JPH06306657A - Regenerating method for picking waste liquid containing fluoric acid - Google Patents

Abstract

PURPOSE:To obtain a regenerated liquid in an optimum concn. for pickling by removing Ni salt, Cr salt and Fe salt from the waste liquid used for pickling a stainless steel by using an org. solvent and by evaporating and condensing the removed aq. soln. CONSTITUTION:The rolled product of the stainless steel to be treated is pickled by the mixed acid aq. soln. of nitric acid and fluoric acid in a pickling tray 1. An effluent pickle waste liquid is introduced in a liquid storage tank 3. The pickle waste liquid in the liquid storage tank 3 consists of nitric acid, fluoric acid, Fe, Cr and Ni, and is brought into contact with the org. solvent 5 to extract Fe content, and some Fe- extracted waste liquid is supplied to a liquid storage tank 10, and a remainder is drought into contact with the org. solvent 5 to remove Cr and Ni and supplied to me liquid storage tank 10. The effluent from the liquid storage tank 10 is introduced in a concentrator by evaporation 12 and adjusted to a water content by an evaporating operation and introduced in the pickling tray 1 to reuse. In this way, the effluent is concentrated by evaporation so that the metallic salts remaining in a regenerated acid may not be crystal-deposited, and the pickling effect of the stainless steel is maximized without replenishing of a fresh acid.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for regenerating a pickling waste solution containing a metal salt and an acid, which is generated when a rolled product of stainless steel is surface-treated with an aqueous pickling solution, by a solvent extraction method. .

[0002]

Rolled stainless steel products generally undergo a final heat treatment process. In order to remove the scale layer formed on the surface of the rolled product in this heat treatment process, first a sandblasting treatment is carried out, and then a pickling treatment with a mixture of nitric acid and hydrofluoric acid is carried out. The pickling waste liquor produced by pickling metals still has large amounts of acid. Therefore, it is desirable to recover nitric acid and hydrofluoric acid from the pickling waste liquid, because not only is this a loss of resources but also pollution may occur if this is discarded.

Conventionally, as a method for recovering and reusing the acid from these pickling waste liquids, there is JP-B-56-42674. According to this method, a waste acid containing a large amount of heavy metal ions is treated with a petroleum-based carbonization of one or more kinds selected from the group of alkyl phosphoric acid for the heavy metal ions containing the largest amount of heavy metal ions contained. By contacting with the organic solvent A diluted with hydrogen, the target heavy metal ions in the waste acid solution are extracted, and the first step of recovering the acid, part or all of the extraction residual liquid after the first step, At least an equivalent amount of sulfuric acid or hydrochloric acid is added to the metal ion contained in the solution to convert the chemical species of the contained metal salt and the hydrogen ion concentration is adjusted, and this solution is then selected from the group consisting of phosphate esters. Alternatively, it comprises a second step of extracting the free acid in the solution into the organic phase and recovering the acid by bringing two or more kinds into contact with the organic solvent B diluted with petroleum hydrocarbon, and the organic solvents A and B are So Wherein the play in the respective steps.

[0004]

[Problems to be solved by the invention] Japanese Patent Publication No. 56-4267
In the method such as No. 4, the concentration of the acid recovered from the pickling waste liquid is lower than the acid concentration at which the pickling effect of stainless steel is the highest, so before reusing the regenerated acid for pickling of stainless steel. It is used for pickling by supplementing with new acid to increase the acid concentration. As a result, there is a problem that the amount of acid used for pickling increases and becomes excessive. It is an object of the present invention to provide a method for regenerating a pickling waste liquid containing hydrofluoric acid, which can appropriately adjust the acid concentration of a liquid regenerated from a stainless steel pickling waste liquid, which solves the above problems.

[0005]

According to the present invention, a pickling waste liquid containing a metal salt and an acid generated when a stainless steel rolled product is surface-treated with an aqueous pickling solution is used to recover the acid using an organic solvent. In the method of reuse for pickling stainless steel, the pickling effect of stainless steel is maximized without replenishing new acid by evaporating and concentrating so that the metal salts remaining in the regenerated acid do not crystallize. It is designed to achieve an acid concentration.

That is, the present invention mainly uses nitric acid in a method of regenerating a pickling waste solution containing a metal salt and an acid generated when a rolled product of stainless steel is surface-treated with an aqueous pickling solution, using a solvent extraction method. And hydrofluoric acid and acid pickling waste solution containing nickel salt, chromium salt and iron salt extracted with organic solvent from hydrofluoric acid and nitric acid are evaporated and concentrated to regenerate an acid suitable for pickling aqueous solution of stainless steel. A method for regenerating a pickling waste liquid containing hydrofluoric acid is provided.

[0007]

The present invention will be described in more detail below. According to the present invention, it is possible to obtain an optimum acid concentration for pickling stainless steel by evaporating the water extracted with an organic solvent from the pickling waste liquid of stainless steel containing hydrofluoric acid in an evaporative concentrator. According to the method of the present invention, it is not necessary to replenish new acid, and it is possible to prevent generation of excess acid even if the regenerated acid is circulated and used for pickling stainless steel.

The above-mentioned conventional method (Japanese Patent Publication No. 56-42674)
In general, an acid extracted with an organic solvent has a metal salt concentration and an acid composition which vary depending on the distribution ratio between the first step of contacting with the organic solvent A and the second step of contacting with the organic solvent B. . The metal salt concentration and the acid concentration are in a proportional relationship, and when the metal salt concentration is lowered by manipulating the distribution ratio of the first step and the second step, the acid concentration is also lowered. Therefore, the metal salt concentration is generally 10 to 30 g / L. , Hydrofluoric acid concentration 50-60g
/ L, nitric acid concentration is controlled to 120 to 130 g / L. When the metal salt concentration is 30 g / L or more, chromium fluoride crystals precipitate, so the metal concentration must be less than 30 g / L.

In the method of the present invention, the pickling effect is obtained by evaporating and concentrating the regenerated acid so that the metal concentration does not exceed 30 g / L and the pickling waste solution containing hydrofluoric acid is evaporated to the extent that chromium fluoride crystals do not precipitate. Since the regenerated acid solution having the highest acid composition can be obtained, the regenerated acid can be recycled and used for pickling stainless steel without generating excess acid.

[0010]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be specifically described below with reference to the process flow chart of FIG. (Example) In the pickling tank 1, for example, 150 to 180 g /
A mixed acid aqueous solution of L nitric acid and 70 to 90 g / L hydrofluoric acid was used as a pickling solution, and the rolled product of the stainless steel to be treated was immersed in the pickling solution.
Led to. The pickling waste liquid in the storage tank 3 is about 170 g of nitric acid /
L, hydrofluoric acid about 80 g / L, Fe about 40 g / L, Cr about 20
It was supplied at a flow rate of 1 m ³ / hr to the first step 5 having a composition of g / L and Ni of about 8 g / L and coming into contact with the organic solvent A (composition: D ₂ EHPA) through the pipe 4. The effluent from which iron was extracted in the first step 5 was about 140 g / L of nitric acid and about 70 of hydrofluoric acid.
g / L, Fe about 3 g / L, Cr about 20 g / L, Ni about 8
It had a composition of g / L.

A part of this effluent was introduced into the second step 8 through the pipe 7, and the rest was supplied to the liquid storage tank 10 through the pipe 6. The effluent introduced into the second step 8 at a flow rate of 0.5 m ³ / hr came into contact with the organic solvent B (composition: TBP) to remove Cr and Ni. The effluent of the second step 8 is 100 g of nitric acid.
/ L, hydrofluoric acid 30g / L, Fe0.1g / L, Cr0.1
It had a composition of g / L and Ni 0.1 g / L, and was supplied to the liquid storage tank 10 through the pipe 9. In the liquid storage tank 10, the effluent of the first step 5 and the effluent of the second step 8 are mixed to produce about 12 nitric acid.
0 g / L, hydrofluoric acid about 50 g / L, Fe about 1.5 g / L, C
The composition was r about 10 g / L and Ni about 4 g / L.

The effluent from the liquid storage tank 10 is led to the evaporative concentrator 12 through the pipe 11, and in the evaporative concentrator 12, the water content is adjusted by the evaporating operation at the evaporating temperature of 50 ° C. and the vacuum degree of 0.1 atm. . The effluent of the evaporative concentrator 12 is about 170 g of nitric acid /
L, hydrofluoric acid about 80 g / L, Fe about 2 g / L, Cr about 15 g
/ L, Ni of about 6 g / L, and was supplied to the pickling tank 1 through the pipe 13. As the above experimental results show for each step, the pickling waste liquid was regenerated to an optimum acid composition for pickling and could be reused.

[0013]

Since the present invention has the above-mentioned structure,
In the method of regenerating the pickling waste solution described at the beginning, the regenerated acid solution recovered using an organic solvent was evaporated and concentrated so that metal salts were not deposited, so the acid concentration of the regenerated solution is optimal for pickling. The concentration can now be changed. Further, since the low-concentration acid does not become surplus, there is an effect that the regenerant can be almost completely utilized for pickling.

[Brief description of drawings]

FIG. 1 is a process flow chart showing a pickling solution treatment system using the method of the present invention.

[Explanation of symbols]

 1 Pickling tank 2 Piping 3 Storage tank 4 Piping 5 First step of organic solvent A 6 Piping 7 Piping 8 Second step of organic solvent B 9 Piping 10 Storage tank 11 Piping 12 Evaporation concentrator 13 Piping

Claims (1)

[Claims] 1. A method for regenerating a pickling waste solution containing a metal salt and an acid generated when a rolled stainless steel product is surface-treated with an aqueous pickling solution, using a solvent extraction method.
To regenerate an acid suitable for a pickling aqueous solution of stainless steel by evaporating and concentrating an acid obtained by extracting hydrofluoric acid and nitric acid with an organic solvent from a pickling waste solution containing mainly nitric acid and hydrofluoric acid and nickel salt, chromium salt and iron salt. A method for regenerating a pickling waste liquid containing hydrofluoric acid, comprising: