Clays as adsorbents

Utilization of organophilic smectite clays as adsorbents of phenol and BTEX compounds... 

According to several studies cited, it is possible to use effective organophilic clays as adsorbents for the removal of organic substances with high toxicity, such as phenols and BTEX compoimds. 

Rianelli, R. S., Pereira, W. C. (2001). Clays as adsorbents of elements potentially contaminating. In Department of Industrial Chemical and Environmental Geochemical, www.cetem.gov.br/publicacao/serie anais IX jic 2001/Renatari.pdf, accessed in August of 2011. 

Mckay, G., Otterbum, M.S., and Aga, J.A. 1985. Fuller s earth and fired clay as adsorbent for dyestuffs. Equilibrium and rate study. Water Res. 24 307-322. 

Hecht SS (2003) Carcinogen derived biomarkers applications in studies of human exposure to secondhand tobacco smoke. Tob Control 13 48-56. doi 10.1136/tc.2002.002816 Hinteregger C, Loidl M, Streichsbier F (1992) Characterization of isofunctional ring cleaving enzymes in aniline and 3-chloroaniline degradation by Pseudomonas acidovorans CA28. FEMS Microbiol Lett 97 261-266. http //www.doi.oig/10.1016/0378-1097(92)90346-P Hodne O, Boufatit M, Khouider A (2004) Use of montmorillonite clays as adsorbents of hazardous pollutants. Desalination 167 141—145... 

Clays have layers of linked (Al, Si)04 tet-rahedra combined with layers of Mg(OH)2 or AI(0H)3- Clays are very important soil constituents and are used in pottery, ceramics, as rubber, paint, plastic and paper fillers, as adsorbents and in drilling muds. 

Adsorption of Metal Ions and Ligands. The sohd—solution interface is of greatest importance in regulating the concentration of aquatic solutes and pollutants. Suspended inorganic and organic particles and biomass, sediments, soils, and minerals, eg, in aquifers and infiltration systems, act as adsorbents. The reactions occurring at interfaces can be described with the help of surface-chemical theories (surface complex formation) (25). The adsorption of polar substances, eg, metal cations, M, anions. A, and weak acids, HA, on hydrous oxide, clay, or organically coated surfaces may be described in terms of surface-coordination reactions ... 

Because clays (rocks) usually contain more than one mineral and the various clay minerals differ in chemical and physical properties, the term clay may signify entirely different things to different clay users. Whereas the geologist views clay as a raw material for shale, the pedologist as a dynamic system to support plant life, and the ceramist as a body to be processed in preparation for vitrification, the chemist and technologist view clay as a catalyst, adsorbent, filler, coater, or source of aluminum or lithium compounds, etc. 

Barrer, Xeolites and Clay Minerals as Adsorbents and Molecular Sieves, Academic Press, New York, 1978. 

Bors J, Dultz S, Riebe B (2000) Organophilic bentonites as adsorbents for radionuclides I. Adsorption of ionic fission products. Appl Clay Sci 16 1-13... 

Kowalska M, Gtiler H, Cocke DL (1994) Interactions of clay minerals with organic pollutants. Sci Total Environ 141 223-240 Kukkadapu RK, Boyd SA (1995) Tetramethylphosphonium-smectite and tetramethylammonium-smectite as adsorbents of aromatic and chlorinated hydrocarbons - effect of water on adsorption efficiency. Clays Clay Miner 43 318-323... 

Mortland MM, Shaobai S, Boyd SA (1986) Clay-organic complexes as adsorbents for phenol and chlorophenols. Clays Clay Miner 34 581-595... 

Table 1 shows that Uranium is largely present as adsorbed and exchangeable forms in clays, which make up average 30.4% of the total contents in the soils over a known uranium deposit, Xinjiang. 

Another important feature of this type of sorption is that the nature of the cations serving as the counterions on the faces of clays affects the intensity of NAC sorption. These minerals bear a net negative charge in their interior due to iso-morphic substitutions (e.g., inclusion of a Al3+ in place of a Si4+ in the crystal lattice). As a result, the clay s exterior is covered by cations like potassium and sodium. NAC sorption is much greater when the clay has adsorbed potassium rather than calcium or sodium. This result has been interpreted to mean that the large hydrated ions of sodium and calcium can block NAC access to sites on a clay s surface, while the much less hydrated potassium ions can serve as counterions without blocking NAC... 

Natural minerals and rocks can be modelled as mixtures of clay-like adsorbents and oxide-like adsorbents. Various isotherms calculated from these assumptions are similar to experimentally observed isotherms for adsorption of Eu(III) on montmorillonite and corundum. Montmorillonite is of course a clay mineral, but it does have oxide-like groups. 

The usual way of representing polymer adsorption onto clay surfaces is to plot an isotherm showing the amount of polymer adsorbed in grams per gram of clay as a function of the equilibrium concentration of polymer in units of g cm 3. We have to be careful in comparing our results with standard isotherms because we are measuring the total amount of PEO inside the clay. This absorbed mass is not necessarily adsorbed onto the clay surfaces, but may be located in the interlayer solution. To reflect this difference, we have used the unusual nomenclature absorption isotherm rather than the usual adsorption isotherm in the presentation of the data. 

Removal of heavy-metal ions has been a major focus in environmental remediation and cleanup. Various materials, such as activated charcoal, clays, sihca gels, and ion-exchange resins have been used as adsorbents. Functionahzed mesoporous sihcas have recently proved to be a promising or even better alternative. Mercier etal. prepared a... 

The biological functions of such plant secondary metabolites (PSMs) have been debated for a long time. They often have antimicrobial functions, but also serve as repellents and feeding inhibitors against herbivorous insects and vertebrates, notably birds and mammals. Animals have evolved many mechanisms to cope with phenolics in their diet. These start with food processing. For instance, beavers consume experimental sticks of the phenolics-rich witch hazel only after leaving them in the water for 2-3 days, apparently to leach out unpalatable compounds (Miiller-Schwarze et al. 2001). Many birds and mammals eat clay to adsorb phenolics so they never will be absorbed in the intestines. If they are taken up in the blood stream, such PSMs will eventually be rendered harmless by oxidation and other processes, followed by conjugation, in the liver. They then will be excreted in the urine. 

Owing to its inert nature, magnesium aluminum silicate has few incompatibilities but is generally unsuitable for acidic solutions below pH 3.5. Magnesium aluminum silicate, as with other clays, may adsorb some drugs. This can result in low bioavailability if the drug is tightly bound or slowly desorbed, e.g., amfetamine sulfate, tolbutamide, warfarin sodium, and diazepam. ... 

Early work by the Public Health Engineering Department, Government of West Bengal (PHED, 1991) reported that arsenic is present as adsorbed ions on clay particles/quartz particles and also as primary arsenic mineral(s) . X-ray diffraction of the arseniferous horizons was reported to have shown traces of arsenopyrite. The reported As contents of sediments from Kochua, West Bengal were extremely low, <0.2 mg kg" in all cases, and below the detection limit (probably about O.I mg kg ) in the sandy horizons. 

The interaction between some organic contaminants and mineral surfaces has recently attracted attention as a way of cleaning up contaminants in natural waters. The large cation exchange capacity of smectite clay minerals (Section 4.5.2), in particular, has prompted research into their use as a catalyst, i.e. a substance that alters the rate of a chemical reaction without itself changing. Clay catalysts have potential applications as adsorbents to treat contaminated natural waters or soils. 

Many national programs plan to surround containers of their nuclear waste in a geologic repository, with a backfill of compacted bentonite clay (Fig. 13.33). A chief function of the clay backfill is to adsorb radionuclides and so retard their release from the engineered barrier system. Conca (1992) measured the apparent diffusion coefficient (D ) and apparent distribution coefficient (K [ml/g]) of some radionuclides in bentonite clay as a function of clay moisture content and compaction density. Measurements were made for clay densities from 0.2 to 2.0 g/cm, which correspond to porosities of 93 to 25%, respectively. With decreasing porosity, values declined by roughly 10 to 10 -fold. However, for the same porosity reduction, values were usually lowered by 10-fold and more, indicating less adsorption with compaction (Fig. 13.38). 

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