Sorption desorption experiments

In order to test the reversibility of metal-bacteria interactions, Fowle and Fein (2000) compared the extent of desorption estimated from surface complexation modeling with that obtained from sorption-desorption experiments. Using B. subtilis these workers found that both sorption and desorption of Cd occurred rapidly, and the desorption kinetics were independent of sorption contact time. Steady-state conditions were attained within 2 h for all sorption reactions, and within 1 h for all desorption reactions. The extent of sorption or desorption remained constant for at least 24 h and up to 80 h for Cd. The observed extent of desorption in the experimental systems was in accordance with the amount estimated from a surface complexation model based on independently conducted adsorption experiments. 

In line with the general objectives in the present chapter we propose to discuss only the leaching and sorption/desorption experiments conducted by Aboul-Kassim [1] and Eldin et al. [66, 67]. In addition, the approach taken by these authors to predict the behavior of toxic compounds in the leachates from various SWMs/COMs is also discussed. 

Laboratory experiments, transport modeling, field data, and engineering cost analysis provide complementary information to be used in an assessment of the viability of an MNA approach for a site. Information from kinetic sorption/ desorption experiments, selective extraction experiments, reactive transport modeling, and historical case analyses of plumes at several UMTRA sites can be used to establish a framework for evaluation of MNA for uranium contamination (Brady et al, 1998, 2002 Bryan and Siegel, 1998 Jove-Colon et al, 2001). The results of a recent project conducted at the Hanford 100-N site provided information for evaluation of MNA for a °Sr plume that has reached the Columbia River (Kelley et al, 2002). The study included strontium sorption-desorption studies, strontium transport and hydrologic modeling of the near-river system, and evaluation of the comparative costs and predicted effectiveness of alternative remediation strategies. 

Figure 8. Expanded sample bed original sample expanded about 40% as a result of the intraparticle swelling occurring during the course of sorption-desorption experiments...

In nitrogen sorption/desorption experiments, BET areas and total pore volumes rank clearly in the order A>B>C (Figures 3a,b,c). 

The sorption/desorption experiments were carried out as a function of a both above and below the Tg of the matrix. The data obtained from both experiments closely resembled Fickian diffusion. Below 0.55a (between 0 < Mt and Mf < 0.5) and above 0.55a (between 0.08 < Mf and Mf < 0.75) initial slope of Mf/Mf vs. curves were linear with respect to abscissa (R > 0.98). Diffusion coefficients were obtained using the linear portion of the normalized moisture sorption (Mt/Moo vs. curves from Equation 46.14. 

On the other hand, sorption/desorption experiments with copper and clay minerals have shown that true cation exchange (with BaCl2) is relatively insignificant and that the triethanolamine reagent (added to raise the pH of the solution) effects the release of additional metal compounds, which may be more appropriately designated as easily extractable phases (41). Extraction of humate phases was performed with O.IIV NaOH the same reagent was used for the determination of the concentrations of humic substances by comparison with standard humic acids (42). 

TABLE 3.2. Testing Parameters of Sorption/Desorption Experiments on Cadmium... 

In many early experiments, hysteresis was observed for highly hydrophobic compounds such as PCBs (79, 80). Since the time to reach equilibrium can be quite long for strongly hydrophobic compounds, a solute may have never reached equilibrium during the sorption isotherm experiment. Consequently, Kj would be underestimated, which leads to the discrepancy between the sorption and desorption coefficients that was attributed to hysteresis. The case for hysteresis being an artifact is supported by recent data for tetrachlorobenzene (log K = 4.7), illustrating that sorption and desorption require approximately two days to reach equilibrium with approximately equal time constants (78). Finally, the diffusion model is consistent with the observation that the extent of hysteresis was inversely related to particle size (81). 

On the other hand, Aboul-Kassim [1] assessed the environmental impact of hazardous waste materials in landfills by (1) characterizing the different organic compound fractions present in such wastes and their leachates, (2) determining the toxic effect of each fraction and individual organic compounds, and (3) studying the chemodynamics (i.e., fate and transport) of such leachates by using a battery of laboratory experiments (such as sorption/desorption, photolysis, volatilization, biodegradation). 

The sorption/desorption processes were studied by a batchtype technique. Aqueous solutions were prepared by mixing rock powders with distilled-deionized water. For the sorption experiments, portions of these aqueous solutions were loaded with tracer quantities of a single radioactive nuclide and contacted with wafers of a given rock type. For the desorption experiments, wafers from the sorption experiments were contacted with the remaining portions of the aqueous solutions. 

The up/down effect was also apparent in the data of the desorption experiment (Table VIII). However, only desorption data for shale differ significantly from the sorption data,... 

Procedure. At the completion of the sorption and desorption experiments, the rock wafers were placed in... 

The integral permeability coefficient P may be determined directly from permeation steady-state flux measurements or indirectly from sorption kinetic measurements 27 521 activity is usually replaced by gas concentration or pressure (unless the gas deviates substantially from ideal behaviour and it is desired to allow for this) and a<>, ax (p0, Pi) are the boundary high and low activities (pressures) respectively in a permeation experiment, or the final (initial) and initial (final) activities (pressures) respectively in an absorption (desorption) experiment. 

Rounds, S.A., B.A. Tiffany, and J.F. Pankow. 1993. Description of gas-particle sorption kinetics with an intraparticle diffusion model desorption experiments. Environ. Sci. Technol. 27 366-377. 

Chemical and microbiological transformations of the pesticide while the experiment is being conducted could also cause nonsingularity in pesticide-soil sorption-desorption isotherms. Hamaker and Thompson (1972) theorized that a portion of a sorbed pesticide is more strongly held than... 

Soil Sorption-Desorption Rate Constants release rate constants kd for labile PCBs sorbed to utility substation soils are k = 1.90 d 1 from Conkelley subsurface soil, 0.4-m deep, consist of sand and silt with 0.13% OC, k = 0.88 d 1 from Tarehee surface soil consist of sand and silt with 0.02% OC and k = 0.37 d 1 from Conkelley surface soil consist of silt with 0.01% OC, rates derived from first day gas-purge experiments release rate constants kd for nonlabile PCBs sorbed to utility substation soils are k = 0.00413 d 1 from Conkelley subsurface soil, 0.4-m deep, consist of sand and silt with 0.13% OC, k = 0.00099 d 1 from Tarehee surface soil consist of sand and silt with 0.02% OC and k = 0.00052 d 1 from Conkelley surface soil consist of silt with 0.01% OC, rates derived from 120-195 d experiments (Girvin et al. 1997). 

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