Assessment of natural and enhanced peloids from the Copahue thermal system (Argentina): Effects of the drying procedure on lidocaine adsorption

Abstract Four peloids with therapeutic properties from the Copahue geothermal system were comparatively studied. Three of them were naturally produced within the “Chancho” lagoon (ChL), the “Sulfurosa” lagoon (SL), and the “Verde” lagoon (VL), whereas the last one was the result of an industrial-scale maturation experience called “Maturation lagoon” (ML). The liquid phase of the peloids presents percentages of mineral-medicinal water ranging between 55.6% (SL) and 77.4% (VL), which is classified as acidic and sulphate-rich with significant quantities of calcium and sodium cations. The solid phase study evidenced that VL is a phyllo-peloid constituted mainly of clay minerals, while the other three materials were classified as sulfo-peloids due to the high content of sulfur in their composition. The clay minerals found in all peloids were dioctahedral smectite and kaolinite. Two drying methods were studied for the samples: the stove-drying method (SD) and the freeze-drying method (FD). The materials obtained by FD showed a greater adsorbent capacity and were more easily dispersible in water, being used to prepare the so-called “enhanced” peloids. This type of peloid consists of a drug adsorbed on its solid phase, that can be released improving the peloid's therapeutic effect. Lidocaine (LID) was used as an adsorbate, achieving adsorption values of 30 mg.g−1 for the natural peloids, thus reaching similar proportions to those of commercial formulations. Drug release tests performed with enhanced peloids showed that in aqueous media up to 50% of LID was desorbed within one hour when the raw material was ML. The high potential of these improved peloids for prolonged drug release is emphasized.