JPS5930717A - Method for recovering boric acid from sea water - Google Patents

Abstract

PURPOSE:To manufacture efficiently boric acid by treating sea water in a specified stage using an ion exchange resin. CONSTITUTION:(1, 2) Sea water is treated to adjust the pH to 8-10, the CO2 content to <=40ppm and the content of solid fine particles to <=10ppm, and (3) the sea water is brought into contact with an ion exchange resin to allow contained boric acid to be adsorbed on the resin. (4) A mineral acid contg. boric acid is brought into contact with the resin to desorb the boric acid from the resin, (5) 1/5-3/5 of the boric acid contained in the mineral acid is recovered, and at the same time, the mineral acid contg. the remaining boric acid is recovered. (6, 7, 8) The recovered boric acid is dissolved in an aqueous soln. contg. boric acid, the soln. is brought into contact with an alkalifying agent, and the reaction product of the mineral acid with the agent is separated and removed. (9) Part of boric acid is separated and recovered from the aqueous soln. contg. boric acid, and at the same time, the aqueous soln. contg. the remaining boric acid is recovered. The mineral acid contg. boric acid recovered in the stage 5 is used in the stage 4, and the aqueous soln. contg. boric acid recovered in the stage 9 is used in the stage 6.

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 a component of new ceramics, as a neutron shielding material, as a property modifier for metals such as steel, and demand is increasing accordingly. Such boron compounds are generally manufactured using boric acid as a raw material, but
There are concerns about stably obtaining large amounts of boric acid due to the limited amount of boric acid present and the limited areas where boric acid exists.

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 there is also boron, mainly in the form of boric acid (about 15 to 20 ppm (boric acid: H, B
It has been known for some time that the content of However, for example, in a method for producing magnesia clinker from magnesium salt in seawater, this boric acid is said to be harmful in that it reduces the physical properties of the clinker. Therefore, in order to remove this boric acid, the boric acid content in the seawater is reduced by contacting seawater with hydrated magnesium and adsorbing the boric acid to the hydrated magnesium, and then the desired magnesia clinker is extracted. A method of manufacturing 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 about 8 to 1O and reducing the carbon dioxide content of the seawater to 4'Oppm or less; (2) performing the above treatment. The pH value of seawater is about 8-10
Its solid particulate component content is reduced to 10p while maintaining
pm or less; (3) a step of bringing the seawater subjected to the above treatment into contact with a boric acid-adsorbing ion exchange resin to adsorb boric acid contained in the seawater onto the ion exchange resin; (4) ) desorbing the adsorbed boric acid by contacting the ion exchange resin with a mineral acid containing boric acid; and (5) desorbing the absorbed boric acid from the mineral acid containing boric acid. 115 to 315 of boric acid are separated and recovered,
At the same time, a step of recovering the mineral acid whose boric acid content has been reduced; (6) a step of dissolving the separated and recovered boric acid in an aqueous solution containing boric acid; (7) contacting the obtained boric acid solution with an alkalizing agent (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) a step of separating and recovering a part of boric acid from the boric acid solution and recovering a boric acid-containing aqueous solution at the same time, and the boric acid content recovered in the above step (5) is Using at least a part of the reduced mineral acid as part or all of the boric acid-containing mineral acid in the step (4) above, and using the boric acid-containing aqueous solution recovered in the step (9) above. At least a portion of the solution is added to the above (6
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 the boric acid-containing aqueous solution in the process of

In addition, between the above steps (4) and (5),
If necessary, a step can be inserted in which most of the undesorbed boric acid is desorbed 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 separates and recovers boric acid contained in seawater.
By using a plurality of processes in combination, it is possible to carry out the process efficiently and economically.

The practical first step of the present invention is to adjust the pH value of seawater to about 8 to 1.
0, and the carbon dioxide content of the seawater was adjusted to 40 ppm.
It consists of the following steps. In other words, approximately 70 to 1100 pp 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 is reduced. In order for this to progress at a high level that is practically meaningful,
It is necessary to reduce the carbon dioxide content in seawater to 40 ppm or less (preferably 30 ppm or less, particularly preferably 20 ppm or less) in advance, and also to reduce the carbon dioxide content in seawater containing sodium chloride or other various salts and compounds. In order to efficiently adsorb boric acid to the ion exchange resin, the pH of the seawater needs to be adjusted to about 8 to 10.

A method for adjusting the pH of seawater to the above range and removing a predetermined amount of carbon dioxide is to add an alkali such as milk of lime to the seawater to adjust the pH to the predetermined range and remove the carbon dioxide contained in 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 substantial second step of the present invention is to reduce the solid particulate component content of the seawater to 10 ppm or less (preferably, while maintaining the pH value of the seawater treated as described above at about 8 to 10).
5 ppm or less).

The seawater produced in the first step usually contains solid particulate components such as silicon dioxide, magnesium hydroxide, and calcium carbonate.

If these solid particulate components adhere to the surface of the ion exchange resin in the third step, they will reduce the boric acid adsorption ability of the resin, and also cause the seawater to pass through the column filled with the ion exchange resin. When using a method of adsorbing boric acid by passing the seawater through the column, solid particulate components may cause problems such as blocking the seawater passageway in the column. 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 troubles in advance, it is necessary to reduce the content of solid particulate components to 10 ppm or less in this step. Solid particulate components enter seawater,
If it is contained in an amount exceeding this upper limit (10 ppm), it will interfere with the boric acid adsorption operation using the ion exchange resin as described above, and the purity of the boric acid obtained later will be undesirable for practical purposes. level.

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. An example of a filter material used for such a purpose is a combination of anthracite and sand with different particle sizes.The substantial third step of the present invention is to filter seawater that has passed through the second step as described above. The process consists of a step of causing boric acid contained in seawater to be adsorbed onto the ion exchange resin by bringing it into contact with a boric acid adsorbing ion exchange resin.

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 selectively adsorbent ion exchange resins include Amberai XE-243, a copolymer of chloromethylated styrene/divinylbenzene and N-methylglucamine;
Anbarai) IRA-743, and Diaion 5A
Examples include N-1.

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.
Examples include a method of stirring. 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 boric acid that does not contain the boric acid, and separating and recovering the boric acid 115 to 315 contained in the mineral acid from the mineral acid containing the desorbed boric acid. and, at the same time, a step of recovering mineral acid whose boric acid content has been reduced.

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. There are or those mineral acids and new (
(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 sulfuric acid used). The amount of energy and time 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. 115 to 315 (preferably 1/4 to 2/
4), the ion exchange resin can be used without adversely affecting the boric acid adsorption capacity of the ion exchange resin and its desorption properties, and while keeping the amount of newly replenished mineral acid to a relatively small amount. It has been found that the boric acid adsorbed on the resin can be efficiently desorbed, and that the boric acid can be easily separated from the boric acid-containing desorption solution.

The mineral acid used in the desorption solution in the present invention is preferably selected from industrially used mineral acids such as sulfuric acid and 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 an 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, which was adsorbed with boric acid. A mineral acid such as sulfuric acid (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 butyric content.
It will be reused to adsorb boric acid in seawater.

In the fifth step of the present invention, from the mineral acid (desorption liquid) containing the desorbed boric acid, 115 to 315 (preferably 1/4 to 2/
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 some of the desorbed boric acid)
is used as the desorption liquid in the fourth step, after being supplemented with mineral acid or diluted with water, if necessary.

The boric acid separated and recovered in the fifth step is usually a powder consisting of free-flowing plate-like crystals, and because it has gone through the various operations described above, 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 may be all or part of the boric acid-containing aqueous solution recovered in the ninth step described later, or the boric acid-containing aqueous solution diluted with water, or
Use one that has undergone processing such as H adjustment. 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 hydride 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, the removal of impurities such as mineral acids and iron contained in the boric acid solution will be insufficient, making it difficult to obtain the high purity boric acid that is the objective of the present invention. Cheap. 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. 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. Even 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 Since the reaction products with mineral acids have very low solubility in water, they easily precipitate from boric acid solution systems 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. .

In this step, a part of the boric acid contained in the solution is precipitated by cooling the boric acid solution, for example, 25 to 75% by weight, preferably 35 to 65% by weight, and this is separated by filtration. This can be done using methods such as: 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 diluted with water.
After adjusting the pH by adding acid or alkali, the solution is recycled and used as a solvent for dissolving the sulfur 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 new ceramics, a neutron shielding material, a physical property modifier for metals such as steel, etc.

In addition, 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 very high. Most of the mineral acids such as sulfuric acid are recycled,
Only a small amount is discharged to the outside, which is advantageous in reducing the cost of recovering and processing boric acid and reducing the amount of waste.

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 (HgBOs) content: 17.8p
pm, carbon dioxide content: 84 ppm) was introduced into a container, and 18 kg of quicklime was added to it to reduce the pH of the seawater.
H was adjusted to about 9. When the precipitated calcium carbonate was separated by filtration, the carbon dioxide content of the filtrate was approximately 14 p.
It was pm.

(2) Pass this filtrate through a filter material that combines anthracite (fine particulate carbon) and sand of different particle sizes,
The content of solid particulate components in the filtered seawater was reduced to approximately 2 ppm.

(3) Next, the above treated seawater was mixed with Amparite XE-2
Column packed with 43 ion exchange resin (column diameter: 55
cm, resin amount: 100 cm), and a boric acid adsorption operation was performed.

(4) After the adsorption operation is completed, the ion exchange resin is first washed with water, and then approximately 2.8% by weight of boric acid is added to the ram.
The boric acid desorption operation was performed by introducing 2N-sulfur m701 contained in the reactor. Then, the new 2N-sulfuric acid was added for 30
The desorption operation of boric acid was continued.

Next, 600 grams 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 content.

(5) The solvent was partially removed by heating boric acid-containing desorption solution (a mixture consisting of a mineral acid containing desorbed boric acid and a part of washing water) 3001, and its volume was reduced to 60 grams. . Next, this concentrated desorption solution was cooled to about 20° C., and the precipitated boric acid crystals were separated by filtration.

The amount of boric acid crude crystals separated was 1440 g, and the boric acid purity of the boric acid crude crystals was 72.4% (most of the remainder was impurities such as sulfuric acid, iron, and water). By drying, boric acid with a purity of 87% was obtained in the form of very free and fine plate-like crystals.

The desorption liquid (mother liquor) from which the boric acid crystals were filtered was 58 grams,
This mother liquor contained 1980 g of boric acid. This mother liquor was adjusted to 2N by adding 124Q of water and used as a desorption liquid for the next desorption of boric acid.

(6) The crude boric acid crystals (near purity 2.4%) separated in step (5) above were added to 20 grams of a boric acid-containing aqueous solution (boric acid concentration: 5.3% by weight), and then It was heated to ℃ to dissolve the boric acid crude crystals.

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

(8) Calcium sulfate precipitated from the above reaction solution was filtered out at 60°C. The filtered calcium sulfate was 250 g, which contained 7.5 g of boric acid and 4
It contained 3.8g 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 is 9
The weight was 93g, and the purity was 99.1%.

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

Patent applicant: Ube Chemical Industry Co., Ltd. Agent: Patent Attorney: Yasuo Yanagawa

Claims (1)

[Claims] 1゜Substantially: (1) A step of 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) Performing the above treatment. The pH value of seawater is about 8~1O
its solid particulate content while maintaining
pm or less; (3) a step of bringing the seawater subjected to the above treatment into contact with a boric acid-adsorbing ion exchange resin to adsorb boric acid contained in the seawater onto the ion exchange resin; (4) ) Desorbing the adsorbed boric acid by contacting the ion exchange resin with a mineral acid containing boric acid; (5) desorbing the absorbed boric acid from the mineral acid containing boric acid; Separate and recover boric acid 115 to 315,
At the same time, a step of recovering the mineral acid whose boric acid content has been reduced; (6) a step of dissolving the separated and recovered boric acid in an aqueous solution containing boric acid; (7) contacting the obtained boric acid solution with an alkalizing agent a step of reacting the mineral acid contained in the boric acid solution with the alkalizing agent; (8) separating and removing the reaction product of the mineral acid and the alkalizing agent from the boric acid solution; and (9) a step of separating and recovering a part of boric acid from the boric acid solution and recovering a boric acid-containing aqueous solution at the same time, and the boric acid content recovered in the above step (5) is Using at least a part of the reduced mineral acid as part or all of the boric acid-containing mineral acid in the step (4) above, and using the boric acid-containing aqueous solution recovered in the step (9) above. At least a portion of the solution is added to the above (6
) A method for recovering boric acid from seawater, characterized in that it is used as part or all of a boric acid-containing aqueous solution in the process of (a). 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
Its solid particulate component content is reduced to 10p while maintaining
pm or less; (3) A step of bringing the treated seawater into contact with a boric acid-adsorbing ion exchange resin to adsorb boric acid contained in the seawater onto the ion exchange resin; (4 ) Desorbing the adsorbed boric acid by contacting the ion exchange resin with a mineral acid containing boric acid; (5) The ion exchange resin subjected to the above step substantially contains boric acid. (6) desorbing most of the undesorbed boric acid by contacting with a mineral acid that does not contain the boric acid; Separate and collect 315,
At the same time, a step of recovering the mineral acid whose boric acid content has been reduced; (7) a step of dissolving the separated and recovered boric acid in an aqueous solution containing boric acid; (8) contacting the obtained boric acid solution with an alkalizing agent (9) a step of separating and removing the reaction product of the mineral acid and the alkalizing agent from the boric acid solution; and. (lO) Separate and recover a part of boric acid from the boric acid solution,
At the same time, from the process of recovering the boric acid-containing aqueous solution,
In addition, at least a portion of the mineral acid with reduced boric acid content recovered in step (6) above is used as part or all of the mineral acid containing boric acid in step (4) above. , and seawater characterized in that at least a part of the boric acid-containing aqueous solution recovered in the step (lO) above is used as part or all of the boric acid-containing aqueous solution in the step (7) above. Method for recovering boric acid from.