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Kinetics of Calcite Dissolution as Affected by Carbon Dioxide Partial Pressure¹

ABSTRACT

Research was conducted to determine the effect of CO₂ on the kinetics of soil mineral dissolution. It was found that in soils or overburden materials in which CaCO₃ is the dominant weatherable mineral, the kinetics of dissolution was not a simple diffusion controlled or first-order reaction. In these calcareous systems, the transfer of atmospheric CO₂ to solution was an important rate limiting step in the kinetics of dissolution. At higher PCO₂ values the dissolution of calcite was modeled by three simultaneous reactions on the surface of the calcite. It is postulated that the CO₂ attack consists of an adsorption of CO₂(aq) on the calcite surface followed by hydrolysis of the CO₂ to H₂CO₃. The hydrolysis is apparently catalyzed by the calcite surface because the aqueous hydrolysis, CO₂(aq) + H₂O H₂CO₃, occurs too slowly for the observed rate of reaction.

¹ Contribution from the Dep. of Soil Science and Biometeorology, Utah State Univ., Logan, UT 84322. Published with approval of the Director, Agricultural Experiment Station as Journal paper 3064.

² Post Doctoral Fellow, U. S. Salinity Laboratory, Riverside, CA, 92501 (formerly Research Assistant, Utah State University, Logan, UT), Professor of Soil Chemistry, and Professor of Chemistry, Utah State University, Logan, UT 84322, respectively.

Received for publication January 25, 1985. Accepted for publication June 25, 1985.