JPS6324431B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention uses seawater, brine, or bittern water.
The present invention relates to a method for separating and removing borate ions with good selectivity and high efficiency. When producing magnesium hydroxide from seawater, boric acid compounds dissolved in seawater co-precipitate with magnesium hydroxide, reducing its quality, so methods to remove boric acid compounds from seawater are being researched. . Conventionally, as a method for separating boric acid compounds dissolved in water, chelate resins such as anion exchange resins and boron selective resins derived from polyhydric alcohols,
Alternatively, a method of adsorption separation using a metal hydroxide, typified by magnesium hydroxide, has been proposed. However, the concentration of boric acid in seawater is extremely low at 4 to 5 ppm as boron atoms, and
Since a large amount of various ions coexist, the above-mentioned method does not have sufficient boron selectivity or adsorption ability, and the reality is that no economically effective method has been found. The present inventors, in order to solve such problems,
The present invention was achieved through repeated research on various adsorbents and ion exchangers. That is, the present invention provides a method for separating and removing boric acid ions in seawater, brine, or bittern water.
The water adjusted to pH 2-10 is brought into contact with a rare earth hydrated oxide to adsorb and separate borate ions, and the rare earth hydrated oxide that has adsorbed the borate ions is heated to a pH of 2 to 4 or PH12.
It is desorbed and regenerated by contacting with an aqueous solution adjusted to ~14.
The present invention relates to a method for separating and removing borate ions in seawater, brine, or bittern water, which is characterized by repeated use. In the present invention, brine refers to a solution that is not saturated with salt when seawater is concentrated, or a solution that contains salt but is not saturated, such as underground brine, and bittern water refers to a solution that is not saturated with salt when seawater is concentrated. The residual liquid after separation by analysis etc. Hydrous oxides of rare earth elements according to the present invention include rare earth elements, such as Y, La, Ce, Pr, Nd, Sm,
It is a compound obtained by hydroxylation of metals, oxides, and salts of Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, and Lu. The types of rare earth elements are:
La, Ce, Y, Sm, etc. are preferable, and Ce() is particularly preferable because it has a large adsorption capacity and extremely low solubility. These rare earth hydrated oxides may be used alone or in combination. It can also be used together with other substances such as activated carbon and alumina. These rare earth hydrated oxides are, for example, hydrochloride,
It can be easily obtained as a precipitate by adjusting the pH of the aqueous salt solution, such as by adding an alkaline solution to the aqueous solution of salts such as sulfates and nitrates. The rare earth hydrated oxide can be used as a suspension of the precipitate obtained as described above, or as a cake obtained by filtration, or as a powder after drying. It can also be used as a carrier supported by a known method, such as a granule formed using a suitable organic polymer material. In order to carry out adsorption removal by an engineering method such as a fixed bed or a fluidized bed, it is preferable to use granules with a diameter of 0.1 to 10 mm. The granules can be easily obtained using known organic polymer materials.
The organic polymer materials include phenolic resin, urea resin, melamine resin, polyester resin, diallyl phthalate resin, xylene resin, alkylbenzene resin, epoxy resin, epoxy acrylate resin, silicon resin, urethane resin, fluorine resin, and vinyl chloride resin. , vinylidene chloride resin, polyethylene, chlorinated polyolefin, polypropylene, polystyrene, ABS resin, polyamide, methacrylic resin, polyacetal, polycarbonate, cellulose resin, polyvinyl alcohol,
Polyimide, polysulfone, polyacrylonitrile, etc. can be used, but those that have appropriate water resistance and chemical resistance, are highly hydrophilic, and can form a porous structure are preferred; polyamide, cellulose resin, polysulfone, polyacrylonitrile are preferred. etc. are particularly preferred. Granules with a porous structure obtained using these resins have a sufficient adsorption rate and are suitable for use in engineering methods such as fixed bed or fluidized bed. It is not clear how the rare earth hydrated oxide of the present invention fixes borate ions, but adsorption in the present invention refers to the surface of the rare earth hydrated oxide or the rare earth hydrated oxide in an aqueous solution. Physical and/or physical relationship between the state and borate ions in aqueous solution
Or, it refers to a phenomenon in which borate ions are fixed due to chemical action. When separating borate ions from seawater, brine, or bittern water, adjusting the pH of the water to adjust the dissociation state of borate ions and the surface potential of rare earth hydrous oxides increases the adsorption amount and improves separation. Effective in increasing efficiency. That is, it is best to adjust the pH to 5 to 10, particularly preferably 7 to 9.5. If the pH is lower than 5, the adsorption capacity will be significantly lowered and the efficiency will be poor, and if the pH is higher than 10, the adsorption capacity will be lowered and magnesium in the water will precipitate as hydroxide, which is not preferable. Furthermore, when separating borate ions from seawater, brine, or bittern water, it is preferable to remove carbonate ions in advance because if carbonate ions coexist in the water, they tend to interfere with the adsorption of borate ions. The ion can be prepared by a known method, for example, by adjusting the pH to 4.
This can be easily carried out by adjusting the temperature to 5 or less and aerating or boiling. According to the above method, for example, the concentration of carbonate ions dissolved in normal seawater, 1mM/, can be reduced to 0.1mM/or less. The method for adsorbing borate ions using the rare earth hydrated oxide may be any method as long as the rare earth hydrated oxide is brought into contact with seawater, brine, or bittern water containing borate ions.
For example, a method in which a suspension, cake, powder, or granule of a rare earth hydrated oxide is added to seawater, brine, or bittern water and brought into contact; Effective methods include a method in which water is brought into contact with the porous material, a method in which a porous material, a nonwoven fabric, etc. is impregnated and fixed with a rare earth hydrated oxide, and the fixed body is immersed in the water. Alternatively, after dissolving a water-soluble salt of a rare earth element in the water, the rare earth hydrated oxide can be precipitated by an appropriate method such as adjusting the pH, and dissolved borate ions can be adsorbed. The temperature during the above contact may be room temperature. The temperature can also be increased if desired. The contact time depends on the physical conditions at the time of contact, particle size, etc., but usually
0.5 to 10 minutes is sufficient. The amount of the rare earth hydrated oxide to be added is appropriate depending on the initial concentration and the target concentration, since there is a correlation between the saturated adsorption amount per unit amount of the rare earth hydrated oxide and the concentration of boric acid in the solution. You can set a certain amount. For example, the borate ion in seawater is Ce()
In the case of separation using a hydrous oxide slurry of 3 to 1 Kg-solid content/m ³ , the concentration of boron atoms can be 2 to 0.1 ppm. In addition, the rare earth hydrated oxide that has adsorbed boric acid ions in the above method can be desorbed and regenerated by appropriate methods such as adjusting the pH and adding salt, and can be repeatedly used with the regenerated rare earth hydrated oxide. Can be separated by adsorption. The above desorption can be carried out by bringing the adsorbed rare earth hydrous oxide into contact with an aqueous solution adjusted to pH 12-14. The desorption liquid is an alkaline aqueous solution, and NaOH is particularly preferable as the alkaline species since it has a high desorption efficiency. or,
Rare earth hydrated oxides that are relatively stable to acids, such as Ce() hydrated oxides, can also be desorbed by contacting them with an aqueous solution adjusted to a pH of 2 to 4. The aqueous solution preferably contains inorganic anions and/or organic acid anions such as halogen anions, sulfate ions, nitrate ions, and phosphate ions, and fluoride ions and sulfate ions are particularly preferred because they are particularly effective. The concentration of the anion varies depending on the ion species, but is 0.5 to 1000 mg.
-ion/ is suitable, for example, in the case of sulfate ion, it may be 1 to 50 mg-ion/. Under conditions of PH4 or higher, the desorption efficiency is low, and
Conditions where the pH is below 2 are not preferred because rare earth hydrated oxides are significantly dissolved. Hereinafter, it will be explained in more detail with reference to Examples. Examples 1 to 6 Examples will be shown in which various rare earth hydrated oxides are suspended in natural seawater to adsorb boric acid ions and then desorbed. Rare earth hydrated oxide prepared as below was added to seawater (boric acid concentration: 15 ppm converted to B ₂ O ₃ ), which had been adjusted to pH 3 and decarboxylated in advance, and then readjusted to pH 9, and stirred. did. The boric acid concentration in the sample water after 2 hours was measured by ICP (inductively coupled plasma emission spectrometry), and the equilibrium adsorption amount and removal rate were determined. [Equilibrium adsorption amount] = {[Initial concentration] - [Concentration after adsorption]}/
[Amount added per unit volume] [Removal rate] = 1 - [Concentration after adsorption] / [Initial concentration] Next, the rare earth hydrous oxide that has adsorbed borate ions is separated, and an aqueous NaOH solution adjusted to pH 13.5 is added. The rare earth hydrated oxide was added to the mixture at a ratio of 1 W/V% and stirred. The boric acid concentration in the NaOH aqueous solution after 2 hours was measured to determine the desorption rate. [Desorption rate] = {[Liquid volume] x [Boric acid concentration]
}/{[Ce hydrous oxide amount] x [equilibrium adsorption amount]} [Preparation method of rare earth hydrate oxide] Example 1 (Rare earth chloride from China) & Example 2 (Ce) Rare earth chloride or cerium chloride from China (Special grade reagent)
was dissolved in distilled water, and an equimolar amount of hydrogen peroxide was added to the solution, followed by stirring, and then aqueous ammonia was added to adjust the pH to 9. After that, the cake was heated to 85° C. to decompose excess hydrogen peroxide, and then aged overnight, and the resulting cake was used as a sample. Examples 3 to 6 (La, Sm, Gd, Y) Chlorides of each element (special grade reagent) were dissolved in distilled water, and aqueous ammonia was added to adjust the pH to 9. The resulting precipitate was aged overnight and the resulting cake was used as a sample. As a comparative example, the adsorption rates of hydrated oxides of Mg and Ti were determined in the same manner as in the examples. The hydrated oxide of Ti was prepared in the same manner as in the case of Y, and the hydroxide of Mg was prepared in the same manner as in the case of Y, except that sodium hydroxide was added to adjust the pH to 10.5. The results are shown in Table-1.

【table】

[Table] Examples 7 and 8 Examples are shown in which boric acid ions in brine and bittern water were adsorbed and then desorbed using Ce() hydrous oxide. Brine obtained by concentrating natural seawater (10°Be′,
For boric acid concentration: 42 ppm in terms of B ₂ O ₃ ) and bittern water (33°Be', boric acid concentration: 142 ppm in terms of B ₂ O ₃ ), 67 mg of Ce () hydrated oxide - solid content / B ₂ O ₃ -
The removal rate was determined by adding at a rate of mg. Other conditions such as brine, decarboxylation of bittern water, and pH adjustment were the same as in Example 2. Next, the material that adsorbed borate ions was
Separate Ce hydrated oxide and adjust to PH2.0
It was added to a 30mM/-Na ₂ SO ₄ aqueous solution at a rate of 1W/V% and desorbed by stirring. The desorption rate was determined in the same manner as in Example 2. Table 2 shows the main component composition of the brine and bittern water used. The results are shown in Table-3.

【table】

[Table] Examples 9 to 15 Examples are shown in which Ce() hydrous oxide was desorbed with an alkaline aqueous solution and then re-adsorbed. Ce () hydrated oxide with borate ions adsorbed in the same manner as in Example 2 was suspended in an aqueous solution with the alkaline species and pH adjusted as shown in Table 4 at a ratio of 2W/V% and stirred. After 2 hours, the concentration of boric acid in the solution was measured to determine the desorption rate. Next, it was adsorbed again in the same manner as in Example 2, and the removal rate was determined. Note that the pH of the suspension was adjusted to 9 during re-adsorption. The results are shown in Table 4.

[Table] Shows the removal rate (percentage) during re-adsorption.
Examples 16 to 26 Examples will be shown in which Ce() hydrous oxide was desorbed with an acidic aqueous solution and then re-adsorbed. The desorption rate and the removal rate during re-adsorption were determined for the various acidic aqueous solutions shown in Table 5 in the same manner as in Examples 9-15. In addition, the concentration of Ce in the aqueous solution after desorption was measured by ICP to determine the amount dissolved. The results are shown in Table-5.

[Table] Example 27 Ce () granulated with polyacrylonitrile resin
An example will be shown in which boric acid ions in seawater are adsorbed using a hydrous oxide, further desorbed, and then re-adsorbed. Granules granulated with polyacrylonitrile resin (particle size 1.0 to 0.5 mmφ, intragranular porosity 0.6) are
The sample was filled into a glass column with a packing volume of 20 ml. (The 20ml granules contain Ce() hydrated oxide.
Contains 8.0g. ) Seawater, which had been previously adjusted to pH 3, aerated and decarboxylated, and readjusted to pH 9, was passed through the packed column at a rate of 400 ml/hr for 12 hours. The boric acid concentration of the seawater was 14 ppm (in terms of B ₂ O ₃ ).
Boric acid concentration in seawater at the column outlet after 12 hours,
We measured the boric acid concentration in the total amount of seawater that passed through, 4.8,
The outlet concentration and total adsorption amount after 12 hours were determined. Subsequently, distilled water was passed through the column after adsorption at a rate of 400 ml/hr for 30 minutes to replace seawater, and then a 0.1N NaOH aqueous solution (PH13) was passed at a rate of 60 ml/hr for 6 hours. flowed out from the column
The boric acid concentration in 360 ml of NaOH aqueous solution was measured, and the total desorption amount and desorption rate were determined. Furthermore, the granules after the above desorption were taken out and immersed in 200 ml of hydrochloric acid aqueous solution with a pH of 2 for 1 hour to reduce the pH inside the granules.
After adjusting, the column was refilled. In the same manner as above, the outlet concentration and total adsorption amount were determined 12 hours after passing seawater. Next, at a concentration of 60meq/adjusted to PH2
A Na ₂ SO ₄ aqueous solution was passed through the tube at a rate of 400 ml/hr for 6 hours. The boric acid concentration in the Na ₂ SO ₄ aqueous solution flowing out from the column was measured, and the total desorption amount and desorption rate were determined. Furthermore, the granules were taken out after desorption and heated to PH12.
After adjusting the pH inside the granules by immersing them in 200 ml of NaOH aqueous solution for 1 hour, the column was refilled. Seawater was passed through the tube again in the same manner as above to adsorb borate ions, and the outlet concentration and total amount of adsorption after 12 hours were determined. The above results are shown in Table-6. Note that the desorption rate is a value calculated using the following formula. [Desorption rate] = [Total desorption amount] / [Total adsorption amount before desorption] ×
100

[Table] Example 28 This is an example in which Ce() hydrous oxide was added to natural seawater without decarboxylation treatment and adsorbed. The same procedure as in Example 2 was carried out except that natural seawater was used after being adjusted to pH 9 without being decarboxylated. The results are shown in Table 7 together with Example 2. Note that carbonate ions were determined by anion chromatography.

[Table] As described above, according to the present invention, borate ions can be separated from seawater, brine, or bittern water with good selectivity and high efficiency, and rare earth hydrated oxides can be easily regenerated and used. Therefore, it is suitable as an industrial method for separating and removing borate ions. The method of the present invention can be applied to fields where the absence of borate ions is required in water, such as in the production of magnesium hydroxide from seawater, brine or bittern water.

Claims (1)

[Scope of Claims] 1. When separating and removing boric acid ions in seawater, brine, or bittern water, the water adjusted to pH 5 to 10 is brought into contact with a rare earth hydrated oxide to adsorb and separate the boric acid ions, and Separation and removal of boric acid ions in seawater, brine or bittern water, characterized in that rare earth hydrated oxides that have adsorbed acid ions are brought into contact with an aqueous solution adjusted to PH2-4 or PH12-14 for desorption and regeneration and repeated use. Method. 2. The method according to claim 1, wherein the rare earth hydrated oxide is a Ce() hydrated oxide. 3 Claim 1 characterized in that a rare earth hydrated oxide supported on an organic polymer material is used.
The method described in section.