Separation methods precipitation

The pre-separation methods, precipitation of titan hydroxide, anion-exchange separating and scavenging with lead fluoride, were examined and the higher sensitivity of these methods compared with non-destructive determinations were observed ) for the determination of A1 and V. By anion-exchange chromatography in a mixed solvent system the separation of Lu, Yb and Tb for neutron-activation analysis was possible ). Lu and Yb were eluted in the same fraction, while Tb was obtained in a separate fraction. 

The wastes from uranium and plutonium processing of the reactor fuel usually contain the neptunium. Precipitation, solvent extraction, ion exchange, and volatihty procedures (see Diffusion separation methods) can be used to isolate and purify the neptunium. 

In addition, there are other methods of manufacture of cryoHte from low fluorine value sources, eg, the effluent gases from phosphate plants or from low grade fluorspar. In the former case, making use of the fluorosiHcic acid, the siHca is separated by precipitation with ammonia, and the ammonium fluoride solution is added to a solution of sodium sulfate and aluminum sulfate at 60—90°C to precipitate cryoHte (26,27) ... 

Eor products having relatively low specific activity, such as some compounds labeled with and which are synthesized on the scale of several millimoles, classical organic chemical separation methods may be utilized, including extraction, precipitation, and crystallization. Eor separation of complex mixtures and for products having high specific activity, such as those labeled with tritium, etc, chromatographic methods utilizing paper, thin... 

However, for the past 30 years fractional separation has been the basis for most asphalt composition analysis (Fig. 10). The separation methods that have been used divide asphalt into operationally defined fractions. Four types of asphalt separation procedures are now in use ( /) chemical precipitation in which / -pentane separation of asphaltenes is foUowed by chemical precipitation of other fractions with sulfuric acid of increasing concentration (ASTM D2006) (2) solvent fractionation separation of an "asphaltene" fraction by the use of 1-butanol foUowed by dissolution of the 1-butanol solubles in... 

Los Alamos is processing a wide variety of residues, including Pu-Be neutron sources, polystyrene-Pu02-U02 blocks, incinerator ash, Pu-U alloys and oxides, Pu-Zr alloys and oxides, Pu-Np alloys and oxides, Pu-Th alloys and oxides, etc. Processes have been developed for these scrap items (see Figure 2), but we need to know more about Pu-Np separations Pu-Th separations oxalate precipitations for both plus 3 and plus 4 valences valence stabilization dissolution methods for high-fired impure oxides in-line alpha monitors to measure extremely low concentrations of Pu and Am in HNO3 solutions and solubility of various mixtures of Pu02 and UO2 under a variety of conditions. 

Gordon and Wahl have used the radioisotope "°Ag as a tracer for a study of the exchange of silver between Ag(II) and Ag(I) in acidic media. The precipitation of Ag(phen)2(C104)2, brought about by the addition of o-phenanthroline, formed the basis of the separation method. The experimental data were obtained using a... 

Under conditions where the dismutation reaction is slow the exchange between Au(III) and Au(I) has been shown to proceed at a measurable rate at 0 °C in 0.09 M HCl, an exchange half-time of about 2 min was observed. The isotopic method ( Au) and a separation method based on the precipitation of dipyridine -chloroaurate(III) was used to obtain data. An acceleration in the exchange rate was observed as the HCl concentration was increased. ... 

Peschanski, using the isotopic method ( ° Hg), has found complete exchange (0 °C) in methanol and various other non-aqueous media. The separation methods used were, (a) paper and column chromatography, (b) paper electrophoresis, and (c) precipitation of Hg(I) with chloride. In the presence of cyanide ions, however, less than complete exchange could be observed. Zero-time exchange was again found to vary in the same manner as for aqueous media. Similar effects were observed in the presence of chloride ions. 

Although attempts have been made to study this reaction using ThC as an indicator, the stability of ThC has restricted these investigations. In 1948 the production of 204,206jj enabled more detailed studies to be made by Harbottle and Dodson and by Prestwood and Wahl. In preliminary reports, these authors presented data for the exchange in perchloric - , hydrochloric and nitric s acid media, obtained using separation methods involving precipitation of (a) T1(I) as chromate or bromide and (b) Tl(IlI) as hydroxide. A rate law... 

Barker and Kahn have made a detailed study of the exchange in carbon tetrachloride media using the isotope " Sb to label the Sb(III) species. The reaction was carried out in sealed ampoules covered with A1 foil in the presence of an atmosphere of He or Ar gas. The separation method used involved complexing the Sb(V) with fluoride (brought about by addition of ethanol, HCl and HF) followed by precipitation of the Sb(III) with H2S and finally addition of boric acid and HCl, removal of the CCI4, and treatment with H2S to remove the Sb(V). Zero-time exchange was 5 %. 

The exchange of Mo between the anions Mo(CN)g and Mo(CN)g has been investigated by the isotopic method ( Mo) and the separation methods (a) precipitation of Mo(CN)g with either ethanol or cadmium ions, and (b) precipitation of Mo(CN) with tetraphenylarsonium chloride. Complete exchange was observed by Wolfgang even with reactant concentrations 5x10 M. An estimate of the rate coefficient at 2 °C of >10 l.mole . sec has been sug-geMd. 

Silverman and Dodson made the first detailed isotopic study of this exchange system using the separation afforded by the addition of 2,2 -dipyridyl at pH 5, followed by the precipitation of the ferric iron with either ammonia or 8-hydro-xyquinoline. Dodson , using this separation method, had previously obtained an overall rate coefficient of 16 l.mole" sec at 23 °C for 0.4 M perchloric acid media. The exchange in perchlorate and perchlorate-chloride media was found to conform to a rate law, first order with respect to both total ferrous and ferric ion concentrations, with an observed rate constant (k bs) dependent on the hydrogen-ion concentration, viz. 

Wahl and Deck were able to obtain an estimate of an assumed second-order rate coefficient ( 10 l.mole" .sec at 4°C) using a separation procedure based on the extraction of Fe(CN)e by a chloroform solution of Ph AsCl, in the presence of the ions Co(CN)g and Ru(CN)6, to reduce the exchange between the iron species in the two liquid phases. A similar estimate was obtained using a precipitation method in the presence of the carrier Ru(CN)6. A direct injection technique was used as short reaction times were necessary. Wahl has reviewed the large induced exchanges occurring in the chemical separation methods. The extraction procedure when the carriers Co(CN)6 and Ru(CN) are present provides the most satisfactory method of separation. ... 

Eichler and Wahl have attempted an isotopic study ( Os and Os) of the exchange reaction between Os(dipy)3 and Os(dipy)3 using a direct injection technique so that reaction times 7 x 10 sec were possible. With total osmium 10" M in aqueous sulphate media at 0 °C complete exchange was observed. The separation methods used were, (a) perchlorate precipitation (in presence of iron(II) carrier) and (6) extraction with p-toluenesulphonic acid in nitromethane, of the osmium(II) complex. A lower limit of 1 x 10 l.mole. sec was placed on the rate coefficient (0 °C, 3.0 M H2SO4). Dietrich and Wahl using the line broadening effect produced by Os(dipy)3 on the nmr spectrum of Os(dipy)3 have been able to propose a value of > 5x 10" l.mole . sec at 6 °C in D2O (0.14 M [Cr] and 5x10 M [D- ]). 

The earliest investigation of the exchange reaction between the aquated ions of Co(III) and Co(II) was carried out by Hoshowsky et al., using the isotopic method ( Co). When sulphate salts ( 10 M) were employed, complete exchange was observed between the two oxidation states of cobalt, in a time of less than two min. Two separation methods were employed (a) adsorption on an alumina column, and (b) precipitation of the Co(III) as the cobaltinitrite. 

Purify the biotinylated protein or molecule using dialysis or gel filtration. For small molecule biotinylation where these separation methods may not be appropriate, other procedures may have to be developed, such as reverse-phase chromatography or organic precipitation techniques. 

Radiotracers are uniquely well suited to such studies. The sensitivity of detection means that only very small amounts of tracer need be added to follow the chemical pathway of the relevant species. Furthermore, it matters little what the physical or chemical state of the tracer is, for measurements may be made on liquids, solids or gases. Chromatography, solvent extraction and precipitation are amongst separation methods widely studied by means of radiotracers. In the individual separation steps the distribution of the species may be studied by simple radioactivity measurements, and subsequently the tracer will serve as a yield indicator for the overall procedure. 

Physical separation methods can be based on equilibrium considerations, but the majority are not. Ordinary filtration is an example of a non-equilibrium, physical method and so is ordinary centrifugation— e.g.—the separation of a precipitate from the suspending liquid using an artificial gravity field. There are separation methods, which are called filtration which are not such as gel filtration. Ultracentrifugation in a salt gradient is a physical equilibrium method. 

Most, but not all, chemical separation methods are based on equilibrium in the sense of chemical equilibrium. Clearly, solubility is a chemical question but formation of a precipitate and filtration is a physical separation, which happens to use a favorable Ksp equilibrium... 

Other methods start from crude indanthrone, which is dissolved in sulfuric acid or oleum (sometimes mixed with organic solvents). The product may be precipitated with water. It is more advantageous to separate the precipitated crude pigment, to reslurry it in water, and to heat the resulting aqueous suspension in the presence of a cationic surfactant. Subsequent treatment of the sulfuric acid solution with nitric acid, manganese dioxide, or chromium trioxide is followed by transfer into a solution containing sodium sulfite or iron(II)sulfate. 

Stripping has the technical advantage that the expensive rhodium catalyst remains in the reactor and the disadvantage that the least volatile component (acetic acid) has the lowest concentration of all components in the gas removed by stripping. Distillation as a separation method has the advantage that acetic acid is the most abundant component in the liquid, but now rhodium will be circulated in the system and will remain in the bottom of the distillation unit and it should not precipitate anywhere ... 

Vacuum filtration involves carrying out filtration under reduced pressure and provides a faster method of separating a precipitate from a filtrate than traditional gravity filtration methods. A Buchner, Hirsch or sintered glass funnel can be used during vacuum filtration. 

The purpose of seeking a concentrated strip solution is to reduce the energy required to recover the product from the strip solution. In the case of metal salts, precipitation, electrolysis, direct reduction, and a host of other techniques may be used to generate the final product. In the case of the extraction of organic compounds, distillation, crystallization, or similar separation methods are used. In each case, the more concentrated the strip solution, the less energy is required to recover the desired components. 

The lanthanide group of elements (Table 11.7) is very difficult to separate by traditional methods because of their similar chemical properties. The techniques originally used, like the precious metals, included laborious multiple fractional recrystallizations and fractional precipitation, both of which required many recycle streams to achieve reasonably pure products. Such techniques were unable to cope with the demands for significant quantities of certain pure compounds required by the electronics industry hence, other separation methods were developed. Resin ion exchange was the first of these... 

Americium may be separated from other elements, particularly from the lanthanides or other actinide elements, by techniques involving oxidation, ion exchange and solvent extraction. One oxidation method involves precipitation of the metal in its trivalent state as oxalate (controlled precipitation). Alternatively, it may be separated by precipitating out lanthanide elements as fluorosilicates leaving americium in the solution. Americium may also he oxidized from trivalent to pentavalent state by hypochlorite in potassium carbonate solution. The product potassium americium (V) carbonate precipitates out. Curium and rare earth metals remain in the solution. An alternative approach is to oxidize Am3+ to Am022+ in dilute acid using peroxydisulfate. Am02 is soluble in fluoride solution, while trivalent curium and lanthanides are insoluble. 

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