Adsorption from Dilute Aqueous Solutions

Multisolute Adsorption from Dilute Aqueous Solutions.—Earlier work on adsorption from multicomponent systems has been reviewed in references 2 (p. 103) and 3 (p. 75). The work of Radke and Prausnitz, Fritz and Schliinder, and of Myers and Minka has been developed in a paper on the thermodynamics of multisolute adsorption from dilute aqueous solutions by Jossens, Prausnitz, Fritz, Schliinder, and Myers. The experimental work 

Kraus and F. Nelson, Ext. Abstr. Program-Bienn. Conf. Carbon, 1975, 12, 201 (Cfiem. Abstr., 1978, 88, 66 263). 

Introduction of (84) into (83) and integration gives (81). The experimental data for single solute isotherms are compared in figures with both (81) and (84). 

The new isotherm is related thermodynamically to a variation of the isosteric enthalpy, q t, of the form 

Here qst is the limit of q at zero surface coverage. This equation has the advantage that the spreading pressure, ir, needed in the calculations, can be expressed in an analytical form  

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The rate of adsorption from dilute aqueous solutions by solid adsorbents (zeolites) is a highly significant factor for applications of this process for water quality control. 

When the adsorption of aromatic weak electrolytes is governed by nonelec-trostatic interactions, such as tt-tt dispersion or hydrophobic interactions, the area of the adsorbent occupied by the adsorbate depends on the porosity of the former and the molecular size of the latter. Thus, adsorption from diluted aqueous solution and immersion calorimetry measurements [39] showed that phenol and m-chlorophenol are adsorbed as monolayers by both porous and nonporous carbons with basic surface properties, provided that the adsorptive is undissociated at the solution pH. This did not apply where molecular sieve effects reduced the accessibility of the micropore system. 

This chapter shows that a unified explanation can be given of the adsorption from dilute aqueous solutions of different organic solutes, from nonelectrolytes to electrolytes, polyelectrolytes, and bacteria. Thus, the adsorption process is a complex interplay between electrostatic and nonelectrostatic interactions. Electrostatic interactions depend on the solution pH and ionic strength. The former controls the charge on the carbon surface and on the adsorptive... 

Metal recovery by adsorption from dilute aqueous solutions is an emerging field of interest from the standpoints of both resource conservation and environmental remediation. Many biopolymers derived from microbes and plants are known to bind metals strongly. The use of biopolymers as adsorbents for the recovery or removal of metals from aqueous environments has been a topic of extensive research in recent years [18]. Biopolymers such as cellulosics, alginate carrageenans, lignins, proteins, and chitin derivatives are industrially attractive for a number of reasons. Biopolymers are capable of removing heavy metal ions at parts per... 

Stadnik and Eltekov have considered again their thermodynamic approach to adsorption from dilute aqueous solutions of microporous active carbons. An important problem in the use of the Dubinin-Radushkevich (D.R.) equation for both gas/solid and solution/solid systems is the mode of transition from this equation to the linear (Henry s law) region of the isotherm (see this Vol. p. 65). In a previous papers they found an empirical relationship between the quantity B/ 3 in the D.R. equation ... 

Currently, because of the frequency of their occurrence in wastewaters, the adsorption of phenolic compounds on carbons and the influence of surface oxygen complexes on their uptake are the most frequently studied, Radovic et al. (1997). It is well established that an increase in surface acidity of AC, after an oxidation, causes a decrease in phenol adsorption from dilute aqueous solution. For example. Figure 8.8 shows the adsorption isotherms of phenol on oxidized carbons, Mahajan et al. (1980). There was a large decrease in phenol uptake after oxidation, the effect of oxidation not being trivial. This phenol uptake progressively increased as the surface acidity decreased, and the oxidized sample (heat treatment temperature (HTT) 950 °C) had the same adsorption capacity as the original carbon (about 1.5 xmolg" ). 

Abstract Broad principles of Solid-Liquid calorimetry together with some illustrative examples of its use in the field of catalysis are presented here. The first use is related to the determination of surface properties of catalysts, adsorbents and solid materials in contact with liquids. In particular, it is shown how to evaluate the capacity of a given solid to establish different types of interaction with its liquid environment or to calculate its specific surface area accessible to liquids. The second use includes the measurement of the heat effects accompanying catalytic reactions and the related interfacial phenomena at Solid-Liquid and Liquid-Liquid interfaces. Examples of competitive ion adsorption from dilute aqueous solutions, as well as the formation of surfactant aggregates either in aqueous solution or at the Solid-Liquid interface are considered in view of potential applications in Environmental Remediation and Micellar Catalysis. 

The most common hydrophobic adsorbents are activated carbon and siUcahte. The latter is of particular interest since the affinity for water is very low indeed the heat of adsorption is even smaller than the latent heat of vaporization (3). It seems clear that the channel stmcture of siUcahte must inhibit the hydrogen bonding between occluded water molecules, thus enhancing the hydrophobic nature of the adsorbent. As a result, siUcahte has some potential as a selective adsorbent for the separation of alcohols and other organics from dilute aqueous solutions (4). 

Toth [64] has only considered adsorption of gases in his model but his idea can be extended to adsorption of solutes from dilute aqueous solution [65]. The Toth adsorption model has the form ... 

In addition to anionic species, some metal cations can also be removed via adsorption processes with LDH materials. Recently, Lazaridis reported an interesting removal of two anions (P04 , SCN ) and three cations (Cd , Pb ", Ni " ) from aqueous solutions in single batch systems using uncalcined and calcined (773 K) Mg/Al LDH carbonate materials [148]. It was found that the calcined material showed higher sorption capacities than the uncalcined material for all the ions. Since the sorption capacities are relatively high, the author suggested that LDHs could be considered as a potential materials for sorption of both anions and cations in wastewater treatment systems. Seida et al. have also reported the rapid removal of dilute Pb from dilute aqueous solutions by a column packed with a pyroaurite-like Mg/Fe-COs LDH compound over a wide range of space velocity (Sv = 150-800 min" ) [149]. 

Pierce, M.L. Moore, C.B. (1980) Adsorption of arsenite on amorphous iron hydroxide from dilute aqueous solution. Environ. Sci. Tech. 14 214-216... 

Adsorption of p-Nitrophenol from Dilute Aqueous Solution 138... 

Electrostatic assembly, which involves attractive forces between two oppositely charged entities (polymers, nanoparticles, and substrates), has been proposed in the pioneering work of Her for the assembly of two- and three-dimensional structures.22 The LbL assembly of charged polyelectrolytes was later reported by Decher et al. for the fabrication of multilayer films of polyelectrolytes.10 23 Their technique is based on the consecutive adsorption of polyanions and polycations from dilute aqueous solutions onto a charged substrate (Fig. 13.2). 

Losses of metals from dilute aqueous solution on storage are well documented. To prevent this it is usually necessary to acidify the sample after collection and filtration to pH 1. If the sample is to be analysed subsequently by flame AAS hydrochloric acid should be used (Section III.C.2) alternatively, prior to flameless electrothermal atomic absorption analysis, nitric acid should be added to preserve the sample (IV.B). The type of storage container is also important and high-density polyethylene is the preferred material for sample bottles. Here the adsorptive losses of metals appear to be lower than on glass. To avoid container contamination of the sample the container should be leached with dilute nitric acid for several days prior to use. This will remove surface contamination from the container material. Subsequent to the acid-leach, containers are washed in distilled-deionised water and then with a portion of the sample. Storage of samples for mercury analysis requires special conditions and these will be discussed later. 

Lynam, M. M. Kilduff, J. E. Weber, W. J. Adsorption of p-Nitrophenol from Dilute Aqueous Solution An Experiment in Physical Chemistry with an Environmental Approach, J. Chem. Educ. 1995, 72, 80-84. 

Chapter 7 of our landmark reference [6] discusses various aspects of the adsorption of weak electrolytes and nonelectrolytes from aqueous solution. In particular an attempt is made to elucidate the mechanism of adsorption of undissociated aromatic compounds from dilute aqueous solutions. As discussed in detail in Section VI, the authors concluded that the aromatic ring of the adsorbate inter-... 

Figure 6 n-propanol adsorption (from dilute aqueous n-propanol solutions) of MFI-type zeolites prepared (a) in alkaline medium and (b) in fluoride medium. ... 

Adsorption of Organic Solutes from Dilute Aqueous Solutions... 

Muller, G., Radke, C.J., and Prausnitz, J.M. (1985). Adsorption of weak electrolytes from dilute aqueous solution onto activated carbon. Part I. Single-solute systems. J. Colloid Interface Sci., 103, 466—83. 

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