JP2005288363A - Arsenic adsorbent and production method therefor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To obtain an adsorbent with a drastic improvement in performance of adsorbing arsenic as compared with those of conventional adsorbents, with which water contaminated with arsenic can be purified in large quantities at high speed, treated water containing low-concentration arsenic can be efficiently purified, adsorption activity can be retained for a long period of time so as to enable easy maintenance, and in addition, neither adsorbent nor resin components are eluted. <P>SOLUTION: The arsenic adsorbent comprises a rare earth element hydroxide and a high-molecular resin which coats the surface of the hydroxide, wherein the rare earth element hydroxide has a central void and micropores surrounding the central void and the high-molecular resin, which coats the surface of the hydroxide, constitutes a porous skin layer. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to an arsenic adsorbent comprising a rare earth element hydroxide and a polymer resin that can be used as an adsorbent for arsenic in water, a method for producing the same, and a use thereof.

  Water quality deterioration in lakes, rivers, and groundwater due to natural conditions and wastewater from factory wastewater, especially soil and water pollution by harmful heavy metal compounds are recognized. Among the heavy metal compounds, arsenic is particularly problematic. Of the causative substances of soil contamination, arsenic is eluted due to wind and rain and infiltration of groundwater, and there is a concern that it may cause secondary environmental water pollution. In particular, underground arsenic tends to elute as pentavalent arsenate ions or trivalent arsenite ions, and is reported by the Environment Agency “FY 2002 groundwater quality measurement results” (Ministry of the Environment, Environment Management Bureau, Water Environment Department) According to the Soil Environment Division Groundwater / Ground Environment Office November 27, 2003), 1.5% of the 5,269 wells surveyed had arsenic concentrations of 0.01 mg / l ) And the transcendence rate is far higher than other pollutants. Arsenic is carcinogenic and can cause chronic poisoning if taken for a long time. In nature, arsenic may be detected in hot spring water and mine runoff water, or may be detected constantly in groundwater and spring water above the water quality standard value. The water quality standards are set to 0.025 mg / l or less by the Canadian Insurance and Welfare Agency, and the US Environmental Protection Agency plans to reduce 0.050 mg / l or less to 0.01 mg / l or less. According to the water quality standard value in the domestic water supply law, the arsenic concentration is 0.01 mg / l or less. When the arsenic concentration in water exceeds this value, it is necessary to remove arsenic from the water.

  Conventional methods for removing arsenic in water include a coagulation precipitation method (coprecipitation method) and an adsorption method. In the coagulation precipitation method (coprecipitation method), inorganic flocculants such as aluminum salts and iron salts are added and the pH is adjusted to neutral to form coagulation flocks of metal hydroxides. Etc. are removed. Turbidity, heavy metal ions, etc. are precipitated with this floc. At this time, arsenic is also taken into the aggregated floc and precipitates. The precipitate is removed by gravity separation or the like.

  As a method for removing arsenic, a commonly used coagulation method (coprecipitation method) has a large turbid mass because an inorganic coagulant such as an aluminum salt or an iron salt is added according to the turbid mass of the water to be treated. In some cases, it requires administration of large amounts of flocculant. Furthermore, there is a disadvantage that it takes a long time to remove the flocculation flocs that have taken in arsenic in the sedimentation basin or sedimentation tank, and the installation area of the sedimentation basin or sedimentation tank is large depending on the aggregation capacity. There are drawbacks to the complexity of operation. A polymer flocculant prepared separately may be added for the purpose of accelerating the sedimentation. However, the adjustment of the inorganic flocculant and the polymer flocculant makes the bulk of arsenic contained more than the turbid mass of the water to be treated. The amount of sludge is generated, and there is a drawback that more complicated work is required for the treatment. In addition, trivalent arsenous acid cannot be directly taken in by the coagulation precipitation method (coprecipitation method), so an oxidizing agent such as sodium hypochlorite must be added as a pretreatment to change the form to pentavalent arsenic acid. There are disadvantages that cannot be captured.

  Patent Document 1 (Japanese Patent Laid-Open No. 8-206663) discloses a treatment method for separating agglomerated flocs composed of metal hydroxide and arsenic produced by a coprecipitation method by adding a flocculant with an ultrafiltration membrane or a microfiltration membrane. Has been described. Although this method can reduce the installation area of the treatment facility, the amount of flocculant input is the same as that of the conventional coagulation sedimentation method, and it limits turbidity and sludge that contains a large amount of coagulation floc composed of metal hydroxide and arsenic. Since filtration is performed with an outer filtration membrane or a microfiltration membrane, there is a drawback that frequent washing of the filtration membrane is required. In addition, there is a drawback that more complicated work is required for processing a large amount of sludge containing arsenic. Furthermore, since the arsenic removal treatment method of the invention described in this Japanese Patent Laid-Open Publication uses a large amount of an aggregating agent, the agglomerated floc pH shifts to the acidic side, and the agglomerated floc partially hydrolyzes to remove the precious arsenic. There is also a drawback that the arsenic concentration of the filtered water cannot be reduced because it is released and easily passes through the ultrafiltration membrane or the microfiltration membrane.

  As the adsorption method, generally used is a method in which water to be treated containing arsenic is brought into contact with an adsorbent and removed by adsorbing arsenic. For adsorbents, natural soil, transition metal compounds such as activated carbon, activated alumina, manganese dioxide, titanic acid, zirconium hydrate, lanthanum, yttrium and cerium are used in the form of granules having a diameter of 1.0 to 2.0 mm. It is mentioned that.

  In the adsorption method, use of activated alumina, activated carbon, or transition metal compounds such as titanic acid, zirconium hydrate, lanthanum, yttrium, cerium, etc. In particular, there is a drawback that the frequency of exchanging and regenerating the adsorbent increases.

Among the adsorbents used in the past, activated alumina, in particular, is an adsorbent that has the property that the residual arsenic in the wastewater increases almost in proportion to the amount of water passing, and the arsenic leak is compared after the start of the adsorption process. There was a drawback that the frequency of adsorbent replacement or regeneration maintenance was complicated.
In addition, considering the arsenic adsorption rate of the adsorbent, it is necessary to increase the contact time with the water to be treated as much as possible, and a special column or adsorption tank is required, so that the arsenic treatment efficiency cannot be increased. .

  In view of such circumstances, the invention described in Patent Document 2 (Japanese Patent Laid-Open No. 2000-70923) is provided downstream of the adsorption tower in order to neutralize the weakly acidic treatment liquid in order to quickly and efficiently remove arsenic in the treated water. In order to capture the adsorbent and the adsorbent debris, a arsenic removing device is provided, which is provided downstream of the neutralizer and captures the adsorbent and adsorbent fragments. However, the adsorbent used has a weak adsorbing ability, so that it has a drawback that it is difficult to say that the objective has been sufficiently achieved.

  Rare earth-based adsorbents such as lanthanum, which are said to have a high adsorption amount, are affected by the arsenic concentration in the water, and when the arsenic concentration falls below 1.0 mg / l, the equilibrium adsorption amount suddenly increases. There was a drawback that it decreased. In addition, activated alumina and activated carbon have a drawback that the equilibrium adsorption amount is lower than that of a rare earth-based adsorbent such as lanthanum.

  The invention described in Patent Document 3 (Japanese Patent Application Laid-Open No. 2000-24647) uses an arsenic material characterized by using, as an adsorbent, an alumina support carrying 5 to 60% by weight of a rare earth metal oxide or hydroxide. Although an adsorption removal method has been proposed, the adsorption capability of the adsorbent is weak, and there is a drawback that it is difficult to say that the purpose has been sufficiently achieved.

The invention described in Patent Document 4 (Japanese Patent Publication No. 4-45213) uses arsenic adsorption characterized in that an organic polymer carrier carrying 5 to 50% by weight of a rare earth metal hydrated oxide is used as an adsorbent. However, since the hydrophilic polymer is used for the organic polymer carrier, the hydrophilic resin is eluted at the initial water flow. In the examples, it is assumed that the superficial velocity at the time of passing water is about 10 l / hr. However, if the superficial velocity is increased more than this, water does not sufficiently permeate the adsorbent, resulting in an adsorbed amount. There was a drawback of lowering.
In addition to the adsorbent described in Patent Document 4, in the type of adsorbent that uses a hydrophilic resin, an extra washing step of the adsorbent for removing low-molecular components in the resin, which is the initial elution, is provided. Furthermore, in order to use for beverages, there was a drawback that a final treatment with activated carbon was required in addition to a treatment with an arsenic adsorbent during actual use.

JP-A-8-206663 JP 2000-70923 A JP 2000-24647 A Japanese Examined Patent Publication No. 4-45213

  Under such circumstances, an object of the present invention is to provide an adsorbent in which the adsorption performance of arsenic is significantly improved as compared with conventional adsorbents. In other words, it is possible to purify a large amount of water contaminated with arsenic at a high speed, and also to treat treated water containing low-concentration arsenic efficiently, and to maintain the adsorption activity for a long time. The object of the present invention is to provide an arsenic adsorbent that is easy to maintain since it can be retained, and that does not elute the adsorbent and resin components.

  As a result of diligent research, the present inventors have used rare earth element hydroxide as an arsenic adsorbent component, which is covered with a thin layer of a polymer resin, that is, a skin layer, and has a large amount of voids inside the skin layer. The inventors have found that a structure containing a large amount of element hydroxide brings about a remarkable adsorption ability, and has led to the present invention.

That is, the present invention relates to the following (1) to (10).
(1) An arsenic adsorbent comprising a rare earth element hydroxide and a polymer resin covering the surface thereof, wherein the rare earth element hydroxide has a central cavity and a surrounding fine void, and the rare earth element An arsenic adsorbent characterized in that the polymer resin covering the hydroxide surface is a porous skin layer having water resistance;
(2) The arsenic adsorbent according to (1), wherein the polymer resin is a resin selected from a fluorine resin and an acetalized polyvinyl alcohol resin,
(3) The arsenic adsorbent according to (1) or (2), wherein the rare earth element hydroxide has an average secondary particle diameter of 1 to 6 μm,
(4) Arsenic adsorption according to any one of (1) to (3), wherein the rare earth element hydroxide contains 1 to 10 parts by weight of nitrates per 100 parts by weight of the hydroxide. Agent.
(5) The arsenic adsorbent according to any one of (1) to (4), wherein the rare earth element hydroxide contains 1 to 30 parts by weight of water per 100 parts by weight of the hydroxide. ,
(6) The arsenic adsorbent according to any one of (1) to (5), comprising the polymer resin and 600 parts by weight or more of the rare earth element hydroxide per 100 parts by weight of the polymer resin. ,

(7) A rare earth element hydroxide containing 5 to 30 parts by weight of water is obtained by drying a mixture of the rare earth element hydroxide and water at a low temperature of 100 ° C. or lower, and the hydroxide is then water-resistant. A method for producing an arsenic adsorbent, characterized by being dispersed in a liquid dissolved in an organic solvent that dissolves the resin together with a functional polymer resin, and granulating from the dispersion;
(8) The production of the arsenic adsorbent according to (7), wherein the rare earth element hydroxide has an average secondary particle size of 0.2 to 25 µm and the average particle diameter of the arsenic adsorbent is 0.2 to 2.0 mm. Method,
(9) A method for adsorbing and removing arsenic by bringing water to be treated containing arsenic into contact with the arsenic adsorbent described in (1) to (6) above,
(10) The arsenic adsorption removal method according to (9), wherein the contact is performed in a high superficial velocity range of a superficial velocity of 100 to 200 l / hr,
About.

  The arsenic adsorbent of the present invention has a porous polymer resin as a skin layer, and can contain a large amount of rare earth metal hydroxide with many voids in the skin layer. Is excellent. Moreover, it is possible to efficiently purify contaminated water having a low arsenic concentration. Moreover, since the adsorption activity can be maintained for a long period of time, maintenance is easy. Further, since there is no elution of the adsorbent component into the treated water and no initial elution of the polymer resin, there is no need for a water washing step of the adsorbent as a countermeasure and a final treatment with activated carbon after the arsenic adsorption treatment.

The present invention will be specifically described below.
The arsenic adsorbent of the present invention is a mixture of a polymer resin and a rare earth element hydroxide.
The mixture may have a granular shape or a molded body in which water can pass. Any structure may be used as long as the mixture can be filled and used without any problem. A net-like molded body may be used to meet the purpose. Moreover, if it is a substantially uniform round granular body, the average particle diameter of 0.2 mm-5.0 mm is used preferably. If the particle size is 0.2 mm or less, the packing density becomes high and the water flow resistance becomes high and the workability tends to be inferior, and if it is 5.0 mm or more, the contact area per unit time between the arsenic-containing water and the granular material tends to decrease. As a result, the arsenic adsorption ability tends to be low.

  The granular molded body was obtained by putting a mixed liquid obtained by dispersing a rare earth element hydroxide powder and a polymer resin, the moisture content of which was adjusted in a drier, into a granulator. The obtained granular molded body was washed with water until no solvent elution was observed.

  As the polymer resin, an organic polymer polymer resin or a derivative of these resins having a water resistance that is more heat resistant than an anion exchange resin or a chelate resin and does not elute into water is preferable, and its number average molecular weight is preferably 500 or more. Is better than 2000. A water-soluble hydrophilic resin is not preferable in terms of elution, and at a high temperature, elution is further increased and there is no heat resistance.

Examples of the polymer resin used in the present invention include organic polymers, natural polymers and derivatives thereof excellent in synthetic or natural water resistance.
Here, the water resistance means that the polymer resin does not elute in the treated water even in the initial stage of water passage to the adsorbent, and that there is no elution that causes any trouble for beverages.
Therefore, a general resin excellent in water resistance such as a polyolefin resin such as a polyethylene resin or polyvinyl chloride can be used.
Particularly preferred polymer resins include fluororesins and acetalized polyvinyl alcohol resins.
Specific examples include polyvinylidene fluoride resin, vinylidene fluoride-6-propylene propylene copolymer resin, polytetrafluoroethylene resin, and polyvinyl butyral resin. These polymer resins are easy to contain a rare earth element hydroxide at a high concentration, are excellent in water resistance and chemical resistance, and can be said to be particularly preferable resins.

  The rare earth element hydroxide of the present invention is a 3 (3A) group rare earth element according to the periodic table of elements of 1991, and is scandium Sc, yttrium Y, lanthanoid element, lanthanum La, cerium Ce, praseodymium Pr, neodymium Nd. , Promethium Pm, Samarium Sm, Europium Eu, Cadolinium Gd, Terbium Tb, Dysprosium Dy, Holmium Ho, Erbium Er, Thulium Tm, Ytterbium Yb, Lutetium Lu. Among these, Ce is a preferable element in accordance with the object of the present invention, and tetravalent Ce is preferable. Mixtures of these rare earth hydroxides are also useful.

  It is more preferable that the rare earth element hydroxide of the present invention contains water, and the water content thereof is 1 to 30 parts by weight, preferably 5 to 18 parts by weight with respect to 100 parts by weight of Ce hydroxide. Surprisingly, it is more preferred to meet the purpose of the present application. Because of this water content, it is impossible to think from the conventional level (400 parts by weight per 100 parts by weight of resin) of a polymer resin that was considered impossible in the past and 600 parts by weight or more per 100 parts by weight of the polymer resin. An arsenic adsorbent containing a high amount of rare earth element hydroxide was able to be made, and the arsenic adsorption ability was also 2 to 4 times astonishing. The adsorbent of the present invention shows an adsorption amount that the saturated adsorption amount (equilibrium adsorption amount) cannot be achieved by the prior art as shown in FIG.

The reason for this is not clear, but by adding water, the fluidity of the rare earth element hydroxide is improved and appropriate mixing with the resin is performed, and the surface of the rare earth element hydroxide particles is high as shown in FIGS. The molecular resin forms a skin layer, so that the rare earth element hydroxide is retained inside the particles without flowing out, and the rare earth element hydroxide in which water is secondarily aggregated has an appropriate particle size. And the effect of creating voids in the secondary particles to allow contact with moderate arsenic-containing water, and preventing hydroxide from returning to oxide, resulting in increased arsenic adsorption capacity. Presumed.
The skin layer of the polymer resin in the arsenic adsorbent of the present invention has a thickness of 0.01 to 2 μm, preferably 0.1 to 0.5 μm. If the thickness is less than 0.01 μm, rare earth elements may be eluted, and if the thickness exceeds 2 μm, water may not easily penetrate into the adsorbent during water flow.

The water content is measured by removing resin mixed particles with a resin solubilizer, volatilizing or separating the solvent, and leaving the remaining hydrous rare earth element hydroxide at a high temperature of 800 ° C. for 1 hour. The value obtained by dividing the evaporation by the hydrous rare earth element hydroxide is expressed by the water content.
The secondary particles of the rare earth element hydroxide are aggregates of primary particles having an average particle diameter of 0.01 to 0.1 μm, and the average particle diameter of the secondary particles is preferably 0.2 to 25 μm. ˜6 μm is preferred. If it is 0.2 μm or less, it may be wrapped with resin mixing and contact with arsenic-containing water may be insufficient, and if it is 25 μm or more, mixing with resin may be poor.

  The rare earth element hydroxide can be obtained by neutralizing the rare earth element nitrate with a hydroxyl group. If the pH during the reaction is on the acidic side, the unreacted rare earth element hydroxide is converted to the rare earth element hydroxide. A small amount remains in. Although the specific reason is not clear, as shown in Table 2, the knowledge that 1 to 10 parts by weight of rare earth element nitrate remained per 100 parts by weight of rare earth element hydroxide has higher arsenic adsorption performance. It was found in the process and proved preferable for solving the object of the present invention.

The granular arsenic adsorbent of the present invention is filled in a predetermined container, and water containing arsenic (As (V) and As (III)) having a predetermined concentration is passed through 1 to 20000 times the volume of the adsorbent. Then, the arsenic concentration of the contained water that has passed through is maintained at 0.01 mg / l or less. Moreover, even if the superficial velocity at the time of passing water is 100 to 200 l / hr, far exceeding the conventional level of 10 l / hr, sufficient adsorption performance is obtained. In this case, the pH of arsenic-containing water used for water passage is preferably 4 to 10 so that the adsorption ability of the adsorbent is activated and maintained.
The adsorbent of the present invention can be recovered by a regenerating process by a known method (for example, by the method described in JP-A No. 2000-140626, etc.) when the adsorptive capacity is lowered after long-term use. Can do.

[Example]
Examples of the present invention and comparative examples are shown below.
The SV in the sentence is a superficial velocity (space velocity), a water flow rate per adsorbent, and a water flow rate per 1 l of the adsorbent. For example, if the speed is 20 times that of the adsorbent per hour, it means that water was passed at 20 l / hr.
Further, the water flow rate means how many times the amount of water has flowed per adsorbent volume. For example, when the water flow rate is 200 with 1 l of adsorbent, it means that 200 l of water has flowed.
The saturated adsorption amount is a value indicating how much arsenic can be adsorbed when the arsenic is adsorbed to the adsorbent with an arsenic aqueous solution having a specific concentration, and varies depending on the arsenic concentration.

(Example 1, Comparative Example 1, Comparative Example 2)
A solution was prepared by dissolving disodium hydrogen arsenate heptahydrate (Na ₂ HAsO ₄ .7H ₂ O) in tap water to an (initial) As (V) concentration of 1 mg / l, and pH 7.0 was confirmed. This is hereinafter referred to as tap water arsenic acid-containing liquid. Separately, a cerium nitrate aqueous solution and a sodium hydroxide aqueous solution were neutralized, purified and dehydrated to obtain hydrous cerium hydroxide powder having a moisture content of 30 to 40% by weight. Next, this powder was dried with a low-temperature dryer at 70 ° C. to obtain a hydrous cerium oxide powder having a moisture content of 16% by weight. 833 parts by weight of this powder and 100 parts by weight of polyvinyl butyral resin were dispersed in 700 parts by weight of a solvent N-methyl-2-pyrrolidone to obtain a dispersion. Next, this dispersion was put into a granulator to obtain round particles having an average particle diameter of 0.70 mm and a ratio of 700 parts by weight of cerium hydroxide to 100 parts by weight of the resin. When the cross section of the particle was observed with a microscope, it was as shown in FIGS. Hereinafter, these particles are referred to as adsorbent A.

Apart from this adsorbent A, an arsenic adsorbent described in Patent Document 3 (trade name: Hisokyu, manufactured by Chiyoda Corporation) was prepared as a comparative example.
15 ml of this particle adsorbent A and 15 ml of Hisokyu are each packed in a column tower, and the previous tap water arsenic acid-containing liquid is passed through the column under conditions of a superficial velocity (space velocity; SV) of 10 l / hr. In this experiment, As (V) concentration (mg / l) (treatment solution arsenic concentration) was measured. The result is shown in FIG.

  In addition to the adsorbent A, as a comparative example, the total organic carbon TOC of a conventional product (adsorbent B) manufactured by the present applicant carrying cerium hydroxide with an ethylene-vinyl alcohol copolymer resin as a carrier was measured. The TOC measurement / analysis apparatus was a Shimadzu TOC-VCSH type apparatus, and the sample collection method was a pure water arsenic-containing liquid at a water flow rate of 200 times. The measurement results are shown in Table 1.

The TOC concentration of the adsorbent B in Table 1 is a value at the initial stage of water flow, and elution of the dissolved substance disappears after a while. Therefore, if the adsorbent was washed with water in advance and the treated water was further subjected to final treatment with activated carbon, there was no problem in actual use, but it was thought that the elution itself should be improved. As for the adsorbent of the present invention, it can be clearly seen from Table 1 that elution of dissolved substances in water can be prevented and there is no problem for beverages. From FIG. It can be seen that high adsorption performance is maintained.

(Example 2)
A solution having (initial) As (III) concentration of 1 mg / l prepared by dissolving diarsenic trioxide anhydride (As ₂ O ₃ ) in tap water was confirmed to have a pH of 7.0. An experiment was conducted by changing the number of days of water passage to 15 ml of the adsorbent A of Example 1 packed with this liquid in a column tower under the condition of SV = 10 l / hr, and the concentration of As (III) in the liquid passed through was measured. It was measured. Further, after the adsorbent A after completion of water flow was regenerated with sodium hydroxide, the As (III) concentration was measured under the water flow conditions described above. The regeneration-water flow cycle was performed twice. As shown in FIG. 2, it was found that trivalent arsenous acid that cannot be taken up by the coagulation precipitation method (coprecipitation method) was adsorbed, and that the adsorption performance after the regeneration treatment did not deteriorate.

(Example 3)
A water passage test was performed under the same conditions as in Example 1, and the As (V) concentration and the cerium (Ce) concentration in the water flowed were measured. The result is shown in FIG.
From FIG. 3, it was found that even when arsenic adsorption broke through, the cerium elution amount was extremely low.

Example 4
A solution was prepared by dissolving disodium hydrogen arsenate heptahydrate (Na ₂ HAsO ₄ .7H ₂ O) in pure water to an (initial) As (V) concentration of 100 mg / l, and pH 7.0 was confirmed. Further, a solution was prepared by dissolving diarsenic trioxide anhydride (As ₂ O ₃ ) in pure water to an (initial) As (III) concentration of 100 mg / l, and pH 7.0 was confirmed. 2 ml of the adsorbent A of Example 1 was added to 1 liter of each of the arsenic-containing liquids described above and stirred for 48 hours. The result is shown in FIG. It was found that the adsorbent of the present invention effectively adsorbs arsenic from a low concentration to a high concentration.

(Example 5)
2 ml of the adsorbent A of Example 1 was added to each 1 liter of pure water As (V) -containing liquid and As (III) -containing liquid each having an (initial) concentration of 2 mmol / l and pH adjusted in the range of 5 to 12, and stirred for 48 hours. did. The result is shown in FIG. It has been found that the adsorptivity of the adsorbent of the present invention, particularly the adsorptivity to As (III), is hardly affected by pH.

(Example 6)
The tap water arsenic acid-containing liquid of Example 1 ((initial) As (V) concentration 1 mg / l) was diluted to prepare liquids with (initial) As (V) concentrations of 0.5 mg / l and 0.1 mg / l. Each confirmed pH 7.0. The conditions other than the SV were the same as in Example 1, and the water passage test was performed while changing the SV, and the arsenic removal rate was calculated from the As (V) concentration in the water flowed. The result is shown in FIG.
From FIG. 6, even in a high SV region where SV = 100 l / hr or more, about 70% or more of arsenic can be removed. Especially, in the case of a dilute solution having an (initial) As (V) concentration of 0.5 mg / l or less, about It was found that arsenic was removed at a high rate of 80% or more.

(Example 7)
By changing the concentration of the aqueous sodium hydroxide solution added to the aqueous cerium nitrate solution, the pH during the neutralization reaction was adjusted to obtain hydrous cerium hydroxide powders having different residual cerium nitrate concentrations.
1.5 g of this hydrous cerium hydroxide powder was dispersed in 1 l of the pure water arsenic acid-containing liquid of Example 4 ((initial) As (V) concentration 100 mg / l), adjusted to pH 6.5 to 7.0, and 20 Stir for hours. After the stirring, the filtered filtrate was measured with ICP (inductively coupled plasma), and the arsenic adsorption performance was calculated from the measured values. The results are shown in Table 2.

From Table 2, it was found that the higher the residual cerium nitrate concentration in the hydrous cerium oxide, the higher the arsenic adsorption performance.
From the results of Examples 1 to 7, it is clear that the adsorbent of the present invention has a significantly improved arsenic adsorption performance as compared with the conventional adsorbent. That is, it is possible to purify a large amount of arsenic-contaminated water at a high speed, and also to treat the water to be treated containing low-concentration arsenic efficiently, and to maintain the adsorption activity for a long time. Since it can be held, maintenance is easy, and in addition, the adsorbent and resin components are not eluted.

It is a figure which shows the arsenic (As (V)) adsorption | suction performance of this invention, and is a related figure of a water flow magnification and a process liquid arsenic density | concentration (mg / l). It is a figure which shows the arsenic (As (III)) adsorption | suction performance of this invention, and is a related figure of a water flow magnification and a process liquid arsenic density | concentration (mg / l). It is a related figure of the water flow rate of this invention and a process liquid cerium density | concentration. FIG. 5 is a relationship diagram between liquid phase arsenic concentration (mg / l) and arsenic adsorption amount (g / l) of the present invention. FIG. 6 is a relationship diagram between the liquid pH and the arsenic adsorption amount (mol / l) of the present invention. FIG. 4 is a relationship diagram between SV (l / hr) and an arsenic removal rate of the present invention. It is an internal structure schematic diagram of the adsorption agent of this invention. It is an internal fracture cross-section photograph (100 times) of the adsorbent of the present invention.

Claims (10)

An arsenic adsorbent comprising a rare earth element hydroxide and a polymer resin covering the surface thereof, wherein the rare earth element hydroxide has a central cavity and surrounding fine voids, and the rare earth element hydroxide An arsenic adsorbent characterized in that the polymer resin covering the surface is a porous skin layer having water resistance. The arsenic adsorbent according to claim 1, wherein the polymer resin is a resin selected from a fluororesin and an acetalized polyvinyl alcohol resin. The arsenic adsorbent according to claim 1 or 2, wherein the rare earth element hydroxide has an average secondary particle diameter of 1 to 6 µm. The arsenic adsorbent according to any one of claims 1 to 3, wherein the rare earth element hydroxide contains 1 to 10 parts by weight of nitrates per 100 parts by weight of the hydroxide. The arsenic adsorbent according to any one of claims 1 to 4, wherein the rare earth element hydroxide contains 1 to 30 parts by weight of water per 100 parts by weight of the hydroxide. The arsenic adsorbent according to any one of claims 1 to 5, comprising 600 parts by weight or more of the rare earth element hydroxide per 100 parts by weight of the polymer resin. A rare earth element hydroxide containing 5 to 30 parts by weight of water is obtained by drying a mixture of the rare earth element hydroxide and water at a low temperature of 100 ° C. or lower, and the hydroxide is then converted into a water-resistant polymer. A method for producing an arsenic adsorbent, comprising: dispersing in a liquid dissolved in an organic solvent that dissolves the resin together with the resin; and granulating the dispersion. The method for producing an arsenic adsorbent according to claim 7, wherein the rare earth element hydroxide has an average secondary particle diameter of 0.2 to 25 µm, and the average particle diameter of the arsenic adsorbent is 0.2 to 2.0 mm. A method for adsorbing and removing arsenic by bringing treated water containing arsenic into contact with the arsenic adsorbent according to claim 1. 10. The arsenic adsorption removal method according to claim 9, wherein the contact is made in a high superficial velocity range of a superficial velocity of 100 to 200 l / hr.

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