The influence of thermo-mineral and seawater on the mineralogy and chemistry of residual smectitic soils from Alentejo, Portugal: a case study

Peloid is a natural product developed during the maturation process between a clay material and water and is used in health and wellness centres due to its mineralogical, physiochemical and biological properties. However, the potential therapeutic value of clays in Portugal has not been fully investigated. Therefore, the main objective of this research is to identify the effects of two mineralized waters: thermo-mineral water (sulphurous and hydroxylated water abundant in chloride ions, sodium and calcium) and seawater, on three residual soils from Alentejo, from a morphological, mineralogical and chemical perspective. The peloids morphology is more homogeneous than the residual soils, and the particle size decreases during the maturation process. Thermo-mineral water enriched the peloids in smectite (58 – 76 %), while seawater newly formed Na-minerals (decreasing smectite contents to 39 – 54 %). Smectite is essentially montmorillonite, although there is nontronite and beidelite. The residual soils and peloids have a silicilastic composition (32.23 to 52.85 %), between 14.22 and 20.53 % of Al 2 O 3 , and besides smectite, the mineralogical composition is composed of salts (only in seawater peloids), feldspars, iron oxides, carbonates, and quartz. Morphology and mineralogy enhance the influence of waters in peloids properties and suggest that this samples have potential therapeutic value. Furthermore, physical-chemical, rheological, thermal and biological analysis are needed to support these findings. • Peloid is a natural product used in health and wellness centers • The influence of waters on morphology, mineralogy and chemistry of samples is clear • Particle size decreased in peloids, compared to the starting samples • Seawater peloids show greater incorporation of exchange ions in interstitial layers • Smectite is the main clay mineral and has the greatest therapeutic properties