JP2019048270A - Processing method of waste water - Google Patents

Abstract

To provide a method of processing waste water from which industrially usable alkaline earth metal carbonate can be obtained by effectively utilizing exhaust gas discharged from factory equipment to remove alkaline earth metal ions in the waste water and suppressing scale generation.SOLUTION: A method of processing waste water includes the steps of: contacting an exhaust gas containing carbon dioxide with a first solution containing an alkali metal hydroxide to produce a second solution containing an alkali metal carbonate; and contacting the second solution and waste water containing alkaline earth metal ions to obtain the alkaline earth metal ions in the waste water as alkaline earth metal carbonate.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a method of treating wastewater for removing alkaline earth metal ions in the wastewater.

  Wastewater containing alkaline earth metal ions is formed by precipitation of alkaline earth carbonates such as calcium carbonate and alkaline earth sulfates such as gypsum in equipment and There is a problem that the salts cause the scale to block the pump or piping or the separation membrane.

  As a method of suppressing the generation of scale, for example, in order to process dust containing a large amount of calcium such as chlorine bypass dust, gypsum dihydrate is suspended as seed crystals in the dissolution tank together with dust, and gypsum growth is A method is disclosed to promote and remove alkaline earth sulfate (Patent Documents 1 and 2).

  In addition, as a method of suppressing the generation of scale, when water treatment ash such as incineration main ash, incineration fly ash, bypass dust, melting furnace dust etc, potassium sulfate is made to act on the ash washing filtrate to make gypsum and chloride The potassium chloride is obtained by acting sulfuric acid on the potassium chloride to obtain potassium sulfate and hydrochloric acid, and the obtained potassium sulfate is circulated to act again on the ash washing filtrate, and from the ash washing filtrate, sulfuric acid, gypsum and hydrochloric acid Patent Document 3 discloses a method for producing and recovering the

  Further, as a method of suppressing the generation of scale, there is disclosed a method of precipitating calcium by adding chlorine bypass dust at the time of dissolution of calcium-containing powder such as incinerated fly ash into water (Patent Document 4).

Unexamined-Japanese-Patent No. 2004-041978 JP 2003-326232A Japanese Patent Application Publication No. 2003-002611 WO 2004/030839

  As disclosed in Patent Document 1 or 2, in the method of promoting the growth of gypsum by adding seed crystals together with dust to the dissolving tank, the ions which can be precipitated as gypsum are present in the dust charged to the dissolving tank There is a problem that it takes time to grow as a seed crystal from gypsum and it takes time to process. In addition, a large dissolving tank is required to process a large amount of dust, and the equipment tends to be large.

  As disclosed in Patent Documents 3 and 4, in the method of water treating ash such as incineration main ash, incineration fly ash, bypass dust, melting furnace dust and the like, components such as salts contained in the ash to be treated are Since it is not constant but changes, it may be difficult to suppress the occurrence of scale due to changes in the components of the ash. The treated water treated with ash is discharged to the sewer and finally to the sea. Treated water needs to be treated by sand filter or membrane separator etc. so that the water quality is usually below the standard value established by the Ministry of the Environment before being discharged to the sea, sand filter or membrane separator If a scale occurs in the case, it may cause trouble.

  INDUSTRIAL APPLICABILITY The present invention can effectively use the exhaust gas discharged from plant facilities such as a cement plant and remove alkaline earth metal ions in waste water to suppress the generation of scale, and can be used industrially. It is an object of the present invention to provide a method of treating waste water to obtain an earth metal carbonate.

  As a result of intensive investigations to achieve the above object, the present inventors effectively utilize carbon dioxide in exhaust gas discharged from plant facilities such as a cement plant, and carbon dioxide in the exhaust gas and alkali metal hydroxide And react with each other to obtain an alkali metal carbonate, and by using this alkali metal carbonate to precipitate alkaline earth metal ions in waste water as an alkaline earth metal carbonate, generation of scale is efficiently suppressed. It has been found that the present invention can be accomplished. That is, the present invention is as follows.

[1] A process for producing a second solution containing an alkali metal carbonate by bringing an exhaust gas containing carbon dioxide into contact with a first solution containing an alkali metal hydroxide, and the second solution and the alkaline earth metal And contacting the waste water with metal ions to obtain alkaline earth metal ions in the waste water as alkaline earth metal carbonate.
[2] The method for treating wastewater according to [1], wherein the exhaust gas containing carbon dioxide is an exhaust gas discharged from a thermal power plant, a steel plant, a cement plant, or an incinerator.
[3] The exhaust gas containing carbon dioxide is an exhaust gas discharged from a cement plant, and the exhaust gas is an exhaust gas after passing through an electrostatic precipitator and / or a bag filter, and a combustion gas is extracted from an air duct The waste water treatment method according to the above [1] or [2], which is at least one exhaust gas selected from exhaust gases discharged from a desalting bypass facility that recovers desalted dust.
[4] The method for treating wastewater according to the above [1] to [3], wherein the wastewater containing alkaline earth metal ions is a wastewater obtained by washing chlorine-containing incineration ash.
[5] In the above [4], the waste water containing the alkaline earth metal ion contains chlorine-containing incineration ash and water, and the mass ratio of the chlorine-containing incineration ash to water is 1: 1 to 1:10. Wastewater treatment method described.
[6] The wastewater according to any one of the above [1] to [5], wherein the alkali metal hydroxide is at least one selected from the group consisting of sodium hydroxide, potassium hydroxide and lithium hydroxide How to handle
[7] The molar ratio (carbon dioxide / alkali metal hydroxide) of carbon dioxide contained in the exhaust gas brought into contact with the first solution to the alkali metal hydroxide contained in the first solution is 0.1 to 0.1 The waste water treatment method according to any one of the above [1] to [6], which is 1.0.
[8] The method for treating wastewater according to [1] to [7], wherein the volume ratio of the second solution to the wastewater (second solution / drainage) is 0.01 to 0.1.

  According to the present invention, the exhaust gas discharged from a plant facility such as a cement plant is effectively used to remove alkaline earth metal ions in the waste water to suppress the generation of scale, and an industrially usable alkaline earth It is possible to provide a method for treating waste water which can obtain metalloid carbonates.

FIG. 1 is a flow chart showing each step in the method of treating wastewater according to an embodiment of the present invention. FIG. 2 is a schematic view showing an example for carrying out the step of producing the second solution. FIG. 3 is a flow chart showing each step in the method of treating waste water according to another embodiment of the present invention. FIG. 4 is a flow chart showing each step in the method for treating waste water according to another embodiment of the present invention.

Hereinafter, the present invention will be described.
FIG. 1 is a flow chart showing each step in the method for treating waste water according to an embodiment of the present invention.
As shown in FIG. 1, the method for treating waste water according to one embodiment of the present invention comprises contacting an exhaust gas containing carbon dioxide with a first solution containing an alkali metal hydroxide to form a second containing an alkali metal carbonate. And a step of bringing the second solution into contact with waste water containing alkaline earth metal ions to obtain alkaline earth metal ions in the waste water as alkaline earth metal carbonate.

The exhaust gas containing carbon dioxide (CO ₂₎ gas carbon dioxide (CO ₂₎ containing, thermal power plants, steel mills, it is preferable that exhaust gas discharged from the cement plant or incinerator. When a waste water treatment facility is present in the vicinity of facilities such as a thermal power plant, an iron mill, a cement plant or an incinerator, it is possible to directly use the exhaust gas discharged from the facility for wastewater treatment There is not necessarily a waste water treatment facility in the vicinity of the facility. When exhaust gas discharged from facilities such as thermal power plants, steelworks, cement plants or incinerators is used directly for wastewater treatment, it is necessary to lay a piping duct from the above facility to the wastewater treatment facility over a long distance. , It is not easy to use exhaust gas. In addition, for example, in a cement plant etc., it is not easy to change the route of piping for circulating exhaust gas and change the gas outlet etc. from the existing position, because of the problem of legal regulations.

When the exhaust gas is used directly for the treatment of waste water, when the alkaline earth metal ion contained in the waste water is contained in the form of hydroxide, it reacts rapidly with the carbon dioxide contained in the exhaust gas, As shown in the following formula (I), it can be easily removed from the waste water as alkaline earth metal carbonate.
M _e (OH) ₂ + CO ₂ → M _e CO ₃ + H ₂ O (I)
(In the formula (I), _{M e} is at least one alkaline earth metal atom selected from the group consisting of Mg, Ca, Ba and Sr.)

  On the other hand, when the alkaline earth metal ion contained in the waste water is in the form of a chloride, even if carbon dioxide is brought into contact with the waste water, the pH of the waste water is lowered and the alkaline earth metal carbonate is not produced. Since it dissolves as alkaline earth metal ions, alkaline earth metal ions can not be efficiently removed from the waste water.

In the method for treating waste water according to one embodiment of the present invention, an exhaust gas containing carbon dioxide (CO ₂ ) and an alkali metal hydroxide (M _a OH, in FIG. 1, M _a OH represents an alkali metal hydroxide. And a second solution containing alkali metal carbonate (M _a2 CO ₃ , wherein M _a2 CO ₃ represents an alkali metal carbonate in FIG. 1). including. In the method of treating waste water according to one embodiment of the present invention, it is not necessary to directly contact the exhaust gas and the waste water, so it is not necessary to lay pipes or the like in order to bring the waste gas directly into contact with the waste water. In addition, it is not necessary to significantly change the route of the exhaust gas in order to obtain the exhaust gas discharged from the thermal power plant, the steel plant, the cement plant or the incinerator. Therefore, the exhaust gas discharged from the thermal power plant, the steel plant, the cement plant or the incinerator can be effectively used.

  The exhaust gas containing carbon dioxide can effectively utilize the exhaust gas emitted from a thermal power plant, a steel plant, a cement plant or an incinerator. The exhaust gas containing carbon dioxide used in the method for treating waste water according to one embodiment of the present invention is an exhaust gas discharged from a cement plant since there is no need to change the arrangement of a regulated gas outlet or the like. preferable.

When the exhaust gas containing carbon dioxide is the exhaust gas discharged from the cement plant, the exhaust gas after passing through the electrostatic precipitator and / or the bag filter and the combustion gas are extracted from the exhaust gas duct and removed The exhaust gas is preferably at least one exhaust gas selected from the exhaust gas discharged from a chlorine bypass facility that recovers salt dust.
If the exhaust gas containing carbon dioxide is an exhaust gas after passing through an electrostatic precipitator and / or a bag filter, dust is removed from the exhaust gas by the electrostatic precipitator and / or the bag filter; The alkali metal hydroxide in the first solution can be efficiently reacted to obtain a second solution containing a metal carbonate.
The carbon dioxide in the exhaust gas that has passed through the electrostatic precipitator and / or the bag filter when the exhaust gas containing carbon dioxide is an exhaust gas discharged from a chlorine bypass facility where combustion gas is extracted from the fuel end duct and the desalted dust is recovered. Since carbon dioxide having a concentration similar to that of H.sub.2 is contained, it can be efficiently reacted with the alkali metal hydroxide in the first solution. The concentration of carbon dioxide in the exhaust gas passing through the electrostatic precipitator and / or the bag filter is 15 to 25% by volume, and the concentration of carbon dioxide in the exhaust gas discharged from the chlorine bypass facility is also 15 to 25% by volume.

  When the exhaust gas containing carbon dioxide is an exhaust gas discharged from a cement plant, it may be an exhaust gas before passing through an electrostatic precipitator and / or a bag filter. The exhaust gas before passing through the electrostatic precipitator and / or the bag filter in a cement plant contains dust, and the exhaust gas containing dust is brought into contact with a first solution containing an alkali metal hydroxide. The second solution containing the alkali metal carbonate to be produced may contain dust, but in this case, using a wet scrubber, the second solution containing the alkali metal carbonate It may be processed. Examples of wet scrubbers that process the second solution include jet scrubbers and the like. By treating the second solution using a wet scrubber such as a jet scrubber, dust, hydrochloric acid mist, hydrofluoric acid mist and heavy metals contained in the second solution can be removed. In a wet scrubber, the absorbing solution used to remove dust, hydrochloric acid mist, hydrofluoric acid mist or heavy metals can also be used in water treatment of waste water containing alkaline earth metal ions described later. The waste water containing alkaline earth metal ions is subjected to pH adjustment as described later, and further subjected to water treatment to add a coagulant to remove heavy metal ions and the like. The absorbent used in the wet scrubber can be used in water treatment of waste water containing alkaline earth metal ions, and the coagulant added in the water treatment of waste water containing alkaline earth metal ions can be appropriately removed.

Before contacting the exhaust gas containing carbon dioxide with the first solution containing an alkali metal hydroxide, the exhaust gas containing carbon dioxide is preliminarily removed by a method such as a chemical absorption method, a physical absorption method, a membrane separation method, a cryogenic separation method or an oxygen combustion method. You may make it contact with the 1st solution containing an alkali metal hydroxide as waste gas of the state which collect | recovered the carbon dioxide in waste gas and raised concentration. The chemical absorption method is a method of chemically absorbing CO ₂ from exhaust gas using a solvent such as amine and separating it as a high concentration CO ₂ gas. Physical absorption is a method in which CO ₂ is absorbed in a physical absorption liquid under high pressure and separated as a high concentration of CO ₂ gas. The membrane separation method is a method of separating as a high concentration CO ₂ gas using a membrane through which CO ₂ selectively permeates. The cryogenic separation method is a method of liquefying under cryogenic temperature and separating using the difference in boiling point. The oxyfuel combustion method is a method of burning the oxygen produced by the air separation device and separating it with a high concentration of CO ₂ concentration. The waste water can be treated efficiently by bringing the exhaust gas into contact with the first solution by increasing the concentration of CO _{2 in the} exhaust gas by the method described above.

Alkali metal hydroxide The alkali metal hydroxide is preferably at least one selected from the group consisting of sodium hydroxide, potassium hydroxide and lithium hydroxide. The alkali metal hydroxide is preferably sodium hydroxide because it is inexpensive and easily available.

As shown in Scheme 1 to produce a second solution comprising an alkali metal carbonate _{(M a2 CO 3, M a} HCO 3), and an exhaust gas containing carbon dioxide (CO _2), and an alkali metal hydroxide (M _A second solution containing an alkali metal carbonate can be obtained, as shown by the following formula (II), by contacting with a first solution containing _a OH).
2M _a OH + CO ₂ → M _a2 CO ₃ + H ₂ O (II)
(In formula (II), M _a is at least one alkali metal atom selected from the group consisting of Na, K and Li.)

By bringing exhaust gas containing carbon dioxide (CO ₂ ) into contact with a first solution containing alkali metal hydroxide (M _a OH), an alkali metal hydrogen carbonate (as represented by the following formula (III) M _a HCO ₃ (in FIG. 1, M _a HCO 3 represents an alkali metal hydrogen carbonate) may be formed.
M _a OH + CO ₂ → M _a HCO ₃ (III)
(In formula (III), M _a is at least one alkali metal atom selected from the group consisting of Na, K and Li.)

The molar ratio (carbon dioxide / alkali metal hydroxide) of carbon dioxide contained in the exhaust gas brought into contact with the first solution to the alkali metal hydroxide contained in the first solution is 0.1 to 1.0 Is preferred. The molar ratio of carbon dioxide (CO ₂₎ and alkali metal hydroxides _{(M a OH) (CO 2} / M a OH) is more preferably 0.2 to 0.9, more preferably 0.3 It is 0.8. In addition, M _a is at least one selected from the group consisting of Na, K and Li.
The molar ratio of carbon dioxide contained in the exhaust gas brought into contact with the first solution to the alkali metal hydroxide contained in the first solution (carbon dioxide / alkali metal hydroxide: CO ₂ / M _a OH) is 0. If it is 1 to 1.0, exhaust gas is effectively used to produce a second solution containing sufficient alkali carbonate to remove alkaline earth metal ions from alkaline waste as alkaline earth metal carbonate. Can.

FIG. 2 is a schematic view showing an example for carrying out the step of producing a second solution containing an alkali metal carbonate. As shown in FIG. 2, in the step of producing a second solution containing an alkali metal carbonate, a first water tank 1 for storing a first solution containing an alkali metal hydroxide, and the first water tank 1 The installation provided with the piping 2 which makes the waste gas containing a carbon dioxide contact the 1st solution stored by these can be used. In the step of producing a second solution containing an alkali metal carbonate, if there is a first water tank 1 storing the first solution containing an alkali metal hydroxide and a pipe 2 for contacting an exhaust gas containing carbon dioxide Well, the first water tank 1 for storing a first solution containing an alkali metal hydroxide is disposed at a place where exhaust gas is discharged from a thermal power plant, steel plant, cement plant or incinerator, and the exhaust gas contains carbon dioxide If there is the pipe 2 for introducing the water tank 1 into the water tank 1, the second solution containing the alkali metal carbonate can be manufactured, and a large-scaled apparatus and equipment are not required, so it can be easily implemented. In FIG. 2, reference numeral 3 schematically represents the lead-out path 3 for moving the second solution containing an alkali metal carbonate to another water tank (for example, the second water tank). Further, in FIG. 2, the first water tank 1 is in contact with a first solution containing an alkali metal hydroxide before being brought into contact with an exhaust gas containing carbon dioxide, or after being brought into contact with an exhaust gas containing carbon dioxide. A second solution comprising an alkali metal carbonate is stored.
The step of producing the second solution contributes to the suppression of greenhouse gas emissions by effectively utilizing carbon dioxide in the exhaust gas.

Step of obtaining alkaline earth metal carbonate As shown in FIG. 1, the method of treating waste water according to one embodiment of the present invention comprises the steps of producing the second solution, the second solution, and the alkaline earth metal. The waste water containing ions (M _e ²⁺ , and in FIG. 1, M _e ²⁺ represents an alkaline earth metal ion) is brought into contact with the alkaline earth metal ion in the waste water to form an alkaline earth metal carbonate ( _Me CO _3, in FIG. _1, M e CO ₃ includes a step obtained by the representative.) the alkaline earth metal carbonate. The contact between the second solution containing an alkali metal carbonate and the waste water containing an alkaline earth metal ion may be carried out, for example, by using a second water tank from a first water tank shown in FIG. 2 and a second water tank different from the first water tank. The second solution can be transferred to a second water tank, and the second water tank can be made to have waste water containing alkaline earth metal ions flow into contact with the second solution. The first water tank and the second water tank may be connected by piping, and the first water tank and the second water tank may not be connected by piping, and the second water tank including the alkali metal carbonate The step of producing the solution and the step of obtaining the alkaline earth metal carbonate may be performed separately. In the step of obtaining an alkaline earth metal carbonate, the alkaline earth metal carbonate formed in the solution is precipitated as a crystal in the solution by keeping in contact with carbon dioxide, and the alkaline earth metal carbonate is isolated by filtration. It is preferable to obtain it by filtration from the solution.

An example of the reaction in the step of obtaining alkaline earth metal carbonate by contacting waste water containing alkaline earth metal ion with a second solution containing alkali metal carbonate is shown below.
When the alkaline earth metal ion in the waste water is contained in the waste water, for example, in the form of a hydroxide, an alkaline earth metal carbonate is obtained by the reaction represented by the following formula (IV) or (V) Can.
M _e (OH) ₂ + M a ₂ CO ₃ → M _e CO ₃ + 2 M _a OH (IV)
(In the formula (IV), _{M a} is at least one alkali metal atom selected Na, from the group consisting of K and Li, _{M e} at least to, Mg, Ca, selected from the group consisting of Sr and Ba One kind of alkaline earth metal atom.)

M _e (OH) ₂ + M _a HCO ₃ → M _e CO ₃ + M _a OH + H ₂ O (V)
(Wherein, in the formula (V), M _a is at least one alkali metal atom selected from the group consisting of Na, K and Li, and M _e is at least one selected from the group consisting of Mg, Ca, Sr and Ba) One kind of alkaline earth metal atom.)

As the step of obtaining an alkaline earth metal carbonate from waste water containing an alkaline earth metal ion, for example, the case where the alkaline earth metal ion is in the form of a hydroxide is referred to as the above formula (IV) or the above formula (V) However, the alkaline earth metal ion contained in the waste water is not limited to that in which the hydroxide is dissolved to form an alkaline earth metal ion, and, for example, chloride (M _e Cl ₂ ) It may be dissolved to form an alkaline earth metal ion. Here, M _e is at least one alkaline earth metal atom selected from the group consisting of Mg, Ca, Sr and Ba.

Wastewater Containing Alkaline Earth Metal Ions Waste water containing alkaline earth metal ions is preferably waste water obtained by washing chlorine-containing incineration ash. In the case of waste water from which chlorine-containing incineration ash has been washed, the alkaline earth metal contained in the waste water from which chlorine-containing incineration ash has been washed even if components such as salts contained in the chlorine-containing incineration ash are not constant. The second solution containing alkali metal carbonate in such a concentration that the alkali earth metal carbonate can be obtained from the ions may be brought into contact, and the alkaline earth metal ions causing scale can be removed from the waste water. In the present specification, scale means sulfate such as gypsum, carbonate such as calcium carbonate, and more specifically, scale means gypsum (CaSO ₄ ), calcium carbonate (CaCO ₃ ), barium sulfate (CaCO ₃ ) At least one selected from the group consisting of BaSO ₄ ).

  When waste water containing alkaline earth metal ions is waste water from which chlorine-containing incineration ash is washed and contains chlorine-containing incineration ash and water, the mass ratio of chlorine-containing incineration ash to water is 1: 1 to 1 Preferably, it is 10. When the waste water containing alkaline earth metal ions contains chlorine-containing incineration ash and water, the waste water containing chlorine-containing incineration ash if the mass ratio of chlorine-containing incineration ash to water is 1: 1 to 1:10. The alkaline earth metal ion contained in the above can be removed as an alkaline earth metal carbonate by contacting it with a second solution containing an alkali metal carbonate. When the waste water containing alkaline earth metal ions is a waste water obtained by washing chlorine-containing incineration ash and contains chlorine-containing incineration ash and water, the mass ratio of chlorine-containing incineration ash to water (chlorine-containing incineration ash: water Is more preferably 1: 2 to 1: 8, still more preferably 1: 3 to 1: 6.

The waste water containing alkaline earth metal ions is pH-adjusted with a pH adjuster such as hydrochloric acid, and subjected to a water treatment step of removing heavy metals by addition of a coagulant such as ferric chloride, and then alkali metal carbonate ( _{M a2 CO 3, M a HCO} 3) is preferably contacted with a second solution comprising

FIG. 3 shows a method for treating waste water according to another embodiment of the present invention, in which waste water containing alkaline earth metal ions is subjected to pH adjustment, and further subjected to a first water treatment by addition of a coagulant. It is a flowchart which described the disposal method of waste water including a water treatment process.
As shown in FIG. 3, waste water containing alkaline earth metal ions is subjected to pH adjustment with a pH adjuster such as hydrochloric acid, and a first water treatment step for removing heavy metals by addition of a coagulant such as ferric chloride the after performing, alkali metal carbonates _{(M a2 CO 3, M a} HCO 3) preferably contacted with a second solution comprising a. Alkaline earth contained in waste water by adding a pH adjuster and / or a flocculant to waste water containing alkaline earth metal ions and performing a first water treatment step for pH adjustment and / or removal of heavy metals. The efficiency of the reaction between the metalloid ion and the alkali metal carbonate contained in the second solution can be improved. In the first water treatment step, the absorption liquid of the wet scrubber used for the treatment of exhaust gas containing carbon dioxide is added to the waste water containing alkaline earth metal ions to appropriately remove the coagulant etc. containing heavy metals You may do so.

FIG. 4 shows a method for treating wastewater according to another embodiment of the present invention, wherein the first water-treated wastewater containing alkaline earth metal ions is brought into contact with a second solution comprising an alkali metal carbonate, It is a flow figure which described the disposal method of drainage including the 2nd water treatment process of performing pH adjustment to drainage and the 2nd solution, and also performing the 2nd water disposal by addition of a coagulant.
As shown in FIG. 4, after contacting the waste water containing the alkaline earth metal ion with the second solution containing the alkali metal carbonate, the pH is adjusted with a pH adjuster such as hydrochloric acid, A second water treatment step may be performed to remove heavy metals by the addition of coagulants. By performing the second water treatment step, the efficiency of the reaction of the alkaline earth metal ion contained in the waste water and the alkali metal carbonate contained in the second solution can be further improved. In the second water treatment step, the absorption liquid of the wet scrubber used to treat the exhaust gas containing carbon dioxide is added to the solution containing the waste water and the second solution, and the coagulant etc. containing heavy metals are appropriately You may make it remove.

Volume ratio of waste water containing alkaline earth metal ion to second solution The volume ratio (second solution / drain water) of the second solution containing alkali metal carbonate to waste water containing alkaline earth metal ion is 0.01 It is preferable that it is -0.1. When the volume ratio of the second solution to the drainage is in the range of 0.01 to 0.1, the alkaline earth metal is reacted with the drainage containing the alkaline earth metal ion and the second solution containing the alkali metal carbonate. In the case of obtaining carbonate, drainage can be treated without requiring a large-capacity water tank depending on the amount of drainage. The volume ratio of the second solution containing alkali metal carbonate to the waste water containing alkaline earth metal ions (second solution / drainage) is more preferably 0.01 to 0.09, still more preferably 0. It is 01-0.08.

  The alkaline earth metal carbonate obtained by the method for treating waste water according to one embodiment of the present invention can be suitably used for cement compositions, mortars, materials for concrete, fillers, and building materials.

  EXAMPLES The present invention will next be described in detail by way of examples, which should not be construed as limiting the invention in any way.

Examples 1 to 4 and Comparative Example 1
Preparation of Exhaust Gas Containing Carbon Dioxide (CO ₂ ) A simulated exhaust gas was produced by simulating the exhaust gas discharged from a cement plant and mixed at a ratio of 80% by volume of air and 20% by volume of CO ₂ gas.

Preparation of First Solution Containing Alkali Metal Hydroxide (M _a OH) As _a first solution, tap water is used as a solvent, and 20 mass% sodium hydroxide (NaOH, special grade reagent, manufactured by Kanto Chemical Co., Ltd.) The containing sodium hydroxide solution was prepared.

Step of Producing a Second Solution Containing Alkali Metal Carbonate (M _a2 CO ₃ , MaHCO ₃ ) A second solution containing an alkali metal carbonate is prepared using equipment to produce a second solution shown in FIG. Manufactured. Specifically, as shown in FIG. 2, 500 mL of the sodium hydroxide solution was stored in the first water tank 1 as a first solution. When the simulated exhaust gas 2 is aerated from the piping 2 at a flow rate of 5 L / min for 60 minutes to the sodium hydroxide solution in the first water tank 1, the first solution becomes cloudy in the middle, so sodium bicarbonate is saturated And a second solution containing sodium carbonate (Na ₂ CO ₃ ) was obtained. The content of sodium carbonate in the obtained second solution was 3700 mmol / L.
The content of sodium carbonate in the second solution was measured as follows.
An appropriate amount of the second solution in which sodium carbonate is generated is collected, and 20 mass% hydrochloric acid is dropped to generate CO ₂ gas from the second solution, and the generated CO ₂ gas is granulated calcium chloride after passed through a packed piping by removing water, the piping filled with soda lime to absorb CO ₂ gas, and the mass in front of soda lime passing the CO ₂ gas, after passing a CO ₂ gas The change in mass of soda lime was measured, and the mass of the changed difference was measured as CO ₂ gas absorbed by soda lime. The amount of sodium carbonate contained in the second solution was converted from the measured mass of CO ₂ gas.
The first molar ratio of CO ₂ in the simulated exhaust gas is brought into contact with the solution to sodium hydroxide in the first solution _(CO 2 / NaOH) was 0.740. Here, the density of the sodium hydroxide solution was converted as the density of water 1 g / cm ³ .

Preparation of drainage containing alkaline earth metal ion (M _e ²⁺ ) 5 parts by mass of tap water (flying ash: water is 1: 1) to 1 part by mass of fly ash (chlorinated waste) discharged from a general waste incinerator Water was washed at a rate of 5). After stirring the mixed water of fly ash and water for 30 minutes, solid-liquid separation is performed with a filter press (product name; portable type filter press FS-3C-20, manufactured by Nippon Filter Co., Ltd.) to obtain washing water, It was simulated drainage. The pH of the simulated waste water is 10.8, as the alkaline earth metal ions ^{_(M e 2+),} calcium ion ^{(Ca 2+)} are included, the calcium concentration in the simulated wastewater was 11000mg / L. The calcium concentration in the simulated drainage was measured by an ICP emission spectrometer (inductively coupled plasma emission spectrometer) (ICP-AES, product name: ARCOS, manufactured by SPECTRO).
The obtained simulated waste water is adjusted with hydrochloric acid so that the pH is neutral (pH is 7), ferric chloride, flocculant (product name: Akofloc (registered trademark) A-150, MT Aqua Polymer Co., Ltd.) Heavy metals were removed and the first water treatment was performed (see FIG. 3). When the simulated drainage after the first water treatment was allowed to stand, gypsum was deposited from the simulated drainage and adhered to the wall of the solution. From this, it was confirmed that calcium ion is contained in the simulated drainage.

In the formulation shown in the process chart 1 to obtain an alkaline earth metal carbonate _(M e CO _3), with respect to the simulated waste water obtained by adding a second solution containing sodium carbonate _(Na 2 CO _3), The calcium concentration in the simulated drainage after addition of the second solution was measured. Measurement of calcium concentration was performed in the same manner as measurement of calcium concentration in simulated drainage. The results of calcium concentration in simulated drainage after addition of the second solution are shown in Table 1.

As shown in Table 1, in the waste water treatment method of Examples 1 to 4, the second example containing sodium carbonate (Na ₂ CO ₃ ) obtained by bringing the simulated exhaust gas into contact with the first solution containing sodium hydroxide. By bringing the solution into contact with the simulated drainage, the calcium (Ca) ion concentration in the simulated drainage is reduced, and if calcium ions are precipitated out as calcium carbonate from the simulated drainage and removed, the simulated drainage is removed. It was confirmed that calcium ions can be reduced, and the generation of scale can be suppressed. As shown in Table 1, in Examples 1 to 4, the volume ratio of the second solution to the simulated drainage (second solution / simulated drainage) was 0.01 to 0.075.

On the other hand, as shown in Table 1, in Comparative Example 1, the simulated drainage and the second solution containing sodium carbonate (Na ₂ CO ₃ ) are not in contact with each other. It was speculated that the simulated drainage in Example 1 contained more calcium (Ca) ions and could not suppress the generation of scale such as gypsum.

Example 5
Preparation of Exhaust Gas Containing Carbon Dioxide (CO ₂ ) A simulated exhaust gas was produced by simulating the exhaust gas discharged from a cement plant and mixed at a ratio of 80% by volume of air and 20% by volume of CO ₂ gas.

Preparation of First Solution Containing Alkali Metal Hydroxide (M _a OH) As _a first solution, tap water is used as a solvent, and 20 mass% of potassium hydroxide (KOH, special grade reagent, manufactured by Kanto Chemical Co., Ltd.) is used. A potassium hydroxide solution was prepared.

Step of Producing a Second Solution Containing an Alkali Metal Carbonate (M _a2 CO ₃ , M _a HCO ₃ ) A second solution was produced using equipment to produce a second solution shown in FIG. Specifically, as shown in FIG. 2, 500 mL of the sodium hydroxide solution was stored in the first water tank 1 as a first solution. When the simulated exhaust gas 2 is aerated from the piping 2 at a flow rate of 5 L / min for 60 minutes to the potassium hydroxide solution in the first water tank 1, the first solution becomes cloudy in the middle, so sodium bicarbonate is saturated A second solution containing potassium carbonate (K ₂ CO ₃ ) was obtained. The content of sodium carbonate in the obtained second solution was 1300 mmol / L.
The content of sodium carbonate in the second solution was measured as follows.
An appropriate amount of the second solution in which sodium carbonate is generated is collected, and 20 mass% hydrochloric acid is dropped to generate CO ₂ gas from the second solution, and the generated CO ₂ gas is granulated calcium chloride after passed through a packed piping by removing water, the piping filled with soda lime to absorb CO ₂ gas, and the mass in front of soda lime passing the CO ₂ gas, after passing a CO ₂ gas The change in mass of soda lime was measured, and the mass of the changed difference was measured as CO ₂ gas absorbed by soda lime. The amount of sodium carbonate contained in the second solution was converted from the measured mass of CO ₂ gas.
In addition, the molar ratio (CO ₂ / KOH) of CO ₂ in the simulated exhaust gas to be brought into contact with the first solution to potassium hydroxide in the first solution was 0.365. Here, the density of the sodium hydroxide solution was converted as the density of water 1 g / cm ³ .

Preparation of Waste Water Containing Alkaline Earth Metal Ion (M _e ²⁺ ) Water was washed at a ratio of 5 parts by mass (cement desalted dust: water is 1: 5) to 1 part by mass of cement desalted dust. After stirring the mixed water of cement desalted dust and water for 30 minutes, solid-liquid separation is carried out with a filter press (product name; portable type filter press FS-3C-20, manufactured by Nippon Filter Co., Ltd.) to obtain wash water And simulated drainage. The pH of the simulated drainage was 12.3.
The obtained simulated waste water is adjusted to pH 9 with hydrochloric acid, and using ferric sulfate and a coagulant (product name: Akofloc (registered trademark) A-150, manufactured by MT Aqua Polymer Co., Ltd.) Heavy metals were removed and a first water treatment was performed (see FIG. 3).

Step of obtaining alkaline earth metal carbonate (M _e CO ₃ ) 50 mL of a second solution containing potassium carbonate (K ₂ CO ₃ , special grade reagent, manufactured by Kanto Chemical Co., Ltd.) with respect to 1000 mL of the obtained simulated drainage Was added, and heavy metal was removed using ferric sulfate and a coagulant (product name: Akofurok (registered trademark) A-150, manufactured by MT Aqua Polymer Co., Ltd.), and a second water treatment was performed (Fig. 4). ICP emission spectrometry (inductively coupled plasma emission spectrometry) (ICP-AES, product) content of each component (atom or ion) shown in Table 2 dissolved in simulated drainage after second water treatment Name: measured by ARCOS, manufactured by SPECTRO. The results are shown in Table 2.
Furthermore, the content of calcium (Ca) in the precipitated salt (100% by mass) precipitated from simulated drainage using a crystallization method is ICP emission spectrometry (inductively coupled plasma emission spectrometry) (ICP-AES) Product name: ARCOS, manufactured by SPECTRO). Specifically, the crystallization method is using a rotary evaporator, placing simulated drainage in the rotary evaporator flask, evacuating the inside of the flask with a diaphragm pump, and heating to 60 ° C. with a water bath while The simulated waste water was concentrated to a volume of approximately one fifth (1/5), and the crystals were collected by filtration.

Comparative example 2
Table 2 in the simulated drainage in Comparative Example 2 in the same manner as in Example 5 except that the second solution containing potassium carbonate (K ₂ CO ₃ ) was not added to the simulated drainage in Example 5. The content of each component (atom or ion) shown in Table 1 was measured, and the content of calcium (Ca) in the precipitated salt (100% by mass) precipitated from the simulated drainage in Comparative Example 2 was measured. It shows in 2 and Table 3.

As shown in Table 2, in Example 5, the concentration of calcium (Ca) in the waste water was lower than that of the calcium (Ca) in the waste water of Comparative Example 2. From the results shown in Table 2, in Example 5, the concentration of calcium (Ca) causing the generation of the scale in the drainage is reduced, and calcium ions are precipitated as calcium carbonate and removed from the simulated drainage. For example, it has been confirmed that generation of scale can be suppressed. In addition, as shown in Table 3, the Ca content in the precipitated salt precipitated from the waste water of Example 5 by the crystallization method is as large as 2.60% by mass, and from the waste water of Comparative Example 2 by the crystallization method The Ca content in the precipitated salt deposited was as low as 0.05% by mass. From the results shown in Tables 2 and 3, it contains potassium carbonate (K ₂ CO ₃ ) obtained by bringing the exhaust gas containing carbon dioxide (CO ₂ ) into contact with the first solution containing potassium hydroxide (KOH) It was confirmed that calcium carbonate (CaCO ₃ ) can be obtained from calcium ions contained in the waste water by bringing the second solution into contact with the waste water containing calcium ions (Ca ²⁺ ).

  By effectively utilizing exhaust gas discharged from plant facilities such as a cement plant, alkaline earth metal ions in waste water can be removed to suppress the generation of scale, and the obtained alkaline earth metal carbonate is It is industrially applicable as a raw material for cement compositions, mortars, materials for concrete, fillers, and building materials.

  1: 1st water tank, 2: piping, 3: lead-out route

Claims (8)

  Contacting an exhaust gas containing carbon dioxide with a first solution containing an alkali metal hydroxide to produce a second solution containing an alkali metal carbonate, and using the second solution and an alkaline earth metal ion And D. contacting with the containing waste water to obtain alkaline earth metal ions in the waste water as an alkaline earth metal carbonate.   The method for treating wastewater according to claim 1, wherein the exhaust gas containing carbon dioxide is an exhaust gas discharged from a thermal power plant, a steel plant, a cement plant, or an incinerator.   The exhaust gas containing the carbon dioxide is the exhaust gas discharged from the cement plant, and the exhaust gas after the exhaust gas has passed through the electrostatic precipitator and / or the bag filter, and the combustion gas is extracted from the buttocks duct and desalted dust The waste water treatment method according to claim 1 or 2, wherein the waste water is at least one selected from exhaust gas discharged from a desalination bypass facility that recovers.   The waste water treatment method according to any one of claims 1 to 3, wherein the waste water containing the alkaline earth metal ion is a waste water obtained by washing chlorine-containing incineration ash.   The waste water according to claim 4, wherein the waste water containing alkaline earth metal ions contains chlorine-containing incineration ash and water, and the mass ratio of chlorine-containing incineration ash to water is 1: 1 to 1:10. Processing method.   The method for treating wastewater according to any one of claims 1 to 5, wherein the alkali metal hydroxide is at least one selected from the group consisting of sodium hydroxide, potassium hydroxide and lithium hydroxide.   The molar ratio (carbon dioxide / alkali metal hydroxide) of carbon dioxide contained in the exhaust gas to be brought into contact with the first solution to the alkali metal hydroxide contained in the first solution is 0.1 to 1.0 The waste water treatment method according to any one of claims 1 to 6, wherein   The waste water treatment method according to any one of claims 1 to 7, wherein a volume ratio of the second solution to the waste water (second solution / waste water) is 0.01 to 0.1.