Clay complexes mechanisms

Later work showed similar adsorption-desorption behavior for NACs in clay types other than kaolinite. The adsorption constant was found to increase fairly uniformly for all tested NACs in the ratio of 1 6 12 (kaolinite iUite montmoril-lonite). This ratio is quite close to the relative surface areas of the three minerals illite and montmorillonite have 6 and 16 times more available surface area, respectively, than kaolinite (Haderlein, Weissmahr, and Schwarzenbach, 1996). This observation suggests that a similar EDA complexation mechanism controls the adsorption of NACs to these minerals as well. The authors also showed that TNT,... 

Hydrophobic organic ligands added to a carbon-paste electrode, or immobilized on a chemically modified electrode, can be used for the accumulation of metal ions by the surface-complexation mechanism [89-91], The same goal can be achieved by immobilized ion exchangers such as natural or synthetic zeolites [89], clay minerals [92], silica [93], and ion exchange resins [94] ... 

For surfactants that can decompose according to a nucleophilic substitution mechanism, the type of anion and its nucleophilicity were found to influence the thermal stability of salts and surfactant-clay complexes strongly. In the presence of halide anions, which are strong nucleophilic agents, the degradation path was activated at a lower temperature than it was observed at for PFg, NCSOaCFs), or BF4 anions, for example. 

Many factors affect the mechanisms and kinetics of sorption and transport processes. For instance, differences in the chemical stmcture and properties, ie, ionizahility, solubiUty in water, vapor pressure, and polarity, between pesticides affect their behavior in the environment through effects on sorption and transport processes. Differences in soil properties, ie, pH and percentage of organic carbon and clay contents, and soil conditions, ie, moisture content and landscape position climatic conditions, ie, temperature, precipitation, and radiation and cultural practices, ie, crop and tillage, can all modify the behavior of the pesticide in soils. Persistence of a pesticide in soil is a consequence of a complex interaction of processes. Because the persistence of a pesticide can govern its availabiUty and efficacy for pest control, as weU as its potential for adverse environmental impacts, knowledge of the basic processes is necessary if the benefits of the pesticide ate to be maximized. 

Transport in solution or aqueous suspension is the major mechanism for metal movement from the land to the oceans and ultimately to burial in ocean sediments. In solution, the hydrated metal ion and inorganic and organic complexes can all account for major portions of the total metal load. Relatively pure metal ores exist in many places, and metals from these ores may enter an aquatic system as a result of weathering. For most metals a more common sequence is for a small amount of the ore to dissolve, for the metal ions to adsorb onto other particulate matter suspended in flowing water, and for the metal to be carried as part of the particulate load of a stream in this fashion. The very insoluble oxides of Fe, Si, and A1 (including clays), and particulate organic matter, are the most important solid adsorbents on which metals are "carried."... 

Lewis acids such as SnCl4 also catalyze the reaction, in which case the species that adds to the alkenes is H2C —O— SnC. Montmorillonite KIO clay containing zinc(IV) has been used to promote the reaction. The reaction can also be catalyzed by peroxides, in which case the mechanism is probably a free-radical one. Other transition metal complexes can be used to form allylic alcohols. A typical example is. ... 

Theng BKG. 1971. Mechanisms of formation of clay-organic complexes A review. Clays and Clay Min 19 383-390. 

Organo-mineral association in the subsurface is a natural process controlled by a range of bonding mechanisms, and therefore it is practically impossible to separate one from other. The resulting organo-mineral complex has surface properties different from the original components. For example, hydrophilic clay surfaces may become hydrophobic. 

Mordand MM (1970) Clay-organic complexes and interactions. Adv Agron 22 75-117 Mordamd MM (1986) Mechanism of adsorption of nonhumic organic species by clays. In Huang PM, Schnitzer M (eds) Interaction of soil minerals with natural organics and microbes. Soil Sci Soc Amer, Madison, Wisconsin, pp 59-76... 

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