The kinetics of calcite precipitation from thin films of calcareous solutions and the growth of speleothems: Revisited

Abstract

Using recent data on calcite dissolution and precipitation by Plummer et al., the deposition of CaCO 3 from thin films of supersaturated solutions of H 2O/1bCO 2/1bCaCO 3 to a CaCO 3 surface is calculated. The results are compared to previous calculations by Dreybrodt, which were based on precipitation kinetics as proposed by experiments of Reddy and Nancollas. Though the chemical kinetics of Plummer et al. and Reddy and Nancollas differ markedly, the precipitation rates from thin films of solution are different only by a factor of ∼2. The reason for this behaviour is the generation of CO 2 at the crystal surface, resulting in an increased CO 2 concentration at the surface compared to the bulk. This reduces the supersaturation of the solution at the surface resulting in a markedly decreasing precipitation rate. These results are applied to thin stagnant films of solution in the growth of stalagmites and to continuously flowing films in the precipitation at stalactites and wall sinter. The growth rates are in close agreement to those of the previous calculations with Reddy and Nancollas' data and clarify the question as to how the mechanism of the surface reaction is important in the growth of speleothems