Nitric aqueous chemistry

Cerium (IV) in solution is obtained by treatment of Ce111 solutions with very powerful oxidizing agents, for example, peroxodisulfate or bismuthate in nitric acid. The aqueous chemistry of CeIV is similar to that of Zr, Hf, and, particularly, tetravalent actinides. Thus Ce gives a phosphate insoluble in 4 M HN03 and an iodate insoluble in 6 M HN03, as well as an insoluble oxalate. The phosphate and iodate precipitations can be used to separate Ce from the trivalent lanthanides. Ce is also much more readily extracted into organic solvents by tributyl phosphate and similar extractants than are the Lnm lanthanide ions. 

The aqueous chemistry of NO has been extensively studied. Nitric oxide has a modest solubility of 1.9 mM in water under 1 atm of NO. Descriptions of its reactivity have tended to be highly variable. Recent work indicates that NO is not highly reactive, despite having an unpaired electron, but reacts with O2 to form reactive species. Traces of Oj are the probable source of different conclusions about the reactivity of NO. It should be noted that there have been some recent studies of the general properties of species involved in these sterns, such as the pulse radiolysis of NO, the pK, values of HNOj and 1 0, the reduction potential of NO. and the AGf of ONOjH. ... 

Silver has little tendency to formally lose more than one electron its chemistry is therefore almost entirely restricted to the + 1 oxidation state. Silver itself is resistant to chemical attack, though aqueous cyanide ion slowly attacks it, as does sulphur or a sulphide (to give black Ag S). hence the tarnishing of silver by the atmosphere or other sulphur-containing materials. It dissolves in concentrated nitric acid to give a solution of silver(I) nitrate. AgNOj. 

Nitric oxide is the simplest thermally stable odd-electron molecule known and, accordingly, its electronic structure and reaction chemistry have been very extensively studied. The compound is an intermediate in the production of nitric acid and is prepared industrially by the catalytic oxidation of ammonia (p. 466). On the laboratory scale it can be synthesized from aqueous solution by the mild reduction of acidified nitrites with iodide or ferrocyanide or by the disproportionation of nitrous acid in the presence of dilute sulfuric acid ... 

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. 

Molten salt extraction residues are processed to recover plutonium by an aqueous precipitation process. The residues are dissolved in dilute HC1, the actinides are precipitated with potassium carbonate, and the precipitate redissolved in nitric acid (7M) to convert from a chloride to a nitrate system. The plutonium is then recovered from the 7M HNO3 by anion exchange and the effluent sent to waste or americium recovery. We are studying actinide (III) carbonate chemistry and looking at new... 

It is known from studies carried out over many decades that oxides of nitrogen at high concentrations dissolve in aqueous solution and react to form species such as nitrate and nitrite. With the focus on acid deposition and the chemistry leading to the formation of nitric and sulfuric acids during the 1970s and 1980s, a great deal of research was carried out on these reactions at much lower concentrations relevant to atmospheric conditions (for reviews, see Schwartz and White, 1981, 1983 and Schwartz, 1984). 

Bonner, F. T., and Pearsall, K. A. (1982). Aqueous nitrosyliron(ll) chemistry. 1. Reduction of nitrite and nitric oxide by iron(ll) and (trioxodinitrato)iron(ll) in acetate buffer. Intermediacy of nitrosyl hydride. Inorg. Chem. 21, 1973-1978. 

Protons present in aqueous acid also act as reasonably efficient electron acceptors. If the reduced hydrogen atoms are formed on metallized suspensions, catalytic hydrogenation can result. For example, in contrast to the oxidative chemistry reported earlier for cyclohexene-4,5-bis-dicarboxylic acid (Eq. 28), if the reaction is conducted in the absence of oxygen in aqueous nitric acid, catalytic hydrogenation of the double bond becomes a major pathway, Eq. (34). ... 

In elementary chemistry, we usually deal with acids in more or less dilute aqueous solution and we think of sulfuric, hydrochloric, and nitric acids as being similarly strong because each is essentially completely dissociated in dilute water solution ... 

Gaquer, I., Moisy, P., Madic, C. 1996. Redox chemistry of Np(VI)/Np(V) couple in nitric/nitrous acid aqueous media. 4th Int. Conf. on Nuclear and Radiochemistry, NRC4, St-Malo, France, September 8-13. 

Gas phase molecular aggregates that contain acid molecules have been produced with free jet expansion techniques and detected by using electron impact ionization mass spectrometry. The clusters of aqueous nitric acid paralleled many properties of the condensed phase. Multiple nitric acid molecules were found in the clusters that were sufficiently dilute. The acid molecule was absent in the ionized clusters involving HC1 and only water was evident. Experiments also demonstrated the reactivity of ammonia with aqueous nitric acid and sulfur dioxide clusters and of sulfur trioxide with water clusters. The natural occurrence of acid cluster negative ions offers a means to probe the gas phase acid loading of the atmosphere through laboratory and field studies of the ion chemistry. 

N03 is generated with difficulty in aqueous solution, the primary technique being radiolysis of concentrated nitric acid or nitrate-containing solutions. Its chemistry has recently been reviewed by Neta and Huie (227). Berdnikov and Bazhin gave the first estimate of E° for the N03/N03- couple as 2.3 + 0.1 V (45). This was obtained from gas-phase data and estimated hydration energies. A recent direct measurement of the equilibrium constant for the N02 + N03 N203 reaction... 

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