JP4603495B2 - Alkali recovery method for alkali etching solution - Google Patents

Description

In the alkaline etching treatment of aluminum, when the Al concentration in the etching solution increases, the etching rate decreases and the quality is also adversely affected. The dissolved Al ³⁺ ions combine with an acid to form an anion of AlO ⁻ , and sodium aluminate NaAlO _2.
As it exists in the liquid.
Al + NaOH + H ₂ O → NaAlO ₂ + 3 / 2H ₂
And sodium aluminate hydrolyzes to produce hard Al ₂ O ₃ , which hinders the etching process.
Therefore, it is necessary to remove the production of Al ₂ O ₃ by removing sodium aluminate from the alkaline etching solution. Conventionally, a seed crystal addition method (Buyer method) and a hydrolysis inhibitor addition method have been employed for this purpose.
The former obtains the following reaction by hydrolysis to separate Al.
NaAlO ₂ + 2H ₂ O → NaOH + Al (OH) ₃ (Al ₂ O ₃ )
However, in this method, an excessive apparatus is required and generation of Al ₂ O ₃ is unavoidable, and it is inevitable that Al ₂ O ₃ adheres to the wall and hinders operation.
In the latter case, since Al ₂ O ₃ is not generated, troubles due to Al ₂ O ₃ can be avoided. However, since Al cannot be separated and removed, it is necessary to recycle the etching solution.

An object of the present invention is to solve the following problems in the prior art: (1) Avoid precipitation of alumina (Al ₂ O ₃ ).
(2) It should be possible to process with a small device.
(3) Avoid accumulation of NaCO ₃ and heavy metals.

The present invention introduces an alkaline etching solution of aluminum containing Na into an electrolytic cell, and passes NaAlO ₂ contained in the alkaline etching solution through a two-stage electrodialysis process without producing alumina crystals. (OH) ₃ is separated.

The invention of claim 1 leads to aluminum alkaline etching solution in a first electrolytic bath as a first step, the Na ⁺ were separated on the cathode side through the ion-exchange membrane, OH produced the Na ⁺ in the cathode reaction ^- with Combine to obtain NaOH. Next, as the second step, the anode-side liquid in the first step is supplied to the neutralization tank, and the anolyte of the second electrolytic tank is supplied to the neutralization tank. After the AlO ₂ ⁻ ions in the anolyte are neutralized with H ⁺ ions generated by the anodic reaction in the second electrolytic cell to separate Al ₃ ⁺ ions as Al (OH) ₃ , this solution is subjected to second electrolysis. led to the bath, a Na ⁺ were separated on the cathode side through the ion-exchange membrane, the Na ⁺ and OH produced by the cathodic reaction ^- be coupled with obtaining NaOH.
Through the above steps, NaAlO ₂ contained in the etching solution is separated into NaOH and Al (OH) ₃ without generating alumina or heavy metal, and these can be recovered. And since Al (OH) ₃ is produced | generated and discharged | emitted by the said neutralization tank, Al (OH) ₃ does not produce | generate in an electrolytic cell.
In the invention of claim 2, the treatment liquid in the neutralization tank is introduced to the anode side of the second electrolysis tank and led to the cathode side of the first electrolysis tank.
In the invention of claim 3, the pH of the anolyte is adjusted to pH 10 or more in the first step and from 2 to 8 in the second step. The pH is adjusted by checking the pH of each electrolytic cell as needed, adding an etching solution to the first electrolytic cell as appropriate, and adding the anolyte of the first electrolytic cell to the second electrolytic cell.
If the pH is maintained at 2 or more and 8 or less, NaAlO ₂ is hydrolyzed and separated as Al (OH) ₃ , so that it is not substantially mixed into the second electrolytic cell.

Claim 4 relates to an apparatus for carrying out the method of claims 1 to 3.
The apparatus of this invention comprises a first electrolytic cell equipped with an ion exchange membrane, a second electrolytic cell equipped with an ion exchange membrane, and a neutralization tank. An alkaline etching solution inflow pipe and an outflow pipe to the neutralization tank are connected to the anode side of the first electrolysis tank, and a recovery alkali recovery pipe is connected to the cathode side of the first electrode tank. The sump tank is connected to the outflow pipe of the first electrolysis tank and the outflow pipe connected to the anode side of the second electrolysis tank, and the neutralization tank is connected to the outflow pipe of the liquid in the neutralization tank. The tip of the tube is connected to the anode side of the second electrolytic cell, and a recovery alkali recovery tube is connected to the cathode side of the second electrolytic cell to constitute an alkali recovery device for alkali etching solution.

In the first aspect of the present invention, when an alkali etching solution of aluminum is introduced into the first electrolytic cell as the first step, the reaction of the formula (1) is obtained at the anode, and the reaction of the formula (2) is obtained at the cathode.
Equation ^{(1) NaOH - e - →} Na + + 1 / 4O 2 + 1 / 2H 2 O
Formula (2) H ₂ O + e ⁻ → 1 / 2H ₂ + OH ⁻
Then, when Na ⁺ obtained by the anodic reaction is separated to the cathode side through the ion exchange membrane, the Na ⁺ is combined with OH ⁻ produced by the cathodic reaction to produce NaOH, and O 2 and H 2 are separated as gas. The Therefore, alkali (NaOH) can be recovered by recovering the catholyte.

Then as a second step, the anolyte is supplied to the neutralization tank in the first step, together with the alkali etching solution in the neutralization tank to supply the anolyte in the second electrolytic bath to the neutralizing bath AlO ₂ ^- neutralized with ^{H +} ions generated ions at the anode reaction of the second electrolytic cell for separating the _Al ^{3 +} ions as Al _{(OH) 3.} This reaction is as shown in Formula (3).
Formula (3) NaAlO ₂ + H ₂ O + H + → Na + Al (OH) ₃
After the Al (OH) ₃ is separated and discharged, this liquid is guided to the second electrolytic cell.
The anodic reaction in the second electrolytic cell is as shown in formula (4), and the cathodic reaction is as shown in formula (5).
Formula (4) 1 / 2H ₂ O−e ⁻ → H ⁺ + 1 / 4O ₂
Formula (5) H ₂ O + e ⁻ → 1 / 2H ₂ + OH ⁻
Here, the introduction of process water in the neutralization tank containing Na ^+, Na ⁺ is separated into the cathode side through the ion-exchange membrane, wherein the Na ⁺ is OH generated at the cathode reaction ^- generation NaOH combined with Is done.
Through the above steps, NaAlO ₂ contained in the etching solution is separated into NaOH and Al (OH) ₃ without generating alumina or accumulating heavy metals, and these can be recovered. In particular, Al (OH) ₃ is produced only in the neutralization tank and separated and discharged from the neutralization tank, so that Al (OH) ₃ is not produced in the electrolytic cell.

In the invention of claim 2, the treatment liquid in the neutralization tank is introduced to the anode side of the second electrolysis tank and led to the cathode side of the first electrolysis tank.
This operation balances both the amount of water in the etching solution and [water in the recovered alkali + water in the coagulated and precipitated Al (OH) ₃ + surplus water], and Na can be completely recovered.

In the invention of claim 3, the pH of the anolyte is adjusted to pH 10 or more in the first step and from 2 to 8 in the second step.
The pH of the electrolytic cell gradually decreases as H ⁺ is generated at the anode. However, the higher the pH, the better the current efficiency of the anodic reaction, and when the pH drops to 2 or less, the current efficiency rapidly decreases and the power consumption increases. The pH of the alkaline etching solution is about 13 to 14, but gradually decreases due to electrolysis.
In the invention of claim 3, since the pH of the anolyte in the first electrolytic cell is maintained at 10 or more and the pH of the anolyte in the second electrolytic cell is also maintained at 2 or more and 8 or less, the anodic reaction is performed relatively efficiently. be able to.
The reason for maintaining the pH between 2 and 8 is
NaAlO ₂ + 2H ₂ O → NaOH + Al (OH) ₃
This is because the reaction is not completed unless the pH is 8 or less, whereas when the pH is 2 or less, H ⁺ moves to the cathode side through the ion-exchange membrane and lowers the current efficiency. In addition, at pH 2 or lower, Al in AlO ₂ ⁻ or AL (OH) ₃ is dissolved as Al ₃ ⁺ and the oxidation potential is increased.

FIG. 1 is a schematic view of an apparatus for performing the first step.
An anode electrode 3 and a cathode electrode 4 are attached to the first electrolytic cell 1 across the ion exchange membrane 2.
An alkaline etching solution inflow pipe 5 and a neutralization tank 6 outflow pipe 7 (see FIG. 2) are connected to the anode side of the first electrolytic cell 1, and an alkali recovery pipe 8 and a first electrode are connected to the cathode side. A return pipe 10 from the second electrolytic cell 9 is connected.

FIG. 2 is a schematic view of an apparatus for performing the second step.
An anode electrode 12 and a cathode electrode 13 are attached to the second electrolytic cell 9 with an ion exchange membrane 11 therebetween.
The neutralization tank 6 is connected to the discharge pipe 7 and the outflow pipe 14 to the second electrolytic tank 9, and is provided with an outlet 15 for Al (OH) ₃ . The outflow pipe 14 is connected to the anode side of the second electrolytic cell 9, and the return pipe 10 to the first electrolytic cell 1 is connected to the outflow pipe 14.
An outflow pipe 16 is connected to the anode side of the second electrolytic cell 9, and the other end of the outflow pipe 16 is connected to the outflow pipe 7 of the first electrolytic cell 9. An alkali recovery tube 17 is connected to the cathode side of the second electrolytic cell 9.

  In the above apparatus, the basic flow of the alkaline etching solution is the inflow pipe 5, the first electrolytic tank 1, the outflow pipe 7, the neutralization tank 6, the outflow pipe 14, and the second electrolytic tank 9. A part of the anolyte in the second electrolytic cell 9 flows to the neutralizing cell 6 through the outflow pipe 16 and is mixed with the anolyte in the first electrolytic cell 0 here.

The alkaline etchant used for the aluminum etching process contains NaOH and Al. When this liquid is introduced into the first electrolytic cell, NaOH is electrolyzed at the anode to separate Na ⁺ and move to the cathode side. Since this and OH ⁻ produced by the cathodic reaction combine to produce highly pure NaOH, the alkali in the alkaline etching solution can be collected by collecting the catholyte. See formulas (1) and (2) above.

  In the electrolysis in the first electrolytic cell 1, the pH of the anolyte is measured at any time and the pH is maintained at 10 or more. Therefore, when the pH may be lowered to 10 or less, an alkaline etching solution having a high pH (usually 13-14) is supplied from the inflow pipe 5 to the first electrolytic cell 1 to maintain the pH at 10 or more. Maintain high efficiency, maintain processing speed and reduce power consumption.

Since the Al component is contained in the anolyte, the anolyte is introduced into the neutralization tank 6 from the outflow pipe 7. At the same time, the anolyte in the second electrolytic cell 9 is introduced from the outflow pipe 16 into the neutralization cell 6.
In the neutralization tank 6, NaAlO ₂ contained in the influent from the first electrolytic tank reacts with H + contained in the anolyte of the second electrolytic tank 9 to produce Na ⁺ and Al (OH) _3. Therefore, Al (OH) ₃ is discharged from the discharge port 15.
By this treatment, the Al component is removed from the alkaline etching liquid in the neutralization tank 6, and the treatment liquid supplied to the second electrolytic tank 9 does not contain the Al component.

In the electrolysis in the second electrolytic cell 9, OH ⁻ is generated by the cathode reaction. And the process liquid supplied from the said neutralization tank contains Na ^<+> . Therefore, high-purity NaOH is generated on the cathode side, and this is recovered from the recovery tube 17.
Through the above treatment, the Al component contained in the used alkaline etching solution can be completely recovered, and the alkali (Na) can be recovered as NaOH.

  In the electrolysis in the second electrolytic cell 9, the pH of the anolyte is measured as needed, and the pH is maintained at 2 or more. Therefore, when there is a possibility that the pH may be lowered to 2 or less, supply the first electrolytic cell anolyte overflow with high pH (actually overflow from the gas-liquid separator) to the anode side of the second electrolytic cell 9, The pH is maintained at 2 or more, current efficiency is maintained high, processing speed is maintained, and power consumption is reduced.

560 ml of alkaline etching solution containing 79.6 g / l of total NaOH and 20 g / l of Al per hour was treated in a two-stage electrolytic apparatus using a cation exchange membrane as a diaphragm.
In the first electrolysis step, the battery was operated at a current density of 10 A / dm2, and the anolyte pH was adjusted to 10-11. In the second electrolysis step, the battery was operated at a current density of 5 A / dm 2 and the anolyte pH was maintained at 2-8. The anolyte and overflow from the first electrolytic cell anolyte gas-liquid separator were mixed in a neutralization tank to coagulate and separate Al (OH) ₃ , and the supernatant was supplied as the anolyte to the second electrolytic tank. As a result, 480 ml / hour of total NaOH 92 g / l and Al 4 g / l of NaOH solution were recovered from the first and second electrolytic cells. Further, the aggregate liquid from which Al was separated and recovered as Al (OH) ₃ was 80 ml / hour and the Al concentration was 116 g / l.
(Note: Al in the NaOH recovery solution is probably due to experimental problems.

In the same manner as in Example 1, 360 ml of alkaline etching solution containing 32 g / l of total NaOH and 15 g / l of Al was treated in a two-stage electrolytic apparatus using a cation exchange membrane as a diaphragm.
In the first electrolysis step, the battery was operated at a current density of 1.3 A / dm2, and the anolyte pH was adjusted to 10-11. In the second electrolysis step, the battery was operated at a current density of 2.4 A / dm2, and the anolyte pH was maintained at 2-8. The anolyte and overflow from the first electrolytic cell anolyte gas-liquid separator were mixed in a neutralization tank to coagulate and separate Al (OH) ₃ , and the supernatant was supplied as the anolyte to the second electrolytic tank. As a result, an NaOH solution of 320 ml / hour, total NaOH 34 g / l, and Al 4 g / l was recovered from the first and second electrolytic cells. Further, the aggregate liquid from which Al was separated and recovered as Al (OH) ₃ was 40 ml per hour and the Al concentration was 100 g / l.
(Note: Al in the NaOH recovery solution is probably due to experimental problems.)

  According to the present invention, the Al component contained in the used alkaline etching solution can be completely recovered with a simple apparatus, and the alkali (Na) can be recovered as NaOH. It has availability.

The figure which shows the 1st process of this invention Example Figure showing the second step

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 1st electrolysis tank 2 Ion exchange membrane 3 Anode electrode 4 Cathode electrode 5 Inflow pipe 6 Neutralization tank 7 Outflow pipe 8 Recovery pipe 9 Second electrolysis tank 10 Return pipe 11 Ion exchange membrane 12 Anode electrode 13 Cathode electrode 14 Outflow pipe 15 Discharge port 16 Outflow pipe 17 Recovery pipe

Claims (4)

A first step of introducing an alkaline etching solution of aluminum into a first electrolytic cell, separating Na ⁺ to the cathode side through an ion exchange membrane, and combining the Na ⁺ with OH ⁻ generated by a cathode reaction to obtain NaOH;
Said anolyte is supplied to the neutralization tank in the first step, together with the second in the electrolytic cell anolyte neutralization tank is supplied to the neutralization tank of the first electrolytic bath in the anolyte AlO ₂ ^- ions Is neutralized with H ⁺ ions generated by the anodic reaction of the second electrolytic cell to separate Al ₃ ⁺ ions as Al (OH) ₃ , and then the liquid in the neutralizing cell is supplied to the second electrolytic cell, A method for recovering an alkali of an alkali etching solution, comprising a second step of separating Na ⁺ to the cathode side through an ion exchange membrane and combining the Na ⁺ with OH ⁻ generated by a cathode reaction to obtain NaOH. The liquid on the anode side in the first electrolytic cell and the liquid on the anode side in the second electrolytic cell mixed for neutralization are led to the cathode side of the first electrolytic cell in addition to the anode side of the second electrolytic cell. The alkali recovery method of the alkali etching liquid according to claim 1 The method for recovering an alkali of an alkali etching solution according to claim 1 or 2, wherein the pH of the anolyte is maintained at a pH of 10 or more in the first electrolytic cell and from 2 to 8 in the second electrolytic cell. A first electrolytic cell equipped with an ion exchange membrane, a second electrolytic cell equipped with an ion exchange membrane, and a neutralization tank,
On the anode side of the first electrolysis tank, an alkaline etchant inflow pipe and an outflow pipe to the neutralization tank are connected,
A recovery pipe for recovery alkali is connected to the cathode side of the first electrode tank, and an outflow pipe connected to the anode side of the first electrolysis tank and the second electrolysis tank is connected to the neutralization tank,
The neutralization tank is connected to an outflow pipe for the liquid in the neutralization tank, and the tip of the outflow pipe is connected to the anode side of the second electrolytic tank,
A recovery alkali recovery tube was connected to the cathode side of the second electrolytic cell,
Alkali recovery device for alkali etching solution

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