Laboratory procedures for the modification of soluble and exchangeable cations of geosynthetic clay liners

A novel dialysis procedure to modify the exchange complex composition of the bentonite component of geosynthetic clay liners, as well as to remove the excess soluble salts from the bentonite pores, has been developed in order to overcome the limitations associated with the currently used dialysis methods. Indeed, when the bentonite to be purified is characterized by an aggregated fabric, the presence of less accessible pores does not allow the interlayer exchangeable cations to be replaced by the cationic species contained in the dialysing solution, thus undermining the effectiveness of dialysis in homo-ionising the bentonite specimen. For such a reason, the novel dialysis procedure that is proposed in this study comprises a preliminary treatment phase, which comes before the homo-ionisation phase and is aimed to promote the break-up of the bentonite tactoids through dialysis cycles with deionised water. A natural powdered bentonite has been tested in the laboratory to evaluate the enhancement in the bentonite sodium homo-ionisation that is due to the adoption of the newly developed dialysis procedure, in substitution to the currently used one, showing that such substitution results in an increase in the exchangeable sodium percentage from 35% to 78% at the expense of a decrease in the exchangeable calcium percentage.