The CaCO3-CO2-H2O system in soils

• Main Author: Robbins, C.W.
• Format: Article in Journal/Newspaper
• Language: English
• Published: 1985
• Subjects: Mass Import - unclassified; Carbonic acid
• Online Access: https://eprints.nwisrl.ars.usda.gov/id/eprint/436/; https://eprints.nwisrl.ars.usda.gov/id/eprint/436/1/548.pdf

Equations used to develop the CO2-Ca-pH relationships in calcareous soils are reviewed. The equation PCO2(Ca) = (H)2 Kc, is used to draw a three-dimensional surface and to derive three partial differential equations to illustrate the relationships between CO2 partial pressure, Ca activity and pH. Kc is a combination of Henry's Law constant, the first and second dissociation constants for carbonic acid and the calcite solubility product. The three dimensional CO2-Ca-pH surface illustrates how the three parameters relate to each other under ideal conditions. The partial differential equations are presented to illustrate how changes in one parameter affect the other two. The CO2-Ca-pH surface provides a graphical method for introducing the idea of three component equilibria, while the partial differential equations provide a mathematical representation of these interactions for those with chemical thermodynamics or strong mathematic or modeling backgrounds. Deviations from this ideal model in natural systems are discussed for those who wish to extend the discussion to natural systems.