JPS59100275A - Method for suppressing generation of gaseous nox in pickling of metal - Google Patents

Abstract

PURPOSE:To suppress generation of gaseous NOx and to prevent smut from remaining on the surface of a metal by adding sulfamic acid or its salt to an acid soln. of nitric acid so that the nitrous acid concn. in said acid soln. attains an adequate value in pickling said metal. CONSTITUTION:A metal is pickled with nitric acid by using an acid soln. of nitric acid added with sulfamic acid or its salt such as sodium salt at the amt. at which the nitrous acid concn. in said soln. does not exceed 0.3wt% and at the stoichiometric reaction amt. with the content of the nitrous acid in said acid soln. or below. Then the generation of gaseous NOx in pickling is suppressed; moreover, the remaining of smut on the surface of the pickled steel material, etc. is prevented and the generation of bumping gas is prevented as well. The above-mentioned method is advantageous in terms of economy as it does not require any additional treatment in the case of discarding the used pickling soln.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an improved method for suppressing nitrogen oxide gas generation during nitric and acid cleaning of metals.

Conventionally, austenite, ferrite, martensite, and other various steel materials have been cleaned with a liquid containing nitric acid, such as dilute nitric acid or a mixed injection of dilute nitric acid and hydrofluoric acid. From these nitric and acid washes.

When cleaning steel materials, multi-purpose nitrogen oxide gas (NO
NOx gas (denoted as x gas) is generated and interferes with work.
Although there are many proposals for adding various additives to the pickling solution in order to suppress gas generation, practical problems still remain unsolved. For example, JP-A-53-102232 discloses an excellent method for suppressing the generation of NOx gas during metal pickling by adding sulfamic acid to the nitric acid pickling solution for metals. However, with this method, a dark stain-like deposit called smut remains on the surface of the pickled steel, and when the used pickling solution is disposed of, this waste solution contains a large amount of ferrous iron. Because the compounds are dissolved, the neutralized waste solution cannot be disposed of as is, but it must be disposed of after the dissolved iron compounds are precipitated and removed through an oxidation process called carrier aeration. be. In addition, when the sulfamic acid in the pickling solution is consumed and disappears, bumping gas may occur due to the heat generated when ferrous compounds change to ferric compounds. To continuously clean steel materials,
Concentrated nitric acid must be replenished from time to time.

At that time, gas bumping often occurs.

It may also interfere with on-site pickling work.

Furthermore, it is well known that the generation of NOx gas can be suppressed by adding hydrogen peroxide to the nitric acid washing solution instead of sulfamic acid, for example, as described in Japanese Patent Publication No. 37653/1983. However, the effect of suppressing NOX gas generation is not sufficient and it is difficult to implement.

The inventors of the present invention have long conducted various studies on nitric and acid washing solutions containing sulfamic acid, and have found that by using them in combination with hydrogen peroxide, the formation of ferrous compounds has been eliminated, and the problem of the generation of bumping gases has already been solved. Applications were filed as Japanese Patent Application No. 55-157860 and Japanese Patent Application No. 55-182939, but as a result of further research, we found that the problems related to the generation of bumping gas, waste liquid, and smut were solved by adding sulfamic acid or its salt to the nitric acid washing solution. When adding, eliminate the formation of ferrous compounds by allowing nitrite ions to exist so that the nitrite concentration in the nitric acid washing solution does not exceed 0.3% by weight even without hydrogen peroxide. We have found that the above-mentioned problems can be solved at once.

An object of the present invention is to provide a method for cleaning metal with nitric acid which is extremely effective in suppressing the generation of NOx gas, and furthermore, does not generate bumping gas and does not leave smut on the surface of the pickled metal. Another object of the present invention is to provide a method for cleaning metal with nitric acid, which does not require any additional processing steps when disposing of a used pickling solution.

That is, in the method for washing metal with nitric acid and acid of the present invention, when washing metal with nitric acid, the amount of nitrite and the chemical amount of external beneficial insects are adjusted so that the concentration of nitrite in the nitric acid solution does not exceed 0.3% by weight. This is a method for suppressing NOx gas generation during nitric and acid cleaning of metals, which is characterized by adding sulfamic acid or its salt in an amount below the theoretical reaction amount.

The nitric and pickling solution for metals is usually an aqueous solution containing 3 to 30% by weight of nitric acid, and a preferred pickling method is to use a solution at 20 to 80°C in which various acids such as hydrofluoric acid are added to this. It will be done. As the sulfamic acid or its salt used in the present invention, ordinary commercially available industrial products are sufficient. The sulfamate salt may be any water-soluble salt such as sodium salt or ammonium salt.

A method of adding sulfamic acid or its salt to the nitric acid washing solution in an amount less than the stoichiometric reaction amount with the amount of nitrite in the solution so that the nitrite concentration in the solution does not exceed 0.3% by weight. There is no need to add it to the nitric and acid washing solution before steel treatment.
During use, sample the nitric and acid washing solution, volumetrically analyze the nitrite concentration in the solution using, for example, a sulfamic acid aqueous solution of known concentration, measure the nitrite concentration, and add the required amount of sulfamic acid or its salt. Just do it. It is also possible to continuously measure the nitrite concentration and continuously add it in conjunction with the measurement. Nitrous acid is 0.3% by weight in the nitric acid washing solution.
If more than 100% of the amount of nitrogen is present, the amount of NOx generated increases, which is not preferable.

(See Comparative Example 5) Also, adding an excessive amount of sulfamic acid or its salt to the extent that the nitrous acid concentration becomes 0% by weight for a long period of time may cause the above-mentioned bulge-like gas generation or the treatment of ferrous iron. Problems arise and are not desirable.

As long as the object of the present invention is achieved, the above-mentioned required amount of sulfamic acid or its salt may also contain arbitrary components such as a surfactant.

When cleaning steel materials by the nitric and acid cleaning method for metals of the present invention, not only the nitric acid in the solution but also the added sulfamic acid or its salt are consumed.

If necessary, especially when pickling steel materials continuously, it is necessary to replenish the pickling solution with sulfamic acid or its salt. Of course, it is necessary to replenish nitric acid, but it is advantageous to be able to replenish it as concentrated nitric acid. The method for pickling metals with nitric acid according to the present invention is mainly used for cleaning steel materials, but it can also be used for pickling other metals.

The method for pickling metal with nitric acid of the present invention suppresses the generation of NOx gas when pickling steel materials, prevents smut from remaining on the surface of the pickled steel materials, and removes the used pickling solution. It is extremely practical as it does not require any additional processing steps when it is disposed of. Moreover, it can be carried out extremely efficiently and easily.

This will be explained below with reference to Examples and Comparative Examples.

The technical scope of the present invention is not limited thereto.

Incidentally, % described below indicates weight %.

Comparative Example 1 15% nitric acid and 3% hydrofluoric acid were placed in a 300ml styrene container.
5%, sodium nitrite 0.60% [nitrite equivalent 0.41%
(0.0174 mol)] using 200 g of acid solution containing
SUS410 thin steel with pickling liquid scale (dimensions 30 x 50
x 3mm) into the above acid solution at an appropriate temperature of 30°C,
After a few minutes, the concentration of NOx gas on the liquid surface was measured using a detection tube and found to be 400 ppm.

Example 1 The same bath as in Comparative Example 1 was made, and 0.45 g of sulfamic acid (
0.0046 mol) to bring the nitrite concentration to 0.30%.
The NOx gas concentration was measured in the same manner as Comparative Example 1, except that the NOx gas concentration was reduced to 250 ppm.

Example 2 In Example 1, the amount of sulfamic acid added was 1.15g.
(0.0149 mol), and the nitrite concentration was changed to 0.06 mol.
The same procedure as in Example 1 was carried out except that the concentration was reduced to %. NO
When the x gas concentration was measured, it was suppressed to 40 ppnn.

Comparative example 2 15% nitric acid in a 300ml styrene container.

Hydrofluoric acid 3.5% Sodium nitrate 0.51% [Nitrous acid conversion 0.
35% (0.0149 mol)] was used to prepare a scaled SUS410 steel plate (dimensions 30×
One sheet (50 x 3 mm) was placed in the above acid solution at a liquid temperature of 50°C, and 2 minutes later, the NOx gas concentration on the liquid surface was measured with a detection tube and found to be 400 ppm.

Example 3 The same solution as Comparative Example 2 was prepared, and 1 g of sulfamic acid (0.0
When the concentration of NOx gas was measured in the same manner as in Comparative Row 2, except that 103 mol) was added to lower the nitrous acid concentration to 0.11%, it was suppressed to 110 ppm.

Comparative Example 3 20% nitric acid, 3.0% hydrofluoric acid, 1.42% ferric ion, 0.38% nitrite (0.323
S with scale before pickling using 4 kg of acid solution containing
A bundle of 5 US304Kg steel pieces (outer diameter 14 mm, inner diameter 9 mm, length 450 mm) was put into the above pickling solution at a temperature of 40°C, and after 5 minutes, the NOx gas concentration on the liquid surface was measured using a detection tube. As a result, it was found to be 35 ppm.

Example 4 The same bath as Comparative Example 5 was made, except that 40 g (0.175 mol) of ammonium sulfamate in a 50% aqueous solution was added to adjust the nitrous acid concentration to 0.17% (0.145 mol).
When NOx gas concentration was measured in the same manner as Comparative Example 3, 13
It decreased to 5 ppm.

Example 5 17.25 tons of nitric-fluoric acid solution (nitric acid 9.0%, hydrofluoric acid 4.6%)
%, ferric ion 3.9%, nitrous acid 0.21%), 2 tons of SUS-304 steel pipe is immersed in the above acid solution at a liquid temperature of 47°C, and after 5 minutes, a detection tube detects NOx on the liquid surface. The gas concentration was measured and found to be 150 ppm. Next, 50 kg of sulfamic acid was added to bring the nitrite concentration to 0.07%, and when the NOx concentration was measured 5 minutes after the addition of sulfamic acid, it was suppressed to 25 ppm.

Comparative Example 4 20% nitric acid and 3.0% hydrofluoric acid were placed in a 9 liter PVC bathtub. Ferric ion 0.5%. Nitrous acid 0.47% (0.4 mol)
SUS304 with scale before pickling using 4 kg of acid solution containing
Steel pipe (outer diameter 14mm, inner diameter 9mm, length 450mm) 5
A bundle of books was placed in the above pickling solution at a temperature of 40° C., and after 5 minutes, the concentration of NOx gas on the liquid surface was measured with a detection tube and found to be 370 ppm.

Comparative Example 5 The same bath as in Comparative Example 4 was made, and 10 g of sulfamic acid (0.
NOx gas was measured in the same manner as in Comparative Example 4, except that 103 mol) was added to make the nitrous acid concentration 0.35% (0.3 mol), and it was 350 ppm, indicating that the suppression of NOx gas was insufficient.

Patent applicant: Nissan Chemical Industries, Ltd.

Claims (1)

[Claims] When cleaning metal with nitric acid, the nitrous acid concentration in the nitric acid solution is 0.
．． Suppression of nitrogen oxide gas generation in a metal pickling solution characterized by adding sulfamic acid or its salt in an amount below the stoichiometric reaction amount to the amount of nitrous acid in the solution so as not to exceed 3% by weight. Law.