Quantifying sorption

The amount of a triazine retained or sorbed by soil can range from 0% to 100% of the amount applied, but typically sorption on silt loam, loam, or clay loam surface soils ranges from 50% to 80% of the amount applied. Although sorption of triazines (particularly atrazine) by soils has been studied for more than 40 years, there continue to be numerous studies each year to quantify sorption by different soils and to characterize the factors that affect triazine sorption. For instance, in a review of literature for 1964-1984, Koskinen and Moorman (1985) found 343 published Kd values for sorption of atrazine on 148 soils. These published Kd values averaged 4.0 4.0. From 1985 through 1995, 35 additional references reported Kd or Kf values for atrazine alone (Table 21.6). Average reported Kd values are 2.4 7.3 for 109 surface and subsurface soils (Paya-Perez et al., 1992) and 4.9 1.9 for 117 surface soils (Jaynes et al., 1995). 

The Linear Partitioning Model. Several conceptual and empirical models have been proposed to quantify sorption of hydrophobic organic contaminants (HOCs) by soils and sediments. The simplest of these is the linear partitioning model, in which the solid-phase solute concentration, is assumed to be directly proportional to the aqueous-phase solute concentration, Q i.e.,... 

Gc/ftir has both industrial and environmental appHcations. The flavor and aroma components in fragrances, flavorings, and foodstuffs can be identified and quantified via gc/ftir (see Food additives). Volatile contaminants in air, water, and soil can be analy2ed. Those in air are usually trapped in a sorption tube then injected into the chromatograph. Those in water or soil are sparged, extracted, or thermally desorbed, then trapped and injected (63,64). 

This relative importance of relaxation and diffusion has been quantified with the Deborah number, De [119,130-132], De is defined as the ratio of a characteristic relaxation time A. to a characteristic diffusion time 0 (0 = L2/D, where D is the diffusion coefficient over the characteristic length L) De = X/Q. Thus rubbers will have values of De less than 1 and glasses will have values of De greater than 1. If the value of De is either much greater or much less than 1, swelling kinetics can usually be correlated by Fick s law with the appropriate initial and boundary conditions. Such transport is variously referred to as diffusion-controlled, Fickian, or case I sorption. In the case of rubbery polymers well above Tg (De < c 1), substantial swelling may occur and... 

Sorption. Any reduction in analyte recovery in the presence of solid media may be a reflection of losses through sorption or actual degradation, and in reality it is difficult to quantify degradation due to the unknown extent of the sorption processes. Sorption can be by intercalation (absorption), and/or electrostatic attraction and covalent... 

In Differential vapour sorption a sample of material is placed on an accurate balance in a temperature controlled environment where the humidity of the gas phase can be accurately controlled. The adsorption and desorption behaviour of the sample is quantified with respect to water and hysteresis phenomena are identified. 

Ellis AS, Johnson,TM, Bullen TD (submitted) Using chromium stable isotope ratios to quantify Cr(VI) reduction lack of sorption effects. Environ Sci Technol submitted 9/2003 Ellis AS, Johnson TM, Bullen TD, Herbel MJ (2003) Stable isotope fractionation of selenium by natural microbial consortia. Chem Geol 195 119-129... 

The isotopic effects of sorption remain relatively unknown, with disparate interpretations of its significance during DIR. An important avenue of future research will be to quantify the rates of isotopic exchange between sorbed Fe(II) and Fe(II)3q, and to investigate a range of ferric oxide/hydroxide substrates. Because traditional sorption experiments generally... 

PhC properties most investigated by scientists to date are their water solubility (s, mg/mL), volatility (correlated to the Henry constant H) (pg m atr/pg m wastewater), biodegradability (correlated to pseudo-first-order degradation constant bioi L gSS d ), acid dissociation constant K, distribution and sorption (through the sludge-water distribution coefficient K, expressed in L gSS or the octanol-water partition coefficient Kg ). The main focus has been to find any correlations between these parameters and to determine PhC removal rates during the different treatment steps. Thus, different properties have been quantified for many compounds, and software, such as EPl Suite 4.00 [54], consenting their estimation, is available. 

A tremendous amount of research has been devoted to quantifying and modeling transport processes in the vadose zone, with readily available scientific literature (journals and textbooks) extending over the last half century. Modeling is used to quantify the dynamic redistribution of chemicals along the near surface and deeper subsurface profile, which often also is subject to reactive chemical processes including sorption, dissolution or precipitation, and volatilization. 

In sum, we do not yet know how to predict sorption of apolar and monopolar organic compounds to mineral surfaces submerged in water. If empirical results are available from structurally related compounds, parameters quantifying sorbate hydropho-bic-ity may help us anticipate the intensity of surface associations for new com-pounds in the same compound classes (i.e., interpolating data such as that shown in Fig. 11.7). 

Porous media have much larger solid-to-solution phase ratios (rsw) than surface waters (lakes and rivers). Therefore, even the transport of a chemical with moderate to small solid-water distribution ratios (/Q may be influenced by sorption processes. The basic mathematical tools which are needed to quantify the effect of sorption on transport are described in Section 18.4 and summarized in Box 18.5. 

Step input. All the conclusions drawn for the pulse input can directly be transferred to the step input. The concentrations, if expressed for the nondimensional coordinates , and 9, are not affected by sorption the shape of the concentration curve along x for a fixed time is independent of sorption. Yet, when the front passes by a fixed location x, the time needed for the concentration to increase from, say, 5% to 95% of the maximum concentration, grows as (/w)-1. This can be directly deduced from Table 25.2, where the duration of the passage of the front is quantified by the nondimensional time interval A0 - 095 -05. This value does not depend on sorption, but after transformation back into real time it does (see Eq. 25-42) ... 

The A oii-water partition coefficient is dimensionless. When determined in batch tests sorption is typically indicated as the soil-water distribution coefficeint, Kj, in which the soil is quantified in terms of mass rather than volume ... 

Of particular interest in the present study is the apparent existence of an activated sorption mechanism for nitrogen in partially hydrated zeolite NaA, a further study of which is planned. The less definitely established irreversibly sorbed nitrogen on dehydrated zeolites NaA and NaX, but not on CaA and NaY, is in need of confirmation, and of further characterization. A practical utility of the results is the quantifying of nitrogen uptake from air, which persists even with appreciable sorbed water. This amount can be approximated from the isotherms as the capacity at 0.8 atm. inasmuch as the contribution due to oxygen is very small. Conversely, the isotherms can be used to assess the state of hydration of a zeolite, with the aid of a measurement of the amount of sorbed nitrogen, either by mass loss on evacuation at room temperature in a balance, or by collection of gas evolved on immersion of a sample in water. 

Polymer hydrophilicity can be judged in the cases (a), (c), or (d) of Fig. 14.1. It is defined as the affinity of a polymer for water, which can be quantified by the equilibrium mass gain, W, determined in standard conditions, e.g., in a saturated atmosphere from a sorption experiment. depends on the vapor pressure or activity of water and on the temperature. It varies, typically from 0 to 10% in most networks. 

Loss of compound by sorption onto the walls of the equilibration vessels, volatilization, and chemical or biological degradation also can affect the experimental determination of sorption coefficients. These potential loss mechanisms must be eliminated or accounted for if accurate sorption coefficients are to be determined. It is preferable to measure the concentration of the chemical in both phases and determine the mass balance to quantify potential loss mechanisms. Singh et al., (1990) found that Koc values obtained by measuring only the concentration in the solution phase were consistently higher than with those generated using a mass balance approach when the concentrations in both phases are measured. 

In any evaluation of a remediation scheme utilizing surfactants, the effect of dose on HOC distribution coefficients must be quantified. Very often, only one coefficient value for HOC partitioning to sorbed surfactants has been reported in the literature, presumably because the experimental data covers only the sorption regions where the surfactant molecule interactions dominate at the surface (Nayyar et al., 1994 Park and Jaffe, 1993). However, all of the characteristic sorption regions will develop during an in-situ SEAR application as the surfactant front (i.e., mass transfer zone) advances through the porous medium. Therefore, the relative role ofregional HOC partition coefficients to sorbed surfactant should be considered in any remediation process. Finally, the porosity or solid volume fraction for the particular subsurface system must be taken into account when surfactant sorption is quantified. 

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