JPH04209715A - Fixation of carbonate ion or bicarbonate ion - Google Patents

Abstract

PURPOSE:To improve fixation ratio of carbonate ion or bicarbonate ion by bringing a solution or a solid material containing carbonate ion or bicarbonate ion into contact with an Al-Mg compound oxide shown by a specific formula. CONSTITUTION:An Al-Mg compound oxide shown by the formula (X is <=1 positive number 0<n<1.5) is molded into a granular state by using a binder or powder is supported on a carrier. Then, a solution or a solid material containing carbonate ion or bicarbonate ion and another inorganic anion such as sulfate ion, nitrate ion, phosphate ion, silicate ion or chloride ion is contacted with >=0.5g, based on 1mol existing carbonate ion or bicarbonate ion, of Al-Mg compound oxide for several minutes to several hours. Then the Al-Mg compound oxide having fixed carbonate ion or bicarbonate ion is separated and removed to give a solution or a solid material having extremely reduced carbonate ion or bicarbonate ion.

Description

[Detailed description of the invention]

[00011

[Industrial Application Field] The present invention relates to a method of immobilizing carbonate ions or bicarbonate ions using a specific inorganic ion exchanger, and relates to a method of immobilizing carbonate ions or bicarbonate ions using a specific inorganic ion exchanger. It is useful as a method for purifying inorganic reagents or inorganic industrial chemicals, or treating wastewater. [0002] BACKGROUND OF THE INVENTION Many inorganic reagents or inorganic industrial chemicals (hereinafter referred to as inorganic reagents, etc.) are known to contain carbonate ions or bicarbonate ions (hereinafter referred to as carbonate ions, etc.). For example, sodium salts such as sodium sulfate and sulfur/lium nitrate are manufactured using soda ash as a raw material, and therefore contain impurities such as carbonate ions. In addition, there are also inorganic reagents that contain carbonate ions and the like as impurities in order to absorb carbon dioxide gas in the air, even if carbonate is not used as a raw material. In particular, aqueous solutions such as trisodium phosphate and di-1-lium hydrogen phosphate are alkaline and therefore absorb a large amount of carbon dioxide gas. [0003] However, in recent years, highly pure inorganic reagents and the like have been desired in various fields, and inorganic reagents and the like that do not contain even trace amounts of carbonate or bicarbonate ions have been required. In addition, in fields such as nuclear power generation, biochemistry, or analytical chemistry that use carbonate ions, etc. that contain radioactive carbon, carbonate ions, etc. that contain radioactive carbon are removed and fixed in a safe form. It is required to become [0004] One method for removing carbonate ions and the like from a solution is to boil the solution. However, this method requires energy for heating and has the problem that it cannot be applied to items that cannot be heated. Another method is to adjust the pI-( of the solution to acidic) by taking advantage of the fact that carbonate ions and the like are weak acid ions, so if the pH of the solution is made acidic, carbonate ions and the like can be removed as carbon dioxide gas. However, with this method, p
There is a problem in that it requires an operation of adjusting H again to return to the original pH, and cannot be applied to things where the pH cannot be changed. Furthermore, if carbonate ions, etc. containing radioactive isotopic carbon are removed by the above-mentioned boiling or pH adjustment methods, the carbon dioxide gas released into the atmosphere contains radioisotopic carbon. There is also the problem that a method to completely capture the emitted carbon dioxide gas must be used in combination. (0005) On the other hand, it is possible to use an inorganic anion exchanger as a method of removing carbonate ions, etc., but if a general inorganic anion exchanger is used in an aqueous solution where inorganic anions coexist, carbonate ions etc. It preferentially adsorbs other coexisting inorganic anions, and it is almost impossible to preferentially adsorb carbonate ions and the like. [0006]

[Problems to be Solved by the Invention] The present invention is an object of the present invention to solve the problem of dissolving a solution or a solid substance without boiling the solution, without changing the pH of the solution, and without releasing radioactive carbon into the atmosphere as carbon dioxide gas. The present invention provides a method for preferentially immobilizing carbonate ions and the like. [0007]

[Means for Solving the Problems] As a result of extensive research into substances that can preferentially fix carbonate ions, etc. from solutions or solids in which other inorganic anions coexist, the present inventors have found that certain aluminum We have discovered that magnesium composite oxide is very suitable as such a substance, and have completed the present invention. That is, the present invention provides a method for fixing carbonate ions or bicarbonate ions, which is characterized by bringing a solution or solid containing carbonate ions or bicarbonate ions into contact with an aluminum-magnesium composite oxide represented by the following general formula. It is a method of conversion. MgAlxo+2-, +x)2゛nHzO In the above formula, X is a positive number less than or equal to ]-, n is 0 or more, and 1.5
The number is as follows. [00081 Hereinafter, the present invention will be explained in detail. The aluminum-magnesium composite oxide used in the present invention is represented by the following compositional formula. There is a wide range in composition,
This is because this compound has a structure in which hydrated aluminum oxide is dissolved in hydrated magnesium oxide. MgAlX0(:!-3x)2°nH2O In the above formula, X is a positive number of 1 or less, n is 0 or more, and 1. 5
The number is as follows. The above aluminum-magnesium composite oxide is a combination of an aluminum compound, such as aluminum carbonate or aluminum hydroxide, and a magnesium compound, such as magnesium carbonate or magnesium hydroxide, such that the Al/Mg atomic ratio is 1 or less. and preferably 400 to 900°C, more preferably 500 to 70°C
Obtained by firing at 0°C. In addition, a compound called hydrotalci 1- represented by the following general formula,
Preferably 400-900°C, more preferably 500-900°C
It can also be obtained by firing at 700°C. Mgx-x Alx(OH) 2 A”-,,,・WH
20 (in the above formula) to p- represent a p-valent anion, p represents an integer of 1 or 2, and X and W are numbers that each satisfy the following formula. 0〈x≦085.0≦w<1) [0
[0091] The shape of the aluminum-magnesium composite oxide used in the present invention is not particularly limited and may be in powder form, but in order to facilitate the operation in the method for immobilizing carbonate ions, etc. of the present invention, In other words, to facilitate separation after contact with solutions containing carbonate ions, etc., and to facilitate column passage, powders are formed into granules or pellets using a binder, or powders are supported on a carrier. is good. In addition, if the substance containing carbonate ions etc. is solid,
The shape and/or size of the aluminum-magnesium composite oxide may be different from that of the solid to facilitate separation of the two after treatment. [00101 Aluminum-magnesium composite oxide forms a layered structure when water coexists, even in extremely small amounts, and carbonate ions and the like are immobilized between the layers. By using this compound, carbonate ions and the like can be preferentially immobilized even in a solution in which inorganic anions other than carbonate ions and the like coexist. [0011] Examples of coexisting inorganic anions include hydroxide ions, fluoride ions, chloride ions, bromide ions, iodide ions, nitrate ions, nitrite ions, sulfate ions, sulfite ions, phosphate ions, and phosphate-hydrogen ions. ,
Examples include dihydrogen phosphate ion, phosphite ion, arsenate ion, nitrite ion, chromate ion, silicate ion, and borate ion. [0012] The counter ions of these coexisting inorganic anions may be hydrogen ions in some cases, but generally in acidic solutions there are almost no carbonate ions, so alkali metal ions, alkaline earth metal ions, typical metal ions and other cations, such as lithium ions, sodium ions, potassium ions, cesium ions, magnesium ions, calcium ions, strontium ions, barium ions, aluminum ions, lead ions, ammonium ions, etc. as counter ions. The present invention can be applied to any of the inorganic anions coexisting. In addition to the above, in the case of solutions of soluble salts such as nitrates, transition metals such as iron ions, cobalt ions, nickel ions, titanium ions, tin ions, zirconium ions, manganese ions, etc. are used as counter ions for coexisting inorganic anions. Although ions coexist, the present invention can be applied in the same manner as above in such cases as well. When the above-mentioned coexisting inorganic anion is a sulfate ion, the selective adsorption rate of carbonate ions, etc. is high. etc. can be adsorbed and immobilized with high selectivity. [0013] In order to immobilize carbonate ions and the like, the aluminum-magnesium composite oxide of the present invention must be brought into contact with a solution or solid containing carbonate ions and the like. Generally, there is an extremely thin layer of adhering water on the surface of a solid, so carbonate ions and the like in the solid are eluted into this layer of adhering water. Therefore, as in the case of a solution, even in the case of a solid, carbonate ions and the like can be immobilized by contacting with the aluminum-magnesium composite oxide of the present invention. In the present invention, aluminum-
The preferred time for contacting the magnesium composite oxide with a solution or solid containing carbonate ions etc. cannot be determined unconditionally depending on the object to be treated, but may range from several minutes to several hours.
In some cases, it is several days. Further, the temperature at which the two are brought into contact may be any temperature as long as the solution or solid containing carbonate ions etc. and the aluminum-magnesium composite oxide do not change or deteriorate in quality. [0014] The ratio of the solution or solid to which carbonate ions, etc. are to be immobilized and the aluminum-magnesium composite oxide that is brought into contact with this is 1 mmol of carbonate ions, etc.
per aluminum-magnesium composite oxide.
The amount is preferably 5 g or more, and the conditions for immobilizing carbonate ions, etc., such as the contact time of the aluminum-magnesium composite oxide and the target solution or solid, the contact method or contact temperature, or the pH 1 counterion species and coexistence of the target solution It may be adjusted as appropriate depending on the inorganic anion species, amount, etc. [00151] According to the immobilization method of the present invention, a solution or solid containing carbonate ions and the like coexisting with inorganic anions can be purified. As a specific example of a method for purifying a solution, the aluminum-magnesium composite oxide of the present invention is added to a solution containing carbonate ions, etc. coexisting with inorganic anions, and stirred. There are methods such as separating the aluminum-magnesium composite oxide after contact with the aluminum-magnesium composite oxide, and methods of filling a column etc. with the aluminum-magnesium composite oxide and passing a solution containing carbonate ions, etc. in which inorganic anions coexist. . [00161 Utilizing the immobilization method of the present invention, carbonate ions, etc. containing radioactive carbon isotopes are immobilized on aluminum-magnesium composite oxide, and then solidified using an appropriate solidifying agent to immobilize radioactive It can be safely processed as a solidified product that does not elute carbonate ions containing carbon isotopes. Specific examples of processing methods include the following methods. That is, aluminum-magnesium composite oxide is added and mixed to wastewater containing radioactive carbonate ions, etc., carbonate ions, etc. are immobilized on the aluminum-magnesium composite oxide, and then water is removed by means such as evaporation. Concentrated wastewater can be solidified with cement, etc., or conversely, aluminum-magnesium composite oxide can be added and mixed to concentrated wastewater by first removing water, and carbonate ions can be added to the aluminum-magnesium composite oxide. There is a method of fixing it in a composite oxide and then solidifying it with cement or the like. Needless to say, solids containing radioactive carbonate ions and the like can be treated in the same manner as wastewater. [0017]

[Examples] The present invention will be explained in more detail below with reference to Examples and Comparative Examples. Examples 1 to 4 and Comparative Example 1 100 ml of an aqueous solution containing carbonate ions at a concentration of 85 μ/l in which various inorganic anions coexist was mixed with an aluminum-magnesium composite oxide Mgo7A having the following composition.
10.3011s ・0.13Hz O or strongly basic anion exchange resin Amberlite IRA-400
(trade name, manufactured by Rohm and Haas) under the conditions shown in Clothing 1 below. After 4 hours, the aluminum magnesium composite oxide was filtered off, and the carbonate ion concentration in the filtrate was adjusted to T.
OC (, Total Organic Carbon, TotalO
The results are shown in Table 1. [0018]

[0019] From Table 1 above, after the aqueous solution was brought into contact with the aluminum-magnesium composite oxide, the carbonate ion concentration in the aqueous solution was higher in Example 1 than in Comparative Example 1.
It can be seen that there is a decrease in the case of ~4. In addition, the concentration of carbonate ions in the aqueous solution decreases even though it is much smaller than the concentration of inorganic anions other than carbonate ions, which indicates that carbonate ions are preferentially immobilized. . [00201 Example 5 Using bentonite as a binder, 100 g of aluminum-magnesium composite oxide formed into granules having a particle size of about O05 to 1°0 was packed into a glass column with a diameter of 10 m + m, and the concentration was 200 g/ l of sodium sulfate and a solution containing carbonate ions at a concentration of 150 mg/l,
The solution was passed through at SV=5 eml and a temperature of 30°C. When the carbonate ion concentration of the column outlet liquid was measured, it was 10 Ing/l or less up to a liquid flow rate of 200 times. [00211 Example 6 To 100 parts by weight of a powder mixture containing 0.248 parts by weight of sodium carbonate per 1,00 parts by weight of helium sulfate, 5 parts by weight of aluminum-magnesium composite oxide was added and mixed. , 75 parts by weight of this mixture was solidified with 100 parts by weight of cement as dry powder, 75 parts by weight of frame aggregate (sand) and 50 parts by weight of water. This solidified product was added to 1000 parts by weight of water and heated at 80° C. for 2 hours. After passing the solidified product through the mouth, the carbonate ion concentration in the water was analyzed and found to be 10 mg/l or less. [0022] Comparative Example 2 A solidified product was prepared in the same manner as in Example 6 except that the aluminum-magnesium composite oxide was not added, and the elution of carbonate ions from this solidified product was measured. As a result, the carbonate ion concentration in water was It was 60μ/l. [0023]

Effect of the invention: Compared to conventional methods, the method of immobilizing carbonate ions, etc. according to the present invention does not require heating of the target solution or pH adjustment.
To easily and efficiently immobilize carbonate ions, etc. from solutions or solids in which carbonate ions, etc. and other inorganic anions coexist, without the need for adjustment, and without emitting carbon dioxide gas into the atmosphere. This is an excellent method that can preferentially immobilize carbonate ions and the like that have radioactive carbon atoms in some cases. Furthermore, by absorbing carbon dioxide gas in the atmosphere into, for example, an alkaline aqueous solution and then immobilizing carbonate ions in this solution using the present invention, it is possible to solve the current problem of immobilization of carbon dioxide gas in the atmosphere. It can also be applied.

Claims (1)

[Claims] Claim 1: A solution or solid containing carbonate ions or bicarbonate ions is brought into contact with an aluminum-magnesium composite oxide represented by the following general formula,
Method for immobilizing carbonate ions or bicarbonate ions. MgAl_XO_(_2_+_3_X_)_/_2・n
H_2O In the above formula, X is a positive number of 1 or less, and n is a number of 0 or more and 1.5 or less.