Dissolution of carbonate rock by water vapour and CO2

In contrast to water-saturated systems, the dissolution of carbonates in water-unsaturated conditions has hardly been studied so far, although it is of importance for many systems including soils or technical systems like gas drainage layers e.g. in landfills. The aim of our study is to determine the dissolution of three different carbonate containing limestones at different CO2-partial pressure in water vapour saturated atmosphere and under conditions typical for gas drainage layers. Due to condensation the gravel surfaces are surrounded by water films in which dissolution of the rock material can occur until the water films are dripping off. After a passage of 5 cm the leachate waters are Ca-saturated with respect to CaCO3. The magnesium content of the leachates exceeds the expected value from the material composition. Generally, dissolution of carbonate rocks in water-unsaturated systems appears to be controlled by the renewal rate of the surface water film rather than by chemical reaction kinetics.