JPH07128273A - Measuring device for iron ion concentration in pickling solution - Google Patents

Abstract

PURPOSE:To provide a measuring device for iron ion concentration in pickling solution which is applied to a device for continuously picking a stainless steel band. CONSTITUTION:This measuring device has 1) a device for supplying a pickling solution from a pickling line 11 to a flow cell 13 in a fixed quantity through a constant pump 12, 2) a device 16 for diluting the pickling solution in the flow cell 13 with pure water into an optional dilution, 3) a device 17 for automatically dropping an oxidizing agent to the diluted pickling solution in the flow cell, 4) an A/D converter 20 for oxidation-reduction potential and monitoring thereof which is set in the flow cell 13 to measure the change of the oxidation- reduction potential in each operation of the above 1)-3), and 5) an arithmetic device 19 for calculating iron ion concentration from the oxidizing agent titre when the oxidation-reduction potential begins to sharply change in the operation of 3), each oxidation-reduction potential of 1)-3), and the dilution in 2).

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an apparatus for measuring the concentration of iron ions in a pickling solution, which is applied to an apparatus for continuously pickling stainless steel strips.

[0002]

2. Description of the Related Art For example, when measuring the iron ion concentration in a pickling solution obtained by continuously pickling a stainless steel strip or the like, a manual chemical analysis was conventionally used. Although various measurement methods by this chemical analysis have been proposed, the "chelate titration method" using EDTA (ethylenediaminetetraacetic acid), which is often used among them, will be described below.

1) Measurement of Fe ³⁺ (ferric ion) concentration A buffer (hydrochloric acid-sodium acetate, p-) was added to a sample (pickling solution).
Chloraniline) was added and sulfosalicylic acid was added to sample 1
The pH is adjusted to 2-3 by adding about 0.2 g per 00 ml. Next, titrate with a concentration of 0.1 to 0.05 ml / L EDTA standard solution, and when the color of the solution changes from blue → green → yellow in order, the point where the green color completely disappears and turns yellow is taken as the end point. . Here, the concentration of ferric ion (Fe ³⁺ ) is determined from the titration amount, assuming that 0.1 mol / L EDTA ... 1 ml = 5.585 mg Fe.

2) Fe²⁺(Ferrous iron ion) concentration measurement Short time after adding ammonium persulfate as an oxidant to the sample
Boiled, Fe²⁺For Fe ³⁺To excess and then excess oxidation
The agent is also completely decomposed. After cooling, Fe of 1) above³⁺Dark
As in the measurement of the degree, add a buffering agent and add sulfosalicylic acid.
In addition, the pH is adjusted to 2-3. After this, EDTA standard
Titrate with liquid, Fe³⁺Determine the (ferric ion) concentration. This
Is the total amount of ferrous and ferric ions,
Chi, Fe²⁺+ Fe³⁺= Fe^TOTALIs shown. Therefore, ferrous ion (Fe²⁺), Above
Ferric ion (Fe³⁺) Below
As shown, total iron ions (Fe^{TO TAL})
Obtained by subtracting from the concentration. Fe²⁺= Fe^TOTAL-Fe³⁺

[0005]

[Problems to be Solved by the Invention]

 1) Problems related to the prior art The chelate titration method has a small amount of discoloration of the indicator mixed with other impurities.
There is a problem that it is hindered by heavy metals and the like. Also,
Fe in an oxidizing pickling solution such as a mixture of nitric acid and hydrofluoric acid
³⁺When performing the titration analysis with EDTA, the EDTA
Fe self-catalyzing²⁺For Fe³⁺Because it oxidizes to
Fe³⁺The concentration readings were analyzed more than they actually were, and as a result,
Conversely, Fe ²⁺The concentration shows a small measured value,
Accuracy error occurs.

2) Further, conventionally, since manual analysis is performed each time, it is desired to constantly monitor the iron ion concentration in the pickling solution continuously.

[0007]

The structure of the iron ion concentration measuring device in the pickling solution according to the present invention for solving the above-mentioned problems is as follows: 1) acid A device for supplying a fixed amount of the pickling solution from the washing line to the flow cell, 2) a device for diluting the pickling solution into the flow cell to an arbitrary dilution ratio with pure water, and 3) an oxidizing agent for the diluted pickling solution in the flow cell. 4) a device for automatically dropping the redox potential, and 4) an oxidation-reduction potential installed in a flow cell for measuring a change in the redox potential in each of the operations 1) to 3) and an A / D converter for monitoring the redox potential. And 5) the iron ion concentration from the titration amount of the oxidant when the redox potential starts to change rapidly in the operation of 3) above, the redox potentials of 1) to 3) and the dilution rate of 2) above. And a computing device for computing That.

[0008]

[Action]

 1) Sample (pickling solution) from the pickling line via a metering pump
Is transferred into the flow cell in a fixed amount. 2) First, using the redox electrode for the original sample,
Ask for rank. 3) Adjust the concentration of the pickling solution in the flow cell from the dilution water supply device.
Dilute to arbitrary ratio with the dilution water of. 4) Obtain the redox potential of the diluted sample. 5) Add oxidizer to diluted sample with automatic titrator
However, the redox potential suddenly rises due to the calculation of the calculation device.
Finding the starting point, ferrous ions (Fe ²⁺)
Ask for degrees. 6) Redox potential at dilution and ferrous ion (F
e²⁺) ′ Concentration, ferric ion (Fe³⁺) ′
Is calculated by the calculation device and the first
Iron ion concentration (Fe²⁺) Concentration and ferric ion (F
e³⁺) Obtain the concentration. 7) After titration, immediately discharge from the flow cell and
Be prepared

[0009]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A preferred embodiment of the apparatus for measuring the concentration of iron ions in a pickling solution according to the present invention will be described in detail below with reference to the drawings.

FIG. 1 is a schematic view of an iron ion concentration measuring apparatus according to this embodiment. In the figure, reference numeral 11 is a pickling line, 1
2 is a metering pump, 13 is a flow cell, 14 is a reference electrode,
Reference numeral 15 is a platinum electrode, 16 is a dilution water supply device, 17 is an automatic titration device, 18 is a discharge device, 19 is a calculation device, and 20 is A /
Each D converter is shown in the figure.

That is, as means for supplying a fixed amount of sample from the pickling line 11 to the flow cell 13 for sample powder analysis,
A metering pump 12 was installed. As a means for diluting the sample in the flow cell 13 to an arbitrary magnification, a dilution water supply device 1
6 was installed, and an automatic titrator 17 for automatically dropping the oxidant to the sample in the flow cell 13 was installed. Further, an oxidation-reduction electrode composed of a reference electrode 14 and a platinum electrode 15 for monitoring the oxidation-reduction potential of the sample in the flow cell 13 is provided, and measurement data is sent to the arithmetic unit 19 via the A / D converter 20. ing. A / D
The converter 20 is responsible for the acquisition of measurement data and the command to each processing unit.

Next, the procedure for measuring the iron ion concentration in the pickling solution using this apparatus will be described.

From the pickling line 11, a fixed amount of the sample is supplied to the flow cell 13 for measuring a fixed amount by a metering pump 12. First, the redox potentials (φRP) of the original sample were measured with the redox electrodes 14 and 15, and the Fe ²⁺ / Fe ³⁺ concentration ratio (mol / L) / (was calculated by the formula (1) shown in the following "Equation 1". mol /
L) is calculated.

[Equation 1] Next, the sample is diluted with distilled water or the like to supply the dilution water 16
The original sample is diluted to an arbitrary dilution ratio by. The redox potential of the diluted sample is measured, and the (Fe ³⁺ ) ′ / (Fe ²⁺ ) ′ concentration ratio is determined in the same manner as described above. The oxidizing agent is dropped onto the diluted sample by the automatic titrator 17, and the redox potential 14 of the reference electrode 14 and the platinum electrode 15 is dropped.
As shown in FIG. 2, the amount of dropping is determined until the peak of 15 rapidly starts rising. From this drop amount, the equivalent amount of (Fe ²⁺ ) ′ (ferrous iron ion) is determined. For example, the reaction formula in the case of titration with permanganate is as shown in formula (I) below.

[Chemical 1] That is, 1 mol of KM _n O ₄ is equivalent to 5 mol of Fe ²⁺ . These reactions are represented by the following formulas (II) and (II
It is the sum of the two redox systems of I).

[Chemical 2] The ferric ion concentration (Fe ³⁺ ) ′ is determined from the redox potential φRP ′ at the time of dilution and the ferrous ion concentration (Fe ²⁺ ) ′ according to the following equation (2).

[Equation 2] From these, the total iron ion concentration at the time of dilution is calculated by the formula (3) shown in the following "Equation 3".

[Equation 3] The total iron ion concentration (Fe) at the time of dilution is shown in the following "Equation 4".
Calculation is performed using the dilution ratio according to the formula (4) shown in.

[Equation 4] From the redox potential (φRP) of the original sample to the iron ion concentration
Distribution ratio (Fe³⁺/ Fe ²⁺), The total iron ion concentration
(Fe), ferrous ion (Fe²⁺), Ferric iron
On (Fe³⁺) Calculate the concentration. After the titration, the sample is immediately blown by the ejector 18.
-Down. Flow cell 13 after measurement is washed with sample solution
Prepare for the next measurement. In addition, sample collection, discharge, etc.
It is controlled from the arithmetic unit 19 via the A / D converter 20.
In addition, the measured value is stored in the arithmetic unit 19 via the A / D converter 20.
Read into and used for calculations.

[0014]

【Example】

(Example 1) As a sample, a nitric acid-based pickling solution having a solution temperature of 50 ° C was used. FIG. 3 shows the correlation between the result of measurement of Total-Fe concentration by wet analysis (hand analysis) that has been conventionally performed and the result of measurement of Total-Fe concentration by this system.

In actual operation, the Total-Fe concentration is 2
Since it is 0 g / L or less, the total Fe concentration is in good agreement with the conventional method, and there is no problem in measurement accuracy.

Regarding the breakdown of Total-Fe, the difference between the conventional method and this system is shown in FIG. When the Fe ³⁺ concentration is high, there is almost no Fe ³⁺ / Fe ²⁺ concentration ratio in both. However, when the Fe ²⁺ concentration becomes high (Fe ³⁺ / Fe ²⁺
A difference occurs between the two when the concentration ratio decreases. The cause of this is that in-situ measurement is performed by this system, but in the conventional method, sampling and titration are performed, so there are the following problems. During the period between sampling and analysis, some of the Fe ²⁺ ions are converted to Fe ³⁺ ions by undergoing air oxidation. When the sample is a non-oxidizing acid solution (eg hydrochloric acid, sulfuric acid)
Is not a problem, but in the case of oxidizing acid solutions such as nitric acid,
An indicator such as EDTA exhibits a catalytic action by itself, and oxidizes a part of Fe ^{2+ in} the sample to Fe ³⁺ . For these reasons, there is a difference between the analysis results of this device and the conventional method. Therefore, it can be seen that the measurement method using this device is superior to the conventional method in terms of analysis value details as well.

By measuring the iron ion concentration by using the measuring apparatus according to the present embodiment described above, I.V. Automation can be achieved in measuring iron ion concentration, II.
We were able to improve the measurement accuracy and further reduce the cost of III.

I Since the automated sensor is of the ion electrode type, the measured value can be directly output as a voltage, which simplifies the measured value processing circuit. Since the measured value can be taken out as an electric output, it can be combined with a signal for managing and controlling the pickling solution such as replenishment of the acid solution, and the system can be automated. II Measurement accuracy If the activity is corrected, the same electric output value as pH can be obtained, so there is no practical problem with measurement accuracy. On the other hand, in the case of manual analysis, there are slight variations due to individual differences. In the EDTA method, a large amount of Fe ²⁺ causes an error. III Cost Since the sensor is an ion electrode, it is cheaper than ion chromatography. It is an electrode type, so maintenance is easy to perform against dirt and the like, and the diluting operation shortens the time of exposure to strong acid, and extends the life of the electrode.

[0019]

As described above in connection with the embodiments, according to the present invention, the measurement of the iron ion concentration in the pickling solution can be automated by the conventional method and can be detected online, and the measurement accuracy is improved. This has the effect of reducing the running cost associated with.

[Brief description of drawings]

FIG. 1 is a schematic view of an iron ion concentration measuring device according to this embodiment.

FIG. 2 is a Fe ²⁺ titration curve diagram with KM _n O ₄ .

FIG. 3 is a correlation diagram of Total-Fe concentration.

FIG. 4 is a graph showing the Fe ³⁺ / Fe ²⁺ concentration ratio.

[Explanation of symbols]

 11 Pickling Line 12 Metering Pump 13 Flow Cell 14 Reference Electrode 15 Platinum Electrode 16 Diluting Water Supply Device 17 Automatic Measuring Device 18 Discharge Device 19 Computing Device 20 A / D Converter

Claims (1)

[Claims] 1. A measuring device for measuring iron ion concentration in a pickling solution, comprising: 1) a device for supplying a fixed amount of the pickling solution to a flow cell from a pickling line; and 2) pure water of the pickling solution into the flow cell. A device for diluting to an arbitrary dilution ratio with 3), a device for automatically dropping an oxidant into a diluted pickling solution in a flow cell, and 4) a change in redox potential in each of the operations 1) to 3) above. A / D converter installed in the flow cell for measurement and an A / D converter for monitoring the same, and 5) Oxidizing agent titration amount when the redox potential starts to change rapidly in the operation of 3) above. 1. An apparatus for measuring iron ion concentration in a pickling solution, comprising: an arithmetic unit that calculates the iron ion concentration from the redox potentials of 1) to 3) and the dilution rate of 2) above. .