Ceramics-Silikáty 44, (2) 48 - 53 (2000)

Electro-ultrafiltration (EUF) method was employed at 20, 40 and 80 °C for investigation of potassium extraction from a K⁺- saturated ˂2 μm fraction of a bentonite. Up to 85% of total potassium present in the sample was extracted. At least three different sites of K⁺ desorption were found on bentonite particles dispersed in water. EUF analyses of duration of 30 - 40 minutes were optimal for adequate information on K+ sites. Experiments at 20 °C and voltages 50-350 V caused desorption of K⁺ from the external surface of particles, which terminated after extraction of about 9 mg K/g clay, i.e. 22% of total potassium present. Increase in voltage to 400 V applied at 20 °C caused onset of K⁺ desorption from the weaker interlayer sites, observed also at 40 °C and 50 - 150 V. These sites are supposed to occur mainly in swelling interlayers of smaller quasicrystals, close to the layers of lower negative charge. At 200 V started K⁺ desorption from the stronger interlayer sites, occurring probably predominantly in the less swelling interlayers of bigger particles, next to highly charged layers. As expected, no sharp border appears between the weaker and stronger interlayer sites, they cover combined 63% of total potassium present in the investigated material.