JP3025576B2 - How to recycle pickling liquid - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention recovers precious metal ions added to a pickling solution as a pickling catalyst and hydrochloric acid or nitric acid salt, which is the main agent of the pickling solution, from used pickling waste liquid and recycles it. It is about the method.

[0002]

2. Description of the Related Art A stainless steel strip is rolled in its manufacturing process.
The product is formed while repeating annealing, and the oxide scale generated at that time is dense and strong Cr ₂ O ₃ or FeO.
· Cr ₂ O ₃ from consisting film and by covering the steel strip surface.
For this reason, in continuous pickling treatment equipment installed in a continuous pickling line or a continuous annealing pickling line, in order to remove oxide scale, it is usually necessary to use a mechanical or chemical method such as shot blasting, molten alkali salt immersion or neutral salt electrolysis. A method combining chemical preliminary descaling and pickling treatment has been used. Conventionally, as a pickling solution for stainless steel, an aqueous solution of nitric hydrofluoric acid has been used for pickling of austenitic stainless steel, and an aqueous solution of hydrochloric acid or sulfuric acid has been used for pickling of ferritic stainless steel.

[0003] As a means of improving productivity in the pickling process, increasing the sheet passing speed is performed. However, in the current pickling method, the cutting efficiency is low, so that the cutting is insufficient and the scale remains. Since the surface appearance deteriorates and the length of the pickling equipment is extended to secure the pickling time, equipment costs and running costs increase, which leads to an increase in product prices.
There is a problem in improving productivity using the current pickling solution. In addition, the use of different pickling solutions depending on the type of steel causes a decrease in productivity and an increase in cost, which causes an increase in product cost.

In order to solve this problem, a technique that can descaling stainless steel with high cutting efficiency is required. As means therefor, Pd, P with low hydrogen excess voltage
By adding a noble metal ion such as t or Rh, a method of promoting a hydrogen generation reaction as a cathode reaction at the time of pickling and promoting a metal dissolution as an anodic reaction can be mentioned.
For example, in Japanese Patent Application No. 3-109625, Pd, P is added to an aqueous solution of hydrochloric acid or an aqueous solution of a mixed acid of hydrochloric acid and nitric acid.
A high-speed pickling technique for stainless steel using a pickling solution to which noble metal ions such as t and Rh are added is disclosed.

[0005] These pickling solutions can provide high cutting ability, but the waste solution after pickling treatment contains P added as a pickling catalyst.
If expensive noble metal ions such as t, Pd, and Rh are contained, and if the noble metal ions cannot be recovered, it is necessary to newly add the noble metal ions to replenish the noble metal ions lost together with the drainage liquid. However, the cost of the additional precious metal ions increases due to the high price of the compound, and the drug cost increases, which is a major problem in industrially implementing the present technology. Therefore, in order to industrially add the noble metal ions to the pickling solution to improve the pickling ability, it is essential to establish a technology capable of reducing the cost of the noble metal ions by collecting the added noble metal ions. is there.

[0006] The pickling waste liquid contains high concentration of HCl and metal chlorides generated in the pickling process.
When disposing without collecting hydrochloric acid from waste liquid,
A large-capacity hydrochloric acid tank is required to supply a large amount of hydrochloric acid required for the preparation of the pickling solution, which increases the cost of auxiliary equipment and increases the cost of chemicals due to the cost of hydrochloric acid. It is also necessary to recover hydrochloric acid from methane.

Therefore, in order to industrially implement the present technology, it is necessary to add noble metal ions and H, which is a base of the pickling solution.
It is necessary to construct a liquid circulation system for collecting and reusing Cl.

In particular, when recovering precious metal ions, when the present technology is applied industrially, the F dissolved in the pickling process is used.
e, base metal ions such as Cr, Ni, etc.
By using it until a high concentration level of 0 g / liter is reached, about 10
Noble metal ions are collected and reused from a system containing a base metal ion having a high concentration of 00 to 2000 times, and it is necessary to collect only the noble metal ions by suppressing contamination of impurities such as Fe, Cr, and Ni. There is.

[0009]

The object of the present invention is to solve the above was added highly concentrated aqueous HCl or HCl with noble metal Pt aqueous solution of HNO ₃ as a base, Pd, or more one or two of the Rh ions An object of the present invention is to construct a pickling circulation system for efficiently recovering and reusing precious metal ions and high-concentration HCl from used pickling waste liquid in pickling treatment using a pickling solution.

Generally, in the pickling process performed industrially, base metal ions such as Fe, Cr, and Ni dissolved in the pickling process are used until the concentration reaches a high concentration of 80 to 160 g / liter during pickling. In contrast, Japanese Patent Application No. 3-109
As shown in Japanese Patent No. 265, even if the precious metal ions are excessively added, the effect of improving the cutting ability reaches saturation and becomes economically disadvantageous. Noble metal ion addition amount is 500-6
The concentration is about 100 mg / liter or less, and the ratio of the concentration of the base metal ion to the concentration of the noble metal ion to be collected in the discharged pickling waste liquid is several hundred to several thousand times. As an example, the composition of a waste solution in the case of using an acid washing solution to which platinum ions of hydrochloric acid are added is shown in Table 1. In this solution, the concentration of platinum ions to be recovered is only 75 mg / liter. The concentration ratio between the base metal ion and the noble metal ion is 1064
It has also doubled. Therefore, when recovering the noble metal ions from the pickling waste liquid, Fe, Cr, Ni, etc., which are impurities from a system containing a high concentration of base metal ions several hundred to several thousand times higher than the noble metal ions to be recovered, are mixed. It is necessary to selectively recover only a small amount of noble metal ions while suppressing the amount of noble metal ions.

[0011]

[Table 1] On the other hand, as a method for recovering HCl from HCl-based pickling waste liquid, many recovery techniques such as spray medium baking method and vacuum distillation method have been put into practical use.
This is a technology for recovering only Cl or recovering not only free HCl but also all HCl including HCl obtained by thermally decomposing metal chlorides in pickling waste liquid, and recovering useful metals contained in the waste liquid. That is not taken into account at all.

Therefore, in the waste liquid treatment from the pickling process using a pickling solution to which a noble metal ion is added as a pickling catalyst, only the noble metal ion is recovered while suppressing the incorporation of base metal ions such as Fe, Cr and Ni. In addition, it is indispensable to construct a pickling solution circulation system that can achieve both efficient recovery of HCl.

By constructing a system for recovering and reusing precious metal ions and high-concentration HCl from used pickling waste liquid, the cost of chemicals is reduced, and a high-concentration HCl aqueous solution disclosed in Japanese Patent Application No. 3-109625 is disclosed. Industrial applicability of pickling using a pickling solution to which one or two or more ions of noble metals Pt, Pd, Rh are added based on an aqueous solution of HCl and HNO ₃ is made possible.

[0014]

SUMMARY OF THE INVENTION The present invention provides a high concentration HCl solution.
Pt ⁴⁺ , Pd from the pickling waste liquid in the pickling process in the pickling process using an aqueous solution or an aqueous solution of HCl and HNO ₃ and adding one or more of the ions of the noble metals Pt, Pd, and Rh. Noble metal ions such as ²⁺ and H
A method of circulating pickling liquid for collecting and reusing Cl. Preliminary recovery of acid by means of vacuum distillation or diffusion dialysis as pretreatment to recover HCl and reduce acid concentration in waste liquid. After that, when vacuum distillation was carried out, the amount of the liquid was further reduced due to the vacuum distillation, and the precipitated metal chloride mainly composed of FeCl ₂ was filtered out. By contacting with an adsorbent such as a sieve,
After the precious metal ions are adsorbed to the adsorbent, the recovered HCl obtained by the pre-recovery of the acid and the recovered HCl recovered from the liquid after the noble metal ion adsorption treatment are subjected to a concentration treatment, or The noble metal ions are taken out by backwashing the adsorbent that has adsorbed the noble metal ions using the HCl solution as it is as a backwash solution,
That is, the present invention is characterized in that noble metal ions, HCl and HNO _{3 corresponding} to a recovery loss are added to an HCl solution containing noble metal ions to prepare a pickling solution composition, which is reused as a pickling solution.

In the present invention, as a method of recovering noble metal ions, the adsorption of noble metal ions to an adsorbent such as activated carbon or molecular sieve is used. As previously mentioned,
About 50 noble metal ions targeted for recovery are contained in the pickling waste liquid.
In addition to being contained at a concentration of 0 mg / liter or less, Fe,
Base metal ions such as Cr and Ni are contained at a high concentration of 80 to 160 g / l, and the standard oxidation-reduction potential of these ions is as shown in Table 2, and the target noble metal to be recovered is The oxidation-reduction potential of the ions is higher than that of the base metal ions such as Fe, Cr, and Ni, which are impurities. When the metal ions are adsorbed to an adsorbent such as activated carbon or molecular sieve, the standard oxidation-reduction potential is higher. Noble metal ions are preferentially adsorbed. As an example, the composition of the waste liquid after treatment in the treatment of bringing the waste liquid having the composition shown in Table 1 into contact with activated carbon to adsorb metal ions is shown in Table 3, and about 84% of the noble metal ion Pt ²⁺ is adsorbed. However, the base metal ions Fe, Cr, Ni
Only about 1% of these ions were adsorbed, and only noble metal ions could be selectively adsorbed and recovered.

However, at this time, as shown in FIG. 1, the dependence of the noble metal ion adsorption rate on the acid concentration in the waste liquid is large, and in order to increase the adsorption rate, the acid concentration in the waste liquid must be suppressed to 2N or less. desirable.

[0017]

[Table 2]

[Table 3] Therefore, in the treatment of the pickling waste liquid according to the present invention, first, a preliminary recovery such as vacuum distillation or diffusion dialysis is carried out to reduce the acid concentration in the waste liquid to reduce the noble metal to an adsorbent such as activated carbon or molecular sieve. It is possible to increase the ion adsorption rate and increase the recovery efficiency of precious metal ions in the present waste liquid treatment system. In addition, when the acid concentration in the waste liquid is sufficiently lower than 2N, the adsorption of the noble metal ion can be carried out as it is without performing the preliminary recovery of the acid.

However, the preliminary recovery of the acid carried out here is f
The purpose is only to reduce the free acid concentration, the recovery of the remaining free acid and the Cl constituting the metal chloride
^It is necessary to carry out the secondary recovery of the acid for recovering-as hydrochloric acid after the noble metal ion adsorption treatment, but by performing the preliminary recovery treatment of the acid first, most of the free acid is removed. The load of the secondary recovery treatment of the acid from the liquid after the noble metal ion adsorption treatment can be reduced, and the secondary acid recovery equipment can be downsized. Therefore, in order to improve productivity by modifying existing pickling equipment so that it can use a pickling liquid with high cutting ability, the acid consumption and waste liquid discharge per unit time generally increase accordingly. Although it is necessary to increase the waste liquid treatment equipment and the acid recovery equipment due to the increase, in the present invention, by performing the preliminary recovery of the acid, the load of the secondary recovery of the acid using the existing hydrochloric acid recovery equipment is changed before the pickling liquid is changed. It is possible to significantly improve the pickling ability by changing the pickling solution without increasing the existing hydrochloric acid recovery equipment.

Further, when vacuum distillation is applied as a means for preliminarily recovering the acid, the amount of the liquid decreases during the preliminarily recovering process of the acid, so that the metal chloride such as Fe, Cr, Ni or the like dissolved in the pickling waste liquid. When the concentration of the substance reaches a supersaturated state, a part of the metal chloride precipitates and precipitates, and the concentration of the base metal ion contained in the waste liquid decreases, so that the F mixed into the precious metal to be recovered is reduced.
e, Cr, Ni and other impurities can be reduced, and HCl having a higher HCl concentration than the pickling waste liquid before vacuum distillation can be recovered.
By omitting the acid concentration treatment of l, the effect that the liquid circulation flow can be simplified can also be obtained.

From the above, as shown in FIG. 2, the treatment flow of the waste liquid in the method of the present invention is as follows. First, the pickling waste liquid discharged from the pickling tank is subjected to an acid preparatory treatment such as distillation under reduced pressure or diffusion dialysis. By performing the recovery treatment, the free acid concentration is reduced, secondly, the metal chloride precipitate deposited by performing the filtration treatment is removed, and thirdly, the filtration tower is filled with an adsorbent such as activated carbon. 4) The noble metal ions are adsorbed on the adsorbent by passing the pickling waste liquid of 4).
By discharging metal oxides of base metals such as Cr and Ni, hydrochloric acid is recovered and precious metal ions are adsorbed on the adsorbent.

After that, the recovered hydrochloric acid solution is used as it is or after being subjected to acid concentration using a distillation apparatus as a backwashing liquid to backwash an adsorbent such as activated carbon to which noble metal ions have been adsorbed, so that the noble metal ions can be activated carbon or the like. And eluted in a hydrochloric acid solution as a backwash liquid. The resulting hydrochloric acid solution containing the noble metal ions is subjected to component adjustment by addition of the noble metal ions and hydrochloric acid corresponding to the recovery loss and nitric acid consumed in the pickling reaction process, and stored in a storage tank. It can be reused as a washing liquid. As a result, most of the noble metal ions such as Pt ⁴⁺ , Pd ²⁺ added as hydrochloric acid, nitric acid and pickling catalyst are recovered.
A system is constructed to reuse and recycle precious metals and high-concentration hydrochloric acid from waste liquor when preparing the pickling solution.

Further, the system is a closed circuit, and what is discharged in the course of processing is used as a metal chloride of metals such as Fe, Cr and Ni discharged during secondary recovery of acid and an acid pre-recovery means. Metal chlorides, such as Fe, Cr, and Ni, discharged when vacuum distillation is performed. These are Fe, Cr, and Ni as valuable metals by appropriate means.
It is possible to recover a metal such as Ni or use it as a metal oxide or metal chloride.

[0023]

EXAMPLE After mechanically descaling a hot rolled sheet S of SUS430 by shot blasting,
According to the present invention, the pickling waste liquid obtained when the pickling / cutting processing was performed through the three-stage continuous pickling tanks P ₁ , P ₂ , and P ₃ was performed.

FIG. 3 shows a process for treating pickling waste liquid according to the present invention.

The pickling solution in the figure is passed in a cascade flow relative to the steel sheet S, from first pickling tank P ₁ P
50 mg / l of d ²⁺ , 170 g / l of HCl, 80 g / l of cutting metal ions such as Fe, Cr, and Ni dissolved in the pickling process, and the cutting metal is in the form of a metal chloride. Cl liberated during the pickling waste liquid when dissolved in the wash liquid ^- pickling waste liquid containing a concentration of 112 g / l is discharged.

This solution was subjected to a concentration treatment by distillation under reduced pressure, that is, an acid preliminary recovery treatment by distillation under reduced pressure. The distillate obtained contains 220 g / l of HCl.

The distillation residue in the vacuum distillation was subjected to a filtration treatment to remove the precipitates and precipitates of some of the supersaturated metal chlorides such as Fe, Cr and Ni. The filtered precipitate was a metal chloride and was subjected to metal chloride treatment. The filtrate was subjected to vacuum distillation of
The concentration is reduced to 20 g / l and the Pd ²⁺ concentration is 26
2 g / l, dissolved metal ion concentration to 277 g / l, Cl ^- concentration released from metal chlorides to 389
It is contained in a state concentrated to g / liter. The filtrate was passed through an activated carbon adsorption tower to preferentially adsorb Pd ²⁺ . The pickling solution after the adsorption of Pd ²⁺ is treated in a hydrochloric acid recovery facility using a spray medium baking method to recover hydrochloric acid,
Metal oxides of metals such as Fe, Cr, and Ni were recovered as valuable metals.

220 g / l of recovered HCl obtained in the above and 200 g / l of recovered HC obtained in
1 was acid concentrated with an extractive distillation apparatus,
A concentrated HCl solution having an acid concentration increased to 1 g / liter was stored in a storage tank together with new HCl to compensate for the recovery loss.

The concentrated HCl solution in the storage tank was heated to 80 ° C. by a heater, and the solution was backwashed by passing it through an activated carbon packed column adsorbing Pd ²⁺ . The liquid after back washing is Pd
²⁺ is dissolved in HCl solution, and PdCl
₂ , HCl, HNO ₃ and water were added to add 50 mg of Pd ²⁺ .
/ L, HCl and 294 g / l, feeding the HNO ₃ to the third San'araiso P ₃ was prepared in the pickling solution containing a concentration of 10 g / l, the pickling liquid circulation system of fast pickling process is satisfied .

It is to be noted that the activated carbon packed tower has two columns, and by alternately repeating the operation of backwashing at the time of adsorption on the other side, the pickling waste liquid can be continuously treated.

[0031]

According to the present invention, the following effects can be obtained.

(1) A liquid circulation system for high-speed pickling treatment that enables the selective recovery and reuse of precious metal ions in waste liquid by suppressing the contamination of impurities such as Fe, Cr, and Ni. Is completed.

(2) 90% or more of the noble metal ions in the waste liquid can be recovered and reused.

(3) A pickling liquid circulating system is formed that can simultaneously recover high-concentration HCl and recover and reuse precious metal ions, thereby improving the use efficiency of the pickling liquid.

(4) The liquid circulation system is a closed system, and no harmful substances are discharged.

[Brief description of the drawings]

FIG. 1 is a diagram showing a relationship between an acid concentration in a waste liquid and an adsorption rate of a noble metal ion.

FIG. 2 is a view showing a wastewater treatment flow in the method of the present invention.

FIG. 3 is a diagram showing processing steps in which the present invention is implemented.

──────────────────────────────────────────────────続 き Continued on the front page (58) Field surveyed (Int. Cl. ⁷ , DB name) C23G 1/00-3/00

Claims (1)

(57) [Claims] 1. A pickling waste solution in a steel plate pickling process using a hydrochloric acid-based pickling solution or a salt-nitric acid-based pickling solution containing a noble metal catalyst is used as an acid solution by a method such as distillation under reduced pressure or diffusion dialysis. Preliminary removal treatment reduces the acid concentration of the residual solution, then contacts the activated carbon or molecular sieve adsorbent to adsorb the noble metal ions to the adsorbent, and then recovers from the waste liquid after the adsorption treatment When the preliminarily removed hydrochloric acid or the above-mentioned acid is removed, the acid recovered during the preliminary removal treatment or the solution subjected to the concentration treatment is used as a backwash liquid to backwash the adsorbent that has adsorbed the noble metal ions. The noble metal ions are taken out, and the hydrochloric acid solution or the nitric acid solution containing the noble metal ions obtained by this backwashing treatment is reused as the pickling solution after adjusting the components. How to recycle the pickling liquid used.