The variations in surface area of a sepiolite (Toledo, Spain) after acid and heat treatments (1 n to 5 n, HNO3, 110°C to 900°C for 100 h) have been studied. Surface areas have been determined from N2 adsorption isotherms at 77 K using B.E.T., Langmuir and Dubinin-Radushkevich equations. S
BET values range from 65 up to 391 m2 g−1, the maximum value corresponding to the sample activated with 1 n HNO3 solution and treated at 300°C. S
L and S
D-R values are similar, but slightly larger than the corresponding S
A correlated study has been carried out with samples activated with 1 n and 2 n HNO3 solutions and heat treated at 110, 200, 300, 400 and 500°C for 10 h. S
BET values of these samples are rather similar to those of the corresponding samples treated during 100 h.