Kaolinite clay particles

Other studies use soil or sediment samples for a more accurate indication of microbial activity in natural environments. In these samples, organic matter and clay particles play a role in metal toxicity.76112113 Both organic material and clay particles in soil can bind metals and reduce their bioavailability. For example, Pardue et al.87 demonstrated that much less solution-phase cadmium was required to inhibit trichloroaniline (TCA) dechlorination in a mineral-based soil than in a soil containing a higher concentration of organic matter. Other studies have shown that adding clay minerals to a medium mitigates toxicity. Clay minerals, such as kaolinite, montmorillonite, bentonite, and vermiculite, can bind to metals to decrease the amount that is bioavailable.112 115... 

More than 20 different types of clay can be actually distinguished. Those most appreciated for making ceramics, for example, kaolinite, are built up of combinations of the basic structural units described above. The particles of most consist of platelets (very small, flat sheets) that, when stacked together, form layered arrangements having extensive surface areas, much like the pages of a book. Other common clay particle shapes are fibrous or tubular. 

Adsorption on Kaolinite. For kaolinite, the polymer adsorption density is strongly dependent on the solid/liquid ratio, S/L, of the clay suspension. As S/L increases, adsorption decreases. This S/L dependence cannot be due totally to autocoagulation of the clay particles since this dependence is observed even in the absence of Ca2+ at pH 7 and at low ionic strength where auto-coagulation as measured by the Bingham yield stress is relatively weak (21). Furthermore, complete dispersion of the particles in solvent by ultra-sonication before addition of... 

Figure 3.3. The left structure represents kaolinite, a 1 1 clay mineral, and the right structure, a 2 1 clay mineral. These representations are intended to show surface groups, surface pairs of electrons, unsatisfied bonds, and associations between clay particles. Note that clay structures are three-dimensional and these representations are not intended to accurately represent the three-dimensional nature nor the actual bond lengths. Also, the brackets are not intended to represent crystal unit cells.

FIG. 1.12 Electron micrograph of two different types of particles that represent extreme variations from spherical particles (a) tobacco mosaic virus particles (Photograph courtesy of Carl Zeiss, Inc., New York) and (b) clay particles (sodium kaolinite) of mean diameter 0.2 fim (by matching circular fields). In both (a) and (b), contrast has been enhanced by shadow casting (see Section 1.6a.2a and Figure 1.21). (Adapted from M. D. Luh and R. A. Bader, J. Colloid Interface Sci. 33, 539(1970). 

Galactomannans have been used as flocculents (for the purification of ores, for example) and a study has been made of the gum structure by electron microscopy. The smallest fiber-diameter for an evaporated film of guar gum was found260 to be 4 nm, but, when a kaolinite-guar gum flocculate was examined, the diameter of the smallest fiber that was attached to the kaolin was found to be 10 nm. It is suggested that flocculation is caused by polymer bridging of the clay particles. 

Clay colloids provide a good example of the kinds of structures that can be formed upon flocculation. The association of plate-like clay particles is complicated by the fact that minerals such as montmorillonite, illite, and kaolinite can exhibit different surface charges at different particle surfaces. 

In carrier flotation, small-sized (several pm diameter) particles become attached to the surfaces of larger particles (perhaps 50 pm diameter, the carrier particles) [630]. The carrier particles attach to the air bubbles and the combined aggregates of small desired particles, carrier particles, and air bubbles float to form the froth. An example is the use of limestone particles as carriers in the flotation removal of fine iron and titanium oxide mineral impurities from kaolinite clays [630]. The use of a fatty acid collector makes the impurity oxide particles hydrophobic these then aggregate on the carrier particles. In a sense, the opposite of carrier flotation is slime coating, in which the flotation of coarse particles is decreased or prevented by coating their surfaces with fine hydrophilic particles (slimes). An example is the slime coating of fine fluorite particles onto galena particles [630],... 

Deflocculation, including its secondary effects, is a result of ion exchange on the surface of clay particles. The efficacy of this colloid-chemical adjustment is illustrated by the example reported by Norton (1952) addition of NaOH solution to mono-disperse fraction of H -kaolinite prepared by dialysis gives rise to an (approximately) 200-fold decrease in apparent viscosity, affected instantaneously in the region of pH 5-6, where complete exchange of ions for Na " has taken place. 

Figure 7.42 Effect of HCl and NaOH on the formation and stability of E. co/i-kaolinite complexes. The ordinate signifies the number of cells adhering to one clay particle. Addition of sodium hydroxide decreases adhesion.

Various soils (Table 1) were used in the course of experiments quartz sand and sand-clay mixes consisting of quartz sand with kaolinite or montmorilIonite clay particles. The weight content of clay particles was chosen as 7 and 14%. 

The analysis of hydrate formation under cooling to sub-zero temperatures shows that there is an activation of the hydrate formation process during the freezing of the remaining pore water. Some 10-25 % of the total amount of CO2 hydrate is formed during the water freezing process. This portion increases in samples with clay particles, in particular for kaolinite. 

As clay particles decrease in size, the relative importance of broken bonds increases. This effect is illustrated in Fig. 10.3, which plots clay CEC versus particle size. As expected, the size effect is most important for kaolinite and decreasingly important for illite and the smectite clays nontron-ite and saponite. Thus, in the size range from 1.0 to 0.1 /tim, the CEC of the Georgia kaolinite increases from about 3.4 to 7.3 meq/100 g. The plot shows that this increase of about 4 meq/100 g is practically negligible for the smectites, which have CEC values of 60 meq/100 g or more. 

The cation exchange capacity of clays results from lattice imperfections or defects, isomorphous substitutions, and/or broken bonds on clay particle surfaces. Explain how the CEC s of kaolinite, the smectites, and illite, and their variation with pH, reflect these sources of their surface charge. 

As a result, the permeabilities in these domains within the formation become more uniform. Reduction in permeability in the more permeable domains improves the mobility ratio of waterflood. Premature breakthrough is thus reduced, and the efficiency of the waterflood is improved (Boston et al., 1969). Poorly cemented clay particles, such as kaolinite and illite, can become detached during aqueous flow, especially when flowing brines become fresher. 

Eventually, the average masses N(t) and 5(0 depend on the mass value affected to each aggregate constituent. For monosized latex particles the mass 1 is attributed to single particles. When, as for oxides and clays, the original colloid is polydisperse in mass and size, the mass 1 is attributed either to particles of diameter d, of the smallest constituent (as for aluminum oxide) or to particles characterized by the average diameter dn given by the counter (as for the kaolinite clay). This choice only affects the absolute values of 5(f) or N(t) but does not modify the exponents of the power laws used to express fragmentation and breakup rates. 

The observed microscopic structure or particular interparticle associations were found to correlate with bicarbonate ion concentration, although, as mentioned earlier, small concentrations of organic surfactants released by the caustic extraction process (that would also correlate with bicarbonate concentration) cannot be ruled out. Figure 25 shows MFT created without caustic [the other six lease owners (OSLO) process]. No structure comparable with that observed in the MFT from the Clark extraction process is evident in this sample despite its similar particle size distribution and weight percent solids. Kaolinite clays in deionized... 

Cranston and Buckley (18) examined the retention of latex beads, kaolinite clay, dissolved organics, and dissolved inorganics on five different membrane and fiber filters. Their interest was to select filters that gave the best particle retention and the most consistent gravimetric results. The Nuclepore membrane performed best except for retention of dissolved humic materials Nuclepore membranes were particularly good for not retaining dissolved salts from seawater filtration. 

More evidence for electrokinetically assisted surface transformations in kaolinite clay was found when a clean specimen of the clay was permeated with polymer-coated dispersed nanoiron particles of positive surface charge (Sun et al., 2006) under an electrical gradient of O.lV/cm (Pamukcu, Hannum, and Wittle, 2008). 

E.A.C. Follett, W. J. McHardy, B. D. Mitchell, and B.F.L. Smith, Chemical dissolution techniques in the study of soil clays. Clay Minerals 6 23 (1965). E.A.C. Follett, The retention of amorphous, colloidal ferric hydroxide by kaolinites, J. Soil Sci. 16 334 (1965). A. W. Fordham and K. Norrish, Electron microprobe and electron microscope studies of soil clay particles, Aust. J. Soil Res. 17 283 (1979). 

---