Influence of solid–liquid compositions and contact time during maturation on the properties of artificial peloids for use in pelotherapy

Peloids are natural therapeutic muds or clays used in balneotherapy and other health treatments. The aim of this study is to prepare and qualify three artificial peloids by the maturation for 360 days of some Tunisian smectitic clays with a naturally chlorinated sodic mineral water from a spring in Korbous, Tunisia. This allows us to understand the behavior and the physicochemical changes that affect the clays during maturation process, whose purpose is to provide suitable raw materials as a solid phase for peloids preparation. The results showed that parameters such as mineralogy, geochemistry, granulometry, cation exchange capacity, consistency parameters (Atterberg limits and plasticity index), specific surface area, cooling kinetics and pH are all affected by the geochemistry of the thermal water used during maturation. Mineralogical modifications are mostly concerning the clay minerals' contents, particularly smectite, and subordinately the dissolution of gypsum and the neoformation of halite. Improvement of plasticity index and cooling kinetics can be explained by the ability of water molecules, and especially cations, to diffuse into the clay particles. Main exchangeable cations are Na+ and Ca2+, along with Mg2+ and K+, which promote swelling and better water retention and consequently of heat in thermal spa treatments. Chemical composition of major elements is closely linked to their mineralogical compositions, and also to the chemical composition of the thermal water used in their maturation. Safety profiles of the peloids obtained at different maturation times were evaluated, in particular their content of potentially toxic elements such as arsenic.