JPS5841462B2 - Method for measuring acid concentration in mixed pickling solution of hydrofluoric acid and strong acid - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for measuring the acid concentration of a mixed acid (hereinafter simply referred to as mixed acid) of hydrofluoric acid and a strong acid such as nitric acid, sulfuric acid, or hydrochloric acid used for pickling metal materials. It is.

The mixed acid used for pickling metal materials contains hydrogen ions, fluorine ions, strong acid anions, hydrofluoric acid molecules, strong acid molecules,
There are metal ions, various complex ions made of metal ions and fluorine ions, and compounds of metals and fluorine.

For example, when pickling steel materials with a mixed acid of hydrofluoric acid and nitric acid, ions or molecules generated by the following reaction are present in the pickling solution.

HNO-+H+HNO3-・・・・・・・・・・・・・・・
・・・・・・・・・・・・(1) HF:H"+F-・
・・・・・・・・・・・・・・・・・・・・・・・・(2)
HF 10F −:HF−・・・・・・・・・・・・・・・
・・・・・・・・・(3)2Fe+6H+″2Fe3
+2H2↑・・・・・・・・・・・・(4)Fe3”+
HF: FeF"10H" -+-・-+-+++(5
)FeF2" 10HF: FeF2" 10H+...=(6
)FeF2+HF=FeF3↓+H4−・・・・−・−
・---(7) Among these ions and molecules, fluorine ions (F-) and nitrate ions (NO3-) are effective for pickling.
) and hydrogen ions (H+) in equilibrium with these.

As long as the mixed acid is new and there are no metal ions, (1)
.

(2), (3) As the pickling process progresses, iron ions dissolve in the mixed acid (4), (5)
, (6), (7) reaction progresses, complex ion (F
eF2'', FeF, i) Further produces iron fluoride (FeF3).

In order to measure the acid concentration of such pickling solutions, titration method is generally used, but due to the influence of metal ions,
In the case of conductivity titration, the point of inflection of conductivity change is unclear, and in the case of indicator titration, the point of color change is unclear, causing problems in concentration measurement.

As a method for directly and easily measuring fluorine ions (F-) and hydrogen ions (H+), a method using an ion-selective electrode has been proposed (Japanese Patent Application Laid-open No. 83492-1983). Even in the method using
It is not possible to obtain the true acid concentration because it also measures

Furthermore, since the hydrogen ion concentration in the target pickling solution is usually high, the dissociation of hydrofluoric acid is close to zero, and the fluorine ion concentration is very small compared to the hydrofluoric acid concentration.

Therefore, measurement is difficult with an ion-selective electrode that only selects fluorine ions.

Furthermore, if the mixed acid is diluted or neutralized to dissociate hydrofluoric acid for this purpose, the balance of equations (4) to (7) will be disrupted, making measurement difficult.

An object of the present invention is to provide a method for reliably and accurately measuring only fluorine ions and strong acid anions effective for pickling in a mixed acid pickling solution.

The method of the present invention involves dialyzing and recovering fluorine ions and strong acid anions in a mixed acid pickling solution using an anion exchange membrane.
Furthermore, after diluting with a salt solution generated by neutralizing a weak acid and a strong base, the ion concentrations of each of the fluorine ions and strong acid anions were measured using ion-selective electrodes.
The method is characterized in that the acid concentration of the mixed acid is determined based on this value.

The present invention will be explained in detail below with reference to the drawings.

In FIG. 1, reference numeral 1 denotes a recovery tank that recovers a mixed acid containing metal ions as a new mixed acid (hereinafter referred to as recovered acid) that does not contain metal ions.

The recovery tank is partitioned by an anion exchange membrane 2.

Put the mixed acid used for pickling on the left side, and water on the right side.

The capacity of this recovery tank is made sufficiently larger on the left side than on the right side.

By doing this, the fluorine ion (F-
) and strong acid anions undergo diffusion dialysis through the anion exchange membrane 2 and migrate into the water on the right.

At this time, hydrogen ions (H''), which are positive ions, also migrate because their ionic radius is small.

Equilibrium is reached when the concentrations of fluorine ions, strong acid anions, and hydrogen ions become equal on the left and right sides of the anion exchange membrane 2.

The concentration at this time is characterized by the volume on the left side and the volume on the right side of A1.

Also, the ratio f of the concentration on the right side increasing with time (1)
(t) can be found by

Substituting equation (8) into equation (9) yields.

Therefore, without disturbing the balance of complex ions in the mixed acid being used, it is possible to obtain recovered acid free of metal ions and having an acid concentration that has the relationship shown in equation (10) with the concentration of the mixed acid on the right side of the recovery tank. can.

Note that if it takes time to perform diffusion dialysis of ions in the anion exchange membrane, the time can be shortened by applying ultrasonic vibration.

The recovered acid obtained in the above manner is also a mixed acid of hydrofluoric acid and a strong acid, so the amount of hydrogen ions is large compared to the amount of fluorine ions, and the hydrofluoric acid is hardly dissociated, so fluorine ions cannot be selected as is. Measuring the concentration of hydrofluoric acid using a polar electrode is difficult.

For this purpose, as shown in FIG. 1, the recovered acid is introduced into a mixing tank 3 and diluted with a diluent contained in a dilute solution tank 4.

The diluent must neutralize hydrogen ions in the recovered acid and dissociate hydrofluoric acid, and must also act as an ionic strength buffer.

In order to neutralize hydrogen ions, it is necessary to use an aqueous solution of a salt that becomes slightly alkaline through hydrolysis, that is, a salt obtained by neutralizing a weak acid with a strong base.

In addition, since it can be used as an ionic strength buffer, it needs to be a salt with a high charge when ionized.

A case where thorium citrate is used as an example of such a diluent will be described.

Hydrofluoric acid dissociates almost completely when the hydrogen ion concentration reaches 10-5 mol/l or more, so the recovered acid is diluted with citric acid.
- The dilution rate and the concentration of the sodium citrate solution are determined so that the hydrogen ion concentration becomes 10-5 mol/l or less when diluted with the sodium citrate solution.

For example, if the maximum concentration of nitric acid is 1 mol/l, the maximum concentration of hydrofluoric acid is 1 mol/l.
1 mol/l of recovered acid! When the concentration of the recovered acid is diluted to 1/10 with a sodium citrate solution, the hydrogen ion concentration becomes less than 10-5 mol/l.

The recovered acid is diluted in the mixing tank 3 of FIG. Detect.

The concentration of each ion is measured by the electromotive force of the electrode using the respective voltmeters 8 and 9, and the mixed acid concentration can be determined from this value.

Further, the mixing tank 3 may also serve as the detection tank 4.

By doing this, the concentration of the mixed acid containing metal ions can be measured without being affected by metal ions and using an ion-selective electrode, making it easy to automate and accurately measure nitric acid in a relatively short time. and the concentration of hydrofluoric acid can be measured.

Next, an example in which the measurement of mixed acid concentration was automated using the method of the present invention will be described with reference to FIG.

When it becomes necessary to measure the concentration, water is supplied from a water source (not shown) to the water showers 19, 20.21 for a certain period of time to clean the insides of the liquid tanks 4, 5.6 and the conduits connecting them.

At this time, the solenoid valve 23°26.27 is kept open, and the wash water is discharged through the solenoid valve 23°2T.

After the wash water is completely drained, pump 16 is driven once to open solenoid valve 24 and close solenoid valves 23, 26, and 27, and a standard solution of known concentration is transferred from standard solution tank 14 to liquid tank 4. At the same time, a water shower 20 is applied to the liquid tank 5.
A certain amount of water is supplied from the tank and maintained in this state for a certain period of time.

Then, since the liquid tanks 4 and 5 are separated by the anion exchange membrane 28, the acid concentration in the liquid tank 5 increases.

After a certain period of time has elapsed, the solenoid valve 26 is opened and the liquid tank 5 is opened.
Transfer the liquid to the liquid tank 6, drive the pump 17, open the solenoid valve 25, supply a certain amount of diluent from the diluent tank 13, dilute it, and stir it with the Stark-22 while connecting the fluorine ion selective electrode T. Each concentration is detected by an ion-selective electrode 8 (e.g., a nitrate ion-selective electrode) that is selective for strong acid anions in the test solution, and a comparison electrode 9 that generates a voltage that serves as a reference voltage for these two electrode potentials. Voltmeter 10
The electromotive force is measured and stored in the calculation unit 11.

When this measurement is completed, the electromagnetic valve 27 is opened and the liquid in the liquid tank 6 is discharged.

Now that the concentration of the standard solution has been measured, the concentration of the test solution is then measured.

First, water is supplied to the water showers 18, 19, 20, 21 for a certain period of time, and the liquid tank 1, filter 2, temperature regulator 3, liquid tank 4,
Clean 5, 6 and the conduit connecting them.

At this time, the pump 15 is driven and the solenoid valves 23, 2
6.27 is left open and the wash water is discharged through the solenoid valve 23.27.

After the cleaning continues for a certain period of time and the cleaning water is completely drained, the solenoid valves 23, 26, and 27 are closed, and the sample liquid is sampled with a sampling device (not shown) and put into the liquid tank 1 and then filtered into the filter 2.
, a constant amount is supplied to the liquid tank 4 through the temperature regulator 3.

At the same time, a certain amount of water is supplied from the water shower 20 to the liquid tank 5.

After that, the concentration is detected by the same method as the concentration measurement of the standard solution described above, and this result is input to the calculation section 11.

The calculation unit 11 calculates the voltage when the standard solution is measured as VS, and the voltage when the test solution is measured as Vi.

This calculation result is displayed on the display section 12, and all measurements are completed.

The coefficient can be determined by experiment using a mixed acid with a known concentration, or by preparing two standard solutions with different concentrations and measuring the concentration of one standard solution with O8t. Let the electromotive force of the ion-selective electrode be ■s1,
The concentration of the other standard solution may be determined by calculating the electromotive force of the ion-selective electrode at the time when the concentration of this standard solution is measured as vs2.

By controlling the above flow using a relay sequence, a sequencer, a microcomputer, etc., the mixed acid concentration can be automatically measured.

As described above, according to the method of the present invention, when pickling metal materials using a mixed acid of hydrofluoric acid and a strong acid such as nitric acid, sulfuric acid, or hydrochloric acid, the acid concentration can be accurately measured at any time, and the concentration of the mixed acid can be precisely controlled. can be done.

[Brief explanation of drawings]

FIG. 1 is a principle diagram for carrying out the method of the present invention, and FIG. 2 is a system diagram of an apparatus showing an embodiment of the method of the present invention.

Claims (1)

[Claims] 1. Fluoride ions and strong acid anions in the pickling solution are dialyzed and recovered using an anion exchange membrane, diluted with a salt solution generated by neutralizing a weak acid and a strong base, and then collected using an ion-selective electrode. A method for measuring the acid concentration of a mixed pickling solution of hydrofluoric acid and strong acid, characterized by measuring the concentration of each ion.