JP5800436B2 - Boric acid recovery method and recovery apparatus - Google Patents

Description

  The present invention relates to a boric acid recovery method and a recovery apparatus that recover boric acid from wastewater or solid waste containing a boron compound and an alkali metal compound.

Various gases such as boric acid and sulfur are contained at a relatively high concentration in the exhaust gas discharged from the glass melting furnace in the production of the boron component-containing glass.
For this reason, this exhaust gas cannot be released into the atmosphere as it is, for example, after being treated with an alkali such as sodium hydroxide to remove harmful substances and then released into the atmosphere.

Wastewater and solid waste by-produced by such exhaust gas purification are often treated as industrial waste.
However, these waste water and solid waste contain a large amount of useful substances such as boron compounds and alkali metal compounds. In particular, boric acid is expensive, and if it can be recovered from wastewater treated with exhaust gas and reused, the production cost of the boron component-containing glass can be reduced. Also, from the viewpoint of environmental problems, it is preferable to recover as much useful substances as possible from wastewater and solid waste.

  Therefore, various methods have been proposed for recovering boric acid and the like from wastewater and solid waste containing a boron compound, as well as wastewater generated as a by-product in exhaust gas treatment in the production of boron component-containing glass.

For example, Patent Document 1 describes that waste water obtained by purifying exhaust gas generated when glass is melted is neutralized and then dried and used as a glass raw material.
Specifically, the exhaust gas discharged from the glass melting furnace is purified by contacting with water in a spray tower, or the exhaust gas purified with water is purified by a wet electric dust collector and released into the atmosphere. At this time, the waste water discharged from the spray dryer or wet electrostatic precipitator is neutralized with slaked lime and then dried, and the obtained solid is reused as a glass raw material.

Patent Document 2 describes that boric acid is recovered along with purification of exhaust gas by cooling exhaust gas containing boric acid and the like discharged from a glass melting furnace or the like.
Specifically, the exhaust gas is cooled to 70 ° C. or less by a method such as a combined use of a water spray type cooling means and an air mixing type cooling means, so that gaseous boric acid in the exhaust gas is precipitated as a solid, Next, boric acid is recovered and the exhaust gas is purified by a dry electrostatic precipitator.

Further, Patent Document 3 discloses boric acid from an ion exchange resin that has adsorbed boron by treating wastewater containing boron, such as nickel plating solution and aluminum surface treatment solution that have become waste liquid, and wastewater discharged in glass production. The recovery method is described.
In this method, first, sulfuric acid is passed through an ion exchange resin that has adsorbed boron to obtain a boron eluent. The boron eluent is neutralized by adding sodium hydroxide, and then concentrated by heating to precipitate and separate sodium sulfate. After cooling the remaining mother liquor to 35 to 40 ° C., sulfuric acid is added to adjust the pH to 4 to 6, thereby precipitating boric acid and separating the boric acid with a centrifugal separator or the like. The acid is recovered.

Japanese Unexamined Patent Publication No. 2004-238236 Japanese Unexamined Patent Publication No. 2003-305331 Japanese Unexamined Patent Publication No. 2002-29732

  By utilizing these methods, boric acid can be recovered and reused from waste water containing solid boron compounds or solid waste.

Here, exhaust gas discharged from a glass melting furnace or the like includes not only components dissolved in the furnace but also combustion exhaust gas components of the used fuel.
Therefore, in the method described in Patent Document 1, when a sulfur compound is contained in the exhaust gas, such as when heavy oil is used as a fuel for a glass melting furnace, a sulfur compound such as sulfate is also melted as a glass material for recycling. It will be thrown into the furnace. Thus, when sulfur compounds, such as a sulfuric acid, are contained in a glass raw material, sulfur components other than entering from a raw material will be concentrated, and problems, such as a glass quality fall, will arise.
Therefore, in this method, only wastewater and the like produced as a by-product in the purification of exhaust gas using a fuel that does not substantially contain sulfur can be treated.

Similarly, even when the exhaust gas is cooled and the boric acid is precipitated / recovered as a solid, as in the method described in Patent Document 2, if the exhaust gas contains sulfur, the exhaust gas is precipitated as a solid. When the temperature is lowered to the temperature, the temperature of the exhaust gas becomes lower than the acid dew point, and sulfuric acid is also precipitated. If sulfuric acid is deposited, the apparatus will be corroded, and the recovered boric acid will also contain sulfuric acid.
For this reason, even with this method, only exhaust gas using fuel that does not substantially contain sulfur can be treated.

On the other hand, in the method described in Patent Document 3, the wastewater generated as a by-product by treating the exhaust gas containing sulfur components as in the case of using heavy oil as the fuel for the glass melting furnace, The acid can be recovered.
However, in this method, since the waste water is treated with the ion exchange resin, a procedure for eluting boron from the ion exchange resin is required. When the waste water concentration is high, an ion exchange resin device necessary for the waste water treatment is provided. There is a problem of becoming very large. In addition, when the boron eluent contains various substances other than boric acid, sufficiently high-purity boric acid cannot be recovered.

  An object of the present invention is to solve the problems of the prior art, and can also treat liquids and solids containing sulfur components, such as wastewater produced by treating exhaust gas containing sulfur components, Another object of the present invention is to provide a boric acid recovery method and recovery apparatus that can recover high-purity boric acid from high-concentration liquids and liquids and solids containing various substances other than boron compounds. .

To achieve the above object, the present invention provides a boric acid recovery method for recovering boric acid from a liquid to be treated containing at least one of waste water containing a boron compound and an alkali metal compound and solid waste,
Concentrate after adding an acid to the liquid to be treated and adjusting the pH to less than 4, or adjusting the pH to be less than 4 by adding an acid after concentrating the liquid to be treated,
The solution to be treated which is concentrated and pH-adjusted and does not contain insoluble matter is cooled to an aqueous solution in which boric acid crystals are precipitated,
Separating the boric acid crystals from the aqueous solution in which the boric acid crystals are precipitated,
50 to 90% by mass of the filtrate after separating the boric acid crystals is added to the liquid to be treated before the concentration and pH adjustment,
The separated boric acid crystal is heated with a boric acid aqueous solution or water to dissolve the boric acid crystal, and the heated boric acid crystal is dissolved to cool the recrystallizing liquid. And an aqueous solution in which boric acid crystals are reprecipitated, and separating the boric acid crystals from the aqueous solution in which the boric acid crystals are reprecipitated,
A boric acid recovery method (1) is provided in which at least a part of the filtrate after separating the re-precipitated boric acid crystals is added to the liquid to be treated before the concentration and pH adjustment.

The present invention is also a boric acid recovery method for recovering boric acid from a liquid to be treated containing at least one of waste water and solid waste containing a boron compound and an alkali metal compound,
After adding an acid to the liquid to be treated and adjusting the pH to less than 4, it concentrates to precipitate an alkali metal salt, and the alkali metal salt is removed from the liquid to be treated on which the alkali metal salt has precipitated,
Alternatively, the liquid to be treated is concentrated to precipitate an alkali metal salt, and after removing the alkali metal salt from the liquid to be treated on which the alkali metal salt has been deposited, an acid is added to adjust the pH to less than 4.
The concentration and pH adjustment and dilution of the liquid to be treated from which the alkali metal salt has been removed by adding water,
The diluted liquid to be treated is cooled to an aqueous solution in which boric acid crystals are precipitated,
Separating the boric acid crystals from the aqueous solution in which the boric acid crystals are precipitated,
The filtrate after separating the boric acid crystals is added to the liquid to be treated before the concentration and pH adjustment,
The separated boric acid crystal is heated with a boric acid aqueous solution or water to dissolve the boric acid crystal, and the heated boric acid crystal is dissolved to cool the recrystallizing liquid. And an aqueous solution in which boric acid crystals are reprecipitated, and separating the boric acid crystals from the aqueous solution in which the boric acid crystals are reprecipitated,
A boric acid recovery method (2) is provided in which at least a part of the filtrate after separating the re-precipitated boric acid crystals is added to the liquid to be treated before the concentration and pH adjustment.

Further, the present invention is an apparatus for recovering boric acid from a liquid to be treated containing at least one of waste water and solid waste containing a boron compound and an alkali metal compound,
A concentrator for concentrating the liquid to be treated;
A pH adjuster in which an acid is added to adjust the pH of the liquid to be treated to less than 4;
A crystallizer for adjusting the pH and cooling the liquid to be treated that does not contain insoluble matter to form an aqueous solution in which boric acid crystals are precipitated;
A recovery device for separating and recovering the precipitated boric acid crystals from the aqueous solution;
A liquid feeding device for sending 50 to 90% by mass of the filtrate after separating and recovering the boric acid crystals to the liquid to be treated before the concentration and pH adjustment;
A heating and dissolving apparatus for heating the liquid for treatment for recrystallization in which an aqueous boric acid solution or water is added to the separated and recovered boric acid crystals to dissolve the boric acid crystals;
A crystallizer for heating the recrystallized liquid for recrystallization in which boric acid crystals are dissolved to cool the boric acid crystals into an aqueous solution in which the boric acid crystals are reprecipitated;
A recovery device for separating and recovering the reprecipitated boric acid crystals from the aqueous solution;
A liquid feeding device for sending at least a part of the filtrate after separating and recovering the reprecipitated boric acid crystals to the liquid to be treated before the concentration and pH adjustment;
A boric acid recovery device (1) is provided.

The present invention also provides:
An apparatus for recovering boric acid from a liquid to be treated containing at least one of waste water containing a boron compound and an alkali metal compound and solid waste,
A concentration device for concentrating the liquid to be treated to precipitate an alkali metal salt;
A removal device for removing the precipitated alkali metal salt from the liquid to be treated;
A pH adjuster in which an acid is added to adjust the pH of the liquid to be treated to less than 4;
A crystallization device in which the alkali metal salt is removed by the removal device, and the liquid to be treated whose pH is adjusted by the pH adjustment device is cooled to form an aqueous solution in which boric acid crystals are precipitated;
A recovery device for separating and recovering the precipitated boric acid crystals from the aqueous solution;
A liquid feeding device for sending the filtrate after separating and recovering the boric acid crystals to the liquid to be treated before the concentration and pH adjustment;
A heating and dissolving apparatus for heating the liquid for treatment for recrystallization in which an aqueous boric acid solution or water is added to the separated and recovered boric acid crystals to dissolve the boric acid crystals;
A crystallizer for heating the recrystallized liquid for recrystallization in which boric acid crystals are dissolved to cool the boric acid crystals into an aqueous solution in which the boric acid crystals are reprecipitated;
A recovery device for separating and recovering the reprecipitated boric acid crystals from the aqueous solution;
A liquid feeding device for sending at least a part of the filtrate after separating and recovering the reprecipitated boric acid crystals to the liquid to be treated before the concentration and pH adjustment;
A boric acid recovery device (2) is provided.

  According to the present invention, from wastewater and solid waste containing boron compounds and alkali metal compounds, such as wastewater and solid waste by-produced by purification of boric acid-containing exhaust gas discharged from the production process of borosilicate glass, High purity boric acid can be recovered by simple operation.

It is a flowchart for demonstrating an example of the boron collection | recovery method (1st aspect) of this invention. It is a flowchart for demonstrating an example of the boron collection | recovery method (2nd aspect) of this invention. It is a conceptual diagram for demonstrating an example of the to-be-processed liquid processed with the boron collection | recovery method of this invention.

  Hereinafter, the boric acid recovery method of the present invention will be described in detail with reference to the accompanying drawings.

FIG. 1 shows a flowchart of an example of the boric acid recovery method (first aspect) of the present invention, and FIG. 2 shows a flowchart of an example of the boric acid recovery method (second aspect) of the present invention.
As shown in FIG. 1 and FIG. 2, the boric acid recovery method of the present invention (hereinafter also simply referred to as recovery method) utilizes crystallization (crystallization / crystallization) by cooling from a solution to be treated. The acid is recovered. Hereinafter, unless it is specified that it is the first aspect or the second aspect, it will be described as the contents common to the first aspect and the second aspect.

The waste water and solid waste in the present invention both contain a boron compound and an alkali metal compound. In the present invention, a boron compound is distinguished from an alkali metal compound, and a compound containing a boron atom and an alkali metal atom such as sodium borate is regarded as a boron compound unless otherwise specified. Therefore, an alkali metal compound is an alkali metal compound containing no boron atom unless otherwise specified. Further, the boron compound is not limited to the alkali metal and may contain various constituent elements. Similarly, the alkali metal compound may contain various constituent elements other than boron.
The waste water in the present invention consists of water containing a boron compound and an alkali metal compound, and the solid waste in the present invention consists of a solid (powder etc.) containing a boron compound and an alkali metal compound. These waste water and solid waste may contain compounds other than boron compounds and alkali metal compounds.
These are exhausted from an industrial process that handles boron compounds and alkali metal compounds, and in particular, an exhaust gas treatment process in which exhaust gas discharged from a borosilicate glass manufacturing process described later is brought into contact with a basic aqueous alkali metal compound solution. It is preferable that it is the waste_water | drain or solid waste discharged | emitted from.
The liquid to be treated in the present invention is a liquid to be treated containing at least one of the waste water and solid waste, and as shown in FIG. 1 or FIG. 2, in the case of the waste water, the waste water itself may be used. It may be a water dilution obtained by adding water. In the case of the solid waste, it is an aqueous solution obtained by adding water to the solid waste. Moreover, as shown in FIG. 1 or FIG. 2, the said waste water can be used as the water added to solid waste, and the mixture of solid waste and waste water is diluted with water to make the liquid to be treated in the present invention. You can also.
Furthermore, an aqueous solution (such as a filtrate) containing boric acid after depositing boric acid crystals described below and separating the crystals can also be used as at least part of the diluted water.
Furthermore, these liquids to be treated may be a mixture of two or more thereof.

Examples of the waste water and solid waste in the present invention include, for example, FPD (Flat Panel Display) glass, borosilicate glass used for solar cell glass, glass melting furnace, molten glass forming furnace, etc. The waste water and solid waste by-produced when purifying the exhaust gas discharged | emitted from are illustrated.
In the manufacture of borosilicate glass, since boron oxide is volatile, boron oxide volatilizes from high-temperature glass raw materials and molten glass that are in the process of melting, and is mixed into exhaust gases such as combustion exhaust gas. It is discharged from the manufacturing process of borosilicate glass as exhaust gas. For this reason, purification of this exhaust gas is required, and in many cases, purification is performed using an aqueous solution or powder of a basic compound in order to perform efficient purification. As the basic compound, an alkali metal compound, particularly a sodium compound is used. Specific examples of the alkali metal compound include water-soluble basic sodium compounds such as sodium hydroxide, sodium bicarbonate, and sodium carbonate.

FIG. 3 conceptually shows an example of the exhaust gas purification process.
In the purification process shown in FIG. 3, the exhaust gas discharged from the glass melting furnace for producing borosilicate glass is first cooled to about 200 ° C. with water or an aqueous sodium hydroxide solution in a cooling tower. At this time, if necessary, sodium hydroxide or sodium hydrogen carbonate (only sodium hydroxide aqueous solution is shown in FIG. 3) is added as a detoxifying agent.
Next, sodium hydrogen carbonate powder or the like is added to the cooled exhaust gas as necessary, and the exhaust gas is purified with a bag filter. Further, the exhaust gas purified by the bag filter is purified by treating with sodium hydroxide or the like in a venturi scrubber and released into the atmosphere as a purified exhaust gas. The alkali metal compound such as sodium hydroxide added in the exhaust gas purification process may be added as a solid or an aqueous solution, or both a solid and an aqueous solution may be added.

In this purification process, solid waste collected by the bag filter and waste liquid from the venturi scrubber may contain boric acid, boron oxide, sodium borate, sodium hydroxide, sodium chloride, sodium fluoride, sodium sulfate, nitric acid. Various boron compounds and alkali metal compounds such as sodium are contained.
Therefore, in the recovery method of the present invention, the solid waste collected by the bag filter in this purification process can be handled as the solid waste in the present invention, and the waste liquid discharged from the venturi scrubber is used as the present invention. Can be treated as drainage. Hereinafter, these waste liquids and solid waste are also referred to as waste water and solid waste.

  That is, in the boric acid recovery method of the present invention, when the by-product by the exhaust gas purification process shown in FIG. 3 is treated, waste water discharged from the venturi scrubber is treated with waste water containing a boron compound and an alkali metal compound. To do. The solid waste collected by the bag filter is a solid waste containing a boron compound and an alkali metal compound. Therefore, the to-be-processed liquid in the said this invention is obtained using these.

  In the exhaust gas purification process shown in FIG. 3, when solid waste and waste liquid containing boron compounds and alkali metal compounds are discharged from the cooling tower, these were also collected by the bag filter. Similarly to the waste water discharged from the solid waste or the venturi scrubber, the waste water containing the boron compound and the alkali metal compound can be handled as the solid waste.

  In the recovery method of the present invention, the waste water and solid waste containing the boron compound and the alkali metal compound are limited to waste water and solid waste by-produced in the purification of exhaust gas in the borosilicate glass manufacturing process. The various waste water and solid waste containing a boron compound and an alkali metal compound are illustrated.

The solid waste and waste water in the present invention may each contain a sulfur compound, a chlorine compound, a fluorine compound, etc. in addition to the boron compound and the alkali metal compound. These components other than the boron compound and the alkali metal compound are compounds containing neither boron nor an alkali metal as constituent elements as defined above. Therefore, for example, sodium chloride, sodium fluoride, sodium sulfate, sodium nitrate and the like are alkali metal compounds in the present invention. The solid waste and waste water in the present invention may each contain a small amount of a sulfur compound, a chlorine compound, or a fluorine compound, but it is preferable that the solid waste and the waste water do not substantially contain.
The boron compound contained in the solid waste and waste water in the present invention is preferably mainly boric acid and sodium borate. The alkali metal compound contained in the solid waste and waste water in the present invention is preferably mainly sodium sulfate and sodium chloride, and may contain relatively small amounts of sodium fluoride, sodium nitrate, etc. in addition to these. .
As a constituent element ratio (mass ratio) of the compound contained in the solid waste and waste water in the present invention, the alkali metal amount is 0.6 to 13, and the sulfur amount is 0 in terms of a relative ratio where the boron amount (mass) is 1. It is preferable that -6 and the amount of chlorine are 0-6. Note that sulfur and chlorine in this constituent element ratio are mainly elements in alkali metal compounds such as sodium sulfate and sodium chloride.
Typical examples of solid waste and wastewater containing various compounds having such constituent element ratios include wastewater and solid waste by-produced by purification of exhaust gas discharged from the borosilicate glass manufacturing process. The present invention can recover high-purity boric acid from such waste water and solid waste.

As the concentration of each constituent element contained in the liquid to be treated in the present invention including at least one of the waste water and the solid waste, the boron concentration is 10 to 40 g / L, the sodium concentration is 20 to 400 g / L, and the sulfur concentration is 0. It is preferable that it is -200g / L and a chlorine concentration is 0-200g / L. In addition, sulfur and chlorine in each constituent element concentration are constituent elements in the alkali metal compound.
Moreover, it is considered that many of the compounds in the liquid to be treated are ionized. For example, it is considered that borate ions, sodium ions, sulfate ions, chloride ions, fluoride ions, nitrate ions and the like are present in the liquid to be treated.
In addition, it is preferable that a to-be-processed liquid does not contain an insoluble content. However, as long as it does not contain an insoluble component at the stage of heating to an aqueous solution, it may contain an insoluble component that is dissolved by heating. If necessary, the insoluble matter can be removed by filtration or the like from the liquid to be treated before heating.

In the recovery method of the present invention, as a preferred embodiment, as shown in FIG. 1, such a liquid to be treated is heated to obtain a heated aqueous solution. This heated aqueous solution needs to contain no insoluble matter. If insoluble matter is present in the heated aqueous solution, the insoluble matter is removed by filtration or the like.
Although the heating temperature of heating aqueous solution is not specifically limited, 50 degreeC or more is preferable. When the heating temperature of the heated aqueous solution is less than 50 ° C., the boric acid recovery rate is low, and the precipitated boric acid crystals do not grow sufficiently, resulting in inconvenience that the separation performance deteriorates.
The heating temperature of the heated aqueous solution is preferably 100 ° C. or lower, and more preferably 70 ° C. to 80 ° C.
Thereby, the recovery rate and separation performance of boric acid crystals can be improved.

  In the recovery method of the present invention, as described above, the heating of the liquid to be treated is performed as a preferred embodiment and is not an essential step.

Next, an acid is added to the heated aqueous solution (in the case where heating is not performed, the liquid to be treated; hereinafter, the liquid to be treated and the heated aqueous solution are also simply referred to as the liquid to be treated) to adjust the pH to less than 4.
In the present invention, the pH adjusting device (pH adjusting tank) is adjusted so that the pH of the liquid to be treated is less than pH 4 in the heated state (when not heated, the pH of the liquid to be treated is less than pH 4. The same applies hereinafter). ), It is possible to recover boric acid crystals with high purity. In addition, by adjusting the pH before cooling crystallization, the cooling operation can be performed after converting the alkali metal borate in the aqueous solution to boric acid, and control of the particle shape and particle diameter of the boric acid crystal Becomes easy. Further, this also improves the purity of boric acid.

Further, when the pH of the liquid to be treated whose pH is adjusted is 4 or more, boric acid having a sufficient purity cannot be recovered when the solid content concentration of the liquid to be treated is high. Boric acid having a large amount of impurities such as alkali metal borate is difficult to reuse as a raw material for borosilicate glass that does not contain an alkali metal component. Further, when the obtained boric acid is further purified by a recrystallization method, it becomes difficult to obtain high-purity boric acid.
The pH of the liquid to be treated whose pH is adjusted is less than 4, preferably 3.5 or less, more preferably less than 3.5, and still more preferably 1 to 3.
Thereby, higher purity boric acid crystals can be recovered.

The acid used for adjusting the pH of the liquid to be treated is not particularly limited, and various inorganic acids such as sulfuric acid, hydrochloric acid, and nitric acid can be used. Such acid is preferably sulfuric acid.
When boric acid is recovered from wastewater or the like by-produced by purification of exhaust gas discharged from a borosilicate glass melting furnace, sulfate ions are often included in the wastewater or the like. Therefore, by using sulfuric acid for pH adjustment, addition of extra components to the liquid to be treated can be suppressed.
Moreover, when hydrochloric acid is used for pH adjustment, chloride ions may cause corrosion of the crystallizer, and use of sulfuric acid is more preferable.

In addition, in the collection | recovery method of this invention, pH adjustment is not limited to performing after heating a to-be-processed liquid.
That is, the pH of the liquid to be treated may be adjusted before heating the liquid to be treated as shown by the dotted line in FIG. 1 or after concentration described later.

The to-be-treated liquid whose pH has been adjusted is preferably concentrated in a concentrating device before cooling to obtain a concentrated to-be-treated liquid. By concentrating, the recovery rate of boric acid can be improved.
As a concentrating device, for example, a known evaporating and concentrating device that heats and evaporates a liquid to be treated from a nozzle on the surface of a plurality of heat transfer tubes in which a heating fluid such as steam flows in a decompressed concentration crystal can Etc. can be used. In such a concentrator, the liquid to be treated in the concentrated crystal can is circulated to a nozzle that is sprayed on a plurality of heat transfer tubes by a circulation pump.
The vapor generated in the concentrating device is condensed and introduced into a condensed water tank, and the condensed water in the condensed water tank is used as dilution water, washing water for each device or washing water for crystals in the recovery process.

In the recovery method of the present invention, either the first mode or the second mode described later is selected depending on the concentrations of boron and sodium (Na) in the liquid to be treated.
The first aspect is preferred when the Na salt does not precipitate when the liquid to be treated is concentrated to a boron concentration suitable for crystallization and the pH is adjusted. When Na salt precipitates when the liquid to be treated is concentrated to a boron concentration suitable for crystallization, or when the liquid to be treated is concentrated to a boron concentration suitable for crystallization and pH adjustment is performed, the second salt described later is used. This embodiment is preferred.

Specifically, according to the mass ratio (Na / B) of sodium (Na) and boron (B) contained in the liquid to be treated before concentration and pH adjustment, the first mode and the second mode described later are used. Select which one to apply.
When the liquid to be treated contains Na ₂ SO ₄ and NaCl, the first embodiment is preferable if the mass ratio (Na / B) is 3.6 or less, and the mass ratio (Na / B) exceeds 3.6. If so, the second embodiment is preferable.
When the liquid to be treated does not contain Na ₂ SO ₄ and contains NaCl, the first aspect is preferable if the mass ratio (Na / B) is 3.9 or less, and the mass ratio (Na / B) is 3 If it exceeds .9, the second embodiment is preferred.
When the liquid to be treated contains Na ₂ SO ₄ and does not contain NaCl, the first aspect is preferable if the mass ratio (Na / B) is 3.1 or less, and the mass ratio (Na / B) is 3 If it exceeds 0.1, the second embodiment is preferred.

In the first aspect, concentration is performed to such an extent that insoluble matter does not precipitate. In addition, an insoluble matter here is a crystalline solid which precipitates when a content component exceeds saturation solubility as a result of performing concentration and pH adjustment.
In the second embodiment, the concentration is performed so that an alkali metal salt which is an insoluble substance is precipitated. An Na salt that is an alkali metal salt contained in the liquid to be treated, such as sodium sulfate (Na ₂ SO ₄ ) or sodium chloride (NaCl), is precipitated as impurities.
In both the first aspect and the second aspect, in order to improve the recovery rate of boric acid, it is preferable that the solid concentration of the liquid to be treated whose pH is adjusted by concentration is 15% by mass or more. In other words, it is preferable to concentrate until the solid content concentration of the liquid to be treated is 15% by mass or more.

  On the other hand, the solid content concentration of the liquid to be treated after concentration is preferably 30% by mass or less because of difficulty in handling and deterioration of crystal quality due to insufficient stirring.

  Although concentration temperature is not specifically limited, 50 to 100 degreeC is preferable. By setting the concentration temperature within the above range, the recovery rate of boric acid can be improved. The temperature at the time of concentration may be different from the temperature of the liquid to be processed at the time of manufacturing the liquid to be processed or pH adjustment. Usually, the concentration is performed at a temperature comparable to or higher than the liquid to be treated after pH adjustment. Moreover, in vacuum concentration etc., you may become below the temperature of the to-be-processed liquid after pH adjustment. The decompression is preferably performed at 10,000 Pa to 80000 Pa, more preferably 20000 Pa to 70000 Pa. The temperature of the heated aqueous solution after concentration is preferably 50 ° C. to 100 ° C., particularly preferably 70 ° C. to 80 ° C., like the temperature of the heated liquid to be treated.

However, in the first aspect, it is preferable that no insoluble matter is generated by the concentration under any conditions.
In the second aspect, it is preferable that the alkali metal salt deposited on the concentrated liquid does not exceed 10% by mass in consideration of equipment load.

In the case of the second aspect, by adjusting the tip speed of the impeller of the circulation pump of the concentrator, the particle size of the precipitated Na salt is controlled, and the Na salt is selectively removed in the removal step. .
Specifically, the tip speed of the impeller of the circulation pump is set to, for example, 10 to 18 m / sec, and thereby the particle diameters of sodium salt and sodium sulfate that are precipitated Na salts are set to about 100 to 300 μm. . At this time, the particle diameter of the boric acid crystals that are undesirably precipitated is 20 to 50 μm, and the Na salt that is an impurity can be separated from the concentrated liquid containing boric acid by the subsequent cyclone.
The solid-liquid separation device is not limited to a cyclone, and separation of large-diameter crystals by a horizontal continuous centrifugal separator, classification by a fluidized bed, or a batch-type sedimentation separation method may be used.

In the second aspect, since the pH adjustment step of adding acid to the liquid to be treated is performed before the concentration step, the alkali metal borate in the liquid to be treated is previously converted into boric acid and an alkali metal salt. Then, since concentration is performed, the alkali metal salt crystal including the alkali metal salt generated by this conversion can be grown in the concentration step, thereby efficiently removing the alkali metal salt in the removal step. be able to.
In the case of the second aspect, the liquid to be treated from which the crystals of the Na salt as an impurity have been removed by the cyclone is introduced into the crystallization stock solution tank as a crystallization stock solution. Dilution water is added to the crystallization stock solution tank to dilute the liquid to be treated (referred to as a dilution step). In this way, since the liquid to be treated is diluted with water for dilution, precipitation of impurities other than boric acid crystals can be suppressed in the subsequent crystallization process.

In the recovery method of the present invention, as shown in FIG. 1 or FIG. 2, the treatment is performed in the order of “(heating of liquid to be treated →) pH adjustment → concentration” (hereinafter referred to as Embodiment 1). As described above, no limitation is made.
That is, as another embodiment of the first aspect and the second aspect, after the liquid to be treated is heated to 50 ° C. or more (however, as described above, heating is not essential), the concentration is performed. In a state where the liquid to be treated (the liquid to be treated in which Na salt crystals are removed by a cyclone after concentrating and precipitating Na salt crystals as impurities) is 50 ° C. or higher, sulfuric acid or the like As a concentrated pH-adjusted liquid adjusted by adjusting the pH by adding an acid and adjusting the pH to less than 4, preferably 3.5 or less, more preferably less than 3.5, and even more preferably 1 to 3. It is also possible (hereinafter referred to as Embodiment 2).
Also in this case, for the same reason as described above, the concentration of the solid content of the concentrated liquid to be treated whose pH is adjusted is preferably 15% by mass or more, and 30% by mass or less. preferable.

  In the first embodiment, since the highly acidic liquid to be treated after adjusting the pH by adding sulfuric acid is heated and concentrated by the concentrating device, the concentrating device needs to use an expensive material that is not easily corroded. On the other hand, in the second embodiment, since the pH adjustment step is performed after the concentration step in the concentrator, the concentrator does not need to use an expensive material compared to the first embodiment and can reduce the cost.

  Furthermore, the following embodiment is mentioned as another embodiment of a 2nd aspect.

(Embodiment 3 of the second aspect)
In Embodiment 2 of the second aspect, a pH adjustment step is provided between the removal step and the crystallization step. In this case, the liquid to be treated after the removal step (corresponding to a saturated solution of an alkali metal salt) As a result of adding an alkali metal salt generated with the conversion of the alkali metal borate by adjusting the pH, a new alkali metal salt crystal may be generated. In this case, since the entire amount of the alkali metal salt crystals is supplied to the crystallization stock solution tank, the amount of dilution water used to suppress the mixing of the alkali metal salt crystals into the crystallization process may increase. Thereby, the boric acid concentration in the diluted crystallization undiluted solution also decreases, and the amount of boric acid crystals precipitated in the crystallization step may decrease.
In that case, as a form different from Embodiments 1 and 2 of the second aspect, a pH adjustment step can be provided between the concentration step and the removal step (not shown).
In this embodiment, at least a part of the alkali metal salt crystals newly generated by pH adjustment is removed in the removal step, so that water for dilution is provided compared with the case where a pH adjustment step is provided between the removal step and the crystallization step. The amount of boric acid that can be recovered in the crystallization step can be increased. However, in this case, since the removal step is performed in a state where the pH is low, in order to reduce the acid resistance load in the removal step, a pH adjustment step is provided between the removal step and the crystallization step. It is preferable. In addition, since the alkali metal salt crystals precipitated by the addition of sulfuric acid tend to be microcrystals, when separating the alkali metal salt crystals with a cyclone or the like, the alkali metal salt crystals may not be efficiently removed, In that case, it is preferable to add sulfuric acid before the concentration step.

(Embodiment 4 of the second aspect)
Before the concentration step, the pH is adjusted so that at least a part of the alkali metal borate in the liquid to be treated is converted into boric acid and an alkali metal salt (preferably pH 4 to 6, more preferably pH 4 to 5.5, further Preferably, pH 4 to 5) is performed, and after the removal step, pH adjustment (preferably less than pH 4, more preferably pH 1 to 3) can be performed in order to increase the purity of boric acid (not shown).
In this embodiment, since the pH of the liquid processed by the concentrator is relatively high, the use of expensive materials can be suppressed, the cost can be reduced, and at least a part of the alkali metal borate is converted before the concentration step. As a result, the alkali metal salt generated in this process grows to a particle size that is suitable for removal in the concentration step, so that it can be removed efficiently in the removal step, resulting in a reduction in the amount of diluting water and crystallization. The amount of boric acid crystals precipitated in the process can be increased.

Next, the pH-adjusted liquid to be treated (preferably, the pH-adjusted liquid to be treated) is cooled to a certain temperature to precipitate boric acid crystals. That is, a boric acid crystal is precipitated by crystallization by cooling (cooling crystallization) with a crystallization apparatus (crystal can). In cooling crystallization, boric acid crystals are precipitated as a result of a decrease in the solubility of boric acid crystals as the temperature of the aqueous solution decreases during the cooling operation. Hereinafter, the temperature at the end of the cooling operation is referred to as the cooling temperature.
In the present invention, boric acid can be selectively recovered from a liquid to be treated containing a boron compound or an alkali metal compound by utilizing crystallization. Moreover, since boric acid can be selectively recovered by crystallization, boric acid can also be recovered from wastewater and solid waste produced as a by-product by purifying exhaust gas containing sulfur components. Furthermore, as described above, after adjusting the pH of the heated aqueous solution with an acid, cooling and precipitating the boric acid crystal by crystallization makes it easy to control the particle shape and particle diameter of the boric acid crystal. Furthermore, the purity of the boric acid crystal to be recovered can be improved.
In particular, in the case of the second embodiment, prior to cooling crystallization, the liquid to be treated is concentrated to precipitate and remove the alkali metal salt as an impurity. Also, it is possible to recover boric acid with high purity.

In addition, as also shown in Patent Document 3, after cooling the liquid to be treated containing boric acid (boron compound), a method of adjusting the pH to a predetermined acidity by adding sulfuric acid or the like can also form boric acid crystals. The boric acid can be recovered by precipitation.
However, in this method, boric acid crystals are instantaneously precipitated by adjusting the pH, so impurities such as Na salts are easily taken into boric acid crystals, and adhere to the crystal surface because they are microcrystalline. Since the amount of water containing impurities such as Na salt increases, high purity boric acid crystals cannot be obtained when various compounds are mixed in the liquid to be treated.
Further, in this processing order, boric acid crystals are instantaneously precipitated, which causes a disadvantage that the shape of the boric acid crystals is distorted.

Although the said cooling temperature is not specifically limited, 30 degreeC or more and less than 50 degreeC are preferable. When the cooling temperature is 50 ° C. or higher, there is a disadvantage that the boric acid crystals cannot be sufficiently precipitated and the recovery rate is deteriorated.
Conversely, when the cooling temperature is less than 30 ° C., there arises a disadvantage that crystals of alkali metal compounds such as sodium sulfate are precipitated as mixed crystals.
Further, the difference between the temperature of the liquid to be treated whose pH is adjusted before cooling and the cooling temperature is suitably 10 ° C. or higher, preferably 20 ° C. or higher. Most preferably, it is 30 degreeC or more. By increasing this temperature difference, the recovery rate of boric acid crystals can be improved.

  Thereby, mixing of impurities can be minimized and the recovery rate of boric acid crystals can be further improved.

In addition, it is preferable to perform precipitation of the boric acid crystal | crystallization by cooling the to-be-processed liquid adjusted pH.
By cooling under reduced pressure and precipitating boric acid crystals, scale formation on the heat transfer surface, which is a concern when the jacket cooling method is adopted, can be suppressed, and the maintenance of the equipment becomes easy and boric acid The recovery rate of boric acid can be improved by reducing the loss of crystals.
In this case, the height of the pressure is not particularly limited, but it is preferably 10000 Pa to 70000 Pa, more preferably 20000 Pa to 60000 Pa at the start of cooling, and preferably 1000 Pa to 15000 Pa, more preferably at the end of cooling. It is preferable to reduce the pressure at 2000 Pa to 8000 Pa.

After boric acid crystals are precipitated by cooling the liquid whose pH has been adjusted, the precipitated crystals are separated from the aqueous solution by a recovery device (centrifugal separator) in the recovery step, and the boric acid crystals are recovered. . At this time, it is preferable that the temperature of the aqueous solution containing the crystals is maintained at the cooling temperature, preferably 30 ° C. or higher and lower than 50 ° C., to perform the separation operation.
The boric acid crystal separation method is not particularly limited, and various known separation methods for separating a solid component from a liquid, such as filtration, centrifugation, and sedimentation, can be used.

Here, the boric acid which did not precipitate is contained in the filtrate after separating the boric acid crystals.
Therefore, this filtrate is sent to a liquid to be treated containing at least one of waste water and solid waste by a liquid feeding device, and reused as a raw material for the liquid to be treated (hereinafter also referred to as adding a filtrate to the liquid to be treated). It is preferable to do this. That is, it is preferable to use this filtrate as the drainage or diluted water for solid waste. For example, a mixture of the solid waste collected by the bag filter and the filtrate can be added to the liquid to be treated (or used as the liquid to be treated), and the solid waste and the filtrate can be used. If necessary, water can be added to the mixture to obtain the liquid to be treated. Thereby, the recovery rate of the boric acid from the said waste liquid or solid waste can be improved more.

Here, the remaining filtrate from which the boric acid crystals are first separated contains a lot of boric acid, but also contains impurities. Therefore, in the first aspect, if the amount of the filtrate used in the liquid to be treated is too large, the impurities are gradually concentrated, and the impurity concentration in the liquid to be treated becomes high and proper processing cannot be performed. There is a risk of it.
Therefore, the filtrate added to the liquid to be treated and reused is preferably part of the filtrate. Specifically, the filtrate added to the liquid to be treated is preferably 50% by mass to 90% by mass with respect to the entire filtrate after separating the boric acid crystals. Thereby, the recovery rate of boric acid can be suitably improved while preventing adverse effects due to an increase in impurities in the liquid to be treated.
In the second aspect, the Na salt, which is an impurity contained in the liquid to be treated, is concentrated and precipitated by a concentrating device and removed by a cyclone as a removing device, so that the alkali metal salt concentration is high. Even when the treatment liquid is concentrated, the concentrated liquid can be obtained with almost no alkali metal crystals. Therefore, the filtrate that is added to the liquid to be treated and reused can be at least a part of the filtrate, preferably the whole. Thereby, the recovery rate of boric acid can be improved suitably.
In both the first aspect and the second aspect, a part of the treated water after recovering the boric acid crystals is discarded, and the remaining part is returned to the addition step. Therefore, by adjusting the amount of treated water discarded, that is, When the alkali metal salt concentration of the liquid to be treated is high and a load is imposed on the concentration step and the removal step, the amount of treated water can be increased to facilitate the concentration step and the removal step. On the other hand, when the load of the concentration process or the removal process is not large, the waste amount of treated water can be reduced and the boric acid recovery rate can be increased.

Thus, the boric acid crystals recovered by the recovery method of the present invention are sufficiently high purity, and can be used as they are as raw materials for borosilicate glass.
However, depending on the application and the like, the recovered boric acid crystals may not be sufficiently clean, and the purity of the boric acid crystals may not reach a desired value. In that case, the recovered boric acid crystals may be washed with a boric acid aqueous solution or water containing no alkali metal component. The boric acid crystal may be washed by a known method. The boric acid aqueous solution not containing an alkali metal component includes not only alkali metal compounds but also boron compounds containing alkali metal atoms such as sodium borate, compounds containing alkali metal atoms other than these compounds, alkali metal ions, and the like. No boric acid aqueous solution.

  Moreover, the purity of the recovered boric acid crystals may not be sufficiently high depending on the application. In that case, it is preferable to further improve the purity of the boric acid crystal by recrystallization (recrystallization treatment). If necessary, the recrystallization treatment may be carried out twice or more, but a sufficiently high-purity boric acid crystal can be usually obtained by one recrystallization treatment.

In the recrystallization treatment, as shown in FIG. 1 or FIG. 2, the recovered boric acid crystals are added with water (or an aqueous boric acid solution not containing an alkali metal component. Or an aqueous boric acid solution that is a filtrate after recrystallization described later. (Hereinafter also referred to as a boric acid aqueous solution) to form a liquid for recrystallization, and the boric acid crystals are dissolved by heating with a heating and dissolving apparatus.
There are no particular limitations on the amount of water or boric acid aqueous solution added to prepare the recrystallization liquid, and it may be set appropriately according to the amount of boric acid crystals. The heating temperature is not particularly limited as long as it is a temperature at which boric acid crystals can be dissolved, but is preferably 50 ° C to 100 ° C, and more preferably 70 ° C to 80 ° C.

Next, the recrystallization liquid is cooled to 30 ° C. or higher and lower than 50 ° C. to reprecipitate boric acid crystals. That is, boric acid crystals are reprecipitated by cooling crystallization with a crystallizer (crystal can). The difference between the pre-cooling temperature of the recrystallization liquid and the post-cooling temperature is suitably 10 ° C. or higher, preferably 20 ° C. or higher. Most preferably, it is 30 degreeC or more. By increasing this temperature difference, the recovery rate of boric acid crystals in the recrystallization process can be improved.
The reason for limiting the cooling temperature range is the same as in the previous crystallization. For the same reason as described above, the reprecipitation of boric acid crystals by cooling is preferably performed under the same reduced pressure as before.

In this manner, after reprecipitation of boric acid crystals by cooling crystallization, the boric acid crystals are separated again from the aqueous solution containing boric acid crystals by a recovery device (centrifugal separator) in the same manner as described above. Then, the recrystallized boric acid crystals are recovered.
The boric acid crystal obtained by purification by this recrystallization treatment is a higher-purity boric acid crystal with less impurities such as an alkali metal compound.

Here, boric acid that has not precipitated is also contained in the filtrate after separating the boric acid crystals again in this recrystallization treatment (hereinafter referred to as the filtrate after recrystallization).
Therefore, as shown in FIG. 1 or FIG. 2, the filtrate after this recrystallization is at least partly at least one of drainage and solid waste by a liquid feeding device, like the filtrate after boric acid crystal separation described above. It is preferably sent to the liquid to be treated and reused as a raw material for the liquid to be treated (hereinafter also referred to as adding a filtrate to the liquid to be treated). Thereby, the collection | recovery rate in the collection | recovery of boric acid from a to-be-processed liquid and a recrystallization process can be improved more.
Also at this time, similarly to the above, solid waste may be added / mixed to the filtrate and added to the liquid to be treated (or may be used as the liquid to be treated).
5 to 100% by mass, preferably 10 to 75% by mass, more preferably 15 to 50% by mass of the filtrate after separating the reprecipitated boric acid crystals is added to the liquid to be treated before the concentration and pH adjustment. In addition, it is preferable to add 0 to 95 mass%, preferably 25 to 90 mass%, more preferably 50 to 85 mass% of the filtrate to the recrystallization liquid.

Here, the recrystallized filtrate also contains impurities such as alkali metal compounds. However, the impurities contained in the filtrate after recrystallization are impurities that have once adhered to or mixed in the boric acid crystals separated by crystallization, and are quantitatively small.
Therefore, in order to improve the recovery rate of boric acid, it is advantageous that the filtrate after recrystallization is reused as a raw material of the liquid to be treated and added to the liquid to be treated as much as possible. The total amount is preferably added to the liquid to be treated and reused.

  The alkali metal content (amount converted to alkali metal atoms) in the boric acid obtained by the recovery method of the present invention is preferably 0.5% by mass or less, and more preferably 1000 ppm or less. More preferably, it is 500 ppm or less. In the recovery method of the present invention, the alkali metal content in the boric acid before the recrystallization treatment can be 0.5% by mass or less. Moreover, alkali metal content can be 500 ppm or less by performing a recrystallization process once.

The waste water and solid waste in the present invention are both waste water or solid waste discharged from the exhaust gas treatment process in which the exhaust gas discharged from the borosilicate glass manufacturing process is brought into contact with the basic alkali metal compound aqueous solution. Is preferred.
As the borosilicate glass, a borosilicate glass having a small amount of alkali metal components (oxides of alkali metals such as sodium and potassium) or substantially free of alkali metal components (that is, alkali-free) is preferable.
The borosilicate glass is preferably a borosilicate glass having the following composition (1) or (2) in terms of oxide-based mass percentage. However, the following R represents an alkali metal. Further, a small amount (preferably 3 mass in total) of metal oxides (Fe ₂ O ₃ , SnO ₂ etc.), non-metal oxides (sulfur oxide (SO ₃ ) etc.), halogens (Cl, F) etc. other than the following. % Or less, more preferably 2% by mass or less, and further preferably 1% by mass or less).
SiO _2: 40 to 85 wt%, Al ₂ O _3: 1~22 wt%, B ₂ O _3: 2~20 wt%, MgO: 0 to 8 mass%, CaO: 0 to 14.5 wt%, SrO : 0-24 wt%, BaO: 0 to 30 wt%, R ₂ O: 0 wt% (1).
SiO _2: 58 to 66 wt%, Al ₂ O _3: 15~22 wt%, B ₂ O _3: 5~12 wt%, MgO: 0 to 8 mass%, CaO: 0 to 9 wt%, SrO: 3 Non-alkali glass containing ˜12.5 mass%, BaO: 0 to 2 mass%, MgO + CaO + SrO + BaO: 9 to 18 mass% (2).

Borosilicate glass containing an alkali metal component used in a heat-resistant container or a physics and chemistry instrument is usually a borosilicate glass having an alkali metal component (R ₂ O) content of about 2 to 10% by mass in the composition (1). It is.
On the other hand, as a borosilicate glass used as a substrate of a liquid crystal display element, a borosilicate glass having a very low alkali metal component, more preferably a borosilicate glass having a low alkali metal component, more preferably a non-alkali borosilicate glass is used. . Borosilicate glass called alkali-free borosilicate glass (alkali-free glass) is borosilicate glass having an alkali metal component (R ₂ O) content of 0.1% by mass or less in the composition (1), and the composition ( It is a borosilicate glass that does not substantially contain an alkali metal oxide other than being contained as an inevitable impurity in 2) (for example, 0.1% by mass or less of alkali metal oxide).

  The borosilicate glass in the production process of borosilicate glass that is a discharge source of waste water and solid waste in the present invention is preferably a borosilicate glass having a small amount of the alkali metal component (that is, less than 2% by mass), The alkali metal component is more preferably 1% by mass or less of borosilicate glass. Particularly preferred is a borosilicate glass having an extremely small alkali metal component (that is, 0.1% by mass or less), which is referred to as the above alkali-free borosilicate glass.

The amount of the alkali metal component in the borosilicate glass is a requirement that restricts where the boric acid recovered by the present invention is used. The kind of borosilicate glass that can be used as the borosilicate glass raw material is restricted by the amount of the alkali metal component that is an impurity in the recovered boric acid. If the amount of the alkali metal component in the recovered boric acid is large, it becomes difficult to use the boric acid as a raw material for a borosilicate glass having a low alkali metal component, and in particular, it may not be used as a raw material for an alkali-free borosilicate glass. There is.
For this reason, as described above, the alkali metal content in boric acid obtained by the recovery method of the present invention (amount converted to alkali metal atoms) is preferably 0.5% by mass or less, and 1000 ppm or less. It is more preferable that More preferably, it is 500 ppm or less. Such highly pure boric acid can be used as a raw material for alkali-free borosilicate glass.
Therefore, for example, boric acid recovered from waste liquid or solid waste produced as a by-product by treatment of exhaust gas discharged from the manufacturing process of alkali-free borosilicate glass is converted to alkali-free borosilicate glass (alkali metal content is 2 mass). Can be reused as a raw material.

  The boric acid recovery method of the present invention has been described in detail above. However, the present invention is not limited to the above-described example, and various improvements and modifications may be made without departing from the gist of the present invention. Of course.

  Hereinafter, the present invention will be described in more detail with reference to specific examples of the present invention. Needless to say, the present invention is not limited to the following examples.

<First aspect>
[Example 1]
The exhaust gas discharged from the glass melting furnace for producing borosilicate glass was purified by the purification process shown in FIG. In this purification process, a liquid to be treated was prepared by dissolving solid waste collected by the bag filter in waste water discharged from the venturi scrubber (hereinafter, this liquid is referred to as mother liquid).
1000 mL of this mother liquid was separated, and first heated to 75 ° C. to obtain a heated aqueous solution. Subsequently, sulfuric acid was added to the heated aqueous solution to adjust the pH to 2.
Subsequently, this heated aqueous solution whose pH was adjusted was concentrated at 75 ° C. until just before the solid was precipitated. This concentrated heated aqueous solution (pH adjusted) contained boron 32 g / L, sodium 60 g / L, and sulfate ions 61 g / L.

The concentrated heated aqueous solution (pH adjusted) was cooled from 75 ° C. to 35 ° C. to precipitate boric acid crystals.
The to-be-processed liquid which precipitated the boric acid crystal | crystallization was filtered at 35 degreeC, and the boric acid crystal | crystallization was collect | recovered.

  When the purity of the recovered boric acid was measured by ion chromatography, the impurity concentration in the recovered boric acid crystal was 0.7 mass% for sulfate ions and 0.4 mass% for sodium.

[Example 2]
The boric acid crystals recovered in Example 1 were added with an amount of water such that a 75 ° C. aqueous solution became a saturated aqueous solution to prepare a recrystallization liquid. This recrystallization liquid to be treated was heated to 75 ° C. to dissolve the entire amount of boric acid crystals, thereby producing a saturated aqueous solution.
Next, the 75 ° C. saturated aqueous solution was cooled to 35 ° C. to reprecipitate boric acid crystals.
The aqueous solution in which the boric acid crystals were reprecipitated was filtered at 35 ° C. to recover the boric acid crystals.
When the purity of the collected boric acid was measured in the same manner as in Example 1, impurities, sodium ions, sulfate ions, chlorine ions, and fluorine ions in the boric acid crystals were all 100 ppm or less.

[Comparative Example 1]
Boric acid crystals were collected in the same manner as in Example 1 except that the amount of sulfuric acid added to adjust the pH of the heated aqueous solution was adjusted so that the pH of the heated aqueous solution adjusted to pH 4 was adjusted.
When the purity of the recovered boric acid crystals was measured in the same manner as in Example 1, the impurity concentration in the recovered boric acid crystals was 1.7% by mass for sulfate ions and 1.0% by mass for sodium.

[Comparative Example 2]
1000 mL of the same mother liquid as in Example 1 was separated and heated to 75 ° C. This heated aqueous solution was cooled to 35 ° C. to precipitate sodium borate, and then sulfuric acid was added to the cooled aqueous solution to adjust the pH to 2 and convert it into boric acid crystals.
The precipitated boric acid crystals were collected by filtration in the same manner as in Example 1.
When the purity of the recovered boric acid crystals was measured in the same manner as in Example 1, the impurity concentrations were 2.4% by mass for sulfate ions and 1.8% by mass for sodium.
From the above results, the effects of the present invention are clear.

<Second aspect>
[Example 3]
The exhaust gas discharged from the glass melting furnace for producing borosilicate glass was purified by the purification process shown in FIG. In this purification process, wastewater discharged from the venturi scrubber was used as a stock solution. In the second aspect, the liquid to be treated contains a large amount of alkali metal salt. In order to reproduce the liquid to be treated in this process, a liquid prepared by adding sodium sulfate and sodium chloride to the stock solution discharged from the scrubber was prepared for the purpose of obtaining the liquid to be treated with an increased alkali metal salt concentration ( Hereinafter, this liquid is referred to as mother liquid).
1440 mL of this mother liquid was taken out and sulfuric acid was added to adjust the pH to 2.
Subsequently, this pH adjusted liquid was concentrated at 75 ° C. to precipitate a solid content. Subsequently, it isolate | separated into solid content and a supernatant liquid by filtration using a filter paper. The solid content was 69 g. The condensed water when concentrated was 430 g.

  This solid content was analyzed by ion chromatography. As a result, 36.2% by mass of sodium, 44.4% by mass of sulfate ions, 17.8% by mass of chloride ions and 0.9% by mass of boron were contained. It was. Therefore, it is considered that this solid content is mainly a mixed crystal of sodium sulfate and sodium chloride.

  After adding 5 wt% pure water to the supernatant, it was cooled from 75 ° C to 35 ° C to precipitate boric acid crystals. The to-be-processed liquid which precipitated the boric acid crystal | crystallization was filtered at 35 degreeC, and the boric acid crystal | crystallization was collect | recovered.

  When the purity of the recovered boric acid crystal was measured by an ion chromatography method, the impurity concentration in the recovered boric acid crystal was 0.4 mass% for sulfate ions and 0.7 mass% for chloride ions.

[Example 4]
10 wt% pure water was added to the supernatant obtained in the same manner as in Example 3, and then cooled from 75 ° C. to 35 ° C. to precipitate boric acid crystals. The to-be-processed liquid which precipitated the boric acid crystal | crystallization was filtered at 35 degreeC, and the boric acid crystal | crystallization was collect | recovered.
When the purity of the recovered boric acid crystal was measured by an ion chromatography method, the impurity concentration in the recovered boric acid crystal was 0.4 mass% for sulfate ions and 0.8 mass% for chloride ions.

[Comparative Example 3]
The supernatant obtained by the same operation as in Example 3 was cooled from 75 ° C. to 35 ° C. without adding pure water to precipitate boric acid crystals. The to-be-processed liquid which precipitated the boric acid crystal | crystallization was filtered at 35 degreeC, and the boric acid crystal | crystallization was collect | recovered.
When the purity of the recovered boric acid crystal was measured by an ion chromatography method, the impurity concentration in the recovered boric acid crystal was 0.5% by mass for sulfate ions and 6.7% by mass for chloride ions.

Although the present invention has been described in detail and with reference to specific embodiments, it will be apparent to those skilled in the art that various modifications and variations can be made without departing from the scope and spirit of the invention.
This application is based on Japanese Patent Application 2011-035896 filed on February 22, 2011 and Japanese Patent Application 2011-209254 filed on September 26, 2011, the contents of which are incorporated herein by reference.

  Boric acid that can be used as a borosilicate glass raw material can be recovered from wastewater and solid waste containing boron compounds and alkali metal compounds, such as wastewater and solid waste discharged in the manufacturing process of borosilicate glass. .

Claims (12)

A boric acid recovery method for recovering boric acid from a liquid to be treated containing at least one of waste water and solid waste containing a boron compound and an alkali metal compound,
Concentrate after adding an acid to the liquid to be treated and adjusting the pH to less than 4, or adjusting the pH to be less than 4 by adding an acid after concentrating the liquid to be treated,
The solution to be treated which is concentrated and pH-adjusted and does not contain insoluble matter is cooled to an aqueous solution in which boric acid crystals are precipitated,
Separating the boric acid crystals from the aqueous solution in which the boric acid crystals are precipitated,
50 to 90% by mass of the filtrate after separating the boric acid crystals is added to the liquid to be treated before the concentration and pH adjustment,
The separated boric acid crystal is heated with a boric acid aqueous solution or water to dissolve the boric acid crystal, and the heated boric acid crystal is dissolved to cool the recrystallizing liquid. And an aqueous solution in which boric acid crystals are reprecipitated, and separating the boric acid crystals from the aqueous solution in which the boric acid crystals are reprecipitated,
A method for recovering boric acid, wherein at least part of the filtrate after separating the reprecipitated boric acid crystals is added to the liquid to be treated before the concentration and pH adjustment. When the liquid to be treated before concentration and pH adjustment contains Na ₂ SO ₄ and NaCl, the mass ratio (Na / B) of sodium (Na) and boron (B) contained in the liquid to be treated is 3. 6 or less,
When the liquid to be treated does not contain Na ₂ SO ₄ and contains NaCl, the mass ratio (Na / B) is 3.9 or less,
The boric acid recovery method according to claim 1, wherein when the liquid to be treated contains Na ₂ SO ₄ and does not contain NaCl, the mass ratio (Na / B) is 3.1 or less. A boric acid recovery method for recovering boric acid from a liquid to be treated containing at least one of waste water and solid waste containing a boron compound and an alkali metal compound,
After adding an acid to the liquid to be treated and adjusting the pH to less than 4, it concentrates to precipitate an alkali metal salt, and the alkali metal salt is removed from the liquid to be treated on which the alkali metal salt has precipitated,
Alternatively, the liquid to be treated is concentrated to precipitate an alkali metal salt, and after removing the alkali metal salt from the liquid to be treated on which the alkali metal salt has been deposited, an acid is added to adjust the pH to less than 4.
The concentration and pH adjustment and dilution of the liquid to be treated from which the alkali metal salt has been removed by adding water,
The diluted liquid to be treated is cooled to an aqueous solution in which boric acid crystals are precipitated,
Separating the boric acid crystals from the aqueous solution in which the boric acid crystals are precipitated,
At least a part of the filtrate after separating the boric acid crystals is added to the liquid to be treated before the concentration and pH adjustment,
The separated boric acid crystal is heated with a boric acid aqueous solution or water to dissolve the boric acid crystal, and the heated boric acid crystal is dissolved to cool the recrystallizing liquid. And an aqueous solution in which boric acid crystals are reprecipitated, and separating the boric acid crystals from the aqueous solution in which the boric acid crystals are reprecipitated,
A method for recovering boric acid, wherein at least part of the filtrate after separating the reprecipitated boric acid crystals is added to the liquid to be treated before the concentration and pH adjustment. When the liquid to be treated before concentration and pH adjustment contains Na ₂ SO ₄ and NaCl, the mass ratio (Na / B) of sodium (Na) and boron (B) contained in the liquid to be treated is 3. More than 6,
When the liquid to be treated does not contain Na ₂ SO ₄ and contains NaCl, the mass ratio (Na / B) is more than 3.9,
The boric acid recovery method according to claim 3, wherein when the liquid to be treated contains Na ₂ SO ₄ and does not contain NaCl, the mass ratio (Na / B) is more than 3.1.   The method for recovering boric acid according to claim 3 or 4, wherein in the concentration of the liquid to be treated, the particle diameter of the alkali metal salt to be deposited is controlled to selectively remove the alkali metal salt.   5 to 100% by mass of the filtrate after separating the reprecipitated boric acid crystals is added to the liquid to be treated before the concentration and pH adjustment, and 0 to 95% by mass of the filtrate is used for the recrystallization. The method for recovering boric acid according to any one of claims 1 to 5, which is added to the liquid to be treated.   When the solid content of the waste water and the solid waste contain at least boron, alkali metal, sulfur and chlorine as elements, and the mass ratio of the elements is 1 for boron, the alkali metal is 0.6 to 13, sulfur The boric acid recovery method according to any one of claims 1 to 6, wherein is 6 or less and chlorine is 6 or less.   The method for recovering boric acid according to any one of claims 1 to 7, wherein the alkali metal component in the recovered boric acid is 0.5 mass% or less.   The waste water discharged from the exhaust gas treatment step, wherein the waste water and the solid waste are both brought into contact with at least one of the alkali metal compound solid and the alkali metal compound aqueous solution, or the exhaust gas discharged from the borosilicate glass production step, or The method for recovering boric acid according to any one of claims 1 to 8, which is a solid waste.   The method for recovering boric acid according to claim 9, wherein the alkali metal content of the borosilicate glass is less than 2 mass% in terms of mass percentage based on oxide. An apparatus for recovering boric acid from a liquid to be treated containing at least one of waste water containing a boron compound and an alkali metal compound and solid waste,
A concentrator for concentrating the liquid to be treated;
A pH adjuster in which an acid is added to adjust the pH of the liquid to be treated to less than 4;
A crystallizer for adjusting the pH and cooling the liquid to be treated that does not contain insoluble matter to form an aqueous solution in which boric acid crystals are precipitated;
A recovery device for separating and recovering the precipitated boric acid crystals from the aqueous solution;
A liquid feeding device for sending 50 to 90% by mass of the filtrate after separating and recovering the boric acid crystals to the liquid to be treated before the concentration and pH adjustment;
A heating and dissolving apparatus for heating the liquid for treatment for recrystallization in which an aqueous boric acid solution or water is added to the separated and recovered boric acid crystals to dissolve the boric acid crystals;
A crystallizer for heating the recrystallized liquid for recrystallization in which boric acid crystals are dissolved to cool the boric acid crystals into an aqueous solution in which the boric acid crystals are reprecipitated;
A recovery device for separating and recovering the reprecipitated boric acid crystals from the aqueous solution;
A liquid feeding device for sending at least a part of the filtrate after separating and recovering the reprecipitated boric acid crystals to the liquid to be treated before the concentration and pH adjustment;
Boric acid recovery device. An apparatus for recovering boric acid from a liquid to be treated containing at least one of waste water containing a boron compound and an alkali metal compound and solid waste,
A concentration device for concentrating the liquid to be treated to precipitate an alkali metal salt;
A removal device for removing the precipitated alkali metal salt from the liquid to be treated;
A pH adjuster in which an acid is added to adjust the pH of the liquid to be treated to less than 4;
A crystallization device in which the alkali metal salt is removed by the removal device, and the liquid to be treated whose pH is adjusted by the pH adjustment device is cooled to form an aqueous solution in which boric acid crystals are precipitated;
A recovery device for separating and recovering the precipitated boric acid crystals from the aqueous solution;
A liquid feeding device for sending the filtrate after separating and recovering the boric acid crystals to the liquid to be treated before the concentration and pH adjustment;
A heating and dissolving apparatus for heating the liquid for treatment for recrystallization in which an aqueous boric acid solution or water is added to the separated and recovered boric acid crystals to dissolve the boric acid crystals;
A crystallizer for heating the recrystallized liquid for recrystallization in which boric acid crystals are dissolved to cool the boric acid crystals into an aqueous solution in which the boric acid crystals are reprecipitated;
A recovery device for separating and recovering the reprecipitated boric acid crystals from the aqueous solution;
A liquid feeding device for sending at least a part of the filtrate after separating and recovering the reprecipitated boric acid crystals to the liquid to be treated before the concentration and pH adjustment;
Boric acid recovery device.

Images