Texture evolution of montmorillonite under progressive acid treatment: change from H3 to H2 type of hysteresis

Abstract

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.

Acid Hydrolysis of Octahedral Mg2+ Sites in 2:1 Layered Silicates: An Assessment of Edge Attack and Gallery Access Mechanisms

“…Octahedral cations such as A13+, Fe 3+, Fe z+, and Mg 2+ can be depleted by treating the clay minerals with acids at elevated temperatures (Johnson et al 1964; with the rates of depletion generally following the order Mg 2+ > Fe 2 § Fe 3+ > AP + Luce et al 1972;Rice and Strong 1974). There has been considerable interest in the acid hydrolysis of 2:1 clay structures, especially palygorskite (Corma et al , 1990Gonzalez et al 1989), sepiolite (Corma et al 1986;Rodriguez-Reinoso et al 1981), montmorillonite (Mendioroz et al 1987;Rhodes and Brown 1992;Srasra et al 1989), and vermiculite (Suquet et al 1991). BET surface areas as high as 500 m2/g have been reported for the amorphous silicates derived from some of these minerals.…”

Acid Activation of a Ferrous Saponite (Griffithite): Physico-Chemical Characterization and Surface Area of the Products Obtained

“…Numerous papers about acid activation of montmorillonite (the principal silicate in the smectite group), sepiolite (a fibrous magnesic silicate), vermiculite and other silicates can be found in the literature (Lrpez Gonzfilez et al 1981;Mendioroz et al 1987;Cetisli and Gedikbey 1990;Suquet et al 1991;Pesquera et al 1992). However, in spite of the growing interest in the study of saponite, no references to acid activation of this silicate have been found.…”

Characterization and catalytic properties of a saponite clay modified by acid activation

“…Numerous studies have been reported on the acid activation of clays, especially montmorillonite (Mendioroz et al, 1987;Rhodes & Brown, 1992;Mokaya et al, 1993), palygorskite (Gonzalez et al, 1989;Corma et al, 1990), vermiculite (Suquet et al, 1991) and sepiolite (Corma et al, 1986;Lopez Gonzalez et al, 1981). One reason for this interest is that acid-activated clays exhibit significantly different physical and chemical characteristics compared to their non-activated counterparts, e.g., they usually possess higher surface areas, acidities and pore volumes.…”