Separation and Concentration

Equipment. From the appHcations standpoint, magnetic equipment falls into one of four broad categories tramp iron removal, magnetic particle separation and concentration, product cleaning, or eddy current separation on nonmagnetic metaUics. 

A similar process has been devised by the U.S. Bureau of Mines (8) for extraction of nickel and cobalt from United States laterites. The reduction temperature is lowered to 525°C and the hoi ding time for the reaction is 15 minutes. An ammoniacal leach is also employed, but oxidation is controlled, resulting in high extraction of nickel and cobalt into solution. Mixers and settlers are added to separate and concentrate the metals in solution. Organic strippers are used to selectively remove the metals from the solution. The metals are then removed from the strippers. In the case of cobalt, spent cobalt electrolyte is used to separate the metal-containing solution and the stripper. MetaUic cobalt is then recovered by electrolysis from the solution. Using this method, 92.7 wt % nickel and 91.4 wt % cobalt have been economically extracted from domestic laterites containing 0.73 wt % nickel and 0.2 wt % cobalt (8). 

Flotation. Flotation (qv) is used to remove suspended soHds from wastes and for the separation and concentration of sludges (52,53). The waste flow is pressurized in the presence of sufficient air to approach saturation. When the pressurized air—Hquid mixture is released to atmospheric pressure in the flotation unit, minute air bubbles are formed. As they rise in the Hquor the sludge floes and suspended soHds are floated to the surface where the air—soHd mixture can be skimmed off. 

Displacement chromatography is suitable for the separation of multicomponent bulk mixtures. For dilute multicomponent mixtures it allows a simultaneous separation and concentration. Thus, it permits the separation of compounds with extremely low separation fac tors without the excessive dilutiou that would be obtained in elution techniques. 

A mixture of 12.6 g of benzoyl chloride in 100 cc of ethylene chloride is added dropwise to a suspension of 25.6 g of 3ethylene chloride and 21.8 g of triethylamine within 18 minutes at room temperature while stirring. The mixture is stirred at room temperature for a further 14 hours, 200 cc of water are added, the organic phase is separated and concentrated to an oil in a vacuum. Upon adding ether/dimethoxy ethane to this oil, crude 6-ben zoy I-3absolute ethanol with the addition of a small amount of coal, the compound has a melting point of 125°C to 127°C (decomp.). Displacement of the halogen with hydrazine leads to the formation of endralazine. 

That benzene hexachloride isomer mixture is then the raw material for lindane production. The production of lindane per se is not a chemical synthesis operation but a physical separation process. It is possible to influence the gamma isomer content of benzene hexachloride to an extent during the synthesis process. Basically, however, one is faced with the problem of separating a 99%-plus purity gamma isomer from a crude product containing perhaps 12 to 15% of the gamma isomer. The separation and concentration process is done by a carefully controlled solvent extraction and crystallization process. One such process is described by R.D. Donaldson et al. Another description of hexachlorocyclohexane isomer separation is given by R.H. Kimball. 

Cooperative effects are of considerable interest for high capacity chromatography of BAS, since for practical purposes high-selectivity bonding is possible only in cooperative processes. This is very important for carrying out the sorption, separation and concentration of BAS. 

Accurate quantitation in GC/MS requires the addition of a known quantity of an internal standard to an accurately weighed aliquot of the mixture (matrix) being analyzed. The internal standard corrects for losses during subsequent separation and concentration steps and provides a known amount of material to measure against the compound of interest. The best internal standard is one that is chemically similar to the compound to be measured, but that elutes in an empty space in the chromatogram. With MS, it is possible to work with isotopically labeled standards that co-elute with the component of interest, but are distinguished by the mass spectrometer. 

Ultrafiltration (UF) is used for the separation and concentration of macromolecules and colloidal particles. Ultrafiltration membranes usually have larger pore sizes than RO membranes, typically 1 to 100 nanometer (nm). Operating pressures are generally low (30-100 psig). Applications include electropaints, gray water, emulsions, oily wastes, and milk, cheese, and protein processing. 

Correlation between composition and properties of phosphate ester surfactants was exemplified by octyl phosphate with an optimum of foam inhibition and surfactant properties [301]. In separation and concentration of rare earth metals by liquid surfactant membranes 2-ethylhexylphosphonic acid mono-2-ethylhexyl ester was used as carrier [302]. 

The same analytical methods as for liquid sodium have been applied. Distillation separates and concentrates the impurities prior to analysis. Amalgamation has poor recovery value for oxygen compared to distillation (Table 1). ... 

Diphtheria (adsorbed) Cultures of C. diphtheriae in liquid medium 1 Separation and concentration of toxin 2 Conversion of toxin to toxoid 3 Adsorption of toxoid to adjuvant 3+3 quantal assay in guinea-pigs using intra-dermal challenge Inoculation of guinea-pigs to exclude residual toxin... 

Nuclear fuel reprocessing was first undertaken with the sole purpose of recovering plutonium, for weapons use, from uranium irradiated in nuclear reactors. These reactors, called the production reactors, were dedicated to transmuting as much of the uranium as possible to plutonium. From its original scope of recovering exclusively plutonium, with no attempts to either recover or recycle uranium, nuclear fuel reprocessing has since grown into a much more sophisticated and complex operation with expanded scope. It is now called upon to separate uranium and plutonium from the fission products, and to purify these elements to levels at which these fissile materials can be conveniently recycled for reuse. The present scope also extends to fission products separation and concentration. 

ASTM E 1385-90, Standard Practice for Separation and Concentration of Flammable or Combustible Liquid Residues from Fire Debris Samples by Steam Distillation, American Society for Testing and Materials, Philadelphia, PA (1991). 

Just as the aqueous, alkaline fuel cell can be adopted to C02 separation and concentration, the molten carbonate fuel cell (MCFC) can function in this application as well. Recall that the MCFC cathode operates with the net reaction... 

Some of the types of equilibria involved in the unit operations separation and concentration are listed in the introduction, Section 9.17.1. Those which depend most on coordination chemistry, and for which details of metal complex formation are best understood, are associated with hydrometallurgy. Once the metal values have been transferred to an aqueous solution, the separation from other metals and concentration can be achieved by one of the following processes.3... 

More than 90% of the nickel and cobalt in laterite ores (1.0-1.6% nickel) can readily be leached by sulfuric acid at >240 °C, typically producing large volumes of relatively dilute leach solution containing 3-6 gL-1 of nickel and around 40 gL-1 H2S04.98 In addition to nickel and cobalt these leach solutions contain Al, Cr, Ca, Cu, Fe, Mg, Mn, Na, Si, and Zn.89 The design of reagents and protocols for the separation and concentration of metal values in these streams has depended heavily on differences in the coordination chemistry of the components. 

The concentration of organic materials in seawater is too low to merit direct utilization of many of the modern analytical instruments concentration by a factor of a hundred or more is necessary in many instances. Furthermore, the water and inorganic salts interfere with many of the analytical procedures. Separation of the organic components from seawater therefore accomplishes two purposes it removes interfering substances, and at the same time concentrates enough organic matter to make analysis possible. It is not surprising that considerable effort has been put into methods of separation and concentration. 

Using the newer methods, such as gas chromatography, liquid-liquid chromatography, fluorometry, and mass spectrometry, it is possible to measure many compounds at the parts-per-billion level, and a few selected compounds with special characteristics at the parts-per-trillion level. Even with these sensitivities, however, a considerable concentration must usually be undertaken to permit the chemical or physical fractionation necessary to render the final analyses interpretable. A major effort has therefore been expended on the study of methods of separation and concentration, and this is discussed further in Chap. 8. 

If it were possible to identify or quantitatively determine any element or compound by simple measurement no matter what its concentration or the complexity of the matrix, separation techniques would be of no value to the analytical chemist. Most procedures fall short of this ideal because of interference with the required measurement by other constituents of the sample. Many techniques for separating and concentrating the species of interest have thus been devised. Such techniques are aimed at exploiting differences in physico-chemical properties between the various components of a mixture. Volatility, solubility, charge, molecular size, shape and polarity are the most useful in this respect. A change of phase, as occurs during distillation, or the formation of a new phase, as in precipitation, can provide a simple means of isolating a desired component. Usually, however, more complex separation procedures are required for multi-component samples. Most depend on the selective transfer of materials between two immiscible phases. The most widely used techniques and the phase systems associated with them are summarized in Table 4.1. 

Separation and concentration by means of hyperfiltration (reverse osmosis). 

Standard Practice for Separation and Concentration of Ignitable Liquid Residues in Extracts from Samples of Fire Debris by Gas Chromatography, ASTM E138701, ASTM, West Conshohocken, PA, 2001. 

The ability to coat paramagnetic beads with antibodies to surface antigens of bacteria has been exploited to separate and concentrate organisms from the sample. The bacteria can then be lysed, and the DNA released into the supernatant can be amplified by PCR. Such an approach has found a wide range of applications, among which is the detection of Helicobacter pylori in water and stool specimens (El). 

The extraction of technetiiun by different organic solvents is used in numerous separation and concentration procedures. Technetium is extracted as pertechnetate or, in lower oxidation states, as a complex compound. TcO can be extracted by the following main types of reactions ... 

Notice that none of the flow sheets uses solvent extraction exclusively. Because the aqueous chemistry of osmium and ruthenium is very complex, most operators remove these elements by distillation of the tetraoxides, MO4. Also, it has been advantageous to use ion exchange to separate and concentrate rhodium. The various extraction routes for individual elements are discussed in the following sections. 

Solvent extraction is now a proven technology for the commercial extraction, separation, and concentration of a wide range of metals both from primary and secondary sources (see Chapter 14). In recent years, there has been a reduction in the development, production, and marketing of new commercial extractants as the overall costs of such activities increases. However, the use of established reagents in new hydrometallurgical applications continues to expand. 

This phenomenon can be exploited for separation and concentration of solutes. If one solute has certain affinity for the micellar entity in solution then, by altering the conditions of the solution to ensure separation of the micellar solution into two phases, it is possible to separate and concentrate the solute in the surfactant-rich phase. This technique is known as cloud point extraction (CPE) or micelle-mediated extraction (ME). The ratio of the concentrations of the solute in the surfactant-rich phase to that in the dilute phase can exceed 500 with phase volume ratios exceeding 20, which indicates the high efficiency of this technique. Moreover, the surfactant-rich phase is compatible with the micellar and aqueous-organic mobile phases in liquid chromatography and thus facilitates the determination of chemical species by different analytical methods [104]. 

Diphenyl telluropyran-4-one (typicalprocedure)7° 120 mL (0.12 mol) of a 1.0 M solution of lithium triethylborohydride in tetrahydrofuran are added to 7.65 g (60 mmol) of powdered tellurium under nitrogen, and the mixture stirred at 20°C for 4 h. A solution of sodium ethoxide (prepared from 5.52 g (0.24 mol) of sodium and 240 mL of absolute alcohol) is added to the dilithium telluride, 13.8 g (60 mmol) of bis(phenylethynyl) ketone are dissolved in a mixture of 150 mL of tetrahydrofuran and 150 mL of 1 M sodium ethoxide in ethanol this solution is poured as quickly as possible into the deep-purple-coloured dilithium telluride soluhon. The flask containing the reaction mixture is immediately placed in a water bath at 50°C and the temperature slowly increased over 30 min until ethanol begins to condense on the side of the flask. The water bath is removed and the mixture is stirred overnight at 20°C. Dichloromethane (400 mL) is then added, the resultant mixture is washed with 800 mL of water, and the organic phase is separated and concentrated to an oil. The oil is dissolved in 600 mL of dichloromethane, and the solution is filtered through a pad of sand. The filtrate is washed with 200 mL of 2% aqueous sodium chloride soluhon, dried with anhydrous sodium sulphate, filtered and evaporated. The brownish solid residue is triturated with 20 mL of butanenitrile and the fine yellow solid is collected by filtration yield 10.9 g (51%) m.p. 126-129°C (from acetonitrile). 

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