JPS60216882A - Treatment of waste water containing boron - Google Patents

Abstract

PURPOSE:To reduce the consumption of a regenerative agent by passing the waste liquid from the first ion-exchange bed through the second ion-exchange bed through which sulfuric acid is previously passed in regenerating an ion- exchange resin used for removing boron. CONSTITUTION:The water to be treated is passed through an OH-type basic anion-exchange resin 6 and an OH-type weakly basic anion-exchange resin 8, and tetrafluoroboric acid and boric ions are removed. When both ion-exchange resins 6 and 8 are regenerated, the waste liquid, generated in passing caustic soda through the first ion-exchange bed 6, is passed through the second ion-exchange bed 8 through which sulfuric acid is previously passed. The consumption of a regenerative agent is reduced in this way.

Description

[Detailed Description of the Invention] [Technical Field of the Invention] The present invention relates to a method for treating boron-containing wastewater, in which the boron in the water to be treated is removed in advance as a precipitable compound, and then the remaining boron is removed using an ion exchange resin. Concerning the configuration to be removed.

[Technical background of the invention and its problems]

Boron is contained in wastewater from coal-fired boilers and smoke washing wastewater from garbage incinerators, and forms complexes with borate ions (B(h”-)) or fluorine, resulting in tetrafluoroborate ions (BF
It exists in the form of +-). Such boron is an essential element for plants, but the amount required is extremely small, and excessive intake has a negative effect on their growth. I
It is strictly regulated by ordinances such as I and below.

Conventional methods for treating wastewater containing boron include adsorption using an ion exchange resin and solid-liquid separation as an insoluble precipitate using aluminum sulfate, but neither method is an effective removal method.

When adsorbing boron with ion exchange resin, treated water,
Boron adsorption capacity often differs depending on the form of boron inside. For example, in the case of water to be treated that contains both borate ions and tetrafluoroborate ions, an ion exchange resin that selectively adsorbs borate ions is used to adsorb the tetrafluoroborate ions to eliminate boron in the treated water. It is difficult to reduce the concentration to 1 F111/1 or less. Similarly, boric acid ions are adsorbed using an ion exchange resin that selectively adsorbs ions forming fluorine particles such as tetrafluoroboric acid ions, and boron 8M in the treated water is
It is difficult to reduce Maro to 1/1 or less.

As described above, it is difficult to reduce the boron concentration of the treated water to 1η/l or less by treating a liquid containing both borate ions and tetrafluoroborate ions using a single ion exchange resin.

In addition, I-ion exchange resins that adsorb boron generally have a low adsorption capacity, and therefore have the drawback of requiring a large amount of regenerating agent, which requires frequent regeneration.

On the other hand, the method of solid-liquid separation as an insoluble precipitate using aluminum sulfate requires adding a large amount of aluminum sulfate and slaked lime in an amount equal to or more than the aluminum sulfate to neutralize the pH, resulting in a large amount of sludge. There was a drawback that this occurred.

In particular, a high concentration of boron of several 10 to 100. try/ 1
Unlike Kuzuyudai, the boron concentration in the treated water was reduced to 1.
In order to reduce the amount to η/l or less, more aluminum sulfate or slaked lime is required, which is not an economical treatment method.

Furthermore, depending on the form of boron in the water to be treated, there are cases where solid-liquid separation is easy and cases where solid-liquid separation is difficult. Stable boron concentration in treated water of 1■ regardless of the form of boron
/j! It is difficult to do the following.

[゛Object of the invention]

In view of the above problems, the present invention aims to remove tetrafluoroborate ions and borate ions as much as possible by passing the water to be treated through an OH type basic anion exchange resin and an OH type weakly basic anion exchange resin. At the same time, when regenerating the ion exchange resin, the waste liquid from the first ion exchange layer through which caustic soda was passed is passed through the second ion exchange layer through which sulfuric acid has been passed in advance, thereby reducing the amount of regenerating agent used. That is.

[Summary of the invention]

The present invention separates boron from the water to be treated containing tetrafluoroborate ion (BF4-) and borate ion (B(h'-) as a precipitating compound, and fills the supernatant water with an OH type basic anion exchange resin. Water was passed through the first ion exchange layer to remove remaining tetrafluoroborate ions, and the effluent was then passed through a second ion exchange layer filled with an OH type weakly basic anion exchange resin to remove any remaining tetrafluoroborate ions. a step of removing borate ions adsorbed by the first ion exchange layer; and a step of removing the tetrafluoroborate ions adsorbed by the first ion exchange layer by passing caustic soda into
2. This waste liquid is passed through a second ion exchange layer after removing the adsorbed boric acid ions by passing sulfuric acid through it to regenerate the ion exchange resin. Most of the boron was removed as a precipitable compound, and the remaining tetrafluoroborate ions and borate ions were removed using two types of ion exchange resins, and the first and second ions adsorbed these ions. This system regenerates the ion exchange layer and reuses the recycled waste liquid.

[Embodiments of the invention]

Next, embodiments of the present invention will be described with reference to the accompanying drawings.

Water to be treated (a) consisting of wastewater discharged, garbage incinerator smoke washing wastewater, etc.
is introduced into the acidic reaction tank 1. Next, aluminum sulfate b is injected into the reaction tank 1, and agitation treatment is performed at the stirring 112 under acidic conditions. The residence time in the reaction tank 1 is preferably 3 hours or more, and if the water to be treated a contains a large amount of tetrafluoroborate ions, the pH is lowered to 4 or less by injecting sulfuric acid C into the reaction tank 1. do. By adjusting the pH to 4 or less in the presence of aluminum sulfate b, tetrafluoroborate ion (BF4-) is decomposed into fluoride and boric acid according to the following reaction formula, and is converted into tetrafluoroborate in the next step. The ion load can be reduced.

2A1(SOJi +3118F4 +91120→
4^j! F3+6112304 +3Hg The water d flowing out from the BO3 acidic reaction tank 1 is sent to the alkaline reaction tank 3.
Slaked lime e is injected into this reaction tank 3 and stirred by a stirrer 4 under alkaline conditions.

The residence time in the alkaline reaction tank 3 is preferably 0.5 hours or more. Further, the pH inside the alkaline reaction tank 3 is preferably 10 or higher, preferably 12 or higher. The form of the hydroxide produced in this alkaline reaction tank 3 is not clear, but it is insoluble and has good sedimentation properties.
Facilitates solid-liquid separation in step 5.

The alkaline reaction tower outflow water f is introduced into a solid-liquid separation tank 5 and separated into supernatant water Q and coagulated precipitate.

Through the above steps, free fluorine ions are removed from the water to be treated (a), and some of the tetrafluoroborate ions are made into insoluble precipitates, and some of the borate ions are also made into insoluble precipitates in the supernatant liquid (q). Boron concentration is reduced.

The obtained supernatant water 0 is transferred to a one-stage ion exchange resin column 7 having a first ion exchange layer 6 filled with an OH type anion exchange resin.
will be introduced in The ion exchange resin used in the first-stage ion exchange resin column 7 is a 0f-1 type basic anion exchange resin, and can be used in either a weakly basic or strongly basic form, but in particular, tetrafluoroborate ion is used. A resin that selectively adsorbs is desirable.

The contact residence time between the supernatant water Q and the first ion exchange layer 6 is
It is usually desirable to pass the liquid at 5V=6 (1/h) t' for 5 minutes or more.

Effluent water i from the first-stage ion-exchange resin column 7 is introduced into a two-stage ion-exchange resin column 9 having a second ion-exchange layer 8 made of an OH type weakly basic anion-exchange resin. The ion exchange resin used in the two-stage ion exchange resin column 9 is O
Among H-type weakly basic anion exchange resins, resins that selectively adsorb borate ions are particularly desirable. The contact residence time between the outflow water from the first stage ion exchange resin column 7 and the second ion exchange layer 8 is 5 minutes or more, and it is usually desirable to pass the water at 5V=6 (1/h).

Tetrafluoroborate ions (BF4−) and borate ions (B(h”−)) contained in supernatant water q are transferred to the respective ion exchange layers 6 through the above-described one-stage and two-stage ion exchange treatments.
．． 8, and the boron concentration is ly/j! The following clear treated water j is obtained.

Note that the supernatant water Q needs to be passed through the first ion exchange layer 6 and the second ion exchange layer 8 in this order. This is because the ion exchange resin filled in the first ion exchange layer 6 selectively adsorbs tetrafluoroborate ions and hardly adsorbs borate ions. Further, the ion exchange resin of the second ion exchange layer 8 adsorbs borate ions, but also tetrafluoroborate ions. For this reason, when the supernatant water Q is passed through the second ion exchange station 8, borate ions and tetrafluoroborate ions are simultaneously adsorbed, rapidly reducing the adsorption capacity. In addition, if water is passed through the first and second ion exchange layers 6.8 in this order, trace amounts of tetrafluoroborate ions not adsorbed by the first ion exchange layer 6 will be removed from the second ion exchange layer 6.8.
can be adsorbed by the ion exchange layer 8.

Each ion exchange resin that exchanges and adsorbs tetrafluoroborate ions or borate ions through ion exchange,
As soon as the adsorption concentration decreases, it is regenerated.

A caustic soda aqueous solution K is passed through the first ion exchange layer 6 that has adsorbed tetrafluoroborate ions, and a sulfuric acid aqueous solution 1 is passed through the second ion exchange layer 8 that has adsorbed borate ions.
Regenerated waste liquids m and n are obtained, respectively.

Next, in order to return the second ion exchange layer 8 from the 804 type to the OH type, the regenerated waste liquid m from the first stage ion exchange resin tower 7 is transferred to the second ion exchange layer 8.
The liquid is passed through the ion exchange layer 8 of.

The resin of the first ion exchange layer 6 that has exchanged and adsorbed tetrafluoroborate ions will not reduce the regeneration efficiency even if it is simply regenerated with caustic soda, but the resin of the second ion exchange layer 6 that has exchanged and adsorbed borate ions will not reduce the regeneration efficiency. Regeneration of the resin No. 8 with caustic soda simply changes the resin to an OH type, which results in poor regeneration efficiency.

Therefore, the second ion exchange layer 8 is regenerated using sulfuric acid, which has higher regeneration efficiency than caustic soda. However, if only sulfuric acid regeneration is performed, boron will leak into the treated water when the flow of the water to be treated is resumed, so it is necessary to return the second ion exchange layer 8 from the SO+ type to the OH type. Therefore, in the regeneration step of the second ion exchange layer 8, after performing sulfuric acid regeneration, the regenerated waste liquid m from the first stage ion exchange resin tower 7 containing a large amount of caustic soda is
is passed through the second ion exchange layer 8, and this ion exchange layer 8
The resin is returned from the SO4 type to the OH type to obtain recycled waste liquid p. At this time, the tetrafluoroborate ions contained in the recycled waste liquid m of the first-stage ion exchange resin tower 7 (a large amount of tetrafluoroborate ions desorbed during the regeneration of the first ion exchange layer 6 are present). , are not exchanged and adsorbed by the second ion exchange layer 8.

The waste liquid finally generated in the regeneration process is a two-stage ion exchanger containing high concentrations of sulfate ions and borate ions! ! These are a regenerated waste liquid n from the resin tower 9, and a regenerated waste liquid p containing a high concentration of caustic soda and tetrafluoroborate ions. These liquids n and p are either mixed and returned to the acidic reaction tank 1, or returned to the acidic reaction tank 1 or the alkaline reaction tank 3, respectively, without being mixed. Either one is determined depending on the properties of the water to be treated a or the operating conditions of the apparatus.

The concentration of tetrafluoroborate ions in treated water a is high,
Alternatively, if the tetrafluoroborate ion exchange adsorption capacity of the first ion exchange layer 6 is small, the recycled waste liquid p is returned to the acidic reaction tank 1, and the tetrafluoroborate ions contained in the recycled waste liquid p are removed. It is best to decompose it into fluoride and borate ion.

As a result, the tetrafluoroborate ion concentration decreases, and the resin load on the first ion exchange layer 6 is reduced. In this case, the regenerated waste liquid n from the two-stage ion exchange resin tower 9 is returned to the alkaline reaction tank 3.

In addition, when the tetrafluoroborate ion concentration and borate ion concentration of water to be treated a are low, and when it is necessary to reduce the amount of chemicals in pretreatment, a two-stage ion exchange resin containing a large amount of sulfate ions can be used. The recycled waste liquid n from the tower 9 can be returned to the acidic reaction tank 1, and the recycled waste liquid p containing a large amount of caustic soda can be returned to the alkaline reaction tank 3. In this case, the amount of sulfur 11c and slaked lime e added to the acidic reaction tank 1 or the alkaline reaction 4!13 will be reduced.

The final coagulated sediment is sludge consisting of aluminum-containing aquatic products and boron compounds adsorbed to these aquatic products, and is drawn out from the lower end of the solid-liquid valve 11 tank 5 and subjected to dewatering treatment as necessary. and assimilation treatment.

〔Effect of the invention〕

According to the present invention, boron in the water to be treated containing tetrafluoroborate ions and borate ions is separated as a precipitable compound, and the supernatant water is passed through the first ion exchange layer filled with an OH type basic anion exchange resin. Water is used to adsorb the remaining tetrafluoroborate ions, and then the water is passed through a second ion exchange layer filled with an OH type weakly basic anion exchange resin to adsorb the remaining borate ions. Most of the boron in water is pre-separated as precipitable compounds and is
Since only a small amount of tetrafluoroborate ion and a small amount of borate ion remain in the supernatant water passed to the second ion exchange resin tank, the load on each ion exchange resin is reduced. It is possible to improve adsorption performance and maintain adsorption performance for a long period of time. In addition, since water is passed through the first and second ion exchange layers and tetrafluoroborate ions and borate ions are adsorbed and removed separately using ion exchange resins suitable for each, the removal rate is high, and boron in the treated water is removed. Concentration 1sy
/J or less. Furthermore, caustic soda was passed through the first ion exchange layer that adsorbed tetrafluoroborate ions, sulfuric acid was passed through the second ion exchange layer that adsorbed borate ions, and then caustic soda was passed through the first ion exchange layer. Since the waste liquid from the ion exchange layer is passed through the second ion exchange layer, the tetrafluoroborate ions or borate ions adsorbed on the resin can be released and the ion exchange performance can be regenerated. The waste liquid from the first ion exchange layer containing caustic soda is further passed through the second ion exchange layer to form an OH
By making it into a mold, it is possible to impart adsorption performance for borate ions and to save regeneration chemicals.

[Experimental example of invention]

EXAMPLE 2 An experiment was conducted on waste NTX wastewater treatment using the apparatus of the above-mentioned example.

Drainage wastewater (PH7.1-7.3, boron concentration 330-3
60mg-B/j! , evaporation residue 1.2%) was added with 4 g/J of aluminum sulfate, and stirred for 3 hours.
Thereafter, 6 g/l of slaked lime was added, stirred for 30 minutes, and then left to stand for about 1 hour to perform solid-liquid separation. The boron concentration of the coagulation sedimentation supernatant water is boric acid boron (BO3-8) 120■/A,
Boron tetrafluoroborate (BF4-8) 5 m9
/ 1 ”'C was there.

When this supernatant water was passed through the first stage ion exchange resin column 7, the tetrafluoroboric acid boron concentration of the effluent was 200.
Average 0.5m for B and V! It was below I-B/1. In addition, the boric acid boron 8Imaro at this time is 108m9-BI
It was 3. Furthermore, when the effluent water from the first-stage ion-exchange resin tower 7 was passed through the second-stage ion-exchange resin tower 9, the boric acid boron concentration of the treated water was 20B, V and an average of 0.5In.
! J-B/1 or less, and the total boron concentration is 1 mg −
It became 8/1 or less.

Next, when the boron concentration of the treated water exceeded 1 - BI3, the supply of raw water was stopped and regeneration was performed.

The first ion exchange layer 6 was regenerated using caustic soda at a regeneration level of 65 g Na/l resin and 5V2 (1/h). As a result, the concentration of boron tetrafluoroborate (BF4-8) from this ion exchange layer 6 was 300189/
A liquid of Jl was obtained, and the boron desorption rate was 100%.

Furthermore, the two-stage ion exchange resin tower 9 is regenerated using sulfuric acid, and the regeneration level is 48 gH! 30+/j! -Resin, 5V2
(1/h). As a result, the concentration of boric acid boron (BO3-B) from the ion exchange layer 8 was 717 mfl/1.
A liquid with a boron 1112 deposition rate of 100% was obtained.

Furthermore, the regenerated waste liquid of the first stage ion exchange resin tower 7 is fully opened to 5V.
The liquid was passed through the second ion exchange layer 8 at a rate of 2 (1/h). As a result, a liquid with a boron tetrafluoroborate (BF, -8) concentration of 300189/1 was obtained from the second ion exchange layer 8. From this result, the first stage ion exchange resin column 7
It was found that boron tetrafluoroborate contained in the recycled waste liquid was not adsorbed by the second ion exchange layer 8.

[Brief explanation of the drawing]

The figure is a process explanatory diagram of a treatment method showing an embodiment of the present invention. 6. First ion exchange layer, 8. Second ion exchange layer.

Claims (2)

[Claims] (1) Boron in the water to be treated containing tetrafluorophonate ions (BF Imaichi) and borate ions (BO3'-) is separated as a precipitating compound, and the supernatant water is filled with an OH-type basic anion exchange resin. The remaining tetrafluoroborate ions were removed by passing water through the first ion exchange layer, and the effluent was then passed through the second ion exchange layer filled with an OH type weakly basic anion exchange resin.
A step of passing water through the ion exchange layer to remove remaining borate ions, and removing the tetrafluoroborate ions adsorbed by the first ion exchange layer by passing caustic soda through it, and passing this waste solution through sulfuric acid. and a step of regenerating the ion exchange resin by passing liquid through the second ion exchange layer after removing the boric acid ions adsorbed by the ion exchange layer. A, a. 6□
Tsu element. Ah, wastewater. Treatment method. (2) Boron-containing wastewater according to claim 1, characterized in that aluminum sulfate is added to the water to be treated and stirred, and then slaked lime is added and stirred to produce a precipitable compound containing boron. Processing method.