Extraction, primary

In case B the solvents are partially miscible, and the miscibihty is nearly constant through the extractor. This frequently occurs when all solute concentrations are relatively low. The feed stream is assumed to dissolve extraction solvent only in the feed stage and to retain the same amount throughout the extractor. Likewise, the extraction solvent is assumed to dissolve feed solvent only in the raffinate stage. With these assumptions the primary extraction-solvent rate moving through the extractor is assumed to be S, and the primary feed-... 

The combined filtrates or total aqueous extracts are cooled to about room temperature and filtered to remove any residual solids from solution. The clarified aqueous extract is then concentrated to about 70 gallons at a temperature below about 50°C, thus reducing the volume to about one-third the original volume. The resulting concentrate is cooled to room temperature or below and filtered to remove any tar or gum that may have separated. The presence of tar or gum at this stage of the process will vary depending upon the starting material and the manner in which the primary extraction has been carried out. It has baen found, however, that unless any tar or gum present in the initial extract is removed by the procedure described, it will seriously interfere with the further concentration and crystallization steps hereinafter described. 

It is best to wash extraction equipment using the pure extracting solution to be used in the primary extraction. For example, if an aqueous acid solution is to be used, then this same solution should be used in cleaning equipment. This is also true when an organic extractant is to be used. When water is to be... 

Following initial sample extraction, the primary extract must frequently be subjected to some kind of further cleanup including liquid-liquid partitioning, diphasic dialysis, solid-phase extraction, matrix solid-phase dispersion, immunoaffinity chromatography cleanup, liquid chromatography cleanup, or online trace enrichment. In some instances, some of these procedures are used in combination in order to attain higher purification levels. 

Equipment and Instrumentation. Solid-phase extraction columns were obtained from J. T. Baker. Octadecyl (C18) and octyl (C8) 1-mL low-displacement columns were used as the primary extraction columns. Cyano and diol... 

Though TBP and DOSO adducts of Pu(IV) were observed when HTTA was used as the primary extractant, no such adducts were reported with the Pu(IV)-HPMBP system (110, 111). On the other hand, synergism was observed for Pu(IV) extraction with HTTA, HPMBP, and HPBI (with stringent stereochemical requirements) when TOPO was used as the auxiliary ligand (27, 33). Other tetravalent actinide ions such as Th(IV) and Np(IV) have shown similar extraction behavior (29, 30, 34). Some adduct formation constants (I<0 for U(VI) and tetravalent actinide ions are listed in Table 2.4. It is necessary to consider both electronic and steric factors of the ligands to explain the observed trends. 

In the primary extraction, however, a hydrocarbon solvent is added. This allows a relatively sharp separation between the middlings and the aqueous bottom layer. A fraction with boiling range of octane is suitable, since it then becomes the azeotropic entrainer for the water. An aromatic solvent—e.g., toluene—might be better, but it may require another separation later. 

In the final extraction because of solvent addition in the primary extraction, the mineral matter readily separates from the bottom aqueous... 

The analysis of CAD and alkamides has been completed using a variety of analytical techniques that include high-performance liquid chromatography (HPLC), capillary electrophoresis, gas chromatography (GC), GC-mass spectrometry (GC-MS), liquid chromatography-mass spectrometry (LC-MS), and nuclear magnetic resonance (NMR). Sample preparation methodologies utilize hexane, methanol and ethanol as the primary extraction solvents. 

Process selection. The processes just described recovered neptunium only partially and in variable yield because of the difficulty in controlling the distribution of neptunium valence between 5 and 6 in the primary extraction step with nitrite-catalyzed HNO3 and the incomplete reduction of neptunium from valence 5 to 4 in the partitioning step with feirous ion. This section describes a modified Purex process that could be used if more complete recovery of neptunium were required. It is based on process design studies by Tajik [Tl]. The principal process steps are shown in the material flow sheet Fig. 10.32. In the primary decontamination step, pentavalent vanadium oxidizes neptunium to the extractable hexavalent state. In the partitioning step, tetravalent uranium reduces plutonium to the inextractable trivalent state while converting neptunium to the still-extractable tetravalent state. 

Anion exchange was investigated for application as a small-scale, primary extraction process to recover plutonium directly from dissolved irradiated uranium in 8N HNO3. A 50-kg U/day pilot plant was operated (76). Even with two cycles of ion exchange the fission product activity with the plutonium was undesirably high. Resin stability is another potential problem which was not resolved fully. 

Looking at the biological function, the primary extractives are necessary for maintaining the metabolism and supply of the components for the biosynthesis of the secondary substances. Typical primary substances include carbohydrates (sugars), which can be found for example as monosaccharides, disaccharides and as starch as well as fats and proteins. As sapwood is responsible for the constant water and nutrient supply of the whole tree, mainly primary extractives are involved, which are also used by various micro-organisms as a source of food. 

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