JP5746407B1 - Method and apparatus for purifying muddy water containing arsenic - Google Patents

Abstract

An object of the present invention is to provide a method for efficiently purifying muddy water containing arsenic using a small amount of iron powder in a narrow space. An object of the present invention is to adsorb mud containing arsenic and iron powder to adsorb arsenic to iron powder; to separate iron powder from a mixture obtained in the adsorption process by magnetic force; and An iron powder separated in the separation step, or an arsenic in the recovery step, wherein the iron powder separated in the separation step is treated with an acid to recover the adsorption ability of the iron powder to arsenic. This can be solved by a method for purifying muddy water containing arsenic, in which the iron powder whose adsorptive capacity has been recovered is reused in the adsorption step. [Selection] Figure 1

Description

  The present invention relates to a purification method and a purification device for mud water containing arsenic.

  In particular, the present invention addresses the problem of naturally occurring arsenic, that is, arsenic originally contained in the ground due to natural causes, manifesting at the surface due to large-scale underground development such as shield excavation work. Is. Since this is a naturally derived pollution, the content standard of the Soil Contamination Countermeasures Law originally intended for surface layer pollution in urban areas such as chemical factories is sufficiently satisfied, but there are construction soils that exceed the elution standard several times. It is a ground environmental problem that occurs in large quantities.

  Until now, the following conventional technique 1 or conventional technique 2 has dealt with the soil containing natural arsenic generated in construction work in Japan. In both cases, the project could be carried out in the construction area without taking any special measures against hazardous metals.

<Prior art 1: Sea surface reclamation as construction soil>
"Ministerial Ordinance Establishing Judgment Criteria for Waste Containing Metals, etc. to be Released to Landfill Sites, etc. Specified in Article 5, Paragraph 1 of the Law Enforcement Ordinance on the Prevention of Marine Pollution and Marine Disasters" (February 1973) On the 17th General Order No. 6, final revision: Ministry of the Environment Ordinance No. 19 on May 30, 2014), the so-called “judgment standards related to bottom sediment” It is generally allowed up to 10 times the soil environment standard. Regarding arsenic, the soil elution amount standard is 0.01 mg / L, whereas the bottom sediment determination standard is 0.1 mg / L. Therefore, it is possible to clear the elution concentration of almost all naturally-derived arsenic-contaminated soil, and if there is a receiving destination for sea land reclamation, it was possible to carry out arsenic as it is without processing ( In the Tokyo metropolitan area, new sea surface disposal sites and Minamimotomaki Pier are examples.)

<Prior art 2: Dispose as sludge if the heavy metal elution amount standard is exceeded>
Based on the concentration control during construction or judgment in the pre-investigation, there was a method of transporting the generated soil exceeding the heavy metal elution standard to the designated contractor as construction sludge and converting it to cement raw material or disposal site.

  However, although the prior art 1 has a track record in a relatively large-scale business, the disposal location and the disposal capacity are tight, and the public works of the local government are prioritized. For conventional technology 2, the disposal capacity (acceptable amount) is also limited, and against the amount of naturally-derived contaminated soil expected to be generated from large-scale projects implemented in the Tokyo metropolitan area and Chukyo area in the future, This is an overwhelming situation.

  By the way, the knowledge that iron powder adsorbs heavy metals containing arsenic is a known fact in the field of wastewater treatment around 1980 (for example, Non-Patent Documents 1 and 2). For example, the following prior arts 3 and 4 are known as methods for adsorbing arsenic with iron powder.

<Prior Art 3: Method of adsorbing arsenic on iron powder and selecting magnetic force with a superconducting magnet separator>
There has been proposed a method in which iron powder is mixed with muddy water containing arsenic and reacted for a certain period of time, and thereafter the iron powder is recovered by a magnetic separation device using a superconducting magnet (Non-patent Document 3).

<Prior Art 4: Method of adsorbing arsenic to iron powder and collecting it with a centrifuge>
There has been proposed a method in which iron powder is mixed with muddy water containing arsenic and reacted for a certain period of time, and then the iron powder is recovered by a centrifugal separator using a specific gravity difference (Non-patent Document 4).

Problems and effects of batch processing of harmful substances in wastewater with iron powder, Tetsuo Katsura, PPM, Vol. 7, No. 9, pp. 24-37, 1976 Treatment of hazardous substances such as heavy metals in wastewater by the iron powder method, Toshimune Kimura, PPM, Vol. 13, No. 9, pp. 47-56, 1982 Extraction technology of arsenic in mud using iron powder and magnetic separation, Shinjiro Ito et al., 20th Annual Conference on Groundwater / Soil Contamination and Prevention Measures, 8-12, 2014 Detoxification technology for arsenic-contaminated soil using iron powder, Toshihiko Miura et al., Obayashi Institute of Technology Research Report, No. 77, pp. 1-7, 2013

  The separation method using the superconducting magnet in the prior art 3 requires utilities other than electricity and water such as a cooling solvent (liquid helium or liquid nitrogen) to form and maintain the superconducting state, although it depends on the material of the magnet. There is a problem of doing. Further, since the processing capacity is relatively small compared to the occupied area, it is indispensable to use a plurality of expensive devices in a large-scale construction project.

  The centrifugal separation method in the prior art 4 has a problem that about 30% of the earth and sand content is separated together with the iron powder. Further, the screw decanter type centrifugal separator has a problem that the occupied area becomes very large.

  Furthermore, in both of the above prior art 3 and prior art 4, the iron powder for arsenic adsorption can be used repeatedly a certain number of times until the saturated adsorption amount is reached, but when applied to large construction projects, arsenic purification There is a problem that the amount of iron powder used becomes enormous.

  The present invention has been made in view of the problems of the prior art, and an object of the present invention is to provide a method and apparatus for efficiently purifying muddy water containing arsenic using a small amount of iron powder in a narrow space.

  The present inventors use a magnetic separator using a small and inexpensive permanent magnet that is widely used without using a superconducting magnet separator or a large centrifuge, and repeatedly use iron powder. In addition, it was found that muddy water containing arsenic can be efficiently purified using a small amount of iron powder in a narrow space by restoring the adsorption ability of iron powder to arsenic as needed.

That is, the present invention includes the following.
[1]
An adsorption process in which mud containing arsenic and iron powder are mixed to adsorb arsenic to the iron powder;
A separation step in which iron powder is magnetically separated from the mixture obtained in the adsorption step; and if necessary, the iron powder separated in the separation step is treated with an acid to recover the iron powder's ability to adsorb arsenic. Process;
Including
A method for purifying mud water containing arsenic, wherein the iron powder separated in the separation step or the iron powder whose adsorption ability to arsenic has been recovered in the recovery step is reused in the adsorption step.
[2]
The method according to [1], further comprising a strengthening step of forming an amorphous ferric oxide film on the surface of the iron powder whose arsenic adsorption capacity has been recovered in the recovery process, thereby strengthening the arsenic adsorption capacity of the iron powder. Purification method.
[3]
The purification method according to [1] or [2], wherein muddy water containing arsenic is continuously purified.
[4]
The purification method according to any one of [1] to [3], wherein the iron powder is used in an amount of 5% by weight or less based on the weight of the muddy water.
[5]
The purification method according to any one of [1] to [4], wherein the separation step is performed using a magnet having a surface magnetic flux density of 2000 to 13000 gauss.
[6]
The purification method according to any one of [1] to [4], wherein the separation step is performed using a ferrite magnet or a neodymium magnet.
[7]
The purification method according to any one of [1] to [6], wherein the acid used in the recovery step is ascorbic acid.
[8]
The purification method according to [7], wherein ascorbic acid is used at a concentration of 0.1 to 2 mol / L.
[9]
A device for purifying muddy water containing arsenic,
Mixing tank in which mud containing arsenic and iron powder are mixed to adsorb arsenic to iron powder;
A magnetic separation device for magnetically separating iron powder from the mixture obtained in the mixing tank;
A first return line for returning the iron powder separated by the magnetic separator to the mixing tank;
If necessary, the iron powder separated by the magnetic separation device is treated with acid to recover the adsorption capacity of iron powder to arsenic; and the iron powder whose arsenic adsorption capacity has been recovered in the recovery apparatus is a mixing tank A second return line to return to;
A purification device comprising:
[10]
A strengthening device that strengthens the adsorption ability of iron powder to arsenic by forming an amorphous ferric oxide film on the surface of the iron powder that has recovered the adsorption ability of arsenic in the recovery device; and A third return line for returning the reinforced iron powder to the mixing tank;
The purification device according to [9], further comprising:

  According to the present invention, muddy water containing arsenic can be efficiently purified using a small amount of iron powder in a narrow space.

An example of the purification procedure of contaminated mud water is shown. The outline of the purification device of a 1st embodiment is shown. The outline of the purification apparatus of 2nd Embodiment is shown. The outline of a magnetic separator is shown. A belt conveyor type reinforcing device is shown. The result of an arsenic adsorption test is shown.

  Hereinafter, the present invention will be described in detail.

<Method for purifying muddy water containing arsenic>
The present invention relates to a method for purifying muddy water containing arsenic (hereinafter also referred to as “contaminated muddy water”), which includes an adsorption step, a separation step, and a recovery step. It is preferable that the purification method according to the present invention further includes a strengthening step. The purification method according to the present invention may further include an arsenic elution step. An example of the contaminated mud water purification procedure is shown in FIG. Hereinafter, each step will be described.

[1. Adsorption process]
The adsorption step is a step of mixing mud containing arsenic and iron powder. Since iron powder can adsorb arsenic, arsenic in mud water can be adsorbed to iron powder by mixing mud water containing arsenic and iron powder.

  The contaminated muddy water in the present invention is not particularly limited as long as it contains arsenic, but in particular, surplus muddy water containing natural arsenic generated by muddy-type shield excavation work is targeted. Since surplus muddy water is continuously generated in shield excavation work, it is preferable to purify surplus muddy water continuously.

  As the iron powder in the present invention, a metal iron-based material conventionally used for adsorbing arsenic can be used. For example, it is desirable to use iron powder having an average particle size of 10 to 500 μm, preferably 20 to 200 μm, particularly preferably 50 to 100 μm. By using the iron powder having such an average particle size, arsenic contained in the contaminated mud water can be adsorbed efficiently.

  In the present invention, iron powder can be used repeatedly. Moreover, the adsorption | suction ability with respect to arsenic of iron powder can also be recovered in the recovery process described below. Therefore, a large amount of muddy water can be purified by repeatedly using a small amount of iron powder. For example, iron powder can be used in an amount of 5% by weight or less, more specifically 2 to 5% by weight, based on the weight of the muddy water. By reducing the amount of iron powder used, the material cost and the amount of secondary waste can be reduced.

  The mixing time of the iron powder and the contaminated mud is appropriately changed depending on the nature of the soil, the concentration of arsenic, the amount of iron powder used, etc., and can be 5 to 60 minutes, 15 to 30 minutes, or the like.

[2. Separation process]
The separation step is a step of separating iron powder by magnetic force from the mixture obtained in the adsorption step.

  In the present invention, iron powder can be separated by a magnetic separation device including a small and inexpensive permanent magnet that is widely used without using a large and expensive superconducting magnet. Examples of the magnet used in the separation step include a magnet having a surface magnetic flux density of 2000 to 13000 gauss, preferably 4000 gauss or more, more preferably 10,000 gauss or more. Specific examples include permanent magnets such as ferrite (isotropic and anisotropic) magnets, neodymium magnets, samarium cobalt magnets, alnico magnets, and ferrite magnets or neodymium magnets are particularly suitable. By using such a magnet, iron powder can be separated at a low cost and in a narrow space.

  The iron powder separated in the separation step is reused in the adsorption step. By reusing iron powder, the amount of iron powder to be used can be reduced, and the material cost and the amount of secondary waste can be reduced.

[3. Recovery process]
The recovery step is a step of recovering the adsorption ability of the iron powder separated in the separation step with respect to arsenic as necessary. The recovery step can be performed by treating iron powder with an acid.

  Normally, the iron powder separated in the separation step is reused as it is in the adsorption step, but arsenic is adsorbed to the iron powder to the limit by repeating the reuse. As a result, the iron powder cannot adsorb arsenic. In this case, when new iron powder is used, the amount of iron powder to be used increases, and the material cost and the amount of secondary waste increase. Here, if necessary, the use of new iron powder can be avoided by restoring the adsorption ability of the used iron powder to arsenic.

  In the present invention, “as necessary” means that a person who implements the present invention determines as appropriate. That is, the person who implements this invention can determine suitably the timing which implements a recovery process. Therefore, it is not always necessary that arsenic is adsorbed to the iron powder before the recovery step.

  For example, the arsenic concentration of contaminated mud water is investigated, the number of reuses of iron powder that is assumed to be able to sufficiently adsorb arsenic is set in advance, and the recovery process is performed after the number of reuses. May be. Alternatively, arsenic is adsorbed by iron powder, the arsenic concentration of muddy water is measured, and the recovery step may be performed when it is determined that the arsenic concentration is not sufficiently reduced.

  The recovery step can be performed by treating iron powder with an acid. Examples of the acid include organic acids and inorganic acids. Examples of the organic acid include all organic acids having a reducing action such as ascorbic acid, citric acid, and oxalic acid. Examples of the inorganic acid include sulfuric acid, hydrochloric acid, nitric acid, and adithionic acid. Although it does not specifically limit, it is preferable to use ascorbic acid from a viewpoint of the recovery effect of adsorption ability, cost, environmental harmony, etc.

  Ascorbic acid is preferably used at a concentration of 0.1 to 2 mol / L, more preferably 0.5 to 1 mol / L.

  As a method of treating iron powder with an acid, it is not necessary to use a special method, and the iron powder and acid may be brought into contact with each other. For example, the method etc. which immerse iron powder in an acid are mentioned. The dipping time may be set in consideration of the amount of iron powder, the acid concentration, and the amount of the acid solution, and may be in the range of, for example, the shortest 30 minutes to 24 hours.

  In addition, while preparing two groups of iron powder and performing the recovery | restoration process with respect to the iron powder of one group, you may use the iron powder of the other group for an adsorption | suction process. Thereby, it can prevent that purification | cleaning of contaminated mud water is interrupted in the case of a recovery process.

[4. Strengthening process]
The strengthening step is a step of strengthening the arsenic adsorption ability of the iron powder subjected to the recovery step. The strengthening step can be performed by forming an amorphous ferric oxide coating on the surface of the iron powder.

  Usually, the iron powder whose arsenic adsorption capacity has been recovered in the recovery process is reused in the adsorption process. Since the adsorption capacity of the recycled iron powder has been recovered, new contaminated mud water should be able to be purified efficiently. However, surplus muddy water is continuously generated in shield excavation work, and the arsenic concentration of surplus muddy water may be high depending on the excavation site. In this case, there is a possibility that the contaminated mud water cannot be sufficiently purified by the normal adsorption capacity of iron powder. In that case, if the usage-amount of iron powder is increased, material cost and the amount of secondary waste will increase. Here, by strengthening the iron powder adsorption capacity, it becomes possible to sufficiently purify contaminated mud water having a high arsenic concentration without increasing the amount of iron powder used.

  The strengthening step can be performed by forming an amorphous ferric oxide coating on the surface of the iron powder. Specifically, an amorphous ferric oxide coating can be formed by treating the surface of the iron powder with a ferrous sulfate solution or the like and drying it.

  As a method of treating the surface of the iron powder with the ferrous sulfate solution, the surface of the iron powder and the ferrous sulfate solution may be contacted and then dried in the air. For example, a method of immersing iron powder in a ferrous sulfate solution or spraying a ferrous sulfate solution on the iron powder and then drying it may be used.

[5. Arsenic elution process]
The arsenic elution step is a step of eluting arsenic contained in mud (solid content) of contaminated mud water into the water before performing the adsorption step. The arsenic content of mud can be further reduced by positively eluting arsenic contained in the mud (solid content) and then performing adsorption with iron powder.

  The arsenic elution step can be carried out by treating the contaminated mud with acid or alkali. Specifically, acid or alkali may be added to the contaminated mud and stirred. The stirring time can be set to 5 to 30 minutes, for example, and can be added simultaneously with the iron powder.

  Examples of the acid include sulfuric acid, phosphoric acid, and oxalic acid. Examples of the alkali include sodium hydroxide and potassium hydroxide.

  As described above, the purification method according to the present invention includes an adsorption step, a separation step, and a recovery step, preferably further includes a strengthening step, and optionally further includes an arsenic elution step. Note that the steps included in the purification method according to the present invention are not limited to those described above, and may include additional steps as necessary. For example, a solid-liquid separation step for solid-liquid separation of muddy water from which iron powder has been separated in the separation step may be included.

  In the purification method according to the present invention, iron powder can be separated by a magnetic separation apparatus using a small and inexpensive permanent magnet that is widely used without using a superconducting magnet (separation step). In the purification method according to the present invention, the iron powder can be reused, and the iron powder adsorption capacity can be recovered as necessary (recovery process). If the arsenic concentration of the contaminated mud water becomes high, the iron powder can be recovered. Powder adsorption ability can be strengthened (strengthening step). Therefore, the contaminated mud can be purified at a low cost in a narrow space, and the amount of secondary waste can be reduced. Moreover, the continuously generated contaminated mud can be purified continuously. Furthermore, even if the arsenic concentration of contaminated mud water becomes high, it can respond without increasing the amount of iron powder.

<Purification device for muddy water containing arsenic>
A purification apparatus according to the present invention for carrying out the above purification method will be described below with reference to the drawings. However, the following embodiment is only an example, and the embodiment of the purification apparatus according to the present invention is not limited thereto. In the range which does not deviate from the meaning of this invention, the apparatus which consists of a further structure is included by this invention. In addition, the overlapping part is abbreviate | omitted suitably in description of each following embodiment.

[First Embodiment]
As shown in FIG. 2, the first embodiment of the present invention relates to a purification apparatus including a mixing tank 101, a magnetic separation device 102, a first return line 103, a recovery device 104, and a second return line 105.

  The mixing tank 101 mixes contaminated mud water and iron powder to adsorb arsenic to the iron powder. The mixing tank 101 includes a stirrer 108 that mixes contaminated mud water and iron powder, and includes a mixture delivery line 109 that delivers a mixture obtained by mixing to the magnetic separation device 102. The outlet end of the mixture delivery line 109 is located above or inside the magnetic separation device 102 so that the mixture can be introduced into the magnetic separation device 102.

  The magnetic separation device 102 separates the iron powder having adsorbed arsenic in the mixing tank 101 from the mixture by magnetic force. A purified muddy water storage container 110 for storing the purified muddy water is disposed below the magnetic separation device 102.

  The first return line 103 returns the iron powder separated by the magnetic separation device 102 to the mixing tank 101.

  The recovery device 104 treats the iron powder separated by the magnetic force separation device 102 with an acid as necessary to recover the adsorption ability of the iron powder to arsenic. The recovery device 104 includes a recovery iron powder delivery line 112 that delivers the iron powder whose adsorption capacity has been recovered to the magnetic separation device 111. The outlet end of the recovery iron powder delivery line 112 is located above or inside the magnetic separation device 111 so that the iron powder can be put into the magnetic separation device 111.

  The magnetic separation device 111 separates the iron powder whose adsorption capacity has been recovered in the recovery device 104 by magnetic force. An arsenic-containing solution storage container 113 that stores a solution containing arsenic removed from the iron powder by the acid treatment is disposed below the magnetic separation device 111. The arsenic-containing solution can also be used a plurality of times, and a line for returning the solution from the arsenic-containing solution storage container 113 to the recovery device 104 can be provided.

  The second return line 105 returns the iron powder recovered by the magnetic separation device 111 and recovered to the mixing tank 101.

  As the magnetic separation device, it is preferable to use a general-purpose simple maglet separator. For example, as shown in FIG. 4, the magnet separator includes a magnet core 901, an outer cylinder 902 that covers the outer periphery of the magnet core 901, a roller 903 that squeezes moisture out of iron powder attached to the outer cylinder 902, and a roller 903. And a scraper 904 that peels off the iron powder squeezed from the outer cylinder 902.

  In the purification apparatus according to the present invention, iron powder can be separated by a magnetic force from a small and inexpensive magnet that is widely used without using a large and expensive superconducting magnet. Therefore, a magnet having a surface magnetic flux density of, for example, 2000 to 13000 gauss, preferably 4000 gauss or more, more preferably 10,000 gauss or more can be used as the magnet core. Specifically, permanent magnets such as ferrite (isotropic and anisotropic) magnets, neodymium magnets, samarium cobalt magnets, and alnico magnets can be used as the magnet core.

  Examples of the recovery device include a container containing an acid for recovering the iron powder adsorption ability.

  In the purification apparatus of the first embodiment configured as described above, contaminated mud water and iron powder are mixed in the mixing tank 101, and arsenic is adsorbed to the iron powder in the mixture. The mixture is delivered to the magnetic separation device 102 via the mixture delivery line 109, and the iron powder is separated from the mixture by magnetic force. The purified muddy water from which the iron powder is separated is stored in the purified muddy water storage container 110. The iron powder separated by the magnetic separation device 102 is returned to the mixing tank 101 via the first return line 103, but is sent to the recovery device 104 as needed to recover the adsorption capacity. The iron powder whose adsorptive capacity has been recovered is returned to the mixing tank 101 via the second return line 105. The arsenic-containing solution can also be used a plurality of times, and a line for returning the solution from the arsenic-containing solution storage container 113 to the recovery device 104 can be provided.

  According to the purification apparatus of the first embodiment, contaminated mud water can be purified at a low cost in a narrow space, and the amount of secondary waste can be reduced. Moreover, according to the purification apparatus of 1st Embodiment, the polluted mud which generate | occur | produces continuously can be purified continuously.

[Second Embodiment]
As shown in FIG. 3, the second embodiment of the present invention includes a mixing tank 201, a magnetic separation device 202, a first return line 203, a recovery device 204, a second return line 205, a strengthening device 206, and a first The present invention relates to a purification device including three return lines 207.

  The second embodiment differs from the first embodiment in that it includes a strengthening device 206, a third return line 207, and the like.

  The strengthening device 206 forms an amorphous ferric oxide coating on the surface of the iron powder whose arsenic adsorption ability has been recovered by the recovery device 204, thereby strengthening the arsenic adsorption ability of the iron powder. The strengthening device 206 includes a strengthened iron powder delivery line 215 that delivers iron powder with enhanced adsorption capacity to the magnetic separation device 214. The exit end of the reinforced iron powder delivery line 215 is located above or inside the magnetic separation device 214 so that the iron powder with enhanced adsorption ability can be put into the magnetic separation device 214.

  The magnetic separation device 214 separates the iron powder whose adsorption capacity is enhanced in the strengthening device 206 by a magnetic force. A used strengthened solution storage container 216 that stores the ferrous sulfate solution used for forming the amorphous ferric oxide coating is disposed below the magnetic separation device 214.

  The third return line 207 returns the iron powder with enhanced adsorption ability separated by the magnetic separation device 214 to the mixing tank 201.

  Examples of the strengthening device include a container containing a ferrous sulfate solution for forming an amorphous ferric oxide coating on the surface of iron powder. Instead of the reinforcing device 206 and the magnetic force separating device 214, a belt conveyor type reinforcing device 306 as shown in FIG. 5 may be used. The strengthening device 306 includes a belt conveyor 317 that conveys iron powder and a spraying means 318 (for example, a nozzle) that sprays the ferrous sulfate solution onto the iron powder.

  In the purification apparatus of the second embodiment configured as described above, when the arsenic concentration of the contaminated mud becomes high, the iron powder whose adsorptive capacity separated by the magnetic separation apparatus 211 is recovered is sent to the strengthening apparatus 206. It is delivered and the adsorption capacity is enhanced. The iron powder with enhanced adsorption capacity is returned to the mixing tank 201 via the third return line 207.

  According to the purification device of the second embodiment, the contaminated mud can be purified at a low cost in a narrow space, and the amount of secondary waste can be reduced. Moreover, according to the purification apparatus of 2nd Embodiment, the polluted mud which generate | occur | produces continuously can be purified continuously. Furthermore, according to the purification apparatus of 2nd Embodiment, even if the arsenic density | concentration of contaminated mud water becomes high, it can respond, without increasing the quantity of iron powder.

  EXAMPLES Hereinafter, although this invention is demonstrated in detail using an Example, the technical scope of this invention is not limited to this.

<Example 1: Arsenic adsorption test>
Contaminated mud water with a specific gravity adjusted to 1.3 was prepared using actual contaminated soil whose elution concentration exceeded about 4 times the arsenic elution amount standard value of 0.01 mg / L. Iron powder of 5% of the weight of the contaminated mud was added and mixed for 30 minutes, and then the iron powder was magnetically separated. Both the arsenic elution amount of the dehydrated cake obtained from the purified mud water and the arsenic concentration of the filtrate were in agreement with the standard values. The results are shown in FIG.

<Example 2: Adsorption capacity recovery test>
Arsenic adsorption iron powder 2g, and 100mL of arsenic solution adjusted to a concentration of 10mg / L are sealed in a vial. Each time the concentration decreases, it is equivalent to 1mg of new arsenic (corresponding to a concentration of 10mg / L with 100mL solution) A continuous batch test was conducted to add.

  When the effect of reducing the arsenic concentration became low, the iron powder was immersed in 0.1 M ascorbic acid solution for 30 minutes, and the arsenic adsorption effect was confirmed again by a continuous batch test.

The main test results are shown in Table 1.

(Evaluation of adsorption speed)
When the adsorption rate is the amount of arsenic that the iron powder unit weight adsorbed in 1 hour from the concentration decrease at 1 hour immediately after the start of the test, 0.475 mg-As / (g-Fe · hr). After that, when arsenic was added multiple times, the rate of concentration decrease gradually slowed, and the adsorption rate dropped to 0.0031 mg-As / (g-Fe · hr) before the functional recovery.

  After that, the iron powder whose adsorptive capacity was recovered had an adsorption rate of 0.430 mg-As / (g-Fe · hr). From this, it was possible to recover the reactivity of the iron powder by being immersed in the ascorbic acid solution, and to recover to about 90% of the initial state.

(Evaluation of saturated adsorption amount)
The amount of arsenic adsorbed before reaching the saturated adsorption amount from the initial state and no decrease in concentration was observed (before immersion in ascorbic acid) was 1.8 mg per gram of iron powder.

  Thereafter, the amount of arsenic adsorbed until the decrease in concentration was not observed again after the treatment for 30 minutes in the ascorbic acid 0.1 M solution was 1.5 mg per 1 g of iron powder. From the above, it was possible to recover the residual adsorption amount of iron powder to 83% of the initial value.

  In addition, the iron concentration in the ascorbic acid solution of the said Example was 55 mg / L, and was 5.5 mg per 100 mL of solutions. Since the amount of iron powder was 2 g, the amount of dissolved iron was 0.28%, and it was also confirmed that there was almost no loss.

  Actually, it is possible to further improve the adsorption performance to be recovered by appropriately setting the concentration of ascorbic acid solution and the immersion time within a range where there is no loss of iron powder.

<Example 3: Adsorption capacity enhancement test>
By immersing 100 g of iron powder in 200 mL of a 1M solution of ferrous sulfate and drying at 60 ° C., an amorphous ferric oxide coating was formed on the surface of the iron powder, and the iron powder adsorption performance was enhanced. 140 g of iron powder with enhanced adsorption capacity was prepared. 2 g of iron powder with enhanced adsorption capacity and 100 mL of an arsenic solution adjusted to a concentration of 10 mg / L are sealed in a vial bottle, and each time the concentration decreases, it is successively equivalent to 1 mg of arsenic (to a concentration of 10 mg / L with a 100 mL solution). A continuous batch test was added to add).

  The test data of the normal iron powder for comparison is the same as the test data until the adsorption ability shown in Table 1 is recovered. In the iron powder with enhanced adsorption capacity, even when arsenic was added 8 times, a significant reduction in arsenic concentration was confirmed each time. On the other hand, with normal iron powder, no significant decrease in arsenic concentration was observed after adding arsenic three times (about 170 hours).

The cumulative amount of arsenic adsorption was 1.8 mg / g for normal iron powder, whereas it was 5.49 mg / g for iron powder with enhanced adsorption capacity, and the adsorption capacity was improved almost three times ( Table 2).

101, 201 ... Mixing tank 102, 202 ... Magnetic separation device 103, 203 ... First return line 104, 204 ... Recovery device 105, 205 ... Second return line 206, 306 ... Strengthening device 207・ ・ Third return lines 108 and 208 ・ ・ Stirrers 109 and 209 ・ ・ Mixture delivery lines 110 and 210 ・ ・ Purified mud storage containers 111 and 211 ・ ・ Magnetic separators 112 and 212 ・ ・ Recovered iron powder delivery line 113 ··· Arsenic-containing solution container 214 ·· Magnetic separation device 215 · · Strengthened iron powder delivery line 216 · · Used reinforcing solution container 317 · · Belt conveyor 318 · · Dispersing means 901 · · Magnet core 902 · · Outer cylinder 903, Roller 904, Scraper

Claims (5)

(1) An adsorption step in which muddy water containing arsenic and iron powder are mixed to adsorb arsenic to the iron powder , and a separation step in which iron powder is separated from the mixture obtained in the adsorption step by magnetic force ,
A cycle in which the iron powder separated in the separation step is reused in the adsorption step ;
(2) An adsorption process in which mud containing arsenic and iron powder are mixed to adsorb arsenic to iron powder,
A separation step of magnetically separating iron powder from the mixture obtained in the adsorption step; and
A recovery process in which the iron powder separated in the separation process is treated with an acid to restore the adsorption ability of the iron powder to arsenic;
A cycle in which the iron powder having recovered arsenic adsorption ability in the recovery step is reused in the adsorption step; and
(3) An adsorption process in which mud containing arsenic and iron powder are mixed to adsorb arsenic to iron powder,
A separation step of magnetically separating iron powder from the mixture obtained in the adsorption step;
A recovery step of treating the iron powder separated in the separation step with an acid to restore the adsorption ability of the iron powder to arsenic; and
A strengthening step of forming an amorphous ferric oxide coating on the surface of the iron powder whose arsenic adsorption capacity has been recovered in the recovery process, and strengthening the arsenic adsorption capacity of the iron powder,
A cycle of reusing iron powder with enhanced arsenic adsorption capacity in the adsorption process in the adsorption process;
A method for purifying muddy water containing arsenic.   The purification method according to claim 1, wherein the iron powder is used in an amount of 5% by weight or less based on the weight of the muddy water.   The purification method according to claim 1 or 2, wherein the separation step is performed using a magnet having a surface magnetic flux density of 2000 to 13000 gauss.   The purification method according to claim 1, wherein the acid used in the recovery step is ascorbic acid. A device for purifying muddy water containing arsenic,
Mixing tank in which mud containing arsenic and iron powder are mixed to adsorb arsenic to iron powder;
A magnetic separation device for magnetically separating iron powder from the mixture obtained in the mixing tank;
A first return line for returning the iron powder separated by the magnetic separator to the mixing tank;
A recovery device for treating the iron powder separated by the magnetic separation device with an acid to recover the adsorption ability of the iron powder to arsenic;
A second return line for returning the iron powder whose arsenic adsorption capacity has been recovered in the recovery device to the mixing tank;
A strengthening device that strengthens the adsorption ability of iron powder to arsenic by forming an amorphous ferric oxide film on the surface of the iron powder that has recovered the adsorption ability of arsenic in the recovery device; and A third return line for returning the reinforced iron powder to the mixing tank;
A purification device comprising:

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