Saponitic clays from the Madrid basin : accessory-minerals influence in hydrothermal reactivity

Abstract Some hydrothermal alteration tests have been carried out on two selected clays which contain saponite as major component with illite or sepiolite representing the main accessory minerals in the bulk composition of saponitic clays. Both samples show an important increment of silica in solution and in removable amorphous silica when temperature rises from 60°C to 175°C. The same trend is observed related to K + adsorption. Occurrence of sepiolite causes different behaviour in irreversible K + fixation processes. A drastic degradation of sepiolite at 175°C, was detected by means of XRD together with slight increases in CEC while no irreversibly fixed K + was detected. On the opposite, significative amounts of fixed K + increasing with reaction time and lower levels of removable amorphous silica were the main features observed in the illite-saponite sample, where CEC remains almost constant with temperature and reaction time.

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