KR20200125461A - Removal method of selenium - Google Patents

Abstract

The present invention relates to a method capable of simply and efficiently removing contaminants such as selenium or heavy metals including selenium from contaminated water or contaminated soil and, more specifically, to a removal method of selenium, comprising a step of making the contaminated water or contaminated soil including selenium contact with a mixture of 20 to 98 mass% of iron and 2 to 70 mass% of iron sulfide.

Description

How to remove selenium {REMOVAL METHOD OF SELENIUM}

The present invention relates primarily to a method of removing selenium from contaminated water or contaminated soil.

Heavy metals such as selenium, arsenic, lead, cadmium and chromium, and pollutants such as fluorine are harmful to the human body and cause health disorders, and thus environmental pollution by these pollutants is a problem. These heavy metals are included in groundwater, river water, lake water, various industrial drainage, and the like, and environmental standards and drainage standards have been established. When heavy metals in water exceed these water quality standards, it is necessary to remove these heavy metals from the water.

Among these contaminants, several methods have been reported so far as a method of purifying water contaminated with selenium (hereinafter, sometimes referred to as “contaminated water”). For example, there is a method of purifying drainage, groundwater or soil leachate containing selenium and heavy metals by contacting iron sulfide powder having a purity of 30 to 80% containing at least Fe in addition to FeS (Patent Document 1).

In addition, there is known a wastewater treatment method in which wastewater is passed through an iron sulfide filter medium (FeS-based) at a predetermined acid concentration, and reduction and elution of a precipitant are simultaneously performed (Patent Document 2). In the same method, selenium-containing water is treated by adding a metal of copper, iron or zinc or a compound of these metals to the selenium-containing water, and then sulfiding by supplying H ₂ S, NaSH or Na ₂ S to form a precipitate. A method of doing this has also been reported (Patent Document 3).

Japanese Patent No. 4264226 Japanese Patent Application Publication No. 48-25966 Japanese Patent Publication No. 2006-116469

However, the iron sulfide powder used in the technique described in Patent Document 1 and whose purity has been adjusted is not easy to manufacture at a specified concentration. This is because even if the Fe powder and the FeS powder are mixed as they are in a powder state and liquefied/mixed, they are separated due to the difference in specific gravity, making it difficult to make a mixture of uniform components. Therefore, it is considered that it is cumbersome and extremely difficult to purify contaminated water or the like with iron sulfide powder of a predetermined purity.

In addition, the method described in Patent Document 2 is to generate a substance having reducibility and precipitation cohesiveness such as ferrous sulfate, hydrogen sulfide, metallic iron, sulfur, etc. produced by the reaction of an iron sulfide filter medium and a non-acidic liquid to remove heavy metals. That's the way. However, even if iron sulfide and slight acid are reacted, metallic iron is not produced and only hydrogen sulfide is generated, so in the mechanism in which the purification proceeds in this technology, it is thought that the reducibility is mainly expressed by hydrogen sulfide, and the reduction of metallic iron. It is not a technique to use.

In addition, in the method described in Patent Document 3, after adding a metal or a metal compound such as copper, it is necessary to supply and sulfide by blowing H ₂ S gas or the like as a separate step. It is thought that it also costs equipment and the like.

The present invention has been made in view of the above problems, and an object thereof is to provide a method for easily and efficiently removing contaminants such as selenium or heavy metals including selenium from contaminated water or contaminated soil. .

The present inventor repeated intensive examination and found that the above problems can be solved by the following configuration.

That is, the selenium removal method according to an aspect of the present invention includes contacting a mixture of contaminated water or contaminated soil containing selenium and 98 to 20% by mass of iron and 2 to 70% by mass of iron sulfide. Characterized in that.

Moreover, in the said removal method, it is preferable that the mixing ratio in the said mixed powder is 83-50 mass% of iron powder and 17-50 mass% of iron sulfide powder.

In addition, it is preferable that the iron powder is atomized iron powder.

Moreover, it is preferable that the said iron powder contains sulfur, and further it is preferable that the sulfur content in the said iron powder is 0.3-5 mass %.

According to the present invention, it is possible to provide a method capable of simply and efficiently removing contaminants such as selenium or heavy metals including selenium from contaminated water or contaminated soil. In addition, when contaminated water or contaminated soil contains other heavy metals in addition to selenium, it is also possible to remove them efficiently.

1 is a graph integrating a comparison of iron powder alone conditions and iron powder + FeS powder conditions in Examples.
Fig. 2 is a graph integrating a comparison of FeS content alone conditions and iron content + FeS content conditions in Examples.

The present invention relates to a method for efficiently removing the contaminants from groundwater, river water, lake water, various industrial drains, etc., contaminated with at least selenium and, in some cases, contaminated with heavy metals such as arsenic, lead, cadmium, fluorine and chromium. will be. In the present invention, the term "heavy metals of selenium, arsenic, lead, cadmium and chromium" means that it includes single metals, compounds (especially oxides), salts and ions of selenium, arsenic, lead, cadmium and chromium.

As a result of intensive investigation, the present inventors made contact with contaminated water or contaminated soil containing selenium and a mixture of 98 to 20% by mass of iron and 2 to 70% by mass of iron sulfide, without passing through a cumbersome process, It has been found that it can significantly reduce selenium concentrations in water or contaminated soils.

Hereinafter, embodiments of the present invention will be described more specifically, but the present invention is not limited to these embodiments.

(Mixed portion)

In this embodiment, the mixed powder used to remove selenium is a mixed powder obtained by mixing iron (Fe) powder and iron sulfide (FeS) powder.

The type of iron powder used in the present embodiment is not particularly limited, and any iron powder industrially available can be used. Examples of the type of iron powder include atomized iron powder, cast iron powder and sponge iron powder, and these iron-based complete alloy powders and partial alloy powders. Among these, atomized iron powder produced by an atomization method capable of mass production and matching components and particle sizes is preferable.

In the iron powder used in the present embodiment, the smaller the particle diameter (average particle diameter) is, the higher the surface area (specific surface area) is, and the higher the removal performance of heavy metals. On the other hand, the larger the particle diameter of the iron powder, the higher the yield and the handling property is improved, but the removal rate of heavy metals decreases. From this point of view, the preferred average particle diameter of the iron powder as a raw material is 1000 µm or less (more preferably 100 µm or less). In addition, the "average particle diameter of iron powder" in this specification means the cumulative body phase percentage or the cumulative body weight percentage in the particle size distribution obtained by the dry sieve classification test using a sieve specified in JIS Z 8801 (2006). It means the particle diameter of this 50 mass %.

The iron powder may contain sulfur (S). The reason is, first, it is useful to improve the performance of removing heavy metals such as arsenic and selenium from contaminated water. In other words, it was found that the ability to remove heavy metals such as selenium from contaminated water was improved by containing a predetermined amount of S in iron, and the technical significance was acknowledged, so it was first applied by the same applicant (Japanese Patent Publication No. 2006- 312163, 2008-43921, 2009-82818). By using such iron powder as a raw material for a treatment agent, the removal performance for heavy metals is further improved.

From the viewpoint of removing heavy metals such as selenium, arsenic, lead, cadmium and chromium, the sulfur content in the iron powder contained in the mixed powder of the present embodiment is preferably 0.3% by mass or more. Further, the sulfur content is more preferably 0.6% by mass or more, and still more preferably 0.7% by mass or more. On the other hand, since it is difficult to stably contain sulfur in iron powder, the sulfur content is preferably 5% by mass or less. A more preferable upper limit is 3% by mass or less. In addition, in this embodiment, the "sulfur content" is a value measured using a carbon/sulfur analyzer by a combustion method.

The reason why the removal performance of heavy metals is improved by including sulfur in iron is, first, oxidation of the surface of iron powder is accelerated by the action of sulfur contained in iron powder (anode reaction of iron: Fe→Fe ²⁺ +2e ⁻ ). In addition, the adsorption of heavy metals present in the form of metal ions or compound ions to iron during contamination is promoted by iron ions efficiently generated on the surface of the iron and rapidly growing iron oxides or hydroxides. It is thought that this is because the removal of heavy metals proceeds efficiently.

In addition, the iron powder of this embodiment may contain phosphorus (P). It is thought that by using iron containing an appropriate amount of phosphorus (P), heavy metals such as selenium, arsenic, cadmium, lead and chromium in contaminated water or contaminated soil can be efficiently removed. The reason why the removal performance of heavy metals is improved by using iron powder containing phosphorus is considered to be the same as in the case where sulfur is added (see Japanese Patent No. 5044553 by the same applicant).

When the iron powder contains phosphorus, the content is preferably 0.1% by mass or more from the viewpoint of removing heavy metals such as selenium, arsenic, lead, cadmium, and chromium. Further, the phosphorus content is more preferably 3% by mass or more. On the other hand, since it is difficult to stably contain phosphorus in the iron powder, the phosphorus content is preferably 5% by mass or less. A more preferable upper limit is 3% by mass or less.

Next, the type of iron sulfide powder used in the mixed powder of the present embodiment is not particularly limited, and industrially available iron sulfide powder or iron sulfide powder having an increased specific surface area by pulverizing iron sulfide in order to improve reactivity, etc. It is possible to use.

The size (average particle diameter) of the iron sulfide powder is not particularly limited, but, for example, from the viewpoint of increasing the reactivity by increasing the specific surface area, the preferred average particle diameter of the iron sulfide powder as a raw material is 20 μm or less (more preferably 10.3 μm or less. )to be.

Here, the average particle diameter means the average value of the feret diameter, and can be measured by the method described in Examples to be described later.

In this embodiment, one of the main features is to use a mixed powder obtained by mixing iron powder and iron sulfide powder as separate powders. In this respect, the technique disclosed in Patent Document 1 discloses that selenium can be purified by using FeS powder containing Fe or the like as an impurity. Because Fe and FeS have reducibility, selenium in the liquid is reduced to tetravalent or single-valent selenium (zero-valent), and tetravalent selenium or single-valent selenium is introduced into the colloid of the generated iron hydroxide to be coprecipitated and separated in water. However, in this technology, since Fe and FeS are in permanent contact, a kind of battery is already formed in the step of being introduced into the aqueous solution. That is, it is thought that Fe and FeS are melted and integrated. In this state, it is not easy to adjust the purity to a specified concentration in the FeS powder containing Fe.

However, in this embodiment, since Fe and FeS are not integrated and are added as a mixture, they are not in permanent contact. Therefore, it is added to selenium-contaminated water, and only when there is contact with each other, the transfer of electrons will be facilitated. However, as the inventors have repeatedly studied, it has been found that even if a mixture powder of Fe and FeS without permanent contact is added, selenium purification performance is higher than that of using each of them alone. Further, by further investigation, it was found that the mixing ratio of Fe and FeS is also important, and thereby, compared to the conventional method, selenium purification with high degree of design freedom and ease of design became possible.

That is, the mixed powder of the present embodiment is a mixed powder obtained by mixing the above-described iron powder and iron sulfide powder at a mixing ratio of 98 to 20% by mass of iron and 2 to 70% by mass of iron sulfide. By using the mixed powder in which iron powder and iron sulfide are mixed in such a ratio, it is possible to efficiently reduce the selenium concentration in contaminated water or contaminated soil as a purification control.

Further, in consideration of cost and safety, more preferable mixing ratios are 83 to 50% by mass of iron and 17 to 50% by mass of iron sulfide. In terms of cost, for example, if FeS and Fe are mixed and used repeatedly, Fe is easily recovered with a magnet and used repeatedly, but FeS must be added each time it is repeated, and it is thought that the cost increases as the amount of FeS used increases. . Regarding safety, since it is harmful by generating sulfur oxide (SOx) when burning, it is preferable to limit the amount used.

(Contaminated water and contaminated soil)

The contaminated water or contaminated soil to be purified (to remove selenium) in this embodiment contains at least selenium. Further, in addition to selenium, a heavy metal or a heavy metal-containing compound may be further included. Here, "heavy metal" is a metal species with a specific gravity of 4.5 or more at 25°C. Specifically, in addition to selenium, lead, arsenic, chromium, and fluorine may be mentioned. As said heavy metal compound, cadmium nitrate, sodium hydrogen arsenate, sodium selenate, potassium dichromate, etc. are mentioned, for example. As the heavy metal ion or heavy metal compound, for example, cadmium ion (Cd ²⁺ ), non-acid ion (AsO ₄ ^3- ), selenate ion (SeO ₄ ^2- ), lead ion (Pb ²⁺ ), chromium ion (Cr ⁶⁺ ) and the like.

In the present embodiment, the contaminated water refers to water or groundwater contaminated with selenium or the like as described above. These may be provided as it is for purification treatment, or before performing the purification treatment, filter filtration or the like may be performed as necessary.

(Selenium removal treatment)

The selenium removal method of the present embodiment includes a step (contact step) of bringing the mixed powder as described above into contact with contaminated water or contaminated soil for which selenium is to be removed.

There is no particular limitation on the means for bringing the mixed powder into contact. For example, in the case of contaminated water, selenium contained in the contaminated water can be removed by putting the mixed powder of the present embodiment into contaminated water to be removed from selenium and making it contact by stirring or the like. The pH at the start of treatment in the contaminated water is not particularly limited, but is preferably adjusted to, for example, about pH 3 to 9.5. If the pH is less than 3, acid and iron react to generate hydrogen. The generated hydrogen is not suitable because it will peel off heavy metals on the iron surface. On the other hand, when the alkali concentration is high (ph>9.5), an iron hydroxide film is formed on the iron surface, which is not preferable because there is a fear that the performance of purifying heavy metals by Fe may be lost.

In the case of contaminated soil, since selenium in the soil is eluted from moisture (chemical water, hygroscopic water, parental water, gravitational water, rainwater, etc.) present in the soil, the eluate contained in this soil is extracted and the solution It can be treated like the contaminated water. In addition, when the contaminated soil does not contain moisture, similar treatment is possible by adding water to the contaminated soil to prepare a solution in which water-soluble components in the contaminated soil are eluted.

In addition, there is no particular limitation on the amount of the mixture to be added to the eluate from contaminated water or contaminated soil, and may be appropriately set according to the amount or degree of contamination of contaminated water or contaminated soil. Usually, as the lower limit of the contact amount based on the mixed content, 0.1 g is preferable and 0.2 g is more preferable with respect to 1000 mL of contaminated water or contaminated soil eluate. On the other hand, as the upper limit of the contact amount, 100 g is preferable, 10 g is more preferable, and 1 g is still more preferable. When the contact amount is 0.1 g or more, fluctuations in the removal effect due to fluctuations in the performance of the mixed powder can be suppressed. On the other hand, when the contact amount is 10 g or less, the effect is not saturated, and an effect suitable for the amount of the mixed component is obtained (improvement of cost performance).

In addition, the contacting step is performed under a temperature of 0 to 60°C and atmospheric pressure. The preferred lower limit of the temperature in the contacting step is 5°C or higher, more preferably 10°C or higher, still more preferably 20°C or higher, and more preferably 22°C or higher. Further, the preferred upper limit is 40°C or less, more preferably 35°C or less, still more preferably 30°C or less, and further preferably 27°C or less. The atmospheric pressure varies somewhat depending on the weather (clear/rain; high pressure/low pressure), but changes in atmospheric pressure caused by these are also included in the "atmospheric pressure" in the present specification.

As described above, the present specification discloses techniques of various aspects, among which the main techniques are summarized below.

A selenium removal method according to an aspect of the present invention includes contacting a mixture of contaminated water or contaminated soil containing selenium and 98 to 20% by mass of iron and 2 to 70% by mass of iron sulfide. It is characterized. With this configuration, it is possible to provide a method capable of easily and efficiently removing contaminants such as selenium or heavy metals including selenium from contaminated water or contaminated soil.

Moreover, in the said removal method, it is more preferable that the mixing ratio in the said mixed powder is 83-50 mass% of iron powder and 17-50 mass% of iron sulfide powder. Thereby, it is thought that the above-described effect can be obtained more reliably.

In addition, it is preferable that the iron powder is atomized iron powder. Thereby, there is an advantage that it becomes easier to match the component and particle diameter of the iron powder. Further, stabilization of components and particle sizes leads to stabilization of purification performance.

Further, it is preferable that the iron powder contains sulfur, and further, the sulfur content in the iron powder is preferably 0.3 to 5% by mass. As a result, it is considered that the function of removing heavy metals such as selenium is further improved.

Hereinafter, the present invention will be described in more detail using examples, but the present invention is not limited at all by these examples.

<Example>

First of all, each material used in this test is as follows:

<Iron>

As the raw iron powder, the following iron powders A to C prepared by the water atomization method were used.

ㆍIron powder A: iron alloy powder (atomic iron powder, average particle diameter 70 µm, sulfur content 1% by mass)

ㆍIron powder B: iron alloy powder (atomic iron powder, average particle diameter 70 µm, sulfur content 0.3 mass%)

ㆍIron powder C: pure iron powder (atomic iron powder, average particle diameter 70 µm, sulfur content 0.009 mass%)

<Iron sulfide>

For the iron sulfide source, reagent grade iron sulfide was purchased from Wako Junyaku Co., Ltd., and iron sulfide powder pulverized with a mortar was used.

The particle diameter of iron sulfide used in this test is as follows. Take a small amount of iron sulfide with preparat, add a few drops of hexane and disperse it with a spatula, etc. to make the particles evenly, then dry the hexane to prepare an observation sample, and observe the transmission with an NIKON OPTIPHOT/WRAYCAM (optical microscope equipped with a CCD camera) As a result, when the particle diameter was observed with the free software ImageJ, the average ferret diameter = 10.3 µm and the area radius average = 6.3 µm.

<yellow>

Fine powdered sulfur "S 200 mesh" was purchased from Hosoi Chemical High School Co., Ltd., and it was used as a sulfur source.

<Selenium>

As the selenium source, sodium selenate purchased from Wako Pure Chemical Industries, Ltd. was used.

(Test Examples 1 to 38)

To a polyethylene container having an inner volume of 500 mL, 250 mL of a sodium selenate solution (adjusted with deionized water) adjusted to 1 mg/L was aliquoted, and iron powder or a mixture of iron powder and FeS was added at the ratio shown in Table 1. In addition, the pH was left unadjusted. For the pH measurement, a pH meter manufactured by Horiba Seisakusho Co., Ltd. (body type = D-52, pH electrode type = 9615S) was used.

Then, shaking was performed for 24 hours at room temperature at 25°C with a horizontal shaker at a rotation speed of 140 rpm and a shaking width of 4 cm. Thereafter, after stopping the stirring and measuring the pH, the test water was filtered by suction with a membrane filter having a pore diameter of 0.45 µm, and the residual selenium concentration (mg/L) in the solution was measured by the hydrogen compound generation atomic absorption method.

Table 1 shows the results.

(Test Examples 39 to 43)

The test was carried out in the same manner as in Test Example 1, except that iron powder or a mixed powder of iron powder and S was added at the ratio shown in Table 2. The results are shown in Table 2.

(Review)

From the results of Tables 1 and 2, the conditions of iron powder alone without the addition of FeS powder (Test Examples 8, 16, 24, 34 and 37) or the conditions of FeS powder alone without the addition of iron powder (Test Examples 25 to 30) In contrast, it was confirmed that the Se concentration tends to decrease by mixing both FeS powder and iron powder and adding them as a mixed powder. This is also clear from the graph of Fig. 1 combining the comparison of the iron powder alone condition and the iron powder + FeS powder condition, and the graph of Fig. 2 combining the comparison of the FeS powder alone condition and the iron powder + FeS powder condition.

On the other hand, in the condition in which the similar compound S was added instead of FeS (Test Examples 39 to 43), the residual concentration of Se was high, and the superiority of FeS was shown compared to S.

It was also confirmed that even if the iron powder type (iron powder A to C) was changed, it was possible to further lower the residual Se concentration by adding FeS in each iron powder type.

Claims (7)

A selenium removal method comprising contacting contaminated water or soil containing selenium with a mixture of 98 to 20% by mass of iron and 2 to 70% by mass of iron sulfide. The method of claim 1,
The removal method in which the mixing ratio in the said mixed powder is 83-50 mass% of iron powder and 17-50 mass% of iron sulfide powder. The method according to claim 1 or 2,
The iron powder is atomized iron powder, the removal method. The method according to claim 1 or 2,
The removal method, wherein the iron contains sulfur. The method of claim 3,
The removal method, wherein the iron contains sulfur. The method of claim 4,
The removal method, wherein the sulfur content in the iron powder is 0.3 to 5% by mass. The method of claim 5,
The removal method, wherein the sulfur content in the iron powder is 0.3 to 5% by mass.

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