Vermiculite hydrophobicity

Giese et al. [48] have compiled a list of y+ and y values for a variety of clay minerals. Smectites, vermiculites, and micas tend to be very hydrophilic, with y > 28mJ/m2 and with a sizable electron acceptor parameter as well (y+ > 1 mJ/m2). Illites, on the other hand, were reported to be moderately hydrophobic (y varied from 14 to 19mJ/m2) and tended to have y+ — 0. 

Illite as a non-swelling clay mineral of layer structure plays a very important role in our studies. This special role is due to the fact that both sides of the surface of the silicate lamellae are made up of Si04-tetrahedron planar lattices, and this structure - even when hydrophobized - is identical with the surface structure of montmorillonite and vermiculite, both of which are of the swelling type. 

A number of sorbents have been proposed to clean water surfaces from oil [318]. The use of hydrophobic aerosil was proposed for this purpose, which, however, can hardly be accomplished for economic reasons. More promising seems to be the proposal to use natural materials for oil absorption, such as turf, diatomite, vermiculite, swelled perlite. A method has been proposed for the modification of perlite by a consequent treatment with cationic surfactants and higher carboxylic acid salts. Such modification of swelled perlite increases its oil capacity up to 600%, the water absorption decreases 10 -100-fold, and the sinkability decreases considerably. The degree of oil removal from the water surface is, according to in vitro tests data, 98 - 99%. Methods have been found to use oil-saturated sorbents. 

The adsorption of crude oil was performed in dehydrated (expanded) and hydrophobized vermicuHte samples, denoted here as EV (expanded vermicuHte) and HV (hydrophobized vermiculite), respectively. Vermiculite samples with five different grain sizes were used 100-150, 150-200, 200-250, 250-325, and 325-400 mesh. The crude oil had the following properties density, 34.2 °API (at 15.6°C) and viscosity, 8.4 cP (at 37.8°C) ... 

The hydrated vermiculite samples were expanded (dehydration process) by heating them at 800°C for 30 min. The hydrophobization process was performed by heating the EV samples with camauba (Copernicia cerifera) wax to produce a 10%... 

Based on the 20 values for the 100 diffraction peak, the interlayer distance for the hydrated and anhydrous samples can be calculated as 1.34 and 0.95 nm, respectively. The observed decrease of the interlayer distance for the expanded sample can be associated with the release of water molecules observed under heating [3]. On the other hand, the hydrophobized matrix exhibits the same XRD pattern of the expanded one. Based on this fact, it can be concluded that the hydrophobizant molecules are adsorbed on the surface of the vermiculite grains and not into the interlayer space, that is, there is not the formation of an vermiculite—hydrophobizant intercalation compound. 

Table 8.1 Results for adsorption of crude oil on expanded and hydrophobized vermiculite samples...

Figure 8.4 UV-Vis spectroscopic results for the adsorption of crude oil from a water—oil emulsion on anhydrous (a) and hydrophobized (h) vermiculite samples.

Based on the experimental data, it can be concluded that hydrated vermiculite exhibits a very low adsorption capacity for crude oil. On the other hand, anhydrous (expanded) and hydrophobized matrices show high adsorption capacities. The 10% hydrophobized matrix shows a 50% increase in adsorption capacity, in comparison with the expanded one. For adsorption process performed in a water—oil emulsion (50 ppm of oil), the saturation of the soHd hydrophobized matrix is achieved after 60 min. 

Carbon nanotubes (CNTs) have a unique one-dimensional stmcture, laige specific surface area, and are oleophilie and hydrophobic [64]. As filter materials, CNTs exhibit seleetive separation eharacteristics for different solutions [65, 66]. The CNTs directly synthesized on the surface of expanded vermiculite eould signifieantly improve the oil sorption capaeity by forming a hydrophobie surface [67],... 

The structure and the sorption properties of partially hydrophobized silicates (do-decylammonium and dodecyldiammonium vermiculites) were investigated in aqueous solutions of n-butanol. The alcohol is preferentially adsorbed on the surface. The interlayer composition is calculated from adsorption and X-ray diffraction data. In the air-dried state the organic cations lie flat on the interlamellar surface. In aqueous n-butanol solutions, the basal spacing of dodecylammonium vermiculite gradually increases with the extent of n-butanol adsorption because the chains increasingly point away from the surface. The basal spacing of dodecyldiammonium vermicuiite is virtually independent of the interlayer composition, because the expansion of the interlayer space is sterically restricted and a... 

FIG. 28 Schematic representation of the hydrophobic vermiculite at different basal dis-tances (a) monolayer (b) bridging (c) bilayer orientation. 

Vermiculite from South Africa was made hydrophobic by cation exchange with dodecylammo-nium and dodeeyldiammonium ehloride. Before the adsorption and mieroealorimetrie measurements, these organophilie vermieulites were dried in a vacuum dessicator overnight at 340 K. The butanol-water solutions were prepared by diluting the lower, butanol-saturated phase with... 

Perlite or vermiculite, treated with a cationic fluorinated surfactant, is claimed to be hydrophobic and effective in cleaning oil spills [231]. 

In spite of the fact that both hydrophilic and hydrophobic clay and other minerals particles surfaces consist of metal oxides, with the oxygen atoms in all cases prominently exposed at the surface of the mineral, some are very hydrophobic. As shown above (Table 8.3), hydiophilicity is mainly determined by a high value of the electron donor parameter (7 ) of the polar component (7 ) of the surface teninon. This strong dectixm-donicity (Lewis basicity) is mainly due to the relatively loosely bound oxygen atoms at the surface of hydrophilic clay particles, such as smectites, vermiculites, micas or other metal oxide surfaces, such as silica (see Chapter 9 for the 7 -values of various clay and other mineral particles). 

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