Dolomite dissolution in aqueous solutions in the presence of nucleotides and their structural components at 25 °C and pCO2 ~ 1 atm

Abstract

The kinetics and stoichiometry of dolomite dissolution were investigated in deionized water at 25°C and pCO2 ~1atm in the absence (control) and presence of various nucleotides and their structural components at low concentrations (1mM). Dissolutions were conducted in “free-drift” mode and rates estimated based on the accumulation rate of calcium and magnesium ions in solution. The additives considered in this study are likely present at low concentrations (<mM) in deep, carbonate aquifers targeted for CO2 geological sequestration. Results of our control experiment are consistent with rates and stoichiometries reported in earlier studies. In the presence of nucleotides, dolomite dissolution was inhibited and proceeded incongruently, yielding a Mg:Ca solution ratio ≥2. An investigation of the nucleotide structural components (nucleosides, nitrogenous bases and phosphates) revealed that, whereas they nearly all inhibited dolomite dissolution, only phosphate salts (mono-, di-, tri-, and hexametaphosphate) lead to incongruent dissolution. Examination of the surface morphology and phosphate analysis of the solids reacted in the presence of nucleotides and phosphate salts revealed the formation of a solid phosphate phase on the dolomite surface, likely a Ca rich-phosphate phase that accounts for the observed dissolution incongruency.