Method of treating alkaline waste liquid

Abstract

To provide a method of treating alkaline waste liquid without using an acidic solution and without adding a load to the environment.SOLUTION: An alkaline waste liquid of a pH of below 13.0 is used as an alkaline waste liquid to be treated. Gypsum is added to the alkaline waste liquid to prepare a mixed solution, to create a state in which the mixed liquid is in contact with the atmosphere to allow the gypsum, an alkaline solution present in the alkaline waste liquid, and carbon dioxide in the atmosphere to react with each other, to generate calcium carbonate and a sulfate in the mixed liquid. When the pH of the mixed liquid is lowered to near neutral, additional alkaline waste liquid and / or waste gypsum are added to the mixed liquid.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a method for treating alkaline waste liquid, and more particularly to a treatment method capable of disposing of alkaline waste liquid inexpensively and safely without imposing an environmental burden.

Background Art

[0002] Since disposable plastic containers such as PET bottles consume a large amount of energy and emit a large amount of carbon dioxide during production and disposal, the recycling of returnable bottles for containing beverages and seasonings is again developing recently while the use of disposable plastic containers is being reconsidered. Recycling of returnable bottles requires washing of the bottles after use, and the production of alkaline cleaning liquid for decomposing organic substances and rinsing water and the neutralization treatment at the time of disposal involve energy consumption and carbon dioxide generation, which has become an obstacle to the further spread of recycling of returnable bottles.

[0003] For example, Japanese Patent Application Laid-Open No. 2013-154313 (Patent Document 1) discloses a technique for treating alkaline waste liquid in which, through a step of adjusting the alkaline waste liquid to pH 1 to 5 and making the alkaline waste liquid acidic, the resin component dissolved in the alkaline waste liquid is decomposed to facilitate adsorption by activated carbon. In this technique, in order to make the pH of the alkaline waste liquid acidic once, sulfuric acid having a concentration of 20 to 40% by mass or hydrochloric acid having a concentration of 20 to 35% by mass is added to the alkaline waste liquid to adjust the pH.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] According to the invention described in Patent Document 1, an acidic solution (for example, sulfuric acid) that is dangerous to handle due to the pH of the alkaline waste liquid is required.

[0006] An object of the present invention is to provide a method for treating alkaline waste liquid without using an acidic solution and without imposing an environmental burden.

Means for Solving the Problems

[0007] The present invention improves a method for treating an alkaline waste liquid by adding a substance that lowers the pH of the alkaline waste liquid to an alkaline waste liquid having a pH of less than 13.0. In the treatment method of the present invention, a state in which the alkaline waste liquid is in contact with the atmosphere is created, a mixed liquid containing gypsum is created in the alkaline waste liquid, and gypsum is reacted with the alkaline solution in the alkaline waste liquid and carbon dioxide in the atmosphere to generate calcium carbonate and sulfate in the mixed liquid. Then, when the pH of the mixed liquid has dropped to near neutrality, fresh alkaline waste liquid and / or gypsum waste material is added to the mixed liquid.

[0008] According to the present embodiment, since carbon dioxide in the atmosphere is utilized, no energy consumption for generating carbon dioxide is required. And since fresh alkaline waste liquid and / or gypsum waste material is added to the mixed liquid when the pH of the mixed liquid has dropped to near neutrality, the reaction can be continuously continued.

[0009] In order to supply carbon dioxide in the atmosphere into the reaction tank, the mixed liquid may be stirred with the reaction tank open to the atmosphere, or the atmosphere may be injected into the mixed liquid. If the mixed liquid is stirred with the reaction tank open to the atmosphere, carbon dioxide is constantly supplied into the mixed liquid, and the reaction is promoted. According to experiments, the preferable stirring speed for this stirring is 100 to 300 rpm, but the present invention is not limited to this speed range. If the stirring speed is within this range, the reaction can be efficiently accelerated even when using carbon dioxide in the atmosphere.

[0010] The reaction in the mixed liquid becomes the following reaction when the alkaline waste liquid mainly contains sodium hydroxide.

[0011] CaSO 4 ·2H2 O + 2NaOH + CO 2 (in the air) → CaCO 3 + Na 2 SO 4 + 3H 2 O If gypsum in gypsum waste is used, the alkaline waste liquid and gypsum waste can be treated simultaneously, and calcium carbonate can be precipitated.

[0012] The neutrality criterion preferably is after the pH becomes less than 8.6.

[0013] It has been confirmed that if the center of the solid-liquid ratio of gypsum waste and alkaline waste liquid in the mixed solution is 1 g / 20 mL, the necessary reaction can be obtained only with carbon dioxide in the air.

[0014] The gypsum waste may be finely pulverized.

[0015] The present invention creates a first mixed solution by adding gypsum to an alkaline waste liquid with a pH of 13.0 or higher, and purifies slaked lime in the first mixed solution so that carbon dioxide does not dissolve in the mixed solution during the reaction. When the pH of the first mixed solution drops below 13.0, a first treatment of adding the alkaline waste liquid to the first mixed solution is performed, and a state where a second mixed solution obtained by adding gypsum to the alkaline waste liquid with a pH below 13.0 in the first treatment is in contact with the air is created, and the gypsum, the alkali in the alkaline waste liquid, and carbon dioxide in the air are reacted to generate calcium carbonate and sulfate in the second mixed solution. When the pH of the second mixed solution drops to near neutrality, a second treatment of adding a new alkaline waste liquid with a pH below 13.0 and / or gypsum to the second mixed solution may be performed. By doing so, even an alkaline waste liquid with a high pH can be effectively treated.

Brief Description of the Drawings

[0016]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Embodiments for Carrying Out the Invention

[0017] Hereinafter, with reference to the drawings, embodiments of the treatment method for alkaline waste liquid of the present invention will be described in detail.

[0018] [First Embodiment] FIG. 1 is a diagram showing the basic process of the treatment method for alkaline waste liquid of the present invention. In this basic process, a mixed solution obtained by adding gypsum waste material to an alkaline waste liquid with a pH less than 13.0 to be treated is brought into a state of contact with the atmosphere. As the alkaline waste liquid with a pH less than 13.0, for example, an alkaline cleaning solution and rinsing water used for washing returnable bottles can be used as the alkaline waste liquid. In this way, carbon dioxide CO 2 in the atmosphere reacts with the gypsum and the alkaline solution in the alkaline waste liquid to generate calcium carbonate and sulfate (for example, sodium sulfate) in the mixed solution. The calcium carbonate generated in the mixed solution precipitates. In this embodiment, the gypsum in the gypsum waste material is used as the added gypsum.

[0019] If the pH of the mixed solution drops to near neutrality, additional fresh alkaline waste liquid and / or gypsum (gypsum waste material) can be added to the mixed solution to further increase the production of calcium carbonate. When the pH of the mixed solution has dropped to near neutrality, the mixed solution can be heated with electrical energy to remove sulfates. Also, when discharging the mixed solution, precipitated calcium carbonate can be obtained without removing sulfates using electrical energy. The neutrality criterion obtained from the experiment is that the pH becomes less than 8.6.

[0020] According to this embodiment, in order to utilize carbon dioxide in the atmosphere, it is not necessary to consume energy for generating carbon dioxide. And when the pH of the mixed solution drops to near neutrality, fresh alkaline waste liquid and / or gypsum (gypsum waste material) are added to the mixed solution, so the reaction can be continuously continued.

[0021] To supply carbon dioxide in the atmosphere into the reaction tank, the mixed solution may be stirred with the reaction tank open to the atmosphere, or the atmosphere may be injected into the mixed solution. For example, when the mixed solution is stirred with the reaction tank open to the atmosphere, carbon dioxide is constantly supplied into the mixed solution, and the reaction is promoted.

[0022] [Example 1] Figure 2 shows the configuration of the experimental equipment 1 for experimentally verifying the effects of the first embodiment. In this experimental equipment 1, a glass beaker 2 is placed on a stirrer 3 called a magnetic stirrer, and a stir bar 4 consisting of a magnet rotated by the stirrer 3 is placed inside the glass beaker 2. The stir bar 4 rotates inside the glass beaker 2. Also, a pH electrode 5 is arranged inside the glass beaker 2, the output of the pH electrode 5 is input to a pH meter 6, and the output of the pH meter 6 is analyzed by a personal computer 7. These experimental devices are commercially available and not specially manufactured.

[0023] In the glass beaker 2, 200 mL of an aqueous solution with a pH not exceeding 13 was prepared by dissolving sodium hydroxide reagent in water, which mimicked the alkaline waste liquid mixed with the alkaline cleaning solution and the rinsing solution used for washing returnable bottles. Also, as gypsum, 10 g of a gypsum reagent (manufactured by Fujifilm Wako Pure Chemical Corporation), which was a model substance of crushed gypsum board waste material, was added to create a mixed solution. The particles of gypsum in this gypsum reagent were measured with a laser diffraction / scattering particle size distribution analyzer (SALD - 2200 type, manufactured by Shimadzu Corporation), and the average particle size was 55.7 μm. Then, stirring was carried out at room temperature for 36 hours. The change in the pH of the mixed solution was measured with a pH meter 6, and the result presented in a table on a personal computer 7 is shown in Figure 3. Since the reaction in the mixed solution is such that the alkaline waste liquid mainly contains sodium hydroxide, the following reaction occurs.

[0024] CaSO 4 ·2H 2 O+2NaOH+CO 2 (in the atmosphere)→CaCO 3 +Na 2 SO 4 +3H 2 O According to the treatment method of this embodiment, it is possible to simultaneously treat the alkaline waste liquid mainly containing sodium hydroxide and the gypsum waste material.

[0025] The tendency of the change in the pH of the mixed solution is similar to the tendency of the decrease in sodium hydroxide in the alkaline waste liquid and the change in the amount of calcium carbonate generated. That is, as the amount of pH decrease increases, the amount of sodium hydroxide decrease in the alkaline waste liquid increases, and the amount of calcium carbonate generated tends to increase. From Figure 3, it can be seen that the reaction is not continuous, and after an induction time with little initial pH change, the pH tends to rapidly decrease from a certain point. Also, from Figure 3, the higher the initial pH (data curves A > B > C), the longer it takes for the pH to approach a value close to neutral. The closer the initial pH of the mixed solution is to 13, the longer the duration of the high pH (about 24 hours), and the closer the initial pH is to 12, the shorter the duration of the high pH (within 12 hours). And when the pH of the mixed solution becomes less than 8.6, which is the neutral pH, the reaction stops.

[0026] Note that if the stirring speed is within the range of 100 to 300 rpm, it has been confirmed that even when using carbon dioxide in the atmosphere, the reaction can be efficiently accelerated. Also, if the center of the solid-liquid ratio of the gypsum waste material and the alkaline waste liquid in the mixed solution is 1 g / 20 mL, it has been confirmed that the necessary reaction can be obtained only with carbon dioxide in the atmosphere. Considering the actual operability, the preferable range of the solid-liquid ratio is 1 g / 10 mL to 1 g / 50 mL, but the present invention is not limited to this range.

[0027] Figure 4 shows the actual pH change of the test when treating the alkaline waste liquid mainly containing sodium hydroxide, which is the rinsing wastewater for bottle washing, by the treatment method of the present invention. The pH of the alkaline waste liquid, which is the rinsing wastewater for bottle washing, is 11.0, the solid-liquid ratio of the gypsum waste material and the alkaline waste liquid in the mixed solution is 1 g / 20 mL, and the stirring speed is 200 rpm. From the results of Figure 4, it was also confirmed that the same results as in Figure 3 were obtained.

[0028] [Second Embodiment] Figure 5 is a diagram showing the basic process of the second embodiment of the method for treating alkaline waste liquid and gypsum waste material of the present invention. In this basic process, the first treatment and the second treatment are carried out. In the first treatment, a first mixed solution is prepared by adding gypsum of the gypsum waste material to the alkaline waste liquid with a pH of 13.0 or higher to be treated, and slaked lime is purified in the first mixed solution so that carbon dioxide does not dissolve in the first mixed solution during the reaction. Then, when the pH of the first mixed solution drops below 13.0, the alkaline waste liquid with a pH of 13.0 or higher is added to the first mixed solution.

[0029] In the first treatment, the reaction of the following reaction formula occurs in the mixed solution.

[0030] CaSO 4 ·2H 2 O + 2NaOH → Ca(OH) 2 + Na 2 SO 4 + 2H 2 O The slaked lime Ca(OH) generated in the first treatment 2 After being recovered, in the second treatment, a state is created where a second mixture obtained by adding gypsum of gypsum waste material to an alkaline waste liquid whose pH dropped below 13.0 in the first treatment is in contact with the atmosphere, and the gypsum, the alkali in the alkaline waste liquid, and carbon dioxide in the atmosphere are reacted to generate calcium carbonate and sulfate in the second mixture. Then, when the pH of the second mixture drops to near neutrality, a new alkaline waste liquid whose pH dropped below 13.0 and / or gypsum waste material is added to the second mixture. By doing so, even an alkaline waste liquid with a high pH can be effectively treated.

Industrial Applicability

[0031] Since carbon dioxide in the atmosphere is utilized, there is no need to use an acidic solution and no need to consume energy for generating carbon dioxide. And since a new alkaline waste liquid and / or gypsum waste material is added to the mixture when the pH of the mixture drops to near neutrality without using an acidic solution such as sulfuric acid, the reaction can be continuously continued.

Explanation of Symbols

[0032] 1 Experimental equipment 2 Glass beaker 3 Stirrer 4 Stirring bar 5 pH electrode 6 pH meter 7 Personal computer

Claims

1. A method for treating alkaline waste liquid by adding a substance that reduces the pH of the alkaline waste liquid to alkaline waste liquid with a pH of less than 13.0, creating a state in which the alkaline waste liquid is in contact with the atmosphere, creating a mixed liquid by adding gypsum to the alkaline waste liquid, and reacting the gypsum with the alkali in the alkaline waste liquid and carbon dioxide in the atmosphere to produce calcium carbonate and sodium sulfate in the mixed liquid, a method for treating alkaline waste liquid in which when the pH of the mixed liquid drops to near neutrality, fresh alkaline waste liquid and / or gypsum is added to the mixed liquid to treat the alkaline waste liquid.

2. The method for treating alkaline waste liquid according to claim 1, wherein the mixed liquid is stirred in a state where the reaction tank filled with the mixed liquid is placed under atmospheric release to create a state in which the mixed liquid is in contact with the atmosphere.

3. The method for treating alkaline waste liquid according to claim 1, wherein the alkaline waste liquid is alkaline circulating water used in the washing process or the alkaline circulating water with rinsing water added thereto, and contains sodium hydroxide as a main component.

4. The method for treating alkaline waste liquid according to claim 1, wherein after the pH of the mixed liquid becomes less than 8.6, the mixed liquid is discharged as wastewater from the reaction tank.

5. The method for treating alkaline waste liquid according to claim 1, wherein the gypsum is gypsum in gypsum waste materials.

6. The method for treating alkaline waste liquid according to claim 5, wherein the center of the solid-liquid ratio of the gypsum waste materials and the alkaline waste liquid in the mixed liquid is 1 g / 20 mL.

7. The method for treating alkaline waste liquid according to claim 1, wherein the gypsum waste materials are finely pulverized.

8. Create a first mixed liquid by adding gypsum to alkaline waste liquid with a pH of 13.0 or higher, and prevent carbon dioxide from dissolving in the first mixed liquid during the reaction. Purify slaked lime in the first mixed liquid. When the pH of the first mixed liquid drops below 13.0, a first treatment of adding the alkaline waste liquid with a pH of 13.0 or higher to the first mixed liquid, A method for treating alkaline waste liquid, which comprises creating a state in which a second mixed liquid obtained by adding gypsum to the alkaline waste liquid whose pH has fallen below 13.0 in the first treatment is in contact with the atmosphere, reacting the gypsum with the alkali in the alkaline waste liquid and carbon dioxide in the atmosphere to produce calcium carbonate and sodium sulfate in the second mixed liquid, and when the pH of the second mixed liquid has dropped to near neutrality, performing a second treatment of adding a new alkaline waste liquid whose pH has fallen below 13.0 and / or gypsum into the second mixed liquid.

9. The method for treating alkaline waste liquid according to claim 8, wherein the gypsum is gypsum in gypsum waste materials.

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