On treatment of a bentonite from La Serrata-Sierra de Nijar, Spain, with HC1 of increasing concentration (1-8 N), an evolution in the hysteresis loops of the corresponding N2 adsorption-desorption isotherms is revealed. In the first stages of the attack, an opening of the bentonite lamellae is produced by abstraction of interlayered cations and corresponding water molecules. Thus, an accessibility, otherwise impossible, of nitrogen to the internal surface of the samples with subsequent increase in N2 adsorption occurs. A second stage is produced when the octahedral aluminum sheet is dissolved as the acid attack progresses.In both stages H3 loops as well as pore ranges are preserved. At higher HC1 concentrations, the partial destruction of the tetrahedral sheet and the texture of the resulting amorphous free silica, together with the random occlusion of the unaltered montmorillonitic interlamellar spaces, result in changes of texture, slit-shaped pores becoming ink-bottle pores and H3-type hysteresis changing to the H2 type. Pore size increases and total pore volume decreases. Specific surface areas grow from 61 m2 g"1 for the natural sample to 345 m2 g"1 for the 8 N HC1 treated sample, passing through a maximum of 416 m2 g"1 for the 4 N HC1 treated specimen, depending on which of the effects described above predominates. Cientifica y Tecnica for financial support of this work under Projects 83051 and 678/553, respectively.

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