Composition and physico-chemical properties of peloids used in Spanish spas: A comparative study

Abstract This study analyses and characterises the thermal and non-thermal properties of five peloids from different Spanish locations. Three of the peloids designated as ARCH, ARN and RAP were made from medical mineral water and clay. The peloid designated as BOI was made from medical mineral water and a mixture of peat and clay, and the fifth peloid designated as LOP was derived from a natural sedimentary environment (lagoon) wherein the clayey silt sediment was matured in sea water. The samples were compared by means of physical and physico-chemical determinations namely, grain-size analysis, BET specific surface area, plasticity index, CEC and exchangeable cations, instrumental texture analysis and thermal parameters. The results showed significant differences between the different peloids studied, especially with regard to their composition and some non-thermal properties. The highest values for BET, plasticity index and CEC were observed in the sample composed of Na-saturated trioctahedral smectite. The mixing of peat with clay also favoured high values for CEC and plasticity index. The instrumental texture analysis showed similar values for cohesiveness and springiness in all the peloids, but there were differences in hardness and adhesiveness. Regarding the thermal properties, the values were similar within a relative narrow range for retentivity, t37 parameter, and relaxation time. Despite the differences in the composition of the peloids, the values achieved for instrumental texture analysis and thermal parameters were comparable with those of the reference TERDAX peloid.