KR20170105408A - Purification treatment agent and purification treatment method - Google Patents

Abstract

And a purification treatment method and a purification treatment method which are excellent in the removal performance of heavy metals mainly containing cadmium.
The purification treatment agent of the present invention is a purification treatment agent for removing cadmium from polluted water or contaminated soil and is characterized by containing a metal component made of iron or an alloy thereof and a nonmetal reducing agent. The non-metallic reducing agent may be sodium thiosulfate, ascorbic acid, urea, anisole or a combination thereof. The metal powder may be an atomized powder. The metal component may contain sulfur. The sulfur content of the metal powder is preferably 0.05 mass% or more and 5 mass% or less. The mass ratio of the content of the non-metallic reducing agent to the metal powder is preferably 0.01 or more and 4 or less. The purification treatment method of the present invention is a purification treatment method for removing cadmium from contaminated water or contaminated soil and a step of bringing the purification treatment agent into contact with the contaminated water or the contaminated soil.

Description

TECHNICAL FIELD [0001] The present invention relates to a purification treatment agent and a purification treatment method,

The present invention relates to a purification treatment agent and a purification treatment method.

Contaminants such as heavy metals such as arsenic, selenium, lead, cadmium, and chromium are harmful to human bodies and cause health hazards, and environmental pollution caused by these pollutants has been a problem. Heavy metals are included in groundwater, river water, lakes and marshes, and industrial drainage, and environmental standards and drainage standards are set. If heavy metals in water exceed these water quality standards, it is necessary to remove these heavy metals from the water.

As a method for continuously purifying water and soil contaminated with these pollutants (hereinafter also referred to as "polluted water" and "contaminated soil"), various methods (adsorption methods) for adsorbing and removing contaminants using an adsorbent are proposed . In this adsorption method, the contaminated water including contaminants is continuously passed through the adsorption tower filled with the adsorbent, and the contaminated water is adsorbed and removed by contacting the adsorbent.

As the adsorbent used in the above adsorption method, activated carbon, activated alumina, zeolite, titanic acid, zirconia hydrate and the like are known. In the method using these adsorbents, it is possible to achieve a good removal efficiency by selecting the kind of the adsorbent depending on the kind of the contaminant. However, since these adsorbents are generally expensive, there is a drawback have.

On the other hand, as a method for treating polluted water, it is known to adsorb arsenic in water to iron powder, and various proposals have been made to improve the adsorption ability of iron powder. For example, Patent Document 1 discloses iron powder whose surface is coated with iron hydroxide as an arsenic removal agent. Also, in Patent Documents 2 to 6, the iron anode reaction (Fe? Fe ^{2 +} + 2e ^- ) is promoted by the addition of sulfur or phosphorus by using a predetermined amount of sulfur containing iron or phosphorus, Cadmium, arsenic, and other heavy metals is promoted by a mechanism for promoting the reduction reaction or the insolubilization reaction.

Despite these improvements, the ability of the adsorbent to remove heavy metals has been improved, but there has been a desire to develop a technique that exhibits higher adsorption efficiency.

As a method for removing cadmium using iron powder, Patent Document 7 is given. This is because, as a metal-based reducing agent, iron sulfide powder containing at least Fe in addition to Fe and having a purity of 30 to 80% is brought into contact with the contaminated water to reduce the hexavalent selenium, coprecipitate with the colloid of iron hydroxide, precipitate heavy metals as sulfides, Is precipitated as a hydroxide to remove them in water. However, since FeS is used in a large amount in this technology, it is expected that it will be difficult to establish economically. In this technology, it is described that the concentration of cadmium can be made 0.05 ppm (0.05 mg / L) or less. However, the regulation value of cadmium in the recent "Decree of Revision of Part of the Enforcement Regulations of Water Pollution Control Law" ppm (0.03 mg / L), which is not necessarily achieved. In fact, the inventors investigated the residual concentration of cadmium by mixing iron with FeS and found that the concentration can only be reduced to 0.54 ppm (0.54 mg / L) with respect to the initial concentration of 1 ppm (1 mg / L). That is, the cadmium removal performance is not sufficient by mixing FeS with iron powder only.

Japanese Patent Application Laid-Open No. 2006-272260 Japanese Patent Application Laid-Open No. 2006-312163 Japanese Patent Application Laid-Open No. 2008-043921 Japanese Patent Application Laid-Open No. 2009-082818 Japanese Patent No. 4755159 Japanese Patent No. 5046853 Japanese Patent No. 4264226

SUMMARY OF THE INVENTION The present invention has been made based on the above-described circumstances, and an object of the present invention is to provide a purification treatment agent and a purification treatment method which are excellent in the removal performance of heavy metals mainly containing cadmium.

The invention made to solve the above problems is characterized in that it contains a metal component made of iron or an alloy thereof and a non-metallic reducing agent, which removes cadmium from polluted water or contaminated soil.

As a result of intensive studies, the inventors of the present invention have found that the removal of heavy metals including cadmium is remarkably improved by adding a non-metallic reducing agent to iron or its alloy metal powder as a cleaning agent. Although this mechanism is not clear, it is presumed that the presence of the non-metallic reducing agent in addition to the metal powder accelerates the reduction of heavy metal ions in contaminated water or contaminated soil containing heavy metals and adsorbs on metal powders. That is, according to the purification treatment agent, heavy metals mainly containing cadmium can be efficiently removed.

The material of the non-metallic reducing agent may be sodium thiosulfate, ascorbic acid, urea, anisole or a combination thereof. By using such a material as a nonmetal reducing agent, the removal effect of heavy metals can be promoted.

The metal powder may be an atomized powder. By using the atomized powder as the metal powder in this way, the cost can be reduced while improving the homogeneity of the purification treatment agent.

The metal component may contain sulfur. As described above, since the metal component contains sulfur, the removal effect of heavy metals can be promoted.

The sulfur content of the metal powder is preferably 0.05 mass% or more and 5 mass% or less. By setting the sulfur content of the metal powder within the above range, it is possible to further promote the removal effect of the heavy metal while suppressing the cost.

The mass ratio of the content of the non-metallic reducing agent to the metal powder is preferably 0.01 or more and 4 or less. By setting the content of the non-metallic reducing agent to the above range, the effect of removing the heavy metal can be promoted while suppressing the cost.

The polluted water or contaminated soil further includes arsenic, selenium, lead, chromium, or a combination thereof, and these elements may be removed. Since the purification treatment agent is excellent in reactivity between the metal component and the ions of the element, it is possible to effectively remove these heavy metals and the like.

Another object of the present invention is to provide a purification treatment method for removing cadmium from contaminated water or contaminated soil, and a process for bringing the purification treatment agent into contact with the contaminated water or the contaminated soil .

In the purification treatment method, the purification agent containing the metal component and the nonmetal reducing agent is contacted with the polluted water or the contaminated soil, so that the heavy metal mainly containing cadmium can be efficiently removed.

Here, " heavy metal " is a metal species having a specific gravity at 25 ° C of not less than 4.5. The "content of sulfur" is a value measured using a carbon-sulfur analyzer by a combustion method.

INDUSTRIAL APPLICABILITY As described above, the purification treatment agent and the purification treatment method of the present invention are excellent in the removal performance of heavy metals mainly containing cadmium.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, embodiments of the purification treatment method and the purification treatment agent according to the present invention will be described.

[Purification treatment agent]

The purification treatment agent of the present invention is used for removing at least cadmium from contaminated water or contaminated soil containing heavy metals and contains a metal component made of iron or an alloy thereof and a nonmetal reducing agent. The purification treatment agent may contain, in addition to the metal powder and the non-metal-based reducing agent, other components such as a solvent within the range not hindering the effect of the present invention. In addition, an additive such as a pH adjuster may be included.

<Metal powder>

The metal powder adsorbs heavy metals such as cadmium on its surface. Heavy metals exist as heavy metal ions in water. By reacting these ions with metal powders, the heavy metals are insolubilized and precipitated near the surface of the metal powders. As a result, the metal powder can adsorb heavy metals on its surface.

The metal powder is not particularly limited as long as it is a powder mainly composed of iron or an alloy thereof, and any metal powder available industrially can be used. Examples of the kind of metal powder include iron-based complete metal powder (prealloy alloy powder) or partial metal powder (premix alloy powder) such as atomized iron powder, cast iron powder and sponge iron powder. Examples of the element other than iron contained in the alloy include carbon, sulfur, nickel, copper, zinc, aluminum, and cobalt. Here, the &quot; main component &quot; refers to a component (for example, 50 mass% or more) most contained on the mass basis among the components constituting the metal powder.

As the metal powder, an atomized metal powder produced by the atomization method is preferable. Since the atomized metal powder can be mass-produced, the purification treatment agent can be used for a large-scale treatment in a treatment facility or the like. In addition, the atomized metal powder can easily align components and particle diameters. The atomized metal powder may be a completely metal powder atomized with an iron alloy, or may be a partially alloyed powder obtained by atomizing iron powder and attaching metal powder thereto.

The upper limit of the average particle diameter of the metal powder is preferably 1000 占 퐉, more preferably 500 占 퐉, and even more preferably 100 占 퐉. On the other hand, the lower limit of the average particle diameter of the metal powder is preferably 1 mu m. If the average particle diameter exceeds the upper limit, the surface area of the metal powder becomes small, and the removal rate of heavy metals and the like may be lowered. On the other hand, when the average particle diameter is less than the lower limit, the yield is lowered and the handling property may be lowered. Here, the "average particle diameter" means the particle diameter at which the cumulative mass becomes 50% in the particle diameter distribution obtained by a dry body classification test using a sieve defined in JIS-Z-8801 (2006).

The metal powder may contain sulfur as an alloy element. The presence of sulfur improves the removal performance of the heavy metal of the metal powder. The reason why the removal performance of heavy metals is improved by containing sulfur in the metal powder is thought to be as follows. That is, the oxidation of the surface of the metal powder is promoted by the action of sulfur (the iron anode reaction: Fe → Fe ^{2 +} + 2e ^- ), iron ions efficiently generated on the surface of the metal powder, It is considered that the adsorption of heavy metals present in the form of metal ions or compound ions in the contaminated water or contaminated soil to the metal powders is promoted and the removal of heavy metals proceeds efficiently with this.

The upper limit of the content of sulfur in the metal powder is preferably 5% by mass, more preferably 4% by mass, and still more preferably 3% by mass. On the other hand, the lower limit of the content is preferably 0.05% by mass, more preferably 0.1% by mass, still more preferably 0.8% by mass. If the content exceeds the upper limit, the adsorption efficiency of the heavy metal of the metal powder may be lowered. Further, the cost of the purification treatment agent may be unnecessarily increased. Conversely, when the content is less than the lower limit described above, there is a possibility that the above-described action of improving the removal performance of heavy metals by sulfur is insufficient.

<Nonmetal reducing agent>

The non-metallic reducing agent is not particularly limited as long as it can reduce heavy metal ions or ions of the compound. Examples of the material include sodium thiosulfate, ascorbic acid, urea, sodium hydrosulfite, anisole dioxide, . Among these, sodium thiosulfate, ascorbic acid, urea, anisole and a combination thereof are preferable. By using such a non-metallic reducing agent, it is possible to improve the removal performance of the heavy metal while suppressing the cost.

The lower limit of the mass ratio of the content of the nonmetal reducing agent to the metal powder is preferably 0.01, more preferably 0.2. On the other hand, the upper limit of the mass ratio is preferably 4, more preferably 2, and still more preferably 1. When the mass ratio is less than the lower limit, mixing with the metal component becomes insufficient, and the removal performance of the heavy metal may be insufficient. Conversely, if the mass ratio exceeds the upper limit, the removal performance of the heavy metal reaches the limit, while the cost may increase.

<Contaminated water or contaminated soil>

The polluted water or the contaminated soil to which the purification treatment agent purifies includes cadmium. The contaminated water or contaminated soil may further contain a heavy metal or heavy metal-containing compound or fluoride other than cadmium. In the contaminated soil, since the heavy metals in the soil are eluted with the water (chemical water, hygroscopic water, capillary water, gravity water, rain water, etc.) present in the soil, the effluent can be purified by the same treatment agent as the contaminated water. Further, in the case where the contaminated soil does not contain water, purification treatment is possible by adding water to the contaminated soil to make a solution in which the water-soluble component in the contaminated soil is eluted.

(Heavy or heavy metal compounds)

The heavy metal or heavy metal compound exists as a heavy metal ion or heavy metal compound ion in contaminated water or contaminated soil and is dissolved in contaminated water or contaminated soil. Of the heavy metals in the heavy metal or heavy metal-containing compound, cadmium, arsenic, selenium, lead, chromium, and combinations thereof are preferable, in particular, those which are preferably removed.

Examples of the heavy metal compound include cadmium nitrate, sodium hydrogen sulfate, sodium selenium, potassium dichromate, and the like. Examples of the heavy metal ions or heavy metal compounds, such as cadmium ions (Cd ^{+ 2),} non-ionic dispersion (AsO ₄ ^{3 -),} selenium acid ion (SeO ₄ ^2-), lead ions (Pb ^2+), chromium ion ( Cr ⁶⁺ ) and the like.

The basic estimation mechanism by which heavy metals are adsorbed to the metal components of the purification treatment agent can be considered as follows.

Cadmium and selenium are dissolved in water in the form of cadmium ion (Cd ^{2 +} ) and selenium ion (Se ^{2 -} ), respectively. Since the anodic reaction of iron is promoted in the purification treatment agent, cadmium ions and selenium ions are efficiently reduced to metal cadmium and metal selenium, respectively, and precipitated on the metal powder surface. As a result, cadmium ion or selenium ion can be efficiently removed in water.

Arsenic is dissolved in water in the form of dissociation ions (AsO ₄ ^{3 -} ). In order to remove this non-dissociated ion, a compound may be produced by reacting the ion with an iron ion. By using a non-metallic reducing agent and a metal powder, iron ions can be efficiently released into water. As a result, it is possible to efficiently remove non-dissociated ions in water by precipitating insoluble iron (iron and iron compound) on the surface of the metal powder (that is, by adsorbing heavy metals to the metal powder).

The chromium ion and the lead-containing ion react with the iron ion contained in the metal powder to form an iron compound, so that it can be precipitated as an insoluble compound on the surface of the metal powder. As a result, it is possible to efficiently remove chromium ions and lead-containing ions from the water.

[Purification treatment method]

Next, embodiments of the purification treatment method of the present invention will be described in detail.

This purification treatment method removes at least cadmium from contaminated water or contaminated soil containing heavy metals. The purification treatment method mainly includes a step of bringing the purification treatment agent into contact with contaminated water or contaminated soil (contact step).

<Contact Process>

In this step, the purification treatment agent is brought into contact with the contaminated water or contaminated soil. The contact method is not particularly limited and includes, for example, a method of charging the cleaning agent into a suitable container and continuously passing contaminated water or contaminated soil through the container, adding the cleaning agent to the contaminated water or contaminated soil, And the like.

The amount of the cleaning agent to be brought into contact with the contaminated water or the contaminated soil is not particularly limited, but the lower limit of the contact amount based on the metal powder contained in the cleaning agent is preferably 0.1 g, more preferably 0.2 g is more preferable. On the other hand, the upper limit of the contact amount is preferably 100 g, more preferably 10 g. If the contact amount is less than the lower limit, there is a possibility that the purifying effect is fluctuated due to the fluctuation of the performance of the metal powder. On the contrary, if the contact amount exceeds the upper limit, the effect is saturated, and therefore, an effect suited to the amount of metal powder can not be obtained.

When the purification treatment agent is added to the polluted water or contaminated soil, the upper limit of the amount of the purification treatment agent added is preferably 4 g, more preferably 2 g, in terms of the mass of metal powder to 1 mg of cadmium in the contaminated water or contaminated soil. On the other hand, the lower limit of the addition amount is preferably 0.1 g, more preferably 0.3 g, in mass of metal powder to 1 mg of cadmium in contaminated water or contaminated soil.

The upper limit of the agitation time in the case of adding the purification treatment agent to the contaminated water or contaminated soil is preferably 72 hours, more preferably 36 hours. On the other hand, the lower limit of the stirring time is preferably 10 minutes, more preferably 30 minutes. If the agitation time exceeds the upper limit, the removal amount of cadmium or the like is less likely to be improved as compared with the stirring time, and the removal efficiency may be lowered. Conversely, when the stirring time is less than the lower limit, there is a fear that cadmium and the like can not be sufficiently removed.

The lower limit of the pH of the contaminated water or the contaminated soil eluate immediately after the addition of the purifying agent is preferably 2, more preferably 3. On the other hand, as the upper limit of pH, 10 is preferable, and 9 is more preferable. If the pH is lower than the above lower limit, hydrogen tends to be generated and the adsorption performance of the metal powder may be deteriorated. On the other hand, if the pH exceeds the upper limit, the formation of iron hydroxide becomes remarkable, and there is a fear that the adsorption performance of the metal powder is lowered. In particular, when sodium thiosulfate is used as the non-metallic reducing agent, it is preferable that the pH is 2 or more and 4 or less or 8 or more and 10 or less. The pH can be adjusted, for example, by adjusting the amount of the nonmetal reducing agent added, adding a solvent such as water or a pH adjusting agent. Examples of the pH adjuster include inorganic acids such as hydrochloric acid, sulfuric acid, nitric acid and phosphoric acid, and organic acids such as formic acid, acetic acid and oxalic acid.

This purification treatment method makes it possible to efficiently remove a heavy metal mainly composed of cadmium because a cleaning agent containing a metal component made of iron or an alloy thereof and a nonmetal reducing agent is contacted with contaminated water or contaminated soil.

<Examples>

Hereinafter, the present invention will be described more specifically by way of examples, but the present invention is not limited thereto.

[Examples 1 and 2 and Comparative Examples 1 to 3]

In a 500 mL container made of polyethylene, 250 mL of an aqueous solution prepared by adjusting cadmium nitrate to ion concentration of 1 mg / L by ion exchange water was added as contaminated water. To this solution, a purifying agent containing a metal component and a non-metallic reducing agent or FeS was added so that the solid / liquid ratio (g / mL) was as shown in Table 1. Here, the "solid / liquid ratio" is a ratio of the total solid amount (g) to the total liquid amount (mL) in the mixture of the purification treatment agent and the polluted water. In Comparative Example 2, only FeS was used as a purifying agent, and in Comparative Example 3, only a non-metallic reducing agent was used as a purifying agent. The kinds of metal powders used in each of the examples and comparative examples are as described later. Thereafter, the pH and oxidation-reduction potential (ORP) of the mixture were measured, and then the mixture of the purification treatment agent and the contaminated water was treated with a horizontal shaker at a temperature of 25 캜, a revolution of 140 rpm, Shake for an hour and stir. After the shaking, the pH and oxidation-reduction potential were measured, and the mixed solution was subjected to suction filtration with a membrane filter having a pore diameter of 0.45 탆, and the residual cadmium concentration of the contaminated water after the treatment was measured by ICP emission spectroscopy (JIS-K0102 . The results are shown in Table 1. Further, the pH of the mixture was adjusted with hydrochloric acid.

A: pure iron (atomized iron powder, average particle diameter 70 mu m, sulfur content 0.009 mass%)

B: iron alloy powder (atomized iron powder, average particle diameter 70 mu m, sulfur content 1 wt%)

From Table 1, it can be seen that the use of the purification treatment agent in which the metal component and the nonmetal reducing agent (sodium thiosulfate) are mixed can significantly reduce the cadmium concentration compared to Comparative Example 1 in which the metal component is used in combination with FeS. On the other hand, in Comparative Examples 2 and 3 using FeS or sodium thiosulfate alone, the cadmium removal effect was significantly low.

[Examples 3 to 13]

Filtration and measurement were carried out under the same conditions as in Example 2 except that the mixing ratio of the metal component and the nonmetal reducing agent, the solid / liquid ratio, and the pH were changed to the values shown in Table 2. [ The results are shown in Table 2. &Quot; &lt; 0.001 &quot; in the table indicates that it is smaller than the lower limit value (0.001 mg / L) of the measurement.

From Table 2, it can be seen that the cadmium removal performance is enhanced by increasing the mixing mass ratio of the nonmetal reducing agent to metal powder to more than 0.04. Further, it can be seen that cadmium can be effectively removed by adjusting the pH before the treatment (before stirring) of the mixture to 2 or more and 10 or less, preferably 3 or more and 10 or less.

[Examples 14 to 19]

Stirring and filtration and each measurement were carried out under the same conditions as in Example 2 except that the non-metallic reducing agent shown in Table 3 was used. The results are shown in Table 3. In Examples 16 and 19, the anisole was partially dissolved and remained.

From Table 3, it can be seen that cadmium can be efficiently removed even when a non-metallic reducing agent other than sodium thiosulfate is used. It can also be seen that by using the element, it is possible to effectively remove cadmium regardless of pH.

[Examples 20 to 23]

Except that 250 mL of the aqueous solution adjusted so that the cadmium concentration and the concentration of the additional heavy metal contained in the compounds shown below were respectively adjusted to 1 mg / L as ion-exchanged water as the contaminated water, And each measurement was performed. The results are shown in Table 4. The heavy metal compounds used in the examples are as follows.

Example 20: Sodium disodium hydrogenphosphate

Example 21: Sodium selenite

Example 22: Potassium dichromate

Example 23: Lead nitrate

From Table 4, it can be seen that cadmium and other heavy metals can be effectively removed from the contaminated water containing heavy metals other than cadmium by the purification treatment agent and the purification treatment method.

INDUSTRIAL APPLICABILITY As described above, the purification treatment agent and the purification treatment method of the present invention are excellent in the removal performance of heavy metals mainly containing cadmium.

Claims (8)

It is a purifying agent that removes cadmium from polluted water or contaminated soil,
Characterized by containing a metal powder made of iron or an alloy thereof and a non-metallic reducing agent. The purifying agent according to claim 1, wherein the material of the nonmetal reducing agent is sodium thiosulfate, ascorbic acid, urea, anisole or a combination thereof. The purifying agent according to claim 1 or 2, wherein the metal component is an atomized component. 3. The purifying agent according to claim 1 or 2, wherein the metal component contains sulfur. 5. The purifying agent according to claim 4, wherein the sulfur content of the metal powder is 0.05% by mass or more and 5% by mass or less. 3. The purifying agent according to claim 1 or 2, wherein the mass ratio of the content of the non-metallic reducing agent to the metal powder is 0.01 to 4. 3. The purification treatment agent according to claim 1 or 2, wherein the contaminated water or contaminated soil further contains arsenic, selenium, lead, chromium or a combination thereof, and also removes these elements. A purification treatment method for removing cadmium from polluted water or contaminated soil,
A purification treatment method comprising the step of bringing the purification treatment agent according to claim 1 or 2 into contact with the contaminated water or the contaminated soil.