JPS6054394B2 - How to prepare pickling solution - Google Patents

Description

[Detailed description of the invention] The present invention relates to a method for preparing a metal pickling solution.

It is well known that when plates made of iron or iron alloys are subjected to metal plating, painting, or other surface treatments, pickling is performed for purposes such as rust removal prior to these treatments. Generally, the solution used for pickling is an aqueous mineral acid solution such as hydrochloric acid or sulfuric acid, and the waste liquid produced by pickling metals still contains a large amount of acid.

If this is disposed of, not only will it be a loss of resources, but it will also create a pollution problem, which will require neutralization, which will increase costs. Therefore, in recent years, attempts have been made to recover and reuse acids from these waste liquids, and in particular, a metal pickling system that combines diffusion dialysis using an anion exchange membrane has been proposed. According to such a system, a part of the solution in the pickling tank is taken out of the tank and subjected to diffusion dialysis to recover and reuse the acid. At the same time, the solution to be treated is further treated with iron compounds, etc. in a separate process depending on the case. are collected and then discarded. Starting with such a system,
Even in other methods of effectively utilizing acid, the amount of acid consumed is significantly reduced compared to conventional methods. Although this has significantly increased the effective utilization rate of acid, another problem has been found that various impurities unavoidably introduced from metals and chemicals used during pickling accumulate in the pickling solution. Among these, accumulation of copper components causes various problems. That is, when copper ions accumulate above a certain concentration, they deposit and adhere to the surface of metals such as iron, which adversely affects the surface treatment in the next step. Therefore, the present invention proposes a method for preparing a metal pickling solution that prevents these adverse effects.

That is, the present invention extracts a part of the pickling solution from the pickling tank, adds thereto a soluble sulfur compound, preferably at least one compound selected from thiourea and its derivatives, and then transfers at least part of it to the pickling tank. This is a method for preparing a metal pickling solution, which is characterized in that it is circulated and supplied to a metal pickling solution. In particular, in a preferred embodiment of the present invention, a soluble sulfur compound is added to the pickling liquid extracted from the pickling tank according to the amount of copper in the liquid, and then at least one part of the liquid to be treated is separated from the precipitate. After the precipitate has been separated, part of the circulating fluid is subjected to diffusion dialysis using an anion exchange membrane to recover the acid, which is then resupplied to the pickling tank. There is a particular thing. Therefore, in this specification, the expression "resupply of the pickling solution" refers to the process of returning the pickling solution extracted from the pickling tank to the pickling tank with or without some kind of treatment, that is, the circulation of the pickling solution. It also includes a mode in which most of the liquid extracted during diffusion dialysis treatment is discarded, and only specific components are supplied to the pickling tank together with newly supplied water. According to the present invention, impurities contained in the circulating fluid, particularly copper components, are separated from the circulating fluid as a hardly soluble sulfur compound as a precipitate or removed as a suspension by adding a soluble sulfur compound.

The soluble sulfur compounds used in the present invention include substances that form insoluble salts with copper, such as sulfur compounds of alkali metals such as sodium sulfide, sodium hydrogen sulfide, and sodium polysulfide, or thiourea, ethylthiourea, diethylthiourea, and butylthiourea. Urea, thiourea derivatives such as phenylthiourea, or sulfur-containing or thiourea-based removers commonly used as heavy metal removers, such as Olitor (trade name: manufactured by Oriental Giken), Inhibitani Ivit S6OO (
There are substances that form a matrix with copper ions and precipitate, such as (trade name: manufactured by Asahi Chemical Industry Co., Ltd.). Among them, those using thiourea and its derivatives have the effect of the present invention! It is preferred because the fruit is extremely large. The amount of the sulfur compound added varies depending on the concentration of impurities, especially copper ions, in the externally circulating fluid, or the type of soluble sulfur compound, but it is necessary to have at least an amount that will react with the copper ions in the externally circulating fluid.

However, if too much is added, the precipitated or suspended matter of copper and sulfur compounds may be redissolved, so the amount must be set in advance. Generally 0.5 to 5 for copper content
Molar amounts are used, preferably 1 to 3 molar amounts. The present invention will be specifically explained below using FIG.

In the figure, 1 is a pickling tank, which is generally a 1-W normal, preferably 4-8 normal aqueous solution of a mineral acid such as hydrochloric acid or sulfuric acid. There is a pickling solution containing several weight percent of iron sulfate, etc., and the metal to be treated is treated by a known cleaning method such as immersing the metal in this or exposing the metal to a shower of the pickling solution. . In the present invention, at least a portion of the pickling liquid in the pickling tank is extracted through the vibrator 11, and is allowed to settle if necessary,
In some cases, a portion is bypassed by the vibrator 21 and returned to the pickling tank, and the remainder is fed into a suitable reaction tank 2, where a soluble sulfur compound is added and reacted. The structure of the reaction tank is not particularly limited, but one with a stirrer is preferable.

Furthermore, if the reaction produces an odor, it is also preferable to attach a deodorizing device.

In this case, an activated carbon tower is suitable, but a removal tower using an alkali solution is also effective. Generally, soluble sulfur compounds can be added anywhere in the extraction line from the pickling tank as long as it is before the separation process, but generally a mixing tank is provided and the reaction is carried out by adding continuously or intermittently while stirring etc. It is better. A reaction time of one powder or less is usually sufficient. Therefore, it is preferable that the reaction tank be of a continuous supply and discharge type. Then, if necessary, the circulating liquid after the reaction is caused to flow down through a flocculation tank to a settling tank 3, or by a forced separator replacing this, solid-liquid separation is performed, and a clear liquid (acid) is extracted through a vibrator 12. At least a portion is recycled and re-supplied to the pickling tank via paths 13 and 14.

In a preferred embodiment of the present invention, at least a portion of the liquid that has reached the vibrator 12 is branched, and the vibrator 15 is used to divide the liquid into the diffusion dialysis device 4.
Processed by

This device is a generally known diffusion dialysis device, and an anion exchange membrane is used as the dialysis membrane. One of the features of the present invention is that impurities, particularly copper concentration, in the pickling solution are reduced by reacting the pickling solution undergoing diffusion dialysis treatment with soluble sulfur compounds in advance.

Normally, it is relatively easy to remove iron, chromium, nickel, etc. from the pickling solution using the diffusion dialysis method, but since copper ions exist as complex ions in the hydrochloric acid solution, the hydrochloric acid solution is subjected to diffusion dialysis. When treated, removal is difficult. However, among the various metal ions that coexist in the pickling solution, if copper ions, in particular the concentration of which must be strictly limited, are removed, other metal ions, etc., may generally be present in relatively large amounts. Although it does not cause any substantial harm in the pickling process,
After all, it is undesirable for them to accumulate in large quantities. Therefore, a part of the solution from which copper ions have been removed by adding soluble sulfur compounds is further supplied to a diffusion dialysis device that uses an anion exchange membrane as a dialysis membrane to separate other metal ions, etc. By recovering the acid and supplying it to a pickling tank, metal ions other than copper are mainly removed from the circulation system. However, supplying the entire liquid to be treated after removing copper ions to the dialysis tank unnecessarily increases the capacity of the dialysis tank, increases the installation area and equipment costs, and also increases running costs. This is not desirable. That is, it is preferable from the viewpoint of cost because the minimum necessary amount of liquid is subjected to dialysis treatment according to the allowable concentration of impurities such as metal ions other than copper ions. Therefore, one of the preferred embodiments of the present invention is to extract a portion of the pickling liquid from the pickling tank, add a soluble sulfur compound, and then supply a portion of the treated liquid from which the precipitate has been separated to a diffusion dialysis device. There is a method in which the acid is recovered and re-supplied to the pickling tank, and the remaining liquid to be treated is circulated and supplied to the pickling tank.

Further, it is preferable to create a reducing atmosphere by adding a reducing agent such as sodium thiosulfate in advance to the pickling solution to be subjected to the diffusion dialysis treatment. By doing so, the dissolved metal is in a low valence state and difficult to form negatively charged complex ions that often occur in a saturated valence state, thereby improving acid separation efficiency. Additionally, the reducing agent is effective in removing copper. In the diffusion dialysis device, water is supplied to one end, and acid is collected thereto, and a vibrator 16
This leads to tank 5. On the other hand, the liquid from which the acid has been removed is discharged from the system through 17. This is disposed of after performing recovery processing for metal components as necessary. In tank 5,
Depending on the condition of the pickling tank, additional acid is added, water is replenished, or other chemicals are added, and the pickling tank is resupplied from the vibrator 18 with or without passing through the vibrator 14. The amount of circulation in the pickling tank in the present invention varies depending on the process, but generally the purpose is to improve the stirring state in the pickling tank, or to maintain the acid concentration in the tank within a predetermined range.
Furthermore, the amount may be selected to suit the desired purpose, such as maintaining the concentration of impurities unavoidably brought into the tank below a certain limit.

Generally, it is preferable to keep the copper component as an impurity at 600 ppm or less, preferably 500 ppm or less. In addition, when at least a portion of the circulating fluid is subjected to diffusion dialysis treatment, the amount supplied to the diffusion dialysis device must be the amount that can keep the salts of metals such as iron produced as by-products in the pickling tank below a certain concentration. The amount of liquid sufficient to remove the amount of metal salt by-product per unit time in the tank may be supplied to the diffusion dialysis apparatus and treated.

Examples of the present invention are shown below, but the present invention is not limited to these Examples.

Example 1 Assuming the process shown in Figure 1, hydrochloric acid,
Prepare an acid solution with a dissolved iron content of 50 fI/' and a dissolved copper content of 500 ppm, place 500 cc of the prepared solution in a beaker, and add 1, 3, and 5 times the equivalent of sodium sulfide to the dissolved concentration while stirring with a magnetic stirrer. The reaction time and copper ion concentration in the remaining solution were measured for each case.

In the same manner, thiourea was added in an equal amount to the dissolved copper concentration.
In addition, when thiourea is added in an equivalent amount to the dissolved copper concentration, and 1'5 equivalent of sodium thiosulfate is added to the thiourea, Oritol S (trade name:
The amount of residual copper ions was measured when an equivalent amount of (manufactured by Oriental Giken) was added. Copper ion analysis was carried out by conventional atomic absorption spectrometry. Table 1 shows the relationship between the reaction time and the amount of copper ions dissolved in the solution in each case. Example 1 A test device was made according to the steps shown in FIG. 1, and a pickling experiment of a stainless steel plate was conducted.

In this example, the composition of the pickling solution was 4.5 N of hydrochloric acid, 36 y/' of dissolved iron, and 0.5 N of heavy metals as impurities (as copper).
Drive so that the speed is 45y/'. That is, the pickling tank liquid is 7
After taking it out of the tank for 21/hour and removing solid suspended matter in a storage tank that also serves as a stabilization tank, 64.8 tons =
Add 咄二#God Exel and react.

The reaction time is about 5 minutes. The circulating fluid leaving the reaction tank is
Hydrochloric acid 4.29N1 Iron content 38.7 da/l, copper content 0.060
This is a solution containing f/f. After passing through a settling tank using polypropylene cotton as a filter medium, 5.76e/Hr is returned to the pickling tank, and the remaining 1.44'/Hr is separated and subjected to diffusion dialysis. The dialysis tank used was a device with an effective area of 1.57 mm using NeoSepta AFN (trademark: anion exchange membrane manufactured by Tokuyama Soda Co., Ltd.) as a diaphragm. Dialysis conditions are 1.62
Feed water at e/Hr and recover acid.

The recovered liquid was 3.78N hydrochloric acid and contained iron content of 4.86'/', copper content of 0.045y/e, and was 1.53e/Hr. While newly adding 10.8N hydrochloric acid at 392.4'/Hr, the solution is re-supplied to the pickling tank. With the circulation system described above, the system was balanced and stable pickling could be performed.

[Brief explanation of the drawing]

FIG. 1 is a process diagram showing the processing system of the present invention.

Claims (1)

[Claims] 1. Preparation of a metal pickling solution, characterized in that a part of the pickling solution is extracted from a pickling tank, a soluble sulfur compound is added thereto, and at least a part of the solution is circulated and supplied to the pickling tank. Method. 2. The method for preparing a metal pickling solution according to claim 1, wherein after adding the soluble sulfur compound, at least a part of the solution from which the precipitate has been separated is circulated and supplied to the pickling tank. 3. The metal pickling solution according to claim 2, in which a part of the liquid to be treated after separating the precipitate is supplied to a diffusion dialysis device, the acid is recovered, and the acid is re-supplied to the pickling tank. Preparation method. 4. The method for preparing a metal pickling solution according to claim 1 or 2, wherein the soluble sulfur compound is at least one compound selected from thiourea and its derivatives.