JP2006231325A - Treatment method of waste water - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a means for efficiently removing boron from waste water including boron at a high concentration, and to provide a means for efficiently removing iodine after removing boron when waste water includes iodine in addition to boron. <P>SOLUTION: The treatment method of waste water comprises: a process of adjusting pH of waste water including iodine and/or iodine ion, and boron and/or boron ion into 8 to 14; a process of concentrating the waste water so that the concentration of the boron and/or boron ion expressed in terms of boron becomes 0.5 mass% or more; a process of depositing a boron content by cooling the liquid obtained in the concentration process and adjusting pH of the liquid into 1 to 7; and a process of removing the deposited material obtained in the deposition process of the boron content and separating the boron and/or boron ion. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  TECHNICAL FIELD The present invention relates to a wastewater treatment method, and more specifically, wastewater treatment method for removing precipitated boron by acidifying the pH of the concentrated wastewater after evaporating and concentrating the wastewater under alkaline conditions, and boron The present invention relates to a wastewater treatment method including a step of removing iodine after the removal.

  Boron compounds are used in various fields, and some waste water generated by the use contains boron compounds. The amount of boric acid used in Japan is 35,000 t / year, which is a relatively inexpensive compound and is often discarded without being recovered.

  Under these circumstances, the Water Pollution Control Law was revised in 2001, and boron drainage regulations began. The drainage standard for draining boron into the ocean is 230 ppm or less, whereas the drainage standard for draining into a general river is 10 ppm or less, and boron has to be removed by some method. As a method for removing boron from general industrial wastewater, a coprecipitation removal using a magnesium salt or a removal method using an ion exchange resin or a boron adsorbent is known (see Patent Document 1 and Patent Document 2). However, removal of high concentration boron is economically disadvantageous because the amount of added chemicals and the amount of sludge generated is large, and the frequency of regeneration of the ion exchange resin is increased.

  On the other hand, iodine is used as an industrial raw material in daily life, such as X-ray contrast media, pharmaceuticals, bactericides and fungicides, and industrially as a catalyst stabilizer, photographic raw material, and polarizing film. It is used for feed additives, herbicides, etc. for agriculture. However, in these applications, iodine is rarely used alone, and is used by mixing with various substances. As is well known, it is often used together with an organic stabilizer in a liquid or a solvent used in an industrial material production process.

  Conventionally, iodine, iodine compounds, and their aqueous solutions used in the industry are usually treated as wastewater, but due to the bactericidal properties of iodine, microorganisms for wastewater treatment are killed, and not only iodine but also BOD load As a result, organic substances that can cause spillage are also discharged as wastewater. As a result, the wastewater becomes an environmental burden, and it leads to the dissipation of iodine, which is a valuable resource worldwide.

As a method for recovering iodine from wastewater containing iodine, for example, iodine-containing water is obtained by free-iodination of iodine in iodine-containing water with an oxidizing agent such as chlorine to obtain iodine as a precipitate, followed by a pressure melting method. There are known methods for purification. However, if organic substances are present in iodine-containing water, there are problems such as poor precipitation of free iodine, an increase in the amount of oxidizer used, processing takes time, and organic substances are mixed as impurities in iodine. It was not always a good means.
JP 2004-074038 A JP-A-9-010766

  Accordingly, an object of the present invention is to provide means for efficiently removing boron from wastewater containing boron at a high concentration. Another object of the present invention is to provide means for efficiently removing iodine after removing boron when the wastewater contains iodine in addition to boron.

  Said subject is solved by following (1)-(15).

  (1) Adjusting the pH of the waste water containing iodine and / or iodine ions and boron and / or boron ions to 8 to 14, and the concentration of boron and / or boron ions (in terms of boron) is 0.5 A step of concentrating to at least mass%, a step of precipitating boron by cooling the liquid obtained in the step of concentrating and adjusting the pH of the liquid to 1 to 7, and precipitating the boron And a step of separating the boron and / or boron ions by removing precipitates obtained in the step of causing wastewater to be treated.

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

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

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

  (5) The step of adjusting the pH of the waste water to 8 to 14 includes 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 (1) to (4), wherein the method is performed using a method.

  (6) In the step of precipitating the boron content, the temperature of the liquid after cooling is −10 to 60 ° C., and the pH of the liquid is 1 to 4, in any one of (1) to (5) The method described.

  (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 of boron and / or boron ions (in terms of boron) is 0.5 A step of concentrating to at least mass%, a step of precipitating boron by cooling the liquid obtained in the step of concentrating and adjusting the pH of the liquid to 1 to 7, and precipitating the boron The precipitate obtained in the step of removing the boron and / or boron ions is separated, and chlorine is supplied to the liquid obtained in the separation step to oxidize iodine and / or iodine ions. And a step of recovering iodine by sedimentation, and a method of treating waste water.

  (8) The said concentration process is a method as described in said (7) performed by heating evaporation.

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

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

  (11) The step of adjusting the pH of the waste water to 8 to 14 includes 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 (7) to (10), wherein the method is performed by using.

  (12) In the step of precipitating the boron content, the temperature of the liquid after cooling is −10 to 60 ° C., and the pH of the liquid is 1 to 4, any one of (7) to (11) The method described in 1.

  (13) The pH of the liquid in the step of precipitating boron is adjusted to 1 to 7 using at least one acid selected from the group consisting of sulfuric acid, hydrochloric acid, nitric acid, and phosphoric acid. The method according to (1) or (7).

  (14) In the step of precipitating the boron content, the method further includes a step of adding 0.01 to 10% by mass of an adsorbent to the liquid in order to remove organic substances contained in the liquid. the method of.

  (15) The method according to (14), wherein the adsorbent is activated carbon or acidic clay.

  According to the present invention, boron can be efficiently removed from wastewater containing boron at a high concentration, and when the wastewater contains iodine in addition to boron, iodine is efficiently removed after removing boron. be able to.

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

  FIG. 1 is a flow sheet showing an embodiment of the wastewater treatment method according to the present invention. As shown in FIG. 1, wastewater 1 containing iodine and / or iodine ions, and boron and / or boron ions is sent to a pH adjustment tank 3, and an alkaline pH adjuster 2 is added to adjust the pH to 8 to 14, preferably Is adjusted to 11-13. This is because the release of iodine in the waste liquid is suppressed and boric acid is not easily precipitated during the subsequent evaporation and concentration. In this case, 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 a solid or as an aqueous solution. From the viewpoint of solubility, sodium hydroxide and potassium hydroxide are more preferable.

  The liquid whose pH is adjusted to alkaline has a concentration of boron and / or boron ions (in terms of boron) in the concentration can 4 of 0.5% by mass or more, preferably 0.5 to 4.8% by mass, more preferably 1 Evaporated and concentrated to ˜4.5% by mass. Under the present circumstances, the distillate 5a which the generated vapor | steam condensed can be used as the dilution water 5b of the boron removal liquid 12 as needed so that it may mention later.

  The evaporated and concentrated 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. In order to remove boron thereafter, the pH is adjusted to 1 to 7, preferably 1 to 4, with an acidic pH adjuster, and crystallization 9 is performed. As the acidic pH adjuster to be used, sulfuric acid, hydrochloric acid, nitric acid and phosphoric acid are preferable, and sulfuric acid is more preferable in consideration of the post-process. In this pH adjustment step, the temperature of the liquid may increase, and therefore a step of cooling the liquid may be performed after the pH adjustment.

  At this time, when organic substances are present in the waste water, the precipitation of free iodine that may occur in the chlorine oxidation process during the production of iodine and may be contained in the waste water may be deteriorated, and the iodine recovery rate may be reduced. In order to prevent this, an adsorbent of preferably 0.01 to 10% by mass, more preferably 0.05 to 1.0% by mass, can be added to the waste water. Organic substances can be removed by this adsorbent, and the precipitation of free iodine can be improved. The adsorbent is preferably activated carbon or acidic clay. Moreover, the timing which adds adsorbent may be after the process of the boron removal 10 mentioned later.

  The precipitated boron and the adsorbent when the adsorbent is added are removed by boron removal 10 to obtain a boron removal liquid 12. For boron removal 10, solid-liquid separation operations such as filtration and decantation may be performed. An apparatus that can be used for the solid-liquid separation, such as a screw decanter, is washed by adding the diluted water 5b after the separation operation, and the diluted water 5b relaxes the saturated state of boric acid in the boron removing liquid 12. Thus, reprecipitation of the supersaturated boric acid due to the difference between the liquid temperature and the outside air temperature can be prevented.

  The boron removing liquid 12 can be diluted to a predetermined concentration with the dilution water 5b in order to perform the subsequent iodine recovery step.

  FIG. 2 shows another embodiment of the wastewater treatment method according to the present invention.

  As shown in FIG. 2, the diluted water 25b is added to the liquid 32 after removing boron and diluted in the same manner as in FIG. Crystals are precipitated. The liquid in which the iodine crystals are precipitated is sent to the melter kettle 35 to precipitate the precipitated free iodine. The supernatant is overflowed into treated water 37, and the precipitated iodine is recovered as iodine 36 from the lower part.

  By concentrating the wastewater containing iodine and / or iodine ions and boron and / or boron ions, and further adjusting the pH of the concentrate to 4 or less, the adsorption efficiency of activated carbon in organic matter removal is improved. The purpose of using activated carbon is to improve the sedimentation of iodine crystals obtained by chlorination in the crystallization tank when iodine is taken out from the waste water after boron removal.

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

Example 1
804 g of waste water having a boron concentration of 5,915 mg / liter adjusted to pH 12 was concentrated under reduced pressure to obtain 229 g of a concentrated solution. After adding concentrated sulfuric acid 16g to this concentrated liquid 204g and adjusting pH to 4, it stirred, cooling to 5 degrees C or less, and deposited boron. Thereafter, boron precipitated by filtration was removed.

The filtrate after removing boron was 168 g, and the boron concentration was 5,682 mg / liter.
The absolute amount of boron was 4,195 mg before the treatment, but became 730 mg after the treatment, and decreased to 1/5 or less of that before the treatment.

(Example 2)
An aqueous solution adjusted to pH 12 and having a boron concentration of 6,000 mg / liter and an iodine concentration of 7.8% by mass was concentrated under reduced pressure in the same manner as in Example 1. The concentration of boron in the obtained concentrated liquid was 22,000 mg / liter, and the concentration of iodine was 23.3 mass%. To 200 g of this concentrated solution, 0.6 g of coconut shell powder activated carbon (Shirakaba (registered trademark)) (corresponding to 0.1% by mass of the aqueous solution before concentration under reduced pressure) and 15.1 g of concentrated sulfuric acid are added, and pH is adjusted to 3. It was adjusted. The mixture was stirred for 30 minutes after pH adjustment, and further stirred for 30 minutes under cooling with an ice-water bath. The precipitated boron and activated carbon were filtered to obtain 172 g of filtrate. 126 g of this filtrate was diluted with 126 g of water, chlorine was blown until the ORP (oxidation-reduction potential) value of the diluted solution exceeded 700 mV, and the sedimentation property of the precipitated free iodine was visually confirmed. The result was good.

(Comparative example)
Coconut shell powder activated carbon (Shirakaba (registered trademark)) and concentrated sulfuric acid were added to 200 g of an aqueous solution adjusted to pH 12 and having a boron concentration of 6,000 mg / liter and an iodine concentration of 7.8% by mass, The pH was adjusted to 3-5. A total of 5 samples were prepared in which the amount of activated carbon added was changed from 0.1 to 0.5% by mass in increments of 0.1% by mass with respect to 200 g of the liquid whose pH was adjusted as described above. The pH of each sample was adjusted and stirred at room temperature for 30 minutes. Thereafter, the activated carbon was filtered, and chlorine was blown into the obtained filtrate until the ORP value of the filtrate exceeded 700 mV, and the sedimentation property of the precipitated free iodine was visually confirmed. As a result, 0.5% by mass was good, 0.4% by mass was almost good, 0.3% by mass was somewhat good, and the amount of activated carbon below that was not improved.

It is a flow sheet which shows one embodiment of the waste water treatment method by the present invention. It is a flow sheet which shows the other embodiment of the waste water treatment method by this invention.

Explanation of symbols

1,21 ... Drainage,
2, 22 ... alkaline pH adjuster,
3, 23 ... pH adjustment tank,
4, 24 ... evaporation concentration,
5a, 25a ... distillate,
5b, 25b ... dilution water,
6, 26 ... Cooling,
7, 27 ... acidic pH adjuster,
8, 28 ... pH adjustment,
9, 29 ... crystallization,
10, 30 ... solid-liquid separation,
11, 31 ... boron content,
12, 32 ... Boron removal solution 33 ... Dilution treatment solution,
34 ... chlorine,
35 ... Melter kettle,
36 ... Iodine,
37 ... treated water.

Claims (15)

Adjusting the pH of the waste water containing iodine and / or iodine ions and boron and / or boron ions to 8-14;
A step of concentrating so that the concentration of boron and / or boron ions (in terms of boron) is 0.5% by mass or more;
Cooling the liquid obtained in the step of concentrating and adjusting the pH of the liquid to 1 to 7 to precipitate boron,
Removing the precipitate obtained in the step of precipitating boron, and separating boron and / or boron ions;
Wastewater treatment method.   The method according to claim 1, wherein the step of concentrating is performed by heat evaporation.   The method according to claim 1 or 2, wherein the step of concentrating is performed continuously.   The said concentration process is a method of any one of Claims 1-3 performed until the density | concentration (boron conversion) of the said boron and / or a boron ion becomes 0.5-4.8 mass%.   The step of adjusting the pH of the waste water to 8 to 14 is performed 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 4, wherein:   6. The method according to claim 1, wherein, in the step of depositing the boron content, 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 waste water containing iodine and / or iodine ions and boron and / or boron ions to 8-14;
A step of concentrating so that the concentration of boron and / or boron ions (in terms of boron) is 0.5% by mass or more;
Cooling the liquid obtained in the step of concentrating and adjusting the pH of the liquid to 1 to 7 to precipitate boron,
Removing the precipitate obtained in the step of precipitating boron, and separating boron and / or boron ions;
Supplying iodine to the liquid obtained in the separating step, oxidizing iodine and / or iodine ions, and precipitating to recover iodine;
Wastewater treatment method.   The method according to claim 7, wherein the concentration step is performed by heat evaporation.   The method according to claim 7 or 8, wherein the step of concentrating is performed continuously.   The method according to any one of claims 7 to 9, wherein the step of concentrating is performed until the concentration of boron and / or boron ions (in terms of boron) is 0.5 to 4.8% by mass.   The step of adjusting the pH of the waste water to 8 to 14 is performed 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 10.   The method according to any one of claims 7 to 11, wherein, in the step of depositing the boron content, the temperature of the liquid after cooling is -10 to 60 ° C, and the pH of the liquid is 1 to 4.   The adjustment of the pH of the liquid in the step of depositing boron to 1 to 7 is performed using at least one acid selected from the group consisting of sulfuric acid, hydrochloric acid, nitric acid, and phosphoric acid. 8. The method according to 1 or 7.   The method according to claim 7, further comprising a step of adding 0.01 to 10% by mass of an adsorbent to the liquid in order to remove organic substances contained in the liquid in the step of depositing boron.   The method according to claim 14, wherein the adsorbent is activated carbon or acid clay.

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