Heavy metal insolubilizing material, and heavy metal insolubilizing method using the same

Abstract

To provide a heavy metal insolubilizing material for insolubilizing heavy metal contained in a heavy metal contaminant (for example, incineration ash, soil, and drainage water), which can exhibit an excellent insolubilization effect to a plurality of kinds of heave metal (for example, arsenic and hexavalent chromium), in a short time (for example, 2 to 3 hours).SOLUTION: A heavy metal insolubilizing material contains an iron compound composed of either or both of ferrous sulfate monohydrate and ferrous chloride tetrahydrate, and a magnesium compound composed of one or more selected from the group consisting of magnesium sulfate heptahydrate, magnesium sulfate nonhydrate, and magnesium sulfite hexahydrate. A ratio of the iron compound in the total amount of the iron compound and the magnesium compound is 5 to 80 mass%. The heavy metal insolubilizing material can be prepared in a powdery form.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a heavy metal insolubilizing material and a method for insolubilizing heavy metals contained in heavy metal pollutants such as soil, incineration ash, and wastewater using the heavy metal insolubilizing material. [Background technology]

[0002] By-products from factories (such as incineration ash, fly ash, and slag) can contain heavy metals at concentrations that exceed the environmental standards for soil. In addition, wastewater from factories can also contain heavy metals. For this reason, many insolubilizing materials have been proposed that can suppress the elution of heavy metals contained in heavy metal pollutants (e.g., incineration ash, soil, wastewater, etc.) targeting multiple types of heavy metals.

[0003] As an example, Patent Document 1 describes an insolubilizer for soil and incineration ash contaminated with heavy metals consisting of lead and hexavalent chromium and all or one or more harmful substances selected from arsenic, selenium, boron, and fluorine, the insolubilizer including an acidic iron salt (e.g., ferrous sulfate, etc.) and a magnesium salt (e.g., semi-burnt dolomite, light-burnt dolomite, light-burnt magnesium, etc.).

[0004] As another example, Patent Document 2 describes an insolubilizing material for insolubilizing heavy metals contained in waste, the insolubilizing material containing an iron chloride-containing substance, which contains iron chloride as a main component, and in which the proportion of the iron chloride-containing substance that passes through a sieve with a mesh size of 500 μm relative to the total amount of the iron chloride-containing substance is 50 mass % or more, and the proportion of the iron chloride-containing substance that passes through a sieve with a mesh size of 250 μm or less is 90 mass %.

[0005] As another example, Patent Document 3 describes a method for immobilizing heavy metals in fly ash, which comprises adding water and piperazinecarbodithioic acid or a salt thereof (a highly stable chelating agent) to the fly ash and kneading the mixture. Patent Document 3 also describes that the heavy metals in fly ash to be immobilized are generally metals that can be insolubilized from an aqueous solution by chelating with a dithiocarbamic acid group, and that examples of such metals include lead, mercury, chromium, cadmium, zinc, copper, nickel, arsenic, and selenium. It also describes that lead, mercury, chromium, cadmium, zinc, and copper are particularly preferred due to their high chelating effect. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Japanese Patent Application Laid-Open No. 2014-54602 [Patent Document 2] Patent Publication No. 2021-104469 [Patent Document 3] Japanese Patent Application Publication No. 8-224560 Summary of the Invention [Problem to be solved by the invention]

[0007] In each of the above-mentioned Patent Documents 1 and 2, a plurality of types of heavy metals are insolubilized together in the examples. Furthermore, in Patent Document 3, the examples show the effect of inhibiting elution of only lead. However, as described above, taking into consideration the mechanism by which heavy metals are insolubilized from aqueous solutions by chelating with dithiocarbamic acid groups, it is presumed that it is also possible to insolubilize both lead and mercury, for example.

[0008] However, in Patent Document 1, when an insolubilizer containing semi-burned dolomite or the like is used, a curing period of one day or more is generally set up. In this case, if the material to be treated is removed immediately after using the insolubilizer (for example, after 2 to 3 hours), there is a problem that the material to be treated will be handled with insufficient insolubilization effect. In Patent Document 2, it is necessary to select iron chloride having a specific particle size (for example, a specific type selected from multiple types of ferrous chloride dihydrate). In Patent Document 3, since the chelating agent is an organic substance, if the chelating agent is exposed to soil for a long period of time, the chelating agent may be decomposed by microorganisms in the soil, causing the insolubilized heavy metals to be re-eluted. Furthermore, since the chelating agent cannot form chemical bonds with harmful substances (e.g., fluorine, boron, etc.) that exist in the form of anions in soil, it cannot insolubilize these harmful substances.

[0009] An object of the present invention is to provide a heavy metal insolubilizing material for insolubilizing heavy metals contained in heavy metal pollutants (e.g., incineration ash containing heavy metals, soil containing such incineration ash, wastewater containing heavy metals, etc.), which is capable of exhibiting an excellent insolubilizing effect on multiple types of heavy metals (e.g., arsenic and hexavalent chromium) in a short period of time (e.g., 2 to 3 hours), and a method for insolubilizing heavy metals using the heavy metal insolubilizing material. [Means for solving the problem]

[0010] As a result of extensive research conducted by the present inventors to solve the above-mentioned problems, they discovered that a heavy metal insolubilizing material containing an iron compound consisting of either or both of ferrous sulfate monohydrate and ferrous chloride tetrahydrate, and one or more magnesium compounds selected from the group consisting of magnesium sulfate heptahydrate, magnesium sulfate anhydrate, and magnesium sulfite hexahydrate, can exhibit excellent insolubilizing effects on multiple types of heavy metals (e.g., arsenic and hexavalent chromium) in a short period of time (e.g., 2 to 3 hours), and thus completed the present invention.

[0011] The present invention provides the following [1] to [5]. [1] A heavy metal insolubilizing material characterized by containing an iron compound consisting of either or both of ferrous sulfate monohydrate and ferrous chloride tetrahydrate, and a magnesium compound consisting of one or more selected from the group consisting of magnesium sulfate heptahydrate, magnesium sulfate anhydrate, and magnesium sulfite hexahydrate. [2] The heavy metal insolubilizing material according to [1] above, wherein the proportion of the iron compound in the total amount of the iron compound and the magnesium compound is 5 to 80 mass %. [3] The heavy metal insolubilizing material according to [1] or [2] above, which is in the form of a powder. [4] A method for insolubilizing heavy metals contained in heavy metal pollutants using the heavy metal insolubilizing material according to any one of [1] to [3] above, wherein the heavy metal pollutants contain one or more elements selected from the group consisting of fluorine, boron, arsenic, hexavalent chromium, lead, selenium, cadmium, mercury, and cyanide, and the method for insolubilizing heavy metals comprises a mixing step of adding the heavy metal insolubilizing material to the heavy metal pollutants and mixing them. [5] The method for insolubilizing heavy metals according to [4] above, wherein the heavy metal contaminants are (a) a powder or granular material such that when 30 parts by mass of water having a pH of 7.8 is added to 100 parts by mass of the powder or granular material to prepare a mixture, the pH of the mixture becomes 10 or higher, or (b) a liquid material having a pH of 10 or higher. [Effects of the Invention]

[0012] When added to and mixed with heavy metal contaminants, the heavy metal insolubilizing material of the present invention can exhibit excellent insolubilizing effects against multiple types of heavy metals (e.g., combinations of arsenic and hexavalent chromium, combinations of fluorine and boron, and combinations of fluorine, arsenic, and hexavalent chromium) in a short period of time (e.g., 2 to 3 hours). The heavy metal insolubilizing material of the present invention can be in a powder form, and therefore does not require the piping or pumps for pressure transfer that are required when the material is in the form of a solution, and is therefore excellent in handleability (ease of handling).In addition, since the heavy metal insolubilizing material of the present invention has excellent solubility in water, it can also be used in the form of a solution using existing solution-based equipment. DETAILED DESCRIPTION OF THE INVENTION

[0013] [Heavy metal insolubilizer] The heavy metal insolubilizing material of the present invention contains an iron compound consisting of either or both of ferrous sulfate monohydrate and ferrous chloride tetrahydrate, and a magnesium compound consisting of one or more selected from the group consisting of magnesium sulfate heptahydrate, magnesium sulfate anhydrate, and magnesium sulfite hexahydrate. In this specification, "heavy metals" refers to fluorine, boron, arsenic, hexavalent chromium, lead, selenium, cadmium, mercury, and cyanide. All of these are substances specified in the soil environmental standards established by the Ministry of the Environment. Although fluorine, boron, selenium, and cyanide are not heavy metals, they are included in the "heavy metals" in this specification.

[0014] In the present invention, the proportion of the iron compound in the total amount (100% by mass) of the iron compound (either or both of ferrous sulfate monohydrate and ferrous chloride tetrahydrate) and the magnesium compound (one or more selected from the group consisting of magnesium sulfate heptahydrate, magnesium sulfate anhydrate, and magnesium sulfite hexahydrate) is preferably 5 to 80% by mass, more preferably 6 to 75% by mass, even more preferably 7 to 70% by mass, and particularly preferably 8 to 65% by mass. When the proportion is 5% by mass or more, the effect of insolubilizing the heavy metals can be further enhanced when the heavy metals are arsenic, hexavalent chromium, etc. When the proportion is 80% by mass or less, the effect of insolubilizing the heavy metals can be further enhanced when the heavy metals are fluorine, etc. The ratio is based on the mass including water of hydration (water molecules) for both the iron compound and the magnesium compound.

[0015] The iron compound and magnesium compound constituting the heavy metal insolubilizing material of the present invention can both be in the form of powder. Furthermore, these iron compounds and magnesium compounds have the advantage that they are less likely to solidify when stored in powder form because they have low deliquescence. Therefore, the heavy metal insolubilizing material of the present invention can be prepared as a mixture (premix) of a powdered iron compound and a powdered magnesium compound, and can be stored, distributed, and used.

[0016] In the present invention, materials (other materials) other than the above-mentioned iron compounds and magnesium compounds can be included in the heavy metal insolubilizing material of the present invention, within the scope that does not impair the effects of the present invention. Examples of other materials include light-burned magnesia, magnesium chloride, light-burned dolomite, and the like. In order to further enhance the effects of the present invention, the proportion of other materials is preferably 20 mass% or less, more preferably 15 mass% or less, even more preferably 10 mass% or less, and particularly preferably 5 mass% or less, of the total amount (100 mass%) of the heavy metal insolubilizing material of the present invention.

[0017] [Method for insolubilizing heavy metals] The method for insolubilizing heavy metals of the present invention is a method for insolubilizing heavy metals contained in heavy metal pollutants using the above-mentioned heavy metal insolubilizing material, wherein the heavy metal pollutants contain one or more of the above-mentioned heavy metals (specifically, one or more selected from the group consisting of fluorine, boron, arsenic, hexavalent chromium, lead, selenium, cadmium, mercury, and cyanide), and the method includes a mixing step of adding the heavy metal insolubilizing material to the heavy metal pollutants and mixing them.

[0018] Examples of heavy metal contaminants include powdery or granular materials such as incineration ash, fly ash, and slag from factories (referred to as "powdery and granular materials" in this specification), liquid materials such as wastewater from factories, and soil contaminated by these powdery and granular materials or liquid materials. When the heavy metal contaminants are in the form of a powder or granule, the powder or granule is preferably such that when 30 parts by mass of water having a pH of 7.8 is added to 100 parts by mass of the powder or granule to prepare a mixture, the pH of the mixture becomes 10 or higher (particularly preferably 11 or higher). When the pH is 10 or higher, the effect of insolubilizing heavy metals can be further enhanced. When the heavy metal contaminants are in a liquid state, the pH of the liquid is preferably 10 or higher, more preferably 11 or higher, and particularly preferably 12 or higher. When the pH is 10 or higher, the effect of insolubilizing heavy metals can be further enhanced. [Example]

[0019] The present invention will be specifically described below with reference to examples, but the present invention is not limited to these examples. [1. Insolubilizing material] The following materials were used as the insolubilizing material. (1) Iron compounds (a) Ferrous sulfate monohydrate (powder; manufactured by Fuji Titanium Industry Co., Ltd.) (b) Ferrous chloride tetrahydrate (powder; manufactured by Kojundo Chemical Laboratory Co., Ltd.) (c) Ferrous sulfate heptahydrate (for comparison; powder; Fujifilm Wako Pure Chemical Industries, Ltd.) (2) Magnesium compounds (a) Magnesium sulfate heptahydrate (powder; manufactured by San-Esu Gypsum Co., Ltd.) (b) Magnesium sulfate anhydrate (powder; manufactured by Mai Chemical Industry Co., Ltd.) (c) Magnesium sulfite hexahydrate (powder; manufactured by Yoneyama Pharmaceutical Co., Ltd.) (d) Dolomite hydroxide (for comparison; powder; manufactured by Tamasa Kogyo Co., Ltd.) (e) Light-burned magnesia (for comparison; powder; manufactured by Taiheiyo Cement Corporation) (f) Magnesium chloride (for comparison; powder; manufactured by Kanto Chemical Co., Ltd.)

[0020] [2. Heavy metal pollutants] The heavy metal contaminants used were those shown in Table 1 (wastewater, incineration ash). In Table 1, the amount of fluorine and other substances eluted from the incineration ash and the pH indicate the amount of fluorine and other substances eluted from the mixture when 30 parts by mass of water (pH: 7.8) is added to 100 parts by mass of incineration ash to prepare the mixture. In Table 1, "-" for the amount of "boron" eluted in "wastewater" and "-" for the amount of "arsenic" eluted in "incineration ash" indicate that both were below the detection limit.

[0021] [Table 1]

[0022] [3. Testing insolubilization performance using wastewater] [Example 1] A heavy metal insolubilizing material was obtained by mixing 10 parts by mass of ferrous sulfate monohydrate and 90 parts by mass of magnesium sulfate heptahydrate (a total of 100 parts by mass). The heavy metal insolubilizer was added to the wastewater so that the liquid-solid ratio (wastewater:heavy metal insolubilizer) was 50:1, and after mixing, the resulting mixture was shaken and the concentrations of fluorine, arsenic, and hexavalent chromium in the mixture were measured 30 minutes (0.5 hours) and 360 minutes (6 hours) after addition. [Examples 2 to 4, Comparative Examples 1 and 2] The experiment was carried out in the same manner as in Example 1, except that the material composition of the heavy metal insolubilizing material was changed as shown in Table 2. In Table 2, "magnesium sulfite" refers to magnesium sulfite hexahydrate. The results are shown in Table 2. In Table 2, "<0.01" and "<0.02" indicate "less than 0.01 mg / liter" and "less than 0.02 mg / liter," respectively.

[0023] [Table 2]

[0024] From Table 2, it can be seen that in Examples 1 to 4, in a short time of 0.5 hours (30 minutes), the fluorine concentration decreased from 12.4 mg / liter (see Table 1) to 1.3 to 2.4 mg / liter, the arsenic concentration decreased from 0.5 mg / liter (see Table 1) to 0.04 mg / liter or less, and the hexavalent chromium concentration decreased from 0.9 mg / liter (see Table 1) to 0.1 mg / liter or less. On the other hand, in Comparative Example 1, the concentrations of all of fluorine, arsenic, and hexavalent chromium were found to be higher than those in Examples 1 to 4 after 0.5 hours (30 minutes). It can be seen that in Comparative Example 2, the concentrations of fluorine and arsenic were much higher than those in Examples 1 to 4 after 0.5 hours (30 minutes).

[0025] [4. Testing insolubilization performance using incineration ash] [Example 5] A heavy metal insolubilizer was obtained by mixing 20 parts by mass of ferrous sulfate monohydrate and 80 parts by mass of magnesium sulfate heptahydrate (a total of 100 parts by mass). The obtained heavy metal insolubilizer was left to stand for 3 hours in a room at 30°C and a relative humidity of 70%, and then its insolubilization performance for incineration ash was examined using the following procedure. First, 30 parts by mass of water (pH: 7.8) was added to 100 parts by mass of incineration ash and mixed to obtain a mixture, and then 5 parts by mass of heavy metal insolubilizer was added to this mixture and mixed to obtain a treated sample. The samples were placed in polyethylene bags and stored in a sealed state, and the amount of eluted heavy metals (fluorine, boron, and hexavalent chromium) in the samples was measured 2 hours and 24 hours after sample preparation in accordance with the elution test prescribed in Environment Agency Notification No. 46 of 1991 (sometimes abbreviated as Environmental Notification No. 46). [Examples 6 to 7, Comparative Examples 3 to 5] The experiment was carried out in the same manner as in Example 5, except that the material composition of the heavy metal insolubilizing material was changed as shown in Table 3. The results are shown in Table 3. In Table 3, "magnesium sulfite" and "<0.02" indicate the same as in Table 2.

[0026] [Table 3]

[0027] Table 3 shows that in Examples 5 to 7, in the short time of 2 hours after the preparation of the treated samples (hereinafter referred to as "2 hours after the elapsed time"), the fluorine concentration decreased from 1.1 mg / liter (see Table 1) to 0.62 to 0.72 mg / liter, the boron concentration decreased from 2.4 mg / liter (see Table 1) to 0.8 to 1.0 mg / liter, and the hexavalent chromium concentration decreased from 0.2 mg / liter (see Table 1) to less than 0.02 mg / liter. On the other hand, in Comparative Example 3, ferrous sulfate heptahydrate was used, and therefore the concentrations of fluorine, boron, and hexavalent chromium were higher after 2 hours than in Example 5, which used ferrous sulfate monohydrate. In Comparative Example 4, magnesium chloride was used as the magnesium compound, and therefore the concentrations of fluorine, boron, and hexavalent chromium were higher after 2 hours than in Example 6, in which magnesium sulfite hexahydrate was used. In Comparative Example 5, light-burned magnesia was used as the magnesium compound, and therefore the concentrations of fluorine and boron were higher after 2 hours than in Example 5, which used magnesium sulfate heptahydrate, and Example 7, which used magnesium sulfate anhydrate.

Claims

1. A heavy metal insolubilizing material characterized by containing an iron compound consisting of either or both of ferrous sulfate monohydrate and ferrous chloride tetrahydrate, and a magnesium compound consisting of one or more selected from the group consisting of magnesium sulfate heptahydrate, magnesium sulfate anhydrate, and magnesium sulfite hexahydrate.

2. 2. The heavy metal insolubilizing material according to claim 1, wherein the proportion of the iron compound in the total amount of the iron compound and the magnesium compound is 5 to 80 mass %.

3. 2. The heavy metal insolubilizing material according to claim 1, wherein the heavy metal insolubilizing material is in the form of a powder.

4. A method for insolubilizing heavy metals contained in heavy metal pollutants using the heavy metal insolubilizing material according to any one of claims 1 to 3, comprising: The heavy metal contaminants include one or more selected from the group consisting of fluorine, boron, arsenic, hexavalent chromium, lead, selenium, cadmium, mercury, and cyanide, and A method for insolubilizing heavy metals, comprising a mixing step of adding the heavy metal insolubilizing material to the heavy metal contaminants and mixing them.

5. 5. The method for insolubilizing heavy metals according to claim 4, wherein the heavy metal contaminants are (a) a powder or granular material such that when 30 parts by mass of water having a pH of 7.8 is added to 100 parts by mass of the powder or granular material to prepare a mixture, the pH of the mixture becomes 10 or higher, or (b) a liquid material having a pH of 10 or higher.

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