The bentonites in pelotherapy: thermal properties of clay pastes from Sardinia (Italy)

On the basis of a previous detailed characterization of the Sardinian bentonites for pelotherapy applications [Cara, S., Carcangiu, G., Padalino, G., Palomba, M., Tamanini, M., 2000. The bentonites in pelotherapy: chemical, mineralogical and technological properties of materials from Sardinia deposits (Italy). Appl. Clay Sci. 16, 117–124 (this issue)], three commercial bentonites have been selected for detailed studies. The thermal properties of the pastes, prepared with these bentonites at different moisture, have been compared with the properties of a peloid, commonly used in the spa of Benetutti (northern Sardinia). The cooling kinetics of the bentonites along with the thermal mud have been studied using an experimental apparatus that reproduces the conditions during the application of a cataplasm. A mathematical model for the cooling kinetics has been obtained by means of a theoretical cooling equation, with instrumental constants derived from a reference paste (TiO2 at 50% moisture). The heat capacity of the pastes introduced into the model was calculated from chemical and mineralogical data. The methodology developed can be used in other laboratories of the thermal centres to determine the quality and ability of the bentonitic materials for pelotherapy.