JP2000140626A - Method for regenerating arsenic adsorbent - Google Patents

Abstract

PROBLEM TO BE SOLVED: To efficiently desorb arsenic adsorbed on an arsenic adsorbent to such a degree that the adsorbent can be reused by carrying out treatment with an alkali and an oxidizing agent. SOLUTION: A used arsenic adsorbent containing hydrous oxide of a rare earth element and/or hydrous oxide of zirconium is regenerated by treatment with an alkali and an oxidizing agent, preferably an oxidizing agent which does not deteriorate the structure and performance of the adsorbent. Hydrogen peroxide or sodium hypochlorite is particularly preferably used as the oxidizing agent. The oxidizing agent may be used alone before alkali treatment or may be used as a mixture with the alkali regenerating agent. When the oxidizing agent is used alone before alkali treatment, pH in reaction may be in any of acidic and alkaline regions. Hydroxide of an alkali metal may be used as the alkali agent and sodium hydroxide or potassium hydroxide is preferably used because a high desorption rate is attained.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a method for regenerating an adsorbent having arsenic ions, particularly arsenite ions, adsorbed thereon.

[0002]

2. Description of the Related Art Conventionally known methods for regenerating an adsorbent containing a hydrated oxide of a rare earth element adsorbed with arsenic and a hydrated oxide of zirconia include conditions of high liquid ratio and high temperature (for example, (See Japanese Unexamined Patent Publication (Kokai) No. 61-187931), which is difficult to regenerate and has a low desorption rate, and is currently practically disposed of as industrial waste.

[0003]

SUMMARY OF THE INVENTION An object of the present invention is to provide a condition for easy desorption in order to regenerate and reuse an adsorbent having adsorbed arsenic.

[0004]

Means for Solving the Problems The inventors of the present invention have conducted intensive studies to solve the above-mentioned problems, and as a result, have completed the present invention. That is, in the regeneration of an arsenic adsorbent containing a hydrated oxide of a rare earth element and / or a hydrated oxide of zirconia, this is an adsorbent regeneration method in which treatment is performed using an alkali and an oxidizing agent. According to the present invention, the oxidizing agent may be any one which can oxidize arsenite ion into arsenite ion in general, and can efficiently desorb adsorbed arsenic.

[0005] The hydrated oxide of a rare earth element of the present invention is a compound obtained by hydroxylation of an oxide or a salt of a rare earth element, and may be used alone or as a mixture of two or more kinds or a complex formed by coexisting various metal ions. It is a metal hydrated oxide. Although any rare earth element may be used, cerium and lanthanum can be used.

The oxidizing agent used preferably does not degrade the structure and performance of the adsorbent, and hydrogen peroxide, sodium hypochlorite and the like are particularly preferable.

[0007] These oxidizing agents may be used alone before the alkali treatment, or may be used as a mixture with an alkali regenerating agent. When used alone before the alkali treatment, the reaction pH may be in the acidic or alkaline range. The amount of the oxidizing agent to be added is at least 0.1 times, preferably at least 0.6 times the molar amount of the arsenic adsorption amount.

As the alkali agent, hydroxides of alkali metals can be used, and sodium hydroxide and potassium hydroxide are particularly preferable because of their high desorption ratio. The concentration of the alkaline solution varies depending on the type of the adsorbent.
Or more, preferably 1N or more. The amount of the alkaline solution used varies depending on the type of the adsorbent, the contact method, and the like. The batch regeneration by immersion does not increase the desorption rate unless a large amount is used. However, since the treatment liquid contains a large amount of arsenic, considering the necessity of treatment such as coagulation,
The smaller the better, the better the amount of adsorbent is 1-20
Double amount, preferably 5 to 12 times.

[0009] The reaction temperature affects the desorption rate and desorption equilibrium, and although heating is effective, the effect can be sufficiently increased even at room temperature. The contact time depends on the method, temperature and type of adsorbent at the time of contact, but it usually takes about 1 minute to 3 days to reach equilibrium, and practically 1 minute to
180 minutes is sufficient.

The adsorbent of the present invention is a hydrated oxide of rare earth and zirconia and formed into an arbitrary shape such as granular, thread-like, band-like or plate-like by a method of supporting the same on a suitable porous carrier. Anything may be used. As the material used for the carrier, various inorganic and organic materials can be used, but a known organic polymer material is preferable from the viewpoint of supporting processing, supporting strength, chemical durability and the like. Moreover, what precipitated in the inorganic porous body may be sufficient.

The adsorbent is brought into contact with, for example, an aqueous solution containing arsenic, and the arsenic in the aqueous solution is adsorbed and removed.
The present invention is effective for regenerating the adsorbent.

[0012]

Now, the present invention will be described in further detail with reference to Examples.

Examples 1 to 5 In the regeneration operation of the present invention, the type of oxidizing agent and the reaction p
Table 1 shows examples in which H is changed.

The arsenic adsorbent was prepared by the following method. An ethylene-vinyl alcohol copolymer (Soarnol E type, manufactured by Nippon Synthetic Chemical Co., Ltd.) is dissolved in dimethyl sulfoxide at a concentration of 12% by weight, and cerium hydroxide containing hydroxerium is added to the solution at 6 times the weight of the polymer. And sufficiently dispersed by stirring.
The mixture was formed into granules using water as a coagulation bath. The molded body was washed with water until no solvent was detected in the washing water. The obtained adsorbent had an average particle diameter of 0.7 mm, and the retention amount of the cerium hydroxide as cerium oxide was 0.4 g / ml of the adsorbent.

5 mg-A of arsenic ion as arsenic
s / ml-3 ml of hydrogen peroxide, sodium hypochlorite, and sodium peroxydisulfate, in which 1 ml of the above adsorbent having adsorbed the adsorbent was adjusted so as to have a molar ratio twice as much as the arsenic adsorption amount. Mixing and stirring for 1 hour in a beaker with 100 ml of an aqueous solution of an oxidizing agent of the species, then discarding the solution, using an IN-NaOH solution as an alkali regenerating solution, immersing the adsorbent for arsenic in this and stirring for 20 hours The arsenic concentration in the liquid afterwards was measured to determine the amount of desorption.

Under these regeneration conditions, the desorption rate showed a high value of 35 to 80% regardless of the pH of the solution at the time of the oxidizing agent treatment.

[0017]

[Table 1]

Comparative Example 1 In the same manner as in Examples 1 to 5, Table 1 shows the results of ordinary alkali treatment alone when no oxidizing agent was added. The desorption rate was extremely low at 2%.

Examples 6 to 8 Table 2 shows examples in which the concentration of the oxidizing agent was changed in the regeneration operation of the present invention.

The arsenic adsorbent prepared in the same manner as in Examples 1 to 5 was treated with 7 mg-A
s / ml-15 ml of adsorbent adsorbed, 2
A 4 mm, 60 mm long acrylic column was packed.
In the regeneration method, sodium hypochlorite as an oxidizing agent was mixed with 180 ml of a 2N-NaOH solution as an alkali regenerating agent to arsenic so that the molar ratio was 0.5, 1.0, and 2.0 times as much as arsenic. aqueous solution and regenerated by 3 hours through water at a rate of SV4hr ~ ^1, was determined desorption amount by measuring the arsenic concentration in the column discharge solution.

By this operation, the desorption rate showed a high value when the molar ratio of sodium hypochlorite was 0.5, 1.0, and 2.0 times.

[0022]

[Table 2]

Comparative Example 2 In the same manner as in Examples 6 to 8, Table 2 shows the results of only the alkali treatment when no oxidizing agent was added. 2% desorption rate
It was extremely low.

Examples 9 to 14 In the regeneration operation of the present invention, Table 3 shows an example of the relationship between the alkali concentration and the desorption rate depending on whether or not an oxidizing agent is added, using an adsorbent composed of a hydrated oxide of zirconia.

The method for preparing the arsenic adsorbent was the same as in Examples 1 to 5, except that hydrous zirconium oxide was used instead of hydrous cerium hydroxide. The obtained adsorbent has an average particle size of 0.1.
8 mm, the retention amount of the zirconium hydroxide as an oxide was 0.17 g / ml of adsorbent.

The arsenite ion was previously converted to arsenic by 4 mg-A
s / ml-3 ml of the adsorbent having adsorbed the adsorbent was used as a regenerating solution in 0.2% and 2N NaOH, and the amount of the oxidizing agent (sodium hypochlorite) added was 0 in molar ratio with respect to the amount of arsenic adsorbed. .
Aqueous solution 60 mixed and adjusted to 34-1.5 times volume
Then, the mixture was stirred in a beaker, and the arsenic concentration in the liquid after 20 hours was measured to determine the desorption amount.

By this operation, even when the alkali concentration was low, the desorption rate showed a high value of 56 to 90% by adding an oxidizing agent (sodium hypochlorite).

[0028]

[Table 3]

Comparative Examples 3 to 6 In the same manner as in Examples 9 to 14, Table 3 shows the results of the alkali treatment alone when no oxidizing agent was added. When not treated with an oxidizing agent, the desorption rate showed a low value of 8 to 34%.

[0030]

As described above, the regeneration method of the present invention can efficiently desorb adsorbed arsenic and can desorb arsenic to such an extent that it can be reused. Can be reduced.

Claims (1)

[Claims] 1. A method for regenerating an adsorbent for arsenic containing a hydrated oxide of a rare earth element and / or a hydrated oxide of zirconia, comprising treating with an alkali and an oxidizing agent. .