Palygorskite, composition

The term fibrous, as applied to zeolites, does not necessarily indicate flexibility. Flexibility, however, is one of the physical properties of cotton stone found on the Isle of Skye, Scotland. This locality provides a feathery sample of mesolite, (Na2Ca2Al6SigO30 8H2O), whose composition and structure place it in the same group as natrolite. The similarity between appearance of this sample and that of the mountain flax variety of palygorskite emphasizes the difficulty of identifying fibrous minerals based on morphology alone. 

Sepiolite and palygorskite have a rather special composition and seem to be related to specific mineral parageneses. They appear to be stably associated with montmorillonite, corrensite, serpentine, chert, sulfates, carbonates and various salts. They are found in deposits typified by processes of chemical precipitation or solution-solid equilibria (Millot, 1964) and are therefore rarely associated in sediments with large quantities of detrital minerals. Their chemical environment of formation is in all evidence impoverished in alumina and divalent iron. Their frequent association with evaporites, carbonates and cherts indicate that they came from solutions with high chlorinity. 

High pressure studies using natural sepiolite and palygorskite (Frank-Kameneckiji and Klockova, 1969) indicate that these minerals can contain variable quantities of silica because they exsolve quartz while retaining their basic structural and mineral identity. These experiments also demonstrate that the natural minerals are compositionally intermediate between talc or montmorillonite and quartz. These latter phases are formed upon the thermal breakdown of sepiolite and palygorskite under conditions of 1 and 2Kb total pressure. Both sepiolite and palygorskite appear to remain stable in sequences of buried rocks, at least up to the depth where fully expandable dioctahedral montmorillonite disappears (Millot, 1964). 

Since neither mineral is conspicuously alkali-rich, the M R -2R -3R plot is not appropriate to represent their bulk compositions. Both sepiolite and palygorskite contain small but variable amounts of Ca, Mg,... 

Figure 39. Compositions of natural sepiolites and palygorskites as a function of the variables Si-R -R where R Mg + Fe + Ca, R = Fe + + Al. Crosses = sepiolite, dots = palygorskite.

Given the chemical data for natural mineral compositions, it should be possible to construct a phase diagram including those phases that are likely to occur with sepiolite and palygorskite in a system where the mass of the components is an extensive variable of the system (a closed system). 

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.

Christ et al. (1969) found that X-ray diffraction powder data for palygorskite samples show both orthorhombic and monoclinic structures and suggested that the variations in symmetry reflect variations in chemical composition. The present data suggest the most likely difference is octahedral Fe. 

Only a few analyses have been made of palygorskite but it is enough to indicate that the composition is probably as variable as that of the 2 1 minerals. Some of the variations are due to the presence of montmorillonite which is commonly intimately associated with the attapulgite and is difficult to remove. 

Caillere, S., 1934. Observations sur la composition chimique des palygorskites. Compt. Rend. 198 1795-1798. 

Similarly to the case of the hydrophobic clay minerals described above, isotherms determined on HDP-palygorskite are S-shaped (Fig. 18). Surface modification by HDP" -cations has a double effect. On increasing the amount of HDP-cations the liquid sorption capacities decrease, since the micropores get clogged. On the other hand, the polarity of the surface decreases and the azeotropic composition indicates the displacement of the alcohol on the surface[50]. 

Palygorskite (T), and sepiolite (5) are the end members of a modular series named palysepiole (pa/ygorskite -f sepiohit) polysomatic series P S [47] kalifersite is the P Si member. Falcondoite [51] and loughlinite [52] differ from sepiolite only in the composition of the O sheet in the TOT ribbons the same situation holds for yofortierite [53] and tuperssuatsiaite [54] in comparison to palygorskite. 

Clay constitutes the most abundant and ubiquitous component of the main types of marine sediments deposited from outer shelf to deep sea environments. The clay minerals are conventionally comprised of the <2 pm fraction, are sheet- or fiber-shaped, and adsorb various proportions of water. This determines a high buoyancy and the ability for clay to be widely dispersed by marine currents, despite its propensity for forming aggregates and floes. Clay minerals in the marine environments are dominated by illite, smectite, and kaolinite, three families whose chemical composition and crystalline status are highly variable. The marine clay associations may include various amounts and types of other species, namely chlorite and random mixed layers, but also ver-miculite, palygorskite, sepiolite, talc, pyrophyllite, etc. The clay mineralogy of marine sediments is therefore very diverse according to depositional environments, from both qualitative and quantitative points of view. 

Figure 13 Tetrahedron layers of composition Si20s in the structures of (a) pentagonite Ca(VO)[SLOiQ 4hhO-(b) palygorskite /A Mg / S/ljOio rOW -S O (c) sepyolite MgQ[Sl40 ok(O.OH) -8H20 and (d) antygorite...

Rong, J., Sheng, M., Li, H., and Ruckenstein, E. 2002. Polyethylene-palygorskite nanocomposite prepared via in situ coordinated p>olymerization. Polymer Composites 23 658-665. 

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. ... 

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