-. The presence of 0.05 mol/kg citrate and
EDTA4- increases calcite dissolution rates by as much
as a factor of 35 and 500, respectively, compared to rates in
organic anion-free solutions. Further calcite dissolution experiments
were performed in the presence of organic polymers similar to
bacterial exudates, cell exopolysaccharides, and analogs of microbial
cell envelopes: alginate, lichen extract, humic acid, pectin,
and gum zanthan. In no case did the presence of <100 ppm of these
organics change calcite dissolution rates by more than a factor
of 2.5. Results obtained in this study suggest that the presence
of aqueous organic anions negligibly affects calcite forward dissolution
rates in most natural environments. Some effect on calcite reactivity
may be observed, however, by the presence of organic anions if
they change substantially the chemical affinity of the fluid with
respect to calcite.』
1. Introduction
2. Theoretical background
3. Experimental methods
4. Results
5. Discussion
5.1. Relative effects of organic ligands on calcite dissolution
rates
5.2. Modeling of ligand-effected carbonate mineral dissolution
5.3. Geological applications
6. Conclusions
Acknowledgments
References