Adsorption on clays

Fig. 5.3 First order plots of potassium adsorption on clay, where is the quantity of potassium adsorbed at time t, and K is the quantity of potassium adsorbed at equilibrium (Sparks and Jardine 1984)...

Competitive adsorption on clay and soils surfaces between a heavy metal contaminant (Cu) and a cationic herbicide (chlordimeform) was reported by Maqueda... 

The amount of adsorbed chemical is controlled by both properties of the chemical and of the clay material. The clay saturating cation is a major factor affecting the adsorption of the organophosphorus pesticide. The adsorption isotherm of parathion from an aqueous solution onto montmorillonite saturated with various cations (Fig. 8.32), shows that the sorption sequence (Al > Na > Ca ) is not in agreement with any of the ionic series based on ionic properties. This shows that, in parathion-montmoriUonite interactions in aqueous suspension, such factors as clay dispersion, steric effects, and hydration shells are dominant in the sorption process. In general, organophosphorus adsorption on clays is described by the Freundhch equation, and the values for parathion sorption are 3 for Ca +-kaoUnite, 125 for Ca -montmorillonite, and 145 for Ca -attapulgite. 

In order to increase the yields of good quality, high viscosity lubricating oils which were in demand at that time, the industry was faced with the problem of developing more efficient methods for separating the oil from the asphaltic materials in the residue. In many cases the residue represented a substantial proportion of the crude oil. Investigations undertaken included chemical treatment with sulfuric acid (35), removal of the asphaltic materials with metallic chlorides (50, 66), and adsorption on clay (56). Solvent precipitation of the asphalts also was studied (11,18, 19, 38, 78). 

Asphaltic materials may be separated from the residue by adsorption on clay. The oil is percolated through a relatively tall column of comparatively coarse clay or mixed with a selected clay of fine mesh at relatively high temperatures, and the spent clay is removed by filtration. 

Column chromatography is generally used for compositional analyses (ASTM D-2007 ASTM D-2549). The former method (ASTM D-2007) advocates the use of adsorption on clay and clay-silica gel followed by elution of the clay with pentane to separate saturates, elution of clay with acetone-toluene to separate polar compounds, and elution of the silica gel fraction with toluene to separate aromatic compounds. The latter method (ASTM D-2549) uses adsorption on a bauxite-silica gel column. Saturates are eluted with pentane aromatics are eluted with ether, chloroform, and ethanol. 

Answer 16.4 The leachate monitored by the piezometers located in the pit revealed that a threat to local groundwater exists. (What are the concentrations of the various ions ) A plume of leachate entering the local groundwater is observed in the direction of the water level gradient. Contamination is noticeable at a distance of how far (use the scale of the maps) The mentioned observation that metals found in the leachate do not show up in the monitoring wells is explainable by adsorption on clay material in the soil. However, this means that a hallow of metals is formed in the soil and it may reach local groundwater in the future. Therefore, metals observed in the leachate should be measured periodically in the monitoring wells. 

The publications on amino acid adsorption on clay minerals before 1974 are summarized in the book by Theng (1974). It provides information on the adsorbed quantity of different amino acids on cation-exchange montmorillonites and the characteristic IR bands of amino acid-montmorillonites adsorption compounds. Usually, only the adsorbed quantity of amino acids on montmorillonites is shown, and no adsorption mechanism is usually hypothetized (e.g., Friebele et al. 1981 Rak and Tarasevich 1982), except in Stadler and Schindler (1993a) where the adsorption is evaluated by the surface-complexation model, and the possible surface complexes are given for p-alanine. 

The structure of the organic molecules may also undergo changes as a result of adsorption on clay minerals, causing catalytic transformations (Chapter 1, Section 1.3.5). The cations of the clay minerals may also effect these transformations. 

Several sets of experimental data providing proton adsorption and ion adsorption on clays and clay-containing soils are described below and modeled later. The description starts with two monmorillonite samples, continues with illite, and finishes with a kaolinitic soil. 

This retardation is caused by adsorption on clays and organic materials. The adsorption capacity is in turn a function of the surface area and availability of these materials to the adsorbing species in question. In real soils, and especially those of sedimentary origin, the adsorbant components are to be found as discrete lenses of low permeability rather than as an evenly distributed phase as is essentially assumed in the laboratory methodologies for determining the retardation factors. In these lenses penetration to the bulk of the adsorption sites is restricted to diffusion and the small residual convection fluxes. 

Bostick, B. C., Vairavamurthy, M. A., Karthikeyan, K. G., and Chorover, J. (2002). Cesium adsorption on clay minerals an EXAFS spectroscopic investigation. Environ. Sci. Technol. 36, 2670-2676. 

This list may be lengthened when the effects of adsorption are considered, because a molecule bound on a surface may be activated for photodegradation even if the reaction is not favorable for the same molecule dissolved in solution. For example, paraquat apparently photodecomposes more rapidly when adsorbed on layer silicate minerals than when in solution (Helling et al., 1971). This phenomenon may be related to the fact that adsorption on clay shifts the UV absorption band of paraquat to longer wavelength (256 - 275 nm) and closer to the atmospheric window for UV light (see Figure 10.20). In other words, adsorption on clay increases the probability that paraquat will absorb UV radiation and thereby decompose. 

Equation 10.20 describes the S-shaped isotherm commonly observed in studies of organic molecule adsorption on clays from aqueous solution. 

The Mechanism of Anionic Surfactant Adsorption on Clay and Silica... 

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