Carbon Dioxide, Bicarbonate and Carbonate Ions in Aqueous Solutions at Deep Earth Conditions

Abstract

We investigate the effect of pressure, temperature and acidity on the composition of water-rich carbon-bearing fluids at thermodynamic conditions that correspond to the Earth's deep Crust and Upper Mantle. Our first-principles molecular dynamics simulations provide mechanistic insight into the hydration shell of carbon dioxide, bicarbonate and carbonate ions, and on the pathways of the acid/base reactions that convert these carbon species into one another in aqueous solutions. At temperature of 1000 K and higher our simulations can sample the chemical equilibrium of these acid/base reactions, thus allowing us to estimate the chemical composition of diluted carbon dioxide and (bi)carbonate ions as a function of acidity and thermodynamic conditions. We find that, especially at the highest temperature, the acidity of the solution is essential to determine the stability domain of carbon dioxide, bicarbonate and carbonate ions.

arXiv comment8 pages, 6 figures

References in corpus (5)

• Canonical sampling through velocity-rescaling
• Separable Dual Space Gaussian Pseudo-potentials
• The fate of carbon dioxide in water-rich fluids at extreme conditions
• A microscopic description of acid-base equilibrium
• Large presence of carbonic acid in CO${}_2$-rich aqueous fluids under Earth's mantle conditions

Cited by in corpus (2)

• Nanoconfinement Facilitates Reactions of Carbon Dioxide in Supercritical Water
• Formation of abiogenic hydrocarbons in supercritical fluids under Earth's upper mantle conditions