JP4709498B2 - Crystalline layered double hydroxide powder, method for producing the same, molded product, and method for immobilizing harmful substances - Google Patents

Description

  The present invention relates to a crystalline layered double hydroxide powder, a method for producing the same, a molded body, and a method for immobilizing harmful substances.

  Layered double hydroxide is a generic name for naturally occurring minerals such as hydrotalcite and hydrocalumite, and is a hydroxide of elements that are abundant in nature such as magnesium, calcium, and aluminum. Is the main skeleton. For example, as shown in Patent Document 1 for hydrotalcite and Patent Document 2 for hydrocalumite, the synthesis thereof can be performed relatively easily.

These layered double hydroxides are known to have an anion exchange action. And if this anion exchange action can immobilize anionic harmful substances such as arsenic, fluorine, boron, selenium, hexavalent chromium and nitrite ion, it will improve the safety of waste, harmless It is expected to contribute to improving the quality of contaminated water, preventing leaching of harmful substances, improving soil, and promoting the stabilization of harmful substances at waste disposal sites.
Japanese Patent Publication No. 50-30039 JP-A-4-154648

  However, conventional layered double hydroxides are preferentially ion-exchanged with carbon dioxide in the air or carbonate ions in the water, so that they do not ion-exchange with the intended anion in the usual way, and are harmful to anions. The expected effect in immobilizing the substance was not obtained. This is because the layered double hydroxide containing carbonate ions produced in the prior art is highly crystalline and contains carbonate ions between the layers, resulting in large crystals and low anion exchange performance. It is thought that it is because.

  Therefore, in view of the above problems, the present invention has a high anion adsorption effect and ion exchange with the target anion, a crystalline layered double hydroxide powder, a production method thereof, a molded body, and a method for immobilizing a harmful substance The purpose is to provide.

  In order to solve the above problems, an acidic solution containing magnesium ions is added to an alkaline solution containing aluminum ions at a stretch and mixed, and the resulting precipitate is immediately dried or dried after filtration, so that the crystallite size is 20 nm or less. It was found that a layered double hydroxide was obtained. Furthermore, the production of the crystalline layered double hydroxide powder containing no carbonate ions is achieved by using a raw material that does not contain carbonate ions. The inventors have found out that the present invention can be obtained and have arrived at the present invention.

Crystalline layered double hydroxide powder according to claim 1 of the present invention have the general formula does not contain carbon ^{_{[Mg 2+ 1-x Al 3+}} x (OH) 2] [A n- x / n · zH 2 O] (Here , A ⁿ⁻ is an n-valent anion, 0 <x <1), and the crystallite size is 20 nm or less.

Molded body according to claim 2, wherein the present invention is characterized in that molding a crystalline layered double hydroxide powder according to claim 1 Symbol placement.

The method of immobilizing the toxic substances according to claim 3 of the present invention, the crystalline layered double hydroxide powder according to claim 1 Symbol placement, is characterized by adding to the object containing harmful substances.

The method for producing a crystalline layered double hydroxide powder according to claim 4 of the present invention is a method for producing the crystalline layered double hydroxide powder according to claim 1, wherein carbonic acid is not included. a step of producing a precipitate combined mixing an alkaline solution comprising an acidic solution and an alkaline containing magnesium ions and the aluminum ions, the precipitate and a step of powdered drying, mixed with magnesium ions and aluminum ions The molar ratio is in the range of 2: 1 to 5: 1 .

The method for producing a crystalline layered double hydroxide powder according to claim 5 of the present invention is a method for producing the crystalline layered double hydroxide powder according to claim 1, wherein carbonic acid is not included. comprising a step of producing a precipitate combined mixing an alkaline solution containing an acidic solution and the aluminum ion containing magnesium ions, and a step of powdered drying the precipitate, the molar ratio of magnesium ion and aluminum ion mixing Is in the range of 2: 1 to 5: 1 .

The method for producing a crystalline layered double hydroxide powder according to claim 6 of the present invention is characterized in that, in claim 4 or 5 , the produced precipitate is vacuum dried or freeze vacuum dried.

  According to the crystalline layered double hydroxide powder of the present invention, the anion exchange ability is excellent, and ion exchange with the intended anion can be effectively performed.

  According to the molded article of the present invention, it is possible to easily separate and remove harmful substances from factory waste liquid, sewage, etc. by molding into a filter medium.

  According to the method for immobilizing a harmful substance of the present invention, the crystalline layered double hydroxide powder can be ion-exchanged with a target anion to immobilize the harmful substance.

  According to the method for producing a crystalline layered double hydroxide powder of the present invention, a crystalline layered double hydroxide powder having a small crystallite size and excellent anion exchange ability can be produced without being carbonated.

  Further, since the crystalline layered hydroxide powder of the present invention is a powder, it has excellent adsorption amount, fluid dispersibility, and filling properties. Moreover, by making it into powder, crystal growth can be suppressed and storage stability is high. Furthermore, since it is a powder, compared with the case of a slurry form, there exists an effect that it is easy to convey, and can be easily spread | dispersed to the target object which removes a harmful substance, and is easy to handle.

  Hereinafter, the crystalline layered double hydroxide powder of the present invention, a production method thereof, a molded body, and a method for immobilizing a harmful substance will be described.

The crystalline layered double hydroxide in the present invention is a general formula [M ²⁺ _1−x M ³⁺ _x (OH) ₂ ] [A ⁿ⁻ _{x / n} · zH ₂ O] (where M ²⁺ the divalent metal cation, M ³⁺ is a trivalent metal cation, a ^n-n-valent anion, be those represented by 0 <x <1), specifically, Hydro Examples include talcite, delautersite, leebesite, pyroaulite, tacobite, suchihite, make snelite, manasseite, barbournite, chlormagaluminite, joglenite, hydrocalumite. The crystalline layered double hydroxide of the present invention does not contain carbonic acid, has a crystallite size of 20 nm or less, and an average crystallite size of 10 nm or less.

In addition, when the divalent metal cation M ²⁺ is magnesium ion Mg ²⁺ and the trivalent cation M ³⁺ is aluminum ion Al ³⁺ , it is a hydrotalcite. The formula is Mg ²⁺ _1-x Al ³⁺ _x (OH) ₂ (A ⁿ⁻ ) _{x / n} · zH ₂ O. In the most common composition of crystalline hydrotalcite, it is known that the molar ratio of aluminum ions to magnesium ions is 1: 3 (x = 0.25).

Further, when the divalent metal cation M ²⁺ is a calcium ion Ca ²⁺ , it is a hydrocalumite.

  Next, the first method for producing the crystalline layered double hydroxide powder of the present invention will be described. First, under conditions not containing carbonic acid, an acidic solution containing a divalent metal cation and a trivalent metal cation and an alkaline solution containing an alkali are mixed at a time to form a precipitate.

The condition not containing carbonic acid means that the divalent metal cation M ²⁺ and the raw material of the trivalent cation M ³⁺ and alkali do not contain carbonic acid. It is preferable to use water that has been decarboxylated, but the crystalline layered double hydroxide powder of the present invention can be produced even with ordinary water that has not been decarboxylated. Furthermore, it is preferable to produce the crystalline layered double hydroxide powder under the conditions where carbonic acid does not exist in the subsequent steps.

Further, when preparing an acidic solution containing the divalent metal cation M ²⁺ and the trivalent cation M ³⁺ , it may be made acidic by adding nitric acid or hydrochloric acid.

Here, the case where the divalent metal cation M ²⁺ is a magnesium ion Mg ²⁺ and the trivalent cation M ³⁺ is an aluminum ion Al ³⁺ will be described as an example. As long as it is a magnesium compound that is soluble in acid or water, it may be either naturally produced or synthesized, and is not limited to a specific substance. For example, magnesium hydroxide, magnesium oxide, magnesium nitrate, magnesium chloride and the like can be used, and these magnesium sources may be used alone or in combination of two or more.

  The aluminum ion source may be either a naturally occurring or synthesized one as long as it is an aluminum compound that is soluble in acid, alkali, or water, and is not limited to a specific substance. For example, aluminum hydroxide, aluminum oxide, aluminum oxide hydroxide, sodium aluminate, aluminum nitrate, aluminum chloride and the like can be used. These aluminum sources can be used alone or in combination of two or more. May be used.

Here, the general formula of hydrotalcite composed of aluminum ions and magnesium ions is Mg ²⁺ _1-x Al ³⁺ _x (OH) ₂ (A ⁿ⁻ ) _{x / n} · zH ₂ O, which is crystalline. In the most common composition of hydrotalcite, the molar ratio of magnesium ions to aluminum ions is 3: 1 (x = 0.25), so the molar ratio of magnesium ions to aluminum ions in the acidic solution is A range of 2: 1 to 5: 1 is preferable. By setting it as this range, the crystalline layered double hydroxide powder can be produced advantageously in terms of mass balance without wasting the aluminum source and the magnesium source.

  As an alkaline solution containing an alkali for mixing with an acidic solution containing a divalent metal cation and a trivalent metal cation, a solution having a pH of 8 to 14 is preferably used. Further, during mixing, the alkaline solution is vigorously stirred to quickly produce a crystalline layered double hydroxide having a small crystallite size. Since the crystallite size of the crystalline layered double hydroxide is small, the solution becomes colloidal when mixed. In addition, as a method of mixing the acidic solution and the alkaline solution, it is preferable to add the acidic solution to the alkaline solution and mix them at once, or drop the acidic solution into the alkaline solution and mix them, but other methods are possible. Also good.

  Here, the alkali contained in the alkaline solution is not limited to a specific substance as long as the aqueous solution is alkaline. For example, sodium hydroxide, potassium hydroxide, calcium hydroxide, aqueous ammonia, sodium borate, potassium borate and the like can be used. Any of these alkalis may be used alone or in combination of two or more.

  When an acidic solution containing a divalent metal cation and a trivalent metal cation and an alkaline solution containing an alkali are mixed at a time to form a precipitate, the precipitate is then immediately solid-liquid separated. As a method of solid-liquid separation, conventional methods such as suction filtration, centrifugation, freeze thawing and filtration can be used. Thus, by immediately solid-liquid separating the precipitate, the crystalline layered double hydroxide crystal does not grow, and the crystallite size is controlled to 20 nm or less and the average crystallite size is controlled to 10 nm. After solid-liquid separation, the solid phase is washed with water, so that crystal growth can be more reliably stopped and the crystallite size can be reduced to 20 nm or less.

  Next, the solid phase obtained by the solid-liquid separation is dried and powdered. As a drying method, vacuum drying or freeze vacuum drying is preferable in order to prevent carbonation of the crystalline layered double hydroxide. Alternatively, it may be quickly dried with hot air.

  Note that the solid-liquid separation step may be omitted, and the precipitate may be dried as it is after the formation of the precipitate. In this case, in order to remove impurities after drying, it is preferable to wash the powder obtained by drying with water or the like. Even when a solid-liquid separation step is performed, the powder obtained by drying may be washed with water or the like in order to remove impurities after drying.

  The crystalline layered double hydroxide powder of the present invention thus obtained has a crystallite size of 20 nm or less and an average crystallite size of 10 nm. When the crystallite size exceeds 20 nm, the anion exchange performance as an anion adsorbing effect other than carbonate ions is abruptly deteriorated. However, the crystalline layered double hydroxide powder of the present invention has a crystallite size of 20 nm or less. Yes, with high anion exchange performance.

  In addition, since the crystalline layered hydroxide powder is a powder, it has excellent adsorption amount, dispersibility in fluid, and filling properties. Moreover, by making it into powder, crystal growth can be suppressed and storage stability is high. Furthermore, since it is a powder, compared with the case of a slurry form, it has the effect that it is easy to carry, is easy to spread on the target object from which harmful substances are removed, and is easy to handle.

  Next, a second method for producing the crystalline layered double hydroxide powder of the present invention will be described. In this second method, an acidic solution containing a divalent metal cation is prepared, an alkaline solution containing a trivalent metal cation is prepared, and the acidic solution and the alkaline solution are mixed together to form a precipitate. Let Since the other steps are the same as those in the first method, detailed description thereof is omitted. Also in this method, a crystalline layered double hydroxide powder having a crystallite size of 20 nm or less and high anion exchange performance can be produced.

  The crystalline layered double hydroxide powder of the present invention can be used for immobilization of harmful substances. For example, by adding the crystalline layered double hydroxide powder of the present invention as it is or as a slurry dispersed in a liquid such as water to a target object such as contaminated soil containing harmful substances, Hazardous substances can be fixed on the crystalline layered double hydroxide powder and detoxified.

  In addition, the crystalline layered double hydroxide powder of the present invention is molded into a filter medium, and the filter medium is used to filter a target object such as waste liquid or sewage containing a harmful substance, thereby including a target substance contained in the target object. Can be fixed to the filter medium, and harmful substances can be easily separated and removed from the object. In the case of producing a molded product such as this filter material, only the crystalline layered double hydroxide powder of the present invention may be molded, or it may be molded by blending a known organic or inorganic binder. . As the molding method, conventional methods such as granulation, extrusion, pouring, and pressing can be used. Alternatively, it may be supported on an existing filter by applying the crystalline layered double hydroxide powder of the present invention or the like to provide a filter medium.

As described above, the crystalline layered double hydroxide powder of the present invention has the general formula [M 2 ⁺ _1−x M ³⁺ _x (OH) ₂ ] [A ⁿ⁻ _{x / n} · zH ₂ without carbonic acid. O] (wherein, M ²⁺ is a divalent metal cation, M ³⁺ is a trivalent metal cation, a ^n-n-valent anion, 0 <x <1) is represented by crystallite Since the size is 20 nm or less, the sum of the surface areas of the crystals is increased, and as a result, the anion exchange performance is excellent, and the target anions can be effectively ion-exchanged.

  Further, since the molded body of the present invention is formed by molding the crystalline layered double hydroxide powder of the present invention, the harmful substances contained in the object are fixed to the molded product, and the harmful substances are easily separated and removed from the object. be able to.

  In the method for immobilizing a harmful substance of the present invention, the crystalline layered double hydroxide powder of the present invention is added to an object containing a harmful substance, so that the crystalline layered double hydroxide powder is the target negative. By exchanging ions with ions, harmful substances are fixed to the crystalline layered double hydroxide powder, and the object can be detoxified.

  The method for producing a crystalline layered double hydroxide powder according to the present invention includes an acidic solution containing a divalent metal cation and a trivalent metal cation and an alkaline solution containing an alkali under a condition not containing carbonic acid. A step of generating a precipitate by mixing at a time, or a step of generating a precipitate by mixing an acidic solution containing a divalent metal cation and an alkaline solution containing a trivalent metal cation at once. A crystalline layered double hydroxide powder having a small crystallite size and excellent anion exchange ability without carbonation can be produced.

  Further, since the molar ratio of the divalent metal cation to the trivalent metal cation to be mixed is in the range of 2: 1 to 5: 1, the raw material of the divalent metal cation and the trivalent metal cation is used. A hydrotalcite-like material can be produced advantageously in terms of material balance without being wasted.

  Furthermore, since the produced precipitate is vacuum-dried or freeze-dried, carbonation of the crystalline layered double hydroxide can be surely prevented.

  As described above, the crystalline layered double hydroxide powder of the present invention, the production method thereof, the molded body, and the method of immobilizing a harmful substance have been described. Is possible.

  Hereinafter, the crystalline layered double hydroxide powder of the present invention, the production method thereof, the molded product and the method of immobilizing harmful substances will be described more specifically.

  Magnesium ions as divalent metal cations and aluminum ions as trivalent metal cations were used. An acidic solution was prepared by dissolving 1 mol of magnesium nitrate hexahydrate as a magnesium source and 0.5 mol of aluminum nitrate nonahydrate as an aluminum source in 1 L of distilled water. And 3.5 mol of sodium hydroxide was dissolved in 1 L of distilled water to prepare an alkaline solution. When an acidic solution was added to the alkaline solution all at once, a gel-like precipitate was immediately formed. The mixed solution was dried as it was with a vacuum drying apparatus (manufactured by Chuo Kakoki Co., Ltd .: vibration dryer VH type) to obtain a powder. Thus, when dried using a true drying apparatus, a powder is obtained without passing through the pulverization step, so that one of the pulverization steps can be omitted as compared with the case of Example 2 described below. Since the powder thus obtained contains sodium nitrate in addition to the layered double hydroxide, it was washed with hot water at 40 ° C. for 1 minute, and then quantified filter paper No. Filtered with 5C. The filtered residue was further dried at 110 ° C. for 1 hour with a hot air dryer and pulverized with a flat work mill for 30 seconds to obtain a powder product. The obtained powder was confirmed to be a crystalline layered double hydroxide not containing carbonic acid by analysis using an X-ray diffractometer.

  Further, when the crystallite size was determined by the Scherrer method using an X-ray diffractometer, it was confirmed that the crystallite size was 20 nm or less and the average crystallite size was 10 nm or less.

  A gel-like precipitate was produced in the same manner as in Example 1, and the quantitative filter paper No. Filtered with 5C. The filtration residue was dried with a hot air dryer at 110 ° C. for 2 hours. According to the present embodiment, it is possible to easily perform the drying as compared with the case of using the vacuum drying of the first embodiment. The resulting mass was coarsely pulverized for 30 seconds with a flat mill and then washed with hot water at 40 ° C. for 1 minute to remove sodium nitrate. Filtered with 5C. The filtered residue was further dried at 110 ° C. for 1 hour with a hot air dryer and pulverized with a flat work mill for 30 seconds to obtain a powder product. The obtained powder was confirmed to be a crystalline layered double hydroxide containing no carbonic acid by analysis using an X-ray diffractometer.

  Further, when the crystallite size was determined by the Scherrer method using an X-ray diffractometer, it was confirmed that the crystallite size was 20 nm or less and the average crystallite size was 10 nm or less.

  As a magnesium source, commercially available light-burned magnesia was added to 1 L of nitric acid (30% solution) little by little until it became almost neutral. In 1 L of this solution, 3.5 mol of magnesium ions were present. Next, 400 g of waste aluminum hydroxide gel was added to 2 L of an aqueous sodium hydroxide solution (3 mol / l) as an aluminum source and stirred. In 2 L of this solution, 1.5 mol of aluminum ions were present. When an acidic solution containing magnesium was added to the alkaline solution containing these aluminum ions all at once, a gel-like precipitate was immediately formed. Thereafter, a powder was obtained in the same manner as in Example 1. The obtained powder was confirmed to be a crystalline layered double hydroxide containing no carbonic acid by analysis using an X-ray diffractometer.

  Further, when the crystallite size was determined by the Scherrer method using an X-ray diffractometer, it was confirmed that the crystallite size was 20 nm or less and the average crystallite size was 10 nm or less.

  30 parts of water was added to 100 parts of powder obtained by adding 20 parts of alumina cement to 100 parts by weight of the powder obtained in Example 1, and mixed for 15 minutes with a planetary mixer manufactured by Fuji Powder Co., Ltd. Then, it was extruded to a diameter of 3 mm by a vacuum extruder manufactured by Nitto Seiki Co., Ltd. and further cut to a length of 10 mm. The obtained molded product was dried with a hot air dryer at 60 ° C. for 1 hour to obtain a cylindrical molded body.

  Using the powders and molded bodies prepared in Examples 1 to 4 above, tests were conducted on the adsorption effect of hexavalent chromium and boron.

  In addition, as comparative examples, commercially available for the purpose of removing, recovering, insolubilizing, and detoxifying harmful anionic substances (arsenic, fluorine, boron, selenium, hexavalent chromium, cyan, phosphorus, sulfuric acid, nitrous acid, etc.) and harmful heavy metals Used hydrotalcite powder.

  As a test method, 100 ml of a standard solution of hexavalent chromium and boron having a predetermined concentration was dispensed into a plurality of plastic beakers, and the powders, molded bodies, or comparative examples prepared in Examples 1 to 3 were used for this. 1 g of each was added separately, and stirred at room temperature with a magnetic stirrer for 1 hour. Then, quantitative filter paper No. The mixture was filtered with 5C, and the concentrations of hexavalent chromium and boron in the filtrate were measured with a spectrophotometer. Moreover, about the molded object produced in Example 4, 3.0g was added with respect to 100 ml of standard solutions of the hexavalent chromium and boron of predetermined density | concentration, and it stirred at normal temperature for 1 hour.

  The results of this test are shown in Table 1. In the comparative example, almost no adsorption of hexavalent chromium was confirmed, and the adsorption effect of boron was not good, but when the powders and molded bodies of Examples 1 to 4 were used, hexavalent chromium and boron In both cases, a very good adsorption effect was confirmed. Further, the molded body of Example 4 did not collapse even after stirring for 1 hour.

Claims (6)

Formula that does not contain carbonate ^{_{[Mg 2+ 1-x Al 3+}} x (OH) 2] [A n- x / n · zH 2 O] ( ^{wherein, A n-n-valent} anion, 0 <x < A crystalline layered double hydroxide powder represented by 1) having a crystallite size of 20 nm or less. Molded article characterized by being molded crystalline layered double hydroxide powder according to claim 1 Symbol placement. The method of immobilizing the toxic substances, characterized in that the crystalline layered double hydroxide powder according to claim 1 Symbol placement, it is added to the object containing harmful substances. A method of manufacturing a crystalline layered double hydroxide powder according to claim 1, under conditions that do not contain carbonate, engaged mixing an alkaline solution comprising an acidic solution and an alkaline containing magnesium ions and the aluminum ions comprising a step of producing a precipitate, and a step of powdered drying the precipitate, the molar ratio of the mixed magnesium ions and the aluminum ions 2: 1 to 5: crystalline, characterized in that the first range A method for producing a layered double hydroxide powder. A method of manufacturing a crystalline layered double hydroxide powder according to claim 1, under conditions that do not contain carbonate, the precipitate combined mixing an alkaline solution containing an acidic solution and the aluminum ion containing magnesium ions comprising a step of generating and the step of powdered drying the precipitate, the molar ratio of the mixed magnesium ions and the aluminum ions 2: 1 to 5: crystalline layered double, characterized in that the first range Method for producing hydroxide powder. 6. The method for producing a crystalline layered double hydroxide powder according to claim 4 or 5, wherein the produced precipitate is vacuum dried or freeze vacuum dried.