JPH06262170A - Treatment of fluorine-containing waste water - Google Patents

Abstract

PURPOSE:To sharply reduce the treating cost of waste water and the generated quantity of sludge without requiring special pretreatment and expensive materials when treating dilute fluorine-contg. waste water to a high degree. CONSTITUTION:After fluorine contained in a feed liquid 1 is adsorbed by gel aluminum hydroxide, the fluorine adsorbed gel aluminum hydroxide 3 is made to interact with calcium at pH 8 to desorb the fluorine and then the gel aluminum hydroxide is dissolved at >pH11 to filter off and separate calcium fluoride 6 that has been mixed in. The filtrate is made to have pH 7 to regenerate gel aluminum hydroxide 8, which is repeatedly used for fluorine treatment.

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 fluorine-containing wastewater, and more particularly to a method for advanced treatment of dilute fluorine-containing wastewater at low cost with high fluorine treatment efficiency and extremely small sludge generation.

[0002]

2. Description of the Related Art Fluorine is used in large amounts in the form of hydrofluoric acid not only in the chemical industry but also in metal / glass processing, semiconductor manufacturing, etc., and the amount of its use has been remarkably increasing in recent years. On the other hand, fluorine is a harmful substance to the human body and the environment, and the cost increase for the treatment of fluorine-containing wastewater is becoming extremely serious for each factory. Fluorine contained in various industrial wastewater is regulated by the Water Pollution Control Law to a concentration of 15 ppm or less. In addition, many local governments have set stricter addition standards, most of which are 1 ppm or less to 8 ppm or less, but the most stringent regulation value is 0.8 ppm or less.

Generally, as a method of removing fluorine in wastewater, a method of adding a calcium salt to generate calcium fluoride according to the reaction formula (1) and performing solid-liquid separation is fundamental.

Ca ²⁺ + 2F ⁻ → CaF ₂ ↓ (1) Ca (OH) ₂ and CaCl which are inexpensive as calcium salts
₂ can be used, and is highly efficient for treating a high concentration fluorine-containing waste liquid. However, due to the solubility of calcium fluoride, the treatment concentration that can be achieved by this method is about 8 ppm even under ideal conditions, and the reaction is disturbed in the actual industrial waste liquid in which various substances coexist, and the fluorine concentration is usually 20 to 30 p
The limit is about pm. Therefore, more advanced treatment is required to achieve the national environmental standard of 15 ppm, or the local government's additional standard.

The method currently generally used as the advanced treatment technique is to dissolve an aluminum salt such as aluminum sulfate in a primary treatment liquid having a fluorine concentration of several 10 ppm, and
It is coprecipitated by utilizing the fact that fluorine is adsorbed to the gel aluminum hydroxide produced according to the reaction formula (2) by neutralizing around H = 7. Aluminum salt is cheap, and the amount of fluorine treatment increases as the amount of aluminum salt added increases.
It is quite possible to reach pm. 3Al ₂ (SO ₄ ) ₃ + 6NaOH → 3Na ₂ (SO ₄ ) + 6Al (OH) ₃ ↓ (2) However, this method requires tens to hundreds of times the amount of fluorine in the waste liquid, and a large amount of aluminum salt is generated. The gelled aluminum hydroxide in 1 must be disposed of as sludge. While the amount of waste liquid containing fluorine increases, the disposal of this large amount of sludge has become the biggest problem in the treatment of waste liquid containing fluorine due to the shortage of waste disposal sites and the soaring treatment costs in recent years.

Under these circumstances, various methods have been proposed in the past as a technology for advanced treatment of fluorine-containing waste liquid that produces a small amount of sludge.

For example, a method using a fluorine adsorbent is one in which fluorine is adsorbed and removed, then fluorine is desorbed and recovered by a chemical to regenerate the adsorbent, and this adsorbent is repeatedly used. Is significantly less. In the case of porous alumina, which has been reported as a fluorine adsorbent for a long time, the adsorbed fluorine is desorbed by immersing it in an alumina sulfate solution. Recently, compounds of rare earth elements show extremely high selective adsorption to fluorine, and therefore, an adsorbent using cerium oxide (Japanese Patent Laid-Open No. 60-153940).
Etc. are receiving attention in part. In the case of cerium oxide, fluorine can be adsorbed in an acidic liquid and desorbed in an alkaline manner. In addition, gelled aluminum hydroxide is used as a fluorine adsorbent, and after neutrally adsorbed fluorine is completely desorbed at pH = 10 or more, calcium salt is added to fix the calcium fluoride as calcium fluoride, and the fluorine is neutralized again. There is also a method used for adsorption treatment (Japanese Patent Publication No. 55-35994).

The method using an anion exchange resin is not suitable for fluorine treatment because the electronegativity of fluorine ion is extremely high and the ion exchange rank is usually the lowest. An ion exchange resin in which a metal is supported on a chelate resin that forms a coordinate bond with a metal ion because it easily forms a complex ion (Japanese Patent Laid-Open Publication No. 5 (1999) -58242).
7-107287, JP-A-58-36632, etc.) are being studied for practical use as effective fluorine adsorbents. These resins are treated with alkali and treated with "-OH
Adsorbed fluorine can be desorbed by forming a "type" and then treated with an acid to be regenerated for fluorine adsorption such as "-Cl type".

[0009]

However, any of the above-mentioned methods for treating a fluorine-containing waste liquid for the purpose of reducing the amount of sludge generated has various problems in practical use, and is not suitable for industrial scale. Implementation is difficult. For example, in the method using a porous alumina or a rare earth element type fluorine adsorbent, the adsorbent is expensive and the durability of the adsorbent is not sufficient when repeating adsorption / desorption operations with a chemical. In particular, the deterioration of the mixed adsorbent in which even a trace amount of the oxidizing agent and the reducing agent is mixed in the waste liquid is remarkable. Furthermore, if calcium fluoride generated in the primary treatment remains, it will cover the surface of the adsorbent and reduce its ability to adsorb fluorine.Therefore, another adsorption treatment or precision filter may be used to separate these substances prior to the adsorption treatment. Processes such as treatment are required. In addition, the method of using inexpensive gel aluminum hydroxide as a fluorine adsorbent,
When desorbing fluorine at pH = 10 or more, a considerable part of the gel-like aluminum hydroxide dissolves as an aluminate, but if calcium is added to this for desorption fluorine fixation, insoluble aluminium is formed at the same time as calcium fluoride is formed. Calcium acid is produced and aluminum is consumed, and this production of calcium aluminate also leads to an increase in the amount of sludge. Furthermore, the gel-like aluminum hydroxide, which is a mixture of calcium fluoride and calcium aluminate, has a significantly reduced fluorine-adsorbing ability due to the interference of these substances.

On the other hand, in the treatment method by ion exchange, the resin is expensive and the treatment conditions are severely restricted. That is, as in the case of the adsorbent, a small amount of an oxidizing agent is mixed, so that the resin is severely deteriorated by dissolution, and when the fine particles of calcium fluoride produced in the primary treatment remain, the resin is adsorbed by the adsorption of fluorine. The ability is lost. Furthermore, when the waste liquid contains phosphoric acid, the exchange priority of the fluorine ions with respect to the resin is inferior to that of the phosphate ions, so that the treatment efficiency is significantly reduced. Therefore, a step of thoroughly removing these inhibitory substances is required prior to the ion exchange treatment, and as a result, the total treatment is complicated and the cost is not commensurate with the sludge reduction amount.

The present invention solves the above problems and realizes advanced treatment of fluorine-containing waste liquid which does not require special pretreatment or expensive materials, has low cost, has few restrictions on treatment conditions, and produces a very small amount of sludge. To do.

[0012]

[Means for Solving the Problems] A first step of treating a fluorine-containing wastewater by allowing gel-like aluminum hydroxide to act on the fluorine-containing wastewater as a fluorine adsorbent to adsorb fluorine to the gel-like aluminum hydroxide, The second step of desorbing fluorine by acting calcium ions on the adsorbed gel aluminum hydroxide to generate calcium fluoride, and completely dissolving the fluorine desorbed gel aluminum hydroxide in an alkaline manner, A gel-like material which includes a third step of separating calcium fluoride and other insoluble contaminants by filtration and a fourth step of neutralizing the filtrate to regenerate the gel aluminum hydroxide, and which is regenerated in the fourth step. Aluminum hydroxide used as a fluorine adsorbent again
It is characterized by being repeatedly used in the step of.

[0013]

The present invention will be described below with reference to the drawings. FIG. 1 is a flow chart showing an embodiment of the present invention. The symmetry of the treatment here is the supernatant liquid after the calcium salt is added to the fluorine-containing waste liquid discharged from the semiconductor factory as the primary treatment and most of the fluorine is fixed as calcium fluoride. The thing of about 25 ppm is used. First, as shown in FIG. 1 (1), this primary treatment liquid was used as a stock solution 1, and aluminum was used at 400 p
Add gel aluminum hydroxide to pm.
This gel aluminum hydroxide is aluminum sulfate,
It is obtained by neutralizing an aluminum salt solution such as aluminum chloride or sodium aluminate. The pH of the stock solution and gelled aluminum hydroxide was set to 7 in the reaction tank 2,
After stirring for 30 minutes, the fluorine in the stock solution is adsorbed on the gelled aluminum hydroxide.

Subsequently, a polyacrylamide polymer flocculant was added to precipitate the fluorine-adsorbed gel-like aluminum hydroxide 3 as shown in FIG. 1 (2), and 90% of the stock solution was separated and discharged as a supernatant 4. The slurry containing the remaining fluorine-adsorbed gel-like aluminum hydroxide 3 was transferred to the regeneration tank 5 and pH =
The pH is adjusted to 8, and in order to generate calcium fluoride, calcium chloride is added while maintaining this pH, and the mixture is stirred for 30 minutes. Here, the amount of calcium chloride added is approximately stoichiometric with respect to the amount of fluorine adsorbed on the fluorine-adsorbing gel aluminum hydroxide 3. At pH = 8, the gel-like aluminum hydroxide is hardly dissolved, but the fluorine adsorption power is greatly reduced compared to the case of pH = 7. Therefore, by adding calcium ions, fluorine can be easily desorbed and calcium fluoride can be generated. PH =
Even with No. 7, calcium fluoride is produced, but since gel adsorption strength of aluminum hydroxide is strong, stirring for a long time is required for sufficient reaction.

Next, as shown in FIG. 1 (3), the pH of the slurry containing calcium fluoride 6 produced is adjusted to 11 or higher to completely dissolve the gelled aluminum hydroxide, and the aluminate solution 7 is obtained. To do. Subsequently, as shown in FIG. 1 (4), the calcium fluoride 6 is separated by filtration,
As shown in (5), by adjusting the pH of the filtrate to 7, regenerated gel aluminum hydroxide 8 containing no contaminants can be produced, and this is again treated by advanced treatment of the fluorine-containing wastewater in FIG. 1 (1). It can be reused as a product without being discharged to the outside of the system.

FIG. 2 shows changes in processing characteristics when the gel-like aluminum hydroxide is circulated and used according to the above-mentioned procedure. Compared with the first time, the treatment capacity of the second time is slightly reduced in the process of forming calcium fluoride from the fluorine adsorbed on the gel aluminum hydroxide, as shown in Fig. 1 (2), where all the fluorine cannot be immobilized. This is because a certain amount of fluorine remains. However, conversely, since fluorine can be fixed to a certain amount each time in this step, residual fluorine does not accumulate, and the processing capacity after the second time does not decrease any more and is almost stable. It should be noted that, in this example, when the gel-like aluminum hydroxide is circulated and used, the gel-like aluminum hydroxide is gradually reduced due to elution or the like, and it is recognized that the treatment capacity is gradually reduced by that amount, but it is necessary. Correspondingly, the processing capacity could be completely recovered by replenishing the gel aluminum hydroxide in a reduced amount.

As described above, according to the present invention, it is possible to carry out the treatment under the same conditions as the coagulation-sedimentation method by neutralizing the aluminum salt solution, which has been generally performed as the advanced treatment of the fluorine-containing waste liquid, and to perform the special pretreatment. It is possible to realize advanced treatment of fluorine-containing waste liquid, which does not require the use of expensive materials or expensive materials, does not generate coagulation sedimentation sludge, which has been generated in large amounts in the past, and has extremely stable treatment capacity.

In the above example, gel aluminum hydroxide was added to the stock solution so that the aluminum concentration was 400 ppm, and stable treatment could be performed to a fluorine concentration of about 2.5 ppm. If you want to lower the concentration, you can increase the amount of gelled aluminum hydroxide used.

[0019]

As described above, the method for treating fluorine-containing wastewater according to the present invention is a method for treating fluorine-containing wastewater by allowing gel aluminum hydroxide to act on the fluorine-containing wastewater as a fluorine adsorbent to adsorb fluorine on the gel aluminum hydroxide. And a second step of desorbing fluorine by causing calcium ion to act on the gel-like aluminum hydroxide having adsorbed fluorine at a pH of 7 or more and less than 10 to produce calcium fluoride, and The third step of completely dissolving the desorbed gel-like aluminum hydroxide in an alkaline solution having a pH of 11 or more, and filtering and separating calcium fluoride and other inert contaminants, and neutralizing the filtrate to obtain the gel-like aluminum hydroxide. And a gel-like aluminum hydroxide regenerated in the fourth step as a fluorine adsorbent. By repeatedly using it in the process, special pretreatment and expensive materials are not required in advanced treatment of wastewater containing low concentration fluorine, high treatment efficiency of low concentration fluorine is obtained, and treatment cost and sludge generation amount are extremely low. There is an effect that can be suppressed.

[Brief description of drawings]

FIG. 1 is a flowchart showing a procedure of an embodiment of the present invention.

FIG. 2 is a diagram showing a change in treatment characteristics when gelled aluminum hydroxide is circulated and used according to the procedure of FIG.

[Explanation of symbols]

 1 undiluted solution 2 reaction tank 3 fluorine-adsorbing gel-like aluminum hydroxide 4 supernatant 5 regeneration tank 6 calcium fluoride 7 aluminate solution 8 gel-like aluminum hydroxide

Claims (2)

[Claims] 1. A process for treating fluorine-containing wastewater by allowing gel-like aluminum hydroxide as a fluorine adsorbent to act on fluorine-containing wastewater to adsorb fluorine to the gel-like aluminum hydroxide.
And a second step of desorbing fluorine by causing calcium ions to act on the gel-like aluminum hydroxide having adsorbed fluorine to generate calcium fluoride, and the gel-like aluminum hydroxide having desorbed fluorine is alkalinized. The third step is to completely dissolve the solution in water and to separate the calcium fluoride and other insoluble contaminants by filtration. The fourth step is to neutralize the filtrate and regenerate the gel aluminum hydroxide.
And a step of repeatedly using the gel aluminum hydroxide regenerated in the fourth step as a fluorine adsorbent in the first step again. 2. The pH of the gel-like aluminum hydroxide having adsorbed fluorine is 7 or more and less than 10 and the calcium ions are allowed to act on the gel-like aluminum hydroxide having desorbed fluorine.
The method for treating fluorine-containing wastewater according to claim 1, wherein the solution is completely dissolved in an alkaline solution of 11 or more.