Acid activation of a Spanish sepiolite: physico-chemical characterization, free silica content and surface area of products obtained

A sepiolite from Vallecas (Spain) was treated with solutions of HC1 (1.25, 2.5, 5.0, 10.0 and 20.0 wt%) at 25°C for 2, 6, 24 and 48 h, respectively. The resulting solids were characterized by XRD, FT-IR and thermal analyses, along with SEM, TEM and nitrogen adsorption isotherms at 77 K. The free silica was digested and determined in all samples. Several samples were seen to have specific surface areas up to 450 m2/g, with a maximum value of 549 m2/g in the sample treated with 1.25 wt% HCl for 48 h. A sudden decrease in specific surface areas was observed when free silica was digested.