JPS647011B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for recovering boric acid from seawater. More specifically, the present invention relates to a method for recovering high purity boric acid from seawater.

In recent years, boron and its compounds have attracted attention as components of neuceramics, neutron shielding materials, and physical property modifiers for metals such as steel, and demand is increasing accordingly. Such boron compounds are generally manufactured using borax as a raw material, but due to the limited amount of borax and the limited areas where borax exists, large quantities are produced. There are concerns about obtaining a stable supply of borax.

The present invention focuses on boron, which is mainly contained in the form of boric acid in seawater, and aims to provide a method for separating and recovering boric acid as high-purity boric acid using a highly economical method. It is something to do.

In seawater, there are large amounts of sodium chloride and magnesium salts, but also boron,
Approximately 15-20 ppm, mainly in the form of boric acid (boric acid:
It has been known for some time that the amount of H ₃ BO ₃ contained in However, for example, in a method for producing magnesia clinker from magnesium salt in seawater, boric acid is said to be harmful in that it reduces the physical properties of clinker. Therefore, in order to remove this boric acid, the boric acid content in the seawater is reduced by contacting seawater with magnesium hydroxide and adsorbing the boric acid to the magnesium hydroxide, and then the desired magnesia clinker is extracted. A manufacturing method has also been proposed.

The present invention uses an efficient method to separate and recover boric acid in seawater, which has conventionally been eliminated as an undesirable impurity, and to produce various boron compounds that have been found to have many useful uses. The purpose is to obtain highly pure boric acid as a boron source.

That is, the present invention essentially comprises: (1) adjusting the pH value of seawater to approximately 8 to 10 and reducing the carbon dioxide content of the seawater to 40 ppm or less; (2) seawater subjected to the above treatment; The pH value of about 8-10
(3) By contacting the seawater that has undergone the above treatment with a boric acid adsorbing ion exchange resin, the content of solid particulate components is reduced to 10 ppm or less while maintaining the a step of adsorbing boric acid on the ion exchange resin; (4) a step of desorbing the adsorbed boric acid by contacting the ion exchange resin with a mineral acid containing boric acid; and (5) a step of desorbing the adsorbed boric acid. (6) Separation process of separating and recovering 1/5 to 3/5 of the boric acid contained therein from the mineral acid containing boric acid, and at the same time recovering the mineral acid with reduced boric acid content; (6) Separation A step of dissolving the recovered boric acid in an aqueous solution containing boric acid; (7) Bringing the obtained boric acid solution into contact with an alkalizing agent to alkalize the mineral acid contained in the boric acid solution. (8) separating and removing the reaction product of the mineral acid and the alkalizing agent from the boric acid solution; and (9) separating and recovering a portion of boric acid from the boric acid solution. , a step of simultaneously collecting a boric acid-containing aqueous solution, and at least a portion of the mineral acid with reduced boric acid content recovered in step (5) above is converted into a boric acid solution in step (4) above. and at least a part of the boric acid-containing aqueous solution recovered in step (9) above as a mineral acid containing boric acid in step (6) above. This method consists of a method for recovering boric acid from seawater, which is characterized in that it is used as part or all of boric acid.

In addition, between the steps (4) and (5) above,
If necessary, a step can be inserted to desorb most of the undesorbed boric acid by contacting the ion exchange resin that has undergone step (4) with a mineral acid that does not substantially contain boric acid. .

Next, the present invention will be explained in detail.

The present invention makes it possible to separate and recover boric acid contained in seawater efficiently and economically by using a combination of a plurality of steps.

The practical first step of the present invention is to adjust the pH value of seawater to about 8 to 10 and reduce the carbon dioxide content of the seawater.
Consists of a process to reduce the concentration to 40ppm or less. In other words, approximately 70 to 100 ppm of carbon dioxide is normally dissolved in seawater, but in the process of bringing seawater into contact with a boric acid adsorbing ion exchange resin and adsorbing boric acid onto the ion exchange resin, the adsorption In order for carbon dioxide to proceed at a practically meaningful level, the content of carbon dioxide in seawater must be reduced to 40 ppm or less (preferably
30 ppm or less, particularly preferably 20 ppm or less), and in order to efficiently adsorb boric acid contained in seawater containing sodium chloride or other various salts and compounds to the ion exchange resin. , the pH of the seawater needs to be adjusted to about 8-10.

One way to adjust the PH of seawater to the above range and remove a predetermined amount of carbon dioxide is to add an alkali such as milk of lime to the seawater. It is possible to use a method of converting the carbon dioxide present into a water-insoluble salt such as calcium carbonate and removing it by precipitation.

The substantive second step of the present invention is to reduce the solid particulate component content of the seawater to 10 ppm or less (preferably 5 ppm or less) while maintaining the PH value of the seawater that has undergone the above treatment at about 8 to 10. ).

The seawater that has been treated in the first step usually contains
Solid particulate components such as silicon dioxide, magnesium hydroxide, and calcium carbonate are mixed in. When these solid particulate components adhere to the surface of the ion exchange resin in the third step, they cause a decrease in the boric acid adsorption ability.
In addition, when using a method of adsorbing boric acid by passing seawater through a column filled with ion exchange resin, solid particulate components may cause problems such as blocking the seawater passage in the column. There is also. In addition, the solid particulate components attached to the ion exchange resin are dissolved in the mineral acid and mixed into the target boric acid in the process of desorbing boric acid using mineral acid. It will also reduce the Therefore, in order to prevent such various problems in advance, it is necessary to reduce the content of solid particulate components to 10 ppm or less in this step. If solid particulate components are contained in seawater in an amount exceeding this upper limit (10 ppm),
This will interfere with the operation of adsorbing boric acid using the ion exchange resin as described above, and the purity of the boric acid obtained later will be at a level that is undesirable for practical use.

This second step is carried out, for example, by a method in which the seawater that has undergone the first step is passed through a suitable filter material and then supplied to the next third step. Examples of filter media used for such purposes include combinations of anthracite and sand of different particle sizes.

The substantial third step of the present invention is to contact the seawater that has passed through the second step as described above with a boric acid adsorbing ion exchange resin to remove boric acid contained in the seawater from the ion exchange resin. It consists of a process of adsorption to.

Various types of ion exchange resins that can adsorb boric acid are known, but in the present invention, it is possible to use an ion exchange resin containing a polyol group that can selectively adsorb boric acid. desirable. Examples of such ion exchange resins that selectively adsorb boric acid include Amberlyte XE-243, Amberlyte IRA-743, which is a copolymer of chloromethylated styrene/divinylbenzene and N-methylglucamine, and Dia AEON SAN―
1 etc. can be mentioned.

This third step includes, for example, introducing the seawater that has gone through the second step into a column filled with ion exchange resin and allowing it to pass through, or introducing the ion exchange resin into the seawater that has gone through the second step and stirring it. can be mentioned. For industrial application of the present invention, the former method using a column is preferred.

The substantial fourth and fifth steps of the present invention are to apply a mineral acid containing boric acid to the ion exchange resin that has adsorbed boric acid as described above, and then, if necessary, add boric acid to the ion exchange resin. a step of desorbing the adsorbed boric acid from the ion exchange resin by contacting with a mineral acid that does not contain the boric acid;
It consists of the steps of separating and recovering 5 to 3/5 of the mineral acid and, at the same time, recovering the mineral acid with reduced boric acid content.

The mineral acid containing boric acid used for the desorption of boric acid from the ion exchange resin in the fourth step above is all or part of the mineral acid with reduced boric acid content recovered in the fifth step. or a mixture of these mineral acids with fresh (unused) mineral acids or diluted water.

For the sole purpose of desorbing boric acid in the fourth step, it is also possible to use only the new mineral acid as the mineral acid. However, in such a case, it becomes difficult to separate and recover boric acid from the desorption solution with good efficiency (efficiency per mineral acid used), and in order to precipitate and separate boric acid from mineral acid with high efficiency, it is necessary to The amount of energy and time required would be excessive.

On the other hand, the mineral acid used as a desorption liquid is recycled, and the boric acid content in the recycled mineral acid is within a certain range, that is, the boric acid content of the mineral acid eluted from the ion exchange resin. 2/5 to 4/5 of
By adjusting the amount of mineral acid (preferably 2/4 to 3/4), the amount of mineral acid to be newly replenished can be controlled without adversely affecting the boric acid adsorption capacity of the ion exchange resin and its desorption performance. It has been found that the boric acid adsorbed on the ion exchange resin can be efficiently desorbed while keeping the amount to a relatively small amount, and that the boric acid can be easily separated from the boric acid-containing desorption solution.

The mineral acids used in the desorption solution in the present invention include:
Preferably, it is selected from industrially used mineral acids such as sulfuric acid or hydrochloric acid.

The operation for desorbing boric acid from the ion exchange resin in the fourth step involves bringing a desorption liquid into contact with the ion exchange resin. for example,
When the ion exchange resin is packed in a column and used, a general method such as allowing the desorption liquid to flow down from the top of the column may be used.

More specifically, in the third step, alkaline seawater was passed through the ion exchange resin that adsorbed boric acid. Water was first passed through the resin to remove the alkaline content, and then boric acid was absorbed to lower the saturated solubility. A mineral acid such as sulfuric acid contained in a small amount (usually at a concentration of 0.5 to 5N, preferably 1 to 3N) is introduced into an ion exchange resin column and allowed to flow down. Then, if necessary, a mineral acid that does not contain boric acid, such as a new mineral acid, is similarly allowed to flow down the ion exchange resin column. The desorption solution containing boric acid desorbed from the ion exchange resin column is then subjected to boric acid separation and recovery treatment in the fifth step.

On the other hand, the ion exchange resin from which most of the adsorbed boric acid has been desorbed as described above is washed with water to partially recover the remaining boric acid and remove the acid content. It will be reused to adsorb boric acid in seawater.

The fifth step in the present invention is to extract 1/5 to 3/5 (preferably 1/4 to 2/5) of the boric acid contained therein from the mineral acid (desorption liquid) containing the desorbed boric acid. 4) and at the same time recovering the mineral acid with reduced boric acid content, by removing a part of the solvent (mineral acid) from the boric acid-containing desorption solution obtained in the fourth step, This is carried out using a method in which boric acid is precipitated (concentration method), or a method in which boric acid is precipitated by cooling a desorption solution containing boric acid (cooling method). Note that it is preferable to use the concentration method and the cooling method in combination.

The precipitated boric acid is then separated using methods such as filtration, and the filtrate (mineral acid containing a portion of the desorbed boric acid) is refilled with mineral acid or diluted with water, if necessary. After this, it is used as a desorption liquid in the fourth step.

The boric acid separated and recovered in the fifth step is usually a powder consisting of free-flowing plate-like crystals and has been passed through each of the operations described above, so its purity is generally about 85% or more (dry product). conversion).

The boric acid separated and recovered in the fifth step is then subjected to a purification step for high purity. In other words, the boric acid obtained here contains impurities mainly composed of mineral acids, and by subjecting this boric acid to the purification steps from the sixth step onwards to separate and remove these impurities, the boric acid can be further purified. It can be recovered with high purity.

The sixth step is a step of dissolving the separated and recovered boric acid in an aqueous solution containing boric acid. The boric acid-containing aqueous solution used here is all or part of the boric acid-containing aqueous solution recovered in the ninth step described later, or dilution of the boric acid-containing aqueous solution with water, or pH adjustment. Use the one that has been treated as such. In this step, boric acid is usually dissolved in a boric acid-containing aqueous solution under heating.

The seventh step is a step in which mineral acids such as sulfuric acid and hydrochloric acid contained in the boric acid solution are reacted with the alkalizing agent by bringing the boric acid solution obtained in the sixth step into contact with the alkalizing agent. It is. Examples of the alkalizing agent used here include hydroxides and oxides of alkaline earth metals such as calcium and barium, with calcium hydroxide being particularly preferred. The alkalizing agent is preferably added in an amount such that the pH of the boric acid solution after addition of the alkalizing agent is in the range of about 2.5 to 5. If the amount of the alkalizing agent added is too small, impurities such as mineral acids and iron contained in the boric acid solution will not be removed sufficiently, making it difficult to obtain the high purity boric acid that is the objective of the present invention. . On the other hand, if an alkalizing agent is added in such an amount that the PH value of the boric acid solution exceeds 5, the alkalizing agent will easily be mixed into the final boric acid, so high purity boric acid becomes difficult to obtain.

The eighth step is a step of separating and removing the reaction product of the mineral acid and the alkalizing agent produced by the above reaction from the boric acid solution. For example, if sulfuric acid is used as the mineral acid in the fourth step and hydroxides and oxides of alkaline earth metals such as calcium are used as the alkalizing agent in the seventh step, the alkalizing agent and the mineral acid Since the reaction product with water has very low solubility in water, it easily precipitates from the boric acid solution system and can therefore be easily separated by operations such as filtration. However, even if the combination of an alkalizing agent and a mineral acid does not produce a poorly water-soluble reaction product as described above, the physical or chemical characteristics between the reaction product and boric acid may differ. By utilizing a known separation method, the reaction product can be separated and removed from the boric acid solution.

The ninth step is a step of separating and recovering a portion of boric acid from the boric acid solution from which the reaction product of the alkalizing agent and mineral acid has been separated and removed in the eighth step, and at the same time recovering a boric acid-containing aqueous solution. .

This step involves cooling the boric acid solution to remove a portion of the boric acid contained in the solution, e.g.
% by weight, preferably 35-65% by weight,
This can be carried out using a method such as filtration separation. After separating and recovering a portion of the boric acid, the mother liquor (boric acid-containing aqueous solution) can be used as it is, or after dilution with water, pH adjustment by adding acid or alkali, etc.
It is recycled and used as a solvent for dissolving boric acid in the sixth step.

The boric acid separated and recovered in the ninth step above is usually a powder consisting of free-flowing plate-like crystals, and its purity is generally about 95% or more, and depending on the selection of operating conditions in each step, the purity is about 99% or more. % or more. Therefore, the high purity boric acid obtained by the present invention is very useful as a boron source used as a component of neuceramics, as a neutron shielding material, as a property modifier for metals such as steel, etc.

Furthermore, since substantially all of the boric acid contained in the seawater introduced into the recovery treatment system of the present invention is recovered, the recovery treatment efficiency is extremely high.
In addition, most of the mineral acids such as sulfuric acid introduced into the recovery treatment system are recycled and only a small amount is discharged to the outside, which reduces the cost of recovering boric acid and reduces the amount of waste. This is also advantageous in reducing.

As detailed above, the present invention utilizes universally available seawater as a raw material for boron, which is attracting attention for its usefulness in industry, and extracts extremely pure boric acid from the seawater. This method provides a method for separating and recovering in high yield without going through any complicated operations, and therefore has very high industrial utility.

Next, the present invention will be explained in more detail with reference to Examples.

Example (1) Seawater [boric acid (H ₃ BO ₃ ) content: 17.8 ppm,
Carbon dioxide content: 84 ppm] 89.3 m ³ was introduced into a container, and 18 kg of quicklime was added thereto to adjust the pH of the seawater to approximately 9. When the precipitated calcium carbonate was separated by filtration, the carbon dioxide content of the filtrate was approximately 14 ppm.

(2) This filtrate was passed through a filter material made of a combination of anthracite (fine particulate carbon) and sand of different particle sizes, so that the content of solid particulate components in the filtered seawater was approximately 2 ppm.

(3) Next, the above treated seawater was mixed with Amberlite
-243 It was introduced into a column packed with ion exchange resin (column diameter: 55 cm, resin amount: 100), and boric acid was adsorbed.

(4) After the adsorption operation is completed, the above ion exchange resin is first washed with water, and then approximately boric acid is added to the column.
By introducing 2N-sulfuric acid 70 containing 2.8% by weight,
A desorption operation of boric acid was performed. And then,
The desorption operation of boric acid was continued by introducing 30% of new 2N-sulfuric acid.

Next, 600 g of water for washing was introduced into the column and allowed to flow down, thereby recovering a portion of the boric acid remaining in the column and removing the acid component.

(5) Boric acid-containing desorption solution (a mixture consisting of a mineral acid containing desorbed boric acid and a portion of washing water)
Partial removal of the solvent was carried out by heating 300 to bring the volume to 60. Next, this concentrated desorption liquid was cooled to about 20°C, and the precipitated boric acid crystals were separated by filtration.

The separated boric acid crude crystals weighed 1440 g, and the boric acid purity of these boric acid crude crystals was 72.4% (most of the remainder was impurities such as sulfuric acid, iron, and water). Then, by drying this, the purity
87% of the boric acid was obtained as very free-flowing, minute plate-like crystals.

The desorption liquid (mother liquor) after filtering the boric acid crystals is 58
This mother liquor contained 1980g of boric acid. Then, the concentration of sulfuric acid was adjusted to 2N by adding 12 parts of water to this mother liquor, and the solution was used as a desorption liquid for the next desorption of boric acid.

(6) The crude boric acid crystals (purity: 72.4%) separated in step (5) above were added to a boric acid-containing aqueous solution (boric acid concentration: 5.3% by weight) 20, and then
It was heated to 60°C to dissolve the boric acid crude crystals.

(7) While maintaining the obtained crude boric acid crystal solution at 60°C, add an aqueous calcium hydroxide solution (containing 10.0% by weight as CaO) to this solution and stir.
The pH of the boric acid crude crystal solution was set to 4. The amount of calcium hydroxide aqueous solution added here was 280 ml.

(8) Calcium sulfate precipitated from the above reaction solution was filtered off at 60°C. The filtered calcium sulfate weighed 250g, which contained 7.5g of boric acid and 43.8g of calcium oxide.

(9) Next, the filtrate was cooled to 20°C, and the precipitated boric acid crystals were filtered off and dried under reduced pressure. The yield of boric acid crystals was 993 g, and the purity was 99.1%.

The filtrate was 20 and contained 1068 g of boric acid. This was then used as a solvent for dissolving the boric acid crude crystals in the next round.

Claims (1)

[Claims] 1 Substantially: (1) A step of adjusting the pH value of seawater to about 8 to 10 and reducing the carbon dioxide content of the seawater to 40 ppm or less; (2) Performing the above treatment The pH value of seawater is approximately 8 to 10.
(3) By contacting the seawater that has undergone the above treatment with a boric acid adsorbing ion exchange resin, the content of solid particulate components is reduced to 10 ppm or less while maintaining the a step of adsorbing boric acid on the ion exchange resin; (4) a step of desorbing the adsorbed boric acid by contacting the ion exchange resin with a mineral acid containing boric acid; (5) a step of desorbing the adsorbed boric acid; A process of separating and recovering 1/5 to 3/5 of the boric acid contained therein from the acid-containing mineral acid, and at the same time recovering the mineral acid with reduced boric acid content; (6) Separated and recovered A step of dissolving boric acid in an aqueous solution containing boric acid; (7) By bringing the obtained boric acid solution into contact with an alkalizing agent, the mineral acid contained in the boric acid solution is dissolved with the alkalizing agent. a step of reacting; (8) a step of separating and removing the reaction product of the mineral acid and the alkalizing agent from the boric acid solution; and (9) separating and recovering a part of boric acid from the boric acid solution, and at the same time A step of recovering a boric acid-containing aqueous solution, and converting at least a portion of the mineral acid with reduced boric acid content recovered in step (5) above to the boric acid-containing solution in step (4) above. At least a part of the boric acid-containing aqueous solution recovered in step (9) above is used as part or all of the mineral acid in step (6) above. A method for recovering boric acid from seawater, characterized in that boric acid is used in part or in whole. 2 Substantially, (1) Adjusting the PH value of seawater to approximately 8 to 10 and reducing the carbon dioxide content of the seawater to 40 ppm or less; (2) Adjusting the PH value of seawater that has undergone the above treatment. Approximately 8-10
(3) By contacting the seawater that has undergone the above treatment with a boric acid adsorbing ion exchange resin, the content of solid particulate components is reduced to 10 ppm or less while maintaining the a step of adsorbing boric acid to the ion exchange resin; (4) a step of contacting the ion exchange resin with a mineral acid containing boric acid to desorb the adsorbed boric acid; (5) a step of performing the above steps; (6) desorbing most of the undesorbed boric acid by contacting the desorbed ion exchange resin with a mineral acid that does not substantially contain boric acid; and (6) removing the desorbed boric acid from the mineral acid. , a step of separating and recovering 1/5 to 3/5 of the boric acid contained therein, and simultaneously recovering the mineral acid with a reduced boric acid content; (7) The separated and recovered boric acid is converted into a boric acid containing dissolving in an aqueous solution; (8) contacting the obtained boric acid solution with an alkalizing agent to react the mineral acid contained in the boric acid solution with the alkalizing agent; (9) A step of separating and removing a reaction product of a mineral acid and an alkalizing agent from the boric acid solution; and (10) separating and recovering a portion of boric acid from the boric acid solution and simultaneously recovering a boric acid-containing aqueous solution. At least a part of the mineral acid with reduced boric acid content recovered in the step (6) above is converted into a part of the mineral acid containing boric acid in the step (4) above or and use at least a portion of the boric acid-containing aqueous solution recovered in step (10) above as part or all of the boric acid-containing aqueous solution in step (7) above. A method for recovering boric acid from seawater, characterized by: