KR20140031195A - Method and device for recovering boric acid - Google Patents

Abstract

The present invention is a method for recovering boric acid from the treated liquid containing at least one of a wastewater and a solid discharge containing a boron compound and an alkali metal compound, wherein the acid is added to the treated liquid to adjust the pH to less than 4 After the concentration, or after concentrating the to-be-treated solution, adjust the pH to less than 4 by adding an acid, and cool the to-be-treated solution which is concentrated and pH-adjusted and does not contain an insoluble matter into an aqueous solution in which boric acid crystals are precipitated. The boric acid crystals are separated from the aqueous solution in which the boric acid crystals are precipitated, and 50 to 90% by mass of the filtrate after the boric acid crystals are separated is added to the treated solution before the concentration and pH adjustment. A boric acid crystal is dissolved by heating a treatment solution for recrystallization in which an aqueous boric acid solution or water is added to the crystal. At least the filtrate after cooling the to-be-processed recrystallization liquid to make the boric acid crystal re-precipitate, isolate | separates the said boric acid crystal from the aqueous solution in which the said boric acid crystal was reprecipitated, and isolate | separated the said reprecipitated boric acid crystal It relates to a recovery method of boric acid in which a part is added to the liquid to be treated before the concentration and pH adjustment.

Description

Recovery method and recovery apparatus of boric acid {METHOD AND DEVICE FOR RECOVERING BORIC ACID}

The present invention relates to a method for recovering boric acid and a recovery apparatus for recovering boric acid from wastewater or solid discharge containing a boron compound and an alkali metal compound.

In the production of the boron component-containing glass, various substances such as boric acid and sulfur are contained in the exhaust gas discharged from the glass melting furnace at a relatively high concentration.

Therefore, this exhaust gas cannot be discharge | released to the air as it is, For example, it is discharged to air | atmosphere after removing harmful substances by treating with alkali, such as sodium hydroxide.

Drainage and solid discharge by-produced by the purification of such exhaust gas are often treated as industrial waste.

However, these wastewaters and solid discharges contain a large amount of useful substances such as boron compounds and alkali metal compounds. In particular, if boric acid is expensive and this can be recovered and reused from the wastewater treated with the exhaust gas, the production cost of the boron component-containing glass can be reduced. In addition, from the viewpoint of environmental problems, it is preferable to recover as much of the useful substance as possible from the wastewater and the solid discharge.

Therefore, not only the wastewater by-produced by the waste gas process in manufacture of a boron component containing glass, but the various methods of collect | recovering boric acid etc. from the wastewater containing a boron compound, or solid discharge are proposed.

For example, Patent Literature 1 describes that the waste water obtained by purifying the exhaust gas generated at the time of melting of the glass is neutralized and then dried to be used as a raw material for the glass.

Specifically, the exhaust gas discharged from the glass melting furnace is purified by contact with water in a spray tower, or the exhaust gas purified by water is further purified by a wet electrostatic precipitator and discharged into the atmosphere. At this time, the wastewater discharged from the spray dryer or the wet electrostatic precipitator is neutralized with a calcination cycle and then dried to reuse the obtained solid content as the glass raw material.

In addition, Patent Document 2 discloses that boric acid is recovered along with purification of the exhaust gas by cooling the exhaust gas containing boric acid or the like discharged from a glass melting furnace or the like.

Specifically, by cooling the exhaust gas to 70 ° C. or lower by a method such as a combination of a water spray cooling means and an air-mixed cooling means, the boric acid in the form of gas in the exhaust gas is precipitated as a solid, followed by dry The exhaust gas is purified while recovering boric acid by an electrostatic precipitator.

Patent Literature 3 also discloses a method for recovering boric acid from an ion exchange resin in which boron is adsorbed by treating wastewater containing boron, such as a nickel plating solution, an aluminum surface treatment liquid that has become a waste liquid, drainage discharged in glass production, and the like. It is described.

In this method, sulfuric acid is first passed through the ion exchange resin which adsorbed boron, and a boron eluate is obtained. The boron eluate is neutralized by addition of sodium hydroxide, followed by heating and concentration to precipitate and separate sodium sulfate. After cooling the remaining mother liquid to 35-40 degreeC, boric acid is precipitated by adding sulfuric acid and adjusting pH to 4-6, and boric acid is collect | recovered by separating a boric acid with a centrifuge or the like.

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

By using these methods, boric acid can be recovered and reused from wastewater containing a boron compound or the like or solid discharge.

Here, the exhaust gas discharged | emitted from a glass melting furnace etc. contains not only the component melt | dissolved in the furnace but the combustion exhaust gas component of the used fuel.

Therefore, in the method described in Patent Literature 1, when a sulfur compound is contained in the exhaust gas, such as when heavy oil is used as the fuel of the glass melting furnace, sulfur compounds such as sulfates are also introduced into the glass melting furnace as a glass raw material for recycling. Throw it away. Thus, when sulfur compound, such as a sulfuric acid, is contained in a glass raw material, sulfur components other than the raw material will be concentrated, and a problem, such as quality deterioration of glass, will arise.

Therefore, in this method, only waste water by-produced by purification of exhaust gas using a fuel substantially free of sulfur can be treated.

Similarly, also in the method of cooling exhaust gas and depositing / recovering boric acid as a solid like the method of patent document 2, when sulfur is contained in exhaust gas, when exhaust gas is cooled to the temperature which boric acid precipitates as a solid, The temperature of the exhaust gas falls below the acid dew point, and sulfuric acid also precipitates. When sulfuric acid precipitates, corrosion of an apparatus arises, etc. Moreover, sulfuric acid is contained also in the boric acid collect | recovered.

Therefore, also in this method, only the exhaust gas using the fuel which does not contain sulfur substantially can be processed.

On the other hand, if it is the method of patent document 3, boric acid can also be collect | recovered from the waste water etc. which were processed by processing the exhaust gas containing a sulfur component like the case where heavy oil was used as a fuel of a glass melting furnace.

However, in this method, since the drainage treatment is performed in the ion exchange resin, a procedure for eluting boron from the ion exchange resin is required, and when the drainage concentration is high, the ion exchange resin device required for the drainage treatment becomes very large. There is. In addition, when the boron eluate contains various kinds of substances other than boric acid, high-purity boric acid cannot be recovered sufficiently.

An object of the present invention is to solve the problems of the prior art, it is also possible to treat a liquid or a solid containing a sulfur component, such as by-product drainage by treating the exhaust gas containing a sulfur component, and also a liquid of high concentration It is another object of the present invention to provide a recovery method and recovery apparatus for boric acid that can recover high-purity boric acid from liquids or solids containing various substances other than boron compounds.

In order to achieve the above object, the present invention is a recovery method of boric acid for recovering boric acid from the liquid to be treated containing at least one of wastewater and solid discharge containing a boron compound and an alkali metal compound,

After adding acid to the to-be-processed liquid and adjusting to less than pH 4, it concentrates, or after concentrating the to-be-processed liquid and adding acid, it is adjusted to less than pH 4,

Cooling the target liquid which is concentrated and pH-adjusted and which does not contain an insoluble matter is used as an aqueous solution in which boric acid crystals are precipitated,

The boric acid crystals are separated from the aqueous solution in which the boric acid crystals are precipitated,

50-90 mass% of the filtrate after isolate | separating the said boric acid crystal | crystallization is added to the to-be-processed liquid before the said concentration and pH adjustment,

An aqueous solution in which boric acid crystals are reprecipitated by heating a recrystallized solution to which the boric acid aqueous solution or water is added to the separated boric acid crystals to dissolve boric acid crystals, and cooling the to-be-processed liquid for recrystallization in which the heated boric acid crystals are dissolved. The boric acid crystals are separated from the aqueous solution in which the boric acid crystals are reprecipitated.

The recovery method (1) of boric acid which adds at least a part of filtrate after isolate | separating the said reprecipitated boric acid crystal | crystallization to the to-be-processed liquid before the said concentration and pH adjustment is provided.

The present invention also provides a method for recovering boric acid from which boric acid is recovered from a liquid to be treated containing at least one of a wastewater containing a boron compound and an alkali metal compound and a solid discharge.

After adding acid to the said to-be-processed liquid and adjusting to less than pH 4, it concentrates and precipitates an alkali metal salt, and removes an alkali metal salt from the to-be-processed liquid in which the alkali metal salt precipitated,

Alternatively, the treated liquid is concentrated to precipitate an alkali metal salt, and after removing the alkali metal salt from the treated liquid on which the alkali metal salt is precipitated, an acid is added to adjust the pH to less than 4,

Dilute by adding water to the concentrated and pH-adjusted liquid to which the alkali metal salt is removed;

The diluted treated solution is cooled to an aqueous solution in which boric acid crystals are precipitated,

The boric acid crystals are separated from the aqueous solution in which the boric acid crystals are precipitated,

The filtrate after separating the boric acid crystals is added to the treated liquid before the concentration and pH adjustment,

An aqueous solution in which boric acid crystals are reprecipitated by heating a recrystallized solution to which the boric acid aqueous solution or water is added to the separated boric acid crystals to dissolve boric acid crystals, and cooling the to-be-processed liquid for recrystallization in which the heated boric acid crystals are dissolved. The boric acid crystals are separated from the aqueous solution in which the boric acid crystals are reprecipitated.

Provided is a method (2) for recovering boric acid, wherein at least a portion 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.

In addition, the present invention is an apparatus for recovering boric acid from the liquid to be treated containing at least one of wastewater and solid discharge containing a boron compound and an alkali metal compound,

A concentrating device for concentrating the processing liquid;

A pH adjusting device in which an acid is added to adjust the pH of the liquid to be treated to less than 4,

A crystallization device which cools the to-be-processed liquid which does not contain the said pH adjustment and does not contain an insoluble thing, and sets it as the aqueous solution which the boric acid crystal precipitated,

A recovery device for separating and recovering the precipitated boric acid crystals from the aqueous solution;

A liquid feeding apparatus for sending 50 to 90 mass% of the filtrate after separating and recovering the boric acid crystals to the target liquid before the concentration and pH adjustment;

A heat dissolving apparatus for dissolving boric acid crystals by heating a processing liquid for recrystallization in which boric acid aqueous solution or water is added to the separated and recovered boric acid crystals;

A crystallization apparatus for cooling the target liquid for recrystallization in which the boric acid crystals are dissolved by heating, to prepare an aqueous solution in which boric acid crystals are reprecipitated;

A recovery device for separating and recovering the reprecipitated boric acid crystals from the aqueous solution,

Feeding apparatus for sending at least a portion of the filtrate after separating and recovering the re-precipitated boric acid crystals to the treated liquid before the concentration and pH adjustment

It provides a recovery device (1) of boric acid having a.

Further, according to the present invention,

An apparatus for recovering boric acid from a liquid to be treated containing at least one of a wastewater and a solid discharge containing a boron compound and an alkali metal compound,

A concentrating 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 adjusting device 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 an alkali metal salt is removed by said removal device, and an aqueous solution in which boric acid crystals are precipitated by cooling the to-be-processed liquid pH adjusted by said pH adjusting device;

A recovery device for separating and recovering the precipitated boric acid crystals from the aqueous solution;

A liquid feeding apparatus 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 heat dissolving apparatus for dissolving boric acid crystals by heating a processing liquid for recrystallization in which boric acid aqueous solution or water is added to the separated and recovered boric acid crystals;

A crystallization apparatus for cooling the target liquid for recrystallization in which the boric acid crystals are dissolved by heating, to prepare an aqueous solution in which boric acid crystals are reprecipitated;

A recovery device for separating and recovering the reprecipitated boric acid crystals from the aqueous solution,

Feeding apparatus for sending at least a portion of the filtrate after separating and recovering the re-precipitated boric acid crystals to the treated liquid before the concentration and pH adjustment

It provides a recovery device (2) of boric acid having a.

According to the present invention, high-purity is achieved by simple operation from wastewater or solid discharge containing boron compounds and alkali metal compounds, such as waste water and solid discharge by-produced by purification of boric acid-containing exhaust gas discharged from the manufacturing process of borosilicate glass. Boric acid of can be recovered.

1 is a flowchart for explaining an example of the boron recovery method (first embodiment) of the present invention.
2 is a flowchart for explaining an example of the boron recovery method (second embodiment) of the present invention.
3 is a conceptual diagram for explaining an example of the liquid to be treated treated by the boron recovery method of the present invention.

EMBODIMENT OF THE INVENTION Hereinafter, the collection method of the boric acid of this invention is demonstrated in detail with reference to an accompanying drawing.

The flowchart of an example of the recovery method (1st aspect) of the boric acid of this invention is shown in FIG. 1, and the flowchart of an example of the recovery method (2nd aspect) of the boric acid of this invention is shown in FIG.

As shown in Fig. 1 and Fig. 2, the boric acid recovery method of the present invention (hereinafter, also simply referred to as a "recovery method") recovers boric acid from the liquid to be treated using crystallization (crystallization / crystallization) by cooling. It is. Hereinafter, unless the specification of a thing of a 1st form or a 2nd form is specified, it demonstrates as common content of a 1st form and a 2nd form.

Both drainage and solid emissions in the present invention include boron compounds and alkali metal compounds. In this invention, a boron compound and an alkali metal compound are distinguished, and the compound containing a boron atom, such as sodium borate, and an alkali metal atom is considered a boron compound unless there is particular notice. Therefore, an alkali metal compound is an alkali metal compound which does not contain a boron atom unless there is particular notice. In addition, a boron compound is not limited to an alkali metal but may contain various structural elements. The alkali metal compound may likewise contain various constituent elements other than boron.

The drainage in the present invention comprises water containing a boron compound and an alkali metal compound, and the solid discharge in the present invention comprises a solid (powder etc.) containing a boron compound and an alkali metal compound. These wastewater and solid discharge may contain compounds other than a boron compound and an alkali metal compound.

These are discharged | emitted from the industrial process which handles a boron compound and an alkali metal compound, and the wastewater discharged from the waste gas processing process which makes the exhaust gas discharged from the manufacturing process of borosilicate glass mentioned later especially to contact with basic aqueous alkali metal compound aqueous solution. Or solid emissions.

The to-be-processed liquid in this invention is a to-be-processed liquid containing at least one of the said waste water and a solid discharge | emission, As shown in FIG. 1 or FIG. 2, in the case of the said waste water, the drain water may be itself. The water dilution liquid obtained by adding water may be sufficient. In the case of the solid discharge, it is an aqueous solution obtained by adding water to the solid discharge. As shown in FIG. 1 or FIG. 2, the wastewater can be used as water to be added to the solid discharge, and the mixture of the solid discharge and the wastewater can also be diluted with water to be the liquid to be treated in the present invention.

In addition, an aqueous solution (such as a filtrate) containing boric acid after depositing a boric acid crystal described later and separating the crystal may be used as at least part of the dilution water.

Moreover, these to-be-processed liquid may mix 2 or more of them.

As wastewater and solid discharge | emission in this invention, in the manufacture of borosilicate glass used for glass for flat panel displays (FPD), glass for solar cells, etc. as an example, the exhaust gas discharged | emitted from the glass melting furnace, the molten glass forming furnace, etc. was purified. By-product drainage or solid emissions are exemplified.

In the production of borosilicate glass, since boron oxide is volatile, boron oxide is volatilized from a high temperature glass raw material or molten glass during melting, mixed in exhaust gas such as combustion exhaust gas, and borosilicate glass as boron oxide-containing exhaust gas. Is discharged from the manufacturing process. For this reason, purification | purification of this exhaust gas is needed, and in most cases, purification is performed using aqueous solution or powder of a basic compound in order to perform efficient purification. As a basic compound, an alkali metal compound, especially a sodium compound is used. As a specific alkali metal compound, water-soluble basic sodium compounds, such as sodium hydroxide, sodium hydrogencarbonate, and sodium carbonate, are mentioned.

3 shows an example of the purification process of this exhaust gas conceptually.

In the purification | cleaning process shown in FIG. 3, the exhaust gas discharged | emitted from the glass melting furnace for manufacturing borosilicate glass is first cooled to about 200 degreeC with water or aqueous sodium hydroxide solution in a cooling tower. At this time, if necessary, sodium hydroxide or sodium hydrogencarbonate (only the aqueous sodium hydroxide solution is shown in FIG. 3) is added as a decontamination agent.

Subsequently, sodium hydrogencarbonate powder or the like is added to the cooled exhaust gas as needed to purify with a bug filter. In addition, the exhaust gas purified by the bug filter is purified by treatment with sodium hydroxide or the like in a venturi scrubber and discharged to the atmosphere as a purified exhaust gas. In addition, alkali metal compounds, such as sodium hydroxide, added in the purification process of this exhaust gas may be added as solid, may be added as aqueous solution, or both solid and aqueous solution may be added.

In this purification process, various waste compounds such as boric acid, boron oxide, sodium borate, sodium hydroxide, sodium chloride, sodium fluoride, sodium sulfate, sodium nitrate, and alkali metals are contained in the solid waste collected by the bug filter or the waste liquid from the venturi scrubber. Compound is contained.

Therefore, in the recovery method of the present invention, the solid waste collected by the bug filter in this purification process can be treated as the solid discharge in the present invention, and the waste liquid discharged from the venturi scrubber is It can be handled as discharge liquid. In addition, these waste liquids and a solid waste are also called waste water and a solid discharge below.

That is, in the boric acid recovery method of the present invention, in the case of treating the by-product by the purification process of the exhaust gas shown in Fig. 3, the wastewater discharged from the venturi scrubber is a drainage passage containing a boron compound and an alkali metal compound. do. In addition, the solid discharge | emission collected by the bug filter is made into the solid discharge | emission containing a boron compound and an alkali metal compound. Therefore, the to-be-processed liquid in the said invention is obtained using these.

In the exhaust gas purification process shown in FIG. 3, when solid wastes or waste liquids containing boron compounds and alkali metal compounds are also discharged from the cooling tower, they are also solid discharges or venturi collected by a bug filter. Similar to the wastewater discharged from the scrubber, it may be treated as wastewater containing a boron compound and an alkali metal compound or as a solid discharge.

In the recovery method of the present invention, the wastewater and the solid discharge containing the boron compound and the alkali metal compound are not limited to the wastewater and the solid discharge by-produced by the purification of the exhaust gas in the borosilicate glass manufacturing process. Various wastewater and solid discharge | emissions containing a compound and an alkali metal compound are illustrated.

The solid discharge and the wastewater in the present invention may all contain sulfur compounds, chlorine compounds, fluorine compounds, etc., in addition to the boron compound and the alkali metal compound. These components other than a boron compound and an alkali metal compound are compounds which do not contain any of boron and an alkali metal as a structural element like the said definition. Therefore, for example, the said sodium chloride, sodium fluoride, sodium sulfate, sodium nitrate etc. are alkali metal compounds in this invention. The solid discharge and the wastewater in the present invention may all contain a small amount of a sulfur compound, a chlorine compound, and a fluorine compound, but it is preferable that the solid discharge and the waste water not contain substantially.

It is preferable that the boron compound contained in solid discharge and waste water in this invention is mainly boric acid and sodium borate. It is preferable that the alkali metal compound contained in the solid discharge | emission and waste water in this invention is mainly sodium sulfate and sodium chloride, In addition, relatively small amounts of sodium fluoride, sodium nitrate, etc. may be contained in addition to these.

As a constituent element ratio (mass ratio) of the compound contained in solid discharge and waste water in this invention, it is a relative ratio which made boron amount (mass) 1, and the alkali metal amount is 0.6-13, sulfur amount 0-6, and chlorine amount. It is preferable that it is 0-6. In addition, sulfur and chlorine in this structural element ratio are an element in alkali metal compounds, such as sodium sulfate and sodium chloride mainly.

As the solid discharge and the wastewater containing various compounds having such a constituent element ratio, the wastewater and the solid discharge by-produced by the purification of the exhaust gas discharged from the borosilicate glass manufacturing process are typical. The present invention can recover high purity boric acid from such wastewater or solid discharge.

Examples of the concentration of each constituent element included in the liquid to be treated in the present invention including at least one of the wastewater and the solid discharge include boron concentration of 10 to 40 g / L, sodium concentration of 20 to 400 g / L, and sulfur concentration of 0. It is preferable that they are -200 g / L and chlorine concentration is 0-200 g / L. In addition, sulfur and chlorine in each constituent element concentration are mainly constituent elements in an alkali metal compound.

In addition, it is thought that most of the compound in the to-be-processed liquid is ionizing. For example, it is considered that borate ions, sodium ions, sulfate ions, chloride ions, fluoride ions, nitrate ions and the like exist in the liquid to be treated.

In addition, it is preferable that the to-be-processed liquid does not contain an insoluble component. However, as long as it does not contain an insoluble powder in one step with a heating aqueous solution, it may also contain an insoluble powder which melt | dissolves by heating. If necessary, insoluble matters may be removed from the processing liquid before heating by filtration or the like.

In the recovery method of this invention, as shown in FIG. 1, as a preferable aspect, such a to-be-processed liquid is heated to make a heated aqueous solution. This heating aqueous solution needs to contain no insoluble matter. If insoluble matter also exists as a heated aqueous solution, insoluble matter is removed by filtration or the like.

Although the heating temperature of a heating aqueous solution is not specifically limited, 50 degreeC or more is preferable. If the heating temperature of the heated aqueous solution is less than 50 ° C., the recovery rate of boric acid is low, and the boric acid crystals precipitated do not grow sufficiently, resulting in poor separation performance.

The heating temperature of a heating aqueous solution becomes like this. Preferably it is 100 degrees C or less, More preferably, it is 70 degreeC-80 degreeC.

Thereby, the recovery rate and separation performance of a boric acid crystal 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 preferable embodiment and is not an essential step.

Subsequently, an acid is added to a heating aqueous solution (if the heating is not carried out. The processing liquid and the heating aqueous solution are also referred to simply as the 'treatment liquid'), and the pH is adjusted to 4 or less.

In the present invention, the pH adjusting device (pH adjustment) so that the pH of the liquid to be treated is adjusted to less than pH 4 in the heated state (if not heated, the pH of the liquid to be treated is less than pH 4, which is the same below). By adjusting with a tank), boric acid crystals with high purity can be recovered. 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 into boric acid, so that the shape and particle size of the boric acid crystals can be easily controlled. In addition, the purity of boric acid can also be improved by this.

In addition, when the pH of the to-be-processed liquid is 4 or more, boric acid of sufficient purity cannot be collect | recovered when the solid content concentration of a to-be-processed liquid is high. Boric acid with a large amount of impurities such as alkali metal borate is difficult to reuse as a raw material such as borosilicate glass containing no alkali metal component. Moreover, even when refine | purifying the obtained boric acid further by a recrystallization method, it becomes difficult to obtain a high purity boric acid.

The pH of the pH-adjusted to-be-processed liquid is less than 4, Preferably it is 3.5 or less, More preferably, it is less than 3.5, More preferably, it is 1-3.

Thereby, higher purity boric acid crystal can be collect | recovered.

There is no restriction | limiting in particular in the acid used for pH adjustment of the to-be-processed liquid, Various inorganic acids, such as a sulfuric acid, hydrochloric acid, nitric acid, can be used. As such an acid, sulfuric acid is preferable.

In the case of recovering boric acid from waste water by-produced by purification of exhaust gas discharged from the glass melting furnace of borosilicate glass, sulfate ions are often contained in the waste water. Therefore, by using sulfuric acid for pH adjustment, the addition of an extra component to the to-be-processed liquid can be suppressed.

Moreover, when hydrochloric acid is used for pH adjustment, there exists a possibility that chloride ion may corrode a crystallization apparatus, 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, as shown by the dotted line in FIG. 1, pH adjustment of the to-be-processed liquid may be performed before the above-mentioned heating of the to-be-processed liquid, or may be performed after performing the concentration mentioned later.

The pH-adjusted processing liquid is preferably concentrated by a concentration apparatus before cooling, to be a concentrated processing liquid. By concentrating, the recovery rate of boric acid can be improved.

As the concentrating device, for example, a well-known evaporation concentrating device or the like which sprays the processing liquid from a nozzle and evaporates the heat to the surfaces of a plurality of heat transfer tubes through which a heating fluid such as steam flows inside the concentrated crystal can under reduced pressure. It is available. In such a concentration apparatus, the to-be-processed liquid in a concentration crystal can is circulated by the nozzle which spread | spreads to a some heat exchanger tube by a circulation pump.

The steam generated by the condenser is condensed and introduced into the condensate tank, and the condensed water of the condensate tank is used as dilution water, washing water of each apparatus, or washing water of crystals in a recovery step.

In the recovery method of the present invention, one of the first embodiment and the second embodiment described later is selected depending on the concentrations of boron and sodium (Na) in the liquid to be treated.

In the case where Na salt does not precipitate when the liquid to be treated is concentrated to a boron concentration suitable for crystallization and pH is adjusted, the first embodiment is preferred. When Na salt precipitates when the to-be-processed liquid is concentrated to the boron concentration suitable for crystallization, or when a to-be-processed liquid is concentrated to the boron concentration suitable for crystallization, and pH adjustment, the 2nd aspect mentioned later is preferable.

Specifically, according to the mass ratio (Na / B) of sodium (Na) and boron (B) contained in the to-be-processed liquid before concentration and pH adjustment, it selects whether the 1st form and the 2nd form mentioned later are applied. .

When the liquid to be treated comprises a Na ₂ SO ₄ and NaCl, the mass ratio (Na / B) is 3.6 or less when the first mode is a preferable, the mass ratio (Na / B) is greater than 3.6, preferably in the second form.

In the case where the liquid to be treated does not contain Na ₂ SO ₄ but contains NaCl, the first form is preferred if the mass ratio (Na / B) is 3.9 or less, and the second form is preferred if the mass ratio (Na / B) is more than 3.9. Do.

When the liquid to be treated contains Na ₂ SO ₄ and does not contain NaCl, the first form is preferred if the mass ratio (Na / B) is 3.1 or less, and the second form is preferred if the mass ratio (Na / B) is more than 3.1. Do.

In the first aspect, the concentration is carried out to such an extent that insoluble matters do not precipitate. In addition, an insoluble substance here is a crystalline solid which precipitates when a component contains exceeding saturated solubility as a result of concentration and pH adjustment.

In the second embodiment, the concentration is performed so that an alkali metal salt which is an insoluble matter precipitates. To precipitate the alkali metal salt of Na salts, such as sodium sulfate (Na ₂ SO ₄₎ or sodium chloride (NaCl), etc. contained in the liquid to be treated as an impurity.

In the first aspect and the second aspect, in order to improve the recovery rate of boric acid, it is preferable that the solid content concentration of the to-be-processed liquid adjusted to pH be 15 mass% or more by concentration. In other words, it is preferable to concentrate until the solid content concentration of the to-be-processed liquid becomes 15 mass% or more.

On the other hand, it is preferable that solid content concentration of the to-be-processed liquid after concentration be 30 mass% or less because of difficulty of handling and deterioration of crystal quality by insufficient stirring.

Although concentration temperature is not specifically limited, 50 degreeC-100 degreeC is preferable. By making concentration temperature into the said range, the recovery rate of boric acid can be improved. The temperature at the time of concentration may differ from the temperature of the processing liquid at the time of preparation of the processing liquid or at the pH adjustment. Usually, it concentrates at the temperature about the same as the to-be-processed liquid after pH adjustment, or higher than it. In addition, in concentration under reduced pressure, you may be below the temperature of the to-be-processed liquid after pH adjustment. The reduced pressure is preferably 10000 Pa to 80000 Pa, more preferably 20000 Pa to 70000 Pa. As for the temperature of the heated aqueous solution after concentration, 50 degreeC-100 degreeC is preferable like the temperature of the said to-be-processed liquid, and 70-80 degreeC is especially preferable.

In the first aspect, however, even if concentration is performed under certain conditions, it is preferable that insoluble matters are not produced by concentration.

In addition, in the second aspect, in consideration of the equipment load, it is preferable that the alkali metal salt precipitated with respect to the concentrated liquid does not exceed 10% by mass.

In the second aspect, the particle diameter of the precipitated Na salt is controlled by adjusting the tip speed of the impeller of the circulation pump of the concentrating device, 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, whereby the particle diameters of sodium chloride and sodium sulfate, which are precipitated Na salts, are about 100 to 300 µm. At this time, the particle size of the boric acid crystal which is undesirably precipitated is 20-50 micrometers, and Na salt which is an impurity can be isolate | separated from the concentrate containing boric acid by a subsequent cyclone.

As the solid-liquid separation device, not only a cyclone, but also a separation of a large-diameter crystal by a horizontal continuous centrifuge, a classification by a fluidized bed, a batch sedimentation separation method, or the like may be used.

In the second aspect, the pH adjustment step of adding an acid to the liquid to be treated is performed before the concentration step, so that the concentration is performed after converting the alkali metal borate in the liquid to be treated with boric acid and an alkali metal salt in advance. In addition to the alkali metal salts generated by this conversion, crystals of alkali metal salts can be grown in the concentration step, whereby the alkali metal salts can be efficiently removed in the removal step.

In the case of the 2nd aspect, the to-be-processed liquid from which the crystal | crystallization of Na salt which is an impurity by cyclone was removed is introduce | transduced into a crystallization stock solution tank as crystallization stock solution. Dilution water is added to the crystal stock solution tank to dilute the liquid to be treated (called 'dilution process'). Thus, since the to-be-processed liquid is diluted with water for dilution, precipitation of impurities other than a boric acid crystal can be suppressed in a subsequent crystallization process.

In addition, in the recovery method of the present invention, as shown in FIG. 1 or FIG. 2, the treatment is carried out in the order of `` (heating of the liquid to be processed →) pH adjustment → concentration '' (hereinafter referred to as "embodiment 1"). Although not limited, it is as above-mentioned.

That is, as another embodiment of the first aspect and the second aspect, after the processing liquid is heated to 50 ° C. or higher (but heating is not essential as described above, too), concentration is performed, and the concentrated liquid to be treated ( In the case of the second aspect, the pH is adjusted by adding an acid such as sulfuric acid in a state in which the to-be-processed liquid in which Na salt crystals have been removed by cyclone after being concentrated and precipitated Na salt crystals is 50 ° C. or more, The pH may be set to a concentrated pH-adjusted treatment liquid adjusted to less than 4, preferably not more than 3.5, more preferably less than 3.5, and more preferably 1 to 3 (hereinafter referred to as 'second embodiment'). ).

Moreover, also in this case, it is preferable that the solid content concentration of the to-be-processed liquid adjusted to the concentrated pH is 15 mass% or more, and also 30 mass% or less is the same reason as before.

In Embodiment 1, since the to-be-processed liquid with strong acid after pH adjustment by adding sulfuric acid is heat-concentrated with a concentrator, it is necessary to use the expensive material which is hard to corrode. On the other hand, in Embodiment 2, since a pH adjustment process is performed after the concentration process in a concentration apparatus, compared with Embodiment 1, a concentration apparatus does not need to use expensive material, and can reduce cost.

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

(Embodiment 3 of the second embodiment)

In Embodiment 2 of 2nd Embodiment, although the pH adjustment process was provided between the removal process and the crystallization process, in this case, it is alkali metal by pH adjustment to the to-be-processed liquid after a removal process (equivalent to the saturated solution of an alkali metal salt). As a result of addition of the alkali metal salt which arises with the conversion of a borate, the crystal of an alkali metal salt may produce | generate newly. In this case, since the whole amount of alkali metal salt crystals is supplied to the crystallization stock solution tank, the amount of dilution water used to suppress the mixing of crystals of the alkali metal salt in the crystallization step may increase. As a result, the concentration of boric acid in the dilute crystallization stock solution also decreases, and the amount of boric acid crystals deposited in the crystallization step may decrease.

In that case, it may be set as the form different from Embodiment 1, 2 of 2nd aspect, and can provide a pH adjustment process between a concentration process and a removal process (not shown).

In this embodiment, by removing at least a part of the crystals of the alkali metal salt newly generated by pH adjustment in the removal step, the amount of dilution water can be reduced as compared with the case where a pH adjustment step is provided between the removal step and the crystallization step. Thus, the amount of boric acid that can be recovered in the crystallization process can be increased. However, in this case, since the removal process is performed at a low pH, it is preferable to provide a pH adjustment process between the removal process and the crystallization process when reducing the acid resistance load in the removal process. In addition, since the alkali metal salt crystals precipitated by the addition of sulfuric acid tend to become microcrystals, when the crystals of the alkali metal salts are separated by a cyclone or the like, there is a possibility that the crystals of the alkali metal salts may not be removed efficiently. It is preferable to add sulfuric acid before the concentration step.

(Embodiment 4 of the second embodiment)

Prior to the concentration process, pH adjustment (preferably pH 4 to 6, more preferably pH 4 to 5.5, more preferably pH 4 to 5, in which at least a portion of the alkali metal borate salts in the treatment liquid is converted into boric acid and alkali metal salts) ), And after the removal step, pH adjustment (preferably less than pH 4, more preferably pH 1 to 3) may be performed to increase the boric acid purity (not shown).

In this embodiment, since the pH of the liquid processed by a concentrator is comparatively high, use of expensive materials can be suppressed and cost can be reduced, and at least a part of alkali metal borate is converted before a concentration process, and this is accompanied by this. The alkali metal salts generated by the growth are grown to a particle size of a size suitable for removal in the concentration step, and thus can be efficiently removed in the removal step. As a result, the amount of dilution water is suppressed and the amount of boric acid crystals precipitated in the crystallization step is reduced. Can be increased.

Subsequently, the pH adjusted to-be-processed liquid (preferably the concentrated pH adjusted to-be-processed liquid) is cooled to a certain temperature to precipitate boric acid crystals. That is, a boric acid crystal is precipitated by crystallization (cooling crystallization) by what is called cooling by a crystallization apparatus (crystal can). In cooling crystallization, boric acid crystal | crystallizes as a result of falling in the solubility of a boric acid crystal | crystallization with the temperature of aqueous solution falling by cooling operation. Hereinafter, the temperature of the end point of this cooling operation is called cooling temperature.

In this invention, boric acid can be selectively collect | recovered from the to-be-processed liquid containing a boron compound and an alkali metal compound by using crystallization. In addition, since boric acid can be selectively recovered by crystallization, boric acid can also be recovered from the by-product wastewater or solid discharge by purifying the exhaust gas containing the sulfur component. As described above, the pH of the heated aqueous solution is adjusted with acid, followed by cooling to precipitate the boric acid crystals by crystallization, thereby facilitating the control of the grain shape and particle size of the boric acid crystals. In addition, the purity of the boric acid crystals to be recovered can be improved.

In particular, in the case of the second embodiment, the liquid to be treated is concentrated prior to cooling crystallization to precipitate and remove alkali metal salts as impurities, so that boric acid with high purity can be recovered even with a liquid having a high concentration of alkali metal salts.

In addition, as shown in Patent Document 3, after cooling the processing liquid containing boric acid (boron compound), even in the method of adjusting the pH to a predetermined acidity by adding sulfuric acid or the like, boric acid is precipitated by precipitating boric acid crystals. It can be recovered.

However, in this method, since boric acid crystals are precipitated instantaneously by adjusting the pH, impurities such as Na salts are easily introduced into the boric acid crystals, and because they are microcrystalline, they contain impurities such as Na salts attached to the crystal surface. Since the amount to which water adheres increases, high purity boric acid crystals cannot be obtained when various compounds are mixed in the to-be-processed liquid.

Further, in this processing procedure, since boric acid crystals are precipitated instantaneously, a problem arises in 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 cooling temperature is 50 degreeC or more, a problem arises in that a boric acid crystal | crystallization cannot fully precipitate and a recovery rate worsens.

On the contrary, when cooling temperature is less than 30 degreeC, the problem that crystal | crystallization of alkali metal compounds, such as sodium sulfate, precipitates as a mixed crystal arises.

Moreover, 10 degreeC or more is suitable for the difference of the temperature of the pH-processed to-be-processed liquid before cooling, and cooling temperature, and 20 degreeC or more is preferable. Especially 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 suppressed to a minimum, and the recovery rate of boric acid crystal can be improved more.

In addition, it is preferable to perform precipitation of boric acid crystal | crystallization by cooling pH-processed to-be-processed liquid under reduced pressure.

By cooling under reduced pressure and precipitating boric acid crystals, it is possible to suppress the generation of scale on the heat transfer surface, which is concerned when the jacket cooling method is adopted, thereby facilitating the maintenance of the device and the loss of boric acid crystals. By reducing, the recovery rate of boric acid can be improved.

In addition, the height of the pressure is not particularly limited at this time, but at the start of cooling, it is preferable to reduce the pressure to 10000 Pa to 70000 Pa, more preferably 20000 Pa to 60000 Pa, and at the end of cooling, preferably 1000 Pa to 15000 Pa, more preferably It is preferable to reduce the pressure to 2000 Pa to 8000 Pa.

After precipitation of the boric acid crystals by cooling the pH-treated target liquid, the precipitated crystals are separated from the aqueous solution by a recovery device (centrifuge) in the recovery step to recover the crystals of boric acid. At this time, it is preferable that the temperature of the aqueous solution containing the crystal is maintained at the above-mentioned cooling temperature, preferably 30 ° C. or higher and less than 50 ° C., and separation operation is performed.

The separation method of boric acid crystal is not specifically limited, The well-known separation method for separating a solid component in a liquid, such as filtration, centrifugation, and sedimentation, can be utilized variously.

Here, the boric acid which does not precipitate is contained in the filtrate after isolate | separating a boric acid crystal.

Therefore, this filtrate is sent to the to-be-processed liquid containing at least one of waste water and a solid discharge | emission by a liquid feeding apparatus, and it reuses as a raw material of the to-be-processed liquid (henceforth, even if a filtrate is added to the to-be-processed liquid) It is preferable to. That is, it is preferable to use this filtrate as dilution water etc. of the said discharge liquid or solid discharge liquid. For example, the mixture of the solid effluent collected with the above-mentioned bug filter and the filtrate can be added to the treated liquid (or used as the treated liquid), and further, the mixture of the solid discharge and the filtrate can be used. If necessary, water may be added to form the target liquid. Thereby, the recovery rate of boric acid to the said discharge liquid and solid waste can be improved more.

Here, most of the boric acid is contained in the remaining filtrate from which the boric acid crystals are first separated, but also impurities. Therefore, in 1st aspect, when the usage-amount of this filtrate to a to-be-processed liquid is too large, an impurity will gradually concentrate, the impurity concentration in a to-be-processed liquid will become high concentration, and an appropriate process may not be able to be performed. do.

Therefore, it is preferable to make the filtrate added to the to-be-processed liquid and reused as a part of filtrate. Specifically, it is preferable that the filtrate added to the to-be-processed liquid shall be 50 mass%-90 mass% with respect to the whole filtrate after separating a boric acid crystal | crystallization. Thereby, the recovery rate of boric acid can be improved suitably, preventing the adverse effect resulting from the increase of the impurity in a to-be-processed liquid.

In the second embodiment, the Na salt as an impurity contained in the liquid to be treated is concentrated and precipitated in a concentrating device, and is removed by a cyclone as a removal device. Thus, even when the liquid to be treated with a high alkali metal salt concentration is concentrated, Since most crystals of alkali metal are not contained, the liquid after concentration can be obtained. Therefore, the filtrate added to the to-be-processed liquid and reused can be at least one part, preferably all of the filtrate. Thereby, recovery rate of boric acid can be improved preferably.

In both the first and second aspects, part of the treated water after the recovery of the boric acid crystal is discarded, and the remaining part is returned to the addition step, thereby adjusting the waste amount of the treated water, that is, the alkali metal salt concentration of the treated liquid is high. In the case where a load is applied to the concentration step or the removal step, the waste water of the treated water may be increased to facilitate the concentration step and the removal step. On the other hand, when the load of a concentration process or a removal process is not large, the waste volume of a process water can be made small and the recovery rate of boric acid can be improved.

In this way, the boric acid crystal recovered by the recovery method of the present invention is sufficiently high purity water, and can be used as a raw material of borosilicate glass as it is.

However, depending on the application or the like, the recovered boric acid crystals are not sufficiently clean, and the purity of the boric acid crystals may not be satisfied at a desired value. In that case, you may wash | clean the recovered boric acid crystal | crystallization with aqueous boric acid solution or water which does not contain an alkali metal component. In addition, what is necessary is just to wash the boric acid crystal by a well-known method. In addition, the boric-acid aqueous solution which does not contain an alkali metal component contains not only an alkali metal compound but the boron compound containing alkali metal atoms, such as sodium borate, the compound containing alkali metal atoms other than those compounds, alkali metal ion, etc. It does not say boric acid aqueous solution.

In addition, the purity of the recovered boric acid crystals may not be sufficiently high depending on the use or the like. In that case, it is preferable to further improve the purity of the boric acid crystal by performing crystallization again (recrystallization treatment). Although recrystallization processing may be performed twice or more as needed, the boric acid crystal of sufficiently high purity can be obtained normally by one recrystallization process.

In the recrystallization treatment, as shown in FIG. 1 or FIG. 2, an aqueous boric acid solution containing no water (or an alkali metal component) or a boric acid aqueous solution which is a filtrate after recrystallization described later. Boric acid crystals are dissolved by adding a boric acid aqueous solution ') to form a processing liquid for recrystallization and heating with a heat dissolving apparatus.

There is no restriction | limiting in particular in the addition amount of the water and boric-acid aqueous solution for manufacturing the to-be-processed liquid for recrystallization, According to the quantity of boric acid crystal | crystallization, etc., it is set suitably. Moreover, there is no restriction | limiting in particular also in heating temperature, Although what is necessary is just the temperature which can melt | dissolve boric acid crystal, 50 to 100 degreeC is preferable and 70 to 80 degreeC is more preferable.

Subsequently, the to-be-processed liquid for recrystallization is cooled to 30 degreeC or more and less than 50 degreeC, and a boric acid crystal is reprecipitated. That is, boric acid crystal is reprecipitated by cooling crystallization by a crystallization apparatus (crystal can). 10 degreeC or more is suitable for the temperature difference after cooling of the to-be-processed liquid for recrystallization, and cooling, and 20 degreeC or more is preferable. Especially 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 limitation of a cooling temperature range is the same as that of the crystallization mentioned above. In addition, 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 recrystallizing the boric acid crystals by cooling crystallization, the boric acid crystals are again separated from the aqueous solution containing the boric acid crystals by a recovery apparatus (centrifuge) by a known method as described above, and recrystallized. Recover one boric acid crystal.

The boric acid crystal obtained by the purification by this recrystallization process is a higher purity boric acid crystal with less impurities, such as an alkali metal compound.

Here, the boric acid which did not precipitate is contained also in the filtrate after separating boric acid crystal | crystallization in this recrystallization process (henceforth "filtrate after recrystallization").

Therefore, as shown in FIG. 1 or FIG. 2, the filtrate after the recrystallization also includes at least one portion of the drainage and the solid discharge by the liquid feeding device, similarly to the filtrate after the boric acid crystal separation described above. It is preferable to send to a to-be-processed liquid and to reuse as a raw material of the to-be-processed liquid (henceforth adding a filtrate to the to-be-processed liquid). Thereby, the recovery rate in recovery of boric acid from a to-be-processed liquid and recrystallization process can be improved more.

In this case as well, the solid discharge may be added / mixed to this filtrate and added to the liquid to be treated (or may be a liquid to be treated).

5-100 mass%, preferably 10-75 mass%, More preferably, 15-50 mass% of the filtrate after isolate | separating the said reprecipitated boric acid crystal | crystallization is added to the to-be-processed liquid before the said concentration and pH adjustment, Moreover, it is preferable to add 0-95 mass% of the said filtrate, Preferably 25-90 mass%, More preferably, 50-85 mass% to the said to-be-processed liquid for recrystallization.

Here, the filtrate after recrystallization also contains impurities such as an alkali metal compound. However, the impurity contained in the filtrate after recrystallization is an impurity which has adhered or mixed in the boric acid crystal | crystallization which isolate | separated by crystallization once, and is a trace amount.

Therefore, in order to improve the recovery rate of boric acid, it is advantageous to reuse the filtrate after recrystallization as a raw material of the to-be-processed liquid, and to add as much as possible to the to-be-processed liquid, and especially, the whole amount is added to the to-be-processed liquid It is preferable to reuse.

It is preferable that it is 0.5 mass% or less, and, as for the alkali metal content (the amount converted into alkali metal atoms) in boric acid obtained by the collection | recovery method of this invention, it is more preferable that it is 1000 ppm or less. More preferably, it is 500 ppm or less. In the recovery method of this invention, alkali metal content can be made into 0.5 mass% or less in boric acid before recrystallization processing. Moreover, alkali metal content can be 500 ppm or less by performing recrystallization process once.

It is preferable that both the wastewater and the solid discharge | emission in this invention are the wastewater or solid discharge | emission discharged | emitted from the waste gas processing process which contacts exhaust gas discharged from the manufacturing process of borosilicate glass with basic aqueous alkali metal compound aqueous solution.

As borosilicate glass, borosilicate glass which contains few or substantially no alkali metal components (ie, alkali free) of alkali metal components (oxides of alkali metals, such as sodium and potassium) is preferable.

As borosilicate glass, the borosilicate glass of the following composition (1) and (2) is preferable by the mass percentage display on an oxide basis. However, following R represents an alkali metal. In addition, a small amount of metal oxides (Fe ₂ O ₃ , SnO _2, etc.), non-metal oxides (sulfur oxides (SO ₃ ), etc.), halogens (Cl, F) and the like other than the following (preferably 3% by mass or less), More preferably, it may contain 2 mass% or less, More preferably, 1 mass% or less).

(1) SiO ₂ : 40 to 85% by mass, Al ₂ O ₃ : 1 to 22% by mass, B ₂ O ₃ : 2 to 20% by mass, MgO: 0 to 8% by mass, CaO: 0 to 14.5% by mass, SrO: 0 to 24% by mass, BaO: 0 to 30% by mass, R ₂ O: 0 to 10% by mass

(2) SiO ₂ : 58-66 mass%, Al ₂ O ₃ : 15-22 mass%, B ₂ O ₃ : 5-12 mass%, MgO: 0-8 mass%, CaO: 0-9 mass%, Alkali free glass containing SrO: 3-12.5 mass%, BaO: 0-2 mass%, MgO + CaO + SrO + BaO: 9-18 mass%

Borosilicate glass containing alkali metal used in a heat-resistant container or a laboratory instrument, an alkali metal component (R ₂ O) content of the borosilicate glass of about 2 to 10% by mass in general, the composition (1).

On the other hand, as borosilicate glass used as a board | substrate of a liquid crystal display element, borosilicate glass with few alkali metal components, More preferably, borosilicate glass with very few alkali metal components called an alkali free borosilicate glass is used. The alkali-free borosilicate glass, and (non-alkali glass), called borosilicate glass, borosilicate, the composition (1) is an alkali metal (R ₂ O) content of not more than 0.1 mass% in the glass, is inevitable in the above composition (2) Infrared It is borosilicate glass which does not contain alkali metal oxide substantially (for example, 0.1 mass% or less of alkali metal oxide) other than what is contained as an impurity.

It is preferable that the borosilicate glass in the manufacturing process of the borosilicate glass which is the discharge source of waste water and solid discharge in this invention is borosilicate glass with few said alkali metal components (that is, less than 2 mass%), and an alkali metal component is 1 mass% It is more preferable that it is the following borosilicate glass. Especially preferably, it is borosilicate glass with very few alkali metal components (namely 0.1 mass% or less) called the alkali free borosilicate glass.

The quantity of the alkali metal component in the said borosilicate glass becomes a requirement which restricts the use place of the boric acid collect | recovered by this invention. The kind of borosilicate glass which can be used as a borosilicate glass raw material is restrict | limited by the quantity of the alkali metal component which is an impurity in collect | recovered boric acid. When the amount of the alkali metal component in the recovered boric acid is large, it is difficult to use the boric acid as a raw material of the borosilicate glass with less alkali metal component, and there is a possibility that it cannot be used as a raw material of alkali-free borosilicate glass.

For this reason, as mentioned above, it is preferable that it is 0.5 mass% or less, and, as for alkali metal content (amount converted to alkali metal atom) in boric acid obtained by the collection | recovery method of this invention, it is more preferable that it is 1000 ppm or less. More preferably, it is 500 ppm or less. Such high purity boric acid can be used as a raw material of an alkali free borosilicate glass.

Therefore, for example, the alkali-free borosilicate glass (borosilicate glass whose alkali metal content is less than 2 mass%) is used for the boric acid collect | recovered from the waste liquid by-produced by the process of the exhaust gas discharged from the manufacturing process of an alkali free borosilicate glass, and solid discharge. It becomes possible to reuse as a raw material of ().

As mentioned above, although the collection method of the boric acid of this invention was demonstrated in detail, this invention is not limited to the above-mentioned example, Of course, various improvement and change may be made in the range which does not deviate from the summary of this invention.

[Example]

Hereinafter, the present invention will be described in more detail with reference to specific examples of the present invention. It goes without saying that the present invention is not limited to the following examples.

<First Embodiment>

Example 1

By the purification process shown in FIG. 3, the exhaust gas discharged from the glass melting furnace for manufacturing borosilicate glass was purified. In this purification process, the liquid to be treated is dissolved by dissolving the solid discharge collected by the bug filter in the drainage discharged from the venturi scrubber (hereinafter, the liquid is referred to as a 'mother liquid').

1000 mL of this mother liquid was divided | segmented, it heated at 75 degreeC, and was made into the heating aqueous solution. Then, sulfuric acid was added to the heating aqueous solution, and pH was adjusted to 2.

Then, this pH adjusted heating aqueous solution was concentrated until 75 degreeC just before solid precipitated. This concentrated heated aqueous solution (pH adjustment complete) contained 32 g / L boron, 60 g / L sodium, and 61 g / L sulfate ions, respectively.

The concentrated heating aqueous solution (pH adjustment completed) was cooled from 75 degreeC to 35 degreeC, and boric acid crystal was precipitated.

The to-be-processed liquid which precipitated boric acid crystal was filtered at 35 degreeC, and boric acid crystal 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 ion and 0.4 mass% for sodium.

[Example 2]

To the boric acid crystal recovered in Example 1, water in an amount such that the 75 ° C aqueous solution became a saturated aqueous solution was added to prepare a target liquid for recrystallization. This to-be-processed liquid for recrystallization was heated at 75 degreeC, the whole amount of boric acid crystal was melt | dissolved, and the saturated aqueous solution was produced.

Subsequently, the said 75 degreeC saturated aqueous solution was cooled to 35 degreeC, and boric acid crystal was reprecipitated.

The aqueous solution to which the boric acid crystal was reprecipitated was filtered at 35 degreeC, and boric acid crystal was collect | recovered.

Purity of the recovered boric acid was measured in the same manner as in Example 1, and the impurities, sodium ions, sulfate ions, chlorine ions, and fluorine ions in the boric acid crystal were all 100 ppm or less.

Comparative Example 1

Boric acid crystal | crystallization was collect | recovered similarly to Example 1 except having adjusted the addition amount of the sulfuric acid which adjusts pH of a heated aqueous solution, and made pH of the heated aqueous solution adjusted to pH 4.

The purity of the recovered boric acid crystal was measured in the same manner as in Example 1, and the impurity concentration in the recovered boric acid crystal was 1.7% by mass of sulfate ions and 1.0% by mass of sodium.

[Comparative Example 2]

1000 ml of the mother liquid similar to Example 1 was divided | segmented, and it heated to 75 degreeC. This heated aqueous solution was cooled to 35 degreeC, the borate salt of sodium was precipitated, Then, sulfuric acid was added to the cooled completed aqueous solution, pH was adjusted to 2, and it converted to the boric acid crystal.

The precipitated boric acid crystals were collected by filtration in the same manner as in Example 1.

The purity of the recovered boric acid crystals was measured in the same manner as in Example 1, and the impurity concentration was 2.4% by mass of sulfate ions and 1.8% by mass of sodium.

The effect of this invention is obvious from the above result.

&Lt; Second embodiment >

[Example 3]

By the purification process shown in FIG. 3, the exhaust gas discharged from the glass melting furnace for manufacturing borosilicate glass was purified. In this purification process, the wastewater discharged from the venturi scrubber was used as the stock solution. In the second aspect, a large amount of alkali metal salt is contained in the liquid to be treated. In order to reproduce the to-be-processed liquid in this process, in order to obtain the to-be-processed liquid which raised the alkali metal salt density | concentration, the liquid which added sodium sulfate and sodium chloride to the raw liquid discharged | emitted from the scrubber was produced (hereinafter this liquid Referred to as 'mother liquid').

The mother liquid was divided into 1440 mL, sulfuric acid was added, and pH was adjusted to 2.

Then, this pH adjusted liquid was concentrated at 75 degreeC, and solid content was deposited. Subsequently, the filter paper was separated into a solid and a supernatant by filtration. Solid content was 69g. Also, the concentrated condensate was 430 g.

When this solid content was analyzed by the ion chromatography method, 36.2 mass% of sodium, 44.4 mass% of sulfate ions, 17.8 mass% of chloride ions, and 0.9 mass% of boron were contained. Therefore, this solid content is considered to be the mixed crystal of sodium sulfate and sodium chloride mainly.

To this supernatant, 5 wt% of pure water was added, followed by cooling from 75 ° C to 35 ° C to precipitate boric acid crystals. The to-be-processed liquid which precipitated boric acid crystal was filtered at 35 degreeC, and boric acid crystal was collect | recovered.

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

Example 4

10 wt% of pure water was added to the supernatant obtained by the same operation as in Example 3, followed by cooling from 75 ° C to 35 ° C to precipitate boric acid crystals. The to-be-processed liquid which precipitated boric acid crystal was filtered at 35 degreeC, and boric acid crystal was collect | recovered.

The purity of the recovered boric acid crystals was measured by ion chromatography, and the impurity concentration in the recovered boric acid crystals was 0.4 mass% for sulfate ions and 0.8 mass% for chloride ions.

[Comparative Example 3]

The supernatant liquid obtained in 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 boric acid crystal was filtered at 35 degreeC, and boric acid crystal was collect | recovered.

The purity of the recovered boric acid crystals was measured by ion chromatography, and the impurity concentration in the recovered boric acid crystals was 0.5 mass% for sulfate ions and 6.7 mass% for chloride ions.

Although this invention was detailed also demonstrated with reference to the specific embodiment, it is clear for those skilled in the art that various corrections and changes can be added without deviating from the range and mind of this invention.

This application is based on the JP Patent application 2011-035896 of an application on February 22, 2011, and the Japanese patent application 2011-209254 of a September 26, 2011 application, The content is taken in here as a reference.

Boric acid which can be used as a boron silicate glass raw material can be collect | recovered from the wastewater and solid discharge which contain a boron compound and an alkali metal compound, such as wastewater discharged in the manufacturing process of boron silicate glass, and solid discharge.

Claims (12)

A method for recovering boric acid that recovers boric acid from a liquid to be treated containing at least one of wastewater and a solid discharge containing a boron compound and an alkali metal compound,
After adding acid to the to-be-processed liquid and adjusting to less than pH 4, or concentrating, or after concentrating the to-be-processed liquid and adding acid, it is adjusted to less than pH 4,
The concentrated liquid is adjusted to pH, and the to-be-processed liquid containing no insoluble matter is cooled to prepare an aqueous solution in which boric acid crystals are precipitated.
The boric acid crystals are separated from the aqueous solution in which the boric acid crystals are precipitated,
50-90 mass% of the filtrate after isolate | separating the said boric acid crystal | crystallization is added to the to-be-processed liquid before the said concentration and pH adjustment,
An aqueous solution in which boric acid crystals are reprecipitated by heating a recrystallized solution to which the boric acid aqueous solution or water is added to the separated boric acid crystals to dissolve boric acid crystals, and cooling the to-be-processed liquid for recrystallization in which the heated boric acid crystals are dissolved. The boric acid crystals are separated from the aqueous solution in which the boric acid crystals are reprecipitated.
The recovery method of boric acid which adds at least one part of the filtrate after isolate | separating the said reprecipitated boric acid crystal | crystallization to the to-be-processed liquid before the said concentration and pH adjustment. The method of claim 1,
When the liquid to be treated before the 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 treated liquid does not contain Na ₂ SO ₄ but contains NaCl, the mass ratio (Na / B) is 3.9 or less,
When the liquid to be treated does not contain Na ₂ SO _4, and including NaCl, a method for recovering the mass ratio (Na / B) is 3.1 or less acid. A method for recovering boric acid that recovers boric acid from a liquid to be treated containing at least one of wastewater and a solid discharge containing a boron compound and an alkali metal compound,
After adding acid to the said to-be-processed liquid and adjusting to less than pH 4, it concentrates and precipitates an alkali metal salt, and removes an alkali metal salt from the to-be-processed liquid in which the alkali metal salt precipitated,
Alternatively, the treated liquid is concentrated to precipitate an alkali metal salt, and after removing the alkali metal salt from the treated liquid on which the alkali metal salt is precipitated, an acid is added to adjust the pH to less than 4,
Dilute by adding water to the concentrated and pH-adjusted liquid to which the alkali metal salt is removed;
The diluted treated solution is cooled to an aqueous solution in which boric acid crystals are precipitated,
The boric acid crystals are separated 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,
An aqueous solution in which boric acid crystals are reprecipitated by heating a recrystallized solution to which the boric acid aqueous solution or water is added to the separated boric acid crystals to dissolve boric acid crystals, and cooling the to-be-processed liquid for recrystallization in which the heated boric acid crystals are dissolved. The boric acid crystals are separated from the aqueous solution in which the boric acid crystals are reprecipitated.
The recovery method of boric acid which adds at least one part of the filtrate after isolate | separating the said reprecipitated boric acid crystal | crystallization to the to-be-processed liquid before the said concentration and pH adjustment. The method of claim 3,
When the treatment liquid before the 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 treatment liquid is greater than 3.6,
When the treated liquid does not contain Na ₂ SO ₄ but contains NaCl, the mass ratio (Na / B) is greater than 3.9,
When the liquid to be treated does not contain Na ₂ SO _4, and including NaCl, a method for recovering of the mass ratio (Na / B) is greater than 3.1 acid. The method according to claim 3 or 4,
The concentration of the said to-be-processed liquid WHEREIN: The recovery method of boric acid which controls the particle diameter of the alkali metal salt which precipitates, and removes an alkali metal salt selectively. The method according to any one of claims 1 to 5,
5-100 mass% of the filtrate after isolate | separating the said reprecipitated boric acid crystal | crystallization is added to the to-be-processed liquid before the said concentration and pH adjustment, and 0-95 mass% of the said filtrate is the said to-be-processed liquid for recrystallization A recovery method of boric acid added to the. 7. The method according to any one of claims 1 to 6,
When the solid content of the wastewater and the solid discharge contain at least boron, alkali metal, sulfur and chlorine as elements, and the mass ratio of the elements is boron 1, the alkali metal is 0.6 to 13, sulfur is 6 or less and chlorine is A recovery method of boric acid that is 6 or less. 8. The method according to any one of claims 1 to 7,
The recovery method of boric acid whose alkali metal component in collect | recovered boric acid is 0.5 mass% or less. The method according to any one of claims 1 to 8,
A method for recovering boric acid, which is drainage or solid discharge discharged from an exhaust gas treatment step in which the exhaust gas discharged from the manufacturing process of borosilicate glass is brought into contact with at least one of a solid and an alkali metal compound aqueous solution of an alkali metal compound, both of which discharge and solid discharge. . 10. The method of claim 9,
The recovery method of boric acid whose alkali metal content of the said borosilicate glass is less than 2 mass% in the mass percentage of an oxide basis. An apparatus for recovering boric acid from a liquid to be treated containing at least one of a wastewater and a solid discharge containing a boron compound and an alkali metal compound,
A concentrating device for concentrating the processing liquid;
A pH adjusting device in which an acid is added to adjust the pH of the liquid to be treated to less than 4,
A crystallization device which cools the to-be-processed liquid which does not contain the said pH adjustment and does not contain an insoluble thing, and sets it as the aqueous solution which the boric acid crystal precipitated,
A recovery device for separating and recovering the precipitated boric acid crystals from the aqueous solution;
A liquid feeding apparatus for sending 50 to 90 mass% of the filtrate after separating and recovering the boric acid crystals to the target liquid before the concentration and pH adjustment;
A heat dissolving apparatus for dissolving boric acid crystals by heating a processing liquid for recrystallization in which boric acid aqueous solution or water is added to the separated and recovered boric acid crystals;
A crystallization apparatus for cooling the target liquid for recrystallization in which the boric acid crystals are dissolved by heating, to prepare an aqueous solution in which boric acid crystals are reprecipitated;
A recovery device for separating and recovering the reprecipitated boric acid crystals from the aqueous solution,
Feeding apparatus for sending at least a portion of the filtrate after separating and recovering the re-precipitated boric acid crystals to the treated liquid before the concentration and pH adjustment
Boric acid recovery apparatus comprising a. An apparatus for recovering boric acid from a liquid to be treated containing at least one of a wastewater and a solid discharge containing a boron compound and an alkali metal compound,
A concentrating 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 adjusting device 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 an alkali metal salt is removed by said removal device, and an aqueous solution in which boric acid crystals are precipitated by cooling the to-be-processed liquid pH adjusted by said pH adjusting device;
A recovery device for separating and recovering the precipitated boric acid crystals from the aqueous solution;
A liquid feeding apparatus 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 heat dissolving apparatus for dissolving boric acid crystals by heating a processing liquid for recrystallization in which boric acid aqueous solution or water is added to the separated and recovered boric acid crystals;
A crystallization apparatus for cooling the target liquid for recrystallization in which the boric acid crystals are dissolved by heating, to prepare an aqueous solution in which boric acid crystals are reprecipitated;
A recovery device for separating and recovering the reprecipitated boric acid crystals from the aqueous solution,
Feeding apparatus for sending at least a portion of the filtrate after separating and recovering the re-precipitated boric acid crystals to the treated liquid before the concentration and pH adjustment
Boric acid recovery apparatus comprising a.

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