Sepiolite-Palygorskite

Although sepiolite-palygorskite occur frequently in closed basin, evaporite or lake deposits, these minerals are also known in Tertiary and late Paleozoic deep sea, shelf and shallow sea deposits. They have also been reported with persistent frequence by French clay mineralogists in Mesozoic and Tertiary saline and carbonate deposits (Millot, 1964). 

Despite the claim by Bartholome (1966b) that the minerals are predominantly Tertiary in age, they seem to persist in older non-metamorphic sediments of Western Europe. Paleozoic sediments are rare there, being almost always 

The absence of sepiolite and palygorskite from sediments and sedimentary rocks in other parts of the world is most likely due to a lack of attention on the part of researchers who have looked at clay mineral suites in the past. This can be explained in part by the similarity of the respective major low-angle peaks which can be confused with montmorillonite (12 8 sepiolite-one water layer montmorillonite) and illite (10.5 8 palygorskite-slightly expanded illite). A priori there is no reason why these minerals should be particular to French sedimentary rocks except that workers from this country have been particularly alert to their presence. This opinion is reinforced by the now-frequent reports of sepiolite and, to a lesser extent, palygorskite in sea sediments of the Atlantic shelf and ridge, Mediterranean, Red Sea and Pacific deep sea (see JOIDES reports—National Science Foundation Publications). 

Laboratory synthesis of aluminum-free sepiolite (Siffert, 1962  

Wollast, et al., 1968) at 1 atmosphere, 25°C, demonstrates the inherent stability of this mineral at surface conditions. These experimental studies establish the necessity of an alkaline solution (pH 8) and sili v on-centration in aqueous solution controlled by the presence of amorphous silica (20-150 ppm). Calculations based upon laboratory synthesis data suggest that sepiolite could form in equilibrium with quartz (i.e., 10 ppm 

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There are several other types of minerals commonly found in clay particle size mineral assemblages (i.e.,< 2 microns diameter, Krumbein and Pettijhon, 1938). Aside from quartz and amorphous materials, the two most important mineral groups are sepiolite-palygorskite and zeolites. These two groups are similar in that they both contain free 1 0 molecules in their structure. However the Si-0 linkage is quite different in each case. 

Only the pure Mg-Si form of sepiolite has been produced in the laboratory (1 atm 25°C) however, one can suppose that the entire sepiolite-palygorskite series is stable at low temperatures. The extent of solid solution is assumed to be near that represented by the natural minerals in Figure 39. This is probably inaccurate to a certain extent since only 22 analyses were used, but underestimation will probably not affect the chemiographic relations of the phases concerned. 

We will consider only two parageneses or facies of the system relevant to sepiolite-palygorskite minerals that where these minerals are stable and that just above their stability (Figure 42). This is estimated provisionally to be somewhat below 80°C. This temperature is justified through comparison with the observed stability (rv/100°C) of natural aluminous, alkali-bearing montmorillonite, which accompanies sepiolite-... 

Figure 41. Phase diagram for the extensive variables R -R -Si combining the data for synthetic magnesian chlorites and the compositional series of natural sepiolites and palygorskites. Numbers represent the major three-phase assemblages related to sepiolite-palygorskite occurrence in sediments. Chi = chlorite M03 = trioctahedral montmorillonites M02 = dioctahedral montmorillonite Sep = sepiolite Pa = palygorskite Kaol = kaolinite T = talc.

Figure 42. Schematic sedimentary cross-section of a typical northwest Africa marginal sedimentary basin containing sepiolite-palygorskite bearing sediments (after the summary presented by Millot, 1964) K = Kaolinite ...

Palygorskile and Sepiolite. Palygorskite (anapalgite) and sepiolitc arc day minerals in which the 2 1 layers are linked together in chain-likc or a combination of chain-sheet structures. 

Similarly pure beds of kerolite and sepiolite are found in the modern and Pleistocene groundwater wetlands of Amboseli, Kenya (Stoessell and Hay, 1978 Hay and Stoessell, 1984 Hay et al, 1995). The concentration of dissolved silica is also important at higher ratios of Si02 to Mg, chain-structure clay (sepiolite-palygorskite) can precipitate directly from solution, as is also the case at Amargosa. 

Sepiolite/ Palygorskite Phyllosilicates Marine sediments, arid soils, high Si and Mg levels R Moderately high CEC.15 surface area, and sorptive properties... 

One of the questions that can be answered with the help of adsorption measurements concerns the microtexture of natural clay minerals. Several idealized models for the texture of soil clays (see [5]) have been considered, but rather than assuming one model a priori, one should try to gain useful information from experimental relationships between the size of clay particles and apparent density or surface area and internal porosity, as described in Sections 6.1 and 6.2.1. Experiments aiming at the evaluation of the microtextures of clay minerals were carried out by Ben Ohoud and van Damme [95], who studied kaolinite, sepiolite, palygorskite and 20 monoionic montmorillonite samples. The accessible surface area S of consecutive fractions of size r was measured by N2 adsorption using the classical BET method, whereas the open porosity P was measured from the amounts of adsorbed N2 at a relative vapor... 

This chapter reviews the use of the sepiolite/palygorskite group of clays as a nanofiller for polymer nanocomposites. Sepiolite and palygorskite are characterized by a needle-like or fiber-like shape. This peculiar shape offers unique advantages in terms of mechanical reinforcement while, at the same time, it allows to study the effect of the nanofiller s shape on the final composite properties. The importance of the nanofiller shape for the composite properties is analyzed in Section 12.2, introducing the rationale of the whole chapter. After a general description of needle-like nanoclays in Section 12.3, the chapter develops into a main part (Section 12.4), reviewing the preparation methods and physical properties of polyolefin/needle-like clay nanocomposites. 

Polymeric compositions contain clay nucleating agents. The clays are preferably sepiolite, palygorskite/attapulgite, or their combinations. The resulting products llud particular application as insulation and packaging materials. ... 

Palygorskite- Sepiolite Palygorskite, Sepiolite, Loughlinite, Falcondoite, Yofortierite... 

Selective sorption of hydrocarbons by palygorskite and sepiolite Palygorskite/n-heptane + iso-octane Barter et al. (68)... 

Silicates Sheet silicates Clays Sepiolites Palygorskite... 

Table 1 Classification of planar 2 1 clay minerals (non-planar modulated structures (e.g. sepiolite, palygorskite) see [123])...

Four natural silicates were used diatoroite or kieselguhr, sepiolite, palygorskite and bentonite. All of them were from Spanish deposits of great abundance and purity. 

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