Laboratory sorption experiments

Laboratory sorption experiments are used to determine the distribution of a compound between the solid and liquid phases in the absence of other processes involved (e.g. biodegradation, precipitation) under controlled conditions. Sorption experiments are usually performed by adding particulate matter, free of surfactants, to solutions with different known surfactant concentrations at constant temperature (sorption isotherms). The experiments performed at high concentrations of... 

Sorption generally is regarded as a rapid process and, in many laboratory sorption experiments, equilibrium often is observed within several minutes or hours. An equilibration time of 24 hours often is used for convenience. True sorption equilibrium, however, may require weeks to months to achieve (Karickhoff, 1981 Karickhoff, 1984), depending on the chemical and environmental solid of interest. In many instances, an early period of rapid and extensive sorption, followed by a long slow period, is observed (Karickhoff, 1980 Wu and Gschwend, 1986 Brusseau and Rao, 1989 Brusseau et al., 1990 Ball and Roberts, 1991). 

Based upon the data given in the table below that were obtained from a laboratory sorption experiment, a college student who worked for a company as an intern was asked to evaluate the K and n values for a certain type of activated carbon to be used to remove undesirable by-products formed during chemical treatment. What are the values of K and n that the intern should have generated ... 

The XAD-4 quaternary resin used in these studies was prepared by the Ames Laboratory in Ames, Iowa. This resin had been used in studies by the Ames group for the adsorption and selective separation of acidic material in waste waters. For this study, the resin was chosen for its effectiveness in concentrating anionic material from solution. At the same time, it was thought that sufficient sites would be available to effectively adsorb neutral organic compounds from water. The resin was basically an XAD-4 macroreticular cross-linked polystyrene into which a trimethylamine group was introduced. The resin was stored in the chloride form but was converted to the hydroxide form before use in the resin sorption experiments. 

For the second pilot test, the 14-40 SMZ was excavated from the frame, a nylon screen on the barrier frame was removed, and two sections of the frame were refilled with 8-14 mesh (2.4-1.4 mm) SMZ. The remaining one-third of the frame was filled with iron/SMZ pellets as part of another project. After steady water flow was reestablished, chromate and PCE were injected over a period of eight weeks. No plume deflection occurred in the test with the 8-14 SMZ. The SMZ fully intercepted the contaminant plume and prevented migration of contaminants downgradient of the barrier. Near the end of the test, chromate and PCE were detected in samplers installed in the upgradient portion of the SMZ. The estimated retardation factors for chromate and PCE in the pilot test were 44 and 39, respectively. These retardation factors are very close to the values of 42 and 29 for chromate and PCE predicted from laboratory sorption isotherm experiments. 

All chemicals were laboratory grade and dissolved in distilled water. The medium was sterilized by autoclaving, and sorption experiments were performed in sealed 150-mL serum bottles. Subsequent tests for in situ use may need to be performed at mesophilic fermentation temperatures. In a similar manner, the sorbents were also tested for their capacity for the substrate of the possible fermentation, glucose, at a concentration of about 5 g/L. Frequently the glucose was included in the fermentation medium for competitive sorption. 

Many more stories can be told in this regard. The chaimel structure of natural mordenite was not foreseen on the basis of sorption experiments because a relatively small number of blockages or dislocations quite adequately blocked the large charmels. In an experiment in my laboratory, sodium LTA failed completely to sorb tetrachloroethylene (both fully anhydrous) because of its size (The crystal structure of a single crystal in an atmosphere of ca 100 torr of C2CI4 for more than a week was exactly that of fully dehydrated LTA.) we should have honored a simple mechanical calculation of size apparently no alternative mechanism existed. In contrast, statements that Cs ions should not be able to enter sodalite cavities in LTA or FAU, have repeatedly been shown crystallographically to be incorrect such entry of Cs" " appears to occur both in the presence and absence of water. 

Laboratory column experiments were used to identify potential rate-controlling mechanisms that could affect transport of molybdate in a natural-gradient tracer test conducted at Cape Cod, Mass. Column-breakthrough curves for molybdate were simulated by using a one-dimensional solute-transport model modified to include four different rate mechanisms equilibrium sorption, rate-controlled sorption, and two side-pore diffusion models. The equilibrium sorption model failed to simulate the experimental data, which indicated the presence of a ratecontrolling mechanism. The rate-controlled sorption model simulated results from one column reasonably well, but could not be applied to five other columns that had different input concentrations of molybdate without changing the reaction-rate constant. One side-pore diffusion model was based on an average side-pore concentration of molybdate (mixed side-pore diffusion) the other on a concentration profile for the overall side-pore depth (profile side-pore diffusion). 

The determination of R (see Eq. 7.25) by a measurement of the partition coefficient k in the laboratory, by some type of sorption experiment for the determination of adsorbed solid-phase concentration versus solution-phase concentration in equilibrium (so-called isopleths or isotherm), however, supplies values of R which are not comparable with the actual in field retardation factors in a mineral liner, because the specific surface susceptible to the pollutant is very different in both cases. Therefore, based on diffusion coefBcients in free aqueous solutions, the effective diffusion coefficients of organic substances for water-saturated mineral liners were estimated by using a tortuosity factor F= 1/3 (Muller et al. 1997a). Table 7.6 shows the results for various soil materials. 

In (Barone et al. 1992) / = 1.8 is given for acetone, / = 1.7 for 1,4-dioxan and R = 1 for aniline. R. L Johnson and collaborators examined drill cores for pollutant contents of a clay deposit under a hazardous waste landfill which was impacted by leachate (Johnson et al. 1989). The apparent diffusion coefficients were derived from the depth profile of the concentration of the organic pollutants. A tortuosity factor of 0.20-0.33 was found for chloride in this investigation. The following retardation factors can, therefore, be calculated from the measured apparent diffusion coefficients with the effective diffusion coefficients listed in Table 7.5 (see (Muller et al. 1997a), note 16) i = 15 (benzene), R = 56 (trichloroethylene), i = 54 (toluene), R = 21 (1,2-dichloropropane), R= 115 (ethylbenzene), i =115 (naphthalene). The following values were derived from sorption experiments in the laboratory on unaffected drill core samples i = 44 (benzene), R = 65 (trichloroethylene), i = 82 (toluene), R = 269 (ethylbenzene). 

Alumina, ceria, and silica particles are removed in biological wastewater treatment processes by a combination of aggregation, heteroaggregation, and sorption onto biosolids and/or extracellular polymeric substances. Some studies indicate that silica particles are less easily removed than ceria and aluminum particles. Most information on alumina, ceria, and silica removal in biological wastewater systems is from pilot- or laboratory-scale experiments, and relatively few smdies involving real CMP... 

Next, we will focus on a laboratory study of mannan sorption onto both mechanical and chemical pulps that are relevant in the production of wood-containing papers, as chemical pulps are often also added as reinforcement fibers. The sorption experiments were performed with GGMs isolated from spruce, or enzymatically modified guar gum GMs. The amount of sorbed mannan was calculated by measuring the amount of mannan left in solution by acidic methanolysis followed by GC analysis. 

Laboratory scale experiments performed under well-controlled conditions represent a complementary approach towards the characterization of the chemical containment of radionuclides in the undisturbed and fractured shales. Sorption isotherms of Cs for the shale matrix and for calcite are provided in Fig. 6. Batch experiments were carried out in gloveboxes under N2 atmosphere and with synthetic fracture water which approximate in situ and far-field conditions. The liquid/solid ratio was 5mlg . The results show the weaker retention of Cs by calcite fillings than by the shale matrix. Interstrati-fied I/S have strong affinities for many radionuclides (Milton Brown 1986), whereas calcite is known to have small laboratory values for... 

Research into the aquatic chemistry of plutonium has produced information showing how this radioelement is mobilized and transported in the environment. Field studies revealed that the sorption of plutonium onto sediments is an equilibrium process which influences the concentration in natural waters. This equilibrium process is modified by the oxidation state of the soluble plutonium and by the presence of dissolved organic carbon (DOC). Higher concentrations of fallout plutonium in natural waters are associated with higher DOC. Laboratory experiments confirm the correlation. In waters low in DOC oxidized plutonium, Pu(V), is the dominant oxidation state while reduced plutonium, Pu(III+IV), is more prevalent where high concentrations of DOC exist. Laboratory and field experiments have provided some information on the possible chemical processes which lead to changes in the oxidation state of plutonium and to its complexation by natural ligands. 

Bioreactors containing an nndefined anaerobic consortinm rednced TNT to 2,4,6-triaminotoluene (TAT) in the presence of glncose (Dann et al. 1998). The sorption of TAT to montmorillonite clay was irreversible, and the snbstrate conld not be released by solvent extraction or by acid or alkaline treatment. Similar resnlts were obtained with humic acids in which covalent reactions with carbonyl or activated C=C bonding presumably occurred. Results from laboratory experiments nsing i C-labeled TNT in reactors to which... 

Nearly all of the data are collected at room temperature, and there is no accepted method for correcting them to other temperatures. Far fewer data have been collected for sorption of anions than for cations. The theory does not account for the kinetics of sorption reactions nor the hysteresis commonly observed between the adsorption and desorption of a strongly bound ion. Finally, much work remains to be done before the results of laboratory experiments performed on simple mineral-water systems can be applied to the study of complex soils. 

Jurgens et al. [33] carried out a series of laboratory experiments to study the behavior of estrogens in the aquatic environment and set up a model to estimate their likely environmental concentrations in the water column and bed-sediments. According to this study, between 13 and 92% of the estrogens entering a river system would end up in the bed-sediment compartment with the majority of sorption occurring within the first 24 h of contact. 

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). 

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