JP6842839B2 - Arsenic recovery method and arsenic-containing muddy water purification method and purification device - Google Patents

Description

The present invention relates to a method for recovering arsenic, a method for purifying muddy water containing arsenic, and a purification device.

So far, in Japan, the following prior art 1 or prior art 2 has been used to deal with naturally occurring arsenic-containing soil generated during construction work. In each case, it was possible to carry out the project in the construction area without taking any special measures against harmful metals.

<Conventional technology 1: Landfill on the sea surface as soil generated from construction>
"Ministerial Ordinance Establishing Judgment Criteria for Waste Containing Metals, etc. to be Discharged to Landfill Sites, etc. Prescribed in Article 5, Paragraph 1 of the Ordinance for Enforcement of the Law Concerning Prevention of Marine Pollution, etc. According to the standard stipulated in the 17th General Ordinance No. 6, Final Amendment: May 30, 2014 Ministry of the Environment Ordinance No. 19), the so-called "Judgment Criteria for Underwater Sediment", the elution amount standard value of heavy metals is It is generally allowed up to 10 times the soil environmental standard. Regarding arsenic, the soil elution amount standard is 0.01 mg / L, whereas the judgment standard for bottom sediment is 0.1 mg / L. Therefore, it was possible to clear the elution concentration of almost all naturally-derived arsenic-contaminated soil, and if there was a recipient for landfill at sea level, it was possible to carry out arsenic as it was without treatment (). In the Tokyo metropolitan area, the New Marine Disposal Site and Minamihonmaki Pier are examples).

<Previous technology 2: Dispose of as sludge when the heavy metal elution amount standard is exceeded>
Based on the concentration control during construction or the judgment in the preliminary survey, there was a method of transporting the generated soil exceeding the heavy metal elution amount standard to a designated contractor as construction sludge, and then transporting it to a cement raw material or a disposal site.

However, although the prior art 1 has a track record in relatively large-scale projects, the disposal site and disposal capacity are tight, and public works projects of the local governments are prioritized. The disposal capacity (acceptable amount) of the conventional technology 2 is also limited, and the amount of naturally-derived contaminated soil that is expected to be generated from large-scale projects to be implemented in the Tokyo metropolitan area and the Chukyo area in the future The capacity is overwhelmingly insufficient.

By the way, the finding that iron powder adsorbs heavy metals including arsenic has become a known fact in the field of wastewater treatment around 1980 (for example, Non-Patent Documents 1 and 2). As a method of adsorbing arsenic with iron powder, for example, the following conventional techniques 3 and 4 are known.

<Prior technology 3: A method of adsorbing arsenic on iron powder and sorting the magnetic force with a superconducting magnet separator>
A method has been proposed 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 magnetic separation device using a superconducting magnet (Non-Patent Document 3).

<Prior Technique 4: A method of adsorbing arsenic on iron powder and collecting it with a centrifuge>
A method has been proposed 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 centrifuge using a difference in specific gravity (Non-Patent Document 4).

However, in the separation method using a superconducting magnet in the prior art 3, a utility other than electricity and water such as a cooling solvent (liquid helium or liquid nitrogen) is used to form and maintain a superconducting state, depending on the material of the magnet. There is a problem of needing it. In addition, 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 is separated together with the iron powder. Further, the screw decanter type centrifuge has a problem that the occupied area becomes very large. Further, in both the prior art 3 and the prior art 4, the iron powder for adsorbing arsenic can be repeatedly used a certain number of times until the saturated adsorption amount is reached, but when applied to a large-scale construction project, arsenic purification is performed. There is a problem that the amount of iron powder used becomes enormous.

Therefore, Patent Document 1 discloses a method for solving the above-mentioned problems. Specifically, Patent Document 1 uses a magnetic force sorter using a general-purpose small and inexpensive permanent magnet, and repeatedly uses iron powder, and if necessary, the ability to attract iron powder to arsenic. Discloses a method characterized by the recovery of.

Japanese Patent No. 5746407

Problems and Treatment Effects of Batch Treatment of Hazardous Substances in Wastewater by Iron Powder, Tetsuo Katsura, PPM, Vol. 7, No. 9, pp. 24-37, 1976 Treatment of harmful substances such as heavy metals in wastewater by the iron powder method, Toshimune Kimura, PPM, Vol. 13, No. 9, pp. 47-56, 1982 Arsenic Extraction Technology in Muddy Water by Iron Powder and Magnetic Separation, Keijiro Ito et al., 20th Research Meeting on Groundwater / Soil Contamination and its Prevention Measures, pp. 8-12, 2014 Cleaning and detoxifying technology for arsenic-contaminated soil using iron powder, Toshihiko Miura et al., Obayashi Technical Research Institute Bulletin, No. 77, pp. 1-7, 2013

According to the method of Patent Document 1, muddy water containing arsenic can be efficiently purified by using a small amount of iron powder in a narrow space. However, there is still room for improvement in the method of Patent Document 1. That is, the method of Patent Document 1 includes a recovery step of treating the used iron powder with an acidic solution in order to recover the adsorption ability of the used iron powder (that is, the iron powder that has adsorbed arsenic) to arsenic. However, an acidic liquid containing a high concentration of arsenic is generated in the recovery process. A high cost is required to dispose of an acidic solution containing a high concentration of arsenic.

Therefore, an object of the present invention is to provide a method for recovering arsenic from an acidic solution containing a high concentration of arsenic. Another object of the present invention is to provide a method for purifying muddy water containing arsenic and a purifying device incorporating the recovery method.

As a result of diligent studies by the present inventors, it has been found that arsenic can be precipitated and separated from the acidic solution by electrolyzing an acidic solution containing a high concentration of arsenic.

The present invention includes the following embodiments.
[1] An acidic solution containing arsenic generated by treating iron powder adsorbing arsenic with an acidic solution is electrolyzed in an electrolyzer equipped with a cathode and an anode to precipitate and separate arsenic from the acidic solution. Arsenic recovery methods, including.
[2] Arsenic, which comprises electrolyzing an acidic solution containing arsenic and 500 to 23,000 (mg / L) of iron in an electrolyzer equipped with a cathode and an anode to precipitate and separate arsenic from the acidic solution. How to collect.
[3] The method for recovering arsenic according to [2], wherein the concentration of arsenic contained in the acidic solution is 10 to 500 (mg / L).
[4] The method for recovering arsenic according to any one of [1] to [3], wherein the acidic solution is an ascorbic acid solution.
[5] The method for recovering arsenic according to any one of [1] to [4], wherein the cathode is a stainless steel electrode and the anode is a carbon electrode.
[6] Recovery of arsenic according to any one of [1] to [5], wherein the cathode and the anode have a flat plate shape, and the cathode and the anode are arranged in parallel with an interval of 1.0 to 2.0 cm. Method.
[7] (1) An adsorption step of mixing muddy water containing arsenic and iron powder to adsorb arsenic to the iron powder, and a separation step of separating iron powder from the mixture obtained in the adsorption step by magnetic force.
The first cycle of reusing the iron powder separated in the separation step in the adsorption step; and (2) the adsorption step of mixing muddy water containing arsenic and iron powder to adsorb arsenic to the iron powder.
A separation step of separating iron powder from the mixture obtained in the adsorption step by magnetic force, and a recovery step of treating the iron powder separated in the separation step with an acidic solution to restore the adsorption ability of the iron powder to arsenic.
A second cycle in which iron powder whose adsorption capacity for arsenic has been restored in the recovery step is reused in the adsorption step;
Including
The arsenic-containing acidic liquid generated in the recovery step is subjected to the arsenic recovery method according to any one of [1] to [6], and further includes an electrolysis step of precipitating and separating arsenic from the acidic liquid. How to purify muddy water, including.
[8] The method for purifying muddy water containing arsenic according to [7], wherein the acidic liquid obtained in the electrolysis step and from which arsenic is precipitated and separated is reused in the recovery step.
[9] A device for purifying muddy water containing arsenic.
A mixing tank that mixes muddy water containing arsenic and iron powder to adsorb arsenic to the iron powder;
A magnetic force separator that separates iron powder from the mixture obtained in the mixing tank by magnetic force;
A first return line that returns the iron powder separated by the magnetic force separator to the mixing tank;
A recovery device that restores the adsorption capacity of iron powder to arsenic by treating the iron powder separated by the magnetic force separation device with an acidic solution;
A second return line that returns iron powder that has recovered its ability to adsorb arsenic in the recovery device to the mixing tank;
An electrolyzer that electrolyzes an acidic solution containing arsenic generated in a recovery device to precipitate and separate arsenic from the acidic solution; and an acidic solution obtained in an electrolysis device from which arsenic is precipitated and separated is used as a recovery device. Third return line to return;
A device for purifying muddy water containing arsenic.

According to the present invention, arsenic can be recovered from an acidic solution containing a high concentration of arsenic.

An example of a procedure for purifying muddy water containing arsenic is shown. The outline of one embodiment of the purification device is shown. An outline of one embodiment of the magnet separator is shown. The relationship between the energization time and the arsenic removal rate under the electrolysis conditions of Example 1 (electrode spacing: 5.0 cm, contact electrode area: about 400 cm ^{2) is shown.} The relationship between the energization time and the arsenic removal rate under the electrolysis conditions of Example 2 (electrode spacing: 1.5 cm, contact electrode area: about 576 cm ^{2) is shown.} The fluorescence X-ray spectrum of the cathode surface after electrolysis of Example 2 by the energy dispersive X-ray fluorescence analyzer is shown.

<Arsenic recovery method>
One embodiment of the present invention relates to a method for recovering arsenic, which comprises electrolyzing an acidic liquid containing arsenic (hereinafter, also referred to as “contaminated acidic liquid”) to precipitate and separate arsenic from the acidic liquid.

Examples of the contaminated acidic liquid include a contaminated acidic liquid generated by treating iron powder adsorbing arsenic with an acidic liquid. More specifically, as the contaminated acidic liquid, the contaminated acidic liquid generated by treating the iron powder adsorbing naturally-derived arsenic contained in the surplus muddy water generated by the muddy water type shield excavation work with the acidic liquid can be mentioned. Can be done.

In addition, examples of the contaminated acidic liquid include an acidic liquid containing a predetermined concentration of arsenic and a predetermined concentration of iron. Examples of the arsenic concentration include 10 to 500 (mg / L), 50 to 400 (mg / L), 90 to 200 (mg / L) and the like. Examples of the iron concentration include 500 to 23,000 (mg / L), 1,000 to 15,000 (mg / L), 3,000 to 12,000 (mg / L), and the like. ..

Examples of the acid contained in the contaminated acidic liquid include an organic acid and an inorganic acid. 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 adithioic acid.

The electrolysis of the contaminated acidic liquid can be carried out, for example, by an electrolyzer equipped with a cathode and an anode. As the material of the electrode, it is not necessary to use a special material, and a material generally used in the technical field to which the present invention belongs can be applied. Examples of the cathode material include various stainless steels, palladium, nickel, titanium and the like. As the stainless steel, SUS304 or the like, which is widely used as austenitic stainless steel, can also be used. Examples of the material of the anode include carbon, aluminum, copper or titanium, or a titanium plate material plated with platinum.

X / Y when ^{the amount (m 3} ) of the contaminated acidic liquid filled in the electrolyzer ^{is X and the total area (m 2} ) of the cathode and anode parts in contact with the contaminated acidic liquid is Y. Is preferably 0.025 m or less, more preferably 0.020 m or less, and further preferably 0.015 m or less. By setting X / Y to the above value, arsenic can be efficiently precipitated and separated. The lower limit of X / Y is not particularly limited, and examples thereof include 0.010 m and 0.005 m.

The shapes of the cathode and the anode of the electrolyzer are not particularly limited, but are preferably flat plates. Further, it is preferable to arrange the flat plate-shaped cathode and the anode in parallel. The distance between the cathode and the anode is preferably 0.1 to 5.0 cm, more preferably 0.5 to 4.0 cm, still more preferably 0.5 to 3.0 cm, and 1 It is particularly preferably 0 to 2.0 cm. By setting the electrode spacing to the above value, the current value can be increased and arsenic can be efficiently deposited and separated.

By electrolyzing the contaminated acidic liquid, arsenic is deposited on the surface of the cathode, so that arsenic can be recovered from the contaminated acidic liquid. The acidic liquid in which arsenic is precipitated and separated can be reused for treating the iron powder adsorbing arsenic. In addition, the acidic liquid in which arsenic is precipitated and separated can be discarded at a low cost. The recovered arsenic concentrated on the cathode surface can be purified as needed and reused as a resource for various purposes.

<How to purify muddy water containing arsenic>
One embodiment of the present invention relates to a method for purifying arsenic-containing muddy water (hereinafter, also referred to as “contaminated muddy water”), which includes an adsorption step, a separation step, a recovery step, and an electrolysis step. The purification method according to the present embodiment includes, for example, (1) a first cycle including an adsorption step and a separation step and reusing iron powder in the adsorption step; and (2) an adsorption step, a separation step and a recovery step. , A second cycle of reusing iron powder in the adsorption step; further includes an electrolysis step on an acidic liquid containing arsenic. The first cycle and the second cycle can be carried out a plurality of times in any order. An example of the procedure for purifying contaminated muddy water is shown in FIG. Hereinafter, each step will be described.

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

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

As the iron powder, a material mainly composed of metallic iron, which has been 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, and particularly preferably 50 to 100 μm. By using iron powder having such an average particle size, arsenic contained in contaminated muddy water can be efficiently adsorbed.

In the purification method according to the present embodiment, iron powder can be used repeatedly. Further, in the recovery step described below, the ability of iron powder to adsorb to arsenic can be recovered. 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 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 muddy water is appropriately changed depending on the soil properties, the concentration of arsenic, the amount of the iron powder used, and the like, and can be, for example, 5 to 60 minutes, 15 to 30 minutes, and the like.

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

In the purification method according to the present embodiment, iron powder can be separated by a magnetic force separating device including a general-purpose small and inexpensive permanent 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, and more preferably 10000 gauss or more. Specific examples thereof include permanent magnets such as ferrite (isotropic and isotropic) magnets, neodymium magnets, samarium-cobalt magnets, and alnico magnets, and ferrite magnets or neodymium magnets are particularly preferable. By using such a magnet, iron powder can be separated at 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 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 to arsenic, if necessary. The recovery step can be carried out by treating the iron powder with an acidic solution.

Normally, the iron powder separated in the separation step is reused as it is in the adsorption step, but by repeating the reuse, arsenic is adsorbed to the iron powder to the limit. As a result, the iron powder cannot adsorb arsenic. In this case, if new iron powder is used, the amount of iron powder 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 recovering the adsorption ability of the used iron powder to arsenic.

As used herein, the term "as needed" means that the person practicing the present invention decides as appropriate. That is, the timing for carrying out the recovery step can be appropriately determined by the person who carries out the present invention. Therefore, it is not always necessary for arsenic to be adsorbed to the limit on the iron powder before the recovery step is performed.

For example, the arsenic concentration in contaminated muddy water is investigated, the number of times of reuse of iron powder that is expected to be able to sufficiently adsorb arsenic is set in advance, and the recovery process is carried out after the number of times of reuse You may. Alternatively, arsenic may be adsorbed by iron powder, the arsenic concentration in the muddy water may be measured, and a recovery step may be carried out when it is determined that the arsenic concentration has not sufficiently decreased.

The recovery step can be carried out by treating the iron powder with an acidic solution. Examples of the acid contained in the acidic liquid include an organic acid and an inorganic acid. 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 adithioic acid. Although not particularly limited, it is preferable to use ascorbic acid from the viewpoint of recovery effect of adsorption ability, cost, environmental harmony and the like.

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 for treating the iron powder with an acidic liquid, it is not necessary to use a special method, and the iron powder and the acidic liquid may be brought into contact with each other. For example, a method of immersing iron powder in an acidic liquid can be mentioned. The immersion time may be set in consideration of the amount of iron powder, the concentration of acid, and the amount of acidic liquid, and may be, for example, in the range of 30 minutes to 24 hours at the shortest.

Two groups of iron powder may be prepared, and while the recovery step is performed on the iron powder of one group, the iron powder of the other group may be used in the adsorption step. This makes it possible to prevent the purification of contaminated muddy water from being interrupted during the recovery process.

[4. Electrolysis process]
The electrolysis step is a step of electrolyzing an acidic liquid containing arsenic generated in the recovery step to precipitate and separate arsenic from the acidic liquid. The electrolysis step can be carried out as described in the above <Arsenic recovery method>.

The acidic liquid obtained by precipitating and separating arsenic obtained in the electrolysis step can be reused in the recovery step. By reusing the acidic liquid, the amount of the acidic liquid used can be reduced, and the material cost and the amount of secondary waste can be reduced.

Arsenic precipitated and separated in the electrolysis step can be recovered, purified as needed, and reused as a resource in various applications.

[5. Strengthening process]
The purification method according to the present embodiment may further include a strengthening step. The strengthening step is a step of strengthening the adsorption ability of the iron powder for which the recovery step has been carried out to arsenic. The strengthening step can be carried out by forming an amorphous ferric oxide film on the surface of the iron powder.

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

The strengthening step can be carried out by forming an amorphous ferric oxide film on the surface of the iron powder. Specifically, the surface of the iron powder is treated with a ferrous sulfate solution or the like and dried to form an amorphous ferrous oxide film.

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 brought into contact with each other and then dried in the air. For example, a method of immersing the iron powder in a ferrous sulfate solution, or spraying the ferrous sulfate solution on the iron powder and then drying the iron powder can be mentioned.

As described above, the purification method according to the present embodiment includes an adsorption step, a separation step, a recovery step, and an electrolysis step, and optionally further includes a strengthening step. The steps included in the purification method according to the present embodiment are not limited to those described above, and may include further steps if necessary. For example, an arsenic elution step in which arsenic contained in the mud (solid content) of contaminated muddy water is eluted into water before the adsorption step, a solid-liquid separation step in which the muddy water from which iron powder is separated in the separation step is solid-liquid separated, and the like. It may be included.

In the purification method according to the present embodiment, iron powder can be separated by a magnetic force separating device using a general-purpose small and inexpensive permanent magnet (separation step). Further, in the purification method according to the present embodiment, the iron powder can be reused, and the adsorption ability of the iron powder can be restored as needed (recovery step). Further, in the purification method according to the present embodiment, arsenic can be precipitated and separated and the acidic liquid can be reused (electrolysis step). Therefore, according to the purification method according to the present embodiment, contaminated muddy water can be purified at low cost in a narrow space, and the amount of secondary waste can be reduced.

<Muddy water purification device containing arsenic>
The purification device according to the present invention for carrying out the above purification method will be described below with reference to the drawings. However, the following embodiments are merely examples, and the embodiments of the purification device according to the present invention are not limited thereto. A device having a further configuration is included in the present invention without departing from the spirit of the present invention.

As shown in FIG. 2, one embodiment of the present invention includes a mixing tank 101, a magnetic force separating device 102, a first return line 103, a recovery device 104, a second return line 105, an electrolyzer 106, and a third. The present invention relates to a purification device including a return line 107 of the above.

The mixing tank 101 mixes contaminated muddy water and iron powder to adsorb arsenic to the iron powder. The mixing tank 101 has a stirrer 108 that mixes contaminated muddy water and iron powder, and includes a mixture delivery line 109 that sends the mixture obtained by mixing to the magnetic force separator 102. The outlet end of the mixture delivery line 109 is located above or inside the magnetic force separator 102 so that the mixture can be charged into the magnetic force separator 102.

The magnetic force separating device 102 separates the iron powder adsorbed with arsenic in the mixing tank 101 from the mixture by magnetic force. A purified muddy water storage tank 110 for accommodating purified muddy water is arranged below the magnetic force separating device 102.

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

The recovery device 104 recovers the adsorption ability of the iron powder to arsenic by treating the iron powder separated by the magnetic force separation device 102 with an acidic solution, if necessary. The recovery device 104 may have a stirrer (not shown) that mixes the iron powder and the acidic liquid. The recovery device 104 includes a recovery iron powder delivery line 112 that sends iron powder whose adsorption capacity has been restored to the magnetic force separation device 111. The outlet end of the recovery iron powder delivery line 112 is located above or inside the magnetic force separator 111 so that the iron powder can be charged into the magnetic force separator 111.

The magnetic force separation device 111 separates the iron powder whose adsorption ability has been restored by the recovery device 104 by magnetic force. A contaminated acidic liquid accommodating tank 113 for accommodating the contaminated acidic liquid is arranged below the magnetic force separating device 111. The contaminated acidic liquid storage tank 113 includes a contaminated acidic liquid delivery line 114 that sends the contaminated acidic liquid to the electrolyzer 106. The outlet end of the contaminated acidic liquid delivery line 114 is located above or inside the electrolyzer 106 so that the contaminated acidic liquid can be charged into the electrolyzer 106. Since the contaminated acidic liquid can be reused a plurality of times without passing through the electrolyzer 106, a line for returning the contaminated acidic liquid from the contaminated acidic liquid storage tank 113 to the recovery device 104 (not shown). May be provided.

The second return line 105 returns the iron powder whose adsorption capacity has been restored, which has been separated by the magnetic force separating device 111, to the mixing tank 101.

The electrolysis device 106 electrolyzes the contaminated acidic liquid generated in the recovery device 104 to precipitate and separate arsenic from the acidic liquid. The electrolysis device 106 includes a cathode 115 and an anode 116 for performing electrolysis. The electrolyzer 106 may have a stirrer (not shown) for stirring the contaminated acidic liquid.

The third return line 107 returns the acidic liquid obtained in the electrolyzer 106 from which arsenic is precipitated and separated to the recovery device 104.

As the magnetic force separating device, it is preferable to use a general-purpose simple maglet separator. As shown in FIG. 3, for example, 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 water from iron powder adhering to the outer cylinder 902, and a roller 903. It is provided with a scraper 904 for peeling the squeezed iron powder from the outer cylinder 902.

As the magnet core, for example, a magnet having a surface magnetic flux density of 2000 to 13000 gauss, preferably 4000 gauss or more, more preferably 10000 gauss or more can be used. Specifically, as the magnet core, a permanent magnet such as a ferrite (isotropic or isotropic) magnet, a neodymium magnet, a samarium-cobalt magnet, or an alnico magnet can be used.

Examples of the recovery device include a tank containing an acidic liquid for recovering the adsorptive ability of iron powder.

Examples of the electrolyzer include a tank provided with a cathode, an anode, and a power supply device.

In the purification device configured as described above, contaminated muddy water and iron powder are mixed in the mixing tank 101, and arsenic is adsorbed on the iron powder in the mixture. The mixture is delivered to the magnetic force separator 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 tank 110. The iron powder separated by the magnetic force separating device 102 is returned to the mixing tank 101 via the first return line 103, but is sent to the recovery device 104 as necessary to recover the adsorption ability. The timing at which the iron powder is sent to the recovery device 104 can be appropriately determined by the person using the purification device. When the iron powder is sent to the recovery device 104, it is not always necessary that arsenic is adsorbed to the iron powder to the limit. For example, the arsenic concentration of contaminated muddy water is investigated, the number of times of reuse of iron powder that is expected to be able to sufficiently adsorb arsenic is set in advance, and after the number of reuses, the iron powder is recovered. It may be sent to 104. Alternatively, arsenic may be adsorbed by the iron powder, the arsenic concentration in the muddy water may be measured, and when it is determined that the arsenic concentration has not sufficiently decreased, the iron powder may be sent to the recovery device 104. The iron powder whose adsorption capacity has been restored is returned to the mixing tank 101 via the second return line 105. The contaminated acidic liquid contained in the contaminated acidic liquid storage tank 113 is sent to the electrolyzer 106 via the contaminated acidic liquid delivery line 114. In the electrolyzer 106, the contaminated acidic liquid is electrolyzed, and arsenic is precipitated and separated from the acidic liquid. The acidic liquid in which arsenic is precipitated and separated is returned to the recovery device 104 via the third return line 107. The precipitated and separated arsenic can be recovered, purified as needed, and reused as a resource in various applications.

According to the purification device of the present embodiment, contaminated muddy water can be purified at low cost in a narrow space, and the amount of secondary waste can be reduced.

Hereinafter, the present invention will be described in more detail with reference to examples, but the technical scope of the present invention is not limited thereto.

<Example 1>
A solution of about 0.5 mol / L ascorbic acid containing about 200 mg / L of arsenic and about 1000 mg / L of iron was prepared. A 1 L solution of ascorbic acid was filled in the electrolyzer shown in Table 1 and energized to perform electrolysis.

結果を表２及び３並びに図４に示す。通電開始から２４時間後に約３０％のヒ素が除去された。

The results are shown in Tables 2 and 3 and FIG. About 30% of arsenic was removed 24 hours after the start of energization.

<Example 2>
Electrolysis was carried out in the same manner as in Example 1 except that the electrolysis apparatus shown in Table 4 was used. Example 2 differs from Example 1 in the total area of the cathode and the anode portion in contact with the ascorbic acid solution and the distance between the cathode and the anode.

The results are shown in Tables 5 and 6 and FIG. About 50% of arsenic was removed 2 hours after the start of energization, and about 95% of arsenic was removed 8 hours later. It is presumed that by narrowing the electrode spacing, the current value increased and the efficiency of electrolysis improved.

Evaluating at 8 hours after the start of energization when most of the arsenic was removed, it is possible to remove 1 mg of arsenic with a small amount of power of about 0.4 Wh. This result means that arsenic can be removed at a small cost.

It was confirmed by an energy dispersive X-ray fluorescence analyzer that arsenic was deposited on the surface of the cathode (stainless steel). The fluorescent X-ray spectrum is shown in FIG.

In addition, it was confirmed by chemical analysis that arsenic was deposited on the surface of the cathode. Specifically, each electrode piece was immersed in 10 mL of concentrated nitric acid for 5 minutes, and the mixture was analyzed with pure water to 100 ml. The results are shown in Table 7.

101 ... Mixing tank 102 ... Magnetic separator 103 ... First return line 104 ... Recovery device 105 ... Second return line 106 ... Electrolysis device 107 ... Third return line 108 ... Stirring Machine 109 ... Mixture delivery line 110 ... Purification muddy water storage tank 111 ... Magnetic separator 112 ... Recovery iron powder delivery line 113 ... Contaminated acidic liquid storage tank 114 ... Contaminated acidic liquid delivery line 115 ... Cathode 116 ...・ Anode 901 ・ ・ Magnet core 902 ・ ・ Outer cylinder 903 ・ ・ Roller 904 ・ ・ Scraper

Claims (7)

This includes precipitating and separating arsenic from the acidic solution by electrolyzing the acidic solution containing arsenic generated by treating the iron powder adsorbing arsenic with an acidic solution in an electrolyzer equipped with a cathode and an anode. How to collect arsenic. The method for recovering arsenic according to claim 1, wherein the acidic solution is an ascorbic acid solution. The method for recovering arsenic according to claim 1 or 2 , wherein the cathode is a stainless steel electrode and the anode is a carbon electrode. The method for recovering arsenic according to any one of claims 1 to 3 , wherein the cathode and the anode have a flat plate shape, and the cathode and the anode are arranged in parallel at intervals of 1.0 to 2.0 cm. (1) An adsorption step of mixing muddy water containing arsenic and iron powder to adsorb arsenic to the iron powder, and a separation step of separating iron powder from the mixture obtained in the adsorption step by magnetic force.
The first cycle of reusing the iron powder separated in the separation step in the adsorption step; and (2) the adsorption step of mixing muddy water containing arsenic and iron powder to adsorb arsenic to the iron powder.
A separation step of separating iron powder from the mixture obtained in the adsorption step by magnetic force, and a recovery step of treating the iron powder separated in the separation step with an acidic solution to restore the adsorption ability of the iron powder to arsenic.
A second cycle in which iron powder whose adsorption capacity for arsenic has been restored in the recovery step is reused in the adsorption step;
Including
The arsenic-containing acidic solution generated in the recovery step is subjected to the arsenic recovery method according to any one of claims 1 to 4 , further comprising an electrolysis step of precipitating and separating arsenic from the acidic solution. How to purify muddy water. The method for purifying muddy water containing arsenic according to claim 5 , wherein the acidic liquid obtained in the electrolysis step from which arsenic is precipitated and separated is reused in the recovery step. A device for purifying muddy water containing arsenic
A mixing tank that mixes muddy water containing arsenic and iron powder to adsorb arsenic to the iron powder;
A magnetic force separator that separates iron powder from the mixture obtained in the mixing tank by magnetic force;
A first return line that returns the iron powder separated by the magnetic force separator to the mixing tank;
A recovery device that restores the adsorption capacity of iron powder to arsenic by treating the iron powder separated by the magnetic force separation device with an acidic solution;
A second return line that returns iron powder that has recovered its ability to adsorb arsenic in the recovery device to the mixing tank;
An electrolyzer that electrolyzes an acidic solution containing arsenic generated in a recovery device to precipitate and separate arsenic from the acidic solution; and an acidic solution obtained in an electrolysis device from which arsenic is precipitated and separated is used as a recovery device. Third return line to return;
A device for purifying muddy water containing arsenic.

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