JP2009034564A - Adsorbent and separation method for substance X ionized in alkaline solution - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an adsorbent and a separation method capable of separating a substance X ionized in an alkaline solution such as boron and arsenic at a low cost.
A separation method for separating a substance X ionized in an alkaline solution from a solution, wherein a pH adjusting step for ionizing the substance X by adding a pH adjusting agent for bringing the solution to a predetermined pH to the solution. A hydrotalcite-like substance (preferably a hydrotalcite-like substance having a crystallite size of 20 nm or less) and a hydrotalcite-like substance mixing step for adsorbing the anion of substance X; Have
[Selection] Figure 4

Description

  The present invention relates to an adsorbent and a separation method for substance X that is ionized in an alkaline solution.

  Industrial wastewater contains various pollutants, and if it is directly discharged into rivers and soils, there is a risk of having a great adverse effect on the living environment. Therefore, various standards for the disposal of pollutants are established and regulated by the Basic Environment Law and the Water Pollution Control Law.

  Heretofore, for example, anion exchange resins have been used to remove anions that are contaminants (see, for example, Patent Document 1).

  Boron and arsenic are known to be ionized in an alkaline solution because of equilibrium in the aqueous solution as shown in Formulas 1 and 2 (see FIGS. 1 and 2).

Japanese Patent Laid-Open No. 9-174093

However, in order to remove substances such as boron and arsenic from the alkaline solution, a special anion exchange resin that preferentially adsorbs these substances over hydroxide ions (OH ⁻ ) is required, which is costly. The current situation is that it takes a long time.
Therefore, an object of the present invention is to provide an adsorbent and a separation method capable of separating a substance X ionized in an alkaline solution such as boron or arsenic at low cost.

  In order to achieve the above object, the adsorbent of the present invention is an adsorbent for separating the substance X that is ionized in an alkaline solution from the solution, and the hydrotalcite-like substance and the solution have a predetermined pH. And a pH adjuster.

  Another adsorbent of the present invention is an adsorbent for separating the substance X that is ionized in an alkaline solution from the solution, and has hydroxide ions between the layers, and the crystallite size is 20 nm or less. It is characterized by including a hydrotalcite-like substance.

  In these cases, the hydrotalcite-like substance may be one having chloride ions between layers. The substance X to be separated includes arsenic or boron. The hydrotalcite-like substance may be a granular material. Moreover, what contains at least sodium hydroxide can be used for the said pH adjuster.

  Further, the separation method of the present invention is a separation method for separating the substance X that is ionized in an alkaline solution from the solution, the pH adjusting step for bringing the solution into a predetermined pH, and the hydrotalcite-like substance. And a hydrotalcite-like substance mixing step for mixing with the solution.

  Another separation method of the present invention is a separation method for separating a substance X that is ionized in an alkaline solution from a solution, and has hydroxide ions between layers and a crystallite size of 20 nm or less. And a hydrotalcite-like substance mixing step of mixing the hydrotalcite-like substance which is

  In these cases, as the hydrotalcite-like substance, a substance containing chloride ions between layers can be used. The substance X to be separated includes arsenic or boron. Moreover, the said pH adjustment process can be adjusted to predetermined | prescribed pH by mixing sodium hydroxide with the said solution.

  In addition, the separation method of the present invention preferably has a solid-liquid separation step of solid-liquid separation of the hydrotalcite-like substance from the solution containing the hydrotalcite-like substance.

  According to the present invention, since a hydrotalcite-like substance having a main skeleton made of a naturally abundant elemental hydroxide such as magnesium or aluminum and capable of relatively easily synthesizing it is used, boron or arsenic is used. Thus, the substance X ionized in the alkaline solution can be separated at a low cost.

Below, the adsorbent of this invention is demonstrated.
The adsorbent of the present invention is an adsorbent for separating the substance X that is ionized in an alkaline solution from the solution, and has a hydrotalcite-like substance and a pH adjuster that brings the solution to a predetermined pH. It is characterized by that.

Here, the hydrotalcite-like substance is a non _- stoichiometric compound represented by a structural formula of M ²⁺ _1-x M ³⁺ _x (OH) ₂ (A ⁿ⁻ ) _{x / n} · mH ₂ O. M ²⁺ represents a divalent metal and corresponds to Mg ²⁺ , Fe ²⁺ , Zn ²⁺ , Ca ²⁺ , Li ²⁺ , Ni ²⁺ , Co ²⁺ , Cu ^{2+, and the} like. M ³⁺ represents a trivalent metal, and Al ³⁺ , Fe ³⁺ , Mn ^{3+ and the} like are applicable. ^{Incidentally, A n-represents} an anion. As such a hydrotalcite-like substance, any substance may be used. For example, a substance produced by the following method can be used.

  First, an acidic solution containing aluminum ions and magnesium ions is prepared.

  Any aluminum source may be used as long as it generates aluminum ions in water, and is not limited to a specific substance. For example, alumina, sodium aluminate, aluminum hydroxide, aluminum chloride, aluminum nitrate, bauxite, alumina production residue from bauxite, aluminum sludge and the like can be used. These aluminum sources may be used alone or in combination of two or more.

  The magnesium source of magnesium ions is not limited to a specific substance as long as it is a substance that generates magnesium ions in water. For example, calcite of brucite, magnesium hydroxide, magnesite, magnesite, or the like can be used. Any of these magnesium sources may be used alone or in combination of two or more.

Here, the general formula of hydrotalcite composed of aluminum ions and magnesium ions is Mg ²⁺ _1-x Al ³⁺ _x (OH) ₂ (A ⁿ⁻ ) _{x / n} · mH ₂ O (A ⁿ⁻ is an anion). In the most common composition of highly crystalline hydrotalcite, it is known that the molar ratio of aluminum ions to magnesium ions is 1: 3 (x = 0.25). Therefore, the molar ratio of aluminum ions to magnesium ions in the acidic solution is preferably in the range of 1: 5 to 1: 2. By setting it as this range, a hydrotalcite-like material can be produced advantageously in terms of material balance without wasting the aluminum source and the magnesium source.

  In order to adjust the acidic solution to be acidic, it is preferable to use hydrochloric acid.

  Next, the acidic solution containing aluminum ions and magnesium ions is mixed with an alkaline solution containing alkali. This alkaline solution preferably has a pH of 8-11. The mixing of the acidic solution and the alkaline solution can be performed by adding the acidic solution to the alkaline solution all at once, or by dropping the acidic solution into the alkaline solution. Preferably, the acidic solution is acidic depending on the stirring ability at the time of mixing. It is better to mix an appropriate amount of solution and alkaline solution. Of course, other methods may be used as long as the acidic solution and the alkaline solution can be sufficiently stirred.

  Here, the alkali contained in the alkaline solution is not limited to a specific substance as long as the aqueous solution is alkaline. For example, sodium hydroxide or calcium hydroxide can be used. Further, sodium carbonate, potassium carbonate, ammonium carbonate, aqueous ammonia, sodium borate, potassium borate and the like can also be used. Any of these alkalis may be used alone or in combination of two or more.

  Moreover, since highly crystalline hydrotalcite is preferentially ion-exchanged with carbonate ions, if carbonate ions are included, it cannot be efficiently ion-exchanged with the intended anion. Therefore, in the hydrotalcite-like substance, it is preferable that the acidic solution and the alkaline solution do not contain carbonate ions in order to efficiently exchange ions with the target anions.

  In addition, if the aging is not performed after the mixing of the acidic solution and the alkaline solution is completed, hydrotalcite with a small crystallite size (crystallite size) can be obtained without growing crystals of the hydrotalcite-like substance. It is preferable at the point which can manufacture a site-like substance. In this case, since the crystallite size of the hydrotalcite-like substance is small, the solution becomes colloidal when mixed.

In order to prevent aging, after the mixing of the acidic solution and the alkaline solution is completed, the pH of the mixed solution may be lowered to a value at which crystal growth of the hydrotalcite-like substance stops. For example, the hydrotalcite-like substance represented by the general formula Mg ²⁺ _1-x Al ³⁺ _x (OH) ₂ (A ⁿ⁻ ) _{x / n} · mH ₂ O stops ripening when the pH is 9 or less. be able to. Moreover, the hydrotalcite-like substance represented by the general formula Zn ²⁺ _1-x Al ³⁺ _x (OH) ₂ (A ⁿ⁻ ) _{x / n} · mH ₂ O stops ripening when the pH is 5 or less. be able to.

  Moreover, ripening can also be stopped by removing moisture. In order to remove moisture, an appropriate method such as suction filtration or centrifugation can be used.

Therefore, for example, in order to reduce the crystallite size of a hydrotalcite-like substance represented by the general formula Mg ²⁺ _1-x Al ³⁺ _x (OH) ₂ (A ⁿ⁻ ) _{x / n} · mH ₂ O to 20 nm or less. After the mixing of the acidic solution and the alkaline solution is completed, the pH of the mixed solution may be adjusted to 9 or less within 120 minutes, preferably simultaneously. Any method may be used to adjust the pH to 9 or less. For example, there is a method in which an acidic solution and an alkaline solution are mixed and then immediately diluted with water. Of course, after mixing the acidic solution and the alkaline solution, water may be removed within 120 minutes, preferably simultaneously by suction filtration, centrifugation, or the like. In order to prevent aging, the hydrotalcite-like substance may be washed immediately after the mixing of the acidic solution and the alkaline solution is completed. In addition, you may contain chlorides, such as NaCl produced | generated in a synthetic | combination process.

Small hydrotalcite-like substances crystallite size has a large surface area per unit weight, OH ^- and liable desorbed when mixing the hydrotalcite-like substance in a solution, it is possible to adjust the pH to 7 or more . Therefore, if a hydrotalcite-like substance having a small crystallite size is used, a pH adjuster described later is unnecessary. In particular, it is preferable that the crystallite size is 20 nm or less, preferably 10 nm or less, in order to increase these effects. Further, since the surface area per unit weight is large, there is an effect that the anion exchange performance is enhanced.

  In order for the hydrotalcite-like substance thus generated to adsorb the anion of the substance X, the anion of the substance X is more easily intercalated than the anion present between the layers of the hydrotalcite-like substance. Must be a substance. In other words, the hydrotalcite-like substance needs to be adjusted so that the interlayer ions are less likely to be intercalated than the anion of substance X. Here, a known method can be used to adjust the interlayer ions. For example, in order to obtain a chlorine type in which the interlayer ions of the hydrotalcite-like substance are chloride ions, chloride ions such as dilute hydrochloric acid and saline are used. In order to obtain a nitric acid type in which interlayer ions are nitrate ions, a hydrotalcite-like substance may be immersed in dilute nitric acid. Industrially, a chlorine-type hydrotalcite-like substance that is safe and easy to manufacture is preferable, and can be suitably used for removing boron and arsenic.

  The hydrotalcite-like substance thus produced may be used in the form of a slurry, but the slurry may be powdered by filtering, washing, drying and pulverizing. Further, from the viewpoint of ease of handling, etc., it may be a granular body obtained by solidifying a hydrotalcite-like substance. The granule may be manufactured by any method, but for example, it can be manufactured as follows.

  First, a predetermined pressure is applied to the slurry-like hydrotalcite-like substance by a dehydrating device such as a filter press to remove moisture as much as possible. Next, the hydrotalcite-like substance is dried at a temperature lower than the dehydration temperature of the crystal water (the temperature at which the hydrotalcite-like substance crystal water begins to dehydrate). In other words, only water outside the crystal of the hydrotalcite-like substance is dried. Specifically, a hydrotalcite-like material having a moisture content of 70% or less, preferably 65% or less, more preferably 60% or less, and a hydrotalcite-like granular material as a final product having a moisture content of 10% or more. It is dried to 20% or less, preferably 10% to 15%, and more preferably 11% to 12%. Here, the reason why the water content of the hydrotalcite-like granule is maintained at 10% or more is that when the water content of the hydrotalcite-like granule is less than 10%, This is because the granular material absorbs moisture and the volume expands rapidly, and the particle size cannot be maintained. The water content is the mass of water relative to the mass of the entire hydrotalcite-like substance containing moisture. The measurement of the mass of water contained in the hydrotalcite-like substance was performed in accordance with Japanese Industrial Standard “Method for testing water content ratio of soil” (JIS A 1203: 1999).

  The drying temperature may be any temperature as long as it is lower than the dehydration temperature of the crystallization water of the hydrotalcite-like substance. However, in order to increase the particle size of the hydrotalcite-like granule, the temperature is relatively low. It is preferable to dry. However, when dried at a temperature that is too low, the hydrotalcite-like granular material is easily dissolved in water. Therefore, the specific drying temperature is preferably 25 ° C. or more and 125 ° C. or less, preferably 90 ° C. or more and 110 ° C. or less, and more preferably 95 ° C. or more and 105 ° C. or less.

  Further, this drying may be performed in any way, for example, a normal drying furnace or the like may be used. Of course, it can be naturally dried at room temperature. In addition, it is better to adjust the humidity at the time of drying higher in view of the morphological stability of the hydrotalcite-like granular material. For example, the amount of water vapor in the drying furnace may be adjusted so as to be near the saturated water vapor amount (humidity is 90% to 100%).

  Alternatively, the hydrotalcite-like substance thus dried may be sieved to remove the precipitated chloride and the like.

  In addition, the hydrotalcite-like granular material may be adjusted in particle size according to its application. In this case, the particle size of the hydrotalcite-like granule is preferably 0.24 mm or more, preferably 0.36 mm or more, more preferably 1 mm or more and 2 mm or less in consideration of use in a column or the like. The particle size can be adjusted in any way, and can be adjusted by, for example, crushing with a hammer or the like and sieving with a sieve having a target size.

Any pH adjusting agent may be used as long as the pH of the solution can be adjusted so that the substance X becomes an anion. For example, sodium hydroxide (NaOH) can be used. Here, when the substance X is boron or arsenic, as shown in FIGS. 1 and 2, the amount of boron or arsenic present as ions increases as the pH increases. Therefore, when the amount of anion of the substance X increases as the pH of the solution increases, it is better that the pH adjuster can increase the pH as much as possible, and preferably one that can adjust the pH to 8 or more. However, if the pH is too high, the concentration of hydroxide ions (OH ⁻ ) in the solution will increase, and the hydrotalcite-like substance will adsorb more hydroxide ions (OH ⁻ ) than the anion of substance X. become. Therefore, it is preferable that the hydrotalcite-like substance to be used can adjust the pH within a range in which the anion of the substance X is most adsorbed. For example, when the substance X is boron or arsenic, the pH may be adjusted to 9-10.

Next, the separation method of the present invention will be described.
The separation method of the present invention is a separation method for separating a substance X that is ionized in an alkaline solution from a solution, a pH adjusting step for making the solution alkaline with a predetermined pH, and a hydrotalcite-like substance. And a hydrotalcite-like substance mixing step for mixing with the solution.

The pH adjustment step is to adjust the pH of the solution so that the substance X becomes an anion, and a pH adjusting agent or the like that adjusts the pH of the solution may be used. For example, it can be adjusted by mixing an appropriate amount of sodium hydroxide (NaOH) according to the amount of the solution. When the substance X is boron or arsenic, the pH is preferably adjusted to 8 or more, preferably 9 to 10. As described above, if the pH is too high, the concentration of hydroxide ions (OH ⁻ ) in the solution becomes high, and the hydrotalcite-like substance has more hydroxide ions (OH ⁻ ) than the anion of substance X. Adsorbs a lot. Therefore, it is preferable to adjust the pH within a range in which the hydrotalcite-like substance to be used most adsorbs the anion of substance X.

  In the hydrotalcite-like substance mixing step, the hydrotalcite-like substance is sufficiently mixed and stirred in the solution to easily adsorb the anion of substance X. For example, a mixer that stirs by rotating a motor or the like A gas supply means that stirs by supplying bubbles into the container may be used. In the case where the hydrotalcite-like substance is granular, the hydrotalcite-like substance may be packed in a column and the solution may be passed through this column.

  Note that either the pH adjustment step or the hydrotalcite-like substance mixing step may be performed first, and the pH adjustment step may be performed after the hydrotalcite-like substance mixing step. Further, when a hydrotalcite-like substance having a crystallite size of 20 nm or less is used, the pH adjustment step may be unnecessary because the hydrotalcite-like substance itself adjusts the pH of the solution.

  In the solid-liquid separation step, the hydrotalcite-like material that has adsorbed (ion-exchanged) the substance X is separated from the solution that has undergone the pH adjustment step and the hydrotalcite-like material mixing step. For example, the hydrotalcite-like substance and the solution may be solid-liquid separated using a dehydrating means such as a filter press. Further, when the hydrotalcite-like substance is a granular material, it may be packed in a column and let the solution flow. Thereby, the solution which removed or reduced the substance X can be taken out.

  Examples in which the separation method of the present invention is used for removing boron will be described below, but the present invention is not limited to these examples. In addition, the hydrotalcite-like substance of the present example used a crystallite size of 20 nm or less.

Example 1
Prepare 1,000 ml each of distilled water, a boron standard solution having a boron concentration of 20 mg / l, and a sulfuric acid standard solution having a sulfate ion concentration of 1820 mg / l. Next, 13 g of a hydrotalcite-like substance having a crystallite size of 20 nm or less was added and stirred for 180 minutes with a magnetic stirrer. Stirring was carried out in a constant temperature room at 20 ° C. with the temperature of each solution adjusted to 20 ° C. At this time, changes in pH of these solutions were measured with a pH electrode. The relationship between the pH of each solution and the stirring time is shown in FIG. FIG. 3 shows that the pH of pure water, boron solution, and sulfuric acid standard solution is increased.

Example 2
Prepare 1000 ml of a boron standard solution adjusted so that the boron concentration is 20 mg / l. Next, 13 g of a hydrotalcite-like granule having a crystallite size of 20 nm or less was added and stirred for 180 minutes with a magnetic stirrer. Moreover, the adsorption | suction of boron was performed by adjusting the temperature of a boron standard solution to 20 degreeC in a constant temperature room of 20 degreeC. The change in the concentration of this boron standard solution was measured using an absorptiometer (LASA-50 manufactured by DR. LANGGE) and a dedicated reagent for this absorptiometer (LCK307). FIG. 4 shows the relationship between the boron concentration and the stirring time.

  From FIG. 4, it can be seen that the concentration of boron is reduced, and boron is adsorbed to the hydrotalcite-like substance.

Example 3
It is a test which shows the relationship between the adsorption amount of the boron of the adsorption agent of this invention, and the pH of a solution.
Boric acid (H ₃ BO ₃ ) special grade reagent was weighed and dissolved in distilled water to prepare an ion standard solution. The prepared standard solution was diluted, and 100 ml of a reaction solution whose pH was adjusted to 7, 9, and 12 using 25% NaOH _aq was prepared. 1 g of a powdery hydrotalcite-like substance was added to each reaction solution, stirred for 1 hour with a magnetic stirrer, and then filtered using a filter paper (5B). The boron concentration of each reaction solution was measured using an absorptiometer (LASA-50 manufactured by DR.LANGE). The relationship between the initial pH of the solution, the boron concentration, and the boron adsorption amount of the adsorbent of the present invention is shown in Table 1 and FIG.

Example 4
This is a test showing the amount of each ion adsorbed when the adsorbent of the present invention is added to 100 ml of a solution containing boron, sulfate ions and chloride ions.
A predetermined amount of boric acid (H ₃ BO ₃ ), sodium sulfate (Na ₂ SO ₄ ), and sodium chloride (NaCl) is weighed, added to distilled water, and stirred well to prepare a test solution. Further, 25% sodium hydroxide solution (NaOHaq) was used for pH adjustment.
The adsorbent of the present invention was added to 100 ml of the test solution, and stirred for 1 hour with a magnetic stirrer. Changes in the concentration of this solution were measured using an absorptiometer (LASA-50 manufactured by DR. LANGGE), a dedicated reagent for this absorptiometer (LCK307), and an ion analyzer (IA-200 manufactured by Toa DKK). did. Tables 2 and 3 show the relationship between the addition amount of the adsorbent of the present invention, the concentration of each ion, and the adsorption amount. Table 2 is a table | surface which shows each ion adsorption amount of the adsorption agent of this invention in case the initial pH of a solution is 9. Moreover, Table 3 is a table | surface which shows each ion adsorption amount of the adsorption agent of this invention in case the initial pH of a solution is 12.

It is a graph which shows the relationship between pH and the form of boron. It is a graph which shows the relationship between pH and the form of arsenic. It is a graph which shows the change of pH by a hydrotalcite-like substance. It is a graph which shows the density | concentration change of the boron at the time of using the adsorption agent of this invention for a boron standard solution. It is a graph which shows the relationship between the initial pH of a solution, the boron equilibrium density | concentration of a solution, and the boron adsorption amount of the adsorption agent of this invention.

Claims (12)

  An adsorbent for separating substance X ionized in an alkaline solution from the solution, comprising an hydrotalcite-like substance and a pH adjuster for bringing the solution to a predetermined pH. Agent.   An adsorbent for separating substance X ionized in an alkaline solution from the solution, including a hydroxide ion between layers and a hydrotalcite-like substance having a crystallite size of 20 nm or less. Characteristic adsorbent.   The adsorbent according to claim 1 or 2, wherein the hydrotalcite-like substance has chloride ions between layers.   The adsorbent according to claim 1 or 2, wherein the substance X is arsenic or boron.   The adsorbent according to claim 1 or 2, wherein the hydrotalcite-like substance is a granular material.   The adsorbent according to claim 1, wherein the pH adjuster contains at least sodium hydroxide.   A method for separating a substance X ionized in an alkaline solution from a solution, a pH adjusting step for bringing the solution into a predetermined pH, and a hydrotalcite-like substance for mixing a hydrotalcite-like substance with the solution And a mixing step.   A method for separating a substance X that is ionized in an alkaline solution from a solution, wherein a hydrotalcite-like substance having hydroxide ions between layers and having a crystallite size of 20 nm or less is mixed with the solution. And a hydrotalcite-like substance mixing step.   The separation method according to claim 7 or 8, wherein the hydrotalcite-like substance has chloride ions between layers.   The separation method according to claim 7 or 8, wherein the substance X is arsenic or boron.   The separation method according to claim 7, wherein the pH adjustment step adjusts to a predetermined pH by mixing sodium hydroxide into the solution.   9. The separation method according to claim 7, further comprising a solid-liquid separation step of solid-liquid separation of the hydrotalcite-like substance from a solution containing the hydrotalcite-like substance.

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