Alkali solutions, adsorption

Research in this area has been directed toward (a) finding or preparing activated carbons with high micropore volume (or BET surface area) in order to increase the CH4 adsorption capacity, and (b) to increase the bulk density of the carbon (reduce void volume of the storage vessel) to minimize the amount of unadsorbed CH4 in the tank. Chemical activation of carbon precursors by heating in alkali solutions and phosphoric acid to create micropores as well as surfece activation of microporous carbons by heating in COj and steam are common techniques used for this purpose [38, 39]. Table 22.10 summarizes the published values of isothermal deliverable CH4 capacities for several activated carbon samples[18, 40—42]. 

A glass membrane electrode was used to measure the pH of the silicate solutions. Adsorption of the smaller alkali metal cations, K, Na, and Li, caused an underestimation of the pH. The pH error reached several pH units for the most alkaline Li silicate samples. On the other hand, the errors for Na silicates were around 0.5 pH unit and the errors for larger cations were relatively small. Corrections to the measured pH were made by comparison of the electrode response for the silicate solutions with that for alkali metal hydroxide solutions of known concentration. Since the hydroxide content of the base solutions is known, the interference from cation adsorption was calculated and added to the pH measured for the silicate solutions (16). 

These experiments show that it is possible to achieve positive results using EOR after a thorough investigation of the nature of mineral rock constituents of the oil reservoir and the choice of the surfactant delivery method. The dynamic interfacial tension is crucial in EOR. Using a model acidic oil, alkali solutions and surfactants at an optimum ratio, ionised water and surfactant adsorb simultaneous onto the interface, resulting in low dynamic interfacial tension [229]. Combined adsorption of surfactant (alkyl propoxyethoxy sulphate) and polymer (xanthan) was studied in [230]. 

When solutions of beryllium salts are brought together with red-violet solutions of quinalizarin [1,2,5,8-tetrahydroxyanthraquinone (I)] in am-moniacal or caustic alkali solution, a blue-violet precipitate or color appears. Although quinalizarin, as a derivative of alizarin, is a lake-forming dyestuff, which produces red to red-violet adsorption compounds with oxyhydrates of aluminum, zirconium, thorium, etc., its beryllium reaction product seems to be a stoichiometrically defined compound rather than an adsorption complex. In conformity with the fact that the blue product contains two atoms of beryllium combined with one molecule of quinalizarin, it seems proper to view the material as a basic beryllium salt with the structure (II) or (Ila) ... 

The following are some of the typical industrial applications for liquid-phase carbon adsorption. Generally liquid-phase carbon adsorbents are used to decolorize or purify liquids, solutions, and liquefiable materials such as waxes. Specific industrial applications include the decolorization of sugar syrups the removal of sulfurous, phenolic, and hydrocarbon contaminants from wastewater the purification of various aqueous solutions of acids, alkalies, amines, glycols, salts, gelatin, vinegar, fruit juices, pectin, glycerol, and alcoholic spirits dechlorination the removal of... 

The precipitated metallic hydroxides or hydrated oxides are gelatinous in character, and they tend to be contaminated with anions by adsorption and occlusion, and sometimes with basic salts. The values presented in Table 11.2 suggest that many separations should be possible by fractional precipitation of the hydroxides, but such separations are not always practical owing to high local concentrations of base when the solution is treated with alkali. Such unequal concentrations of base result in regions of high local pH and lead to the precipitation of more soluble hydroxides, which may be occluded in the desired precipitate. Slow, or preferably homogeneous, precipitation overcomes this difficulty, and much sharper separations may be achieved. 

Double integration with respect to EA yields the surface excess rB+ however, the calculation requires that the value of this excess be known, along with the value of the first differential 3TB+/3EA for a definite potential. This value can be found, for example, by measuring the interfacial tension, especially at the potential of the electrocapillary maximum. The surface excess is often found for solutions of the alkali metals on the basis of the assumption that, at potentials sufficiently more negative than the zero-charge potential, the electrode double layer has a diffuse character without specific adsorption of any component of the electrolyte. The theory of diffuse electrical double layer is then used to determine TB+ and dTB+/3EA (see Section 4.3.1). 

Except for sensor applications, the intercalation of alkali metal ions in metal hexacyanoferrates was used for adsorption and separation of cesium ions from different aqueous solutions with Prussian blue [43,44] and cupric hexacyanoferrate [45,46],... 

Alkali 10ns in aqueous solution are probably the most typical and most widely studied representatives of non-specific adsorption. The electrochemical term of non-specific adsorption is used to denote the survival of at least the primary hydration shell when an ion is interacting with a solid electrode. As pointed out previously, the generation of such hydrated ions at the gas-solid interface would be of great value because it would provide an opportunity to simulate the charging of the interfacial capacitor at the outer Helmholtz plane or perhaps even in the diffuse layer. 

Sears 189) and Heston et al. 190) used the adsorption of sodium hydroxide for the determination of the surface area of colloidal silica. An empirical factor was used for the conversion of alkali consumption into surface area. This is permissible provided the packing density of surface silanols is constant. The determination was performed in concentrated sodium chloride solution in order to keep down the dissolution of silica. Using the same technique, it was found in my laboratory that all surface silanol groups as determined by other methods are neutralized at pH 9.0. At higher pH, siloxane bonds in the surface were opened. A maximum in the sorption of Na+ ions occurred usually at pH 10.5-10.6 which corresponded to a packing density of ca. 5 OH/100 A. On further addition of alkali, silicate ions H3Si04 went into solution. 

The effect of NaCl concentration on the rate of paraquat adsorption on activated clays is reported by Tsai et al. (2003). The rate constant increases with an increase of salts in the aqueous paraquat solution from 0.046 (g mg min at a NaCl concentration of 0.05 M, to 0.059 (g mg" min" at a solution concentration of 2.50 M NaCl. Studying the effect of various alkali metals ions on paraquat adsorption... 

Fig. 8 Results of the regression analysis of Eq. 56 for surface potential of the air-water interface with the adsorption of alkali dodecyl sulfate molecules as a function of the surfactant concentration in the bulk solution...

Adsorption of cyanide anions can be affected by adsorption of cations. In the solutions containing nonspecifically adsorbed anions, the nature of alkali metal cations was found to influence the measured value of the electrode capacitance at potentials more negative than —0.6 V (versus standard hydrogen electrode (SHE)). At < —l.OV adsorption of CN ions was enhanced in the presence of Li+ and Na+ cations, and inhibited in the presence of Cs+ ions [81]. A combined SERS and density-functional theory has been applied to study cyanide adsorption at Au electrode [82]. The authors have arrived at the conclusion that the polarity of Au—CN bonds falls between that of Au—Cl and Au—Br surface bonds. The binding strength for three different gold surfaces decreased in the order ... 

Lobacz et al. [52] have described partial adsorption ofTl+-cryptand (2,2,2) complex on mercury electrode. From voltocoulom-etry, cyclic voltammetry, and chrono-coulometry, it has been deduced that electroreduction of this complex proceeds via two parallel pathways from the solution and from the adsorbed states, which are energetically close. Also, Damaskin and coworkers [53] have studied adsorption of the complexes of alkali metal cations with cryptand (2,2,2) using differential capacity measurements and a stationary drop electrode. It has been found that these complexes exhibit strong adsorption properties. Novotny etal. [54] have studied interfacial activity and adsorptive accumulation of U02 " "-cupferron and UO2 - chloranilic acid complexes on mercury electrodes at various potentials in 0.1 M acetate buffer of pH 4.6 and 0.1 M NaCl04, respectively. 

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