TWI383958B - Wastewater treatment methods - Google Patents

Description

Wastewater treatment method

The present invention relates to a method for treating wastewater, and more particularly to a method for treating wastewater comprising removing waste water into an acid state, and then decomposing boron to remove boron after the wastewater is subjected to evaporation under alkaline conditions, and includes A treatment method for removing iodine from waste water after removing boron.

Boron is used in various fields because of its use to produce boron in wastewater. Since domestic boric acid is used at a relatively low cost of 35,000 tons per year, it is mostly discarded without recycling.

In the above-mentioned situation, the water pollution prevention law revised in 2001 began to have boron wastewater regulations. The wastewater standard for discharging boron to the sea is 230 ppm or less, and the wastewater standard for discharging into the general river is 10 ppm or less. Therefore, there is a need to remove any boron. A method for removing boron in the general industry is known as a method of removing a magnesium salt by coprecipitation or using an ion exchange resin or a boron adsorbent (see Patent Document 1 and Patent Document 2). However, when the high-concentration boron is removed, the amount of the chemical agent or the amount of the sludge is greatly increased, and the frequency of regeneration of the aforementioned exchange resin is increased, which is economically disadvantageous.

On the other hand, iodine is used as a raw material for the life-related industry, and is used in X-ray imaging agents, pharmaceuticals, bactericidal/killing agents, etc.; as industrial use, it is used in catalyst stabilizers, photographic materials, and polarizing films. At the time of manufacture, etc.; when used for agriculture, it is used for feed additives, herbicides, and the like. However, in such applications, almost no iodine is used, and it is used in combination with various substances. It is known that it is mostly used together with an organic stabilizer in a liquid or the like, or together with a solvent or the like in the step of producing an industrial substance.

In the past, industrially used iodine, iodine compounds, and the like are treated as general wastewater. However, since iodine is bactericidal, microorganisms for wastewater treatment will die, and iodine will not only cause BOD (biochemical oxygen demand; biochemistry). The organic matter that causes the load of the oxygen demand is discharged as waste water, and as a result, the waste water becomes an environmental load, and the loss of iodine for the world's precious resources also becomes a problem.

In the method of recovering iodine from the iodine-containing wastewater, it is known that iodine in iodine-containing water is subjected to free iodination using an oxidizing agent such as chlorine to precipitate iodine, and the obtained iodine-containing water is purified by a pressurized melt method. However, when organic substances are present in the iodine-containing water, there is a problem that the sedimentation property of the free iodine is deteriorated, the amount of the oxidizing agent is increased, the processing time is consumed, and the organic matter is mixed with impurities in the iodine, which is a good means.

[Patent Document] Japanese Patent Laid-Open Publication No. 2004-074038 [Patent Document] Japanese Patent Laid-Open Publication No. Hei 9-010766

The above problems are solved by the following (1) to (15).

(1) A wastewater treatment method comprising: an adjustment step of pH of 8 to 14 of wastewater containing iodine and/or iodide ions, and boron and/or boron ions; concentration of said boron and/or boron ions (with boron a concentration step of 0.5% by mass or more; a liquid obtained by cooling the concentration step; a precipitation step of depositing boron at a pH of 1 to 7; and a precipitate obtained by removing the precipitation step of separating boron, and separating A separation step of boron and/or boron ions.

(2) The method according to (1) above, wherein the concentration step is carried out by heating and evaporation.

(3) The method according to (1) or (2) above, wherein the concentration step is carried out in a continuous manner.

(4) The method according to any one of the above (1) to (3), wherein the concentration step is carried out by bringing the boron and/or boron ion concentration (in terms of boron) to 0.5 to 4.8% by mass.

(5) The method according to any one of (1) to (4) above, wherein the adjusting step of adjusting the pH of the wastewater to 8 to 14 is selected from the group consisting of sodium hydroxide, potassium hydroxide and calcium hydroxide. It is carried out by at least one of an alkali metal salt or an alkaline earth metal salt.

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

(7) A wastewater treatment method comprising: an adjustment step of pH of 8 to 14 of wastewater containing iodine and/or iodide ions, and boron and/or boron ions; concentration of said boron and/or boron ions (with boron The conversion step is a concentration step of 0.5% by mass or more; the liquid obtained by the concentration step is cooled, and the pH of the adjustment liquid is 1 to 7 to precipitate a boron; the precipitate obtained by the precipitation step of removing the boron is separated, and boron is separated. And/or a separation step of boron ions, and a recovery step of supplying chlorine in the separation step, and oxidizing and sedimenting the iodine and/or iodide ions to recover iodine.

(8) The method according to (7) above, wherein the concentration step is carried out by heating and evaporation.

(9) The method according to (7) or (8) above, wherein the concentration step is carried out in a continuous manner.

(10) The method according to any one of the above (7) to (9) wherein the concentration step is carried out by using the boron and/or boron ion concentration (in terms of boron) in an amount of from 0.5 to 4.8% by mass.

(11) The method according to any one of (7) to (10) above, wherein the adjusting step of adjusting the pH of the wastewater to 8 to 14 is selected from the group consisting of sodium hydroxide, potassium hydroxide and calcium hydroxide. It is carried out by at least one of an alkali metal salt or an alkaline earth metal salt.

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

(13) The method according to the above (1) or (7), wherein the adjustment step of the pH of the liquid is from 1 to 7 in the step of precipitating the precipitation of boron, and at least one selected from the group consisting of sulfuric acid, hydrochloric acid, nitric acid, and phosphoric acid is selected. It is carried out by using one or more types of acids (including one type).

(14) The method of the above (7), wherein the precipitation step of the boron precipitation is an addition step of adding an adsorbent to the liquid in an amount of 0.01 to 10% by mass based on the organic substance contained in the removal liquid.

(15) The method according to (14) above, wherein the adsorbent is an acidic clay.

According to the present invention, boron can be removed from a wastewater containing a high concentration of boron with good efficiency, and iodine can be removed after boron removal with iodine in addition to boron.

[Best embodiment of the invention]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, the best mode for carrying out the invention will be described.

Figure 1 is a flow chart showing an embodiment of the wastewater treatment method of the present invention. As shown in Fig. 1, the iodine and/or iodide ions and the wastewater 1 containing boron and/or boron ions are supplied to the pH adjusting tank 3, and the alkaline pH adjusting agent 2 is added to adjust the pH to 8 to 14, Good adjusted to 11 to 13. This is to suppress the iodine in the waste liquid, and it is easy to analyze boron after evaporation and concentration. The alkaline pH adjusting agent used at this time is preferably at least one selected from the group consisting of sodium hydroxide, potassium hydroxide and calcium oxide, but is not limited thereto. The aforementioned alkaline pH adjuster can be used directly in a solid state or in an aqueous solution. From the viewpoint of solubility, sodium hydroxide and potassium hydroxide are more preferred.

The liquid whose pH is adjusted to be alkaline is 0.5% by mass or more (including 0.5% by mass), preferably 0.5 to 4.8% by mass, based on the concentration of boron and/or boron ions (in terms of boron) in the concentration tank 4. It is preferably concentrated by evaporation from 1 to 4.5% by mass. At this time, the distillate 5a in which the vapor is condensed is used as described later, and if necessary, the dilution water 5b as the liquid 12 for boron removal is used.

The liquid concentrated by evaporation is carried out by cooling 6. The temperature of the liquid after cooling 6 is preferably adjusted to -10 to 60 ° C, more preferably 0 to 30 ° C. For subsequent boron removal, crystallization is carried out by adjusting the pH to 1 to 7, preferably 1 to 4 with an acidic pH adjuster. The acidic pH adjuster to be used is preferably sulfuric acid, hydrochloric acid, nitric acid or phosphoric acid, and more preferably sulfuric acid if the subsequent steps are considered. In the step of pH adjustment, when the temperature of the liquid rises, the step of liquid cooling may be performed after the pH adjustment.

At this time, in the case where the organic matter is present in the wastewater, the chlorine oxidation step in the production of iodine may deteriorate the sedimentation property of the free iodine contained in the generated wastewater, and the iodine recovery rate may be lowered. To prevent this, the adsorbent may be added in an amount of 0.01 to 10% by mass, more preferably 0.05 to 1.0% by mass, for the aforementioned wastewater. The organic matter can be removed by the adsorbent to enhance the sedimentation of free iodine. The aforementioned adsorbent is preferably activated carbon or acidic clay. Further, the time at which the adsorbent is added may be after the step of removing 10 by boron described later.

The precipitated boron and the adsorbent when the adsorbent is added can be removed by boron removal 10 to obtain a boron-removed liquid 12. The boron removal 10 can be carried out by a solid-liquid separation operation such as filtration or decantation. The device used for the separation of the employee, such as a spiral decanter, is washed with the addition of the dilution water 5b after the separation operation, and the dilution water 5b can alleviate the boric acid saturation state of the boron-removed liquid 12, preventing the liquid temperature from being around and surrounding. The supersaturated boric acid caused by the difference in temperature is reprecipitated.

Further, the boron-removed liquid 12 is diluted to a predetermined concentration with the dilution water 5b in accordance with the subsequent iodine recovery step.

Figure 2 is a view showing another embodiment of the method of the wastewater in the present invention.

As shown in Fig. 2, the dilution water 25b is added to the liquid 32 after boron removal, and after dilution in the same manner as in Fig. 1, chlorine 34 is added to the dilution treatment liquid 33 to carry out oxidation to precipitate iodine crystals. The precipitated liquid of the iodine crystals is sent to the dissolution furnace 35 to precipitate the precipitated free iodine. The supernatant was subjected to overflow as the treated water 37, and the precipitated iodine was recovered as iodine 36 from below.

The wastewater containing iodine and/or iodide ions and boron and/or boron ions is concentrated, and the pH of the concentrate is adjusted to 4 or less to increase the adsorption efficiency of activated carbon during organic removal. The purpose of using activated carbon is to improve the sedimentation property in the crystallization tank of the iodine crystal obtained by chlorine oxidation when iodine is taken out from the waste water after boron removal.

[Examples]

The following is explained in more detail by way of examples, but the invention is not limited to the examples.

(Example 1)

The 804 g of waste water adjusted to a pH of 12 at a concentration of 5,915 mg/liter was concentrated under reduced pressure to obtain a concentrate of 229 g. After adding 16 g of concentrated sulfuric acid to 204 g of the concentrate to adjust to pH 4, the mixture was stirred while cooling to 5 ° C or lower to precipitate boron. The precipitated boron is removed by filtration.

The filtrate after boron removal was 168 g and the boron concentration was 5,682 mg/l. The absolute amount of boron, relative to 4,195 mg before treatment, became 730 mg after treatment, which was reduced to less than one-fifth of that before treatment.

(Example 2)

An aqueous solution adjusted to a pH of 12 at 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 obtained concentrate had a boron concentration of 22,000 mg/liter and an iodine concentration of 23.3% by mass. In 200 g of the concentrate, coconut shell powder activated carbon [Egretta (registered trademark)] 0.6 g (corresponding to 0.1% by mass of the aqueous solution before concentration under reduced pressure) and concentrated sulfuric acid (15.1 g) were added to adjust the pH to 3. After the pH adjustment, the mixture was stirred for 30 minutes, and further stirred under ice-cold bath for 30 minutes. Filtration of the precipitated boron and activated carbon was carried out to obtain 172 g of a filtrate. To the filtrate of 64 g, 126 g of water was added and diluted, and chlorine was blown until the ORP (oxidation-reduction potential) of the diluted solution exceeded 700 mV, and the sedimentation property of the precipitated free iodine was visually confirmed. The result is good.

(Comparative example)

The coconut shell powder activated carbon [Egretta (registered trademark)] and concentrated sulfuric acid were added to 200 g of an aqueous solution adjusted to a pH of 12 at a boron concentration of 6,000 mg/liter and an iodine concentration of 7.8% by mass, and the pH was adjusted to 3 5. The amount of activated carbon added was 0.1 to 0.5% by mass relative to the aforementioned 200 g of the pH-adjusted pH, and five samples varying in the order of 0.1% by mass were prepared. The pH of each sample was adjusted and stirred at room temperature for 30 minutes. Thereafter, filtration of activated carbon was carried out, and chlorine was injected into the obtained filtrate until the ORP 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 substantially good, and 0.3% by mass was slightly good, and it was not confirmed that the amount of activated carbon below it was improved.

1, 21. . . Waste water

2, 22. . . Alkaline pH adjuster

3, 23. . . pH adjustment tank

4, 24. . . Evaporation and concentration

5a, 25a. . . Distillate

5b, 25b. . . Dilution water

6, 26. . . cool down

7, 27. . . Acidic pH adjuster

8, 28. . . pH adjuster

9,29. . . Crystallization

10, 30. . . Solid liquid separation

11, 31. . . Boron component

12, 32. . . Boron removal liquid

33. . . Dilution solution

34. . . salt

35. . . Dissolution furnace

36. . . iodine

37. . . Treatment water

Figure 1 is a flow chart showing an embodiment of the wastewater treatment method of the present invention.

Fig. 2 is a flow chart showing another embodiment of the wastewater treatment method of the present invention.

twenty one. . . Waste water

twenty two. . . Alkaline pH adjuster

twenty three. . . pH adjustment tank

twenty four. . . Evaporation and concentration

25a. . . Distillate

25b. . . Dilution water

26. . . cool down

27. . . Acidic pH adjuster

28. . . pH adjuster

29. . . Crystallization

30. . . Solid liquid separation

31. . . Boron component

32. . . Boron removal liquid

33. . . Dilution solution

34. . . salt

35. . . Dissolution furnace

36. . . iodine

37. . . Treatment water

Claims (26)

A wastewater treatment method comprising: an adjustment step of pH of a wastewater containing iodine and/or iodide ions, and boron and/or boron ions of 8 to 14; and concentration of the boron and/or boron ions (in terms of boron) a concentration step of 0.5% by mass or more; a step of precipitating the pH of the adjustment liquid at a pH of 1 to 7 while cooling the liquid obtained in the concentration step; and removing the precipitate obtained by the precipitation step of precipitating the boron, separating boron and/or Or a separation step of boron ions. The method of claim 1, wherein the concentration step is carried out by heating and evaporation. The method of claim 1, wherein the concentration step is carried out in a continuous manner. The method of claim 2, wherein the concentration step is carried out in a continuous manner. The method according to any one of claims 1 to 4, wherein the concentration step is carried out by bringing the boron and/or boron ion concentration (in terms of boron) to 0.5 to 4.8% by mass. The method of any one of claims 1 to 4, wherein the adjusting step of adjusting the pH of the wastewater to 8 to 14 is selected from the group consisting of sodium hydroxide, potassium hydroxide and calcium hydroxide. It is carried out by using one kind of alkali metal salt or alkaline earth metal salt. The method of claim 5, wherein the waste water is The adjustment step of pH 8 to 14 is carried out by selecting at least one alkali metal salt or alkaline earth metal salt from the group consisting of sodium hydroxide, potassium hydroxide and calcium hydroxide. The method according to any one of claims 1 to 4, wherein in the step of precipitating boron, the temperature of the liquid after cooling is -10 to 60 ° C, and the pH of the liquid is 1 to 4. The method of claim 5, wherein in the step of precipitating the precipitated boron, the temperature of the liquid after cooling is -10 to 60 ° C, and the pH of the liquid is 1 to 4. The method of claim 6, wherein in the step of depositing boron, the temperature of the liquid after cooling is -10 to 60 ° C, and the pH of the liquid is 1 to 4. The method of claim 7, wherein in the step of precipitating boron, the temperature of the liquid after cooling is -10 to 60 ° C, and the pH of the liquid is 1 to 4. The method of claim 1, wherein the step of adjusting the pH of the liquid in the step of depositing boron is at least one selected from the group consisting of sulfuric acid, hydrochloric acid, nitric acid, and phosphoric acid. One type of acid is carried out. A wastewater treatment method comprising: an adjustment step of pH of a wastewater containing iodine and/or iodide ions, and boron and/or boron ions of 8 to 14; and concentration of the boron and/or boron ions (in terms of boron) a concentration step of 0.5% by mass or more; a step of precipitating boron at a pH of 1 to 7 while cooling the liquid obtained in the concentration step; removing the precipitate obtained by the precipitation step of separating boron, separating the boron and/or boron ions, and In the separation step, chlorine is supplied, and iodine and/or iodide ions are oxidized and sedimented to recover iodine. The method of claim 13, wherein the concentration step is carried out by heating and evaporation. The method of claim 13, wherein the concentration step is carried out in a continuous manner. The method of claim 14, wherein the concentration step is carried out in a continuous manner. The method of any one of claims 13 to 16, wherein the concentration step is carried out by bringing the boron and/or boron ion concentration (in terms of boron) to 0.5 to 4.8% by mass. The method of any one of claims 13 to 16, wherein the adjusting step of adjusting the pH of the wastewater to 8 to 14 is selected from the group consisting of sodium hydroxide, potassium hydroxide and calcium hydroxide. It is carried out by using one kind of alkali metal salt or alkaline earth metal salt. The method of claim 17, wherein the adjusting step of adjusting the pH of the wastewater to 8 to 14 is to select at least one alkali metal salt from the group consisting of sodium hydroxide, potassium hydroxide and calcium hydroxide. Or an alkaline earth metal salt. The method of any one of claims 13 to 16, wherein In the precipitation step of the precipitated boron, the liquid temperature after cooling is -10 to 60 ° C, and the pH of the liquid is 1 to 4. The method of claim 17, wherein in the step of precipitating boron, the temperature of the liquid after cooling is -10 to 60 ° C, and the pH of the liquid is 1 to 4. The method of claim 18, wherein in the step of precipitating boron, the temperature of the liquid after cooling is -10 to 60 ° C, and the pH of the liquid is 1 to 4. The method of claim 19, wherein in the step of precipitating boron, the temperature of the liquid after cooling is -10 to 60 ° C, and the pH of the liquid is 1 to 4. The method of claim 13, wherein the step of adjusting the pH of the liquid in the step of precipitating boron is at least one selected from the group consisting of sulfuric acid, hydrochloric acid, nitric acid, and phosphoric acid. One type of acid is carried out. The method of claim 13, wherein the precipitation step of the boron precipitation is an addition step of adding an adsorbent to the liquid in an amount of 0.01 to 10% by mass based on the organic substance contained in the removal liquid. The method of claim 25, wherein the adsorbent is an acidic clay.