In sepiolite

Both sepiolite and palygorskite contain tetrahedral silicate sheets (with a variety of substitutions for the Si " ), but the apicies of the tetrahedra are thought to point up or down with the transition areas containing Ca and Mg ions, and bound or associated H2O. The arrangement produces a continuous basal oxygen plane that is compartmentalized. Laths or ribbons three chains wide in sepiolite and two chains wide in palygorskite are separated by discontinuous octahedral areas (Fig. 2.16A and B). 

Ovarlez S, Chaze A-M, Giulieii F, Delamare F (2006) Indigo chemisorption in sepiolite. Application to Maya blue formation. Compt Ren Chim 9 1243-1248. 

There is significant Fe substitution in sepiolite giving the species... 

KULBICK1 (G.), 1959. High temperature phases in sepiolite, attapulgite and saponite. Amer. Min. 44, 752-64. 

Attapulgite and sepiolite are clay minerals with a chain structure. The former has five octahedral positions and the latter either eight or nine. Both have relatively little tetrahedral substitution. The octahedral positions in sepiolite are filled largely with Mg and those in attapulgite with approximately half Mg and half Al. 

These results show that zinc ferrite has been formed, but in sepiolite and USY zeolite the enstatite and hercynite networks substitute some of their ions for Fe and Zn, therefore masking the ffanklinite network. In the Zr02 case such substitution does not occur, appearing the pure oxide together with the fi-anklinite (6-8%), as theoretically expected. 

There appear to be very few structural studies of clays involving nuclei other than Si and Al, perhaps for obvious reasons. Many clays, however, do include fluorine in place of some structural hydroxyls, and a study of F second moments in sepiolite appeared recently (43]. The moment analysis indicates F mainly replaces internal structural OFI between the octahedral and tetrahedral layers. 

AhMchs JL, Serna C, Serratosa JM (1975) Structural hydroxyls in sepiolites. Clays Clay Miner 23 119 124... 

Santaren J, Sanz J, Ruiz-Hitzky E (1990) Structural fluorine in sepiolite. Clay Miner 38 63-68... 

Fernandes FM, Ruiz-Hitzky E (2014) Assembling nanotubes and nanofihies eooperativtaiess in sepiolite-carbon nanotube materials. Carbon 72 296-303... 

Intracrystalline sorption of organic componnds in sepiolite Sepiolite/hexane Serna and Femandez-Alvarez (250)... 

Sepiolite is a hydrated magnesium silicate having an internal structure of channels which can accomodate zeolitic water and other molecules. The magnesium ion in sepiolite crystal is exchangeable with various metal ions(l). Loughlinite has a similar structure to sepiolite and is known as natural Na-sepiolite(2), Sepiolite is an effective catalyst for hydrorefining of hydrocarbons, fuel oils(3) and conversion of ethanol into ethylene or bute-l,3-diene(l). 

Table II summarizes the textural data of each series. In general terms, both the surface area and the total pore volume decrease and the average pore radius increases as the sulphur content grows. The radius of the most common pore (mode) stays almost constant in sepiolites and palygorskites throughout the experiments whereas in diatoraites, and especially in bentonites, it first decreases and finally increases with the sulphur load. The BET constant reaches an almost constant value in every series, and nearly the same for all of them, once the value of the monolayer of sulphur deposited has been exceeded, in agreement with the same type of adsorbate/adsorbent interaction.

Pore distribution in sepiolite remains almost unaltered through sulphurization, in spite of the variations shown in Fig. 2b and Table 2. Only a decrease in the 10-100 pm range in favour of that of 0.025-0.25 is appreciated. This distribution can be related to a gradual filling of all pore sizes, resulting in a large decrease in surface area and pore volume that leaves nearly constant the values of mean, median and mode pore radius. The rate of sulphur deposition should decrease in line with the fall in accessible sulphur (Fig. 1). 

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