Selective with ammonia solutions

HydrometaHurgical Processes. The hydrometaHurgical treatments of oxide ores involve leaching with ammonia or with sulfuric acid. In the ammoniacal leaching process, the nickel oxide component of the ore first is reduced selectively. Then the ore is leached with ammonia which removes the nickel into solution, from which it is precipitated as nickel carbonate by heating. A nickel oxide product used in making steel is produced by roasting the carbonate. 

Yosida et al. [41] found that p-t< rr-butylcalix[6]ar-ene can extract Cu from the alkaline-ammonia solution to the organic solvent. Nagasaki and Shinkai [42] described the synthesis of carboxyl, derivatives of calix-[n]arenes ( = 4 and 6) and their selective extraction capacity of transition metal cations from aqueous phase to the organic phase. Gutsche and Nam [43] have synthesized various substituted calix[n]arenes and examined the complexes of the p-bromo benzene sulfonate of p-(2-aminoethyl)calix[4]arene with Ni, Cu , Co-, and Fe. ... 

The conventional selective reduction of NOx for car passengers still competes but the efficient SCR with ammonia on V205/Ti02 for stationary sources is not available for mobile sources due to the toxicity of vanadium and its lower intrinsic activity than that of noble metals, which may imply higher amount of active phase for compensation. As illustrated in Figure 10.9, such a solution does not seem relevant because a subsequent increase in vanadium enhances the formation of undesirable nitrous oxide at low temperature. Presently, various attempts for the replacement of vanadium did not succeed regarding the complete conversion of NO into N2 at low temperature. Suarez et al. [87] who investigated the reduction of NO with NH3 on CuO-supported monolithic catalysts... 

Films deposited from mixed Cd/Pb solutions complexed with ammonia (for Cd) and hydroxide (for Pb), both in a minimum amount to effect dissolution, at pH values between 10 and 13 and deposition temperatures between 60 and 80°C were concluded, from consideration of the XRD, TEM (which showed two different crystal sizes), and optical spectra, to be mixtures of the two sulphides rather than a solid solution [21]. A study of these films for solar-selective surfaces was carried out. 

As early as 1969, Pedersen was intrigued by the intense blue colour observed upon dissolution of small quantities of sodium or potassium metal in coordinating organic solvents in the presence of crown ethers. Indeed, the history of alkali metal (as opposed to metal cation) solution chemistry may be traced back to an 1808 entry in the notebook of Sir Humphry Davy, concerning the blue or bronze colour of potassium-liquid ammonia solutions. This blue colour is attributed to the presence of a solvated form of free electrons. It is also observed upon dissolution of sodium metal in liquid ammonia, and is a useful reagent for dissolving metal reductions , such as the selective reduction of arenes to 1,4-dienes (Birch reduction). Alkali metal solutions in the presence of crown ethers and cryptands in etheric solvents are now used extensively in this context. The full characterisation of these intriguing materials had to wait until 1983, however, when the first X-ray crystal structure of an electride salt (a cation with an electron as the counter anion) was obtained by James L. Dye and... 

High selectivity combined with high yield was found when 3-nitropyridine reacts with a solution of DMSO/water (75/25), ammonia, and potassium permanganate at 22 °C. 6-Amino-3-nitropyridine was obtained in 90% yield only a small amount of 4-amino-3-nitropyridine was formed (01TL4393, 01JCS(P1)376). 

In practice, a buffer solution is prepared by the partial neutralization of the selected weak acid or base with a suitable strong acid or base, or by the addition of the calculated amount of the corresponding salt. The assumption is made that the salt is completely dissociated in solution, e.g. an NHj + NHJ buffer may be produced by the partial neutralization of an ammonia solution with hydrochloric acid or by the addition of the appropriate quantity of ammonium chloride to an initial ammonia solution. To facilitate this practical approach, equation (3.20) may be written in a different form,... 

In the environmental sector ammonia is used in various processes for removing S02 from flue gases of fossil-fuel power plants. The resulting ammonium sulfate is sold as fertilizer. In the selective catalytic reduction process (SCR) the NOx in flue gases is reduced in a catalytic reaction of the nitrogen oxides with a stoichiometric amount of ammonia [1427] - [1430]. Also noncatalytic reduction is applied with ammonia or urea solutions. 

Cu-MCM-41 and Cu-Al-MCM-41 samples have been obtained by ion exchange of the MCM-41 and Al-MCM-41 matrices prepared by hexadecyltrimethylammonium cloride, tetraethyl orthosilicate, aluminum isopropoxide and an ammonia solution. The aluminum concentration affects the MCM-41 textural properties and large amount of extra-framework aluminum species are supposed to be present in Al-MCM-41 with Si/Al = 30. Cu-MCM-41 and Cu-Al-MCM-41 catalysts have been tested for NO selective catalytic reduction by propane in the presence of oxygen, in comparison with microporous Cu-S-1 and Cu-ZSM-5 catalysts with similar copper loading and Si/Al atomic ratio. Cu-Al-MCM-41 catalysts are less active and selective with respect to the Cu-ZSM-5 catalysts indicating that they are not suitable for NO abatement reactions. 

For production of uranium compounds suitable for use in nuclear reactors or for isotope separation, further chemical procedures are applied, as indicated in Fig. 11.9. Nuclear purity means that the compounds are free of nuclides with high neutron absorption cross section, i.e. free of boron, cadmium and rare-earth elements. Selective extraction procedures are most suitable for this purpose. Uranyl nitrate hexa-hydrate (U02(N03)2 6H2O UNH) is obtained by concentration of solutions of U02(N03)2, and ammonium diuranate ((NH4)2U207 ADU) by precipitation with ammonia. 

A chemist who works in the process laboratory of the Athabasca Alkali Company makes frequent analyses of ammonia recovered from the Solvay process for making sodium carbonate. What is the pH at the equivalence point if she titrates the aqueous ammonia solution (approximately 0.10 m) with a strong acid of comparable concentration Select an indicator that would be suitable for the titration. 

Silver may be separated from Ce, Zr, Th, Be, and Fe(III), on strongly acidic cation-exchangers, by converting these metals into anionic complexes, or separated from Cu, U, Al, and Zn by selective elution with nitric acid [14]. After retention of Pb, Ag, and Hg on Dowex 50, lead is eluted first with 0.25 M ammonium acetate, then silver with 0.5 M ammonia solution. Silver has been separated on a cation-exchanger from Hg, Co, Ni, and Zn on the basis of the differing stabilities of their EDTA complexes at pH 4.6 [15]. Silver retained in a column with a macroporous cation-exchange resin bed has been eluted with 2 M HNO3 or 0.5 M HBr in aqueous acetone solution [16]. 

Aliphatic amines are amongst the most important bulk and fine chemicals in the chemical and pharmaceutical industry [13]. Hydroaminomethylation of alkenes to amines presents an atom-economic, efficient and elegant synthetic pathway towards this class of compounds. In hydroaminomethylation a reaction sequence of hydroformylation of an alkene to an aldehyde with subsequent reductive amina-tion proceeds in a domino reaction (see Eq. 4) [14]. Recently, the highly selective hydroamination of alkenes with ammonia to form linear primary and secondary aliphatic amines with a new Rh/Ir catalytic system (] Rh(cod)Cl 2], ] Ir(cod)Cl 2], aqueous TPPTS solution) has been described (see Scheme 2) [15]. The method is of particular importance for the production of industrially relevant, low molecular weight amines. 

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