Nitric acid electrolytic reduction

Reduction of Nitric Acid. Electrolytic reduction of HN03 in the presence of HC1 produces hydroxylammonia chloride ... 

Hydroxylamine is derived from ammonia by replacing one hydrogen atom by a hydroxyl group. It is prepared by the electrolytic reduction of nitric acid, using a lead cathode ... 

Alternatively, hydroxylammonium salts can be made either (a) by the electrolytic reduction of aqueous nitric acid between amalgamated lead electrodes in the presence of H2SO4/HCI, or (b) by the hydrogenation of nitric oxide in acid solutions over a Pl/charcoal catalyst ... 

Table XXVII.—The Electrolytic Reduction of Nitric Acid.

A 1-g. sample is dissolved in concentrated nitric acid, the resulting iodine removed by filtration through a sintered-glass funnel, washed with water, and the washings added to the yellow filtrate. The latter is diluted with water and the copper determined by electrolytic reduction. Anal. Calcd. for Cul Cu, 33.4. Found Cu, 33.1. 

Under -> open-circuit conditions a possible passivation depends seriously on the environment, i.e., the pH of the solution and the potential of the redox system which is present within the electrolyte and its kinetics. For electrochemical studies redox systems are replaced by a -> potentiostat. Thus one may study the passivating properties of the metal independently of the thermodynamic or kinetic properties of the redox system. However, if a metal is passivated in a solution at open-circuit conditions the cathodic current density of the redox system has to exceed the maximum anodic dissolution current density of the metal to shift the electrode potential into the passive range (Fig. 1 of the next entry (- passivation potential)). In the case of iron, concentrated nitric acid will passivate the metal surface whereas diluted nitric acid does not passivate. However, diluted nitric acid may sustain passivity if the metal has been passivated before by other means. Thus redox systems may induce or only maintain passivity depending on their electrode potential and the kinetics of their reduction. In consequence, it depends on the characteristics of metal disso-... 

Non-Reversible Processes. —Reactions of the non-reversible type, i.e., with systems which do not give reversible equilibrium potentials, occur most frequently with un-ionized organic compounds the cathodic reduction of nitrobenzene to aniline and the anodic oxidation of alcohol to acetic acid are instances of this type of process. A number of inorganic reactions, such as the electrolytic reduction of nitric acid and nitrates to hydroxylamine and ammonia, and the anodic oxidation of chromic ions to chromate, are also probably irreversible in character. Although the problems of electrolytic oxidation and reduction have been the subject of much experimental investigation, the exact mechanisms of the reactions involved are still in dispute. For example, the electrolytic reduction of the compound RO to R may be represented by... 

Another aspect of the advantage of bringing the depolarizer to the cathode is seen by comparing the results in Table LXXXV for smooth and spongy copper electrodes. The much larger effective area of the latter permits more intimate contact of the nitric acid with the cathode. It may be noted in this connection that in his extensive work on the electrolytic reduction of organic compounds, Tafel (1900) frequently used a prepared lead electrode, which had been roughened by electrolytic oxidation of the surface to lead dioxide followed by reduction to finely-divided lead by cathodic treatment. 

The 2.54-cm diameter Electropulse Column shown in Figure 1, after completion of uranium runs, was installed at Battelle Memorial Institute (Columbus, Ohio) for uranium-plutonium partition tests. Six electrolytic runs were made under conditions corresponding to partitioning in the first process cycle to determine the effect of uranium reduction efficiency R(u) on t le separation process. The organic feed contained 80 to 83 grams/L of uranium and 0.71 to 0.82 grams/L of plutonium. The nitric acid concentration in the aqueous feed was 2.5 to 2.8 M and in the organic feed 0.2 to 0.3 M. 

Figure 8. Electrolytic Pu (IV) reduction as a function of nitric acid concentration at low Pu (IV) concentration STi...

Experiments on the electrolytic reduction of U and Pu in the aqueous phase in presence of hydrazine were carried out to investigate the effect of various factors influencing the rate of reduction. The potentials of the aqueous solution, which can serve to indicate the course of the reduction process, were measured and operating parameters such as acid concentration, hydrazine concentration, applied potential on the cathode, etc., were investigated. Experimental results indicated that, on Ti-cathode nitric acid could be reduced to nitrous even when there is no HN02 in the initial HNO3 solution and, with a u/Pu ratio ranging from 10 2 to 102, Pu(IV) can be reduced readily when the U/Pu ratio is near or more than 1 at low concentration of Pu. In this case, obviously TT(IV) formed in the process plays an important role in the reduction of Pu(IV). 

The largest group of elements comprises those isolated from solution in the elemental form as a result of reduction, usually electrochemical. In acid solution, the electrolytic deposition of metal on a solid cathode is limited to noble and semi-noble metals. Trace analysis of copper and its compounds may serve as an example [100]. An anodic dissolution technique may be applied for the isolation of macroscopic amounts of copper. A sample in the form of a bar, plate, or wire is the anode in the electrolytic system. When current is passed through the electrolyte (nitric acid + persulphate), Cu is deposited on the graphite cathode, while most trace elements accumulate in the solution. In the trace analysis of platinum, the matrix has been also separated on a cathode [101]. 

Glyoxylic acid is a raw material for various chemicals. It is generally produced by enzymatic or nitric acid oxidation of glyoxal, or electrolytic reduction of oxalic acid. It is also known that alkyl esters of glyoxylic acid are obtained by a vapor-phase oxidation of corresponding alkyl esters of glycolic acid [1]. The yield of ester reached 69 mol% at the conversion of 94%. 

---