Porewater chemistry in compacted bentonite

The porewater chemistry in compacted bentonite was studied in solution–bentonite interaction experiments. The parameters varied in the experiments were the bentonite density, bentonite-to-water ratio (B/W), ionic strength of the solution, and the composition of bentonite. The bentonite types used in the experiments were Volclay MX80 and artificial bentonites prepared from purified MX-80 in sodium form where CaCO3 and CaSO4 were added. At the end of the experiment, the equilibrating external solution and the porewater squeezed out of the bentonite were analyzed to give information for interpretation of the interaction. The equilibrium was modelled with the HYDRAQL code.

The evolution of porewater chemistry was determined by the dissolving components initially present in the bentonite together with the ions entering with water from the surroundings. Ion-exchange processes occurred between the bentonite and the porewater. The concentrations in the external solution and porewater strongly depended on the B/W used. The concentrations in the squeezed porewaters were clearly lower than in the equilibrating waters. The modelling results reasonably fit the experimental data.