Solvent Extraction Systems

Tecator supplies units for carrying out organic solvent extractions on polymers. The Soxtec HT2-HT6 systems are recommended for carrying out solvent extractions of additives in polymers and rubbers. 

Forrest, Analysis of Plastics, Rapra Review Report No. 149, Rapra Technology Ltd., Shrewsbury, UK, 2002,13, 5, 146. 

Patticini, Determination of Mineral Oil in Polystyrene, Perkin Elmer IR Bulletin No. 85, 1981. 

Fiorenza, G. Bonomi and A. Sareda, Materie Plastiche ed Elastomeri, 1965, 31,1045. 

Kawaguchi, K. Ueda and A. Koga, Journal of the Society of Rubber Industry (Japan), 1955,28, 525. 

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Another characteristic of the solvent extraction system is the high solute concentration in both aqueous and organic phases, which influences greatly the size of the required installation. Concentrations of rare-earth oxides (REO) higher than 100 g/L are often reached in both phases. The process therefore requires only relatively small equipment. 

S. B. Watson md R. H. Rmney, Modfcations of the SEPHIS Computer Code for Calculating the Purex Solvent Extraction System, ORNL/TM-5123, Oak Ridge National Laboratory, Oak Ridge, Term., 1975. 

Nuclear Waste. NRC defines high level radioactive waste to include (/) irradiated (spent) reactor fuel (2) Hquid waste resulting from the operation of the first cycle solvent extraction system, and the concentrated wastes from subsequent extraction cycles, in a faciHty for reprocessing irradiated reactor fuel and (3) soHds into which such Hquid wastes have been converted. Approximately 23,000 metric tons of spent nuclear fuel has been stored at commercial nuclear reactors as of 1991. This amount is expected to double by the year 2001. 

Organ oselenium compounds, such as phosphine selenides, are being evaluated in solvent extraction systems for silver and gold (63). Also, potential pharmaceuticals containing selenium have been prepared (64). 

Dionex Corporation - Manufacturers of liquid chromatography systems (IC and HPLC), chromatography software data systems, reversed-phase and ion-exchange columns, and accelerated solvent extraction systems... http //www.dionex.com. 

Nitrite ion is often used in plutonium solvent extraction systems to oxidize Pu(III) to Pu(IV) and to reduce Pu(VI) to Pu(IV). But HONO, produced in HN03 media, is extractable into TBP-diluent systems and can interfere with subsequent reductive stripping of plutonium. There is thus a need to find a reagent comparable to nitrite ion in its reactions with Pu(III) and Pu(VI), but which does not extract into TBP solutions. 

Multidimensional Fluorescence Analysis of Cyclodextrin Solvent—Extraction Systems... 

Solvent extraction is intrinsically dependent on the mass transfer across the interface and the chemical inversion at the interfacial region. Researchers in the field of solvent extraction, especially in the field of analytical chemistry and hydrometallurgy, observed effects of interfacial phenomena in the solvent extraction systems. This gave them a strong motivation to measure what happened at the interface. 

One of the most attractive roles of liquid liquid interfaces that we found in solvent extraction kinetics of metal ions is a catalytic effect. Shaking or stirring of the solvent extraction system generates a wide interfacial area or a large specific interfacial area defined as the interfacial area divided by a bulk phase volume. Metal extractants have a molecular structure which has both hydrophilic and hydrophobic groups. Therefore, they have a property of interfacial adsorptivity much like surfactant molecules. Adsorption of extractant at the liquid liquid interface can dramatically facilitate the interfacial com-plexation which has been exploited from our research. 

When using any solvent extraction system, one of the most important decisions is the selection of the solvent to be used. The properties which should be considered when choosing the appropriate solvent are selectivity distribution coefficients insolubility recoverability density interfacial tension chemical reactivity viscosity vapour pressure freezing point safety and cost. A balance must be obtained between the efficiency of extraction (the yield), the stability of the additive under the extraction conditions, the (instrumental and analyst) time required and cost of the equipment. Once extracted the functionality is lost and... 

The development of multimode reactors for organic synthesis occurred mainly from already available microwave acid-digestion/solvent-extraction systems. Instruments for this purpose were first designed in the 1980s and with the growing demand for... 

Aeromonas, DNA-based biosensor, 3 807 AeroSizer, 78 150—151 Aerosol containers, 7 781-782 Aerosol dispersions, 7 774-775 Aerosol drug dosage forms, 78 717 Aerosol emulsions, 7 773, 774 Aerosol flow reactors, 77 211-212 Aerosol foams, 7 773, 774 Aerosol packaging, 7 771 Aerosol pastes, 7 775 Aerosols, 7 769-787 8 697 economic aspects, 7 786 filling, 7 785-786 formulation, 7 771-780 product concentrate, 7 772-775 propellants, 7 775-781 U.S. production, 1985-2000, 7 770t Aerosol solutions, 7 772-773 Aerosol solvent extraction system (ASES), 24 17, 18... 

Many attempts at classifying solvent extraction systems have been made. Thus Diamond and Tuck [20] have described a classification of the solutes that can be separated by solvent extraction. 

Solvent extraction is a major industrial technique. The usual objective is to selectively remove one or more solutes from a complex mixture. Selectivity usually depends on strong specific solvent-solute interactions or on the formation of complexes between ions and ligands. Thus solvent extraction systems are likely to include a number of chemical reactions and to exhibit large deviations from ideality. The design of liquid extraction processes may require many kinds of data. References (31, 32, 55, 61, 81, and 118) are concerned specifically with solvent extraction. 

Spectroscopic measurements may, in certain cases, yield direct information on these interactions. On the other hand, thermodynamic values, obtained by measuring certain bulk properties of the system, require the aid of statistical mechanical methods to be related to specific interactions between the solute and the solvent. However, the thermodynamic aspects of the solute-solvent interactions reflect the preference of the solute for one solvent over another and, thereby, determine distribution of the solute in a solvent extraction system. 

In many practical solvent extraction systems, one of the two liquids between which the solute distributes is an aqueous solution that contains one or more electrolytes. The distributing solute itself may be an electrolyte. An electrolyte is a substance that is capable of ionic dissociation, and does dissociate at least partly to ions in solution. These ions are likely to be solvated by the solvent (or, in water, to be hydrated) [5]. In addition to ion-solvent interactions, the ions will also interact with one another repulsively, if of the same charge sign, attractively, if of the opposite sign. However, ion-ion interactions may be negligible if the solution is extremely dilute. The electrolyte is made up of... 

This expression is analogous to Eiq. (2.3), in that (1 — (p) expresses the contribution of the solvent and In y+ that of the electrolyte to the excess Gibbs energy of the solution. The calculation of the mean ionic activity coefficient of an electrolyte in solution is required for its activity and the effects of the latter in solvent extraction systems to be estimated. The osmotic coefficient or the activity of the water is also an important quantity related to the ability of the solution to dissolve other electrolytes and nonelectrolytes. 

In ternary systems of relevance to solvent extraction these may be two (partly) immiscible solvents and one (solid) solute, or two (solid) solutes and a single solvent. The latter system may constitute a partial system of quaternary or higher mixtures that involve two liquid phases, which are solvent extraction systems. In principle, however, a system of two solid solutes and a liquid solvent could split into two liquid phases, one rich in the one solute, the second in the other. In general, when one solute crystallizes out from a ternary (two solutes... 

Given a nonionic solute that has a relatively low solubility in each of the two liquids, and given equations that permit estimates of its solubility in each liquid to be made, the distribution ratio would be approximately the ratio of these solubilities. The approximation arises from several sources. One is that, in the ternary (solvent extraction) system, the two liquid phases are not the pure liquid solvents where the solubilities have been measured or estimated, but rather, their mutually saturated solutions. The lower the mutual solubility of the two solvents, the better can the approximation be made. Even at low concentrations, however, the solute may not obey Henry s law in one or both of the solvents (i.e., not form a dilute ideal solution with it). It may, for instance, dimerize or form a regular solution with an appreciable value of b(J) (see section 2.2). Such complications become negligible at very low concentrations, but not necessarily in the saturated solutions. 

A common sitnation is that the electrolyte is completely dissociated in the aqueons phase and incompletely, or hardly at all, in the organic phase of a ternary solvent extraction system (cf. Chapter 3), since solvents that are practically immiscible with water tend to have low valnes for their relative permittivities e. At low solnte concentrations, at which nearly ideal mixing is to be expected for the completely dissociated ions in the aqneons phase and the undissociated electrolyte in the organic phase (i.e., the activity coefficients in each phase are approximately nnity), the distribntion constant is given by... 

The amount of a solute that can be introduced into a solvent depends on its solubility, be it a gas (section 2.7.1), a solid nonelectrolyte (section 2.7.2), or an electrolyte (section 2.7.3). Ternary systems, which are the basic form of solvent extraction systems (a solute and two immiscible solvents), have then-own characteristic solubility relationships (section 2.8.1). 

The free energy is calculated from the stability constant, which can be determined by a number of experimental methods that measure some quantity sensitive to a change in concentration of one of the reactants. Measurement of pH, spectroscopic absorption, redox potential, and distribution coefficient in a solvent extraction system are all common techniques. 

This discnssion is important to solvent extraction systems, as it provides further insight into the aqueous phase complexation. It also has significance for the... 

Before a detailed analysis of the chemical reactions that govern the distribution of different solutes in solvent extraction systems, some representative practical examples are presented to Ulnstrate important snbprocesses assnmed to be essential steps in the overall extraction processes. 

These equations do not provide complete definition of the reactions that may be of significance in particular solvent extraction systems. For example, HTTA can exist as a keto, an enol, and a keto-hydrate species. The metal combines with the enol form, which usually is the dominant one in organic solvents (e.g., K = [HTTA]en i/[HTTA]]jet = 6 in wet benzene). The kinetics of the keto -> enol reaction are not fast although it seems to be catalyzed by the presence of a reagent such as TBP or TOPO. Such reagents react with the enol form in drier solvents but cannot compete with water in wetter ones. HTTA TBP and TBP H2O species also are present in these synergistic systems. However, if extraction into only one solvent (e.g., benzene) is considered, these effects are constant and need not be considered in a simple analysis. 

Because metals differ in size, charge, and electronic stractnre, no two metals behave exactly the same in the same solvent extraction system, not even for the same class of solntes. Nevertheless, there are systematic trends in the formation and extraction of these complexes, as described in Chapter 3. Here, the emphasis is on models that give a quantitative description of the extraction within each type or class. 

These are great simplifications in comparison with the indnstrial solvent extraction systems described in later chapters. Nevertheless, the same basic reactions occur also in the industrial systems, although activity factors must be introduced or other adjustments made to fit the data, and the calcnlation of free... 

Tables 4.S-4.7 and Fig. 4.6 list organic acids commonly used as metal extractants. When the acids are not protonated, dissociated, polymerized, hydrated, nor form adducts, the distribution ratio of the acid HA is constant in a given solvent extraction system ...

The free ligand concentration, [A ], is an important parameter in the formation of metal complexes (see Chapter 3 and section 4.8). In a solvent extraction system with the volumes V and of the aqueous and organic phases, respectively, [A ] is calculated from the material balance ... 

This method is useful when only one species is extracted, but it has litde value for the study of solvent extraction systems that contain several complex species. 

The centrifugal separator of the AKUEVE system is also used for phase separation in the SISAK technique [84]. SISAK is a multistage solvent extraction system that is used for studies of properties of short-lived radionuclides, e.g., the chemical properties of the heaviest elements, and solvent extraction behavior of compounds with exotic chemical states. In a typical SISAK experiment, Fig. 4.34, radionuclides are continuously transported from a production... 

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