Method for producing anion adsorbent and anion adsorption method

Abstract

To provide a method for producing an anion adsorbent that enables suppression of carbon dioxide generation during production of the anion adsorbent, and to provide an anion adsorption method employing the anion adsorbent obtained by the method for producing an anion adsorbent.SOLUTION: The method for producing an anion adsorbent includes a step of preparing a mixture containing baryte and blast-furnace slag, and a step of calcining the mixture to obtain a water-soluble barium salt.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a method for producing an anion adsorbent and a method for adsorbing anions. [Background technology]

[0002] Construction work and other projects generate large amounts of contaminated soil containing naturally occurring heavy metals (hereinafter referred to as "heavy metal-contaminated soil"). Therefore, a simpler and less expensive method for treating heavy metal-contaminated soil is required. Heavy metal-contaminated soil, which is generated in large quantities during excavation work and other projects, is mixed with insolubilizers such as cement and magnesium oxide to suppress the amount of heavy metal leaching, and then sealed with a water barrier such as bentonite. In this way, heavy metal-contaminated soil is treated to prevent contact with rainwater.

[0003] In the insolubilization treatment of heavy metals, heavy metals that exist in the form of cations such as lead and chromium are easily adsorbed by soil and are relatively easy to insolubilize. On the other hand, heavy metals that exist in the form of anions such as arsenic and selenium are less likely to be adsorbed by soil and are difficult to insolubilize. Among them, selenium is mainly found in the form of hexavalent selenium, SeO4 2- and tetravalent selenite SeO3 2- The former, being an oxidized form, has a higher solubility and is extremely difficult to insolubilize. In order to insolubilize selenium, an excessive amount of insolubilizer must be added to the heavy metal contaminated soil. As a result, the volume of the heavy metal contaminated soil after insolubilization treatment increases and it solidifies more than necessary. The increase in the volume of heavy metal contaminated soil puts pressure on the capacity of disposal sites. Furthermore, the solidification of heavy metal contaminated soil makes transportation and construction difficult. Furthermore, selenium acid SeO4 2- is reduced to a less soluble form of selenite, SeO3 2- Therefore, the amount of leaching is suppressed by using a reducing agent to convert selenious acid into selenic acid in many iron oxides and sulfurous acids, but there is a concern that if exposed to the environment for a long period of time, it will be oxidized by contact with oxygen and become selenious acid again, which will increase the amount of leaching.

[0004] One method for insolubilizing selenium without being affected by the redox state is to mix a barium salt with a selenium-containing material. In this method, barium ions generated from the dissolved barium salt react with sulfate ions present in the soil to form sparingly soluble barium sulfate. By incorporating selenic acid into the barium sulfate crystals, selenium can be insolubilized stably against changes in pH and redox potential. For example, the invention described in Patent Document 1 is known as a method for insolubilizing selenium-contaminated soil or selenium-contaminated wastewater using barium ions.

[0005] However, soluble barium salts are expensive. Therefore, it is difficult to use large amounts of soluble barium salts for the purification of contaminated soil or contaminated wastewater. A method for inexpensively producing barium carbonate, a soluble barium salt, is known, for example, as disclosed in Patent Document 2. In this method, carbon is added to barite (barium sulfate crystals) and the resulting mixture is reduced and fired to obtain barium sulfide, a raw material for barium carbonate. This process transfers the oxygen contained in the barium sulfate to the carbon, resulting in the production of soluble barium sulfide. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Japanese Patent Application Laid-Open No. 2010-234306 [Patent Document 2] Patent No. 6011481 Summary of the Invention [Problem to be solved by the invention]

[0007] In the invention described in Patent Document 2, oxygen contained in barium sulfate is transferred to carbon to produce soluble barium sulfide, which is then oxidized to generate carbon dioxide. Carbon dioxide is a greenhouse gas, so it is desirable to reduce its emissions.

[0008] The present invention has been made in consideration of the above circumstances, and aims to provide a method for manufacturing an anion adsorbent that can suppress the generation of carbon dioxide during the manufacture of the anion adsorbent, and an anion adsorption method that uses the anion adsorbent obtained by the method for manufacturing an anion adsorbent. [Means for solving the problem]

[0009] The present invention has the following aspects. [1] preparing a mixture containing barite and blast furnace slag; and calcining the mixture to obtain a water-soluble barium salt. [2] The method for producing an anion adsorbent according to [1], wherein the content of the blast furnace slag in the mixture relative to 1 part by mass of the barite is 0.1 parts by mass or more and 50 parts by mass or less. [3] The method for producing an anion adsorbent according to [1] or [2], wherein the mixture is fired at a temperature of 800°C or higher and 1200°C or lower. [4] The method for producing an anion adsorbent according to any one of [1] to [3], wherein the mixture is fired in an inert gas atmosphere. [5] A method for adsorbing anions, comprising contacting a solution containing an anion of an inorganic compound with an anion adsorbent having a water-soluble barium salt obtained by the method for producing an anion adsorbent according to any one of [1] to [4], thereby adsorbing the anion to the barium salt. [6] The anion adsorption method according to [5], wherein the anion is an oxoacid ion of an inorganic compound. [7] The anion adsorption method according to [6], wherein the anion is a selenate ion or a selenite ion. [Effects of the Invention]

[0010] According to the present invention, it is possible to provide a method for manufacturing an anion adsorbent that can suppress the generation of carbon dioxide during the manufacture of the anion adsorbent, and an anion adsorption method that uses the anion adsorbent obtained by the method for manufacturing an anion adsorbent. DETAILED DESCRIPTION OF THE INVENTION

[0011] [Method of manufacturing anion adsorbent] A method for producing an anion adsorbent according to one embodiment of the present invention includes a step of preparing a mixture containing barite and blast furnace slag (hereinafter referred to as the "first step"), and a step of calcining the mixture to obtain a water-soluble barium salt (hereinafter referred to as the "second step").

[0012] "First step" Barite contains barium sulfate (BaSO4). It is preferable to use crushed barite. The maximum particle size of the barite is preferably 2.0 mm or less.

[0013] The blast furnace slag is not particularly limited as long as it has reducing ability. It is preferable to use pulverized blast furnace slag. The maximum particle size of the blast furnace slag is preferably 2.0 mm or less.

[0014] In a mixture containing barite and blast furnace slag, the content of blast furnace slag per 1 part by mass of barite is preferably 0.1 to 50 parts by mass, more preferably 0.2 to 10 parts by mass. When the content of blast furnace slag is equal to or greater than the lower limit, barium sulfide can be efficiently produced from the mixed barite. When the content of blast furnace slag is equal to or less than the upper limit, the barium content in the produced anion adsorbent is increased, improving the insolubilization efficiency per added amount.

[0015] "Second step" The temperature at which the mixture containing barite and blast furnace slag is fired (firing temperature) is preferably 800°C or higher and 1200°C or lower, and more preferably 1000°C or higher and 1200°C or lower. When the firing temperature is equal to or higher than the lower limit, barium sulfide can be efficiently produced from the mixed barite. When the firing temperature is equal to or lower than the upper limit, barium sulfide can be produced without inputting extra heat energy.

[0016] The time (calcination time) for calcining the mixture containing barite and blast furnace slag is preferably 30 minutes to 5 hours, more preferably 1 hour to 3 hours. When the calcination time is equal to or greater than the lower limit, barium sulfide can be efficiently produced from the mixed barite. When the calcination time is equal to or less than the upper limit, production can be achieved without inputting excess heat energy.

[0017] The mixture containing barite and blast furnace slag may be fired in air or in an inert gas atmosphere, but in order to prevent the generated barium sulfide from being oxidized to form barium sulfate again, it is more preferable to fire the mixture in an inert gas atmosphere, such as nitrogen, argon, or helium.

[0018] In the second step, the oxygen contained in the barium sulfate is absorbed by the blast furnace slag, producing water-soluble barium salts, such as barium sulfide, barium chloride, and barium oxide.

[0019] According to the method for producing an anion adsorbent of this embodiment, a mixture containing barite and blast furnace slag is prepared, and the mixture is calcined to obtain a water-soluble barium salt, thereby suppressing the generation of carbon dioxide during the production of the anion adsorbent. Furthermore, since inexpensive barite is used as a raw material, the production cost of the anion adsorbent can be reduced.

[0020] [Anion adsorption method] An anion adsorption method according to one embodiment of the present invention is a method for adsorbing anions onto a barium salt by contacting a solution containing an anion of an inorganic compound with an anion adsorbent having a water-soluble barium salt obtained by the method for producing an anion adsorbent according to the above-described embodiment.

[0021] Examples of inorganic compounds include inorganic compounds containing inorganic elements such as selenium, arsenic, chromium, fluorine, sulfur, and phosphorus. Specific examples include oxoacids of selenium, arsenic, and chromium, hydrofluoric acid (hydrofluoric acid), sulfuric acid, and phosphoric acid.

[0022] As the inorganic compound, an oxoacid is preferred from the viewpoint of exhibiting a high adsorptivity to a water-soluble barium salt, and a monovalent or divalent inorganic oxoacid containing an inorganic element is more preferred. Here, an oxoacid is an inorganic compound in which a hydroxyl group (-OH) and an oxo group (=O) are bonded to a single inorganic atom, and the proton of the hydroxyl group can be eliminated. In water, an oxoacid can become an oxoacid ion by eliminating the proton.

[0023] As the oxoacid, selenium oxoacid is preferred from the viewpoint of its high adsorption ability to iron-aluminum double hydroxides. As the oxoacid ion of selenium, selenate ion (SeO4 2- ), hydrogen selenate ion (HSeO4 - ), selenite ion (SeO3 2- ), hydrogen selenite ion (HSeO3 - ) are listed.

[0024] The anions of the inorganic compounds contained in the liquid to be treated may be of one type or two or more types.

[0025] The method for contacting the water-soluble barium salt with the liquid to be treated is not particularly limited, and examples include a method of adding water-soluble barium salt powder to the liquid to be treated and stirring it, and a method of pouring the liquid to be treated onto the water-soluble barium salt held on a holding member and allowing it to flow.

[0026] In this embodiment, it is believed that when the liquid to be treated is brought into contact with the water-soluble barium salt, anions contained in the liquid to be treated are trapped and adsorbed by the water-soluble barium salt.

[0027] When a water-soluble barium salt is added to the liquid to be treated and the target anion is adsorbed onto the water-soluble barium salt, the pH of the liquid to be treated (water-soluble barium salt dispersion) during the treatment is preferably 1 or more and 13 or less, more preferably 2 or more and 12 or less. When the pH of the liquid to be treated during treatment is 13 or less, decomposition of the water-soluble barium salt is prevented, and the ability of the water-soluble barium salt to adsorb the target anion can be increased. The lower the pH of the liquid to be treated during treatment, the more protons bond to the hydroxyl groups facing the center of the water-soluble barium salt. This prevents the water-soluble barium salt from becoming negatively charged, making it easier for the water-soluble barium salt to adsorb the target anion. Therefore, from the perspective of increasing the adsorption power of the target anion, the pH of the liquid to be treated during treatment is preferably 1 or more and 13 or less, and more preferably 2 or more and 12 or less. It is preferable that the pH of the liquid to be treated during treatment is 1 or more and 13 or less, since this makes it easier for the water-soluble barium salts to aggregate with each other, making it easier to recover the water-soluble barium salts. The method for adjusting the pH of the liquid to be treated is not particularly limited, and examples thereof include adding hydrochloric acid, sodium hydroxide, or one or more salts of the above.

[0028] The temperature of the liquid to be treated when it is brought into contact with the water-soluble barium salt is not particularly limited, and is preferably 1°C to 99°C, and more preferably 4°C to 80°C, for example. Within the above temperature range, the adsorption capacity of the target anion by the water-soluble barium salt can be increased. At or above the lower limit of the above temperature range, the diffusion rate of the target anion in the treatment liquid increases, further increasing the efficiency of contact with the water-soluble barium salt and adsorption. At or below the upper limit of the above temperature range, the desorption of the once-adsorbed anion from the water-soluble barium salt can be further reduced.

[0029] The amount of water-soluble barium salt that comes into contact with the liquid to be treated is not particularly limited relative to the content of the target anion contained in the liquid to be treated, and can be set to an amount that has been empirically confirmed through preliminary experiments to be capable of sufficiently adsorbing the target anion.

[0030] When an adsorption method is employed in which water-soluble barium salt powder is added to the liquid to be treated and stirred, the water-soluble barium salt that has adsorbed anions can be recovered from the liquid to be treated. Methods for recovering water-soluble barium salt powder from the liquid to be treated include, for example, precipitation, filtration, etc. Precipitation methods include, for example, a method in which the liquid to be treated is allowed to stand to cause precipitation, a method in which aluminum sulfate, PAC, a high molecular weight polymer flocculant, etc. is added to the liquid to be treated to cause flocculation and precipitation, and a method in which the pH of the liquid to be treated is adjusted to 4 to 9 to cause flocculation of water-soluble barium salts.

[0031] An adsorption method can also be employed in which a column is filled with water-soluble barium salt powder and the target solution containing the target anions is passed through the column. In this case, the water-soluble barium salt adsorbs the target anions, and the target solution from which the target anions have been removed is obtained by flowing out the column.

[0032] According to the anion adsorption method of this embodiment, it is possible to adsorb a large amount of anions such as selenium in a solution in which selenium is dissolved and whose pH is higher than neutral.

[0033] Although the embodiments of the present invention have been described in detail above, the present invention is not limited to the above embodiments, and various modifications and variations are possible within the scope of the gist of the present invention as set forth in the claims. [Example]

[0034] The present invention will be explained in more detail below by way of experimental examples, but the present invention is not limited to the following experimental examples.

[0035] [Experimental Example 1] A mixture containing barium sulfate and water-cooled blast furnace slag (Fine Cerament 10A, JIS A 6206) was prepared by mixing the reagent barium sulfate (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.) with the amounts shown in Table 1. The resulting mixture was fired at 1200° C. for 2 hours in a nitrogen atmosphere. The resulting fired product was pulverized, and a barium ion elution test was conducted on the pulverized fired product in accordance with the "Testing Method for Metals, etc. Contained in Industrial Waste" (Environment Agency Notification No. 13, February 1973), to measure the amount and rate of eluted barium ions per unit mass of the mixture. The results are shown in Table 1.

[0036] [Table 1]

[0037] The results shown in Table 1 indicate that firing a mixture of barium sulfate and water-cooled blast furnace slag produces more soluble barium salts than firing barium sulfate and water-cooled blast furnace slag alone.

[0038] [Experimental Example 2] 1.2 g of the calcined material obtained in Experimental Example 1 was added to 30 g of simulated selenium-contaminated soil that had been sieved to particles of 2 mm or less and air-dried, and mixed, followed by the addition of 3.9 g of water. To prevent drying, the mixture of simulated selenium-contaminated soil and the burned material obtained in Experimental Example 1 (hereinafter referred to as the "contaminated soil mixture") was sealed in a polypropylene bag and cured at 20°C for one week. The contaminated soil mixture and water were then mixed at a mass ratio of 1:10 and shaken at 200 rpm for 6 hours. The concentration of selenium eluted from the contaminated soil mixture was measured by inductively coupled plasma mass spectrometry (ICP-MS). The results are shown in Table 2.

[0039] [Table 2]

[0040] The results shown in Table 2 indicate that the eluted selenium concentration is lower when a mixture of barium sulfate and water-cooled blast furnace slag is used than when barium sulfate and water-cooled blast furnace slag are used alone.

Claims

1. preparing a mixture comprising barite and blast furnace slag; and calcining the mixture to obtain a water-soluble barium salt.

2. 2. The method for producing an anion adsorbent according to claim 1, wherein the content of the blast furnace slag in the mixture is 0.1 parts by mass or more and 50 parts by mass or less per part by mass of the barite.

3. The method for producing an anion adsorbent according to claim 1, wherein the mixture is fired at a temperature of 800°C or higher and 1200°C or lower.

4. The method for producing an anion adsorbent according to claim 1 , wherein the mixture is fired in an inert gas atmosphere.

5. An anion adsorption method, comprising contacting a solution containing an anion of an inorganic compound with an anion adsorbent having a water-soluble barium salt obtained by the method for producing an anion adsorbent according to any one of claims 1 to 4, thereby adsorbing the anion to the barium salt.

6. The anion adsorption method according to claim 5 , wherein the anion is an oxoacid ion of an inorganic compound.

7. The anion adsorption method according to claim 6 , wherein the anion is a selenate ion or a selenite ion.

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