JPH1119506A - Activated alumina for adsorbing arsenate ion and adsorption treatment of arsenate ion from aqueous solution by using the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide adsorption material of arsenate ions by which arsenate ions are adsorbed and removed from water to low concentration of <=0.01 ml/1 in terms of arsenic by continuously treating a large amount of water containing the arsenate ions by an inexpensive and simple method. SOLUTION: In the case of using an adsorbent to remove arsenate ions from liquid containing arsenic acid, activated alumina for adsorbing the arsenate ions, in which content of Na2 O is <=0.3 wt.%, wear rate is <=5%, sphere conversion external specific surface area calculated from sieving particle size is 4-20 m<2> /l, BET specific surface area is >=100 m<2> /g, pore volume of 0.2-10 μm pore radius measured by a mercury press-fitting method is >=0.04 cc/g and pore volume of 0.2-1 μm pore radius is >=0.02 cc/g, is used as the adsorbent.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to an activated alumina for arsenate ion adsorption, and more particularly to an activated alumina for arsenate ion adsorption suitable for removing arsenate ions from a liquid containing arsenate ions.

[0002]

2. Description of the Related Art In recent years, coagulation sedimentation, lime softening, adsorption, bioconcentration, reverse osmosis, and the like have been proposed to reduce the arsenic concentration from purified water or wastewater containing various chemical forms of arsenate ions. Various methods such as the method are being studied. Among these, the adsorption method is considered to be particularly advantageous in small and medium-sized facilities because it does not require a large treatment plant area, does not generate waste sludge, and does not require complicated filtration operations.

Activated carbon, activated alumina, magnesia, magnesia-modified slag, titania-modified activated carbon, manganese dioxide, cerium oxide, anion exchange resin, red mud granules and the like are known as adsorbents used in the adsorption method. Above all, activated alumina has been applied as an inexpensive and safe adsorbent.

[0004] An example of using activated alumina for adsorption of arsenic acid is described in "Environmental Progress".
s ", Volume 6, Issue 3, page 150, M. Gho
and J. Sh. R. There is a paper by Yuan. In this paper, a column was filled with a crushed activated alumina mass having a Na ₂ O content of 0.9% by weight, a BET surface area of 218 m ² / g and a particle size of 28 to 48 mesh, and the arsenic was added thereto. Arsenic acid is adsorbed and removed by passing water containing arsenate ions in a conversion of 0.08 to 10 mg / l.

[0005] As another example, a paper by the Fukuoka Prefecture Wide Area Water Supply Corporation, Tsukamoto, Inoue, Matsumoto, Kimura and Kobayashi, described in the 45th Water Supply Research Conference Lecture Book, p. 244 (May, 1994). There is. In this paper, a method in which powdered activated alumina of 325 mesh or more is brought into shaking contact with water containing 0.047 mg / l of arsenic ion in terms of arsenic to adsorb and remove arsenic ions in a batch system, A method is disclosed in which activated alumina is packed in a column and water containing arsenate ions is passed through the column to adsorb and remove arsenate ions.

Another example of using activated alumina for adsorption of arsenic acid is described in "Water Association of Japan", Vol. 65, No. 4, p.
Fukuoka Wide-area Water Supply Corporation Tsukamoto, described on page 4 (1996)
There are papers by Inoue, Matsumoto, Kimura and Kobayashi. In this paper, two types of spherical particles having different particle diameters were used to clarify which of the outer surface of the activated alumina particles and the inner micropore surface dominates the amount of arsenic adsorption when the activated alumina particles adsorb arsenic. Using activated alumina particles, the influence of the particle diameter on the arsenic removal rate and the arsenic distribution inside the activated alumina particles after arsenic adsorption are measured. As a result, it has been concluded that activated alumina adsorbs arsenic almost uniformly up to the center of the particles, and that there is no difference in the arsenic removal rate even when the particle diameter is different (arsenic adsorption is not limited to the outer surface area of the particles). That is,
Using spherical activated alumina having an average particle size of 0.8 mm and 2 mm, arsenic concentrations of 20 mg / l, 100 mg / l and 500 mg / l were used.
Table 1 shows the measurement results of the change over time of the arsenic removal rate (%) for three levels of raw water of mg / l. There is no. The distribution of arsenic from the center of the activated alumina to the outer surface after the adsorption treatment was measured by an energy dispersive X-ray spectrometer, and the results are shown in FIG. Are described as being substantially evenly distributed from the outer surface to the center.

[0007]

SUMMARY OF THE INVENTION The inventors of the present invention usually find that the concentration of arsenic in a reservoir for water supply is 0.2 mg / l.
A low-cost, easy-to-handle adsorbent and aqueous solution that can adsorb and remove large amounts of aqueous solutions as low as 0.01 mg / l and arsenic concentrations of less than 0.01 mg / l, which pass water supply standards. As a result of intensive studies to find a treatment method, it was found that when activated alumina having specific physical properties was used, all of the above objects could be satisfied, and the present invention was completed.

[0008]

That is, the present invention provides Na
_The 2O content is 0.3% by weight or less, the abrasion rate is 5% or less, and the specific spherical external surface area calculated from the sieving particle size is 4 to ²⁰ m ² /
1, the BET specific surface area is 100 m ² / g or more, and the pore volume is 0.2 to 10 μm as measured by mercury porosimetry.
It is an object of the present invention to provide an activated alumina for arsenate ion adsorption characterized in that the pore volume is at least 0.4 cc / g and the pore volume of 0.2 to 1 μm is at least 0.02 cc / g.

The present invention further provides an arsenic concentration of 0.2 mg / l
An aqueous solution of ~0.01mg / l, Na ₂ O content is 0.
3% by weight or less, abrasion rate of 5% or less, specific spherical external surface area calculated from sieving particle size of 4 to ²⁰ cm ² / g, BET specific surface area of 100 m ² / g or more, pore radius measured by mercury intrusion method The pore volume of 0.2 to 10 μm is 0.04 cc / g or more and the pore volume of 0.2 to 1 μm is 0.02 cc / g.
The above-mentioned column was continuously supplied to the column filled with activated alumina, and the arsenate ion in the aqueous solution was reduced to 0.01 mg / arsenic equivalent.
It is an object of the present invention to provide a method for adsorbing arsenate ions from an aqueous solution, which is characterized by adsorbing less than 1 l.

[0010]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below in detail.
The activated alumina for adsorbing arsenate ions of the present invention comprises Na_TwoIncluding O
0.3% by weight or less, wear rate 5% or less, sieving particle size
2-50cm outside spherical specific surface area calculated from ^Two/ G,
BET specific surface area is 100m^Two/ G, measured by mercury intrusion method
The pore volume with a defined pore radius of 0.2 to 10 μm is 0.04
cc / g or more and 0.2-1 μm pore volume of 0.0
2 cc / g or more.

The activated alumina has a Na ₂ O content of about 0.1.
Up to 3% by weight, preferably up to about 0.2% by weight.
Activated alumina from aluminum hydroxide obtained by the Bayer method is usually 0.2 to 0.6% by weight of Na ₂ O.
It contains. Arsenic adsorption by activated alumina is excellent in removal efficiency when the pH of the processing liquid (raw water) is about 5 to 6.
However, when the column is filled with activated alumina having a Na ₂ O concentration of more than 0.3% by weight and used,
Even if the raw water adjusted to 5 to 6 is passed through the column, the pH of the effluent becomes 9 to 11 at the initial stage of passing water, and the arsenic removal rate decreases, which is not preferable.

The activated alumina used in the present invention has a spherical external specific surface area of about 4 to ²⁰ m ² / l, preferably about 6 to 1 m ² / l.
4 m ² / l. According to conventional knowledge, the size of the activated alumina particle size (the size of the external specific surface area) does not affect the arsenic removal efficiency. However, when the activated alumina is packed in a column and this column contains trace impurities, If the raw water for water supply (well water, river water) is continuously supplied and arsenic is removed from this raw water, the smaller the activated alumina particle diameter (the larger the external specific surface area), the better the arsenic removal efficiency Have been found by the present inventors.

[0013] That is spherical equivalent outer specific surface area calculated from the sieving particle size of about 4 to 20 m ² / l, preferably about 6~14m ² /
In the case of l, the column has relatively low liquid permeation resistance, so that high-speed water flow is possible, and when the pore condition satisfies the above range, the column filled with the activated alumina has a long breakthrough time. Meet. Sphere equivalent specific surface area is about 4m ² /
If it is less than 1, the breakthrough time of the column filled with activated alumina will be short, and arsenic removal cost will be high. If the sphere-equivalent outer specific surface area is not less than about 20 m ² / l, liquid flow resistance during column operation is large, and high-speed water flow becomes difficult.

The activated alumina used in the present invention has a BET specific surface area of about 100 m ² / g or more, preferably about 200 m ² / g.
² / g or more. The larger the BET specific surface area, the greater the effect of extending the column breakthrough time on the increase in the outer surface area of the activated alumina particles. If the BET specific surface area is less than about 100 m ² / g, the effect of extending the column breakthrough time on the increase in the external specific surface area of the activated alumina particles decreases.

Further, the activated alumina of the present invention has a pore volume of a pore radius of 0.2 to 10 μm measured by a mercury intrusion method of about 0.04 cc / g or more, preferably about 0.08 cc / g.
As described above, the pore volume of 0.2 to 1 μm is about 0.02 c
c / g or more, preferably about 0.04 cc / g or more. Here, the pore volume with a pore radius of 0.2 to 1 μm represents the macropore volume inside the activated alumina particles, and the pore volume with a pore radius of 0.2 to 10 μm is the macropore volume inside the particles and the particles between the particles. It represents the total value of the gap volume.

The presence of macropores having a pore radius of 0.2 to 10 μm facilitates the diffusion of arsenic into the interior of the particles and prolongs the breakthrough time of a column filled with activated alumina. Macropores and mesopores having a pore radius of less than 0.2 μm (pores having a radius of 2 nm to 100 nm) also help arsenic diffusion, but do not have the effect of extending the breakthrough time as much as macropores having a pore radius of 0.2 to 10 μm.

When the pore volume with a pore radius of 0.2 to 10 μm is 0.04 cc / g or more and the pore volume with 0.2 to 1 μm is 0.02 cc / g or more, activated alumina was filled. The breakthrough time of the column is longer than when there is no macropore having a pore radius of 0.2 to 10 μm. On the other hand, when the pore volume at a pore radius of 0.2 to 10 μm is less than 0.04 cc / g and the pore volume at 0.2 to 1 μm is less than 0.02 cc / g, a column filled with activated alumina Is about the same as when there is no macropore having a pore radius of 0.2 to 10 μm.

The wear rate of the activated alumina particles used in the present invention is about 5% or less, preferably 1% or less. When the wear rate of the activated alumina compact exceeds 5%, or when the activated alumina particles are in the form of powder or agglomerates obtained by crushing, when the powder is packed into a column and used, water after passing through the column is used. Is cloudy or the filter is clogged,
Not only must the activated alumina particles be suspended and washed to remove dust before filling, but also an operation for treating cloudy water is required, which makes the operation complicated, which is not preferable. The particle shape of the activated alumina molded body is not particularly limited, but spherical particles are more preferable because of low wear rate and easy molding.

As described above, the activated alumina for arsenic ion adsorption of the present invention has an Na ₂ O content of 0.3% by weight or less, a wear rate of 5% or less, and an external specific surface area in sphere calculated from sieving particle size of 4%. ２０20 m ² / l, BET specific surface area is 100 m ² / l
g or more, pore radius 0.2 to 10μ measured by mercury intrusion method
m is 0.04 cc / g or more and 0.2 to 1
The active alumina has a pore volume of 0.02 cc / g or more. When the activated alumina is immersed in water at 80 ° C., an acid component having a pH of water of 3 to 6 is coated. Preferably. In this case, the arsenic adsorption performance is improved, and the adsorption operation is facilitated. When the pH of the water when the amount of the inorganic acid applied is immersed in water at 80 ° C. becomes less than 3, the pH of the raw water passing through the column is lowered, and the adsorption efficiency of arsenic acid is reduced. Water) is required. On the other hand, when the pH of the water when the amount of the inorganic acid applied is immersed in water at 80 ° C. does not reach 6, the effect of improving the adsorption of arsenic acid is small.

The method for producing activated alumina for adsorption of arsenic ions having the above-mentioned physical properties of the present invention is not particularly limited. However, the method using rehydratable alumina makes it easy to obtain activated alumina having a large BET specific surface area and particle strength. Recommended from. More specifically, the total Na ₂ O content is about 0.3% by weight, preferably about 0.2% by weight, and more preferably about 0.3% by weight.
1% by weight or less of aluminum hydroxide such as gibbsite is calcined in a hot air stream of about 500 to 1200 ° C. for about 0.1 second to several minutes, and then separated and cooled to obtain rehydration property. Activated alumina powder (hereinafter sometimes referred to as rehydratable alumina) is obtained.

The activated alumina powder having rehydration properties is formed into a desired shape as it is or after further pulverization. The shape of the molded body is not particularly limited as long as the wear rate falls within the range of the present invention, such as a sphere, a column, a ring, and a honeycomb, but is preferably a sphere. Known methods such as tumbling granulation, spray drying, submerged granulation, an oil drop method, and an oil levitation method can be used as the method of forming into a sphere. The compact has a 5% reduction in the wear rate of activated alumina after rehydration and firing.
The molding conditions must be selected below, preferably below about 1%. The rolling granulation method is preferable as an inexpensive molding method having a wear rate of about 5% or less.

In rolling granulation, a combustible organic substance is added to the raw alumina powder, or a rehydratable alumina powder having a narrow particle size distribution (having a quadrant deviation of 1.3 or less, preferably 1.2 or less) as a raw material. By selecting the molding conditions, such as using ()), a molded article having the physical properties applicable in the present invention can be obtained. When a transition alumina powder having a wide particle size distribution having a quadrant deviation value exceeding 1.4 is used, the pore radius is 0.2 to 1 μm.
(Measured by the mercury intrusion method), the pore volume is about 0.01 cc / g, and the pore volume with a pore radius of 0.2 to 10 μm is 0.02 c.
Only those having a small pore volume of about c / g can be obtained. Although the addition of an organic substance increases the pore volume, the abrasion resistance is remarkably reduced.

The molded body after molding is usually separated by a sieving method or the like.
Graded sphere equivalent specific surface area 4 ~ 20m ^TwoAdjust to / l.
The molded body has enough time to rehydrate to increase its mechanical strength,
In water at room temperature to 120 ° C, preferably 50 to 90 ° C
Retained, aged and rehydrated in gas or steam-containing gas
You. Rehydration is generally performed for 1 minute to 1 week. Rehydrated
The spherical molded body is subsequently fired, and the moisture content in the molded body and
Excluding water of crystallization. The firing temperature is about 300 ~ 900 ℃, preferably
About 300-500 ° C, and the baking time is about 10 minutes
100 hours.

The activated alumina after calcining is optionally treated with an acid. After the acid component is deposited on the activated alumina, the activated alumina after the acid component is deposited is retained in 100 ml of water at 80 ° C. for 10 g of the adsorbent for 30 minutes, and then the adsorbent is filtered from the water.
The pH of the water after separation may be applied in such an amount as to give a value of 3 to 6, and the application method is not particularly limited. For example, the spherical activated alumina obtained by the above method may contain an acid component. And a method obtained by contacting with an aqueous solution.

Examples of the method of contacting the activated alumina with the aqueous solution containing an acid component include a method of impregnating the activated alumina with the aqueous solution,
There is a method of supplying and absorbing an aqueous solution corresponding to the water absorption of activated alumina. A molded article impregnated with or absorbed with an acid component is
Operations such as washing with water, filtration, drying and baking may be performed. Washing and filtering are preferred because Na ₂ O in activated alumina decreases. Drying or baking may be omitted.

The acid components to be used include hydrochloric acid, hydrofluoric acid,
At least one of nitric acid, sulfuric acid, aluminum sulfate and acetic acid can be mentioned, and preferred is hydrochloric acid or sulfuric acid or a mixture of sulfuric acid and aluminum sulfate. The concentration of the acid component in the aqueous solution is usually used in the range of 0.001 to 0.5N,
Strictly, it depends on the type of acid, the weight ratio of the acid component to the activated alumina, and the like. Therefore, "10 g of the activated alumina molded body after acid treatment in 100 ml of water at 80 ° C. for 30 minutes, and then the activated alumina When the body is filtered and separated,
The amount at which the pH of the water exhibits a value of 3 to 6 "may be determined by preliminary experiments. In this case, the temperature of the aqueous solution is about 0 to 100.
° C, contact time is about 10 minutes to 24 hours.

The equilibrium adsorption amount of arsenate ion at 25 ° C. of the activated alumina for arsenate ion adsorption of the present invention has an equilibrium concentration of 0.1.
It is about 2 mg / l or more at 1 mg / l and pH 5.5, preferably about 5 mg / l or more. Packing density 0.4 ~ 0.8
kg / l and pressure resistance is usually 0.1 kg or more. An adsorbent or a filtering agent having another function can be added to the activated alumina for arsenate ion adsorption of the present invention as long as the arsenic acid removal performance is not reduced.

The activated alumina for arsenate ion adsorption obtained in the present invention can be applied to the purification of raw water for industrial or domestic use such as rivers, lakes and wells, or industrial water. Particularly suitable for purification. In use,
The adsorption and purification of the water to be treated can be carried out in the form of a fixed bed of a column type, a moving bed, a fluidized bed, a batch type or the like, but a fixed bed of a column type is preferred. The liquid passing speed is suitably about ¹ to 100 h ^{-1 in} SV value, but preferably about 2 to 15 h ^-1 in SV value.

When the water to be treated contains arsenite ions, the treated water may be oxidized in advance to form arsenate ions, and then subjected to adsorption treatment.

If the pH of the water to be treated is out of the range of 4 to 6, a pH adjuster is added to adjust the pH of the water to be treated to 4.
It is preferable to adjust to ６6 and to subject it to arsenate ion removal treatment. Normal raw water is often neutral to weakly alkaline, and may be adjusted by adding hydrochloric acid, sulfuric acid, or sulphate.

[0031]

As described above in detail, according to the present invention, when activated alumina having specific physical properties is selected as an arsenate ion adsorbent, and the activated alumina is packed into a column and applied, the arsenic is used as raw water for water supply. Concentration 0.2mg / l ~ 0.01mg
/ L, an extremely thin aqueous solution is continuously treated for a long time,
It enables the removal of arsenate ions in the aqueous solution after treatment specified as the water quality standard of the Water Supply Law to less than 0.01 mg / l in terms of arsenic. The industrial value thereof is extremely large, for example, the ease of the processing method and the low cost of the processing material.

[0032]

The present invention will be described in more detail with reference to the following examples, but the scope of the present invention is not limited by these examples. In the present invention, the measurement of the outer surface area based on the sieving method, the pore volume by the nitrogen adsorption method and the BE
Measurement of T specific surface area, measurement of pore volume by mercury intrusion method,
The measurement of the pH value, the analysis of As, the measurement of the wear rate, and the measurement of the quadrant deviation value were carried out by the following methods.

External surface area based on a sieving method: A sample dried at 200 ° C. for 3 hours is weighed in a predetermined amount, and the mesh size specified by JISZ8801 is 4.00 mm, 3.35 mm, 2.80 mm,
2.36mm, 2.00mm, 1.40mm, 1.18
mm, 0.71 mm, and 0.36 mm sieves, sieve analysis is performed by selecting three or more sieves having an appropriate aperture corresponding to the particle size distribution of the sample. [The average particle diameter of each fraction obtained in the sieve analysis is obtained. di (cm), The specific surface area in terms of sphere was calculated from the above.

Pore volume and BET specific surface area by nitrogen adsorption method: A sample was dried at 200 ° C. for 3 hours, weighed in a predetermined amount, and used as a gas adsorption / desorption analyzer Omnisorp 3 manufactured by Coulter, Inc.
Vacuum deaeration (150 ° C., 8 h, 2
(× 10 ⁻⁵ Torr or less), and then the adsorption / desorption is measured by a continuous volume method using nitrogen gas.

Pore volume by mercury intrusion method: 200 ° C./3
A predetermined amount of the dried measurement sample was weighed, and the measurement was performed after 30 minutes of vacuum suction by a mercury intrusion method pore volume measuring apparatus (manufactured by Qantachrome) using an autoscan 33.

PH value: 10 g of a sample to be measured was immersed in 80 ° C. water 10
0 ml for 30 minutes, filtered, pH of filtrate after cooling
Was measured with a Horiba F8 type pH meter.

As analysis: Measured according to JIS-K0102.

Abrasion rate: Measured according to JIS-K1464.

The quadrant deviation value was determined from (D75 / D25) × 1/2. (D75: particle size at a cumulative weight of 75% by weight from the particle size distribution table, D25: particle size at a cumulative weight of 75% by weight from the particle size distribution table).

Example 1 [Preparation of activated alumina for removing arsenate ions] The Na ₂ O content obtained from the buyer process was 0.15% by weight, the average particle size was 8 μm, and the particle size distribution had a quadrant deviation of 1.2. Gibbsite (alumina trihydrate) is put into a hot gas at about 700 ° C. and calcined instantaneously. The burning material mainly has a particle size distribution of 4.5%, an average particle size of 7 μ, and a quarter deviation value of 1.2. A rehydratable alumina having crystal forms of χ and ρ was obtained. About 1 kg of the rehydratable alumina thus obtained is mixed with about 0.5 water.
kg, and formed into a sphere having a diameter of about 0.9 mm by a dish granulator, and then sieved with a sieve having openings of 1.18 mm and 0.36 mm to form a sphere having a particle diameter of 1.18 to 0.36 mm. I got a body. Next, the spherical molded body was placed in a container with a lid, sealed and kept at a temperature of 80 ° C. for 16 hours to rehydrate. This compact was placed in an electric furnace, heated to 380 ° C. in 1 hour, and held for 3 hours to obtain spherical activated alumina A. Table 1 shows the properties of the spherical activated alumina A.

[Arsenate ion removal test] The spherical activated alumina A obtained by the above method was added to a glass column shown in FIG.
ml (19.8 g), and raw water having a composition shown in Table 3 containing 0.05 mg / l of sodium arsenate as arsenic was supplied from the top of the column, and the treated water flow rate was 250 ml / h or 125 ml (SV = 10 h ^-1 or (Equivalent to 5h ^-1 )
Arsenic in the raw water was absorbed and removed by adjusting the flow rate so that The test results are shown in Tables 4 and 5. For a pH 5.5 adsorbent, the flow rate is 60000 BV (3000 hours flow)
Up to 7000 BV (1400 hours), the adsorbed solution with a pH of 7.5 did not break through the column, and treated water having an arsenic concentration of 0.01 mg / l or less was obtained.

Example 2 [Preparation of activated alumina for removing arsenate ions] 1.2 kg of the spherical activated alumina A obtained in Example 1 was impregnated in 4.3 L of 0.3% hydrochloric acid solution for 16 hours, washed with water and filtered. Then, it was put in an electric furnace and kept at 250 ° C. for 4 hours to obtain spherical activated alumina B having a characteristic of pH 4 of the eluate at 80 ° C. Table 1 shows the properties of the spherical activated alumina B.

[Arsenic ion removal test] Arsenic ion removal from raw water was performed in the same manner as in Example 1 except that 25 ml of spherical activated alumina B (19.8 g) was used instead of 25 ml of spherical activated alumina B in the arsenate ion removal test. Tested. The test results are shown in Tables 4 and 5. With a pH 5.5 adsorbent, the flow rate is 61000 BV (6100 hours flow)
Up to 8200 BV (1640
Arsenic concentration 0.01 mg without passing through the column
/ L or less of treated water was obtained. In addition, it was possible to prevent the pH of the treated water from rising to 8 or more at the beginning of the liquid passage.

Comparative Example 1 In place of the activated alumina A used in Example 1, a commercially available activated alumina (manufactured by Mizusawa Chemical Industry Co., Ltd., trade name: Mizusawa R)
N) was used. This is called spherical activated alumina C,
Table 2 shows the characteristics.

[Arsenic ion removal test] Arsenic ion removal from raw water was carried out in the same manner as in Example 1 except that 25 ml of spherical activated alumina C (17.8 g) was replaced with 25 ml of spherical activated alumina C in the arsenate ion removal test. Tested. Table 6 shows the test results. This liquid passed through the adsorbent having a pH of 5.5 at a flow rate of 10500 BV (passed for 1050 hours).

Comparative Example 2 [Preparation of activated alumina for removing arsenate ions] The Na ₂ O content obtained from the Bayer process was 0.16% by weight, the average particle size was 18 μm, and the particle size distribution had a quadrant deviation of 2.0. Gibbsite (alumina trihydrate) was charged into a hot gas at about 700 ° C. and calcined instantaneously. The burning material was 5.0%, and the average particle size was 17%.
A rehydratable alumina mainly having crystal forms of χ and ρ having a particle size distribution of μ, quadrant deviation 2.0 was obtained. About 0.5 kg of water was added to 1 kg of the rehydratable alumina thus obtained, and formed into a spherical shape having a diameter of about 3.3 mm using a dish granulator. Then, the apertures were 4.0 mm and 2.36 mm. To obtain a spherical molded product having a particle diameter of 4.00 to 2.36 mm. Next, the spherical molded body was placed in a container with a lid, sealed and kept at a temperature of 80 ° C. for 16 hours to rehydrate. This compact was placed in an electric furnace, heated to 380 ° C. in 1 hour, and held for 3 hours to obtain spherical activated alumina D. Table 2 shows the properties of the spherical activated alumina D.

[Arsenic ion removal test] Arsenic ion removal from raw water was performed in the same manner as in Example 1, except that 25 ml of spherical activated alumina D (21.3 g) was used in the arsenate ion removing test of Example 1. Tested. Table 6 shows the test results. It has a pH of 5.5
6500BV (pass for 650 hours)
It broke through.

Example 3 [Production method of activated alumina for removing arsenate ions] In Example 1, the diameter of a spherical molded article formed by a dish granulator was 0.9 mm.
Is changed to 0.7 mm, and a sieve having an opening of 0.36 mm is set to 0.1 mm.
Sieving instead of 25mm sieve, 1.18-0.36m
A spherical activated alumina F was obtained by the same operation except that a spherical molded body having a particle diameter of m was obtained. Table 1 shows the properties of the spherical activated alumina. [Arsenic ion removal test] An arsenate ion removal test from raw water was performed in the same manner as in Example 1 except that spherical activated alumina A (25 ml) was replaced with spherical activated alumina F (25 ml (16.3 g)). Table 4 shows the test results. The flow rate of the adsorbent at pH 5.5 is 820
Even with 00BV (passing for 8200 hours), the column did not break through, and treated water having an arsenic concentration of 0.01 mg / l or less was obtained.

Comparative Example 3 [Production method of activated alumina for removing arsenate ions] In Comparative Example 2, the diameter of a spherical molded body formed by a dish granulator was 3.3 mm.
Was changed to 1.8 mm, and the apertures were 4.0 mm and 2.3.
A 6 mm sieve was sieved in place of a 2.0 mm and 1.18 mm sieve to obtain a spherical activated alumina E by the same operation except that a spherical molded body having a particle diameter of 2.0 to 1.18 mm was obtained. Obtained. Table 2 shows the properties of the spherical activated alumina. [Arsenic ion removal test] Arsenic ion from raw water was obtained in the same manner as in Example 1 except that 25 ml (16.3 g) of spherical activated alumina A was replaced with 25 ml (21.3 g) of spherical activated alumina E in the arsenate ion removal test. A removal test was performed. The test results are shown in Tables 6 and 7. For the pH 5.5 adsorbent, the flow rate is 16300 BV (1630 hours flow)
Up to 1200 BV (passing for 240 hours) with the adsorbent of pH 7.5, the column did not break through and the arsenic concentration was 0.01 mg /
1 or less of treated water was obtained.

[0050]

[Table 1]

[0051]

[Table 2]

[0052]

[Table 3]

[0053]

[Table 4]

[0054]

[Table 5]

[0055]

[Table 6]

[0056]

[Table 7] Column test of adsorbent pH 5.5 is space velocity 10h
^-1 and column test of adsorbent pH 7.5 is space velocity 5h
^-1 . The unit of arsenic concentration is mg / l. BV: 2 means the volume of activated alumina packed in the column
5 ml. Breakthrough: Arsenic concentration of treated water at column outlet is 0.01 mg / l
Is defined as a breakthrough.

[Brief description of the drawings]

FIG. 1 is a schematic view of an apparatus used for an arsenate ion removal test in Examples and Comparative Examples.

Claims (5)

[Claims] 1. A Na ₂ O content of 0.3% by weight or less, an abrasion rate of 5% or less, an external specific surface area in sphere calculated from sieving particle size of 4 to ²⁰ m ² / l, and a BET specific surface area of 100 m ^2. /
g or more, pore radius 0.2 to 10μ measured by mercury intrusion method
m is 0.04 cc / g or more and 0.2 to 1
An activated alumina for adsorbing arsenate ions, wherein the pore volume of μm is 0.02 cc / g or more. 2. A Na ₂ O content of 0.3% by weight or less, an abrasion rate of 5% or less, an external specific surface area in sphere calculated from sieving particle size of 6 to 14 m ² / l, and a BET specific surface area of 100 m ^2. /
g or more, pore radius 0.2 to 10μ measured by mercury intrusion method
m has a pore volume of 0.08 cc / g or more and 0.2 to 1
2. The activated alumina for arsenate ion adsorption according to claim 1, wherein the pore volume of μm is 0.04 cc / g or more and the particle shape is spherical. 3. An arsenic concentration of 0.2 mg / l to 0.01 mg.
/ L aqueous solution having a Na ₂ O content of 0.3% by weight or less,
The wear rate is 5% or less, the sphere-specific outer specific surface area calculated from the sieving particle size is 4 to ²⁰ m ² / l, and the BET specific surface area is 100 m ^2.
/ G or more, pore radius 0.2 to 10 measured by mercury intrusion method
The pore volume of μm is 0.04 cc / g or more and 0.2 to
Aqueous solution characterized by continuously supplying to a column filled with activated alumina having a pore volume of 1 μm of 0.02 cc / g or more, and adsorbing arsenate ions in the aqueous solution to less than 0.01 mg / l in terms of arsenic. Arsenic ion adsorption method from inside. 4. The aqueous solution according to claim 2, wherein the activated alumina is coated with an acid component having a pH of 3 to 6 when immersed in water at 80 ° C. For treating arsenate ions from water. 5. The method of claim 3, wherein the acid component is at least one of hydrochloric acid, hydrofluoric acid, nitric acid, sulfuric acid, aluminum sulfate and acetic acid.