JP2949545B2 - Treatment and recovery of metal surface treatment waste acid - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for treating and recovering metal surface treatment waste acid.

[0002]

2. Description of the Related Art Conventionally, for a surface treatment such as pickling and etching of ordinary steel, stainless steel and aluminum materials, a single acid or a mixed acid of a volatile acid such as hydrochloric acid or nitric acid is required. It is used with a small amount of sulfuric acid added.

[0003] The waste acid discharged from the above metal surface treatment step contains a free acid of a volatile acid and a metal salt thereof such as iron chloride (aluminum chloride) and iron nitrate (aluminum nitrate). ing.

As a method for treating and recovering such waste acid, application of a distillation method can be considered. For example, in the case of hydrochloric acid waste acid,
HCl has a high specific volatility, so it is easy to distill out as a vapor.In particular, since the solubility of the metal salt contained in the waste acid is high, and in a highly concentrated metal salt solution, the specific volatility of HCl is further increased, the distillation is carried out. HC in mother liquor remaining in the can
1 concentration is very low, and most of the HCl can be distilled and recovered. Also, in the case of nitric acid waste acid, HNO ₃ is not as high as HCl, but has a relatively high specific volatility, and the solubility of metal salts is extremely high as in the case of hydrochloric acid.
O ₃ can be distilled and collected.

However, in the case of hydrochloric acid and nitric acid waste acids, only the free acid can be treated and recovered by the distillation method, and it is difficult to recover the volatile acid component existing as a metal salt.

[0006] Such waste acid is subjected to a dialysis treatment using an ion exchange membrane, for example, an anion exchange membrane (hereinafter referred to as AM).
Recovery treatment can be carried out using a diffusion dialysis device (hereinafter, referred to as DD device) using an electrodialysis device (hereinafter, referred to as ED device) using AM and a cation exchange membrane (hereinafter, referred to as CM). .

For example, the waste acid for etching aluminum foil with nitric acid is an aqueous solution containing free HNO ₃ and Al (NO ₃ ) ₃ , and if this is treated with a DD device, the free HNO ₃ in the waste acid is reduced to AM. can be recovered because it transmits, but Al (nO ₃₎ nO ₃ ^1- min ₃ without being recovered as HNO _3, mixed partially in the recovered acid to reverse as Al (nO _{3) 3.} This is because although the dialysis coefficient of Al (NO ₃ ) ₃ is smaller than that of HNO ₃ , it is only on the order of several tenths, and the contamination cannot be completely prevented.

In an ED device, HNO ₃ is

[0009]

(Equation 1)

H ¹⁺ is transferred to the cathode side and N 1
O ₃ ^1- moves to the anode side and alternately joined CM and AM
Permeates to the fresh water side that passes through the gap and is recovered as HNO ₃ . However, Al (NO ₃ ) ₃ salt is theoretically

[0011]

(Equation 2)

[0012] Although the ionization as a weak electrolyte, since ionization degree is small and most largely exist remains Al (NO _{3) 3,} thus being recovered as HNO ₃ is initially present free Most of the HNO ₃ is Al (NO
₃₎ NO from _{3 3} ¹ it is hardly recovered as HNO _3.

[0013] In short, the waste acid is converted to a DD device or E
In the case of treatment and recovery using the D apparatus, only the free volatile acid can be recovered in the same manner as in the distillation method, and not only those that are present as metal salts cannot be recovered, but also metal ions are considerably entrained in the recovered acid. Therefore, there is a problem that the purity of the recovered acid hinders reuse, and the use of dialysis treatment is limited.

Incidentally, the hydrochloric acid waste previously proposed by the present applicants has been proposed.
Liquid recovery treatment method (for example, see Japanese Patent Publication No. 50-8719)
According to the reference, the hydrochloric acid present as a metal salt is also recovered.
However, in the above recovery method, waste hydrochloric acid is directly
Metal salts in waste acid by feeding sulfuric acid to distillation vessel where sulfuric acid is added
, So that a large amount of sulfate
Is formed, and this sulfate is deposited as crystals.
The need for solid-liquid separation arises. For example, the sulfate that precipitates
In the case of monohydrate, the liquid removal rate during solid-liquid separation depends on the separation means.
However, it is usually about 15 to 30% by weight,
Is large and impractical. The present invention has been made to further solve such a conventional problem.

[0015]

SUMMARY OF THE INVENTION The present invention relates to a method for treating and recovering a volatile acid such as hydrochloric acid or nitric acid and a metal surface treatment waste acid containing a metal salt thereof, wherein the waste acid is dissolved in the waste acid. For the metal, by adding an amount of sulfuric acid in excess of the reaction equivalent and dialyzing the metal salt dissolved in the waste acid with an ion exchange membrane while performing double decomposition, the volatile acid is recovered from the waste acid, A step of recovering the dialysis waste liquid as a sulfate-based solution, adding sulfuric acid to the recovered acid from the above step, and performing distillation while maintaining the sulfuric acid concentration at 25 to 60%, so that the recovered acid is more volatile than the recovered acid. A step of distilling and recovering an acid, and a step of supplying a bottom of a distillation still having a sulfuric acid concentration of 25 to 60% into waste acid which is subjected to dialysis treatment with an ion exchange membrane for metal salt metathesis. Treatment and recovery method of metal surface treatment waste acid characterized by That.

The metal surface treatment waste acid to be treated and recovered according to the present invention contains a free volatile acid and its metal salt as described above. Examples of the kind of the waste acid include hydrochloric acid-based waste acid, nitric acid-based waste acid, and mixed acid-based waste acid such as these, and examples of the metal that forms a salt with the volatile acid such as these include iron or aluminum. In addition, a small amount of sulfuric acid may be added to these volatile acids for the aluminum etching treatment. However, in the present invention, sulfuric acid is added to the waste acid as described below. There is no particular problem even if a small amount of free sulfuric acid or its metal salt is contained therein. In addition, depending on the waste acid, a rare volatile acid may be contained in a high concentration, for example, 10% or more. In such a case, the dialysis means using an ion exchange membrane is required before the treatment and recovery by the method of the present invention. For example, a DD device may be applied to recover some of the free volatile acid in advance.

In treating and recovering the waste acid by applying the method of the present invention, first, sulfuric acid is added to the waste acid so that the amount of the metal dissolved in the waste acid is slightly larger than the reaction equivalent. Is done.

By performing dialysis while adding excess sulfuric acid, substantially all of the metal salts dissolved in the waste acid are metathesized and converted into sulfates and volatile acids. Dialysis treatment, for example, by applying a DD device and / or an ED device, the volatile acid originally existing in a free state in the waste acid as well as the volatile acid existing as a metal salt can be removed. Can be collected well.

For example, nitric acid aluminum foil etching waste acid includes an aqueous solution containing HNO ₃ and Al (NO ₃ ) _{3. When an} excess of H ₂ SO ₄ is added to the reaction equivalent of Al,

[0020]

(Equation 3)

As described above, HNO ₃ is liberated.
When this is processed by a DD apparatus, the generated HNO ₃ is immediately permeated through the AM, and this reaction, combined with the presence of excess H ₂ SO ₄ , leads to an irreversible reaction in which the rightward reaction is dominant, and the original free HNO 3 ₃ as well as Al (NO
_{3) 3} NO in the salt ₃ ¹ is also recovered as HNO _3. At this time, a part of Al ₂ (SO ₄ ) ₃ is dialyzed into the recovered acid and mixed as impurities as in the case of Al (NO ₃ ) ₃ described as the conventional method.

In an ED device, HNO ₃ generated by the addition of H ₂ SO ₄ is immediately

[0023]

(Equation 4)

To the free H which originally existed
Like NO ₃ , HNO passes through AM and CM respectively.
Recovered as ₃ . As a result, the reaction of the above formula (1) becomes an irreversible reaction in which the rightward reaction is dominant, and
NO ₃ ¹⁻ in (NO ₃ ) ₃ is also recovered as HNO ₃ . On the contrary, the excess amount of added H ₂ SO ₄ is temporarily

[0025]

(Equation 5)

[0026] Although the ionization as, SO ₄ ion is the same anion, dialysis coefficient compared to NO ₃ ^1-small but a small amount dialysis contamination.

If the amount of sulfuric acid used in the above substitution reaction is too large, the amount of unreacted H ₂ SO ₄ mixed into the recovered acid increases.
It is suitably from about 0.5 to 1.40, particularly about 1.1 to 1.2 equivalents.

As described above, sulfuric acid is added to the waste acid in an amount equal to or more than the equivalent of the metal dissolved in the waste acid, preferably 1.1 to 1.2 equivalents, and the treatment is performed in the DD apparatus and / or the ED apparatus. By doing so, it is possible to recover almost all the volatile acid originally present in the waste acid in a free state, as well as most of the volatile acid which has been bonded to the metal to form a metal salt.

On the other hand, the dialysis waste liquid contains a small amount of H ₂ SO _{4 and a} volatile acid component, but is a solution mainly composed of a sulfate. For example, in the case of an aluminum-based acid, it is further concentrated to obtain a liquid useful as a flocculant. Sulfuric acid band [Al ₂ (SO ₄ ) ₃ ]
Available as In the case of an iron-based waste acid, FeSO ₄ .7H ₂ O can be effectively used by by-producing FeSO ₄ .7H ₂ O by cooling crystallization.

As described above, in addition to the volatile acid, the recovered acid recovered by the dialysis treatment of the ion exchange membrane contains a small amount of SO ₄ ²⁻ and a metal component. It is not suitable in terms of purity for reuse. Therefore, in the present invention, the recovered acid is purified by distillation.

In the present invention, distillation of the recovered acid is performed while maintaining the sulfuric acid concentration in the distillation still at 25 to 60%.

[0032] Figure 1 is H ₂ O, the gas-liquid equilibrium diagram of a three-component system containing H ₂ SO ₄ and HNO _3, and FIG. 2 H ₂ O, H
The vapor-liquid equilibrium diagrams of the ternary system containing ₂ SO ₄ and HCl are shown respectively.

As is clear from FIGS. 1 and 2, the recovered acid is distilled while maintaining the sulfuric acid concentration in the distillation can at 25 to 60%, preferably 40 to 50%, so that it remains in the distillation can. The distillation treatment can be performed while the concentration of the volatile acid is kept low while the concentration of the distillate recovered acid is increased.
By the way, when the sulfuric acid concentration in the distillation still does not reach 25%, the ratio of volatile acid remaining in the distillation can becomes high, and 60%.
%, There is a problem that a large amount of sulfate precipitates in the distillation still, and neither is preferable.

The recovered acid recovered by the dialysis with the ion exchange membrane is subjected to a sulfuric acid concentration of 25-60% in the distillation still.
By performing distillation while maintaining the pH, volatile acids having high purity and high concentration can be distilled and recovered.

Since the mother liquor in the distillation still contains a large amount of free sulfuric acid in addition to the sulfate, a part of the mother liquor is supplied to the waste acid before being subjected to the dialysis treatment by the ion exchange membrane, and the metal in the waste acid is supplied. It is used as sulfuric acid for metathetically decomposing the salt, and this has the effect of preventing the accumulation of sulfate in the distillation still. Since the added sulfuric acid is consumed for the production of sulfate, it is necessary to supply sulfuric acid in an equivalent amount or more as fresh sulfuric acid.

In the treatment and recovery method of the present invention, sulfuric acid is used to maintain a predetermined concentration of sulfuric acid in the distillation vessel and to distill out a high concentration of volatile acid, and then, together with the waste acid, an ion exchange membrane dialysis apparatus. And is used to metathesize the metal salts in the waste acid to produce free volatile acids and valuable sulphates.

Examples will be described below.

[0038]

EXAMPLE The method of the present invention was carried out based on the flowchart shown in FIG. Tables 1 and 2 show the results. Table 1 shows the case of hydrochloric acid waste acid, and Table 2 shows the case of nitric acid waste acid. In FIG. 3, symbols (1) to (9) are assigned to key points of each line, and the liquid amount and liquid composition of each key point are as shown in Tables 1 and 2.

[0039]

[Table 1]

[0040]

[Table 2]

According to the treatment and recovery method of the present invention, as is apparent from Table 1, the hydrochloric acid-based waste acid 1 and 18 containing 18% of T.HCl was used.
1524 kg / h of high-purity hydrochloric acid of 13.3% from 00 kg / h can be recovered.

As apparent from Table 2, 10.2%
From 931 kg / h of nitric acid waste acid containing T.HNO ₃ to 7.5
% High-purity nitric acid 1065.5 kg / h can be recovered.

[0043]

According to the present invention, the volatile acid contained in the metal surface treatment waste liquid is released,
Most of the metals, including volatile acids that are combined with metals to form metal salts, can be effectively recovered with high-purity volatile acids, and metals dissolved in waste acids, for example, Al, Fe
And the like can be recovered in the form of sulfate having high utility value. Furthermore, metals dissolved in waste acid can be added to sulfuric acid.
Sulphate mainly by dialysis treatment
Separately collected as a solution (dialysis waste liquid)
The distillation process is substantially free of sulfates
Can be carried out in a state, without depositing sulfate
Therefore, metal surface treatment wastewater is eliminated without the need for a solid-liquid separation process.
, High-purity volatile acid can be recovered.

[Brief description of the drawings]

FIG. 1 is a vapor-liquid equilibrium diagram of a ternary system containing HNO ₃ .

FIG. 2 is a vapor-liquid equilibrium diagram of a ternary system containing HCl.

FIG. 3 is a flowchart schematically showing one embodiment of the present invention.

──────────────────────────────────────────────────の Continued on the front page (72) Inventor Susumu Kamiya, 1006 Kadoma Kadoma, Osaka Prefecture Inside Matsushita Electric Industrial Co., Ltd. (72) Inventor Nobuyoshi Kanzaki 1006 Odaka Kadoma, Kadoma City Osaka In-house (56) References JP 50-8719 (JP, B1) (58) Fields investigated (Int. Cl. ⁶ , DB name) C23G 1/36 C23F 1/16 C23F 1/46 C23G 1/02

Claims (1)

(57) [Claims] 1. A method for treating and recovering a volatile acid such as hydrochloric acid, nitric acid and the like and a metal surface treatment waste acid containing a metal salt thereof, wherein the amount of the metal exceeds the reaction equivalent with respect to the metal dissolved in the waste acid. The sulfuric acid is added and the metal salt dissolved in the waste acid is double-decomposed and dialyzed by an ion exchange membrane to recover the volatile acid from the waste acid. A recovering step, a step of distilling and recovering a volatile acid from the recovered acid by adding sulfuric acid to the recovered acid from the above step, and performing a distillation treatment while maintaining the sulfuric acid concentration at 25 to 60%; and Supplying the distillate bottoms having a sulfuric acid concentration of 25 to 60% into waste acid dialyzed by an ion exchange membrane for metal salt metathesis. Treatment collection method.