Carbonic Acid:  An Important Intermediate in the Surface Chemistry of Calcium Carbonate

Calcium carbonate is an important and ubiquitous component of biological and geochemical systems. In this study, the surface chemistry of calcium carbonate with several trace atmospheric gases including HNO₃, SO₂, HCOOH, and CH₃COOH is investigated with infrared spectroscopy. Adsorbed carbonic acid, H₂CO₃, is found to be an intermediate in these reactions. In the absence of adsorbed water, carbonic acid is stable on the surface at room temperature. However, upon water adsorption, carbonic acid dissociates as indicated by the evolution of gaseous CO₂ and the disappearance of infrared absorption bands associated with adsorbed carbonic acid. Thus, it is postulated that under ambient conditions, carbonic acid may be an important albeit short-lived intermediate in the surface chemistry of calcium carbonate.