JPH0975717A - Method for removing arsenate ion - Google Patents

Abstract

PROBLEM TO BE SOLVED: To allow spherical activated alumina having a specified Na2 O content and a specified wear rate to satisfy all of cost, handleability and treating effect as an adsorbent by bringing an adsorbent made of the alumina into contact with water contg. arsenate ions and removing the arsenate ions from the water. SOLUTION: Aluminum hydroxide such as gibbsite is calcined for 0.1sec to several min in a flow of hot air at 500-1,200 deg.C, the calcined body is separated and cooled and the resultant activated alumina powder having rehydratability is pulverized and compacted in a sphere shape to obtain spherical activated alumina having <=0.3wt.% Na2 O content and <=1% wear rate. An adsorbent made of the alumina is brought into contact with water contg. arsenate ions and the arsenate ions are removed from the water. The alumina can satisfy all of cost, handleability and treating effect as an adsorbent.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a method for removing arsenate ions from water. More specifically, the present invention relates to a method for adsorbing and removing arsenate ions from factory wastewater, domestic wastewater, industrial water, tap water, etc., containing arsenate ions.

[0002]

2. Description of the Related Art In recent years, in order to reduce the arsenic concentration to a higher degree than in purified water containing various chemical forms of arsenate ions or in waste water, a flocculation-precipitation method, a lime softening method, an adsorption method, a bio-concentration method, a reverse method. Various methods such as the penetration method have been studied. Of these, the adsorption method is considered to be particularly advantageous in small and medium-scale facilities because it does not require a large treatment plant area, does not generate waste sludge, and does not require a troublesome filtration operation. As the adsorbent used in the adsorption method, activated carbon, activated alumina, magnesia, magnesia modified slag, titania modified activated carbon,
Anion exchange resin, red mud particles, etc. are known, but above all,
Activated alumina is applied as an inexpensive and safe adsorbent.

As an example of using activated alumina for adsorbing arsenic acid, Environmental Progress magazine Vol. 6, No. 3, 150
There is a paper by MMGhosh and JRYuan on the page. In this paper, the Na ₂ O content is 0.9% by weight, the BET surface area is 218 m ² / g, and the particle size is 28 to 48.
The crushed activated alumina lumps of mesh were packed in a column, and water containing low concentration of arsenate ions was passed through the column,
A method for adsorbing and removing arsenic acid is disclosed.

[0004]

However, when crushed activated alumina as an adsorbent is directly packed in a column and used, since water after passing water becomes cloudy, the activated alumina is suspended and washed before packing. Must be removed, which not only complicates the work, but also requires treatment of the cloudy cleaning water. Further, a combined method of controlling the pH of the water to be treated has been taught when activated alumina alone as an adsorbent is insufficient in adsorption capacity, but in this case, the cost of water treatment becomes high. On the other hand, although the application of adsorbents other than activated alumina has been introduced, it is possible to satisfy all of the price, handleability, and treatment effects as an adsorbent, such as being expensive and leaking undesired components from the adsorbent itself. I haven't seen anything yet. In view of such circumstances, the present inventors have conducted intensive studies to find a simple, inexpensive, and efficient method for removing arsenate ions from water, and as a result, completed the present invention.

[0005]

The first aspect of the present invention relates to Na ₂
An adsorbent made of spherical activated alumina having an O content of 0.3% or less and a wear rate of 1% or less is brought into contact with water containing arsenate ions to adsorb and remove arsenate ions from the water. The present invention provides a method for removing arsenate ions in water. A second aspect of the present invention comprises depositing an acid component, 8
The activated alumina of claim 1 having a pH value of 3 to 6 when immersed in water at 0 ° C. is brought into contact with water containing arsenate ions to adsorb and remove arsenate ions from the water. It is to provide a characteristic method for removing arsenate ion in water.

[0006]

BEST MODE FOR CARRYING OUT THE INVENTION The present invention will be described in detail below.
In carrying out the method of the present invention, the adsorbent used for adsorbing arsenate ions has a Na ₂ O content of about 0.3% by weight or less, preferably about 0.2% by weight or less, more preferably about 0.1% by weight or less. Abrasion rate of less than 1% by weight, which is an index of dust resistance, is about 1%
In the following, it is essential that the spherical activated alumina is preferably 0.8% or less. If the wear rate exceeds about 1%,
In addition, a powdery product or a lump product obtained by crushing is not preferable because turbidity occurs in water after the adsorption treatment and a filter is easily clogged or powder is generated. In addition, N in activated alumina
If the amount of a ₂ O (total soda) exceeds about 0.3% by weight, the pH of the water around the activated alumina rises and the adsorption of arsenate ions is hindered.

As the adsorbent for arsenate ions contained in water, the use of spherical activated alumina having a low Na ₂ O content and an excellent resistance to pulverization gives a considerably excellent effect. As a method of imparting an excellent arsenate ion adsorption effect, a spherical activated alumina having the above-mentioned physical properties is added with a specific amount of an acid component, that is, "10 g of the adsorbent after acid treatment is retained in 100 ml of water at 80 ° C for 30 minutes, and When the adsorbent is filtered and separated from the water, a removal method using a spherical activated alumina as an adsorbent, which is formed by depositing and impregnating "amount in which the pH of the water exhibits a value of 3 to 6" is recommended. In this method, when the amount of the acid component deposited / impregnated is large and the pH of the treated water by the above treatment is less than 3, the effect of adsorbing arsenic acid decreases, and at the same time, a neutralizing agent for the treated water is added. A large amount is required, which is not preferable. On the other hand, if the pH exceeds 6,
There is almost no improvement in the adsorption of arsenic acid as compared with the case where the acid component deposition treatment is not performed.

The activated alumina referred to in the present invention may be any known one commonly referred to in the art, and is an aluminum oxide (transition alumina) other than so-called α-alumina. In the method of the present invention, the method for producing the spherical activated alumina having a wear rate of 1% or less is not particularly limited, but it is recommended that the method via rehydratable alumina is easy to obtain an adsorbent having a large BET surface area and strength. It That is, aluminum hydroxide such as gibbsite is instantaneously calcined in a hot air stream at 500 to 1200 ° C. for 0.1 seconds to several minutes, and then separated and separated.
By cooling, activated alumina powder having rehydration properties (hereinafter referred to as rehydration alumina) is obtained. This rehydratable alumina is formed into a spherical shape as it is or after pulverization. The obtained molded product is then held and aged in water, steam or a steam-containing gas at room temperature to 120 ° C., preferably 50 to 90 ° C. for a time sufficient for rehydration in order to increase the mechanical strength of the molded product itself. Rehydrated. Rehydration is generally 1
Minutes to a week. The rehydrated molded body is subsequently fired to remove the attached water and crystal water in the molded body. The firing temperature is usually 300 to 900 ° C., preferably 300 to 500.
C. and the firing time is about 10 minutes to about 100 hours.
A known method may be used to set the total Na ₂ O contained in the spherical activated alumina to 0.3% by weight, and there is no particular limitation, but it is easy to obtain the total Na ₂ O content as aluminum hydroxide as a raw material. It may be 0.3 wt% or less, more preferably 0.1 wt%. However, when the spherical activated alumina is subjected to a treatment for depositing / impregnating it with an acid component, the total content of Na ₂ O in the starting aluminum hydroxide may be high, and it may be contained in the spherical activated alumina after the acid treatment. The total Na ₂ O content may be 0.3% by weight or less.

To deposit the acid component on the activated alumina, 10 g of the adsorbent was held in 100 ml of water at 80 ° C. for 30 minutes, and the adsorbent was filtered and separated from the water. The subsequent water may be applied in such an amount that the pH of the water exhibits a value of 3 to 6, and the application method is not particularly limited. For example, (1) spherical activated alumina having an abrasion rate of 1% or less is used as an acid component. It is obtained by contact with an aqueous solution containing.
(2) Rehydrated alumina powder is contacted with an aqueous solution and molded,
After aging to impart strength to the molded body, the molded body may be brought into contact with an aqueous solution containing an acid component and then baked to obtain a method.

As a method for contacting the activated alumina with the acidic component-containing aqueous solution, there are a method of impregnating the activated alumina with the aqueous solution, a method of supplying and absorbing an aqueous solution having a water absorption rate of the activated alumina, and the like. After contact with the acid component, it may be washed with water, filtered, dried or calcined. After washing with water and filtration, N in activated alumina
It is advantageous because it reduces a ₂ O. In the case of the production method (1), the adsorbing device may be filled in the wet state and used.

As the acid component, at least one of hydrochloric acid, hydrofluoric acid, nitric acid, sulfuric acid and acetic acid is suitable. The concentration of the acid component of the aqueous solution containing the acid component is usually 0.001N to
Although it is 0.5 N, strictly speaking, it depends on the type of acid and the weight ratio of the acid component and activated alumina.
After holding 10 g of the adsorbent in 30 ml for 30 minutes, the conditions for adjusting the pH of the water after filtering and separating the adsorbent from the water to 3 to 6 need to be determined by a preliminary experiment. The temperature of the aqueous solution may be about 0 to 100 ° C., the contact time may be about 1 minute or longer, preferably room temperature to 80 ° C., and the contact time may be about 10 minutes to 24 hours.

The BET surface area of activated alumina is 100 m
² / g or more, preferably 200 m ² / g or more. As for the shape of the adsorbent, the smaller the particle size, the faster the adsorption rate, but the liquid resistance increases, so the particle size is about 0.5 to about 10.
mm is suitable.

The equilibrium adsorption amount of arsenate ion of the adsorbent of the present invention is about 2 mg-As / g or more, preferably about 5 mg-As / g or more at an equilibrium concentration of 0.1 mg / l. The packing density is 0.4 to 1.0 kg / l, the compressive strength is usually 2 kg or more, and the pore volume is 0.3 to 1.0 cm ³ / g. To the adsorbent of the present invention, an adsorbent or a filtering agent having another function can be added as long as the arsenic acid purification performance is not reduced.

The adsorbent obtained by the present invention can be applied to purification of raw water such as river, lake or well water and various industrial wastewater. Upon use, the treated water is adsorbed and purified in a fixed bed, moving bed, fluidized bed, batch type or the like. An appropriate SV value for the liquid passage rate is about ¹ to 100 hr ⁻¹ . In the case of a batch method, a contact time of 1 to 100 hours is suitable. When the water to be treated contains arsenite ions, the water to be treated may be previously subjected to an oxidation treatment to be in the form of arsenate ions and then subjected to an adsorption treatment.

[0015]

As described above in detail, according to the present invention, Na ₂
The adsorbent made of spherical activated alumina having an O content of 0.3% by weight or less and a wear rate of 1% or less is brought into contact with water containing arsenate ions to adsorb and remove arsenate ions from the water. A method for removing arsenate ions in water, which is characterized in that activated alumina having a pH value of 3 to 6 when immersed in water at 80 ° C. formed by applying an acid component is treated with arsenic acid. A method for removing arsenate ions in water according to claim 1, which comprises contacting with water containing ions to adsorb and remove arsenate ions from the water. It is an inexpensive and simple method that enables a high degree of arsenate ion adsorption removal effect, and its industrial value is enormous.

[0016]

EXAMPLES Hereinafter, the present invention will be described in more detail with reference to examples, but the scope of the present invention is not limited by these examples. Incidentally, in the present invention, the pH
The following methods were used to measure values, analyze As, and measure wear rate.

PH value: 10 g of a measurement sample was added to 10 g of water at 80 ° C.
Hold in 0 ml for 30 minutes, filter, pH of filtrate after cooling
Was measured with a Horiba Mfg. Model F8, pH meter. As analysis: Measured according to JIS-K0102. Abrasion rate: Measured according to JIS-K1464.

Example 1 [Manufacturing Method of Purifying Agent] Gibbsite (alumina trihydrate) obtained from the Bayer process was put into a hot gas at about 700 ° C. and instantaneously calcined, and 5% of the caustic raw material had an average particle size. A rehydratable alumina consisting mainly of crystalline forms of χ and ρ with a diameter of 15μ was obtained. 1 kg of rehydratable alumina thus obtained
About 0.5 kg of water is added to the above, and the diameter is 1-2 with a plate type granulator.
After being molded into a spherical shape of mm, the molded body was placed in a container with a lid, sealed, and kept at a temperature of 80 ° C. for 16 hours for rehydration. This molded body was placed in an electric furnace, heated to 380 ° C. for 1 hour and held for 3 hours to obtain activated alumina A. The activated alumina compact A has a Na ₂ O content of 0.25%, a packing density of 0.75 kg / l, an abrasion rate of 0.1%, and a pressure resistance of 6 k.
g, BET surface area is 303 m ² / g, pore volume is 0.4
2 cm ³ / g, pH was 9.8.

Next, 1.2 kg of a molded body of activated alumina A
Was impregnated in 4.3 liters of a 0.3% hydrochloric acid solution for 16 hours, washed with water, filtered, placed in an electric furnace and kept at 250 ° C. for 4 hours to obtain activated alumina B. Activated alumina compact B
Content of Na ₂ O is 0.06%, the packing density is 0.76k
g / l, wear rate 0.1%, compressive strength 4 kg, BE
T surface area is 312 m ² / g, pore volume is 0.38 cm ³
/ G, pH was 4.0.

[Removal test] A 2.4 mg / l As ₂ Na ₂ HAsO ₄ aqueous solution was prepared and used as a sample to be treated. 0.5 liter of this solution was placed in an Erlenmeyer flask, and about 0.2 g of the molded body obtained in the above Example was added as an adsorbent, and the mixture was stirred by a shaker at 30 ° C. for 7 days for adsorption treatment. As a result of examining the As concentration in the liquid after the treatment, the activated aluminas A and B were both below the detection limit (0.005 mg / l).

Claims (3)

[Claims] 1. A Na ₂ O content of 0.3% by weight or less,
A method for removing arsenate ions, which comprises contacting an adsorbent made of spherical activated alumina having a wear rate of 1% or less with water containing arsenate ions to remove the arsenate ions from the water. 2. The adsorbent is spherical activated alumina having a Na ₂ O content of 0.3% by weight or less and a wear rate of 1% or less,
The method for removing arsenate ions according to claim 1, wherein an acid component having a pH of water of 3 to 6 when immersed in water at 80 ° C. is deposited. 3. The method for removing arsenate ions according to claim 2, wherein the acid component is at least one of hydrochloric acid, hydrofluoric acid, nitric acid, sulfuric acid and acetic acid.