The surface properties of sepiolite

Some surface properties of sepiolite were determined for a natural sample and after surface charge saturation with sodium cations. The values obtained are: water/solid contact angle 70.9° and 71.4°, spreading pressure at monolayer coverage 119.2 and 120.3 mJ m−2, spreading pressure at saturation 144.1 and 142.4 mJ m−2 amounts of water adsorbed at monolayer coverage 74.48 and 78.06 mg g−1, surface energy 243.3 and 241.4 mJ m−2, water/solid interfacial energy 7.4 and 7.4 kJ mol−1, enthalpy of water adsorption 52.4 and 52.24 kJ mol−1 respectively. These values are similar to those reported in the literature for palygorskite which is the other member of the clay mineral group.