Extraction extractant dependencies

This type of extraction depends upon the use of a reagent which reacts chemically with the compound to be extracted, and is generally employed either to remove small amounts of impurities in an organic compound or to separate the components of a mixture. Examples of such reagents include dilute (5 per cent.) aqueous sodium or potassium hydroxide solution, 5 or 10 per cent, sodium carbonate solution, saturated sodium bicarbonate solution (ca. 5 per cent.), dilute hydrochloric or sulphuric acid, and concentrated sulphuric acid. 

Resources. World resources of silver are estimated to be about half a million tons. However, only about 250,000 metric tons are considered economically recoverable reserves. These are associated with ores of copper, gold, lead, and 2inc, and extraction depends on the economic recovery of those metals. Canada and the CIS vie for the greatest reserves of silver in the ground. 

The use of an extractant depends on loading capacity, extraction rate, pH range, and the cost of the reagent and the diluent. Loss of the extractant must be minimised because of its high cost. Organic losses to the aqueous phase are also undesirable because of the deleterious effect on cathode deposits. Advances in SX—EW processes are described in Reference 38. 

The separation of components by liquid-liquid extraction depends primarily on the thermodynamic equilibrium partition of those components between the two liquid phases. Knowledge of these partition relationships is essential for selecting the ratio or extraction solvent to feed that enters an extraction process and for evaluating the mass-transfer rates or theoretical stage efficiencies achieved in process equipment. Since two liquid phases that are immiscible are used, the thermodynamic equilibrium involves considerable evaluation of nonideal solutions. In the simplest case a feed solvent F contains a solute that is to be transferred into an extraction solvent S. 

Yttrium and lanthanum are both obtained from lanthanide minerals and the method of extraction depends on the particular mineral involved. Digestions with hydrochloric acid, sulfuric acid, or caustic soda are all used to extract the mixture of metal salts. Prior to the Second World War the separation of these mixtures was effected by fractional crystallizations, sometimes numbered in their thousands. However, during the period 1940-45 the main interest in separating these elements was in order to purify and characterize them more fully. The realization that they are also major constituents of the products of nuclear fission effected a dramatic sharpening of interest in the USA. As a result, ion-exchange techniques were developed and, together with selective complexation and solvent extraction, these have now completely supplanted the older methods of separation (p. 1228). In cases where the free metals are required, reduction of the trifluorides with metallic calcium can be used. 

The rate of extraction depends on the mass transport coefficient (f), the phase contact area (F) and the difference between the equilibrium concentration and the initial concentration of the dissolved component, which is usually expressed as the driving force of the process (a). The rate of extraction (V) can be calculated as shown in Equation (135) ... 

Adsorption, like extraction, depends on equilibrium relationships. Isothermal adsorption is projected by Langmuir isotherms. The model is shown in Figure 7.14, which is based on the linear model of the following equation ... 

Three classes of carbamoylmethylphosphoryl extractants were studied for their ability to extract selected tri-, tetra-, and hexavalent actinides from nitric acid. The three extractants are dihexyl-N,N-diethylcarbamoylmethylphosphonate (DHDECMP), hexyl hexyl-N,N-diethylcarbamoylmethylphosphinate (HHDECMP), and octyl(phenyl)-N,N-diisobutylcarbamoylmethylphos-phine oxide 0< >D[IB]CMP0. The above three extrac-trants were compared on the basis of nitric acid and extractant dependencies for Am(III), solubility of complexes on loading with Nd(III) and U(VI), and selectivity of actinide(III) over fission products. 

Contimious liquid extraction techniques are used when the sample volume is large, the distribution constant is small, or the rate of extraction is slow. The efficiency of extraction depends on many factors including the viscosity of the phases, the magnitude of the distribution constant, the relative phase volumes, the interfacial surface area, and the relative velocity of the phases. Numerous continuous extractors using llghter-than-water and heavier-than-water solvents vee been described [3,2 7,42,73,74]. Generally, either the ligi Pr or heavier density... 

One of the attractive features of SFE with CO2 as the extracting fluid is the ability to directly couple the extraction method with subsequent analytical methods (both chromatographic and spectroscopic). Various modes of on-line analyses have been reported, and include continuous monitoring of the total SFE effluent by MS [6,7], SFE-GC [8-11], SFE-HPLC [12,13], SFE-SFC [14,15] and SFE-TLC [16]. However, interfacing of SFE with other techniques is not without problems. The required purity of the CO2 for extraction depends entirely on the analytical technique used. In the off-line mode SFE takes place as a separate and isolated process to chromatography extracted solutes are trapped or collected, often in a suitable solvent for later injection on to chromatographic instrumentation. Off-line SFE is inherently simpler to perform, since only the extraction parameters need to be understood, and several analyses can be performed on a single extract. Off-line SFE still dominates over on-line determinations of additives-an... 

Takahashi, K., Kondo, Y., Sawano, T., Mori, M., Changes in pH of coffee extract depending on temperature and its quality, Nippon Shokuhin Kogyo Cakkaishi, 26,... 

Hydroalcoholic extracts are made when the active constituents are insoluble in water or when a concentrated dosage form is desired. Hydro alcoholic extracts use concentrated alcohol in varying proportions with water as a solvent. Hydroalcoholic extracts are categorized as tinctures or fluid extracts, depending on the amount of alcohol used. Some patients who simply do not like the taste of alcohol may be counseled to put the dosage of tincture drops into a cup of hot liquid and let it stand for a few minutes to evaporate off most of the alcohol before ingestion. An example of an ethanolic extract is echinacea [5,6]. 

The efficiency of an extraction depends on the magnitude of D and on the relative volumes of the liquid phases. The percentage extraction is given by... 

The efficiency of the extraction depends on the coordinating ability of the solvent, and on the acidity of the aqueous solution which determines the concentration of the metal complex. Coordinating ability follows the sequence ketones > esters > alcohols > ethers. Many metals can be extracted as fluoride, chloride, bromide, iodide or thiocyanate complexes. Table 4.5 shows how the extraction of some metals as their chloro complexes into diethyl ether varies with acid concentration. By controlling... 

Considering that the choice of extractant depends on the size and polarity of the analyte of interest, what extractant would be used to extract all the hydrocarbons from a fuel-contaminated soil Would the type of fuel spilled make a difference in the type of extractant used If so, how ... 

If a substance is soluble in both water and the organic solvent, the result of the extraction depends on the ratio of solubilities if the partition coefficient , e.g. the ratio of the solubility in water to that in ether, is large, correspondingly more ether must be used or the number of extractions must be increased. For this coefficient determines how a substance soluble in two immiscible solvents will distribute itself between them. Whether an aqueous solution should be extracted with a certain amount of ether in one portion or whether it is better to extract several times with smaller portions is... 

Liquid-liquid extraction—depending on difference in solubility in a liquid solvent. 

Sediment-solid and soil-solid samples can be treated in different ways prior to extraction depending on the purpose of the research program. Sediments or soils are stored more conveniently as dried powders. However, this technique is not appropriate if relatively volatile pollutants such as l-ring aryl hydrocarbons (e. g., alkylbenzenes, chlorohydrocarbons, chlorobenzenes), PAH (e.g., naphthalene) are to be determined. In such cases, the sediment or soil should remain frozen prior to analysis and extracted wet. 

Although S-diketones cannot compete with hydroxyoximes for the extraction of copper from acid media, they do have advantages for extraction from ammoniacal leach solutions because, unlike hydroxyoximes, they do not transfer ammonia. The extraction follows Eq. (11.6), and the extent of extraction depends on the concentration of ammonia and ammonium salts. 

Supercritical gas extraction depends on the fact that the vapour pressure of a solid or liquid can be greatly Increased by contacting It with a compressed gas, and that this enhancement Is the more pronounced the greater the gas density ). In principle, It Is consequently possible to transfer Into the vapour phase substances that are otherwise substantially non-volatlle. 

---