JP2017023968A - Method for treating boron-containing water - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for treating boron-containing water capable of efficiently removing boron even if silicon is included in the boron-containing water.SOLUTION: Provided is a method for treating boron-containing water comprising: a first step where aluminum sulfate is dissolved into boron-containing water including boron and silicon; and a second step where calcium hydroxide is added to the boron-containing water after the first step, and ettringite is produced to coprecipitate the boron. In the first step, the addition molar ratio of the aluminum to the boron is controlled to 4 or more. In the second step, the pH of the boron-containing water is controlled to 11.5 or more to 11.8 or less. Even if silicon is included in the boron-containing water, since the production of the substance checking the production of the ettringite is suppressed, the production of the ettringite is promoted, and the boron can be efficiently removed.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a method for treating boron-containing water. More specifically, the present invention relates to a method for treating boron-containing water in which boron is removed from boron-containing water containing silicon together with boron by an ettringite coprecipitation method.

  Boron-containing water (hereinafter referred to as “boron-containing water”) exists in nature as groundwater, seawater, and the like. Boron is also wastewater generated in industries that use boron compounds as raw materials, such as glass industry, pharmaceuticals, cosmetic raw materials, soap industry, electroplating industry, etc. It is contained in wastewater. Depending on the origin of the boron-containing water, silicate ions may also be contained at the same time.

  Boron is an essential micronutrient for animals and plants, but on the other hand, it is known to inhibit plant growth when contained in agricultural water at a concentration of several mg / L or more. Moreover, since there is a risk of health problems when boron is continuously ingested by the human body, the human intake of boron is regulated by law. For example, in the quality standard for tap water, the concentration of boron contained in tap water is regulated to 1.0 mg / L or less. Moreover, the boron concentration is regulated to 230 mg / L or less in the drainage standard for boron into the sea area, and the boron concentration is regulated to 10 mg / L or less in the drainage standard for outside the sea area. Therefore, wastewater containing boron is discharged after performing a treatment for removing boron.

  Silicates in the liquid cause scales generated in piping, valves, pumps and the like. When the scale occurs, problems such as blockage of the liquid supply path occur, so that inspection and maintenance are periodically performed to remove the scale. Therefore, it is preferable that the silicate concentration in the liquid is low when there is no operation requirement.

  Methods for removing boron from boron-containing water include precipitation methods that precipitate boron together with hydroxides such as aluminum and iron, adsorption methods that adsorb boron to hydroxides such as zirconium and magnesium, and evaporation and concentration of boron-containing water. Various methods are known, such as the evaporation and concentration method for crystallizing boric acid, the solvent extraction method for extracting and separating boron with a solvent having an alcohol group, and the reverse osmosis membrane method for separating and removing boron using a reverse osmosis membrane. Yes.

  However, the precipitation method has a problem that a large amount of co-precipitating agent is added to precipitate low-concentration boron, and a large amount of operation materials are required, and the amount of sludge that is a boron-containing starch is large. . Since the adsorption method has a low adsorption capacity of boron to hydroxides such as zirconium and magnesium, it is indispensable to add a large amount of adsorbent and is not practical in terms of efficiency and economy. The evaporative concentration method requires a heat source to concentrate boron-containing water and crystallize boric acid, and is not economical because it requires enormous energy, especially when wastewater with a low boron concentration is targeted. . Moreover, it is necessary to neutralize the boron-containing water after crystallization. In the solvent extraction method, in addition to the treatment of the boron-containing liquid obtained by back-extracting boron from the organic solvent, the treatment of the waste water after the treatment in which a trace amount of the organic solvent is dissolved is indispensable. A treatment such as recovery and removal of the organic solvent with activated carbon or the like is required, which is not economical. In the reverse osmosis membrane method, it is difficult to remove boron until the concentration becomes low only by this method, and therefore, it is necessary to use in combination with other methods. In addition, there is a problem of deterioration in efficiency due to the blockage of the membrane.

  Patent Document 1 discloses a method in which an aluminum compound, a sulfuric acid compound, a calcium compound, and a pH adjuster are simultaneously added to boron-containing wastewater to precipitate precipitates in a reaction solution in which the pH is adjusted to be alkaline. Has been. According to this method, boron can be removed from waste water by precipitating ettringite incorporating boron.

JP 2014-144433 A

  However, the inventor of the present application has found that when silicon is contained in the boron-containing water, the production of ettringite is inhibited and boron cannot be efficiently removed.

  In view of the above circumstances, an object of the present invention is to provide a method for treating boron-containing water that can efficiently remove boron even if silicon is contained in the boron-containing water.

The method for treating boron-containing water of the first invention includes a first step of dissolving aluminum sulfate in boron-containing water containing boron and silicon, and adding calcium hydroxide to the boron-containing water after the first step. And a second step of coprecipitation of boron by producing ettringite.
The method for treating boron-containing water of the second invention is characterized in that, in the first invention, the molar ratio of aluminum to boron is 4 or more in the first step.
The boron-containing water treatment method of the third invention is characterized in that, in the first or second invention, the boron-containing water has a pH of 11.5 or more and 11.8 or less in the second step.

  According to the method for treating boron-containing water of the present invention, even if silicon is contained in the boron-containing water, the production of a substance that inhibits the production of ettringite is suppressed. Can be removed.

It is process drawing of the processing method of the boron containing water which concerns on one Embodiment of this invention. It is a graph which shows the relationship of the residual density | concentration with respect to pH. It is a graph which shows the relationship of the residual density | concentration with respect to pH. It is a graph which shows the X-ray-diffraction pattern of a deposit. It is a graph which shows the relationship of the residual boron concentration with respect to pH. It is a graph which shows the relationship of the residual density | concentration with respect to Al / B. It is a graph which shows the relationship of the residual density | concentration with respect to Al / B. It is a graph which shows the X-ray-diffraction pattern of a deposit.

Next, an embodiment of the present invention will be described with reference to the drawings.
As shown in FIG. 1, the method for treating boron-containing water according to an embodiment of the present invention includes a coprecipitation step of co-precipitation of boron contained in boron-containing water with ettringite, and a starch containing boron and after treatment. And a solid-liquid separation step for separating the liquid. A coprecipitation process consists of the below-mentioned 1st process and 2nd process.

  Boron-containing water contains silicon together with boron. Boron is contained, for example, in the form of borate ions. Silicon is contained, for example, in the form of silicate ions. The concentrations of boron and silicon are not particularly limited. For example, the boron concentration is 10 to 40 mg / L, and the silicon concentration is 40 to 80 mg / L.

In the first step, aluminum sulfate (Al ₂ (SO ₄ ) ₃ ) is added to boron-containing water and dissolved sufficiently.

The second step is performed after the first step. In the second step, calcium hydroxide (Ca (OH) ₂ ) is added to the boron-containing water. Further, the mixture is stirred for a predetermined time while keeping the pH of the boron-containing water constant by adding a pH adjusting agent. This produces ettringite to co-precipitate boron.

Ettringite (calcium aluminate trisulfate hydrate: 3CaO · Al ₂ O ₃ · 3CaSO ₄ · 32H ₂ O) is a crystalline hydrate found in concrete, cement, etc., and the sulfate ions in the crystal and the solution Boron can be taken in by exchanging borate ions therein. Therefore, when ettringite is produced, boron contained in the boron-containing water is taken into the ettringite and co-precipitated. In addition, silicon contained in boron-containing water is also taken into ettringite and coprecipitated in the same manner as boron.

  In the solid-liquid separation step, ettringite incorporating boron is separated as a starch. Thereby, the post-treatment liquid from which boron is removed is obtained.

  This embodiment is characterized by the order of addition of aluminum sulfate and calcium hydroxide. That is, after adding aluminum sulfate to boron-containing water, calcium hydroxide is added. Thereby, the production | generation of the substance which inhibits the production | generation of ettringite is suppressed. This is for the reason explained below.

First, by sufficiently dissolving aluminum sulfate in boron-containing water, aluminum ions and sulfate ions necessary for producing ettringite are prepared in the liquid. Moreover, the pH of boron-containing water can be maintained acidic (pH 3 or less) by adding aluminum sulfate. Thereby, the production | generation of the aluminum hydroxide (Al (OH) ₃ ) which inhibits the production | generation of ettringite is suppressed. Further, carbon dioxide contained in a trace amount in the boron-containing water is removed into the atmosphere. Therefore, even if calcium hydroxide is added, the production of calcium carbonate (CaCO ₃ ) that inhibits the production of ettringite is suppressed.

Next, the pH of boron-containing water can be rapidly increased by adding calcium hydroxide to boron-containing water. Thereby, since it can pass through the pH area | region (9.5-10.5) where the aluminum hydroxide which inhibits the production | generation of ettringite is stably produced | generated as quickly as possible, the production | generation of aluminum hydroxide is suppressed. Similarly, since kaolinite (Al ₄ Si ₄ O ₁₀ (OH) ₈ ), which inhibits the formation of ettringite, can pass through the pH range (10.5 to 11.0) where it is stably produced as quickly as possible. Generation of knight is suppressed.

  As mentioned above, since the production | generation of the substance (aluminum hydroxide, calcium carbonate, kaolinite) which inhibits the production | generation of ettringite is suppressed, the production | generation of ettringite is accelerated | stimulated. As a result, boron can be efficiently removed from the boron-containing water.

  In the first step, the amount of aluminum sulfate added is preferably adjusted so that the molar ratio of aluminum to boron (hereinafter simply referred to as “Al / B”) is 4 or more. This is because if Al / B is 4 or more, the boron concentration of the treated liquid will be below the drainage standard (10 mg / L). Moreover, if Al / B is 5 or more, it is more preferable because boron can be removed until the boron concentration in the solution after treatment falls below the detection limit. On the other hand, as Al / B is increased, the amount of aluminum sulfate added increases and the amount of starch produced increases. From the viewpoint of starch production, Al / B is preferably 6 or less.

  In the second step, the pH of the boron-containing water is preferably adjusted to 11.5 or more and 11.8 or less. This is because, within this pH range, the boron concentration of the treated liquid is not more than the drainage standard (10 mg / L).

  Silicon contained in the boron-containing water can be removed at a lower pH, for example, even at pH 10.5 until the silicon concentration in the treated liquid is below the detection limit. Moreover, even if it is pH12.0, it can be removed until the boron concentration of the liquid after a process will be 5 mg / L or less. Therefore, a wider pH range (pH 10.5 to 12.0) can be adopted from the viewpoint of silicon removal.

  In the second step, the temperature of the boron-containing water is preferably room temperature (20 to 30 ° C.). When the liquid temperature exceeds 35 ° C., ettringite tends to be hardly generated. Therefore, when treating boron-containing water exceeding 35 ° C., such as hot spring water, it is preferable to cool to room temperature in advance and perform the coprecipitation step.

  Even when carbonate ions are contained in the boron-containing water, the production of ettringite can be promoted preferentially by applying this embodiment. In this case, boron and silicon can be removed simultaneously by appropriately adjusting the Al / B in the first step and the pH in the second step.

Next, examples will be described.
[Preparation of boron-containing water]
First, boron-containing water used in the following examples was prepared. In a 1000 mL volumetric flask (PYREX (registered trademark)), boric acid (H ₃ BO ₃ ) as boron, sodium metasilicate (Na ₂ SiO ₃ .9H ₂ O) as silicon, and 1M sodium hydroxide to adjust ionic strength (NaOH) and 1M nitric acid (HNO ₃ ) were added to double the predetermined concentration. A small amount of pure water was added and stirred, and after confirming that the reagent was completely dissolved, the volume was made up with pure water and transferred to a 2000 mL beaker (PMP). A 1000 mL volumetric flask (PYREX (registered trademark)) was again made up with pure water and added to a 2000 mL beaker (PMP). Boron-containing water was obtained by adjusting sodium hydroxide and nitric acid as a pH adjuster to a predetermined pH. The obtained boron-containing water has a boron concentration of 25 mg / L, a silicon concentration of 60 mg / L, and a pH of 8.3. The liquid temperature is room temperature.

(Addition order test)
First, it tested about the addition order of the aluminum sulfate and calcium hydroxide with respect to boron containing water.

Example 1
As a first step, 300 mL of boron-containing water was transferred to a 300 mL beaker (PYREX (registered trademark)), aluminum sulfate was added, and the mixture was stirred with a magnetic stirrer. Here, the addition amount of aluminum sulfate was set to be Al / B (addition molar ratio of aluminum to boron) = 4.

  Next, calcium hydroxide was added to the boron-containing water as the second step. Here, the addition amount of calcium hydroxide was set to be Ca / B (addition molar ratio of calcium to boron) = 12. Moreover, it stirred for 1 hour, using sodium hydroxide and nitric acid as a pH adjuster, maintaining the pH of boron containing water at 11.5.

  Thereafter, suction filtration was performed using a membrane filter (pore diameter: 0.1 μm). The filtrate was measured for boron concentration and silicon concentration with an ICP emission spectrometer. The precipitate after filtration was dried with a heat dryer (45 ° C.) for 1 day. X-ray diffraction measurement was performed using the heat-dried sample.

  As a result, the boron concentration of the filtrate was 6 mg / L, and it was confirmed that it was below the drainage standard (10 mg / L). Moreover, the silicon concentration of the filtrate was 2 mg / L, and it was confirmed that silicon can be sufficiently removed. From the X-ray diffraction pattern of the precipitate, it was confirmed that ettringite was produced.

(Comparative Example 1)
As a first step, 300 mL of boron-containing water was transferred to a 300 mL beaker (PYREX (registered trademark)), and calcium hydroxide was added. Here, the addition amount of calcium hydroxide was set to be Ca / B = 12. The pH of the boron-containing water was adjusted to 11.5 using sodium hydroxide and nitric acid as pH adjusting agents. Next, as a second step, aluminum sulfate was added to the boron-containing water.

  However, the test was stopped because precipitates other than ettringite were generated when calcium hydroxide was added.

(Comparative Example 2)
300 mL of boron-containing water was transferred to a 300 mL beaker (PYREX (registered trademark)), and aluminum sulfate and calcium hydroxide were added simultaneously. Here, the addition amount of aluminum sulfate was Al / B = 4, and the addition amount of calcium hydroxide was Ca / B = 12. Moreover, it stirred for 1 hour, using sodium hydroxide and nitric acid as a pH adjuster, maintaining the pH of boron containing water at 11.5.

  Thereafter, suction filtration was performed using a membrane filter (pore diameter: 0.1 μm). The filtrate was measured for boron concentration with an ICP emission spectroscopic analyzer. The precipitate after filtration was dried with a heat dryer (45 ° C.) for 1 day. X-ray diffraction measurement was performed using the heat-dried sample.

  As a result, the boron concentration in the filtrate was almost the same as the initial boron concentration (25 mg / L) of the boron-containing water, and it was confirmed that the boron was hardly removed. Moreover, it was confirmed from the X-ray diffraction pattern of the precipitate that almost no ettringite was produced.

  From the above, it was confirmed that the addition of calcium hydroxide to boron-containing water followed by the addition of calcium hydroxide promotes the production of ettringite and can efficiently remove boron.

[PH range test 1]
Next, a test was conducted for an optimum pH range of boron-containing water in the second step.

  As a first step, 300 mL of boron-containing water was transferred to a 300 mL beaker (PYREX (registered trademark)), aluminum sulfate was added, and the mixture was stirred with a magnetic stirrer. Here, the addition amount of aluminum sulfate was set to be Al / B = 4.

  Next, calcium hydroxide was added to the boron-containing water as the second step. Here, the addition amount of calcium hydroxide was set to be Ca / B = 12. Moreover, it stirred for 1 hour, using sodium hydroxide and nitric acid as a pH adjuster, keeping the pH of boron containing water constant.

  Thereafter, suction filtration was performed using a membrane filter (pore diameter: 0.1 μm). For the filtrate, the boron concentration, aluminum concentration, and silicon concentration were measured with an ICP emission spectroscopic analyzer, and the sodium concentration, calcium concentration, and sulfate ion concentration were measured with an ion chromatograph. The precipitate after filtration was dried with a heat dryer (45 ° C.) for 1 day. X-ray diffraction measurement was performed using the heat-dried sample.

  The pH of the boron-containing water in the second step was adjusted to 10.5, 11, 11.5, and 12. The results are shown in FIGS. FIG. 2 is a graph showing the relationship of the residual concentration of filtrate to the pH of boron-containing water obtained by an ICP emission spectroscopic analyzer. FIG. 3 is a graph showing the relationship between the residual concentration of the filtrate and the pH of boron-containing water obtained by ion chromatography. FIG. 4 is a graph showing the X-ray diffraction pattern of the precipitate. In FIG. 4, Gypsum, Ettringite, Calcite, Monosulfate, and Calcium Sulfate Hydrate mean gypsum, ettringite, calcium carbonate, monosulfate, and calcium sulfate hydrate, respectively.

  Residual sulfate ion concentration is considered to be an indicator of ettringite formation. Since the residual sulfate ion concentration becomes the lowest at pH 11.5, it is considered that the production of ettringite is promoted at this time. It can be confirmed from the X-ray diffraction pattern that ettringite is produced at pH 11.5.

  From the results of the equilibrium calculation and the X-ray diffraction pattern, substances that are considered to be generated other than ettringite include calcium carbonate, kaolinite, aluminum hydroxide, and calcium sulfate. When the pH is 10.5, it can be seen that ettringite is not generated since the residual sulfate ion concentration has hardly decreased since the addition of the drug. On the other hand, the generation of kaolinite is suggested from the decrease in the residual silicon concentration and the residual aluminum concentration. It can be seen from the X-ray diffraction pattern that calcium sulfate is produced. However, since the residual calcium concentration and the residual sulfate ion concentration have hardly decreased, it is considered that the amount of calcium sulfate produced is very small.

  At pH 11, the residual sulfate ion concentration is lower than at pH 10.5. From this, it can be confirmed that ettringite is produced. A low peak of ettringite can also be confirmed from the X-ray diffraction pattern. Since ettringite is produced, boron is removed compared to pH 10.5, but it is considered that the removal of boron is not sufficient because the amount of ettringite produced is very small.

  When pH is 11.5, a clear ettringite peak can be confirmed from the X-ray diffraction pattern. The reason why the residual boron concentration is greatly reduced is that ettringite is sufficiently produced. The decrease in the residual calcium concentration and the residual sulfate ion concentration compared to those at pH 10.5 and pH 11 is considered to be due to the formation of ettringite. The residual aluminum concentration has not decreased much. This is considered to be because at pH 10.5 and pH 11, aluminum was consumed for the production of substances other than ettringite (such as kaolinite and aluminum hydroxide).

  When the pH is 12, the residual boron concentration is not lowered to the drainage standard (10 mg / L) or less, but the removal amount is larger than when the pH is 10.5 and pH 11. On the other hand, the residual calcium concentration is lower than that at pH 11.5. The peak of calcium carbonate can be confirmed from the X-ray diffraction pattern. When pH is high, the production | generation of calcium carbonate and ettringite competes, and it is thought that the production amount of ettringite is reduced.

[PH range test 2]
Next, a more detailed test was conducted on the optimum pH range of boron-containing water in the second step.

  The test was performed in the same procedure as in “Test for pH range 1” above. Moreover, 11.2, 11.4, 11.6, 11, 8 was added as pH of the boron containing water in a 2nd process. FIG. 5 shows the relationship between the residual boron concentration of the filtrate and the pH of the boron-containing water obtained by the ICP emission spectroscopic analyzer.

  From FIG. 5, it was confirmed that boron could be removed to a drainage standard (10 mg / L) or less if the pH of the boron-containing water was in the range of 11.5 to 11.8.

[Al / B test]
Next, a test was conducted on the optimal range of Al / B in the first step.

  As a first step, 300 mL of boron-containing water was transferred to a 300 mL beaker (PYREX (registered trademark)), aluminum sulfate was added, and the mixture was stirred with a magnetic stirrer.

  Next, calcium hydroxide was added to the boron-containing water as the second step. Here, the addition amount of calcium hydroxide was set to be Ca / B = 12. Moreover, it stirred for 1 hour, using sodium hydroxide and nitric acid as a pH adjuster, maintaining the pH of boron containing water at 11.5.

  Thereafter, suction filtration was performed using a membrane filter (pore diameter: 0.1 μm). For the filtrate, the boron concentration, aluminum concentration, and silicon concentration were measured with an ICP emission spectroscopic analyzer, and the sodium concentration, calcium concentration, and sulfate ion concentration were measured with an ion chromatograph. The precipitate after filtration was dried with a heat dryer (45 ° C.) for 1 day. X-ray diffraction measurement was performed using the heat-dried sample.

  In the first step, the amount of aluminum sulfate added was adjusted, and Al / B was adjusted to 3, 4, 5, 6, 8. The results are shown in FIGS. FIG. 6 is a graph showing the relationship of residual concentration with respect to Al / B obtained by an ICP emission spectroscopic analyzer. FIG. 7 is a graph showing the relationship of residual concentration with respect to Al / B, obtained by ion chromatography. FIG. 8 is a graph showing the X-ray diffraction pattern of the precipitate. Gypsum, Ettringite, and Calcite in FIG. 8 mean gypsum, ettringite, and calcium carbonate, respectively.

  It was confirmed that when Al / B was 4 or more, boron could be removed to a drainage standard (10 mg / L) or less. Further, it was confirmed that if Al / B was 5 or more, boron could be removed until the boron concentration was below the detection limit. On the other hand, the larger the Al / B, the greater the amount of aluminum sulfate added and the greater the amount of precipitate produced. Therefore, Al / B is preferably 6 or less.

  In the case of Al / B = 3, the residual aluminum concentration, the residual calcium concentration, and the residual sulfate ion concentration are significantly higher than those in other conditions. It is thought that ettringite was not produced and boron was not removed.

  The pH history of the solution is related to the phenomenon that the residual concentration of the elements constituting ettringite increases as the amount of aluminum sulfate added is increased. When calcium hydroxide is added, the pH of the solution increases, but the amount of increase in pH is proportional to the amount of drug added. For this reason, when the amount of the drug added is small, the solution is in an atmosphere in which ettringite is difficult to be generated and the reaction does not proceed easily. On the other hand, kaolinite may be generated because the residual silicon concentration is lowered. From the X-ray diffraction pattern, the formation of ettringite can be confirmed when Al / B = 4 or more, but the peak of calcium carbonate is dominant when Al / B = 3.

Claims (3)

A first step of dissolving aluminum sulfate in boron-containing water containing boron and silicon;
After the first step, there is provided a second step of adding calcium hydroxide to the boron-containing water to generate ettringite to co-precipitate boron. The method for treating boron-containing water according to claim 1, wherein the molar ratio of aluminum to boron is 4 or more in the first step. The method for treating boron-containing water according to claim 1 or 2, wherein in the second step, the pH of the boron-containing water is set to 11.5 or more and 11.8 or less.