Clay sorption capacity

In addition to SOM, clay minerals are another important component that may influence contaminant-soil interactions. Expandable 2 1 type clays are usually more reactive than other clay minerals. Park et al. (2003) used a K-saturated montmorillonite as a sorbent to evaluate the availability of sorbed atrazine to three atrazine-degrading bacteria. K-saturated montmorillonite has a high atrazine sorption capacity with a Freundlich sorption... 

Therefore, based on available literature, the following sorption results were expected (l) as a result of the smectite minerals, the sorption capacity of the red clay would be primarily due to ion exchange associated with the smectites and would be on the order of 0.8 to I.5 mi Hi equivalents per gram (2) also as a result of the smectite minerals, the distribution coefficients for nuclides such as cesium, strontium, barium, and cerium would be between 10 and 100 ml/gm for solution-phase concentrations on the order of 10"3 mg-atom/ml (3) as a result of the hydrous oxides, the distribution coefficients for nuclides such as strontium, barium, and some transition metals would be on the order of 10 ml/gm or greater for solution-phase concentrations on the order of 10 7 mg-atom/ml and less (U) also as a result of the hydrous oxides, the solution-phase pH would strongly influence the distribution coefficients for most nuclides except the alkali metals (5) as a result of both smectites and hydrous oxides being present, the sorption equilibrium data would probably reflect the influence of multiple sorption mechanisms. As discussed below, the experimental results were indeed similar to those which were expected. 

Sorption Capacity. The average sorption capacity of the clay determined from isotopic redistribution of Cs 37 between aqueous 0.01 M CsCl solutions and cesium-saturated clay was 0.9I mequiv./ gm. The average sorntion capacity similarly determined by isotopic redistribution of Ba3-33 vas 0.7U mequiv./gm. The maximum relative error in these capacities was estimated at 10%. 

If those sorption capacities were due to ion exchange, it would be expected that preparation of the cesium- and barium-saturated clays would have caused various counter ions such as those of sodium, potassium, magnesium, and calcium to be desorbed from the clay and to appear in. the 1.0 M solutions. The total... 

The ion-exchange capacities discussed above (and the identification of the principal desorbing species) appear consistent with capacities of about O.U to 0.8 mequiv./gm (principal desorbing species being sodium, potassium, calcium and magnesium) reported for a related pacific red clay (7). The sorption capacities given above also appear reasonably consistent with capacities of about 0.8 to 1.5 mequiv./gm, which have been reported for related clay minerals found within the continental United States (8,9>10>12,lU). 

Bader (2) found that various clay minerals have large sorption capacities for dissolved organic compounds. 

The sorption capacity of clay ranges from 1.0 for alcohols and basic compo unds such as allyl alcohol and ammonium hydroxide respectively, to 1.6 for aliphatic halogenated hydrocarbons such as trichloroethylene. Therefore, the sorption capacity of clay is very low when compared to the other materials available. However, this material is one of the most inexpensive materials and can be purchased for approximately 0.04/lb to 0.12/lb depending upon supplier and quantity ordered. 

The sorption capacities range from 3.0 for amines, such as triethylamine, to 7.1 and 8.1 for inorganic acids and inorganic halides, such as nitric acid and phosphorus trichloride, respectively. Therefore, the sorption capacity of expanded minerals is far superior to that of clay and diatomite. However, this material is more expensive than clay but cheaper than diatomite. Micafil/perlite can be purchased for approximately 0.12/lb to 0.31/lb and vermiculite for approximately 0.14/lb, depending upon supplier and quantity ordered. 

Clay minerals, natural and synthetic zeolites, silica and aluminum oxide forms generally are a mineral phase in mineral-carbon adsorbents. Natural aluminosilicates, particularly zeolites, due to the existence in their structure of ultramicropores and micropores (with pore diameter below 2 nm) with hydrophilic properties, exhibit high sorption capacity for particles of water vapor as well as sieve properties. They also demonstrate very good ion exchange properties. For instance, the ion exchange capacity of zeolite NaA is about 700 mval/100 g. 

The Mn ion sorbs both to clay minerals and to iron-oxyhydroxide, and the sediment s exchange capacity increases in proportion to the amount of iron-oxyhydroxide which precipitated in the previous runs. The increasing retardation associated with the increase of the sorption capacity is clearly visible in Figure 7 in the delayed increase of the Mn concentration in run 7 compared to run 1. The retardation is directly related to the number of sorption sites on the iron-oxyhydroxide precipitate which is discussed next. The model shows a reasonable match of the observed concentrations but tends to be less disperse. 

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]. 

Trace elements in cationic form are probably not dominantly sorbed on 001 faces of phyllosilicates because they are always vastly outnumbered by other cations with which they compete (Jackson, 1998). They may be strongly sorbed only on the edges of the phyllosilicates. However, clay minerals also have an important role as carriers of associated oxides and humic substances forming organomineral complexes, which present peculiar sorption capacities different from those of each single soil constituent (Jackson, 1998 Violante and Gianfreda, 2000 Violante et al., 2002c). 

The low-temperature desorption processes are best suited for removal of organics from sand, gravel, or rock fractions. The high sorption capacity of clay or humus decreases partitioning of organics to the vapor phase, making these materials difficult to process. The debris considered in this study will have little or no clay or humus. 

Sorption capacity manifested by binding and exchanging univalent and bivalent cations. Clay soils are characterized by a high sorption capacity. 

Humic acids are soluble in weak alkaline solutions and are essentially insoluble in water and mineral acids. They may be precipitated from solution by the action of mineral acids and bivalent or trivalent cations, however, they are fairly resistant to the acid hydrolysis. They are dark spherocol-loids with a cross-linked structure which plays a part in their high sorption capacity. They exhibit different degrees of a tendency to aggregation and very different degrees of dispersion. In comparison with other types of natural organic substances, the humic acids are characterized by their extraordinary stability in the soil. This stability is due to their ability to form organomineraJ complexes, particularly with clay minerals and with aluminium and iron hydroxides. 

Nanocomposites of iron oxide and silicate were also synthesized for the degradation of azo-dye Orange II (see Table 7) [388, 389]. To improve the sorption capacity, clays were modified in different ways (e.g. treatment by inorganic and organic compounds). Organoclays have recently attracted lots of attention in a number of applications, for example, dithiocarbamate-anchored polymer/organosmectite for the removal of heavy metal ions from aqueous media (see Table 7) [390]. 

The sorption of parathion and Lindane from a hexane solution has been studied using a Woodburn soil (fom = 0.019 68% silt 21% clay). ° An oven-dried soil gives a nonlinear isotherm (Fig. 3.14) that shows a much higher sorption capacity than that observed using water as solvent (Fig. 3.9). It is preferable to make this comparison on a relative basis since parathion, at 20°C, has a higher solubility in hexane (57 g L ) than water (12 mg L ). Thus Ce = 4 ppm C /S = 0.33) in an aqueous system corresponds to a sorption of 55 p,g g of soil. In a hexane system with Ce = 100 ppm (Ce/5h = 0.002) a sorption of 4000 p.gg of soil is observed. Sorption is decreased by water (compare the air- and oven-dried soils), and essentially no sorption is observed if the soil water content is increased to 5%. Decreased sorption at higher temperature would suggest an exothermic adsorption process. Parathion did not sorb to any extent from hexane onto a peat soil (/om = 0.51). The effect of water on the sorption of Lindane on the Woodburn soil from hexane (Fig. 3.15) was more pronounced and it was also demonstrated that parathion could compete with and reduce the sorption of Lindane. 

In the AD expanded saponite, acidity increases, Hgure 5-9C. As expected, the amount of pyridine retained on the clay acid centers monotonically decreases with temperature. If AD is replaced by SCD, Bronsted acidity is enhanced. Figure 5-9D. The steam-aged clays retain their sorption capacity for pyridine. However, their acid site strength is greatly reduced, and after degassing in vacuo for 2h at 200 C, pyridine is essentially removed from the steam-aged expanded clay samples. 

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