Sorption competition

AEC) and the hydrophobicity of the 12-carbon-long chain. For sorption competition with the monovalent ion, Cl , we use Eq. 11-55 (Box 11.2), recognizing that in this case we are interested in an organic anion attracted to the positively charged suspended alumina solid ... 

Basically the experimental parameters affecting the sorption behavior in simple systems (concentration of the adsorbate, solid to liquid ratio, equilibration time, temperature, pH, and ionic strength) are also important in sorption competition. Thus, Table 4.7 has the same columns as Tables 4.1 and 4.2 (specific adsorption in absence of competitors). In simple systems little attention is usually paid to the sequence of addition of reagents, but in studies of sorption competition this factor must not be neglected. The fact that some adsorbate is added (brought in contact with the adsorbent) first makes it a more successful competitor. Let us consider the following experiment. The adsorbent is equilibrated with solution of adsorbate I (adsorbate of interest), then the adsorbent is separated from the solution and contacted with solution of adsorbate 2 (competitor), and then the concentration of adsorbate 1 in solution is determined after certain equilibration time. Only a fraction of adsorbate 1 is released even if adsorbate 2 is a very strong competitor. However, adsorbate 2 added first or simultaneously with adsorbate I would completely prevent sorption of adsorbate 1 at otherwise identical experimental conditions. 

Different experimental approaches to the sorption competition produce somewhat different results. For example some experiments were carried out in the presence of a big excess of the competitor over the adsorbate of interest, and in other studies the concentrations of adsorbate 1 and adsorbate 2 were of the same order of magnitude. Some authors performed their experiments at constant concentration of adsorbate 1 and variable concentration of adsorbate 2, while in other studies the sum of concentrations (adsorbate 1 + adsorbate 2) was constant. When the distribution... 

Experimental studies on sorption competition in specific systems are compiled in Table 4.7. The entries are sorted by the adsorbent and then by the adsorbate (cations first, in alphabetical order, then anions, organic compounds, surfactants and polymers). 

The biogeochemical processes that generally describe the interaction of elements with particles are quite well known dissolution, flocculation, ion exchange, sorption, (co)precipitation, electron transfer, and biological uptake. In aquatic environments these reactions often occur simultaneously and competitively. In order to utilize marine tracers effectively, we must understand how elements are associated with particles and sediments. 

Selectivity of sorption of organic ions by crosslinked polyelectrolytes in competition with small ions, in particular with metal ions, should be considered on the basis of the analysis of thermodynamic relationships of ion exchange. 

The sorption selectivity for more complex ions (e.g., ions of antibiotics) in competition with small ions increases to a still greater extent [59]. Particularly high constants for selective bonding (up to some hundreds and thousand) have... 

Although in many. soils with tow P availability, significant desorption of sparingly soluble Pi forms requires at least millimolar concentration levels of specific carboxylates (e.g., citrate, oxalate) in the soil solution, much lower concentrations (0.1 mM) were necessary to reduce. soil adsorption of Pi, which was applied simultaneously with carboxylates (100). Thus, competition of carboxylates with Pi for P sorption sites in the soil matrix may be a mechanism that can. 

Electrolytes are used to promote the exhaustion of direct or reactive dyes on cellulosic fibres they may also be similarly used with vat or sulphur dyes in their leuco forms. In the case of anionic dyes on wool or nylon, however, their role is different as they are used to facilitate levelling rather than exhaustion. In these cases, addition of electrolyte decreases dye uptake due to the competitive absorption of inorganic anions by the fibre and a decrease in ionic attraction between dye and fibre. In most discussions of the effect of electrolyte on dye sorption, attention is given only to the ionic aspects of interaction. In most cases, this does not create a problem and so most adsorption isotherms of water-soluble dyes are interpreted on the basis of Langmuir or Donnan ionic interactions only. There are, however, some observed cases of apparently anomalous behaviour of dyes with respect to electrolytes that cannot be explained by ionic interactions alone. 

The enhancing effect of NaCl on Cd uptake was due to chloride complexation of Cd (Smolders et al., 1998). High salinity in soils increased the concentrations of chloride complexes of trace elements (such as CdCl or CdCl2°) in soil solution, which increased and correlated best with Cd uptake of both plant species as discussed above. In addition, salinity also affected plant root function, and Na competition with Cd for sorption sites in soil may be a possible contributor. 

Goldberg (2002) found no evidence of any competition in sorption of arsenate and arsenite on Al or Fe-oxides and montmorillonite, but only a small and apparent competitive effect of equimolar arsenate on arsenite sorption on kaolinite and illite. The minor competitive effect in this study was due to the small concentrations of arsenic which is very low for saturation site. Competition for sorption sites is evident by increasing the surface coverage of the sorbents. Arsenate prevents arsenite sorption on metal oxides when the surfaces of the sorbents are saturated by the anions (Jain and Loeppert 2000 Violante and Pigna 2002). 

Barrow NJ (1992) The effect of time on the competition between anions for sorption. J Soil Sci 43 424-428... 

Pigna M, Colombo C, Violante A (2003) Competitive sorption of arsenate and phosphate on synthetic hematites (in Italian). Proceedings XXI Congress of Societa Italiana Chimica Agraria SICA (Ancona), pp 70-76 Quirk JP (1955) Significance of surface area calculated from water vapour sorption isotherms by use of the B. E. T. equation. Soil Sci 80 423-430 Rancourt DG, Fortin D, Pichler T, Lamarche G (2001) Mineralogical characterization of a natural As-rich hydrous ferric oxide coprecipitate formed by mining hydrothermal fluids and seawater. Am Mineral 86 834-851 Raven K, Jain A, Loeppert, RH (1998) Arsenite and arsenate adsorption on ferrihydrite kinetics, equilibrium, and adsorption envelopes. Environ Sci Technol 32 344-349... 

Xing B, Pignatello J (1998) Competitive sorption between 1,3-dichlorobenzene or 2,4-dichlorophenol and natural aromatic acids in soil organic matter. Environ Sci Techno 1 32 614-619... 

The Langmuir isotherm (or Langmuir model) provides an improvement over the K( and Freundlich approaches by maintaining a mass balance on the sorbing sites (Stumm and Morgan, 1996). The model, for this reason, does not predict that species can sorb indefinitely, since the number of sites available is limited. When the calculation carries reactions for the sorption of more than one aqueous species, furthermore, it accounts for competition such a calculation is known as a competitive Langmuir model. 

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