Validation of a clay/porewater interaction model though laboratory experiment.

Abstract : This paper presents an experiment performed to test a geochemical model of the porewater composition of the Opalinus Clay formation. Batch experiments were conducted on crushed argillite in contact with a synthetic solution, using a mixed CO2 + N2 gas phase to fix the PCO2. Small amounts of the suspension were periodically taken from the experimental cell. Analyses of the solution and of the solid fraction reveal that (i) most of the equilibrium between the argillite and the solution is achieved after about three weeks, and (ii) the solution composition, pH and Eh are all in close agreement with the model calculations, with the exception of adsorbed cation distribution on the clay fraction. However, the experiment suggests ways to improve the modeling, by including other minerals such as illite among the controlling phases.