Effects of heat and humidity gradients on MX-80 bentonite geochemistry and mineralogy

Due to the dissolution of low-solubility species and to the loss of exchangeable positions in the smectite, the content of soluble salts in the pore water increased with respect to the original one. The solubilised ions were transported; sodium, calcium, magnesium and sulphate having a similar mobility, which was in turn lower than that of potassium and chloride. The cationic exchange complex was also modified. Smectite dissolution processes (probably colloidal) occurred, particularly in the more hydrated areas. Consequently, an overall decrease of the smectite content with respect to the initial value took place, especially in the most hydrated areas, where the percentage of interestratified illite also increased. On the other hand, the content of cristobalite and calcite increased.