JP2006341139A - Harmful inorganic anion fixing and removing method, and fixing agent used therefor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for easily, inexpensively, and efficiently removing harmful inorganic anions, such as phosphate ions, borate ions, fluoride ions, and arsenate ions, from water containing these anions at relatively low concentrations, and a fixing agent used for the method. <P>SOLUTION: In this removal method, a solution of salts of rare earth elements, containing at least a salt of cerium as a main component, and magnesium hydroxide are added to the water containing the harmful inorganic anions, such as phosphate ions, borate ions, fluoride ions, and arsenate ions, to generate precipitates at a pH of 8-11, and solid-liquid separation is carried out, which can fix the inorganic anions and remove them promptly. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention provides an immobilization method for easily and efficiently immobilizing inorganic anions, particularly harmful inorganic anions such as phosphate ions, borate ions, fluorine ions, and arsenate ions, and reducing the generation of sludge. It relates to the drug used for it.

  For wastewater containing harmful inorganic anions such as phosphate ions, borate ions, fluorine ions, arsenate ions, etc., a standard value to be managed in accordance with environmental standards is set. Conventionally, as treatment methods for these harmful inorganic ion-containing waters, a method of adsorbing with an ion exchange resin, an aluminum compound such as aluminum sulfate or aluminum chloride, and ferric chloride or calcium hydroxide in combination are used for coagulation precipitation. There are known methods for separating precipitates by the method, but none of them are efficient methods, and there is a problem that a large amount of sludge is generated.

  Regarding the removal of boron ions, a method combining a coagulation precipitation method with an anion exchange resin or a selective ion exchange resin has been proposed (see Patent Document 1). There is a problem that a load is applied to the adsorbent resin, which is too costly, and a problem with the treatment of the regenerated solution of the adsorbent resin. Furthermore, a method for treating low-concentration boron-containing wastewater with a rare earth element hydrous oxide has also been proposed (see Patent Document 2). However, since solid is used, the adsorption performance is low and a large amount of use is required. There is a problem that processing takes time. On the other hand, there is a boron removal method in which boron-containing wastewater is once adsorbed on a boron-selective adsorptive ion exchange resin or the like, and a compound that releases rare earth element ions and / or group IVB element ions is added to the concentrated desorbed liquid. Although it has been proposed (see Patent Document 3), a new adsorption device is required, and more complicated adsorption and desorption operations are required. In general, flocs produced by the reaction of rare earth elements and boron are bulky and have poor sedimentation properties. In order to improve these problems, boron is precipitated and separated as a hardly soluble substance by adjusting the pH to 9 to 13 in the presence of a polyvalent anionic substance and rare earth element ions in boron-containing water. A method has been proposed (see Patent Document 4). However, there is a problem that the water content of the obtained sludge is as high as 70 to 80%, and the action on other harmful ions such as phosphate ions and arsenate ions is not disclosed.

  As a phosphate ion adsorbent, a rare earth element hydrated oxide is known (see Patent Document 5). However, since a solid is used, the adsorption capacity is low, a large amount of use is required, and processing takes time. There is a problem. Further, an adsorbent of phosphate ion using magnesium oxide having a specific particle size as an adsorbent is disclosed (see Patent Document 6), but phosphate ion is adsorbed, but its action on borate ion and arsenate ion is It is not disclosed, and the adsorbent is not effective for borate ions and arsenate ions because of its extremely low adsorption performance.

JP-A-57-180493 Japanese Patent Publication No. 3-22238 JP 11-235595 A JP 2004-963 A JP 61-4529 A JP 2005-28272 A

  The present invention is an efficient, low-volume, low-water-content sludge containing undesired inorganic anions such as phosphate ions, borate ions, fluorine ions, and arsenate ions, alone or in combination of two or more. An object of the present invention is to provide a method for removing these inorganic anions. Moreover, it aims at providing the chemical | medical agent used for it.

  As a result of intensive studies to solve the above problems, the present inventors have present a rare earth element salt solution containing cerium as a main component and magnesium hydroxide in the water to be treated, and by controlling to a suitable pH, It was found that harmful inorganic anions such as phosphate ions, borate ions, fluorine ions and arsenate ions dissolved in the water to be treated can be precipitated and separated as hardly soluble substances all at once. It came to complete.

That is, the present invention
[1] To the treated water containing harmful inorganic anions, when the pH of the treated water exceeds 8, the pH is adjusted to 8 or less, and then the rare earth element containing at least a cerium salt as a main component. A method for immobilizing and removing harmful inorganic anions, wherein a salt solution and magnesium hydroxide are present, the inorganic ions are generated as hardly soluble precipitates at a pH of 8 to 11, and solid-liquid separation is performed.
[2] The method for immobilizing and removing harmful inorganic anions according to [1], wherein the harmful inorganic anions are one or more of phosphate ions, borate ions, fluorine ions, and arsenate ions.
[3] The method for immobilizing and removing harmful inorganic anions according to [1] or [2], wherein the rare earth element salt contains at least 90% by mass of a cerium salt.
[4] The method for immobilizing and removing harmful inorganic anions according to any one of [1] to [3], wherein magnesium hydroxide is a water slurry having a concentration of 25 to 45% by mass.
[5] The method for immobilizing and removing harmful inorganic anions according to any one of [1] to [4], wherein a pH adjuster is used.
[6] The method for immobilizing and removing harmful inorganic anions according to [5], wherein the pH adjuster is calcium hydroxide.
[7] A drug for immobilizing and removing ions from a water to be treated containing a harmful inorganic anion, comprising a rare earth element salt containing at least a cerium salt as a main component and magnesium hydroxide.
[8] The agent according to [7], wherein the rare earth element salt contains at least 90% by mass of a cerium salt.
[9] The drug according to [7], wherein magnesium hydroxide is a water slurry having a concentration of 25 to 45% by mass.
About.

  According to the method of the present invention, the agent of the present invention is added to water containing harmful inorganic anions such as phosphate ions, borate ions, fluorine ions, arsenate ions, etc. contained in the water to be treated to adjust the pH. By adjusting the pH, these harmful ions can be efficiently removed as a precipitate by a simple method of producing a precipitate and filtering. Moreover, since the sludge produced | generated is a small amount with a low moisture content, the process cost of sludge can be reduced.

Hereinafter, the present invention will be described in detail.
In the present invention, a rare earth element salt solution containing at least a cerium salt as a main component is combined with magnesium hydroxide and adjusted to pH 8 to 11 to efficiently bind to inorganic anions in the water to be treated. A precipitate is formed. Among these, rare earth element ions in the water to be treated mainly serve as a fixing agent for harmful inorganic anions such as phosphate ions, borate ions, fluorine ions, and arsenate ions. The salt solution of the rare earth element when added to the water to be treated is preferably added to the water to be treated as a hydrochloride, sulfate or nitrate. Although the density | concentration of the salt aqueous solution is not specifically limited, In consideration of operativity, it is 10-40 mass% as a rare earth element oxide, Preferably it is 20-35 mass%.

  The rare earth element salt containing at least a cerium salt as a main component for use in the present invention is a mixture of rare earth element salts containing cerium in an amount of 75 mass% or more, preferably 90 mass% or more. Cerium ions are adjusted to PH 8 to 11 in the presence of magnesium hydroxide to be used together, thereby efficiently combining with inorganic anions in the water to be treated to form precipitates. When the pH is outside this range in the presence of magnesium hydroxide, the pH is adjusted using the pH adjuster. If a large amount of rare earth elements other than cerium is contained, there is a problem that the removal rate of harmful ions in the water to be treated decreases due to the solubility of the compound combined with the anion. Substances that may be mixed in addition to cerium include rare earth elements and IVb elements other than cerium, scandium, yttrium, praseodymium, neodymium, promethium, samarium, europium, gadolinium, terbium, dysprosium, holmium, erbium, thulium, ytterbium, Examples thereof include compounds containing lutetium, titanium, zirconium and hafnium.

  In the present invention, the amount of rare earth element ions added depends on the type, composition and concentration of inorganic anions in the water to be treated, but harmful inorganic properties such as phosphate ions, borate ions, fluorine ions, arsenate ions, etc. The amount is 0.1 to 30 mol, preferably 0.5 to 15 mol, per mol of anion. Chlorine ions, nitrate ions, and sulfate ions that coexist in the water to be treated hardly adsorb to the rare earth element hydroxides, and thus need not be considered. Anionic species that need to be considered as anions with high adsorptivity are phosphate ion, borate ion, fluorine ion, arsenate ion, bicarbonate ion, silicate ion, arsenite ion, hexafluorosilicate ion Etc.

  Magnesium hydroxide used in the present invention itself adsorbs these anions, and not only has a synergistic effect in combination with rare earth element ions, but also enlarges the particle size at the time of precipitation, and has sedimentation and dehydration properties. It produces a good precipitate to facilitate the solid-liquid separation of the precipitate, and at the same time, has the effect of reducing the water content in the filtered sludge. Magnesium hydroxide can be added in the form of powder or water slurry, but it is preferable to use a magnesium hydroxide slurry precipitated from seawater. The magnesium hydroxide slurry is generally available for industrial use, with seawater as a raw material and a concentration of 25 to 45 mass% pure. The amount of magnesium hydroxide used is 0.01 to 10% by mass, preferably 0.05 to 2% by mass, based on the volume of water to be treated, as a pure component.

  In the present invention, a rare earth salt solution and magnesium hydroxide are added to the water to be treated, and then the pH is adjusted to coprecipitate inorganic anions harmful to the precipitate formed. The pH is generally in the range of 8-11, preferably in the range of 8.5-10.5. When the anion to be removed is phosphate ion, fluorine ion, arsenate ion, etc., pH 8.5 to 9.5 is particularly preferable, and borate ion is particularly preferably pH 9 to 10.5. When the pH is 8 or less, the precipitate is not completely formed, or the precipitated particles are colloidal, and the filterability is extremely lowered. On the other hand, if the pH exceeds 11, the efficiency of coprecipitation with rare earth ions decreases and the removal rate of harmful anions decreases.

The order of adding the rare earth salt solution and magnesium hydroxide to the water to be treated is that the rare earth salt solution is added and then the magnesium hydroxide is added. When the pH of the solution after addition is not in the above pH range, the pH is adjusted to a predetermined pH using a pH adjuster. For example, when the pH of the solution after the addition of magnesium hydroxide is 7 or less, calcium hydroxide is added to adjust the pH to the range of 8 to 11 to complete the precipitation.
In general, when the water to be treated is alkaline exceeding pH 8, when a salt solution of rare earth element is added, precipitation of hydroxide of rare earth element is generated. In this case, by adding an acid such as hydrochloric acid, sulfuric acid, nitric acid in advance. The pH of the water to be treated is adjusted to 8 or less, preferably 5-8. In order to achieve the effects of the present invention, it is preferable that precipitates are not generated in the state where the salt solution of the rare earth element is added to the water to be treated. Then, magnesium hydroxide is added, and the rare earth element and magnesium hydroxide are added. A coprecipitate is formed. When the target pH is not reached due to the addition of magnesium hydroxide, the pH is adjusted to a predetermined value using calcium hydroxide as a pH adjusting agent. If the target pH value is exceeded, it can be readjusted using acids such as hydrochloric acid, sulfuric acid, and nitric acid. Precipitation deposited before the addition of magnesium hydroxide is not preferable because it makes the filtration operation difficult due to extremely fine gel particles.

  Furthermore, in the present invention, a flocculant can be used as necessary. In this case, the flocculant is used to agglomerate the precipitate of the inorganic anion precipitated after the addition of the rare earth element ion and magnesium hydroxide, and the solid-liquid separation of the precipitate can be made easier. Specific examples include ferrous chloride, ferric chloride, ferrous sulfate, ferric sulfate, polyferrous sulfate, polyferric sulfate, and other inorganic flocculants, as well as polyacrylamide cationization. Denatured products, polyacrylic acid dimethylaminoethyl ester, polymethacrylic acid dimethylaminoethyl ester, cationic organic flocculants such as polyethyleneimine and chitosan, nonionic organic flocculants such as polyacrylamide, polyacrylic acid, acrylamide and acrylic And anionic organic flocculants such as a copolymer with an acid and / or a salt thereof.

  After the series of steps is completed, the water to be treated is subjected to solid-liquid separation treatment. This solid-liquid separation can be performed by a conventional method, and examples thereof include filtration separation, centrifugal separation, sedimentation separation, and the like. However, solid-liquid separation can be sufficiently performed with an ordinary filtration device.

  In the case where the treatment is performed using a continuous reaction tank and a precipitation tank, a part of the precipitate can be partially circulated in the reaction tank. Furthermore, by performing the above series of treatments, the rare earth element ions and magnesium hydroxide contained in the precipitate can be used efficiently. This makes it possible to remove dissolved inorganic ions to a lower concentration. The circulating precipitate is 10 to 50% by mass, preferably 15 to 30% by mass of the generated precipitate.

  According to the present invention, the sedimentation rate of the generated precipitate is as fast as several seconds to several minutes, and the sludge dehydrated by a normal filter obtains a sludge having a very low moisture content of 60 to 70%. Can do.

Next, the present invention will be described in detail based on examples.
Example 1
It contains boric acid ions at a boron concentration of 50 mg / L (4.63 mM as boric acid ions), 1 L of model drainage with a pH of 6.5, an aqueous cerium nitrate solution (28.3 as CeO _{2 in} which 99% or more of the rare earth elements are cerium). 2.5% (6.75 mM as CeO ₂ ) containing 0.5% by weight and having a specific gravity of 1.68) was added, followed by a commercially available 40% strength magnesium hydroxide slurry (trade name S-40, Nihonkaikai) with stirring. 10 g) was added. After stirring for 15 minutes, flocs with good sedimentation were formed. The pH value of the mixed solution was 8.9. Solid-liquid separation was performed by filtration under reduced pressure, and the boron concentration in the filtrate was measured and found to be 4.6 mg / L. Moreover, 16.0 g of filtration sludge was obtained, and the water content was 68%.

Example 2
Model wastewater 1L (pH 7.8) containing 30 mg / L of borate ion as boron concentration (2.78 mM as borate ion) and 30 mg / L as phosphate concentration (0.97 mM as phosphate ion) Then, 2.5 ml of an aqueous cerium nitrate solution used in Example 1 (6.75 mM as CeO ₂ ) was added, followed by addition of 5 g of 40% strength magnesium hydroxide slurry with stirring. The pH of the mixed solution was 8.34. Furthermore, it adjusted to pH9.5 using calcium hydroxide, and stirred for 15 minutes. A floc with good sedimentation was generated, and solid-liquid separation was performed by filtration under reduced pressure. When the boron concentration and phosphorus concentration in the filtrate were measured, the boron concentration was 4.1 mg / L and the phosphorus concentration was 0.01 mg / L.

Comparative Example 1
In Examples 1 and 2, treatment was carried out in the same manner as in Examples 1 and 2 except that no magnesium hydroxide slurry was added, and the pH was adjusted to 9.5 with 0.1N caustic soda solution. Fine particle flocs were generated, but when filtered under reduced pressure, the filter paper (No. 5A) passed through and solid-liquid separation could not be performed.

Comparative Example 2
In Example 1, boric acid ions as boron concentration 50 mg / L, pH 6.5 model wastewater 1 L (boron ions as 4.63 mM), instead of cerium nitrate aqueous solution, lanthanum chloride aqueous solution (La ₂ O ₃ as 32 .5 mass%) was added (3.4 g (6.86 mM as LaO _1.5 )), 1.0 g of sodium sulfate was added as a precipitation aid, and the pH was adjusted to 11.0 with 0.1N aqueous sodium hydroxide solution. And stirred for 15 minutes. A fluffy frog was formed, and a sediment having a sedimentation volume about twice as much as that of Example 1 was formed. This was subjected to solid-liquid separation by filtration under reduced pressure, and the boron concentration in the filtrate was measured to be 12.1 mg / L. Moreover, the yield of the filtration sludge was 18.4g, and the water content was 79%.

Example 3
Boron ion containing 500 mg / L as boron concentration, 1 L of model wastewater with pH 5.5 (46.3 mM as borate ion), 31% by mass as cerium chloride aqueous solution (CeO _{2 in} which 95% or more of rare earth elements are cerium) 25 g (45.0 mM as CeO ₂ ) was added, followed by 40 g of magnesium hydroxide slurry of 40% concentration with stirring. After stirring for 15 minutes, flocs with good sedimentation were formed. The pH value of the mixed solution was 9.6. Solid-liquid separation was performed by vacuum filtration, and the boron concentration in the filtrate was measured and found to be 8.6 mg / L. Moreover, 76 g (equivalent to 7.6% by mass of the waste water) of filtered sludge was obtained, and the water content was 67%.

Comparative Example 3
20 g of aluminum sulfate and 30 g of slaked lime were added to 1 L of the model waste water of Example 3 as a coagulating precipitant and stirred for 15 minutes. Although sedimentation was not good, solid-liquid separation was performed by filtration under reduced pressure, and the boron concentration in the filtrate was measured and found to be 14.1 mg / L. 156 g (corresponding to 15.6% by mass of the waste water) of sticky filtration sludge was obtained, and the water content was 72%.

Example 4
A phosphate ion-containing model waste water (pH 9.3) in which potassium dihydrogen phosphate is dissolved at a phosphorus concentration of 300 mg / L is adjusted to pH 7.5 with 0.1 N hydrochloric acid, 1 L (9.67 mM as phosphate ions) ) 4.0 g (7.2 mM as CeO ₂ ) of an aqueous cerium chloride solution (containing 31% by mass as CeO _{2 in} which 95% or more of the rare earth element is cerium) is added, followed by 40% strength water with stirring. 10 g of magnesium oxide slurry was added. The pH value after addition was 9.6. After stirring for 15 minutes, flocs with good sedimentation were formed. Solid-liquid separation was performed by vacuum filtration, and the phosphorus concentration in the filtrate was measured and found to be 1.2 mg / L. Moreover, 15.8g (equivalent to 1.6 mass% of waste_water | drain) filtration sludge was obtained, and the moisture content was 65%.

Comparative Example 4
In Example 4, except that the pH of the phosphoric acid-containing model waste water (pH 9.3) dissolved at 300 mg / L in phosphorus concentration was not adjusted, the treatment was performed in the same manner as in Example 4, but immediately after the addition of the cerium chloride aqueous solution. A precipitate was formed, and the pH after adding 10 g of magnesium hydroxide slurry was 11.2. The phosphorus concentration in the filtrate was 13 mg / L.

Comparative Example 5
In Example 4, 4 g of the magnesium hydroxide slurry was added instead of aluminum sulfate, and the pH was adjusted to 9.2 using calcium hydroxide as a pH adjuster. The phosphorus concentration in the liquid was 26 mg / L.

Example 5
1L of arsenic ion-containing model wastewater (pH 6.2) dissolved in potassium dihydrogen arsenide at 5mg / L in arsenic concentration (0.067mM as arsenic ion) (CeO in which 95% or more of rare earth elements are cerium) ₂ as a 31 wt% content) was added 0.5 g (0.9 mM as CeO _2), followed by the addition with stirring of a 40% strength hydroxide magnesium slurry 2.5 g. The pH value after the addition was 7.5. The pH was adjusted to 9.2 using calcium hydroxide, and the mixture was stirred for 15 minutes to produce flocs with good sedimentation. Solid-liquid separation was performed by filtration under reduced pressure, and the arsenic concentration in the filtrate was measured and found to be 0.01 mg / L.

Example 6
As model wastewater containing fluorine ions and phosphate ions, 1 L of model wastewater (pH 5.8) containing fluorine 3 mg / L and phosphorus 6 mg / L (F: 0.15 mM, P: 0.19 mM) was added to cerium chloride. 2 g of an aqueous solution (containing 31% by mass as CeO _{2 in} which 95% or more of the rare earth element is cerium) was added (3.6 mM as CeO ₂ ), and then 5 g of 40% strength magnesium hydroxide slurry was added with stirring. . The pH value after the addition was 7.5. The pH was adjusted to 9.5 using calcium hydroxide, and the mixture was stirred for 15 minutes to produce a floc with good sedimentation. Solid-liquid separation was performed by filtration under reduced pressure, and the fluorine concentration and phosphorus concentration in the filtrate were measured. The results were 0.2 mg / L fluorine and 0.01 mg / L phosphorus.

Example 7
To a model waste water (pH 5.8) having a boron concentration of 30 mg / L as borate ion (2.78 mM as borate ion), an aqueous cerium nitrate solution (28.3 mass% as CeO _{2 in} which 99% or more of the rare earth element is cerium). Containing, specific gravity 1.68) was added 2.0 ml (3.50 mM as CeO ₂ ), followed by addition of 5 g of 40% strength magnesium hydroxide slurry with stirring. The pH of the mixed solution was 7.9. Further, the pH was adjusted to 9.5 using calcium hydroxide, and the mixture was stirred for 15 minutes to produce a floc with good sedimentation. Solid-liquid separation was performed by vacuum filtration, and the boron concentration in the filtrate was measured and found to be 1.6 mg / L.

Comparative Example 6
In Example 7, except that pH adjustment with calcium hydroxide was not performed (pH 7.9), the treatment was performed in the same manner as in Example 7, and the pH value was adjusted to 11.5 using calcium hydroxide. The boron concentrations in the filtrate when treated in the same manner as in No. 7 were 6.9 mg / L and 8.2 mg / L, respectively.

Claims (9)

A rare earth element salt solution containing at least a cerium salt as a main component after adjusting to pH 8 or less when the pH of the treated water exceeds 8 when the treated water containing harmful inorganic anions A method for immobilizing and removing harmful inorganic anions, characterized in that magnesium hydroxide is present, the inorganic ions are produced as hardly soluble precipitates at a pH of 8 to 11, and solid-liquid separation is performed. The method for immobilizing and removing inorganic anions according to claim 1, wherein the harmful inorganic anions are one or more of phosphate ions, borate ions, fluorine ions and arsenate ions. The method for immobilizing and removing harmful inorganic anions according to claim 1 or 2, wherein the rare earth element salt contains at least 90% by mass of a cerium salt. The method for immobilizing and removing harmful inorganic anions according to any one of claims 1 to 3, wherein the magnesium hydroxide is a water slurry having a concentration of 25 to 45 mass%. The method for immobilizing and removing harmful inorganic anions according to any one of claims 1 to 4, wherein a pH adjuster is used. 6. The method for immobilizing and removing harmful inorganic anions according to claim 5, wherein the pH adjusting agent is calcium hydroxide. An agent for immobilizing and removing ions from water to be treated containing harmful inorganic anions, comprising a rare earth element salt containing at least a cerium salt as a main component and magnesium hydroxide. The drug according to claim 7, wherein the rare earth element salt contains at least 90% by mass of a cerium salt. The drug according to claim 7, wherein the magnesium hydroxide is a water slurry having a concentration of 25 to 45 mass%.