JPS60264314A - Method for concentrating phosphoric acid or nitric acid - Google Patents

Abstract

PURPOSE:To concentrate effectively phosphoric acid or nitric acid or an aqueous solution containing the acid, by neutralizing the aqueous solution containing the phosphoric acid or nitric acid with an alkali, concentrating the resultant salt in a reverse osmosis membrane apparatus, and electrolyzing the concentrate with an ion exchange membrane. CONSTITUTION:A washing waste liquor 1 containing phosphoric acid or nitric acid for etching is neutralized with an alkali 2, and the resultant neutralized water 4 is then stored in a holding tank 5. The neutralized water 4 is passed through a high-pressure pump 6 and reverse osmosis membrane apparatuses 7 and 7' in two stages to give permeated water 9' utilizable as washing water. Unpermeated water 8 and 8' containing concentrated phosphates or nitrates is circulated through the holding tank 5 at the same time. The concentrate in the holding tank 5 is then fed to an intermediate chamber (N) of an electrolytic cell 10 divided with a cation exchange membrane 12 and an anion exchange membrane 13, and a current is passed across a cathode 16 and an anode 20 while circulating an alkali 2' through a cathodic compartment (A) and dilute phosphoric acid or nitric acid through an anodic compartment (K) to carry out the electrolysis. Thus, the alkali 2 is obtained from the cathodic compartment (A) and used for neutralization, and phosphoric acid or nitric acid 21 in a high concentration is obtained from the anodic compartment (K).

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method of concentrating an aqueous solution containing phosphoric acid or nitric acid to obtain highly concentrated phosphoric acid or nitric acid. Cleaning wastewater containing acid, nitric acid, and nitric acid.

The purpose is to recover nitric acid at a high concentration.

The aluminum foil electrolytic capacitor manufacturing process involves degreasing the aluminum foil using a strong alkali, and then cleaning with mineral acids such as hydrochloric acid, sulfuric acid, nitric acid, and phosphoric acid as etching to remove impurities on the surface of the aluminum foil. There is.

”Double etching involves sequential immersion in one or more types of mineral acids, but it is a rinsing process in which rinsing with pure water, etc. is always performed after the bath tank in which each immersion is performed in a different type of mineral acid. have.

From these water washing processes, the various mineral acids mentioned above are
Washing wastewater containing about 0 ppm is discharged.

In the case of hydrochloric acid or sulfuric acid, there is no particular problem in discharging it as long as it is neutralized.

However, recently, the death of fish and shellfish due to abnormal algal blooms in lakes and closed sea areas has become a social problem.The cause is said to be due to nitrogen, phosphorus, etc. contained in domestic sewage, industrial wastewater, etc. In the case of the aforementioned phosphoric acid or nitric acid, it is not preferable to discharge it only after neutralizing it.

Physicochemical methods and biological methods have been used to remove nitrogen or phosphorus, but nitrate ions must be removed by biological methods. However, the removal of nitrate ions by biological methods requires consideration of addition of alkalinity and nutrient source (BOD), etc. Furthermore, it is also necessary to treat excess sludge, and the treatment is complicated and not economical. I can't say it's a method.

On the other hand, phosphoric acid has been determined by biological methods to some extent.
Although it can be removed, 9 it is generally removed by a physicochemical method that adds calcium salt and removes it as an insoluble precipitate.

The present inventors have developed a method other than the biological method or the precipitation removal method to treat the cleaning wastewater containing a small amount of phosphoric acid or nitric acid.

For example, we have considered concentrating the acid and recovering it using ion exchange methods, reverse osmosis membrane methods, etc.; Moreover, the concentration of the acid that could be recovered was relatively low, making it impossible to implement it industrially.

On the other hand, in the reverse osmosis membrane method, when phosphoric acid and nitric acid are concentrated, the pH on the concentrated side becomes extremely low, below 1, so an acid-resistant reverse osmosis membrane is required. - or NO3-, the hydrogen ion diameter under pressure is the minimum ion diameter of 0.52 angstroms (Stokes diameter), so it will pass through any reverse osmosis membrane, and the phosphate ion will pass through any reverse osmosis membrane. , nitrate ions, etc. also permeate, so the rejection rate (ion concentration in permeated water/ion concentration in raw water X], OO) is
The problem was that the treatment was incomplete.

Therefore, by neutralizing phosphoric acid or nitric acid in cleaning wastewater with an alkali and treating the phosphoric acid or nitric acid in salt form with a reverse osmosis membrane device, phosphate ions and nitrate ions can be effectively concentrated. , and there is no problem in concentrating phosphate ions and nitrate ions without using an acid-resistant reverse osmosis membrane. However, with this processing method #
The resulting concentrate is an aqueous solution of phosphate or nitrate, and cannot achieve the objective of the present invention of recovering it as an acid.

In view of this, the present inventors have developed an effective method for converting aqueous solutions containing phosphoric acid or nitric acid by skillfully combining salt concentration using a reverse osmosis membrane device and salt decomposition using an electrolytic cell using an ion exchange membrane. It was discovered that it is possible to concentrate highly concentrated phosphoric acid and nitric acid.

That is, in the present invention, when concentrating an aqueous solution containing phosphoric acid or nitric acid to obtain highly concentrated phosphoric acid or nitric acid, by adding an alkali to the aqueous solution and neutralizing it, phosphoric acid or nitric acid can be converted to phosphoric acid or nitric acid. The neutralized solution is treated with a reverse osmosis membrane device to concentrate the salt, and then the concentrated solution is electrolyzed in an electrolytic cell using an ion exchange membrane to form a highly concentrated phosphoric acid or nitrate. The present invention relates to a method for concentrating phosphoric acid or nitric acid, which is characterized by recovering nitric acid.

The present invention will be described below with reference to one drawing, using washing wastewater containing phosphoric acid as an example.

First, an alkali 2 such as sodium hydroxide or aqueous ammonia is added to a cleaning waste water 1 containing about 100 to 500 ppm of phosphoric acid using an injection pump 3 to neutralize it, and the neutralized water 4 is stored in a retention tank 5 .

Next, the high-pressure pump 6 is driven to supply the neutralized water 4 under pressure to the reverse osmosis membrane device 7 to obtain non-permeated water 8 in which phosphate is concentrated, and the non-permeated water 8 is transferred to the retention tank 5. circulate. On the other hand, the permeate water 9 is further supplied under pressure to the reverse osmosis membrane device 7' to concentrate residual phosphates contained in the permeate water 9, and the non-permeate water 8' is sent to the retention tank 5 in the same way. circulate to.

In addition, the permeated water 9' obtained from the reverse osmosis membrane device 7' has 96 to 99% or more of the phosphates in the washing waste water 1 removed,
Therefore, it can be reused as rinsing water for etching processes, etc.

The supply pressure of the liquid to be treated to the reverse osmosis membrane device 7 is 10 to 50k.
The product is preferably a 20 to 30 kglt product, and the amount of water to be supplied and the amount of circulating water may be appropriately determined while taking into account the ion concentrations in the permeated water 9 and non-permeated water 8.

Cellulose acetate, aromatic polyamide, polyetheramide, and polyester crosslinked membranes are commercially available as reverse osmosis membranes.9 The reverse osmosis membrane used in the present invention can be used in a wide pH range and has excellent resistance to bacteria and oxidation. There is no limitation in selecting a particular membrane as long as it is suitable.

In the present invention, the phosphate in the reverse osmosis membrane device 7 is: 1. Condensed, stagnated, and neutralized in the tank 5. 2. There are two methods, such as a method of concentrating with a switch method, and a method of continuously concentrating by supplying neutralized water 4 corresponding to the flow rate of permeated water 9' to the retention tank 5.
You can choose depending on the situation.

Further, in the drawing, two reverse osmosis membrane devices 7 are used in a series, but the invention is not limited to this, and one or more reverse osmosis membrane devices 7 can be used in series depending on the phosphoric acid concentration in the washing wastewater. In addition, phosphoric acid is efficiently recovered in the subsequent electrolytic cell.The concentrated solution, which has been enriched in silicate concentration by the reverse osmosis membrane treatment as described above, is then electrolyzed in the electrolytic cell 10 to obtain phosphoric acid.

That is, the concentrated liquid in the retention tank 5 is circulated through the intermediate chamber N separated by the cation exchange membrane 12 and anion exchange membrane 13 by driving the first circulation pump 11, while it is stored in the alkaline tank 14 in advance. The second circulation pump 15 is driven with an alkali 2' such as aqueous soda or aqueous ammonia.

The liquid is circulated through a cathode chamber A which is separated by a cation exchange membrane 12 and has a cathode 16. Furthermore, dilute phosphoric acid stored in the phosphoric acid tank 17 in advance is transferred to the third circulation pump 1.
9 is driven to circulate the liquid through an anode chamber K which is separated by an anion exchange membrane 13 and has an anode 20.

Each of these liquids is circulated through the cathode 16 and the anode 20.
When a current is passed through, the following electrolysis occurs.

That is, the phosphate ions in the intermediate chamber N are attracted to the anode 20, pass through the anion exchange membrane 13, and move to the anode chamber K, and the cations constituting the phosphate, for example, when the phosphate is sodium phosphate, is a sodium ion, and if the phosphate is ammonium phosphate, an ammonium ion is
It is attracted by the cathode 16, passes through the cation exchange membrane 12, and moves to the cathode chamber A.

Corresponding to the amount of phosphate ions and cations transferred from the intermediate chamber N, oxygen gas is generated and the phosphoric acid concentration increases in the anode chamber, and hydrogen gas is generated and the alkali concentration increases in the cathode chamber A. Concentration increases. −
91 In the present invention, the high concentration phosphoric acid 21 whose concentration has been increased by such electrolysis is recovered outside the system.

Dilute phosphoric acid is stored in the phosphoric acid tank 17 again and the above-mentioned electrolysis is continued. Note that as the electrolysis continues, the concentration of phosphate flowing into the intermediate chamber N decreases.

As the concentration decreases, the electrolytic efficiency decreases,
When the concentration of phosphate decreases to around 11,000pp, the first
The driving of the circulation pump 11 is stopped and the electrolysis is interrupted, and the phosphate whose concentration has decreased in the retention tank 5 is concentrated again by the reverse osmosis membrane devices 7 and 7'.

Alternatively, instead of such batch operation, electrolysis can be performed continuously while concentrating with the reverse osmosis membrane device 7.7' so that the phosphate concentration in the intermediate tank N is always 1000 ppm or more. .

On the other hand, since the concentration of the alkali 2' in the alkali tank 14 increases as the electrolysis continues, this is recovered and reused as the alkali 2 for neutralizing the cleaning waste water, as shown by the dashed line in the figure.

Theoretically, the alkaline content added to washing wastewater 1 is -10- It is recovered in the alkaline tank]4 by electrolysis.

By reusing the alkali 2' as the neutralizing alkali 2, there is no need to replenish the neutralizing alkali from outside the system.

■ The applied voltage in electrolysis is 2~200/possible, preferably 5~]0, and the current is 1~], oh
A m', preferably 2 to 5 A/(1 m').

Although this embodiment describes an example in which phosphoric acid is recovered from washing wastewater containing phosphoric acid, nitric acid can be recovered from washing wastewater containing nitric acid in exactly the same manner. Furthermore, the electrolysis method explained in the drawings is just one example, and there are various methods including the position of the chamber through which the phosphate solution flows, the position of the electrodes, etc. 9 The present invention is not limited to this embodiment. In short, any phosphoric acid 7:: (or nitric acid and alkali) can be recovered from phosphate or nitrate by electrolysis using an ion exchange membrane.

As explained above, according to the present invention, by neutralizing an aqueous solution containing phosphoric acid or nitric acid with an alkali, the solution is concentrated in a reverse osmosis membrane device without being washed as a phosphate or nitrate.

It does not require a particularly acid-resistant reverse osmosis membrane to be used, and it can be concentrated more effectively than concentrating the acid itself, and high-concentration phosphoric acid or nitric acid can be recovered at a relatively low cost in the electrolytic tank after the waste. By recovering the alkali generated by electrolysis and using it to neutralize the phosphoric acid or nitric acid, costs can be further reduced. It can be applied to the treatment of various industrial wastewaters containing acid or nitric acid.

Examples will be described below to make the effects of the present invention more clear.

Example-1 Pure water], phosphoric acid (as T-13PO,) in OOJ
001 was dissolved and neutralized with aqueous ammonia to a pH of 4.5 to 5.0. This was used as raw water and treated according to the flow sheet.

The reverse osmosis membrane device used was 1.00ψX 10], 6
1. A membrane made by Toshi (product name 5P-1, 10) was used, and the raw water was concentrated while being circulated under pressure at 26°C to 30 to 4 ok/aA. After about 5 hours, phosphoric acid in the concentrated water was removed. Fifteen to twenty samples were collected with an ammonium concentration of 2.5 to 3.0%.

On the other hand, the concentration of ammonium phosphate salt in the feed water is 2~amg/
It was ρ. The electrolytic cell has a width of 10 cm, a height of 20 cm, and a thickness of 4 an.
An anion exchange membrane (Aciplex A-101, manufactured by Asahi Kasei Co., Ltd.) is sandwiched close to the anode, platinum-titanium is used as the anode and cathode, respectively, and concentrated water is applied in an upward flow between the cation exchange membrane and the anion exchange membrane. It was introduced as m/h. The electrolytic reaction time is about 12 minutes. 0 on the anode chamber side
．． 05N phosphoric acid aqueous solution is supplied, and 0105N ammonia water is supplied to the cathode chamber side, 60
Vol. 3 with a current of 10 A, mp applied.
- However, the phosphoric acid concentration on the anode chamber side has increased to 2 to 2.5%, and the ammonia water concentration on the cathode chamber side is still 0.5 to 0.7%.
The concentration had increased to the point where it could be recovered sufficiently for neutralization.

Example-2 Pure water 100 (J and nitric acid (as HNoa) 5001T
When 1 g/ρ was dissolved and neutralized with ammonia to pH 6-7, this was used as raw water and treated in the same manner as in Example 1. Nitric acid obtained from the electrolytic cell was approximately 2-2.
It was 4chi.

[Brief explanation of the drawing]

The drawing is an explanatory diagram of a flow showing an example of an embodiment of the present invention. l... Washing waste water, 2... Alkali, 3... Injection pump 4... Neutralized water, 5... Retention tank, 6... High pressure pump 7... Reverse osmosis membrane device, 8 ...Non-permeable water, 9
... Permeated water 10... Electrolytic cell, 11... First circulation pump. 12... Cation exchange membrane, 13... Anion exchange membrane. 14... Alkaline tank, 15... Second circulation pump,
16... Cathode 17... Phosphoric acid tank +' 1B... Dilute phosphoric acid, 19... Third circulation pump 20... Anode, 2
1... High concentration phosphoric acid N... Intermediate chamber, A... Cathode chamber, K... Anode chamber -14=

Claims (2)

[Claims] (1) When concentrating an aqueous solution containing phosphoric acid or nitric acid to obtain highly concentrated phosphoric acid or nitric acid, add an alkali to the aqueous solution to neutralize it, converting the phosphoric acid or nitric acid into phosphoric acid or nitric acid. Then, the neutralized solution is treated with a reverse osmosis membrane device to concentrate the salt, and then the concentrated solution is electrolyzed in an electrolytic cell using an ion exchange membrane to recover highly concentrated phosphoric acid or nitric acid. A method for concentrating phosphoric acid, nitric acid, and nitric acid, which is characterized by (2) Claim 1 for recovering alkali generated by electrolysis and neutralizing an aqueous solution containing phosphoric acid or nitric acid.
Method for concentrating phosphoric acid or nitric acid described in section