Comparison of saponite and montmorillonite behaviour during static and stirring maturation with seawater for pelotherapy

Two different bentonites (saponite and montmorillonite) have been used for maturation with seawater. These bentonites are very rich in phyllosilicates (> 90%), with calcite, silica minerals (quartz, cristobalite) and feldspars (plagioclase) as subordinated minerals. Maduration tests have been realized both in static and stirring conditions and sampling points at 0, 15, 30, 60, 90 and 120 days have been established. Several mineralogical (XRD, SEM-EDX) chemical and physico-chemical (CEC, pH, granulometry, plasticity, conductivity) analytical techniques have been used. Results indicate no mineralogical changes during maturation process but differences in the smectite crystallinity (crystallite size) and basal spacing d(001). The last related with the variation of exchangeable cations (mainly Na+ for Ca2+) within the smectite interlayer. Variations in granulometry, plasticity index and conductivity have also been observed. Similar results are reported for static and stirring procedures, and therefore the former is preferred. Maturation time of between 60 and 90 days would be enough for the bentonite to achieve the optimum physico-chemical properties for its use as a peloid. Between the two bentonites under study, saponite is clearly better than montmorillonite for its application as peloids in pelotherapy. This fact is mainly due to differences in grain size distribution and consequently in the cationic exchange capacity, which enables in saponite a higher retention of water ions making possible their transference to patients, and therefore reaching a better influence in their health.