KR20060087457A - Treating method of waste water - Google Patents

Abstract

Means are provided for efficiently removing boron from wastewater containing boron at high concentrations, and if boron contains iodine in addition to boron, a means for efficiently removing iodine after boron is removed.

Adjusting the pH of the wastewater containing iodine and / or iodine ions and boron and / or boron ions to 8 to 14, and concentrating such that the concentration of boron and / or boron ions (in terms of boron) is 0.5% by mass or more. Boron and / or boron by cooling the liquid obtained in the condensation step and adjusting the pH of the liquid to 1 to 7 to precipitate the boron powder, and removing the precipitate obtained in the boron powder precipitation process. A wastewater treatment method comprising a step of separating ions.

Description

Treating method of waste water

1 is a flow chart showing one embodiment of a wastewater treatment method according to the present invention.

2 is a flowchart showing another embodiment of the wastewater treatment method according to the present invention.

<Description of Major Symbols in Drawing>

1, 21... Drainage,

2, 22... Alkaline pH Regulator

3, 23... pH adjustment tank

4, 24... Evaporative concentration

5a, 25a... Effluent

5b, 25b... Dilution water

6, 26... Cooling

7, 27... Acid pH Adjuster

8, 28... pH adjustment

9, 29... Crystallization

10, 30... Solid-liquid separation

11, 31... Boron powder

12, 32... Boron Removal Liquid

33... Diluted solution

34... Goat

35... Pressurized Melting Bath

36.. iodine

37... Treated water

The present invention relates to a wastewater treatment method, and in detail, after the wastewater is evaporated and concentrated under alkaline conditions, the pH of the concentrated wastewater is acidified to remove the precipitated boron and the boron is removed and then iodine is removed again. It relates to a wastewater treatment method comprising a step of removing.

The boron compound is used in various fields, and the wastewater generated by the use thereof contains a boron compound. The amount of boric acid used in Japan is 35,000 t / year, which is a relatively inexpensive compound, so it is often discarded without recovery.

Under these circumstances, the Water Pollution Prevention Act was amended in 2001 in Japan, and the regulation of boron drainage began. The drainage standard for outflow of boron to the ocean is 230 ppm or less, whereas the drainage standard for outflow to general rivers is 10 ppm or less, and boron must be removed in any way. As a method for removing boron from general industrial drainage, there is known a method of removing coprecipitation with magnesium salt or a method using ion exchange resin or boron adsorbent (Japanese Patent Laid-Open No. 2004-074038, Japanese Patent Laid-Open No. 9-010766). See publication number). However, when the high concentration of boron is removed, the amount of chemicals added or the amount of sludge generated is large, and the regeneration frequency of the ion exchange resin increases, which is economically disadvantageous.

On the other hand, iodine is used as a raw material for life-related industrial use, such as roentgen contrast agent, pharmaceuticals, disinfectant and mildew remover, and is used for the production of catalyst stabilizer, photographic raw material, polarizing film for industrial use, feed additives, herbicides and the like for agriculture. In these applications, however, iodine is rarely used alone and is mixed with various materials. As is well known, it is often used in combination with an organic stabilizer or the like in a liquid or a solvent used in an industrial material production process.

Conventionally, these industrially used iodines, iodine compounds and their aqueous solutions have usually been treated as drainage. The bactericidal properties of iodine kill microorganisms for drainage treatment, and not only iodine but also organic substances that can cause BOD loading. It was drained to drainage, and as a result, drainage became an environmental load or a loss of iodine, a precious resource worldwide.

As a method for recovering iodine from wastewater containing iodine, for example, iodine-containing water is iodine in iodine-containing water with an oxidizing agent such as chlorine, and iodine is obtained by precipitation. There is a known method. However, the presence of organic substances in iodine-containing water deteriorates the sedimentation of free iodine, increases the amount of oxidant used, takes time to process, and the organic substances are mixed in iodine as impurities. Could not.

It is therefore an object of the present invention to provide a means for efficiently removing boron from wastewater containing boron at high concentrations. It is still another object of the present invention to provide a means for efficiently removing iodine after boron is removed when the drainage contains iodine together with boron.

The said subject is solved by following (1)-(15).

(1) A step of adjusting the pH of the wastewater containing iodine and / or iodine ions and boron and / or boron ions to 8 to 14, and the concentration (in terms of boron) of the boron and / or boron ions is 0.5% by mass or more. The step of concentrating so as to cool the liquid obtained in the concentration step, adjusting the pH of the liquid to 1 to 7 to precipitate the boron powder, and removing the precipitate obtained in the boron powder precipitation step, And / or separating boron ions.

(2) The method of (1), wherein the concentration step is performed by heat evaporation.

(3) The method of (1) or (2), wherein the concentration step is performed continuously.

(4) The method according to any one of (1) to (3), wherein the concentration step is performed until the concentration of boron and / or boron ions (in terms of boron) is 0.5 to 4.8 mass%.

(5) The step of adjusting the pH of the wastewater to 8 to 14 is carried out using (1) to (4) using at least one alkali metal salt or alkaline earth metal salt selected from the group consisting of sodium hydroxide, potassium hydroxide and calcium hydroxide. One way).

(6) The method of any of (1) to (5), wherein the temperature of the liquid after cooling is -10 to 60 ° C and the pH of the liquid is 1 to 4 in the precipitation step of the boron powder.

(7) adjusting the pH of the wastewater containing iodine and / or iodine ions and boron and / or boron ions to 8 to 14; and the concentration (boron equivalent) of the boron and / or boron ions is 0.5% by mass or more. The step of concentrating so as to cool the liquid obtained in the concentration step, adjusting the pH of the liquid to 1 to 7 to precipitate the boron powder, and removing the precipitate obtained in the boron powder precipitation step, And / or a step of separating boron ions and supplying chlorine to the liquid obtained in the separation step to oxidize and precipitate iodine and / or iodine ions to recover iodine.

(8) The method of (7), wherein the concentration step is performed by heat evaporation.

(9) The method of (7) or (8), wherein the concentration step is performed continuously.

(10) The method of any of (7) to (9), wherein the concentration step is performed until the concentration of boron and / or boron ions (in terms of boron) is 0.5 to 4.8 mass%.

(11) The step of adjusting the drainage to pH 8 to 14 includes the above (7) to (10) using at least one alkali metal salt or alkaline earth metal salt selected from the group consisting of sodium hydroxide, potassium hydroxide and calcium hydroxide. One way).

(12) The method of any of (7) to (11), wherein in the precipitation step of the boron powder, the temperature of the liquid after cooling is -10 to 60 ° C, and the pH of the liquid is 1-4.

(13) In the step of depositing the boron powder, the pH of the liquid is adjusted to 1 to 7 by using at least one or more acids selected from the group consisting of sulfuric acid, hydrochloric acid, nitric acid and phosphoric acid. Of).

(14) The method of (7), further comprising, in the precipitation step of boron powder, adding an adsorbent of 0.01 to 10% by mass with respect to the liquid in order to remove the organic matter contained in the liquid.

(15) The method of (14) wherein the adsorbent is activated carbon or acid clay.

Hereinafter, preferred embodiments of the present invention will be described with reference to the drawings.

1 is a flow chart showing an embodiment of the wastewater treatment method according to the present invention. As shown in Fig. 1, a drain 1 containing iodine and / or iodine ions and boron and / or boron ions is sent to a pH adjusting tank 3, and an alkaline pH adjusting agent 2 is added to pH 8-14. Preferably, it adjusts to 11-13. This is for suppressing the release of iodine in the waste liquid and not easily depositing boric acid at the time of subsequent evaporation concentration. At this time, the alkaline pH adjuster used is preferably at least one selected from the group consisting of sodium hydroxide, potassium hydroxide and calcium hydroxide, but is not limited thereto. The alkaline pH adjuster may be used as it is or in an aqueous solution. From the viewpoint of solubility, sodium hydroxide and potassium hydroxide are more preferred.

The pH-adjusted liquid has a concentration (in terms of boron) of boron and / or boron ions in the concentration tank 4 of 0.5% by mass or more, preferably 0.5 to 4.8% by mass, more preferably 1 to 4.5% by mass. Concentrated to evaporation. At this time, the effluent 5a in which the generated steam is condensed may be used as the dilution water 5b of the boron removal liquid 12 as necessary, as will be described later.

The evaporated liquid is cooled (6). The temperature of the liquid after cooling (6) is preferably adjusted to -10 to 60 ° C, more preferably 0 to 30 ° C. For the subsequent boron removal, the pH is adjusted to 1-7, preferably 1-4, by an acidic pH adjuster, and crystallization 9 is performed. As the acidic pH adjuster to be used, sulfuric acid, hydrochloric acid, nitric acid, phosphoric acid are preferable, and sulfuric acid is more preferable in consideration of a later process. In this pH adjustment process, since the temperature of a liquid may rise, the process of cooling a liquid again after pH adjustment may be performed.

At this time, if organic matter is present in the waste water, it is possible to deteriorate the sedimentation properties of the free iodine which may be generated in the chlorine oxidation process during iodine production and included in the waste water, and the iodine recovery rate may be reduced. In order to prevent this, it is preferable to add 0.01 to 10% by mass of the adsorbent, more preferably 0.05 to 1.0% by mass, with respect to the drainage. Organic matter can be removed by this adsorbent, and the settling property of glass iodine can be improved. As the adsorbent, activated carbon or acidic clay is preferable. Moreover, the timing of adding an adsorbent may be after the boron removal 10 process mentioned later.

The adsorbent in the case of adding the precipitated boron and the adsorbent is removed by boron removal 10 to obtain a boron removal liquid 12. In the boron removal 10, solid-liquid separation operation, such as filtration and decantation, may be performed. The apparatus which can be used for this solid-liquid separation, for example, a screw decanter or the like, is washed by adding dilution water 5b after the separation operation, and the dilution water 5b saturates the boric acid of the boron removal liquid 12. It can alleviate and prevent re-precipitation of supersaturated boric acid by the difference of liquid temperature and outside air temperature.

Furthermore, the boron removal liquid 12 may then be diluted to a predetermined concentration by the dilution water 5b to perform the iodine recovery process.

2 is another embodiment showing a wastewater treatment method according to the present invention.

As shown in FIG. 2, the dilution water 25b is added to the liquid 32 after boron removal, and it diluted like the case of FIG. 1, and then chlorine 34 is added to this dilution liquid 33, and an oxidation process is carried out. The iodine crystal is precipitated by performing. The liquid in which the iodine crystal is precipitated is sent to the pressure melting furnace 35 to settle the precipitated glass iodine. The supernatant is overflowed into treated water 37, and the precipitated iodine is recovered from the lower portion to iodine 36.

The adsorption efficiency of activated carbon in organic matter removal is improved by concentrating a wastewater containing iodine and / or iodine ions and boron and / or boron ions and adjusting the pH of the concentrate to 4 or less. The purpose of the use of activated carbon is to improve the settling properties of crystallized iodine crystals obtained by chlorine oxidation when iodine is taken out from drainage after boron removal.

EXAMPLE

Hereinafter, although an Example demonstrates this invention in more detail, this invention is not limited to these Examples.

(Example 1)

804 g of waste water having a boron concentration of 5 and 915 mg / liter adjusted to pH 12 was concentrated under reduced pressure to obtain 229 g of a concentrate. 16 g of concentrated sulfuric acid was added to 204 g of this concentrate to adjust the pH to 4, followed by stirring while cooling to 5 ° C or lower to precipitate boron. Thereafter, boron precipitated was removed by filtration.

The filtrate after boron removal was 168 g, and the boron concentration was 5,682 mg / liter.

While the absolute amount of boron was 4,195 mg before treatment, it became 730 mg after treatment and decreased to 1/5 or less before treatment.

(Example 2)

An aqueous solution having a concentration of boron adjusted to pH 12 of 6,000 mg / liter and an iodine concentration of 7.8 mass% was concentrated under reduced pressure in the same manner as in Example 1. The concentration of boron in the obtained concentrate was 22,000 mg / liter, and the concentration of iodine was 23.3 mass%. The pH was adjusted to 3 by adding 0.6 g (equivalent to 0.1% by mass of the aqueous solution before decompression concentration) and 15.1 g of concentrated sulfuric acid to palm tree powder activated carbon (Egret (registered trademark)). It stirred for 30 minutes after pH adjustment, and also stirred for 30 minutes under cooling by ice water bath. Filtration of precipitated boron and activated carbon was carried out to obtain 172 g of filtrate. 126 g of water was diluted with 64 g of the filtrate, and chlorine was blown until the ORP (redox potential) value of the diluted solution exceeded 700 mV, and the sedimentability of the precipitated free iodine was visually confirmed. The result was good.

(Comparative Example)

The pH was adjusted to 3 to 5 by adding palm bark powdered activated carbon (Egret®) and concentrated sulfuric acid to 6,000 mg of boron adjusted to pH 12 and 200 g of an aqueous solution having a concentration of 7.8 mass% of iodine. A total of five samples were prepared in which the amount of activated carbon to be added was changed from 0.1 to 0.5 mass% to 0.1 mass% with respect to 200 g of the liquid whose pH was adjusted above. The pH of each sample was adjusted and stirred for 30 minutes at room temperature. Subsequently, the sedimentation property of the free iodine precipitated was visually confirmed by blowing chlorine into the filtrate obtained by filtration of activated carbon until the ORP value of the filtrate exceeded 700 mV. As a result, it was good at 0.5% by mass, almost good at 0.4% by mass, and slightly good at 0.3% by mass, and no improvement was observed for the amount of activated carbon below that.

According to the present invention, the boron can be efficiently removed from the wastewater containing boron at a high concentration, and if the wastewater contains iodine together with boron, the iodine can be efficiently removed after the boron is removed.

Claims (15)

Adjusting the pH of the wastewater containing iodine and / or iodine ions and boron and / or boron ions to 8 to 14, and Concentrating the concentration of boron and / or boron ions so as to be 0.5% by mass or more; Cooling the liquid obtained in the concentration step and adjusting the pH of the liquid to 1 to 7 to precipitate boron powder; And removing boron and / or boron ions by removing the precipitate obtained in the precipitation process of the boron powder. The method of claim 1, The concentration step is effected by thermal evaporation. The method according to claim 1 or 2, The concentration step is continuous. The method according to any one of claims 1 to 3, And the concentration step is performed until the concentration of boron and / or boron ions (in terms of boron) is 0.5 to 4.8 mass%. The method according to any one of claims 1 to 4, The step of adjusting the pH of the wastewater to 8 to 14 is made using at least one alkali metal salt or alkaline earth metal salt selected from the group consisting of sodium hydroxide, potassium hydroxide and calcium hydroxide. The method according to any one of claims 1 to 5, In the boron powder precipitation step, the temperature of the liquid after cooling is -10 to 60 ° C, and the pH of the liquid is 1 to 4. Adjusting the pH of the wastewater containing iodine and / or iodine ions and boron and / or boron ions to 8 to 14, and Concentrating the concentration of boron and / or boron ions so as to be 0.5% by mass or more; Cooling the liquid obtained in the concentration step and adjusting the pH of the liquid to 1 to 7 to precipitate boron powder; Removing the precipitate obtained in the precipitation step of the boron powder, separating the boron and / or boron ions, And oxidizing iodine and / or iodine ions by supplying chlorine to the liquid obtained in the separation step, and sedimenting to recover iodine. The method of claim 7, wherein The concentration step is effected by thermal evaporation. The method according to claim 7 or 8, The concentration step is continuous. The method according to any one of claims 7 to 9, And the concentration step is performed until the concentration of boron and / or boron ions (in terms of boron) is 0.5 to 4.8 mass%. The method according to any one of claims 7 to 10, The step of adjusting the drainage to pH 8-14 using at least one alkali metal salt or alkaline earth metal salt selected from the group consisting of sodium hydroxide, potassium hydroxide and calcium hydroxide. The method according to any one of claims 7 to 11, In the boron powder precipitation step, the temperature of the liquid after cooling is -10 to 60 ° C, and the pH of the liquid is 1 to 4. The method according to claim 1 or 7, Adjusting the pH of the liquid to 1-7 in the step of depositing the boron powder is a method using at least one acid selected from the group consisting of sulfuric acid, hydrochloric acid, nitric acid and phosphoric acid. The method of claim 7, wherein The said boron powder precipitation process WHEREIN: The method of adding the adsorbent of 0.01-10 mass% with respect to a liquid in order to remove the organic substance which a liquid contains further. The method of claim 14, The adsorbent is activated carbon or acidic clay.

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