Suitability of natural sulphur-rich muds from Copahue (Argentina) for use as semisolid health care products

Copahue volcano is situated in the province of Neuquén, Argentina. The associated geothermal system causes
the occurrence of singular thermal muds with significant presence of sulphur and clay minerals. These
peloids are used in the region for the treatment of rheumatic pathologies and arthritis, muscle and bone
traumas and dermatological pathologies, and, up to the present, were applied as found in the natural mud
pools. This study analyses six natural peloid samples from the Copahue area in order to determine their
mineralogical, chemical and textural characteristics, and to evaluate some technical properties.
The pH of the aqueous fraction of the mud is acidic, ranging from pH 2.2 to 3.4. The water can be considered
as having medium to strong mineralization, according to the concentration of total dissolved solids. The
acidity favours the permanence of ions in solution. The one strongly predominating anion is S042− (and S2− in
equilibrium) with smaller proportions of chloride, fluoride, nitrite and nitrate. As the pH shows, the proton is
the dominant cation, followed by Na+, Ca2+, Mg2+ and K+.
Three of the samples have high elementary sulphur content (39–51%). The main clay minerals in all cases
were beidellite (13% to 39%) and kaolinite (6% to 34%). Other phases detected are alunite (up to 18%), opal,
plagioclase, pyrite and Ti and Fe oxyhydroxides. The organic carbon content is due to the organic matter
supplied by algae, diatoms and other microorganisms.
The adsorption isotherms showed that in comparison to sodium montmorillonite (SWy-2) these peloids
retained 22% to 36% water, whereas in comparison with the kaolinite tested (KGa-1b) the water content was
370% to 600%. The cooling kinetic curves showed a low cooling rate. The poultices prepared with the
different mud samples took 45–95 min to fall from 50° to 25°. They had good workability due to their liquid
limits (45–71%). Application to the skin and the pleasant sensation produced were favoured by the fine grain
size, since the clay–silt fraction (b62 μm) ranged from 92% to 99% depending on the sample, and sandy grit
did not exceed 8%.
Natural peloids from Copahue are a special type of therapeutic mud we could call “clayey–sulphurous mud”,
whose thermal properties are similar to those of other known peloids but with special possibilities for the
treatment of various pathologies due to the presence of sulphur. Development of similar synthetic peloids
could be of interest.