Concentrated nitric acid

The values are precisely defined only for a given nitric acid concentration, as the dependence of rate on nitric acid concentration varies from one compound to another... 

Licensor Weak acid Direct strong nitric (DSN) Nitric acid concentration (NAC)... 

Commercially, nitric acid concentrations are graded in terms of degrees Baumn as follows ... 

The distribution of highly extractable solutes such as and Pu between the aqueous and organic phases is strongly dependent upon the nitrate anion concentration in the aqueous phase. This salting effect permits extraction or reextraction (stripping) of the solute by controlling the nitric acid concentration in the aqueous phase. The distribution coefficient, D, of the solute is expressed as... 

A mathematical model of the operating characteristics of a modem HLW storage tank has been developed (60). This model correlates experimental data for the rate of radiolytic destmction of nitric acid, the rate of hydrogen generation owing to radiolysis of water, and cooling coil heat transfer. These are all functions of nitric acid concentration and air-lift circulator operation. 

Silver sulfide is one of the most insoluble salts known. It is not solubilized by nonoxidizing mineral acids, but it is soluble in concentrated nitric acid, concentrated sulfuric acid, and alkaline cyanide solutions. 

Zirconium resists attack by nitric acid at concentrations up to 70 wt % and up to 250°C. Above concentrations of 70 wt %, zirconium is susceptible to stress-corrosion cracking in welds and points of high sustained tensile stress (29). Otherwise, zirconium is resistant to nitric acid concentrations of 70—98 wt % up to the boiling point. 

Aluminum is resistant to nitric acid at concentrations above 80%. At 50% nitric acid concentration at room temperature, corrosion rates are as high as 0.08 in. (0.20 cm) per year. 

Hydrogen peroxide solutions (27.5-91% by weight) Nitric acid (concentrations >70%)... 

Metal chlorates Lead dioxide Metallic permanganates Metallic dichromates Nitric acid (concentrated)... 

Table 3.24 Maximum nitric acid concentration that can be tolerated by austenitic stainless steels...

Temperature (°C) Stabilising element Nitric acid concentration (%)... 

Nitric acid, concentrated. Analytical reagent grade. 

A kinetic study of nitration by nitric acid in carbon tetrachloride has been briefly reported and is of interest because of the third-order dependence of rate upon nitric acid concentration, for nitration of N-methyl-N-nitrosoaniline. This is believed to arise from equilibria (28) and (29) below, which give rise to a nitrosating species and nitration is achieved through subsequent oxidation of the nitrosated aromatic69. 

Since nitration produces acetic acid, the concentration of this as well as of acetyl nitrate can be shown to depend upon the nitric acid concentration giving kinetics third-order in nitric acid (3.16 actually observed). It follows that in the presence of acetic acid the order in nitric acid should fall to 2 (2.31 observed). Likewise, in the presence of added sulphuric acid, from equilibrium (31) it follows that the order in nitric acid should fall, the observed order in this being 1.4 and 1.7 in added sulphuric acid. The retardation by added nitrate was attributed to competition by this ion for protonated acetyl nitrate, viz. 

For a given concentration of nitrous acid, the first-order rate coefficients increase as the sixth to seventh power of the nitric acid concentration and this catalysed nitration is presumed to be nitrosation followed by oxidation, reactions (41) and (42), viz. 

For 4-nitrophenol (studied in the range 1.4-10 M nitric acid) the first-order rate coefficients (at constant nitrous acid concentration) decrease approximately 50 % as the nitric acid concentration is increased from 2 M to 5 M but increase considerably as it is further increased to 10 M the increase is greater the lower the fixed concentration of nitrous acid and is attributed to the catalysed reaction. The rate decrease was attributed to superimposition upon the normal catalysis noted above for 4-chloroanisole of the effect of lowering of the concentration of the highly reactive phenoxide ion as the acidity was increased. In 10 M nitric acid the anti-catalysed reaction was again observed. 

A decrease in the nitric acid concentration caused R to decrease as it did during a particular run (in which the acid concentration would decrease with time). Thus nitrodesilylation would seem to be of higher order than nitrodeprotonation. 

Hydrogen peroxide solutions (27.5—91% by weight) Nitric acid (concentrations > 70%) Potassiumbromide/chlorate/permanganate/peroxide Sodium chlorate/permanganate/peroxide/chlorite (>40 X. by weight)... 

In the course of the experiment it was felt that the nitric acid concentration was not sufficient and it was decided to interrupt the reaction. When it was noticed that tars formed, the medium was decanted into another container and more concentrated nitric acid poured on to the tar left at the bottom of the reactor. The medium detonated immediately. 

It can be seen from Figure 5.18 that the KD values for zirconium are higher than those for hafnium at all nitric acid concentrations. This is because the dissolution of zirconium nitrate (Zr(N03)4) into zirconyl (Zr02+) and nitrate (NOj) ions takes place to a lower extent as compared to the corresponding dissolution of hafnium nitrate in an aqueous medium. Hence, separation is feasible. However, at higher nitric acid concentrations the separation factor is reduced significantly because the dissociation of hafnium nitrate (Hf(NOs)4) decreases sharply with increasing nitric acid concentration, with the result that the separation factor, p, falls off rapidly. Hence, the separation process calls for the adjustment of the nitric acid concentration to a suitably low value. 

In a titration, it was found that 28.5 cm3 of dilute nitric acid (concentration 0.100 mol dm-3) were exactly neutralised by 25.0 cm3 of potassium hydroxide solution. 

Nitric acid processes. See also Nitric acid concentration (NAC) processes alternative, 17 186... 

---