JPS6235059B2 - - Google Patents

Description

Detailed Description of the Invention The present invention relates to 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, acid concentration of the pickling solution, and iron ion. The present invention relates to a method for measuring concentration and total fluorine ion concentration.

The mixed acid used for pickling metal materials contains hydrogen ions, fluorine ions, strong acid anions, hydrofluoric acid molecules,
In addition to strong acid molecules, there are metal ions, various complex ions made of metal ions and fluorine ions, and compounds of metal and fluorine. For example, when pickling steel materials with a mixed acid of hydrofluoric acid and nitric acid, ions or molecules produced by the following reaction are present in the pickling solution.

HNO ₃ →H ⁺ +NO ⁻ ₃ ……(1) HF〓H ⁺ ＋F ^- ……(2) HF＋F ^- 〓HF ⁻ ₂ ……(3) 2Fe＋6H ⁺ →2Fe ³⁺ ＋2H ₂ ↑ ……(4) Fe ³⁺ +HF〓FeF ²⁺ +H ⁺ …(5) FeF ²⁺ +HF〓FeF ⁺ ₂ +H ⁺ …(6) FeF ⁺ ₂ +HF〓FeF ₃ ↓+H ⁺ …(7) These ions and molecules Among them, fluorine ions (F ^- ), nitrate ions (NO ^- ₃ ), and hydrogen ions (H ⁺ ) that are in equilibrium with these ions are effective for pickling. As the pickling progresses, iron ions are dissolved in the mixed acid, and the reaction of equation (4) progresses, and the reactions of equations (5) and (6), which generate an iron-fluorine complex by the coexisting fluorine ions, proceed.
Finally, iron fluoride is produced and precipitated by the reaction of equation (7). Among the above formulas (1) to (7), the reaction effective for pickling is
(1) and (4), and therefore it is necessary to constantly measure and control the concentrations of hydrofluoric acid and nitric acid during pickling.

On the other hand, if the pickling process is continued while adjusting the acid concentration by replenishing hydrofluoric acid and nitric acid, iron fluoride shown by formula (7) begins to precipitate in the pickling solution. This not only consumes fluorine ions, ie, hydrofluoric acid, in the pickling solution, but also accumulates in the tank, interfering with the pickling process. In order to suppress the production of iron fluoride, it is necessary to control the concentration of the pickling solution so that the total fluoride ions are 60 g/or less and the total iron ions are 30 g/or less, as shown in FIG.

Conventionally, to measure this acid concentration, titration with an alkaline solution such as sodium hydroxide has been performed. However, in this method, due to the influence of coexisting metal ions, the point of curvature of conductivity change is unclear in the case of conductivity titration, and the point of color change is unclear in the case of neutralization titration using an indicator. I can't get accurate values. Furthermore, a method using an ion-selective electrode for measuring hydrofluoric acid and nitric acid by directly measuring fluorine ions and hydrogen ions has been proposed (Japanese Patent Laid-Open No. 49-83492), but the analytical accuracy is not good. Furthermore, no method or apparatus has been found for simultaneously measuring the metal ion concentration and total fluorine ion concentration in the pickling solution.

An object of the present invention is to provide a method for quickly and accurately measuring the concentrations of hydrofluoric acid, strong acid, iron ions, and total fluorine ions in a mixed acid pickling solution containing hydrofluoric acid.

The method of the present invention is as follows: 1. Fluorine ions, strong acid anions, and hydrogen ions in the mixed acid pickling solution are subjected to diffusion dialysis using an anion exchange membrane, and this solution is subjected to diffusion dialysis to neutralize the weak acid and the strong base or the strong acid and the weak base. The resulting salt solution is added and diluted, and the ion concentrations of fluorine ions and strong acid anions are measured using ion-selective electrodes, and based on these values, the acid concentration of the mixed acid is determined.

2 Measure the specific gravity of the mixed acid pickling solution using a hydrometer,
Determine the iron ion concentration from the specific gravity-iron ion concentration correlation curve created in advance, and then determine the fluorine ion combined with the iron ion based on this value.
The method is characterized in that total fluorine ions are measured by calculating the sum with fluorine ions measured separately.

The present invention will be explained in detail below with reference to the drawings.
In Figure 2, 1 is a mixed acid containing metal ions and a new mixed acid containing no metal ions (hereinafter referred to as recovered acid).
This is a collection tank that collects wastewater as waste.

When measuring fluoride ion concentration with a fluoride ion-selective electrode, a sodium citrate solution that serves as an ionic strength buffer and a PH buffer is used, but if a mixed acid containing metal ions is used as a sample.
Since the iron-fluorine complexes shown in formulas (5) and (6) dissociate to liberate fluorine, excess fluorine ions are measured, and true fluorine ions cannot be measured. For this purpose, this recovery tank is used to recover only free fluorine 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 ions (F ^- ) in the mixed acid on the left and the anions of the strong acid 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 cations, also migrate because their ionic radius is small. Fluorine ions on the left and right sides of the anion exchange membrane 2,
Equilibrium is reached when the concentrations of anions and hydrogen ions of the strong acid are equal. The concentration at this time is, assuming that the volume on the left side is V _A and the volume on the right side is V _B , W = V _A / V _A + V _B・C ... (8) W: Concentration relative to equilibrium C: Mixed acid added to the left side It is determined by the concentration of Also, the rate (t) at which the concentration on the right side increases with time (t) is determined by (t)=W(1-E ^- 〓)...(9) t: time T: time constant. Substitute equation (8) into equation (9) (t)=V _A /V _A +V _B・C・(1-E ^- 〓)...
(10) becomes. Therefore, without destroying 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 between the mixed acid and the concentration shown in equation (10) on the right side of the recovery tank. I can do it. 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. Measuring the concentration of hydrofluoric acid is difficult. For this purpose, as shown in FIG. 2, 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. To neutralize hydrogen ions,
It needs to be an aqueous solution of a salt that becomes slightly alkaline upon hydrolysis, that is, a salt obtained by neutralizing a weak acid and a strong base or a strong acid and a weak base. In addition, since it can also be used as an ionic strength buffer, it needs to be a salt with a high charge value when ionized. A case where sodium citrate is used as an example of such a diluent will be described. Hydrofluoric acid has a hydrogen ion concentration of 10 ^-5 mol/
If the concentration is below, it will almost completely dissociate, so determine the dilution rate and the concentration of the sodium citrate solution so that the recovered acid is diluted with a sodium citrate solution and the hydrogen ion concentration becomes 10 ^-5 mol/or less. put. For example, if the recovered acid has a maximum concentration of 1 mol/nitric acid and a maximum concentration of 1 mol/fluoric acid, and the concentration of the recovered acid is diluted to 1/10 with a 1 mol/mol sodium citrate solution, the hydrogen ion concentration will be 10 ^-5 mol/or less. Become.
The recovered acid is diluted in the mixing tank 3 of FIG. Detect. The concentration of each ion is measured as the electromotive force of the electrode by 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 5. In this way, the concentration of a mixed acid containing metal ions can be measured using an ion-selective electrode without being affected by metal ions, making it easy to automate and accurately measure in a relatively short time. The concentration of nitric acid and hydrofluoric acid can be measured.

10 is a tank for measuring specific gravity, into which mixed acid is introduced.
11 is a liquid hydrometer, and 12 is an interface. As the iron ions in the mixed acid increase,
As shown in FIG. 3, the specific gravity of the liquid increases. Since this relationship is correlated, the iron ion concentration can be measured by measuring the specific gravity of the mixed acid. The total fluorine ion is determined by the total amount of fluorine ions in hydrofluoric acid and the fluorine ions in the iron-fluorine complex according to equations (5) and (6). Since the compound form of fluorine differs depending on the concentration of iron and hydrofluoric acid, it can be easily determined by calculation. 13 is a calculator for concentration measurement, and 14 is a display. The calculator calculates the concentrations of hydrofluoric acid, strong acid, iron ions, and total fluorine ions from the information on the measured values of fluorine ions and strong acid ion specific gravity. Also, if the iron ion concentration and total fluorine ion concentration are within the range below curve A in Figure 1,
It has been confirmed that iron fluoride does not precipitate, and that if the total fluoride ion and iron ion concentrations are adjusted to fall within the diagonal lines in the figure, the pickling effect will be great. Therefore, it is important to measure the concentrations of total fluorine ions, iron ions, hydrofluoric acid, and strong acids.

When it becomes necessary to measure the concentration, water is supplied from a water source (not shown) to the water showers 39, 40, 41 for a certain period of time to clean the insides of the liquid tanks 24, 25, 26 and the conduits connecting them. At this time, the solenoid valves 43, 46, 47 are kept open, and the cleaning water is discharged through the solenoid valves 43, 47. After the cleaning water is completely drained, the pump 36 is driven to open the solenoid valve 44 and close the solenoid valves 43, 46, and 47, and a constant amount of standard solution of known concentration is supplied from the standard solution tank 34 to the liquid tank 24. At the same time, a certain amount of water is supplied to the liquid tank 25 from the water shower 40, and this state is maintained for a certain period of time. Then, since the liquid tanks 24 and 25 are separated by the anion exchange membrane 48, the acid concentration in the liquid tank 25 increases. After a certain period of time has elapsed, the solenoid valve 46 is opened and the liquid in the liquid tank 25 is transferred to the liquid tank 26, and the pump 37 is driven and the solenoid valve 45 is opened to supply a certain amount of diluent from the diluent tank 33 and dilute it. Stirrer 42
Fluorine ion selective electrode 27 while stirring
and an ion-selective electrode 28 (for example, a nitric acid ion electrode) that is selective for strong acid anions in the test solution.
Each concentration is detected by the reference electrode 29 that generates a voltage that serves as a reference for these two electrode potentials, and the voltmeter 3
0, the electromotive force is measured and stored in the calculation unit 31. When this measurement is completed, the electromagnetic valve 47 is opened and the liquid in the liquid tank 26 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 38, 39, 40, and 41 for a certain period of time to clean the liquid tank 21, the filter 22, the temperature regulator 23, the liquid tanks 24, 25, and 26, and the conduits connecting these. At this time, the pump 35 is driven and the solenoid valves 43, 46, 47 are kept open, and the cleaning water is discharged through the solenoid valves 43, 47. After the cleaning continues for a certain period of time and the cleaning water is completely discharged, the solenoid valves 43, 46, and 47 are closed, and the test liquid is sampled with a sampling device (not shown).
Put it in the liquid tank 21, filter 22, temperature regulator 2
3, and is supplied in fixed amounts to the liquid tanks 24 and 53 by opening and closing valves 51 and 52. At the same time, a certain amount of water is supplied from the water shower 40 to the liquid tank 25. 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 31. In the calculation unit 31, the voltage when the standard solution is measured is _Vs , and the voltage when the test solution is measured is _Vi , and Ci= _Cs × _10Vs − _Vi / _Kcs : Concentration of the standard solution C _i : Concentration of test liquid K: Calculate the coefficient. The coefficient K is determined by experiment using a mixed acid whose concentration is known in advance. On the other hand, liquid tank 5
3, a liquid hydrometer 49 is inserted, and the result is input to the calculation section 31 through the interface 50. The calculation unit 31 calculates the liquid specific gravity based on the liquid specific gravity measurement value, using a coefficient K determined in advance through experiments, as follows: C _Fe =k×S _g C _Fe : iron ion concentration k : coefficient S _g : liquid specific gravity.

Furthermore, using the coefficient k ₁ which has been experimentally determined in advance based on C _Fe and C _HF , CF = k ₁ ×C _{Fe CF} : Fluorine that combines with iron ions k ₁ : Coefficient C _Fe : Iron concentration Calculate and find C _TF from C _F and C _iasHF . The results of these calculations are displayed on the display section 32, and all measurements are completed. By controlling the above flow using a relay sequence, a sequencer, a microcomputer, etc., it is possible to automatically measure the mixed acid concentration, iron ion concentration, and total fluorine ion concentration.

As described above, when pickling metal materials using a mixed acid of hydrofluoric acid and strong acids such as nitric acid, sulfuric acid, and hydrochloric acid according to the method of the present invention, the acid concentration, iron ion concentration, and total fluorine ion concentration can be accurately determined at any time. It can be measured easily and quickly, and the concentration of mixed acids, etc. can be accurately controlled to prevent excess consumption of hydrofluoric acid.

[Brief explanation of the drawing]

Figure 1 is a phase diagram of the iron-fluorine system, Figure 2 is a principle diagram for carrying out the present invention, Figure 3 is a relationship between mixed acid specific gravity and iron ion concentration, and Figure 4 is iron in the iron-fluorine system. - Phase diagram of fluorine complex; FIG. 5 is a system diagram of an apparatus showing an embodiment of the present invention.

Claims (1)

[Claims] 1 Dialyze fluorine ions, strong acid anions, and hydrogen ions in the pickling solution using an anion exchange membrane,
After diluting this dialysate by adding a salt solution generated by neutralizing a weak acid and a strong base or a strong acid and a weak base,
The fluorine ion and strong acid anion concentrations are measured using an ion-selective electrode, while the specific gravity of the pickling solution is measured using a hydrometer, and the concentrations of hydrofluoric acid, strong acid, iron ions, and total fluorine ions are determined from these measured values. A method for measuring the concentration of a pickling solution containing hydrofluoric acid.