Adsorption–desorption of water vapor by natural and heat-treated sepiolite in ambient air

Abstract A sepiolite from Yunclillos (Spain) has been heat-treated in air in the temperature range of 110–500°C. The heat treatment up to 200°C does not modify the volume of micropores or the non-microporous surface area of the original sepiolite. As the temperature of the heat treatment increases to 500°C there is a decrease in the non-microporous surface area and a loss of microporosity, the original structure not being restored after rehydration for sepiolite heat-treated at 400 and 500°C. In order to analyze the behavior of sepiolite as controller of humidity, working cycles of 24 h with variable temperature and relative humidity (RH) have been simulated and the experimental results have been compared with the adsorption isotherms of water vapor in air. These isotherms are a very good guide to predict the amount of water that the sepiolite can retain–liberate when the RH of the air is modified. Considering the shape of the isotherms, showing a faster increase in the amount of water retained at RH>50%, it is possible to deduce that sepiolite will be especially useful as controller of humidity in environments where the RH is usually very high (80–90%) and sporadically is considerably decreased (below 60%). On the other hand, the thermal treatment of sepiolite at 500°C does not improve the capacity to control the humidity of the environment.