JPS599236B2 - High heat defluoridation wastewater treatment method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for treating fluorine-containing wastewater, and particularly to a method for treating wastewater that can remove fluorine to a high degree.

As pollution problems become more serious, there is a need for purification of wastewater in each country.

It goes without saying that it is necessary and desirable to reduce the emission of fluorine (ions) as much as possible with respect to fluorine-containing wastewater discharged from aluminum smelting industries and the like.

Currently, the discharge standard for fluoride ions in wastewater is uniform nationwide.
5 ppm or less, and some local governments have adopted an upper standard of 8 ppm or less.

However, it is expected that total volume regulations will be introduced in the future, and regulations are expected to become even stricter.

Various methods have been known for treating fluorine-containing wastewater.

For example, (a) a method in which a calcium compound represented by calcium salts such as calcium oxide, calcium hydroxide, or calcium carbonate is added to wastewater to convert the contained fluoride ions into calcium oxide and precipitate and remove the )
A method in which flocculants such as aluminum salts such as aluminum sulfate and sodium alginate are added to the wastewater to coagulate and remove the fluorine ions contained in the wastewater; (c) a method in which calcium salts and phosphates are added to the wastewater to remove the fluorine ions contained A so-called apatite treatment method in which ions are fixed and removed, and (iv) a method in which fluorine ions are removed by treatment using an ion exchange resin have been widely tried.

However, although method (a) is effective when treating wastewater containing a large amount of fluoride ions, it is difficult to reduce the fluorine concentration to 15 ppm or less, and method (a) It is difficult to reduce the fluorine concentration to 8 ppm or less, and it also has drawbacks such as a large amount of sludge generated and poor dewatering properties.

Furthermore, although the method (/→) has a good treatment effect, the amount of phosphoric acid added is the minimum necessary amount, that is, the theoretical molar ratio of Ca
”:PO!: Even if the amount is maintained at a level that satisfies the ratio of 5:3:1, a large amount of phosphate ions will remain in the treated water, so the treatment is not a problem, and the chemical costs are high. In addition, method (d) inevitably has disadvantages such as poor treatment effects due to the low selectivity of the ion exchange resin to fluorine ions.

An object of the present invention is to provide a method for treating fluorine-containing wastewater that overcomes the drawbacks of the prior art and can achieve a high degree of fluorine removal without secondary pollution.

In order to achieve the above object, the present invention adjusts fluorine-containing wastewater to (1) PHIO ~ 12, then adds a water-soluble calcium compound, separates and removes the produced calcium-bubbly-containing precipitate, and clears the resulting clear water. (2) subjecting the primary treated water to reverse osmosis treatment to separate it into concentrated water containing fluorine ions and permeated water; (3) Decarbonating the secondary treated water to obtain tertiary treated water; (4) Injecting the tertiary treated water into an activated alumina-filled zone. It is characterized by sequential processing through the process of passing through.

In the present invention, fluorine-containing wastewater to be treated broadly refers to various types of wastewater as long as fluorine needs to be removed.

The water-soluble calcium compound added to the wastewater after the pH adjustment is not particularly limited as long as it is a known calcified carcass, but slaked lime [C
a(OH)2] is particularly preferred.

The amount of water-soluble calcium compound added may be about 10 times the fluorine concentration in wastewater.

By adding the water-soluble calcium compound, most of the fluorine in the wastewater, generally about 80%, is converted into calcium fluoride and precipitated.

The precipitate can be removed by known separation methods, such as centrifugation,
This may be done by decantation or the like.

The clear water after removing the precipitate has a pH of 4-, which is suitable for the next step.
...Adjusted to 7 (primary treated water).

The pH adjustment can generally be carried out suitably by adding a mineral acid such as hydrochloric acid.

Reverse osmosis treatment of the primary treated water can be carried out by passing the primary treated water through a known reverse osmosis device.

Through this treatment, the primary treated water is separated into permeated water and concentrated water in which ions such as fluorine ions and phosphate ions that interfere with the adsorption of active alumina and salts are concentrated.

The concentrated water is preferably returned to the water-soluble calcium compound addition step described above and treated in the same manner again.

On the other hand, the permeated water is adjusted to pH 6 to 8, which is suitable for the next process (secondary treated water).

The pH adjustment can be carried out by adding mineral acids such as sulfuric acid or alkaline agents such as caustic soda.

As a result of the above treatment, the amount of fluorine in the secondary treatment water is generally reduced to about 1/4 of the amount of fluorine in the primary treatment water.

The secondary treatment water contains ions, mainly carbonate ions, that interfere with the adsorption of activated alumina, and therefore their removal is necessary in order to suitably perform the treatment in the next step.

This removal is achieved by treating the secondary treated water with a known decarboxylation device (tertiary treated water).

The adsorption (selection) order of activated alumina is OH >PO4''>
>F>Fe(CN6)4, Cro42>S 04'
)Fe (CNa) 3-, CrO72》CN-〉
NO3':AMnO4>C1304-.

Therefore, PO43- becomes an ion that interferes with the adsorption of fluorine in activated alumina.

Similarly, HCO3- and C0327 become ions that interfere with the adsorption of fluorine in activated alumina.

Since PO43- is removed by reverse osmosis treatment, HCO3'-, HCO3'-,
This removes interfering ions such as CO32.

The tertiary treated water can be carried out by passing it through an activated alumina packed zone according to known catalytic water passage techniques.

This water flow treatment makes it possible to obtain treated water with a fluorine concentration of 1 ppm or less.

In addition, if the fluorine adsorption ability of activated alumina gradually decreases and exceeds the treatment target value of 1 ppm due to the performance of the activated alumina itself or due to continued water flow, the activated alumina should be replaced. All you have to do is play it back.

The regeneration treatment can be easily carried out by passing a treatment agent such as a mineral acid such as sulfuric acid, an alkaline agent such as caustic soda, or an aqueous solution such as aluminum sulfate through the activated alumina packed zone, followed by washing with water.

The water flow of the treatment agent is, for example, SV5 hr'', 1
It is sufficient to wash with water at SV60hr' for about 1 hour.

When washing with water, it is also possible to use tertiary treated water that has been previously treated with an activated alumina filling zone.

The regeneration treatment agent waste liquid and the washing waste liquid are preferably returned to the water bath calcium addition step described above.

Hereinafter, the case where one activated alumina filling zone (hereinafter sometimes referred to as a filling zone) is mainly used has been explained, but in a preferred embodiment of the present invention, two or more filling zones are used in parallel. It is also possible to perform switching operation.

For example, when two packed zones are used, when one packed zone reaches the treatment target value described above, water flow is switched to the other packed zone, and the former filled zone is filled with activated alumina as described above. Perform regeneration processing.

Next, when the latter filling zone reaches the treatment target value, the water flow is switched to the former filling zone, and the activated alumina regeneration process and the water flow switching are repeated in the same manner.

As is clear from the Examples described later, the present invention has the remarkable effect of achieving a high degree of fluorine removal without worrying about secondary pollution during wastewater treatment.

Example The following treatments were carried out for each of the three types of wastewater samples shown in Table 1.

Primary treatment: Caustic soda was added to the sample to adjust the pH to 11, and then slaked lime was added.

The resulting calcium-bubbly-containing precipitate was separated, and the pH was adjusted to 7 by adding hydrochloric acid to the resulting clear water.

Secondary Treatment 2 The primary treated water was treated with an internal pressure type tubular reverse osmosis device at an operating pressure of 50 Ky,/cx'', and the pH was adjusted to 7 by adding caustic soda to the permeated water.

Tertiary treatment Secondary treatment water is sent to an inner cylinder vertical open type decarbonation tower L
V1 Water was passed at a rate of 0 m/hr.

Final treatment: Activated alumina (Neobead D-3 manufactured by Mizusawa Chemical Co., Ltd.
) was packed into a packed tower to a height of 2 m, and aluminum sulfate 5
The tertiary treated water was passed through an activated alumina packed column which had been regenerated using the related solution at SV5hr' for 1 hour and then washed with water at SV30hr-1 for 1 hour, at SV5hr-1.

When the fluorine concentration was determined for the treated water at each treatment stage, the results shown in Table 2 were obtained.

In the table, the value of the final treated water is 300 times the water flow rate.

Table 2 shows that in the case of the present invention, it is possible to easily achieve a fluorine concentration of 1. It can be seen that this value is much better than that of .

Comparative Example The three types of wastewater samples used in the example were each subjected to the following treatments.

(a) Calcium compound addition treatment: Add caustic soda to the sample to adjust the pH to 11, then add slaked lime to 2.0
The precipitate containing calcium oxide formed after the addition of 0.00 ppm was separated.

(Example) Aluminum salt addition treatment: 2,000 ppm of aluminum sulfate was added to the sample, and the resulting precipitate was separated.

(c) Apaquite treatment: Add sulfuric acid (sample/I61 and 3) or caustic soda (sample/I62) to the sample to treat P.
Adjust H to 7, then Ca2+ to 2,000pp
3,000 ppm of M and PO4'' were added, and the resulting precipitate was separated.

(d) Ion exchange resin treatment: An ion exchange resin (SKIOA, manufactured by Mitsubishi Kasei) was regenerated with a 10 part solution of caustic soda and then washed with water, and the sample was passed through water at an SV of 20 hours.

When the fluorine concentration was determined for each of the treated water, the third
Obtained the results in the table.

Note that in the table, the value (d) is the value 50 times the water flow rate.

Claims (1)

[Claims] 1. After adjusting the fluorine-containing wastewater to (A) PHIO ~ 12, add a water-soluble calcium compound, separate and remove the resulting precipitate containing calcium oxides, and adjust the resulting clear water to pH 4 ~ 7 for primary treatment. The process of obtaining water (B
) The primary treated water is subjected to reverse osmosis treatment to separate it into concentrated water containing fluorine ions and permeated water, and then the permeated water has a pH of 6~
(C) decarbonating the secondary treated water to obtain tertiary treated water; (C) passing the tertiary treated water through an activated alumina-filled zone An advanced defluoridation wastewater treatment method that is characterized by sequential treatment.