Physical and chemical properties of some bentonite deposits of Kimolos Island, Greece

Bentonite deposits of Kimolos Island, Aegean, Greece were investigated in order to determine their physical and chemical properties. Testing included measurement of CEC (cation exchange capacity), swelling capacity, pH, rheological properties and some important foundry properties including green and dry compression strength, shatter index, wet tensile strength, compactability and permeability. The rheological and foundry properties are mainly influenced by the bentonite grade (smectite content) and the degree of disaggregation of the smectite quasicrystals due to the nature of the interlayer cation, the presence of mordenite and undevitrified glass shards, the degree of the oxidation of iron and the type of smectite–opal-CT interaction. Na-activation improves green compressive strength and especially wet tensile strength and decreases permeability, while its influence on the remaining foundry properties is unpredictable. Swelling properties are affected by bentonite grade, expressed by CEC, and the presence of characteristic phases (glass shards and opal-CT) decreases swelling, while zeolites increase CEC. The swelling capacity is closely related to the CEC, if smectite chemistry is controlled. It is shown that although the presence of zeolites like mordenite or small amounts of opal-CT may not affect rheological properties, the bonding properties always deteriorate. However, the presence of undevitrified glass reduces viscosity.