Hazardous substance treatment agent and method for treating wastewater containing hazardous substances

Abstract

To provide a treatment agent for removing a harmful substance such as selenium, and a method for treating waste water using the treatment agent.SOLUTION: A harmful substance treatment agent comprises a mixture including acidic iron hydroxide, metal iron powder and active porous calcium silicate grains. An example of the acidic iron hydroxide is a product of hydration from an aqueous solution including ferrous chloride and ferric chloride. An example of the metal iron powder is atomized iron powder, reduced iron powder or pig iron turning. An example of the active porous calcium silicate grains is tobermorite, zonorite or calcium silicate hydrate. An example of the harmful substance is hexavalent or tetravalent selenium or water-soluble arsenic compound.SELECTED DRAWING: None

Description

Technical Field

[0001] The present invention relates to a treatment agent for removing harmful substances from sludge, wastewater, etc. containing harmful substances, and a method for treating wastewater containing harmful substances.

Background Art

[0002] Wastewater, soil, and sludge discharged from construction sites, chemical factories, mines, etc. may contain selenium as a harmful substance, and it is required to reduce the selenium concentration to 0.1 mg / l or less for discharge. In addition, when it contains harmful substances such as arsenic, its removal is also required.

[0003] As methods for removing selenium in wastewater, an iron powder replacement treatment method, an adsorption treatment method using iron hydroxide, a chemical passivation method, etc. are known. The chemical passivation method includes a method of generating iron hydroxide or iron oxide by a neutralization reaction between an alkaline aqueous solution and an acidic salt of iron such as iron chloride, and precipitating selenium together with it, or a method of generating iron hydroxide or iron oxide by an oxidation reaction of divalent iron, and precipitating selenium together with it.

[0004] Patent Document 1 discloses a method for adsorbing and removing selenium ions such as selenic acid using akaganéite (β-FeOOH). Patent Document 2 discloses that a precipitate formed by adding slaked lime to an aqueous ferric chloride solution is dried to obtain a treatment agent. Patent Document 3 discloses a treatment agent in which a reducing iron-based precipitate formed by slowly oxidizing divalent iron in an alkaline manner is supported on a fiber. Patent Document 4 discloses that after deoxygenating selenium-containing wastewater, a divalent iron salt and an alkali are added to coprecipitate selenium and ferrous hydroxide. Patent Document 5 discloses that selenium is removed by using a treatment agent containing amorphous iron hydroxide in selenium-containing wastewater.

[0005] In the etching process of copper foil and copper products using ferric chloride solution, a large amount of etching waste liquid is generated. Iron powder is added to the etching waste liquid to recover metallic copper and nickel. When the acidic residual liquid is left standing, iron precipitates and is recovered as iron content mainly composed of iron hydroxide and containing a small amount of iron powder and other components as sub-components, and the effective utilization of this is desired.

Prior Art Documents

Patent Documents

[0006]

Patent Document 1

Patent Document 2

Patent Document 3

Patent Document 4

Patent Document 5

Summary of the Invention

Problems to be Solved by the Invention

[0007] An object of the present invention is to provide a treatment agent useful for removing harmful substances such as selenium, and a method for treating wastewater using this treatment agent.

Means for Solving the Problems

[0008] The present invention is a harmful substance treatment agent characterized by comprising a mixture containing acidic iron hydroxide, metallic iron powder, and active porous calcium silicate particles.

[0009] Examples of the acidic iron hydroxide include those formed by the hydration reaction from an aqueous solution containing ferrous chloride and ferric chloride. Examples of the metallic iron powder include atomized iron powder, reduced iron powder, or iron dross. Examples of the active porous calcium silicate particles include those containing 50% by weight or more of one or more selected from tobermorite, zonnolite, and calcium silicate hydrate. Examples of the harmful substances include hexavalent or tetravalent selenium or water-soluble arsenic compounds.

[0010] The present invention also provides a method for treating wastewater containing harmful substances, which comprises adding and mixing the above-mentioned harmful substance treatment agent to wastewater containing hexavalent or tetravalent selenium to remove hexavalent or tetravalent selenium.

Advantages of the Invention

[0011] The harmful substance treatment agent of the present invention has a high ability to remove harmful substances such as selenium without performing operations such as coprecipitation, and is excellent in detoxifying wastewater, sludge, and construction waste.

Embodiments for Carrying Out the Invention

[0012] The harmful substance treatment agent of the present invention contains acidic iron hydroxide, metallic iron powder, and active porous calcium silicate particles. The active porous calcium silicate particles not only function as a carrier but also have adsorption ability and reactivity with harmful substances, enhancing the removal performance.

[0013] The acidic iron hydroxide may be any substance mainly composed of iron hydroxide precipitated from an acidic aqueous solution such as a ferrous chloride solution. Adding an alkali to an iron salt aqueous solution for neutralization and precipitation results in inferior effects. However, adding an insufficient amount of alkali for neutralization is acceptable.

[0014] As the acidic iron hydroxide, there is a dewatered cake generated during the recycling of the iron chloride solution used for etching electronic substrates. This dewatered cake is obtained by adding iron powder to the etching waste liquid (iron chloride solution) to recover copper and nickel as metals, then leaving the acidic residual liquid to cause precipitation, and subjecting this to compression filtration or the like. This dewatered cake contains 50 wt% or more of iron hydroxide (based on the dry state standard) and contains a small amount of iron powder and the like. It may also contain moisture.

[0015] As the metallic iron powder, atomized iron powder, reduced iron powder, or iron dross can be used. The particle size of the metallic iron powder is preferably 100 μm or less.

[0016] As the active porous calcium silicate particles, those containing 50 wt% or more of one or more selected from tobermorite, zonolite, and calcium silicate hydrate are suitable. Preferably, they are particles obtained by crushing lightweight cellular concrete plates for building materials. If waste lightweight cellular concrete plates generated during the demolition work of buildings are used as the lightweight cellular concrete plates, it is also effective for reducing waste. The particle size of the active porous calcium silicate particles is preferably 2 mm or less. Also, the lower limit is preferably 0.05 mm or more.

[0017] The proportions of the acidic iron hydroxide, metallic iron powder, and active porous silica are suitably in the range of 30 - 60 wt% for the active porous silica, 40 - 15 wt% for the acidic iron hydroxide, and 40 - 15 wt% for the metallic iron powder.

[0018] The harmful substance treatment agent of the present invention can be obtained by stirring and mixing raw materials containing acidic iron hydroxide, metallic iron powder, and active porous calcium silicate particles in a state containing an appropriate amount of moisture, drying this mixture if necessary, and crushing it to a predetermined size. When using a dewatered cake as the acidic iron hydroxide, moisture does not need to be added separately. There is no limitation on the shape and particle size of the harmful substance treatment agent, but from the viewpoints of handleability and reactivity, it preferably contains 50 wt% or more of particles of 0.1 - 2 mm.

[0019] Examples of harmful substances to be treated with the harmful substance treatment agent of the present invention include selenium, arsenic, boron, fluorine, etc. Selenium often exists as selenate ions or selenite ions, and the present invention has excellent removal ability for these substances.

[0020] In the method for treating wastewater using the harmful substance treatment agent of the present invention, the harmful substance treatment agent is added to the wastewater containing harmful substances, and they are brought into contact by stirring or the like, and then filtered, so that the harmful substances can be highly removed from the wastewater.

Example

[0021] The present invention will be described with reference to examples. Note that "parts" are parts by weight and "%" is wt%.

[0022] Example 1 As the active porous calcium silicate particles, commercially available lightweight expanded clay aggregate boards (manufactured by Cryon Co., Ltd., SiO2: 49.5%, CaO: 35.3%, Al2O3: 4.4%, Fe2O3: 2.6%, SiO2 / CaO ratio = 1.4) were dried and pulverized to obtain calcium silicate particles with a particle size adjusted to 1.2 mm or less and 0.1 mm or more. As the acidic iron hydroxide, a dehydration cake generated during the recycling of the iron chloride solution used for etching electronic substrates (total Fe: 45.2%, metallic Fe: 2.6%, Cl: 12.5%, moisture: 18.2%, pH: 2 - 3) was used. As the iron powder, reduced iron powder (manufactured by AsTech Irie Co., Ltd., total Fe; 84.4%, metallic Fe; 60.4%, Ca: 0.95%, C: 0.21%, Zn: 0.12%, Mn: 0.17%, apparent specific gravity 7.86, particle size distribution; 100% below 250 mesh (63 μm)) was used.

[0023] 50 parts of the above calcium silicate particles, 25 parts of the dehydration cake, and 25 parts of the reduced iron powder were stirred and mixed at room temperature for 5 minutes using a super mixer to obtain Treatment Agent 1. The average particle size of the treatment agent is 0.3 mm (99% in the range of 0.1 - 2.0 mm), and the bulk specific gravity is 1.0.

[0024] Example 2 As model wastewater, an aqueous selenium-containing solution was prepared by adding commercially available sodium selenite and sodium selenate reagents so that the total selenium concentration was 10 mg / l and the concentrations of tetravalent and hexavalent selenium were 1:1. 1 g of treatment agent 1 was added to 100 ml of this aqueous selenium-containing solution, and the mixture was stirred at 25 °C for 6 h to effect contact for selenium removal. Thereafter, this was filtered through a membrane filter with a pore diameter of 0.45 μm, and the total selenium concentration in the filtrate was measured using ICP emission spectroscopic analysis. The selenium concentration and selenium adsorption amount are shown in Table 1.

[0025] Comparative Example 1 Using 50 parts of calcium silicate particles and 50 parts of dehydrated cake the same as in Example 1, and without using reduced iron powder, treatment agent 2 was obtained in the same manner as in Example 1. The average particle size of treatment agent 2 was 0.3 mm (99% in the range of 0.1 - 2.0 mm), and the bulk specific gravity was 0.8. Selenium removal was carried out in the same manner as in Example 2, except that treatment agent 2 was used instead of treatment agent 1, and the total selenium concentration in the filtrate was measured.

[0026] Comparative Example 2 Using 50 parts of calcium silicate particles and 50 parts of reduced iron powder the same as in Example 1, and without using dehydrated cake, treatment agent 3 was obtained in the same manner as in Example 1. The average particle size of treatment agent 3 was 0.3 mm (99% in the range of 0.1 - 2.0 mm), and the bulk specific gravity was 1.4. Selenium removal was carried out in the same manner as in Example 2, except that treatment agent 3 was used instead of treatment agent 1, and the total selenium concentration in the filtrate was measured. The selenium concentration and selenium adsorption amount are shown in Table 1.

[0027] [Table 1]

[0028] Example 3 Selenium removal was carried out in the same manner as in Example 2, except that the total selenium concentration of the aqueous selenium-containing solution as model wastewater was changed to 0.05 mg / l and the addition amount of treatment agent 1 was changed as shown in Table 2, and the total selenium concentration in the filtrate was measured. Table 2 shows the selenium concentration and the selenium adsorption amount.

[0029]

Table 2

[0030] Example 4 Using an aqueous selenium-containing solution as model wastewater with a total selenium concentration of 0.25 mg / l, and changing the addition amount of Treatment Agent 1 as shown in Table 3, selenium removal was carried out in the same manner as in Example 2, and the total selenium concentration in the filtrate was measured. Table 3 shows the selenium concentration and the selenium adsorption amount.

[0031]

Table 3

[0032] Example 5 As model wastewater, an arsenic-containing aqueous solution (arsenic concentration 21 mg / l) added with semiconductor manufacturing slag was prepared. 1 g of Treatment Agent 1 obtained in Example 1 was added to 100 ml of this arsenic-containing aqueous solution, and stirred and contacted at 25 °C for 6 h to remove arsenic. Then, this was filtered through a membrane filter with a pore diameter of 0.45 μm, and the arsenic concentration in the filtrate was measured using a colorimetric method. Table 4 shows the arsenic concentration and the arsenic adsorption amount.

[0033] Example 6 40 parts of the same calcium silicate particles as used in Example 1, 30 parts of dehydrated cake, and 10 parts of reduced iron powder were stirred and mixed at room temperature for 5 minutes using a super mixer to obtain Treatment Agent 4. The average particle size of the treatment agent was 0.3 mm (99% in the range of 0.1 - 2.0 mm), and the bulk specific gravity was 1.0. As model wastewater, the same arsenic-containing aqueous solution as used in Example 5 was prepared. 1 g of Treatment Agent 4 was added to 100 ml of this arsenic-containing aqueous solution, and stirred and contacted at 25 °C for 6 h to remove arsenic.

[0034] Example 7 40 parts of calcium silicate particles, 10 parts of dehydrated cake, and 30 parts of reduced iron powder, the same as those used in Example 1, were stirred and mixed at room temperature for 5 minutes using a super mixer to obtain Treatment Agent 5. The average particle size of the treatment agent was 0.3 mm (99% in the range of 0.1 to 2.0 mm), and the bulk specific gravity was 1.0. As the model wastewater, the same arsenic-containing aqueous solution as that used in Example 5 was prepared. 1 g of Treatment Agent 5 was added to 100 ml of this arsenic-containing aqueous solution, and the mixture was stirred and contacted at 25 °C for 6 h to remove arsenic.

[0035] Comparative Example 3 Using Treatment Agent 3 obtained in Comparative Example 2, the same arsenic-containing aqueous solution as that used in Example 5 was prepared. 1 g of Treatment Agent 3 was added to 100 ml of this arsenic-containing aqueous solution, and the mixture was stirred and contacted at 25 °C for 6 h to remove arsenic. Table 4 shows the arsenic concentrations and arsenic adsorption amounts in the filtrates of Examples 5 to 7 and Comparative Example 3.

[0036]

Table 4

Claims

1. It consists of a mixture containing acidic iron hydroxide, metallic iron powder, and activated porous calcium silicate particles, and contains acidic iron hydroxide in a proportion of 40 to 15% by weight, metallic iron powder in a proportion of 40 to 15% by weight, and activated porous calcium silicate particles in a proportion of 30 to 60% by weight. A harmful substance treatment agent characterized by this.

2. The harmful substance treatment agent according to claim 1, wherein the acidic iron hydroxide is produced by a hydration reaction from an aqueous solution containing ferrous chloride and ferric chloride.

3. The harmful substance treatment agent according to claim 1 or 2, wherein the metallic iron powder is atomized iron powder, reduced iron powder, or iron dross.

4. The harmful substance treatment agent according to any one of claims 1 to 3, wherein the activated porous calcium silicate particles contain 50% by weight or more of one or more selected from tobermorite, zonnolite, and calcium silicate hydrate.

5. The harmful substance treatment agent according to any one of claims 1 to 4, wherein the harmful substance is hexavalent or tetravalent selenium.

6. The harmful substance treatment agent according to any one of claims 1 to 4, wherein the harmful substance is arsenic.

7. A method for treating wastewater containing harmful substances, characterized by adding and mixing the harmful substance treatment agent according to any one of claims 1 to 5 to wastewater containing hexavalent or tetravalent selenium to remove hexavalent or tetravalent selenium.

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