JPS61187931A - Adsorbent of arsenic in aqueous solution - Google Patents

Abstract

PURPOSE:To remove efficiently arsenic from water or waste water dissolving arsenic in a specified value or above and to make the arsenic concn. to the specified value or below by using the oxide hydrate of rare earth elements to form the adsorbent of arsenic dissolved in an aq. soln. CONSTITUTION:The oxide hydrate of the rare earth elements is produced as a precipitation by adding an alkali soln. in aq. soln. of salt such as the chloride and the sulfate of the rare earth elements and regulating the pH. The cake or the dried powdery material, etc., are obtained by filtering the produced oxide hydrate or fluoride hydrate of the rare earth elements. The adsorbent of arsenic is obtained by molding them in an optional shape such as a grain shape, a yarn shape, a string shape and a band shape with a method depositing them on a suitable porous carrier. In case of separating and removing arsenic dissolved in the aq. soln. by using this adsorbent, it can be selectively removed in the high adsorption quantity by regulating the aq. soln. to about 3-12pH.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a novel adsorbent that immobilizes arsenic dissolved in an aqueous solution.

(Prior Art) Arsenic is contained in wastewater from non-ferrous metal smelting industries and heat wastewater from geothermal power plants. The toxicity of arsenic, especially trivalent arsenic, has been known for a long time, and its presence is estimated at 0.5 ppm by wastewater standards and 0.5 ppm by environmental standards. O2 is regulated to a low level of 5ppm or less. Currently, as a method for treating wastewater containing arsenic, a coagulation-sedimentation method using metal hydroxides such as calcium, magnesium, barium, iron, and aluminum is widely used. Although this method can bring the arsenic concentration below the wastewater standard through relatively simple treatment operations, it requires a large amount of chemicals when treating low-concentration wastewater, such as hot water from geothermal power plants. Furthermore, it is necessary to dispose of a large amount of generated sludge, which poses a practical problem. As alternatives to such metal hydroxide coprecipitation methods, adsorption methods using activated carbon, activated alumina, titanium-activated carbon composite adsorbents, etc., ion exchange methods using anion exchange resins, iron (m) or zirconium supported cation exchange methods are available. Ligand ion exchange methods using resins have been proposed, but these methods are impractical because they have a small adsorption amount for arsenic, insufficient selectivity, and poor durability.

On the other hand, various metal hydroxides or hydrous oxides are known as inorganic ion exchangers, and it is well known that rare earth element compounds also have ion exchange effects.

(Problems to be Solved by the Invention) As mentioned above, the conventional methods for treating wastewater containing arsenic each have their own drawbacks and are not practical. was expected to appear.

(Means for Solving the Problem) The present inventors have developed various metal water solutions for the purpose of providing a practical adsorbent having high adsorption capacity for arsenic dissolved in a low concentration in an aqueous solution. As a result of research on the selective adsorption ability of oxides or hydrated oxides (hereinafter collectively referred to as hydrated oxides) for arsenic, we found that hydrated oxides of rare earth elements have surprisingly high adsorption ability, especially at low concentrations. As a result of the discovery and extensive research for practical application, the present invention was completed.

Therefore, an object of the present invention is to provide an adsorbent that efficiently removes dissolved arsenic at a low concentration, and furthermore, to provide an adsorbent that can efficiently remove arsenic from water or wastewater containing dissolved arsenic at a level exceeding the regulation value. An object of the present invention is to provide an adsorbent that can be used repeatedly by treating drinking water or wastewater with an arsenic concentration below a regulatory value, and desorbing and regenerating the arsenic adsorbed in the adsorbent.

That is, the adsorbent of the present invention is composed of a hydrated oxide of a rare earth element, and preferably the hydrated oxide is supported on a porous carrier using an organic polymer material. It is an adsorbent.

Hereinafter, the adsorbent of the present invention will be explained in detail.

The hydrated oxide of a rare earth element of the present invention refers to a rare earth element, that is, Y SL a s Ce −, P r SN
d.

Pm, Sm, Eu, Gd, 'l'b, Dy, Ho, E
r-.

It is a compound obtained by hydroxylation of oxides and salts of Tm, Yb, and Lu. As for the types of rare earth elements, L
a, Ce, and Y are preferable because they have a large adsorption amount, and in particular Ce
is preferred due to its minimal solubility.

These hydrated oxides of rare earth elements may be used alone or as a mixture of two or more. Also,
Other adsorbents such as activated carbon, hydrous aluminum oxide,
It may be used together with hydrous zirconium oxide, zirconium carbonate, zirconium phosphate, magnesium hydroxide, organic ion exchange resin, etc.

The rare earth hydrated oxide of the present invention can be obtained by adding an alkaline solution to an aqueous salt solution such as hydrochloride, sulfate, nitrate, etc.
By adjusting the pH of the aqueous salt solution, it can be easily obtained as a precipitate. In the preparation, by selecting the type and solution concentration of the metal and its salt, the type and concentration of the alkali, the mixing method and mixing speed of the metal salt aqueous solution and the alkaline solution, and the reaction temperature, the precipitate formation conditions can be selected. Oxides or hydroxides can be produced.

Further, when the rare earth hydrated oxide is prepared by the above-mentioned preparation method, it may be a composite metal hydrated oxide produced by coexisting various metal ions.

Examples of metal elements that can coexist are Al5Zr, Cr
1Co-G a % Fe-, M n % N
t % T t % V % Sn, Ge, Nb, Ta, etc. are mentioned. The amount of these metal elements that can coexist is 40 mo1% or less, more preferably 20 mo1% or less, based on the metal element of the present invention.

Furthermore, the cations and anions used in the above preparation may be present as part of the structure of the hydrated oxide of the present invention. These coexisting cations and anions are, for example, NH,s Nas K, Ca and SOa, N
O3, CZ, etc.

The rare earth hydrated oxide prepared by the above production method has either a hydrous oxide or a hydroxide structure, and the structural characteristics thereof will be explained in detail below.

Among hydrated oxides, hydrated oxides are defined as
As shown in Figure a, it shows the same diffraction pattern as the corresponding metal oxide, but the diffraction line width is wide due to poor crystallinity. It does not have a specific thermal transition point, and as the temperature rises, it gradually loses heat and eventually becomes an oxide with good crystallinity, with a heat loss of 5 to 30% by weight. . In the infrared absorption spectrum, as shown in Figure 2b, < , 3
It shows a broad absorption band near 400 cm-' based on the stretching vibration of the hydroxyl group, and two to three absorption bands based on the bending vibration of the hydroxyl group at 1700-1300 cm-'.

In addition, hydroxide indicates the diffraction pattern of the corresponding metal hydroxide in X-ray diffraction, as shown in Figure 3a.
Thermally, it undergoes a transition to an oxide at a certain temperature. In the infrared absorption spectrum, as shown in Figure 3b, there is a sharp absorption band at 3500 to 3700 cm-', which is characteristic of metal hydroxides, based on the stretching vibration of the hydroxyl group, and a broad band around 3400 cm-' due to the stretching vibration of the hydroxyl group. absorption band, and 1700
2-3 based on the bending vibration of the hydroxyl group at ~1300 cm-'
Shows the absorption bands of books.

As mentioned above, the rare earth hydrated oxide of the present invention can be used for X-ray diffraction,
Each has its own unique characteristics in terms of infrared absorption spectra and thermal properties, but the common characteristics especially related to adsorption performance are:
Around 1500 cm-' in the infrared absorption spectrum and 1
It is important to have an absorption band around 350 cm-', and the structure having this absorption band is extremely important for achieving the effects of the present invention.

The absorption band is based on the hydroxyl group that acts on the adsorption of the present invention, and is characterized by decreasing or disappearing when the hydroxyl group is exchanged with an anion other than the hydroxyl group, such as a sulfate ion.

The heat loss referred to in the present invention is the percentage decrease in the original weight when a sample is heated from room temperature to 800° C. in the case of a hydrated oxide at a rate of 10° C./min.

In addition, the properties and surface condition of the rare earth hydrated oxide particles are extremely important in achieving the effects of the present invention, and it is possible to adjust the structural water or adhering water amount of the particles, the particle size, and the degree of aggregation. Preferably, the particle size is preferably as fine as possible, and the primary particle size as an average particle size is 0.01 to 1μ, particularly preferably 0.01 to 0.
．． 5μ and 0.0 as agglomerated particles with a low degree of aggregation.
Fine particles of about 5 to 5 microns are preferable.

The adsorbent of the present invention is a cake obtained by filtering the metal hydrated oxide or the metal hydrated fluoride by the above-mentioned preparation method, or a dried powder, and the cake is supported on a suitable porous carrier. It is a molded article formed into any shape such as granules, threads, strings, strips, plates, etc. by the above method. The molded body is extremely effective in increasing the practicality of adsorption operations.

The shape of the molded body can be selected from any shape suitable for the method of use, such as granule, filament, and hollow fiber.

Various inorganic and organic materials that can produce the effects of the present invention can be used as the material for the carrier, but known organic polymeric materials are preferred from the viewpoints of supporting processability, carrier strength, chemical durability, and the like.

Examples of organic polymer materials include natural polymers such as alginic acid, chitin, casein, collagen, gelatin, cellulose, and derivatives thereof, phenolic resin, urea resin,
Melanin resin, polyester resin, diallyl phthalate resin, xylene resin, alkylbenzene resin, epoxy resin, epoxy acrylate resin, silicon resin, urethane resin, fluorine resin, vinyl chloride resin, vinylidene chloride resin, polyethylene, chlorinated polyolefin, polypropylene, polystyrene , ABS resin, polyamide, methacrylic resin, polyacetal, polycarbonate, polyvinyl alcohol, polyimide, polysulfone, polyacrylonitrile, etc., and copolymers of the above can be used. Those that can form a structure are preferred, and the above-mentioned polysaccharide or protein-based modified resins, polyamides, cellulose resins, polysulfones, polyacrylonitrile, ethylene-vinyl alcohol copolymers, and the like are particularly preferred.

Various known methods can be applied to the method of supporting the above-mentioned organic polymer material. For example, particles of the metal hydrated oxide are suspended and dispersed in a solution containing a suitable polymer,
A method of forming particles into granules, filaments, hollow fibers, strings, or strips, or polymerizing a suitable polymer monomer by an emulsion or suspension polymerization method in the presence of the metal hydrated oxide particles to form granules. Alternatively, a method may be adopted in which a suitable high molecular weight polymer, the metal hydrated oxide, and various extractants are kneaded and molded, and then the extractant is extracted with an appropriate solvent to make the material porous. In either case, it is necessary to have a porous structure, a sufficient amount of the metal hydrated oxide is supported on the molded body, and the structure must be difficult to leak, and any method that can achieve this purpose is used. It may be a method.

Among these, a particularly preferred method is to dissolve a hydrophilic polymer such as the polysaccharide or protein-based modified resin, cellulose resin, polyacrylonitrile, or ethylene-vinyl alcohol copolymer in an appropriate solvent, and then add the metal to the solution. This is a method in which a hydrated oxide is suspended and formed into particles in a coagulation bath.

The granules obtained by this method have a porous structure, sufficient adsorption rate and low solubility, and can immobilize rare earth hydrated oxide powder.

In particular, when using the polymer, the amount of polymer used is 5 to 50% by weight of the rare earth hydrated oxide, particularly preferably 10% by weight of the rare earth hydrated oxide.
~30% by weight. If it is less than 5% by weight, a sufficient supporting effect will not be exhibited, while if it is more than 50% by weight, the adsorption performance will decrease, which is not preferable.

The hydrated oxide of a rare earth element, which is the arsenic adsorbent of the present invention, exhibits ion-exchange adsorption properties for various ions, but its adsorption characteristics vary depending on the OpH value of the treatment solution and the type and concentration of ions. When the pH of the aqueous solution is low, it exhibits anion exchange properties and exchanges with various dissolved anions, such as chloride ions, sulfate ions, nitrate ions, etc.
When the pH is high, it exhibits cation exchange properties, for example,
Exchange with cations such as magnesium ions and calcium ions.

For example, using hydrous cerium oxide, the relationship between the adsorption performance of the adsorbent for chloride ions, sulfate ions, calcium ions, arsenite ions or arsenous acid, and the pH of the aqueous solution during adsorption is as shown in Figure 1. be.

When separating and removing arsenic in an aqueous solution using the adsorbent of the present invention, as shown in Figure 1, by adjusting the pH to a range of 3 to 12, more preferably 5 to 9, it is possible to selectively and highly adsorb arsenic. It is possible to adsorb and remove in small quantities. When the adsorbent adsorbs arsenic, unlike when adsorbing other ions, there is almost no change in pH, so the above conditions can be satisfied simply by adjusting the pH of the liquid to be treated in advance. I can do it.

The relationship between the adsorption capacity of the adsorbent of the present invention and the arsenic concentration in the aqueous solution is shown in Figure 4, and even in the low concentration range,
It shows an extremely high adsorption capacity compared to other metal hydrated oxides, and is found to be particularly effective in treating low-concentration wastewater such as wastewater from geothermal power plants.

Any method of adsorption using the adsorbent of the present invention may be used as long as the hydrated oxide is brought into contact with an arsenic-containing aqueous solution. A preferred method is to use a molded article made of a molecular material into particles and fill it in an adsorption tower and bring it into contact.

Further, the adsorbent of the present invention can be desorbed by adsorbing arsenic as described above and then brought into contact with an appropriate desorption liquid, and can be used repeatedly. In the above desorption operation, the amount of arsenic adsorbed on the adsorbent, the type and concentration of the desorption liquid, the mixing ratio of the adsorbent and desorption liquid, and the temperature affect the desorption rate and the arsenic concentration in the desorption liquid. .

As the desorption liquid, hydrochloric acid, sulfuric acid, nitric acid or alkali metal hydroxide can be used. In particular, alkali metal hydroxides are preferred because they do not dissolve the adsorbent at all, and sodium hydroxide and potassium hydroxide are particularly preferred because of their high desorption efficiency.

The concentration of the alkaline solution is 0.1 mol/1 or more, preferably 1 mol/1 or more.

The temperature of the above-mentioned desorption operation affects the desorption rate and desorption equilibrium, and heating is effective, and it is preferably 40°C or higher, more preferably 60°C or higher. The contact time depends on the contact method, temperature, and type of adsorbent, but it usually takes about 1 minute to 3 days to reach equilibrium, and in practical terms it takes 1 to 60 minutes. good. The desorption method may be any method as long as the adsorbent is brought into contact with a desorption liquid, and the same method as the above-mentioned adsorption method may be employed.

(Effects of the Invention) Next, the effects of the arsenic adsorbent of the present invention will be described as follows.

(l) Shows excellent adsorption performance in a wide pH range of 3 to 12.

(2) Even when the concentration of arsenic in the liquid phase is low, the equilibrium adsorption amount is large; for example, when the arsenic concentration in the liquid phase is 0.1 pp-
At this time, the amount of adsorption becomes 38n+g/g-adsorbent, and the arsenic concentration in the treated water can be lowered.

(3) Adsorbed arsenic can be desorbed by an alkaline aqueous solution, and it can be used repeatedly.

As mentioned above, the adsorbent of the present invention has extremely high adsorption capacity for arsenic dissolved in an aqueous solution, especially at low concentrations, can be used repeatedly, and has excellent handling properties. This is also clear from the Examples described below. Therefore, it is effective for fixing and removing arsenic contained in wastewater from nonferrous metal smelting industries and thermal wastewater from geothermal power plants.

(Example) Hereinafter, this will be explained in detail using examples.

In addition, the adsorption amount and removal rate in the text were determined by the following formula.

Example 1 An example will be shown regarding the pH dependence of the adsorption performance of hydrous cerium oxide of the present invention for arsenous acid.

Preparation of Hydrous Cerium Oxide 11 Ji 99.9% cerium chloride was dissolved in distilled water, and an equimolar amount of hydrogen peroxide was added to the solution, followed by stirring, and then aqueous ammonia was added to adjust the pH to 10. Thereafter, the excess hydrogen peroxide was decomposed by heating to 85°C.
Aged overnight, filtered and the cake was dried in Cit, N.H.
It was washed with water until ions such as a were no longer detected, then dehydrated and dried in a hot air dryer at 50°C.

The obtained powder had a thermal loss of 15.6%, an average particle size of formed particles of 0.08μ, an average particle size of aggregated particles of 0.4μ, an X-ray diffraction pattern (Figure 2a), an infrared absorption spectrum ( Figure 2b).

Adsorption experiment The concentration of arsenic was 1 mmol/It (75mg-A
s/l), 0. An arsenic-containing aqueous solution was prepared by dissolving diarsenic trioxide in a 1N-NaOH aqueous solution, and after adjusting to various pHs by adding HCl, the hydrous cerium oxide was added to the aqueous solution at a rate of 1 g / l. .

After stirring at room temperature for 2 hours, it was filtered, and the arsenic concentration in the filtrate was measured according to JIS KO102. The results are shown in FIG. 1 as the relationship between the pH of the solution and the amount of arsenic adsorbed.

As a reference example, FIG. 1 shows the results of a similar experiment conducted with chlorine ions, sulfate ions, and calcium ions at an initial concentration of 10 m+aol/1.

Examples 2 to 6 Examples using yttrium, lanthanum, samarium, dysprosium, and thulium as rare earth elements will be shown.

Preparation method of hydrated oxide Nitrate (99.9%, reagent) of each rare earth element was dissolved in distilled water, and an aqueous sodium hydroxide solution was added to adjust the pH to 10. - After late ripening, nitrate ions and Na
It was washed until no ion elution was detected and dried at 50°C.

The obtained hydrated oxides were as shown in Table 1.

Note that the X-ray diffraction diagram and the infrared absorption spectrum diagram for the example of yttrium are shown in Figures 3a and 3b.

Adsorption experiment Regarding the powder, Example 1 was carried out except that pi was adjusted to 8.
The amount of adsorption was determined in the same manner. The results are shown in Table 1.

Table 1 Example 7 Regarding hydrous cerium oxide, the relationship between arsenic concentration and adsorption amount was determined by changing the amount added.

Other than adjusting the pH of the aqueous solution to 5 and varying the amount added,
The amount of adsorption was determined in the same manner as in Example 1.

As a comparative example, the adsorption amounts of amorphous hydrated iron oxide, hydrated zirconium oxide, and α-type hydrated titanium oxide were determined in the same manner. The hydrous oxides of each of the metals mentioned above were prepared according to the method of Abe et al. (Japanese Chemical Journal Vol. 186, No. 8 & 12).

The results are shown in FIG. 4 as the relationship between the arsenic concentration in the solution and the amount of adsorption.

Example 8 An example in which hydrated cerium III oxide was molded into particles using an ethylene-vinyl alcohol copolymer, filled in a column, and an adsorption experiment was conducted.

Preparation of granular molded bodies Ethylene-vinyl alcohol copolymer (Nippon Gosei Chemical Co., Ltd.)
manufactured by Soarnol E, ethylene copolymerization ratio 38 mo1%] was dissolved in dimethyl sulfoxide at a concentration of 10 mol.
Hydrous cerium oxide (the same substance as in Example 1) was added to the solution by 5 times the weight of the polymer, and the mixture was thoroughly stirred and dispersed. The mixture was shaped into granules using water as a coagulation bath. The molded body was washed with washing water until no elution of the solvent was detected. The obtained molded body had an average particle size of 0.5+IImφ and a retained amount of the hydrous cerium oxide of 0.36 g/ml of the molded body.

Column adsorption experiment The above granules IQm6 were prepared with an inner diameter of 10 mm and a length of 150 mm.
packed in a glass column with 5 ppm arsenic, NaCf25
An aqueous solution (adjusted to pH 5) containing 00 ppm and 200 ppm of N az SO was heated to 5V10.
Water was passed at a rate of hr-'. The concentration of arsenic in the column distillate was measured, and the end point was when the distillate concentration reached 0.2 ppm, and the total amount of arsenic adsorbed was determined from the amount of treated solution and the average concentration. As a comparative example, the results of the above example are compared with the results of using an adsorbent prepared by supporting commercially available hydrated zirconium oxide Zr0(OH)t on an ethylene-vinyl alcohol copolymer in the same manner. Shown in 2.

Table 2 Example 9 An example in which the type and concentration of the desorption liquid were changed in the desorption operation of the adsorbent of the present invention is shown.

Arsenic 5mg/mj in advance! - Granular molded body of hydrous cerium oxide adsorbed with adsorbent (manufactured in the same manner as on the day of the example)
with various solutions shown in Table 3 and 10 mj! -Adsorbent/Il
The arsenic concentration was measured after 24 hours. The results are shown in Table 3.

Table 3 Example 10 An example in which the temperature is changed in the desorption operation of the present invention will be shown.

The mixture was maintained at 30°C, 60°C, and 80°C in an oil bath, mixed and stirred in the same manner as in Example 5-c, and the arsenic concentration in the solution was measured after 5 hours. As a result, the desorption rates at 30°C, 60°C, and 80°C were 56%, 74%, and 95%, respectively.

Example 11 An example in which repeated operations of adsorption and desorption were performed using the adsorbent of the present invention is shown.

Preparation of granular moldings 10% by weight of polysulfone resin in dimethylformamide
Hydrous cerium oxide (Example 1) is dissolved in the solution at a concentration of
4 times the weight of the resin was added and thoroughly stirred and dispersed. The mixture was granulated using water as a coagulation bath. The molded body was washed with washing water until no elution of the solvent was detected.

The obtained molded body had an average particle size of 0.5n+a+φ and a retained amount of the hydrous cerium oxide of 0.31 g/ml of molded body.

Adsorption operation Aqueous solution containing arsenic at a concentration of 20 ppm (pH 5)
2 ml of the above molded body was added to 1N and maintained at 80° C. with stirring for 15 hours. The arsenic concentration in the liquid was measured after 15 hours.

After desorption operation and adsorption operation, the molded body is washed with 200ml of 5N-NaOH.
and maintained at 80° C. with stirring for 5 hours. After 5 hours, the arsenic concentration in the desorption solution was measured. The molded body after attachment and detachment is 50m1! The molded product was washed twice with water, 1 HCl was added to neutralize the NaOH in the molded product, and then the molded product was subjected to an adsorption operation again.

The above adsorption and desorption operations were repeated five times. The results are shown in Table 4.

Table 4

[Brief explanation of drawings]

FIG. 1 is a diagram showing the pH dependence of the adsorption amount of arsenous acid or arsenite ions, chloride ions, sulfate ions, and calcium ions by hydrous cerium oxide of the present invention, and FIG.
The figure shows X of the hydrous cerium oxide of the present invention by CuKα radiation
Figure 2b is an infrared absorption spectrum of the hydrous cerium oxide of the present invention, Figure 3a is an X-ray diffraction diagram of indium hydroxide of the present invention using CuKα rays, and Figure 3b is an infrared absorption spectrum of the hydrous cerium oxide of the present invention. Infrared absorption spectrum of yttrium hydroxide, 4th
The figure is a chart showing the relationship between the adsorption amount of hydrous cerium oxide of the present invention and the arsenic concentration in the liquid phase. Fig. 1 2θ (Cu) Ce (b ・nHzOXaEJ fold 2nd fold 2b Hidai・nHzo IR spectrum 2θ CCuKa) Y(OH)sX*rjM Fig. 3b Y(OH)3 IR spectrum

Claims (1)

[Claims] Adsorbent for arsenic in aqueous solution consisting of hydrated oxides of rare earth elements.