WO2017061118A1

WO2017061118A1 - Anion adsorption method

Info

Publication number: WO2017061118A1
Application number: PCT/JP2016/004498
Authority: WO
Inventors: 載泰廣川; 剛野一色; 木村　信夫; 正登天池
Original assignee: 高橋金属株式会社; 日本曹達株式会社
Priority date: 2015-10-09
Filing date: 2016-10-06
Publication date: 2017-04-13
Also published as: JPWO2017061118A1; TWI612998B; JP6644805B2; TW201716128A

Abstract

The present invention addresses the problem of providing a method that further increases the phosphate-ion adsorption efficiency of an adsorbent that has an iron oxyhydroxide as a main component. According to this method, target anions are adsorbed by passing water that contains said anions and that has a fixed pH through an adsorption device that is filled with an anion adsorbent that has an iron oxyhydroxide as a main component. The method is characterized by being executed under conditions wherein the pH of water that is treated at a breakpoint becomes higher than the pH of the water pre-treatment. The treatment is preferably executed under conditions wherein the pH of the water that is treated at the breakpoint becomes at least 0.2 higher than the pH of the water pre-treatment.

Description

Anion adsorption method

The present invention relates to a method for performing adsorption using an anion adsorbent mainly composed of iron oxyhydroxide.
This application claims priority to Japanese Patent Application No. 2015-200830 filed on Oct. 9, 2015, the contents of which are incorporated herein by reference.

In order to remove and purify substances that are harmful to the environment and the human body from various wastewaters, or to recover useful substances such as rare metals, adsorbents, adsorption methods using them, desorption / desorption of adsorbed substances, The collection method is actively researched.
For example, phosphorus is an indispensable component as a fertilizer component and also in the chemical industry, but in Japan, almost 100% depends on imports. On the other hand, when a large amount of phosphorus is contained in the wastewater, it causes eutrophication, and it is not preferable for the environment to discharge such wastewater. In order to solve these problems all at once, removal and recovery of phosphorus compounds such as phosphoric acid contained in waste water have attracted attention.
As an adsorbent capable of efficiently adsorbing and recovering such a phosphorus compound, an adsorbent made of iron oxyhydroxide has been developed and described in

Patent Documents

1, 2, 3, and the like. These are preferably made of iron oxyhydroxide having a β-type crystal structure. β-iron oxyhydroxide has a structure of FeO (OH) _x Cl _1-x (0 <x <1) in which a part of the hydroxyl group is substituted with chlorine, and the adsorption mechanism by this has many unclear points. However, the following is known.
In Patent Document 2, by comparing with an iron oxyhydroxide adsorbent that does not contain chlorine ions, nitrate ions and the like are adsorbed by exchanging them with chlorine ions contained in the adsorbent. It is suggested that Adsorption of phosphate ions is possible without chloride ions, but it is also suggested that there is exchange with chloride ions as well. Further, it is described that the pH of the water to be treated is preferably about 3 to 9 for adsorption of phosphate ions.
In Patent Document 3, in the adsorption process of hypophosphite ions or phosphite ions, pH 3 or higher (when hypophosphite ions are targeted) or pH 3 to 5 (when phosphorous acid is targeted) It is described that, when hydrochloric acid is used for pH adjustment, the adsorption amount of hypophosphite ions or phosphite ions is increased by chloride ions. However, it is described that the adsorption of these ions is different in mechanism from the adsorption of phosphate (orthophosphate) ions.

JP 2006-124239 A WO2006 / 088083 pamphlet JP 2011-235222 A

The anion adsorbents as described above have a high phosphate ion adsorption efficiency. However, a method for further increasing the adsorption efficiency of phosphate ions has been demanded.

The inventor has intensively studied to further increase the adsorption efficiency of phosphate ions in an adsorbent made of iron oxyhydroxide.
As a result, it was found that the adsorption of phosphate ions is promoted under the condition that the pH of the water subjected to the adsorption treatment is higher than the pH of the water before the treatment. The present invention has been completed based on this finding.

That is, the present invention relates to the following inventions.
(1) A method of adsorbing anions by passing water containing a target anion and having a certain pH through an adsorption device filled with an anion adsorbent mainly composed of iron oxyhydroxide. In the adsorption method, the pH of the treated water at the breakthrough point is higher than the pH of the water before the treatment.
(2) The adsorption method according to (1), wherein the treatment is performed under a condition that the pH of the treated water at the breakthrough point is 0.2 or more higher than the pH of the water before the treatment.
(3) The adsorption method according to (1) or (2), wherein the water before treatment is acid and the pH is adjusted to 2.5 to 5.0.
(4) The adsorption method according to any one of (1) to (3), wherein the iron oxyhydroxide is β-iron oxyhydroxide.
(5) The adsorption method according to (4), wherein the average crystallite size of the iron oxyhydroxide is 10 nm or less.
(6) The adsorption method according to (4) or (5), wherein the β-iron oxyhydroxide crystals are granular.
(7) The adsorption method according to any one of (1) to (6), wherein the specific surface area of the iron oxyhydroxide is 250 m ² / g or more.
(8) The adsorption method according to any one of (1) to (7), wherein the concentration of the target anion contained in the water before treatment is 100 mg / L or less.
(9) The adsorption method according to any one of (1) to (8), wherein chlorine ion is contained in water before treatment at 100 mg / L or more.
(10) The adsorption method according to any one of (1) to (9), wherein the target anion is a phosphate ion.

In the method of adsorbing anions using an adsorbent made of iron oxyhydroxide, adsorption of anions is promoted by setting the condition that the pH of the water subjected to the adsorption treatment is higher than that of the water before the treatment. The

It is a figure which shows the TEM image of an iron oxyhydroxide crystal | crystallization. It is a figure which shows the result of the phosphoric acid adsorption test of Example 1-1 [powder B, test liquid I (pH 2.9), water flow rate SV10]. It is a figure which shows the result of the phosphate adsorption test of Example 1-2 [powder B, test liquid I (pH 2.9), water flow rate SV20]. It is a figure which shows the result of the phosphate adsorption test of Comparative Example 1-1 [powder B, test liquid J (pH 7.0), water flow rate SV10]. It is a figure which shows the result of the phosphate adsorption test of Comparative Example 1-2 [powder B, test liquid J (pH 7.0), water flow rate SV20]. It is a figure which shows the result of the phosphate adsorption test of Example 2 [powder C-3, test liquid I (pH 2.9), water flow rate SV30].

The adsorption method of the present invention is a method of adsorbing a target anion by passing water through an adsorption device filled with an anion adsorbent containing iron oxyhydroxide as a main component. It is characterized in that it is carried out under the condition that the pH of (the outflow water from the adsorption device) is higher than the pH of the water before being treated (inflow water to the adsorption device) at the same point.
The breakthrough point is the point at which the concentration of the target anion in the treated water begins to rise. Specifically, it may be determined according to the kind of the target anion, the concentration of the ion in the water before the treatment, etc., but when the phosphate ion is used, for example, 10 mg-P / L (phosphorus As a point).
By adopting this condition, the adsorption amount is 1.5 times to 2.0 times as compared with the condition where the pH of the treated water at the breakthrough point is the same as or lower than the pH of the water before the treatment. To improve.
The pH of the treated water is preferably a condition that is 0.2 or more higher than the pH of the water before the treatment.
The adsorption treatment may be performed under such conditions that the above pH condition is achieved when water is continuously passed to at least the breakthrough point under the same conditions as those actually performed. The water flow may be continued until the breakthrough point is reached or beyond, or the water flow may be stopped before the breakthrough point is reached. In the case of stopping the water flow before reaching the breakthrough point, the pH of the treated water becomes higher than the pH of the water before being treated, preferably at or before the time when the water flow is stopped. It can be determined that the above pH condition is achieved by increasing the ratio by 2 or more.
From the anion adsorbent, the adsorbed target anions can be desorbed by alkali treatment after the water flow is stopped. Further, the anion adsorbent can be regenerated by treating with hydrochloric acid or the like thereafter.

In the method of the present invention, the pH of water before being treated is preferably in the acidic range. The adsorption efficiency is low from neutral to basic. Also in this pH range, the pH of the treated water tends to be rather low. On the other hand, if it is too acidic, iron may be eluted. Specifically, the pH is preferably 2.5 to 5.0, more preferably pH 2.5 to 4.0.
The water before the treatment can be used as it is if it is originally in the above pH range, but if not, it is preferable to adjust the pH. The treated water that was originally neutral or basic needs to be adjusted to the above pH range using an acid. In this case, hydrochloric acid is preferably used because it does not adversely affect the adsorption of the target anion.

As described above, the fact that the pH of the treated water becomes higher than the pH of the water before the treatment suggests that hydroxide ions are flowing out of the adsorbent by the adsorption treatment.
As described above, it was known that exchange with chlorine ions was important for adsorption of anions by iron oxyhydroxide, but exchange with hydroxide ions was not known.
This is because conventionally, water near neutrality is mainly used as water before being treated, and water having a pH of 5 or less has not been used. In addition, the present inventors have used a small particle size as an anion adsorbent mainly composed of iron oxyhydroxide, so that the property of adsorption by exchanging with hydroxide ions is particularly prominent. You might also say that.

The concentration of the target anion contained in the water before the treatment is not necessarily limited, and it depends on the amount of the adsorbent, but it is 100 mg / L or less in order to prevent leakage and increase the adsorption efficiency. Preferably there is.

If the water before treatment contains chlorine ions in addition to the target anions, the adsorption of the target anions is preferably promoted. The concentration of this chlorine ion is not particularly limited, but is preferably 100 mg / L or more, and particularly preferably 500 mg / L or more. In order to adjust the chlorine ion concentration, for example, sodium chloride may be added as a salt that contains chlorine ions and does not adversely affect the adsorbent, and hydrochloric acid may be used to adjust the pH described later. .

The anions to be adsorbed by the anion adsorbent are anions other than chlorine ions, and halogen ions such as fluorine ions, bromine ions and iodine ions; carbonate ions, silicate ions, phosphate ions, pyrophosphate ions, Nitrate ion, nitrite ion, sulfide ion, persulfate ion, sulfate ion, sulfite ion, hyposulfite ion, thiosulfate ion, selenate ion, selenite ion, borate ion, tetraborate ion, arsenate ion , Arsenite ion, perchlorate ion, chlorate ion, chlorite ion, hypochlorite ion, bromate ion, iodate ion, aluminate ion, manganate ion, permanganate ion, chromate ion , Oxo acid ions such as dichromate, tungstate ion, vanadate ion, bismuth acid ion, titanate ion Carboxylate ion, sulfonate ion, organic acid ion such as phosphonate; cyanide, cyanate ion, isocyanate ion, thiocyanate ion, azide ion, and the like.
Of these, phosphate ions and fluorine ions are preferable, and phosphate ions are particularly preferable.

Iron oxyhydroxide includes α-type, β-type, γ-type, amorphous type, and the like depending on the crystal structure.
Of these, β-iron oxyhydroxide has vacancies that readily adsorb chlorine ions, and some of the hydroxyl groups present therein are easily replaced by chlorine ions. Such chlorine ions are further substituted with fluorine ions, nitrate ions, etc., and it is considered that the vacancies play a major role in the adsorption of these anions.
On the other hand, large anions such as phosphate ions do not reach inside the small vacancies that adsorb chlorine ions, and it is considered that different types of vacancies function for the adsorption.
The iron oxyhydroxide used as an anion adsorbent in the present invention is preferably β-iron oxyhydroxide having the above properties.

The iron oxyhydroxide that is the main component of the adsorbent used in the present invention preferably has an average crystallite size of 10 nm or less, and more preferably 5 nm or less.
It has been clarified by the present inventors that the smaller the average crystallite size, the higher the phosphate adsorption rate when used as a phosphate adsorbent in water.
The average crystallite diameter D is calculated from the diffraction line near 2θ = 35 ° characteristic of β-iron oxyhydroxide by X-ray diffraction, using the following Scherrer equation.
D = Kλ / βcos θ
Where β is the half width of the true diffraction peak corrected for the machine width caused by the apparatus, K is the Scherrer constant, and λ is the wavelength of the X-ray.

The anion adsorbent used in the present invention preferably has a content of iron oxyhydroxide as a main component of 99% by mass or more. Most preferably, the content of iron oxyhydroxide is substantially 100% by mass.
The iron oxyhydroxide preferably has a BET specific surface area of 250 m ² / g or more, and the pore volume area distribution (dV / dR) calculated by the BJH method is 100 to 300 mm ³ / g / nm. It is preferable.

As described above, β-iron oxyhydroxide as an anion adsorbent used in the present invention preferably has a hydroxyl group partially substituted with chlorine ions. Even with β-iron oxyhydroxide from which chlorine ions have been completely removed, phosphate ions are adsorbed, but those that are partially substituted with chlorine ions are more efficient in terms of phosphate ion adsorption efficiency. Are better.

The shape of the β-iron oxyhydroxide crystal used in the present invention is preferably granular. Here, granular means that it is not needle-shaped or plate-shaped, and more specifically, the ratio of the major axis / minor axis of the crystal is 3 or less.

As the β-iron oxyhydroxide, for example, a dry gel obtained by a method including a step of reacting an iron compound-containing solution with a base to form a precipitate at pH 9 or lower can be used.
The iron compound is preferably an iron salt, particularly a trivalent iron salt. Specific examples include ferric chloride, ferric sulfate, and ferric nitrate. Among these, ferric chloride is particularly preferable.
The base is used to neutralize the acidic iron compound aqueous solution and generate a precipitate containing iron oxyhydroxide. Specific examples include sodium hydroxide, potassium hydroxide, calcium hydroxide, ammonia, sodium carbonate, potassium carbonate, calcium carbonate and the like. Among these, sodium hydroxide is particularly preferable.
More preferably, the pH during the formation of the precipitate is adjusted to the range of pH 3.3-6. If necessary to adjust this pH, a pH adjusting agent may be used. Specific examples of the pH adjuster include the above bases and strong inorganic acids such as hydrochloric acid, sulfuric acid, and nitric acid.
The precipitate containing β-iron oxyhydroxide as a main component obtained by the above method can be collected by filtration and dried to form a dry gel.

Further, after the above steps, it is preferable to carry out a step of drying the precipitate, and a step of drying the precipitate after bringing it into contact with water.
The two drying steps are preferably performed at 140 ° C. or less, and more preferably at 100 to 140 ° C. The drying temperature requires a long time at a low temperature and is not suitable for efficient production. Further, there is a tendency that the number of anion adsorption sites tends to decrease at a high temperature, and even higher temperature is not preferable because it changes to iron oxide. Drying can be done in air, vacuum, or in an inert gas.
In the step of bringing the dried product into contact with water, impurities such as sodium chloride are eluted to leave pores later, and the specific surface area is increased and the anion adsorption site is also increased.
After bringing the dried product into contact with water, the water is removed and dried again. This drying step is also preferably performed under the same conditions as described above.

Although not limited in any way, for example, β-iron oxyhydroxide having a small particle diameter is preferably used. Specifically, the average particle diameter d50 is 70 μm or less. This can be obtained, for example, by classifying β-iron oxyhydroxide by a method such as sieving. If necessary, dry pulverization may be performed, and classification may be performed by a method such as sieving.

Next, the present invention will be described in more detail with reference to examples, but the present invention is not limited thereto.

Measurement method (powder X-ray diffraction)
The X-ray diffraction (XRD) pattern was measured using an X-ray diffractometer Ultima IV (manufactured by Rigaku Corporation). A CuKα tube was used for the measurement. The average crystallite size was calculated from XRD according to Scherrer's formula.
(Specific surface area)
The specific surface area was measured by a gas adsorption method using a specific surface area measuring device MacsorbHM 1210 (manufactured by Mountec).
(TEM observation and FFT analysis)
The TEM (transmission electron microscope) observation of the sample was performed using a transmission electron microscope JEM 2010F (manufactured by JEOL, acceleration voltage 200 kV). Moreover, the FFT (fast Fourier transform) analysis by this was performed using Digital Micrograph made from Gatan.
(Chlorine ion content in iron oxyhydroxide)
An iron oxyhydroxide sample is dissolved in 3M sulfuric acid, diluted with an alkaline solution to precipitate iron, filtered through a filter, and the filtrate is collected and quantified by ion chromatography (DX-500, manufactured by Nippon Dionex). did.

Production Example 1 (Production of iron oxyhydroxide)
A sodium hydroxide (NaOH) aqueous solution was added dropwise to a ferric chloride (FeCl ₃ ) aqueous solution while adjusting the pH to 6 or less at room temperature, and the final amount of NaOH added was NaOH / FeCl ₃ (molar ratio) = 2.75. To obtain a particle suspension of iron oxyhydroxide. The average particle diameter d50 of the particles in the obtained suspension was 17 μm.
The suspension was filtered, dried in air at 120 ° C., washed with ion-exchanged water, and further dried in air at 120 ° C. to obtain iron oxyhydroxide powder.
The particle diameter of the oxyhydroxide powder (hereinafter referred to as “powder A”) obtained as described above was 0.25 mm to 5 mm. It was confirmed by X-ray diffraction that the crystal structure was β-iron oxyhydroxide and the average crystallite size was 5 nm.
FIG. 1 shows a state observed with a transmission electron microscope (TEM). The crystal shape was granular. The crystallite diameter by TEM observation was 5 to 10 nm, and each crystal was granular, and these were condensed to form particles.
The specific surface area was 280 m ² / g, and the chlorine ion content was 5.8 wt%.

Production Example 2 (Manufacture of iron oxyhydroxide adsorbent powder and classified product)
Iron oxyhydroxide powder A was dry pulverized with a pin mill to obtain powder B. Powder B had a particle size range of 0.6 to 300 μm and an average particle size of 26.5 μm.
Further, powder B was classified with a sieve to obtain the following powders.
Powder C-1: Particle size 10 to 32 μm
Powder C-2: Particle size 32 to 45 μm
Powder C-3: Particle size 45 to 75 μm

Reference measurement example 1 (Batch phosphoric acid adsorption test of adsorbent particles)
Dissolve potassium dihydrogen phosphate in ion-exchanged water, adjust the pH to 3.5 with hydrochloric acid or 7.0 with sodium hydroxide, and test for a concentration of 400 mg-P / L (concentration as phosphorus) Liquids G (pH 3.5) and H (pH 7.0) were prepared.
1 g of each of powders C-1 to C-3 was added to 150 mL of test solutions G and H, followed by stirring and an adsorption test. The liquid was collected after a predetermined time, separated from the solid content with a filter syringe, and the phosphorus concentration in the solution was analyzed by ICP (inductively coupled plasma) to calculate the amount of adsorption. At the same time, the pH was measured. The results are shown in Table 1.

It can be seen that when powders C-1 to C-3 are used as the adsorbent and pH 3.5 is used as the test solution, the pH increases as phosphate ions are adsorbed. On the other hand, when a test solution having a pH of 7.0 is used, the pH drops greatly in the initial stage, and then the pH rises only slightly and does not exceed pH 7.0. In addition, the amount of adsorption is less when the pH of the test solution is 3.5 than when the pH is 7.0. This suggests that phosphate ions are adsorbed by exchange with hydroxide ions at pH 3.5.

Measurement Example 1 (Water-permeable phosphate adsorption test for adsorbent particles)
Dissolve potassium dihydrogen phosphate in ion-exchanged water, adjust the pH to 2.9 with hydrochloric acid or 7.0 with sodium hydroxide, and test the concentration of 100 mg-P / L (concentration as phosphorus) Liquid I (pH 2.9) and J (pH 7.0) were prepared.
The column was filled with 20 g each of powder B and powder C-3, and test liquids I (Examples) and J (comparative examples) were passed from the top of the column at a water flow rate (SV) of 10 (2.6 mL / min), 20 ( 5.3 mL / min) or 30 (7.8 mL / min), collect the liquid from the bottom of the column, separate it from the solids with a filter syringe, and analyze the phosphorus concentration in the solution by ICP. The amount of adsorption was calculated. The breakthrough point was defined as the time when the phosphorus concentration of the liquid coming out from the bottom of the column reached 10 mg-P / L. At the same time, the pH was measured. The test conditions are as follows.
Example 1-1: Powder B, Test Solution I, SV10, 2 times Example 1-2: Powder B, Test Solution I, SV20, 2 times Comparative Example 1-1: Powder B, Test Solution J, SV10 Twice run Comparative Example 1-2: Powder B, Test Solution J, SV20, Twice Example 2: Powder C-3, Test Solution I, SV30

The results are shown in FIGS. The pH of the treated water at the breakthrough point was as follows:
Example 1-1: pH 3.8 (first time), pH 3.8 (second time)
Example 1-2: pH 3.3 (first time), 3.8 (second time)
Comparative Example 1-1: pH 3.2 (first time), 3.2 (second time)
Comparative Example 1-2: pH 3.0 (first time), 3.0 (second time)
Example 2: pH 3.4

The water flow rate at the breakthrough point (flow rate [ml] / adsorbent amount [ml]) is about 280 to 330 in Examples 1-1, 1-2, and 2, and in Comparative Examples 1-1 and 1-2. It is about 140, and it can be seen that the amount of adsorption is clearly larger in the example. The pH of the treated water at the breakthrough point is 0.2 or more higher than the pH 2.9 of the untreated water in the examples, and it can be seen that the amount of adsorption is greatly increased under this condition.

Claims

In a method for adsorbing anions by passing water containing a target anion and having a certain pH through an adsorption device filled with an anion adsorbent mainly composed of iron oxyhydroxide. An adsorption method characterized in that it is carried out under conditions where the pH of the treated water at the excess is higher than the pH of the water before the treatment.
The adsorption method according to claim 1, wherein the treatment is performed under a condition that the pH of the treated water at the breakthrough point is 0.2 or more higher than the pH of the water before the treatment.
The adsorption method according to claim 1 or 2, wherein the water before the treatment is acid and the pH is adjusted to 2.5 to 5.0.
The adsorption method according to any one of claims 1 to 3, wherein the iron oxyhydroxide is β-iron oxyhydroxide.
The adsorption method according to claim 4, wherein the average crystallite diameter of the iron oxyhydroxide is 10 nm or less.
6. The adsorption method according to claim 4, wherein the β-iron oxyhydroxide crystals are granular.
The adsorption method according to any one of claims 1 to 6, wherein the specific surface area of the iron oxyhydroxide is 250 m 2 / g or more.
The adsorption method according to any one of claims 1 to 7, wherein the concentration of the target anion contained in the water before the treatment is 100 mg / L or less.
The adsorption method according to any one of claims 1 to 8, wherein chlorine ion is contained at 100 mg / L or more in water before the treatment.
The adsorption method according to any one of claims 1 to 9, wherein the target anion is a phosphate ion.