JP6602237B2 - Purification treatment agent and purification treatment method - Google Patents

Description

  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 the human body and cause health problems. Therefore, environmental pollution caused by these pollutants is a problem. Heavy metals are contained in groundwater, river water, lake water, various industrial wastewater, etc., and environmental standards and drainage standards are established. When the heavy metals in water exceed these water quality standards, it is necessary to remove these heavy metals from the water.

  As a method of continuously purifying water and soil contaminated with these pollutants (hereinafter also referred to as “polluted water” and “contaminated soil”), various methods of adsorbing and removing pollutants using an adsorbent (Adsorption method) has been proposed. In this adsorption method, contaminated water containing contaminants is continuously passed through an adsorption tower filled with an adsorbent, and the contaminated water is brought into contact with the adsorbent to remove it by adsorption.

  Known adsorbents used in the above adsorption method include activated carbon, activated alumina, zeolite, titanic acid, zirconia hydrate and the like. In the method using these adsorbents, excellent removal efficiency can be achieved by selecting the type of adsorbent according to the type of pollutant, but these adsorbents are generally expensive, so their adsorption If the treatment is carried out with only the agent, there is a disadvantage that the treatment cost becomes high.

On the other hand, as a method for treating contaminated water, it is known to adsorb arsenic in water to iron powder, and various proposals have been made to improve the adsorption capacity of iron powder. For example, Patent Document 1 discloses iron powder whose surface is coated with iron hydroxide as an arsenic removing agent. Further, in Patent Documents 2 to 6, by using iron powder containing a predetermined amount of sulfur and phosphorus, the anode reaction of iron (Fe → Fe ²⁺ + 2e ⁻ ) is promoted by addition of sulfur and phosphorus, and as a result. A method for improving the purification performance by a mechanism that promotes the reduction or insolubilization reaction of heavy metals such as cadmium and arsenic has been proposed.

  These technological developments have improved the ability of the adsorbent to remove heavy metals, but the actual situation is that it is desired to develop a technique that exhibits higher adsorption efficiency.

  Moreover, patent document 7 is mention | raise | lifted as a removal method of cadmium using iron powder. This is because iron sulfide powder containing 30 to 80% purity containing at least Fe in addition to FeS as a metallic reducing agent is brought into contact with contaminated water to reduce hexavalent selenium and coprecipitate with iron hydroxide colloid. In this technique, heavy metals are precipitated as sulfides, and heavy metals that do not generate sulfides are precipitated as hydroxides to remove them from the water. However, with this technology, the amount of FeS used is large, and it is expected that it is difficult to make it economically viable. In addition, this technology describes that the cadmium concentration has been reduced to 0.05 ppm (0.05 mg / L) or less. However, the cadmium regulations in the latest “Ministerial Ordinance to Amend Some of the Enforcement Rules for the Water Pollution Control Law” The value is 0.03 ppm (0.03 mg / L), and it cannot be said that this can be achieved. In fact, when the inventors mixed FeS with iron powder and examined the residual concentration of cadmium, the concentration could be reduced only to 0.54 ppm (0.54 mg / L) with respect to the starting concentration of 1 ppm (1 mg / L). Things turned out. That is, the cadmium removal performance is not sufficient only by mixing FeS and iron powder.

JP 2006-272260 A JP 2006-312163 A JP 2008-043921 A JP 2009-082818 A Japanese Patent No. 4755159 Japanese Patent No. 5046853 Japanese Patent No. 4264226

  This invention is made | formed based on the above situations, and it aims at providing the purification processing agent and purification processing method which are excellent in the removal performance of heavy metals which have cadmium as a main.

  The invention made to solve the above-mentioned problems is a purification treatment agent that removes cadmium from contaminated water or soil, and contains a metal powder made of iron or an alloy thereof and a nonmetallic reducing agent. And

  As a result of intensive studies, the present inventors have found that removal of heavy metals such as cadmium is remarkably improved by adding a non-metallic reducing agent to a metal powder made of iron or an alloy thereof as a purification treatment agent. It was. Although this mechanism is not clear, the presence of a non-metallic reducing agent in addition to the metal powder promotes the reduction of heavy metal ions in the contaminated water or soil containing heavy metals and adsorbs to the metal powder. Guessed. That is, according to the said purification processing agent, the heavy metal which has cadmium as a main can be removed efficiently.

  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 the nonmetallic reducing agent, the effect of removing heavy metals can be promoted.

  The metal powder is preferably atomized powder. Thus, by using atomized powder as the metal powder, it is possible to reduce costs while improving the homogeneity of the purification treatment agent.

  The metal powder may contain sulfur. Thus, the removal effect of a heavy metal can be accelerated | stimulated because metal powder contains sulfur.

  The sulfur content of the metal powder is preferably 0.05% by mass or more and 5% by mass or less. Thus, the removal effect of heavy metal can be further accelerated | stimulated, suppressing cost by making sulfur content of metal powder into the said range.

  The mass ratio of the content of the nonmetallic reducing agent to the metal powder is preferably 0.01 or more and 4 or less. Thus, the removal effect of heavy metal can be accelerated | stimulated, suppressing cost by making content of a nonmetallic type reducing agent into the said range.

  The contaminated water or soil may further contain arsenic, selenium, lead, chromium, or a combination thereof, and these elements may also be removed. Since the said purification treatment agent is excellent also in the reactivity of metal powder and the ion of the said element, removal of these heavy metals etc. can also be performed effectively.

  Moreover, another invention made | formed in order to solve the said subject is a purification treatment method which removes cadmium from contaminated water or contaminated soil, Comprising: The process which makes the said purification treatment agent contact with the said contaminated water or the said contaminated soil It is characterized by providing.

  Since the said purification processing method makes the purification processing agent containing the said metal powder and a nonmetallic type reducing agent contact contaminated water or contaminated soil, the heavy metal which has cadmium as a main can be removed efficiently.

  Here, the “heavy metal” is a metal species having a specific gravity of 4.5 or more at 25 ° C. The “sulfur content” is a value measured using a carbon / sulfur analyzer by a combustion method.

  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.

  Hereinafter, embodiments of a purification treatment method and a purification treatment agent according to the present invention will be described.

[Purification treatment agent]
The purification treatment agent of the present invention is used to remove at least cadmium from contaminated water or contaminated soil containing heavy metals, and contains metal powder made of iron or an alloy thereof and a nonmetallic reducing agent. In addition to the metal powder and the nonmetallic reducing agent, the purification treatment agent may contain other components such as a solvent as long as the effects of the invention are not hindered. Moreover, you may contain additives, such as a pH adjuster.

<Metal powder>
The metal powder adsorbs heavy metals such as cadmium on its surface. Heavy metal exists as heavy metal ions in water, and by reacting these ions with metal powder, the heavy metal is insolubilized and deposited near the surface of the metal powder. 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 that is industrially available can be used. Examples of the metal powder include iron-based complete metal powder (pre-alloy alloy powder) or partial metal powder (pre-mix alloy powder) such as atomized iron powder, cast iron powder, and sponge iron powder. Moreover, as elements other than iron which the said alloy contains, carbon, sulfur, nickel, copper, zinc, aluminum, cobalt etc. are mentioned, for example. Here, the “main component” refers to a component (for example, 50% by mass or more) that is contained most on a mass basis among the components constituting the metal powder.

  As a metal powder, the atomized metal powder manufactured by the atomizing method is preferable. Since the atomized metal powder can be mass-produced, the purification treatment agent can be used for large-scale treatment in a treatment facility or the like. Moreover, atomized metal powder is easy to arrange components and particle sizes. The atomized metal powder may be a complete metal powder obtained by atomizing an iron alloy, or a partially alloyed powder obtained by attaching a metal powder after atomizing the iron powder.

  The upper limit of the average particle size of the metal powder is preferably 1000 μm, more preferably 500 μm, and still more preferably 100 μm. On the other hand, the lower limit of the average particle size of the metal powder is preferably 1 μm. If the average particle size exceeds the upper limit, the surface area of the metal powder may be reduced and the removal rate of heavy metals and the like may be reduced. On the other hand, when the average particle size is less than the lower limit, the yield may be lowered and the handleability may be lowered. Here, the “average particle size” means a particle size distribution obtained by a dry sieving test using a sieve specified in JIS-Z-8801 (2006), and a particle size at which the cumulative mass becomes 50% in this particle size distribution. Say.

The metal powder may contain sulfur as an alloy element. The presence of sulfur improves the heavy metal removal performance of the metal powder. The reason why the removal performance of heavy metals is improved by adding sulfur to the metal powder is considered as follows. In other words, oxidation of the metal powder surface is promoted by the action of sulfur (iron anodic reaction: Fe → Fe ²⁺ + 2e ⁻ ), iron ions generated efficiently on the metal powder surface, rapidly growing iron oxide and hydroxylation. It is considered that the adsorption of heavy metals present in the form of metal ions or compound ions in the contaminated water or the contaminated soil is promoted by the object, etc., and the removal of heavy metals proceeds efficiently.

  As an upper limit of content of the sulfur content in metal powder, 5 mass% is preferable, 4 mass% is more preferable, and 3 mass% is further more preferable. On the other hand, as a minimum of the above-mentioned content, 0.05 mass% is preferred, 0.1 mass% is more preferred, and 0.8 mass% is still more preferred. When the said content exceeds the said upper limit, there exists a possibility that the adsorption | suction efficiency of the heavy metal of metal powder may fall. In addition, the cost of the purification treatment agent may increase unnecessarily. On the other hand, when the content is less than the lower limit, there is a possibility that the effect of improving the removal performance of heavy metal by the above-described sulfur may be insufficient.

<Non-metallic 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, but as the material, for example, sodium thiosulfate, ascorbic acid, urea, sodium hydrosulfite, thiourea dioxide, Anisole etc. are mentioned. Among these, sodium thiosulfate, ascorbic acid, urea, anisole and combinations thereof are preferable. By using a non-metallic reducing agent of such a material, it is possible to improve heavy metal removal performance while suppressing costs.

  As a minimum of mass ratio of content of nonmetallic reducing agent to metal powder, 0.01 is preferred and 0.2 is more preferred. On the other hand, the upper limit of the mass ratio is preferably 4, more preferably 2, and even more preferably 1. When the said mass ratio is less than the said minimum, mixing with a metal powder may become inadequate and there exists a possibility that the removal performance of heavy metal may become inadequate. On the other hand, if the mass ratio exceeds the upper limit, the heavy metal removal performance reaches its peak while the cost may increase.

<Contaminated water or contaminated soil>
The contaminated water or contaminated soil purified by the purification treatment agent contains cadmium. This contaminated water or contaminated soil may further contain a heavy metal other than cadmium, a heavy metal-containing compound or a fluoride. In contaminated soil, heavy metals in the soil elute into the water (chemical water, hygroscopic water, capillary water, gravity water, rainwater, etc.) present in the soil. Can be purified. When the contaminated soil does not contain water, purification treatment can be performed by adding water to the contaminated soil and making a solution that elutes water-soluble components in the contaminated soil.

(Heavy metal or heavy metal compound)
The heavy metal or heavy metal compound exists as heavy metal ions or heavy metal compound ions in the contaminated water or contaminated soil, and is dissolved in the contaminated water or contaminated soil. Of the heavy metals in such heavy metals or heavy metal-containing compounds, those that are particularly desired to be removed include cadmium, arsenic, selenium, lead, chromium, and combinations thereof.

Examples of the heavy metal compound include cadmium nitrate, sodium hydrogen arsenate, sodium selenate, potassium dichromate, and the like. Examples of the heavy metal ions or heavy metal compounds include cadmium ions (Cd ²⁺ ), arsenate ions (AsO ₄ ³⁻ ), selenate ions (SeO ₄ ²⁻ ), lead ions (Pb ²⁺ ), and chromium ions (Cr ⁶⁺ ). Etc.

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

Cadmium and selenium are dissolved in water in the form of cadmium ions (Cd ²⁺ ) and selenium ions (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 are deposited on the surface of the metal powder. As a result, cadmium ions and selenium ions can be efficiently removed from the water.

Arsenic is dissolved in water in the form of arsenate ions (AsO ₄ ³⁻ ). In order to remove the arsenate ion, a compound may be generated by reacting the ion with iron ion. And an iron ion can be efficiently discharge | released in water by using a nonmetallic reducing agent and metal powder. As a result, insoluble iron arsenate (compound of arsenic acid and iron) is deposited on the surface of the metal powder (that is, heavy metal is adsorbed to the metal powder) to efficiently remove arsenate ions from water. it can.

  Since chromium ions and lead-containing ions react with iron ions contained in the metal powder to form iron compounds, they can be precipitated as insoluble compounds on the surface of the metal powder. As a result, chromium ions and lead-containing ions can be efficiently removed from the water.

[Purification treatment method]
Next, an embodiment of the purification treatment method of the present invention will be described in detail.

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

<Contact process>
In this step, the purification treatment agent is brought into contact with contaminated water or contaminated soil. There is no particular limitation on the contact method, for example, a method in which the purification treatment agent is filled in an appropriate container and contaminated water or contaminated soil is continuously passed through the container, and the purification treatment agent is contaminated water or contaminated soil. And the like, and the like.

  The amount of the purification agent to be brought into contact with the contaminated water or the contaminated soil is not particularly limited, but as the lower limit of the contact amount based on the metal powder contained in the purification agent, with respect to 1000 mL of the contaminated water or the contaminated soil eluate, 0.1g is preferable and 0.2g is more preferable. On the other hand, the upper limit of the contact amount is preferably 100 g, and more preferably 10 g. If the contact amount is less than the lower limit, there may be a variation in purification effect due to variations in the performance of the metal powder. On the contrary, when the contact amount exceeds the upper limit, the effect is saturated, so that an effect commensurate with the amount of the metal powder cannot be obtained.

  Moreover, as an upper limit of the addition amount of the purification treatment agent when the purification treatment agent is added to contaminated water or contaminated soil, 4 g is preferable in terms of the mass of metal powder with respect to 1 mg of cadmium in the contaminated water or contaminated soil, and 2 g More preferred. On the other hand, the lower limit of the amount added is preferably 0.1 g, more preferably 0.3 g in terms of the mass of metal powder with respect to 1 mg of cadmium in the contaminated water or contaminated soil.

  As the upper limit of the stirring time when the purification agent is added to contaminated water or contaminated soil, 72 hours is preferable, and 36 hours is more preferable. On the other hand, the lower limit of the stirring time is preferably 10 minutes, and more preferably 30 minutes. When the above stirring time exceeds the above upper limit, the removal amount of cadmium or the like is difficult to improve as compared with the stirring time, and the removal efficiency may be reduced. Conversely, when the stirring time is less than the lower limit, cadmium or the like may not be sufficiently removed.

  In addition, as a minimum of the pH of the contaminated water or contaminated soil eluate immediately after adding the said purification process agent, 2 are preferable and 3 is more preferable. On the other hand, the upper limit of pH is preferably 10, and more preferably 9. If the pH is smaller than the above lower limit, hydrogen is likely to be generated and the metal powder adsorption performance may be reduced. On the other hand, when the pH exceeds the above upper limit, the formation of iron hydroxide becomes remarkable and the adsorption performance of the metal powder may be lowered. In particular, when sodium thiosulfate is used as the nonmetallic reducing agent, the pH is preferably 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 nonmetallic 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.

  In the purification treatment method, a purification treatment agent containing metal powder made of iron or an alloy thereof and a nonmetallic reducing agent is brought into contact with contaminated water or contaminated soil, so that heavy metals mainly including cadmium are efficiently removed. Can do.

  EXAMPLES Hereinafter, although an Example is given and this invention is demonstrated more concretely, this invention is not limited to these.

[Examples 1 and 2 and Comparative Examples 1 to 3]
In a polyethylene container having an internal volume of 500 mL, 250 mL of an aqueous solution prepared by adjusting cadmium nitrate with ion-exchanged water to a cadmium concentration of 1 mg / L was charged as contaminated water. A purification treatment containing metal powder and a nonmetallic reducing agent or FeS was added to this solution so that the solid / liquid ratio (g / mL) was a value 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 agent and the contaminated water. However, Comparative Example 2 used only FeS as a purification treatment agent, and Comparative Example 3 used only a nonmetallic reducing agent as a purification treatment agent. The types of metal powder used in each example and comparative example are as described below. Then, after measuring the pH and oxidation-reduction potential (ORP) of the mixture, using a horizontal shaker, the mixture of the purification agent and contaminated water under the conditions of a temperature of 25 ° C., a rotation speed of 140 rpm, and a shaking width of 4 cm. The mixture was shaken for 1 hour and stirred. After shaking, the pH and oxidation-reduction potential were measured, and the mixed solution was suction filtered with a membrane filter having a pore size of 0.45 μm. The residual cadmium concentration in the contaminated water after treatment was described in 55.3 of JIS-K0102 (2013). Measured by ICP emission spectroscopy. The results are shown in Table 1. The pH of the above mixture was adjusted with hydrochloric acid.
A: Pure iron powder (atomized iron powder, average particle size 70 μm, sulfur content 0.009 mass%)
B: Iron alloy powder (atomized iron powder, average particle size 70 μm, sulfur content 1 mass%)

  From Table 1, it is understood that the cadmium concentration can be greatly reduced by using the purification agent in which the metal powder and the nonmetallic reducing agent (sodium thiosulfate) are mixed, as compared with Comparative Example 1 in which the metal powder is used in combination with FeS. . On the other hand, in Comparative Examples 2 and 3 using FeS alone or sodium thiosulfate alone, the effect of removing cadmium was considerably low.

[Examples 3 to 13]
Agitation, filtration, and measurements were performed under the same conditions as in Example 2 except that the mixing ratio of the metal powder and the nonmetallic reducing agent, the solid / liquid ratio, and the pH were set to the values shown in Table 2. The results are shown in Table 2. In addition, "<0.001" in a table | surface shows that it is smaller than the lower limit (0.001 mg / L) of a measurement.

  From Table 2, it can be seen that the cadmium removal performance is enhanced by making the mixing mass ratio of the nonmetallic reducing agent to the metal powder larger than 0.04. It can also be seen that cadmium can be effectively removed by adjusting the pH of the mixture before treatment (before stirring) to 2 to 10, preferably 3 to 10.

[Examples 14 to 19]
Stirring, filtration, and measurements were performed under the same conditions as in Example 2 except that the nonmetallic reducing agents shown in Table 3 were used. The results are shown in Table 3. In Examples 16 and 19, a part of anisole remained undissolved.

  Table 3 shows that cadmium can be efficiently removed even if a nonmetallic reducing agent other than sodium thiosulfate is used. Moreover, it turns out that cadmium can be removed effectively irrespective of pH by using urea.

[Examples 20 to 23]
With ion-exchanged water, stirring was performed under the same conditions as in Example 2 except that 250 mL of an aqueous solution prepared so that the cadmium concentration and the concentration of additional heavy metal contained in the compound shown below were each 1 mg / L was added as contaminated water. Filtration and each measurement were performed. The results are shown in Table 4. In addition, the heavy metal compound used in each Example is as follows.
Example 20: Disodium hydrogen arsenate Example 21: Sodium selenate 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 contaminated water containing heavy metals other than cadmium by the purification treatment agent and the purification treatment method.

  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 (6)

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