JP3017017B2 - Steel plate acid cleaning solution analysis method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for analyzing a pickling solution of a steel sheet.

[0002]

2. Description of the Related Art In recent years, as a highly accurate and versatile titration method,
Potentiometric titration has been increasingly used.

[0003] This potentiometric titration is a method of performing titration utilizing the difference in the dissociation state in a solvent, but it has been difficult to separate a substance having no difference in the dissociation state. Usually, water is used as a solvent in the standard solution for titration.

For the neutralization titration, there is almost no problem even if an aqueous solution is used. Since the potentiometric titration is a method for performing titration utilizing the difference in the dissociation state in a solvent, it has been difficult to separate a substance having no difference in the dissociation state in an aqueous solvent.

[0005] Further, if a corrosion product or a substance insoluble in the solution is mixed in the solution, it may interfere with the analysis, so that accurate and rapid analysis may not be possible.

[0006]

In order to analyze a substance having no difference in the dissociation state in a water solvent with high reproducibility and high accuracy, it is necessary to use Takazari et al. In Iron and Steel, 70th and 11th. As disclosed in, a substance that is difficult to analyze in potentiometric titration is subjected to diffusion dialysis using an ion exchange membrane in advance, and then a target substance is selectively analyzed using each ion electrode using an ion selective electrode. .

However, in order to analyze many substances at one time, an ion electrode having selectivity for the substances is required.

In addition, it is necessary to remove in advance a substance that interferes with the ion-selective electrode using an ion-exchange membrane or the like. The present invention provides a solution analysis method for solving the above-mentioned problem.

[0009]

The present invention uses a filter for removing a foreign substance from a solution containing hydrofluoric acid and nitric acid. As a titration solution, a solution obtained by dissolving a substance having a base in a solvent as an organic solvent is used. The method is characterized in that it is analyzed by potentiometric titration.

The titration solution in the present invention is 5 mol / mol.
A basic aqueous solution of not less than 14 liters and not more than 14 mol / l is dispersed in an organic solvent,
The method is characterized by using a solution having a concentration of 2.00 mol / liter or less.

The method according to the present invention is characterized in that at least one of methyl alcohol (methanol), ethyl alcohol (ethanol) and acetone is used as an organic solvent for titration in the present invention.

The method according to the present invention is characterized in that the sample solution is mixed with an organic solvent and one or more of methyl alcohol (methanol), ethyl alcohol (ethanol) and acetone are used as the solvent.

Further, the present invention is a method characterized in that sodium hydroxide or potassium hydroxide is used as the substance having a base in the present invention.

[0014]

The operation of the present invention will be described below in detail.

In the present invention, a substance having a base is dispersed in an organic solvent as a standard solution for titration.

The use of an organic solvent as the solvent is a major difference from the conventional standard solution for titration.

The reason why the solvent for the titration solution is defined as an organic solvent is that solvents such as methyl alcohol (methanol), ethyl alcohol (ethanol), and acetone have a lower dielectric constant than water. They are 32.63, 24.3 and 20.7, respectively. Water is 25 ℃
Is 78.5.

For this reason, when the same acidic substance is dissociated in a solvent, it is understood that water having a high activity of the solvent is easily dissociated.

On the other hand, dissociation hardly occurs in a solvent having a low relative dielectric constant, and even a substance that is close to a dissociated state in water can be separated in a solvent having a low relative dielectric constant.
Table 1 shows an example.

Hydrofluoric acid has a pKa of 3.2 in an aqueous solvent, acetic acid has a pKa of 4.8, and the difference is only about 1.6, whereas hydrofluoric acid has a pKa of 7.2 in an ethanol solvent. Acetic acid becomes 10.2 and spreads to about 3.0.

Similarly, it is easily presumed that methanol and acetone also have a lower relative dielectric constant than water, so that the activity of the solvent becomes lower and dissociation hardly occurs.
Conventionally, substances that could not be separated in an aqueous solvent can be separated by using this standard solution for titration.

As the organic solvent, butyl alcohol, amyl alcohol or the like may be used.

In the present invention, an aqueous solution is defined as a solute in a substance which is hardly dissolved in an organic solvent. When a standard solution for titration is prepared, the substance is not directly dissolved in the organic solvent but dissolved in an aqueous solution. This is for dispersing in an organic solvent.

The lower limit of the aqueous solution in which the solute is dissolved is defined as 5 mol / L. This is because, in the case of dispersing at a concentration of mol / liter or less, the influence of the concentration of the aqueous solvent is larger than that of the organic solvent, and accurate analysis cannot be performed.

Also, the upper limit of 14 mol / l is defined as that when the concentration is 14 mol / l or more, it becomes close to the saturated dissolution amount of the solute, so that it is difficult to dissolve the solute. This is because they cannot be mixed.

The reason why sodium hydroxide and potassium hydroxide are specified as basic substances is that they can be dissolved in a large amount in water, so that the concentration of an aqueous solution can be easily, quickly and accurately determined.
This is because they can be mixed.

Further, since these substances are stable even in an aqueous solution, they are resistant to aging. In addition, calcium hydroxide and tetramethylammonium may be used as the basic substance.

In the present invention, the lower limit of the concentration of a solution in which an aqueous solution in which a solute is dissolved is dispersed in an organic solvent is 0.1.
The reason why the molar amount is set to 05 mol / l is that when the amount is 0.05 mol / l or less, a large amount of a standard solution for titration is required for titration, which is industrially uneconomical.

Another reason is that the dispersion of the standard solution concentration becomes large. The upper limit of 2.00 mol / l is defined as that when the concentration is 2.00 mol / l or more, the concentration of water in the titration standard solution increases, so that there is no difference in the dissociation constant in an aqueous solvent. This is because it becomes difficult to separate substances.

Further, the point that a filter for removing foreign matter is provided is also greatly different from the conventional method.

As the material of the filter, Teflon, polypropylene, vinyl chloride or the like which is excellent in acid resistance and corrosion resistance is desirable.

Further, the size of the filter is set to 0.1.
It is desirable to use one according to the purpose, such as 1, 0.3, and 0.5 microns.

Example 1 shows an example of analyzing a mixed solution of hydrofluoric acid, acetic acid and nitric acid by the method of the present invention.

As shown in Example 1, by using the method of the present invention, acid components which could not be separated conventionally can be analyzed with high accuracy.

[0035]

EXAMPLE As a sample solution, 50 wt% hydrofluoric acid, 70 w
Example 1 using t% nitric acid and 100 wt% acetic acid
Formulations were made to the ratios shown in FIG. After sufficiently stirring the sample solution, 5 cc of the sample solution was sampled using a micropipette, and acetone was added to make the solution 50 cc, and potentiometric titration was performed.

The titration standard solution is prepared by dissolving sodium hydroxide in an aqueous solvent to a concentration of 5 to 14 mol / l, and dispersing this solution in an ethanol solvent to form a 0.05 to 2.00 mol / l ethanol solvent titration solution. Was prepared.

For comparison, the conventional method is 0.1
Potentiometric titration was also performed using a solution of mol / liter sodium hydroxide as a titration solution.

In the conventional method, the set value and the analysis value were the same when no separation was possible or when only nitric acid was used, but hydrofluoric acid and acetic acid could not be separated.

On the other hand, when the method of the present invention is used, nitric acid,
Hydrofluoric acid and acetic acid are separated and agree well with the set values.

[0040]

[Table 1]

[0041]

[Table 2]

[0042]

[Table 3]

[0043]

[Table 4]

[0044]

[Table 5]

[0045]

[Table 6]

[0046]

[Table 7]

[0047]

According to the present invention, a method for titrating a substance in an aqueous solution, which has been conventionally difficult to analyze, by using an organic solvent as a solvent is made possible, and a method can be performed accurately, quickly, and simply. Things.

Continuation of the front page (56) References JP-A-7-209236 (JP, A) JP-A-6-66783 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) G01N 27 / 26 G01N 31/16 G01N 1/00 102

Claims (6)

(57) [Claims] 1. A filter for removing foreign substances from a solution containing at least one of hydrofluoric acid, nitric acid, acetic acid, sulfuric acid, and hydrochloric acid, and a solution having a base as a solvent in an organic solvent as a titration solution. A method characterized in that analysis is performed by potentiometric titration using a dissolved solution. 2. The titration solution according to claim 1, wherein a basic aqueous solution of 5 mol / L or more and 14 mol / L or less is dispersed in an organic solvent, and 0.05 mol / L or more and 2.00 mol / L. A method comprising using a solution described below. 3. A method comprising using one or more of methyl alcohol (methanol), ethyl alcohol (ethanol) and acetone as an organic solvent of the titration solution according to claim 1 or 2. 4. A method according to claim 1, wherein the sample solution is mixed with an organic solvent. 5. A method comprising using at least one of methyl alcohol (methanol), ethyl alcohol (ethanol), and acetone as the organic solvent according to claim 4. 6. A method comprising using sodium hydroxide or potassium hydroxide as the substance having a base according to any one of claims 1 to 5 .