JP3291994B2 - How to remove arsenate ions - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] 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 industrial wastewater, domestic wastewater, industrial water, tap water, etc. containing arsenate ions.

[0002]

2. Description of the Related Art In recent years, coagulation sedimentation method, lime softening method, adsorption method, bioconcentration method, reverse method have been developed to reduce arsenic concentration from purified water or wastewater containing various chemical forms of arsenate ions to a high degree. Various methods such as an infiltration method have been studied. Of 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. As the adsorbent used in the adsorption method, activated carbon, activated alumina, magnesia, magnesia-modified slag, titania-modified activated carbon,
Anion exchange resins, red mud granules, etc. are known,
Activated alumina has been applied as an inexpensive and safe adsorbent.

[0003] Examples of the use of activated alumina for adsorption of arsenic acid are described in Environmental Progress, Vol. 6, No. 3, No. 150
There is a paper by MMGhosh and JRYuan on the page. In this paper, the content of Na ₂ O is 0.9% by weight, the BET surface area is 218 m ² / g and the particle size is 28 to 48.
The column was filled with the crushed activated alumina mass of the mesh, and water containing a low concentration of arsenate was passed through the column,
A method for adsorbing and removing arsenic acid is disclosed.

[0004]

However, when crushed activated alumina is directly packed in a column as an adsorbent and used, the water after passing the water becomes cloudy. Must be removed, which not only complicates the operation but also requires the treatment of cloudy washing water. In addition, a method of controlling the pH of water to be treated when activated alumina alone is insufficient as an adsorbent when the adsorbing capacity is insufficient is taught, but in this case, the cost of water treatment increases. On the other hand, the use of adsorbents other than activated alumina is also introduced, but the price, handleability, and treatment effect can be satisfied as an adsorbent, such as being expensive or leaking undesirable components from the adsorbent itself. Things have not yet been seen. Under these circumstances, the present inventors have conducted intensive studies for the purpose of finding a simple, inexpensive, and efficient method for removing arsenate ions from water, and as a result, have completed the present invention.

[0005]

SUMMARY OF THE INVENTION The first aspect of the present invention is that Na ₂
An adsorbent composed 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. And a method for removing arsenate ions in water. Also, a second aspect of the present invention is to apply an acid component,
2. The method according to claim 1, wherein the activated alumina has a pH of 3 to 6 when immersed in water at 0 ° C., and the activated alumina is brought into contact with water containing arsenate to adsorb and remove arsenate from the water. It is another object of the present invention to provide a method for removing arsenate ions in water.

[0006]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, the present invention will be described in detail.
In carrying out the method of the present invention, the adsorbent used for the adsorption of 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. Less than 1% by weight and wear rate which is an index of powdering resistance
In the following, it is essential that the spherical activated alumina is preferably about 0.8% or less. If the wear rate exceeds about 1%,
In addition, a lump having a powdery or crushed shape is not preferred because water after the adsorption treatment becomes turbid and a filter, that is, a powder is easily generated. In addition, N in activated alumina
When the amount of a ₂ O (total soda) exceeds about 0.3% by weight, the pH of water around the activated alumina increases, and adsorption of arsenate ions is inhibited.

As the adsorbent for arsenate ion contained in water, the use of the above-mentioned spherical activated alumina having a low Na ₂ O content and excellent powdering resistance can provide a considerably excellent effect. As a method for imparting an excellent adsorption effect of arsenate ions, a specific amount of an acid component, that is, “10 g of an adsorbent after acid treatment in 100 ml of water at 80 ° C. is retained for 30 minutes, When the adsorbent is filtered and separated from the water, a removal method in which spherical activated alumina formed by applying and impregnating an amount that gives a pH value of the water of 3 to 6 "is recommended. In the method, when the amount of the acid component to be applied and impregnated is large and the pH of the treated water by the above treatment is less than 3, the adsorption effect of arsenic acid is reduced and the water neutralizing treatment agent after the treatment is used. It is not preferable because a large amount is required. 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 acidic coating treatment is not performed.

[0008] The activated alumina referred to in the present invention may be any known one usually called in the art, and refers to an aluminum oxide (transition alumina) other than so-called α-alumina. In the method of the present invention, a method for producing a spherical activated alumina having a wear rate of 1% or less is not particularly limited, but a method via a rehydratable alumina is recommended because an adsorbent having a large BET surface area and strength is easily obtained. You. That is, aluminum hydroxide such as gibbsite is calcined in a hot air stream at 500 to 1200 ° C. for 0.1 second to several minutes, and then separated.
By cooling, an activated alumina powder having rehydration property (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 body is then kept 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 body itself. Rehydrated. Rehydration is generally 1
It takes between a minute and a week. The rehydrated molded body is subsequently fired to remove adhering water and water of crystallization in the molded body. The firing temperature is usually 300 to 900 ° C, preferably 300 to 500 ° C.
° C, and the firing time is from about 10 minutes to about 100 hours.
All Na ₂ O contained in the spherical activated alumina to 0.3% by weight may be any known method, the full Na ₂ O content as aluminum hydroxide as a raw material in a particularly simple but are not limited What is less than 0.3% by weight, more preferably 0.1% by weight may be used. However, in the case of performing the treatment of adhering and impregnating the spherical activated alumina with the acid component, the total Na ₂ O content in the raw material aluminum hydroxide may be high, and the content in the spherical activated alumina after the acid treatment may be high. It is sufficient that the total Na ₂ O content to be obtained is not more than 0.3% by weight.

The acid component is deposited on the activated alumina by holding the activated alumina after the acid component deposition in 10 ml of water at 80 ° C. for 30 minutes and then filtering and separating the adsorbent from the water. The 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) a spherical activated alumina having a wear rate of 1% or less is used as an acid component. In contact with an aqueous solution containing
(2) contacting and forming the rehydratable alumina powder with an aqueous solution;
After aging to give the molded body strength, an aqueous solution containing an acid component is brought into contact with the molded body, followed by baking to obtain a molded body.

As a method of contacting the activated alumina with an aqueous solution containing an acidic component, there are a method of impregnating the aqueous solution with the activated alumina, and a method of supplying and absorbing an aqueous solution corresponding to the water absorption of the activated alumina. After contact with the acid component, washing with water, filtration, drying or baking may be performed. After washing with water and filtration, N in activated alumina
This is advantageous because a ₂ O is reduced. In the case of the production method (1), the wet state may be used by filling the adsorption apparatus.

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 in the aqueous solution containing the acid component is usually from 0.001 N to
Although it is 0.5N, it depends strictly on the kind of acid and the weight ratio of acid component to 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 must be determined by preliminary experiments. The temperature of the aqueous solution is about 0 to 100 ° C, the contact time is about 1 minute or more, preferably room temperature to 80 ° C, and the contact time is about 10 minutes to 24 hours.

The activated alumina has a BET surface area of 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 speed, but the flow resistance increases, so the particle size is about 0.5 to about 10
mm is appropriate.

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 pressure resistance 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 the purification of raw material water such as rivers, lakes or well waters, various industrial wastewaters and the like. In use, adsorption and purification of the water to be treated is performed in a fixed bed, a moving bed, a fluidized bed, a batch system or the like. The flow rate is suitably about ¹ to 100 hr ^{-1 as an} SV value. In the case of a batch type, a contact time of 1 to 100 hours is appropriate. When the water to be treated contains arsenite ions, the water to be treated may be oxidized in advance to form arsenate ions and then subjected to the adsorption treatment.

[0015]

As described above in detail, the present invention, Na ₂
Contacting an 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 with water containing arsenate ions to adsorb and remove arsenate ions from the water. A method for removing arsenate ions in water, in particular, activated alumina having a pH value of 3 to 6 when immersed in water at 80 ° C., which is formed by adhering an acid component, 2. A method for removing arsenate ions in water according to claim 1, wherein the method comprises contacting with water containing ions to adsorb and remove arsenate ions from the water. It is a low-cost and simple method that enables a high arsenate ion adsorption and removal effect, and its industrial value is extremely large.

[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 measurement of the value, the analysis of As, and the measurement of the wear rate were carried out by the following methods.

PH value: 10 g of a measurement sample was added to water 10 at 80 ° C.
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.

Example 1 [Preparation method of purifying agent] Gibbsite (alumina trihydrate) obtained from the buyer process was charged into a hot gas at about 700 ° C. and calcined instantaneously. A rehydratable alumina having a diameter of 15 μ and mainly consisting of crystal forms of χ and ρ was obtained. 1 kg of the rehydratable alumina thus obtained
About 0.5 kg of water, and the diameter is 1-2 with a dish-type granulator.
After forming into a spherical shape of mm, the molded body was put 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 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, a wear 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.

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

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

──────────────────────────────────────────────────続 き Continued on the front page (58) Field surveyed (Int.Cl. ⁷ , DB name) B01J 20/08 C02F 1/28

Claims (3)

(57) [Claims] 1. The method according to claim 1, wherein the content of Na ₂ O is 0.3% by weight or less,
A method for removing arsenate ions, comprising contacting an adsorbent made of spherical activated alumina having a wear rate of 1% or less with water containing arsenate ions to remove arsenate ions from the water. 2. The method according to claim 1, wherein the adsorbent is a spherical activated alumina having a Na ₂ O content of 0.3% by weight or less and a wear rate of 1% or less.
2. The method for removing arsenate ions according to claim 1, wherein an acid component having a pH of 3 to 6 when immersed in water at 80 [deg.] C. is applied. 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.