Multiple extraction

Chemical Separation. A reprocessing facility typically utilizes multiple extraction/reextraction (stripping) cycles for the recovery and purification of uranium and plutonium. For example, a co-decontamination and partitioning cycle is followed by one or more cycles of uranium and plutonium purification. The basic process is illustrated in Figure 3. 

Physical and chemical tests of the final product may need to address two concerns (1) whether the solidified waste exhibits any RCRA defined toxicity characteristics or could be delisted and (2) the potential long term fate of treated materials in the disposal environment. Three tests are available which address the first concern. These are the Extraction Procedure (EP Tox) (40 CFR 261, Appendix II, 1980) and the Toxicity Characteristic Leaching Procedure (TCLP) (40 CFR 261, Appendix II, 1986), and the Multiple Extraction Procedure Test (40 CFR 261, Appendix II, January 1989). It is important to note that these tests are not indicators of expected leachate quality but of potentials. A solidified product which cannot pass the appropriate test (EP Tox or TCLP) would be subject to classification as a hazardous waste. 

Federal Register - Multiple Extraction Procedure Test, Revised 40 CFR 261, Appendix II, January 1989. 

The method procedures are very time-efficient by always using a well defined portion of the extracts, thus avoiding multiple extractions, time-consuming rinses and overloading of the chromatographic cleanup systems with co-extracted sample matrix. 

Sample preparation techniques vary depending on the analyte and the matrix. An advantage of immunoassays is that less sample preparation is often needed prior to analysis. Because the ELISA is conducted in an aqueous system, aqueous samples such as groundwater may be analyzed directly in the immunoassay or following dilution in a buffer solution. For soil, plant material or complex water samples (e.g., sewage effluent), the analyte must be extracted from the matrix. The extraction method must meet performance criteria such as recovery, reproducibility and ruggedness, and ultimately the analyte must be in a solution that is aqueous or in a water-miscible solvent. For chemical analytes such as pesticides, a simple extraction with methanol may be suitable. At the other extreme, multiple extractions, column cleanup and finally solvent exchange may be necessary to extract the analyte into a solution that is free of matrix interference. 

Multiple extractions expression may be derived by considering a certain volume, VB, of the aqueous phase containing ma grams of solute and a certain volume, VQ, of the organic phase. With first extraction concluded, the weight of solute left in the aqueous phase is considered to be mv The equilibrium concentration in aqueous phase is then equal to m1/Va and the equilibrium concentration in organic phase is equal to (m - ma)/V0. The process so far permits the following expression ... 

Dealing with incomplete extraction is particularly challenging when analysing polymers containing unknown additive levels. A common strategy is to perform multiple extractions. When incomplete extraction is suspected, it is also useful to apply an alternative analysis technique, such as spectroscopy or elemental analysis. It is good practice to compare the IR spectrum of the polymer before and after extraction to verify the presence of absorbance bands related to the additive. 

The highest radon production rates occurred in rooms with suspended wooden floors through which air could pass readily. Simple ventilation of the underfloor space with a 30 W fan was effective in reducing radon decay-product concentrations in these rooms, but not below the reference value in all rooms. More rigorous application of this technique with multiple extraction points and a larger fan could clearly serve as an effective remedy. 

You can combine the extracts of a multiple extraction, if they have the same material in them. 

Multiple equilibrium model, 24 131 Multiple extraction procedure (MEP), 25 869... 

Samples containing heavy oil, along with the volatile components can severely contaminate pnrge-and-trap instrumentation, and caution is advised when interpreting the data. For such samples it may be advisable to use a separatory funnel for the water extraction method for semivolatiles (EPA 3520). In this method, the sample is ponred into a funnel-shaped piece of glassware, solvent is added, and the mixtnre is shaken vigorously. After layer separation, the extract (i.e., the solvent layer) is removed. Altered, dried with a desiccant, and concentrated. Multiple extractions on the same sample may increase overall recovery. 

The need to use multiple extraction to achieve efficient extraction required the development of new types of continuously working extractors, especially mixer-settlers and pulsed columns, which were suitable for remotely controlled operations. These new extractors could be built for continuous flow and in multiple stages, allowing very efficient isolation of substances in high yield. A good example is the production of rare earth elements in >99.999% purity in ton amounts by mixer-settler batteries containing hundreds of stages. These topics will be further developed in Chapters 6 and 7. 

Solvent extraction reduction is most frequently performed mainly in connection with the extraction of solid and biological samples by liquid partition. Extractions are typically accomplished using a Soxhlet apparatus that provides the benefits of multiple extractions. By repeated distillation and condensation of the solvent, the apparatus allows multiple extractions using the same (small) volume of solvent. Soxhlet extraction has been a standard method for many decades, and it is often the method against which other extraction methods are measured and verified [14]. 

A vacuum manifold can be used for conducting multiple extractions... 

In multiple extraction of solute from aqueous to organic phase, if the volume of the organic solvent used each time remains constant and equal to the volume of aqueous phase, the weight unextracted after n such operations is ... 

Extraction of 25 different binary mixtures of racemic acids (2-(4-isobutylphenyl)-propionic acid (1), and cis- and trans-chrysanthemic (2)), and various chiral bases with supercritical carbon dioxide permitted the conclusion that molecular chiral differentiation in a supercritical fluid is more efficient than in conventional solvents. In the majority of cases, however, complete separation could not be achieved. In five cases, remarkable partial resolutions were realized (30-75% ee) and resolution was possible on a preparative scale. The pair ds-chrysanthemic acid and (S)-(-i-)-2-(benzylamino)-1-butanol (3) was studied in detail. Pressure, temperature, and time, as well as the molar ratio of base and acid, had a marked influence on the quantity and quality of the products. Increasing pressure or decreasing temperature resulted in higher ee values. (-)-cw-Chrysanthemic acid in 99% ee was obtained from the raffinate in a single extraction step. Multiple extractions produced the (-i-)-cA-acid in 90% ee (see fig. 6.3) (Simandi et al., 1997). 

For difficult separations, multiple extractions are frequently carried out, although in many cases the background is also coextracted. Using multiple extractions, polar interferences may sometimes be transferred from the aqueous into organic solvents that can dissolve minute amounts of water. This problem cannot be eliminated by simple presaturation of the extraction solvent but only by washing the extract with small amounts of water (58). Another relevant issue to be considered in trace residue analysis concerns the purity of the organic solvents, since they can introduce solvent impurities into the sample extract. Therefore, the need for high solvent purification should not be overlooked in some applications. 

SPEs offer distinctive advantages over conventional liquid-liquid extractions. They are relatively fast, require small sample size, eliminate emulsification problems, provide the possibility of performing both cleanup and preconcentration of the extract in one analytical step, and offer high precision. Another great advantage of SPEs over liquid-liquid extractions is solvent savings. Unlike liquid-liquid extractions that often require hundreds of milliliters for single or multiple extractions, SPEs require only a few milliliters of solvents for analyte extraction and cleanup. 

The cleanup procedure used was discussed in the section entitled Resin Elution Concentration. The extraction procedure was not the optimum procedure that would result from the observations. The data indicated that a base extraction at pH >12 and a base-to-solvent ratio of 15 1 with multiple extraction steps were needed to maximize removal of the matrix interferences. However, the extraction efficiency must be balanced against minimal sample destruction and operational ease. 

In order to determine the long term stability, a Multiple Extraction Procedure (MEP) was conducted on one of the most solidified samples according to USEPA SW-846, method 1320 for all eight metals as above. 8 >... 

In order to test the long term stability of the CHEMFIX process, the Multiple Extraction Procedure (MEP) was performed on the soil samples treated with the optimal, reagent ratio B. These results are illustrated in Table 6. 

Carrying this one step further, if we are performing multiple extractions, after n extractions we would have... 

Multiple extractions with the elution mixture significantly aid quantitative recovery. In most cases, three extractions remove 90% to 100% of the protein from the membrane. 

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