JP3079257B2 - Arsenic ion adsorption removal method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to an aqueous solution such as tap water,
The present invention relates to a method for easily removing arsenic ions contained in environmental river water, plating waste liquid, and metal surface treatment liquid water. More specifically, the present invention relates to a novel method for efficiently adsorbing and removing arsenic ions contained in an aqueous solution using a porous material in which a hydrated zirconium oxide is supported in pores.

[0002]

2. Description of the Related Art In recent years, removal of arsenic ions from industrial wastewater, environmental water or tap water has become an important issue due to problems such as environmental pollution. Accordingly, tap water quality standards (0.
01 ppm), water supply environment standards (0.01 ppm), and wastewater standards (0.1 ppm) are successively strengthened, and effective treatment techniques for trace amounts of arsenic ion-containing water are required. In the treatment of arsenic ions, iron salts and aluminum salts are added and then alkalized to make the water insoluble iron hydroxide,
Alternatively, aluminum hydroxide is generated and coagulated and precipitated to change to a hardly soluble substance together with arsenic ions.
It is inevitable that dilute arsenic ions remain in the solution due to the limitation of the solubility product. Therefore, there is a need for more efficient higher-order processing after the primary processing.

[0003] Since arsenic takes the form of an oxoanion species in an aqueous solution, anion exchange resins have been used as one of the higher-order processing techniques, but problems remain in selectivity. In addition, hydrated oxides of cerium (Imai, Journal of the Chemical Society of Japan, 80
7, 1987) or activated alumina (USPa)
t, US Pat. No. 4,824,576 A, 890425, p. 22)
Has been reported to be promising as a selective adsorbent for arsenic ions. However, since these hydrated metal oxides are fine powder, there is a problem in handling when performing operations of adsorption, elution, and regeneration. Of these, in the case of cerium,
Since there is a change in the oxidation number of +3 and +4, there is a problem that the oxidation number is easily affected and deteriorated. In addition, arsenic and phosphorus adsorption resins in which zirconium is supported on a chelate resin by complex formation are commercially available, but there is a problem that zirconium is easily desorbed from the resin in a regeneration process using an acid or an alkali.

[0004]

SUMMARY OF THE INVENTION The present invention overcomes the drawbacks of the conventional arsenic ion adsorbent and selectively and efficiently removes arsenic ions contained in industrial wastewater or tap water to the porous adsorbent. It is an object of the present invention to provide a method for adsorbing and removing the same with good reproducibility. That is, after the hydrous zirconium oxide is dispersed and supported on the surface of the porous material, it is heated and crystallized to have the arsenic ion adsorption ability, and at the same time, the arsenic is converted to a crystalline form in which zirconium is hardly desorbed. It is intended to provide a method for adsorption removal.

[0005]

Means for Solving the Problems The present inventors have conducted various studies in order to develop a method capable of efficiently removing arsenic ions contained in water or the like by a simple column operation and using the same repeatedly. As a result, after dispersing and supporting the hydrated zirconium oxide on the inner surface of the pores of the porous material,
By heating and using an adsorbent that has crystallized hydrous zirconium oxide, arsenic ions contained in the aqueous solution can be selectively removed.
It can be efficiently adsorbed and removed, and this adsorbent can elute adsorbed arsenic ions only by washing with alkali, and can be regenerated by washing with a buffer solution of pH 2 to 6 and water and used repeatedly. And completed the present invention based on this finding.

That is, the present invention provides a compound represented by the general formula MO ₂ .nH ₂
After supporting a hydrated oxide of zirconium represented by O (M in the formula, M is zirconium, n is an integer of 1 to 6) on a porous material such as beads of a porous polymer or activated carbon in a highly dispersed manner,
It is an object of the present invention to provide a method for removing arsenic ions, wherein arsenic ions are selectively adsorbed by an adsorbent material crystallized by a heat treatment.

The adsorbent used in the present invention is such that after impregnating a porous material with ZrOX ₂ (X = Cl, Br, NO ₃ ) or zirconium alkoxide, the reagent is hydrolyzed with an alkali and the surface of the porous material is zirconium. Can be produced by supporting a hydrated oxide. Although there is no particular limitation on the base material of the adsorbent, for example, a porous body, a porous cation exchange resin, an anion exchange resin, a polystyrene foam obtained by mixing and forming an easily soluble filler in a material, and eluted therefrom, Foams such as polyurethane foams, polyethylene foams, polyvinyl chloride foams, polypropylene foams, and phenolic resin foams, activated carbon, and the like are preferable, and cross-linked polyacrylates and cross-linked polystyrenes are particularly preferable. The porous material has a specific surface area of 50 to 800 m ² / g, an average pore diameter of 10 to 100 °,
Those having a particle size in the range of 20 to 200 mesh are preferably used.

In the impregnation of a porous material with a zirconium compound, a zirconium compound represented by the general formula ZrOX ₂ (X = Cl, Br, NO ₃ ) is dissolved in a suitable solvent, and this solution is mixed with a preferably dried porous material. After that, the solvent is removed by distillation. The solvent used at this time includes methanol, ethanol, and water. The impregnation of the porous material with the zirconium alkoxide is performed by dissolving the zirconium alkoxide represented by the general formula M (OR) ₄ (wherein M represents zirconium and R represents a lower alkyl group) in a suitable organic solvent. After the solution is mixed with a preferably dried porous material, the solvent is distilled off.
As the alkyl group of the zirconium alkoxide used at this time, lower alkyl groups methyl, ethyl,
Preferred are n-propyl, isopropyl, n-butyl, isobutyl, tert-butyl and the like. In addition, as a solvent used at this time, for example, benzene, acetone,
Examples thereof include those having a low boiling point such as ethanol.

Next, the zirconium compound ZrOX ₂ or zirconium alkoxide thus supported on the porous material is treated with water, an aqueous medium, etc.
It hydrolyzes ZrOX ₂ and zirconium alkoxide impregnated in the pores of the porous material. As a result, hydrous zirconium oxide is formed, and the hydrous zirconium oxide is supported on the porous material. The pH at this time is not particularly limited.
Alkaline aqueous solutions of 1 to 14 are preferably used. The hydrous zirconium oxide supported as described above is crystallized by hydrothermal treatment and is stably immobilized in the resin. The hydrothermal treatment temperature is preferably from 100C to 180C. The heat treatment time is 5 hours or more, preferably 12 to 20 hours. By such a hydrothermal treatment, the hydrous zirconium oxide crystallizes and is firmly supported by the resin, making it difficult to be desorbed. In the hydrothermal treatment, monoclinic crystals are obtained when an aqueous solution having a pH of 1 to 4 is used, and cubic hydrous zirconium oxide is obtained when an aqueous solution of 0.1 to 5 mol is used.

In the present invention, for the adsorption of arsenic ions by the adsorbent, for example, a column method or a batch method can be used, but a column method which is simple in operation and excellent in processing capacity is advantageous. The pH of the arsenic ion-containing aqueous solution passed through the column is usually selected in the range of 2.0 to 10.0.
If the pH is less than 2.0 and 10.0 or more, the arsenic ion adsorption amount tends to be significantly reduced. Arsenic contains trivalent (As (II
I)) and pentavalent (As (V)) exist.
s (III) is in the range of pH 7 to 10, and As (V) is in the range of pH 3 to 8.
Is the best. In addition, the speed at the time of passing the liquid depends on the concentration of arsenic ions in the liquid to be treated, but usually the superficial velocity is 5%.
It is selected in the range of ２０20 h ⁻¹ .

After the arsenic ions in the liquid to be treated are adsorbed and removed in this way, in the present invention, the alkaline solution is passed through the adsorbent to which the arsenic ions have been adsorbed, so that As ( III) and As (V) are eluted quantitatively. This elution occurs due to ion exchange between arsenic ions on the bound metal ions and OH ⁻ in the alkaline aqueous solution.Therefore, for the type of alkaline aqueous solution to be passed, if OH ⁻ is contained, Well, there is no particular limitation, but usually sodium hydroxide aqueous solution,
An aqueous solution of potassium hydroxide, aqueous ammonia or the like is preferably used. Further, regarding the concentration of the alkaline aqueous solution,
The range in which arsenic ion elution quantitatively occurs is 0.1 to
3 moles are preferred. If this concentration is less than 0.1 molar, OH
^It is difficult to elute all the arsenic ions because the concentration of-is too low. On the other hand, if it exceeds 3 mol, problems may occur in terms of alkali solubility and handling of alkaline aqueous solution, which is not preferable. Even when the alkaline aqueous solution having a concentration of 0.1 to 3 mol is passed, no desorption of the bound zirconium is recognized. Therefore, in the regeneration of the resin to which arsenic ions are adsorbed, the alkaline aqueous solution is passed. This makes it possible to elute only arsenic ions without desorbing zirconium from the adsorbent. The flow rate of the alkaline aqueous solution is usually selected in the range of a superficial velocity of 5 to 20 h ^-1 .

In order to use the adsorbent after passing the alkaline aqueous solution again for adsorption and removal of arsenic ions, the resin is conditioned with a weakly acidic buffer to return the hydroxide ions exchanged for arsenic ions to the acid form. There is a need to. In addition,
The liquid passing speed at this time is usually selected in the range of a superficial superficial speed of 5 to 20 h ^-1 . The buffer used for conditioning the resin is not particularly limited, except for the phosphoric acid type, as long as it has a pH of 2 to 6, and acetic acid-sodium acetate, phthalic acid, citric acid and the like are preferably used. The concentration is
0.1 to 2 mol is preferred. If the pH is 2.0 or more, no metal is eluted during conditioning, and the conditioned adsorbent can be used again after washing with water, and no decrease in arsenic ion adsorption capacity is observed.

In addition, this adsorbent can remove other anions, such as Cl ⁻ , NO ₃ ⁻ , S, in the adsorption removal of arsenic ions.
Even under the condition that O ₄ ^{2- and the} like coexist in an amount of 100 times or more as large as arsenic ion, it is hardly affected by the influence, and the selective adsorption of arsenic ion is extremely excellent.

[0014]

Next, the present invention will be described in more detail by way of examples.

[0015] ZrOCl ₂ · 8H ₂ O in Production Example 1 44 g of (0.13 mol), 2
The crosslinked polyacrylic acid resin beads (50 to 50 ml) dissolved in 50 ml of methanol and washed and dried in advance
After adding 35 g of 100 mesh and a specific surface area of 390 m ² g ^-1 ), the mixture was placed under reduced pressure for 30 minutes, and then methanol was removed by distillation under reduced pressure to obtain dry resin beads. This was transferred to a beaker, 150 ml of 10% aqueous ammonia was added, and the mixture was stirred for 30 minutes. 2-3 supernatant
After removal by repeated decantation, 100 ml of water is added, and the pH is adjusted to 2.0 with hydrochloric acid. The resin and the aqueous solution were transferred to a pressure-resistant reactor (autoclave) and heated at 150 ° C. for 15 hours. Next, the resin beads were filtered, washed sequentially with water and ethanol, and vacuum dried at 50 ° C. to obtain 48 g of a resin. In the X-ray diffraction of the obtained resin, monoclinic Zr
A clear crystal peak of O ₂ was observed.

Production Example 2 120 g of tetra (n-butoxy) zirconium was added to 300
The crosslinked polyacrylic acid resin beads (50 to 1) which were dissolved in
After adding 110 g of 00 mesh and a specific surface area of 390 m ² g ^-1 ), the mixture was placed under reduced pressure for about 1 hour, and then benzene was removed by distillation under reduced pressure to obtain dry resin beads. Transfer this to a beaker and add 500 ml of pH 2.0 water
Was added, and the mixture was allowed to stand for 2 hours. Thereafter, the supernatant was discarded, and 500 ml of water having a pH of 2.0 was again added thereto, followed by heating under reflux for 24 hours. Next, the resin beads were filtered, washed sequentially with water, ethanol and ether, and dried in vacuum at 50 ° C.
0 g of the desired product was obtained. This had a zirconium content of 1.7 mmol g ^-1 and a specific surface area of 280 m ² g ^-1 . In this case, the X-ray diffraction has no clear peak,
The hydrated oxide is assumed to be an amorphous gel. However, by boiling for a long time in a hot aqueous solution, the supported hydrous zirconium oxide crystallized.

Example 1 2 g (wet volume: 5.8 ml) of the adsorbent obtained in Production Example 1 was packed in a column having an inner diameter of 1 cm, and an aqueous solution having a pH of 5.0 containing 10 ppm of arsenic ion (As (V)) was added to a column. .5ml
The solution was passed at min ^-1 and the arsenic concentration after passing through the resin tower was measured. As a result, the arsenic concentration was 0.1 ppm or less at the passage point of 1000 times the resin volume. As in column effluent
The elution concentration of (V) is shown in FIG.

Example 2 2 g (wet volume: 5.8 ml) of the adsorbent obtained in Production Example 1 was packed in a column having an inner diameter of 1 cm, and arsenic ions (As (III))
0.5 ml of an aqueous solution of pH 8.0 containing 10 ppm of
The solution was passed at min ^-1 and the arsenic concentration after passing through the resin tower was measured. As a result, the arsenic concentration was 0.1 ppm or less at the passage point of 400 times the resin volume. As (I in the column effluent
FIG. 2 shows the elution concentration of II).

Example 3 Arsenic ions were eluted by passing 120 ml of a 2 molar aqueous sodium hydroxide solution at 2 ml min ^-1 through the column to which arsenic ions were adsorbed in Example 1. The aqueous solution after passing through the column contained 99% of the arsenic ions adsorbed in Example 1, and no zirconium was detected.

Example 4 Next, a 0.2 mol acetic acid-sodium acetate solution (pH 4.
0) was passed until the pH of the leaked liquid reached 4.0, and further the column was washed with water. Then, an arsenic ion solution having the same composition as in Example 1 was passed. It was measured. As a result, the column showed almost the same adsorption capacity as in Example 1.

REFERENCE EXAMPLE 1 g of an adsorbent is added to 100 ml of an aqueous solution containing 0.02 mol of arsenic ions at a predetermined pH, shaken at room temperature for 24 hours, and then the concentration of arsenic ions remaining in the solution is measured. Then, the relationship between the amount of arsenic ions adsorbed per 1 g of the adsorbent and the pH was determined. The results are shown graphically in FIG.

[0022]

As described above, the arsenic ion adsorbent used in the method of the present invention has a porous property, and the arsenic ion is rapidly diffused into the adsorbent, so that very quick adsorption is achieved. Further, this adsorbent reduces the amount of arsenic ions adsorbed by one.
There is an advantage that it can be quantitatively eluted by treating with about 3 mol of an alkaline aqueous solution or the like, and can be used again with good reproducibility after conditioning and washing with water. Also, in this adsorbent, the hydrated oxide of the supported zirconium has extremely low solubility in acids and alkalis, so the dissolution of metal during elution of arsenic ions and regeneration of the adsorbent is negligibly small, From this point, it can be used with good reproducibility.

Accordingly, the method of the present invention can efficiently and repeatedly adsorb and remove arsenic ions contained in industrial wastewater and the like with extremely simple operation and low treatment cost, and can be said to be a method of extremely high industrial value.

[Brief description of the drawings]

BRIEF DESCRIPTION OF DRAWINGS FIG. 1 is a graph showing the relationship between the volume of a column eluate and the concentration of As (V) ions in a column eluate when As (V) is adsorbed using the adsorbent according to the present invention as a column stationary phase. Show.

FIG. 2 shows the column eluate volume and the concentration of As (III) ions in the column eluate when As (III) was adsorbed using the adsorbent according to the present invention as a column stationary phase. Show.

FIG. 3 is an explanatory diagram showing the relationship between arsenic ion adsorption capacity and pH of the adsorbent used in the present invention.

[Explanation of symbols]

The horizontal axis represents the pH of the solution, and the vertical axis represents the amount of arsenic ion adsorbed (mmol of arsenic ion adsorbed per gram of adsorbent). In the figure, white circles indicate the adsorption capacity of As (III) ions, and black circles indicate the adsorption capacity of As (V) ions.

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-10-165948 (JP, A) JP-A-5-68969 (JP, A) JP-A-2-191543 (JP, A) JP-A-61- 187931 (JP, A) JP-A-58-34039 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) B01D 15/00 B01J 20/06 B01J 20/28-20/34 C02F 1/28 C02F 1/62

Claims (2)

(57) [Claims] An arsenic ion-containing solution is represented by the general formula MO _2.
nH ₂ O (wherein M represents zirconium, n is 1 to 6)
By contacting the zirconium hydrate crystal represented by the formula (1) with an adsorbent material having 5 to 60% by weight supported on the porous material surface, thereby adsorbing the arsenic ion.
The adsorbed ions are eluted with a 0.1 to 3 molar aqueous alkali solution,
A method for adsorbing and removing arsenic ions in an aqueous solution, further comprising regenerating the adsorbent with a buffer having a pH of 2 to 6 and water. 2. The pH of the arsenic ion-containing aqueous solution is 2 to 10.
2. The method of claim 1, wherein