Aqueous Methods

An overview is presented of plutonium process chemistry at Rocky Flats and of research in progress to improve plutonium processing operations or to develop new processes. Both pyrochemical and aqueous methods are used to process plutonium metal scrap, oxide, and other residues. The pyrochemical processes currently in production include electrorefining, fluorination, hydriding, molten salt extraction, calcination, and reduction operations. Aqueous processing and waste treatment methods involve nitric acid dissolution, ion exchange, solvent extraction, and precipitation techniques. 

Recently, rhodium and ruthenium-based carbon-supported sulfide electrocatalysts were synthesized by different established methods and evaluated as ODP cathodic catalysts in a chlorine-saturated hydrochloric acid environment with respect to both economic and industrial considerations [46]. In particular, patented E-TEK methods as well as a non-aqueous method were used to produce binary RhjcSy and Ru Sy in addition, some of the more popular Mo, Co, Rh, and Redoped RuxSy catalysts for acid electrolyte fuel cell ORR applications were also prepared. The roles of both crystallinity and morphology of the electrocatalysts were investigated. Their activity for ORR was compared to state-of-the-art Pt/C and Rh/C systems. The Rh Sy/C, CojcRuyS /C, and Ru Sy/C materials synthesized by the E-TEK methods exhibited appreciable stability and activity for ORR under these conditions. The Ru-based materials showed good depolarizing behavior. Considering that ruthenium is about seven times less expensive than rhodium, these Ru-based electrocatalysts may prove to be a viable low-cost alternative to Rh Sy systems for the ODC HCl electrolysis industry. 

Method of Iqbal et al. (7) for NMOR determination. The published method (2) was used, with slight modifications. In brief, the frozen mouse (stored for 1-7 days in liquid N ) was blended to give a powder and 5-g samples were reblended with 75 mL ice-cold 35% aqueous methanol. The mixture (which was at pH 7.6) was centrifuged at 5 C and the pellets were re-extracted with aqueous methanol. The combined aqueous method extract was extracted twice with CH2C12 Our method was used from then on, i.e., the extract was passed through a Celite column, concentrated, and subjected to GC-TEA as before. 

For many years, research efforts in materials chemistry have focused on the development of new methods for materials synthesis. Traditional areas of interest have included the synthesis of catalytic, electronic, and refractory materials via aqueous methods (sol-gel and impregnation) and high-temperature reactions [1-3]. More recent strategies have focused on the synthesis of materials with tailored properties and structures, including well-defined pores, homogeneously distributed elements, isolated catalytic sites, comphcated stoichiometries, inorganic/organic hybrids, and nanoparticles [4-13]. A feature... 

In addition to the aqueous method for diazotization in aqueous solution, diazonium ions can be generated in organic solvents by reaction with alkyl nitrites. 

Many of the aqueous methods fisted in Table 2 utilize adsorption chromatography, such as silica or alumina chromatography, to purify extracts prior to analysis. 

A non-aqueous method for the titration of procaine and other drugs using trifluoromethanesulfonic acid was reported by Zakhari and Kovar [88]. Solutions of procaine hydrochloride in anhydrous acetic acid, acetic anhydride, their mixture, or in acetone, was titrated with an acetic acid solution of 0.1 M trifluoromethanesulphonic acid or 0.1 M perchloric acid. Titration was effected in the presence or in the absence of mercurous acetate. The end point was detected visually (using crystal violet as indicator) or potentiometrically. 

Although earlier attempts to isolate chromium(II) complexes of various bidentate amines from aqueous solutions produced chromium(III) complexes and hydrogen, the predominantly non-aqueous methods outlined in Scheme 10 provide complexes of ethylenediamine (en), 1,2-diaminopropane (pn), 1,3-diaminopropane (tmd), l,2-diamino-2-methylpropane (dmp), jVjA-dimethylethylenediamine (NNdmn) and N, N -dimethylethylenediamine (NN dmn) (Table 11). In general, ethanol is a suitable solvent but with some amines it is necessary to dehydrate the halide with 2,2-dimethoxypropane (DMP) and dry the ethanol carefully to prevent hydrolysis and oxidation. 

Nonaqueous methods for the determination of surface acidity represent a considerable improvement over aqueous methods because the solvents used (e.g., benzene, iso-octane) do not react with catalyst surfaces as previously described in the case of water. Of the available types of nonaqueous methods (1-3), the simplest is that employing adsorbed indicators. It can be used to determine acid strengths and amounts of surface acids as described in the following section. 

Curiously, only chromium (33), cobalt, and nickel complexes of this 11-atom ligand have been prepared thus far. The complex (l,7-B9C2Hu)2Co has been prepared by both the anhydrous and aqueous methods (18). An X-ray diffraction study of the cesium salt of the cobalt(III) complex confirmed the symmetrical sandwich bonding of the carborane cages but failed to locate the carbon atoms because of disorder in the crystal (48). 

In contrast to aqueous methods, the polyol approach resulted in the synthesis of metallic nanoparticles protected by surface-adsorbed glycol, thus minimizing the oxidation problem The use of polyol solvent also reduces the hydrolysis problem of ultrafine metal particles, which often occurs in aqueous systems. Oxide nanoparticles can be prepared, however, with the addition of water, which makes the polyol method act more like a sol—gel reaction (forced hydrolysis). For example, 5.5-nm CoFe204 has been prepared by the reaction of ferric chloride and cobalt acetate in 1,2- propanediol with the addition of water and sodium acetate. 

Aqueous methods include the use of ion exchange to determine the total number of acid sites,and titration of aqueous slurries of the acidic solids with a standard base. The method cannot be applied to water-sensitive solids. 

Aqueous methods like the Jones oxidation are no good for this, since the aldehyde that forms is further oxidized to acid via its hydrate. The oxidizing agent treats the hydrate as an alcohol, and oxidizes it to the acid. 

Although several new - Reissert compounds were prepared by this method it has been largely displaced by the methylene chloride—water system. The disadvantages of the aqueous method have been discussed. ... 

Until the advent of the methylene chloride-water solvent system the less reactive acid chlorides could be used in the aqueous method but the more reactive acid chlorides required the anhydrous hydrogen cyanide method. This latter method is still sometimes used - and in fact has been used with quinoline and the 2- and 3-carboxylic acid chlorides of methylcyclopentadienyl manganese tricarbonyl."... 

Aqueous methods and conversion methods In aqueous solutions, the Ce " ions would precipitate even in quite acidic solutions while the Ce " " ions would precipitate as Ce(OH)3 at much higher pH values (7-9) Ce(OH)3 precipitate could be oxidized into ceria in air. In nonaqueous solutions, ceria forms with decomposition of appropriate precursor, with or without the oxidation by air or other oxidative species. If doping is a target, the doping ions would be introduced during the synthesis, and the coprecipitation, sol-gel, combustion/spray pyrolysis, or hydrothermal techniques are usually employed for such a task. 

Nonaqueous solution methods In addition to the aqueous methods, ceria nanocrystals could also be obtained through a number of nonaqueous solution mefhods, such as the solvothermal methods, ionic liquids routes, polyol routes, as well as reactions in coordinating high-boiling oil solvents. 

Pyrochemical processing methods may offer unique advantages over more conventional aqueous methods with respect to meeting nonproliferation goals. Some pyrochemical processes are intrinsically proliferation resistant because the process is incapable of producing a weapons-usable product without significant alterations. The product also can be sufficiently radioactive that it is physically difficult to divert. These features warrant the examination of pyrochemical and dry processing methods under current nonproliferation policies. 

A few new Reissert compounds have been made by the aqueous method, but the vast majority by the methylene chloride-water solvent system. A new variation of the latter method, which is particularly useful in cases where pseudo-base formation becomes a problem, - adds a small quantity of benzyltrialkylammonium chloride to the reaction mixture. " The phase transfer agent appears to enhance the transport of the cyanide ion to the methylene chloride phase. 

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