JP2018030748A - Method for producing akaganeite, and anion adsorption method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for producing akaganeite, which can synthesize the akaganeite simply with high yield, and to provide an anion adsorption method using the akaganeite.SOLUTION: This invention relates to: a method for producing akaganeite, comprising a first step of obtaining a first reaction liquid that contains the akaganeite by dissolving an iron(III) chloride and barium hydroxide in water, and then generating the akaganeite in the obtained aqueous solution; and an anion adsorption method, comprising mixing the first reaction liquid obtained by the production method with a liquid to be processed, the liquid containing a sulfate ion and an anion of an inorganic compound other than the sulfate ion to obtain a mixed solution, thereby producing barium sulfate in the mixed solution and adsorbing the anion of the inorganic compound other than the sulfate ion on the akaganeite.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a method for producing akaganeate, which is an iron oxide mineral, and an anion adsorption method. More specifically, the present invention relates to a method for producing akaganate, which is an iron oxide mineral useful for adsorption of anions contained in an aqueous solution, and an anion adsorption method using the akaganate.

Oxide ions such as selenium, arsenic, and chromium may be contained in wastewater from chemical establishments and construction sites. These anions are highly soluble, depending on inorganic flocculants such as sulfuric acid bands (aluminum sulfate) and PAC (polyaluminum chloride) used in conventional general wastewater treatment, and organic flocculants containing polymer polymers. It is difficult to precipitate and remove. Therefore, in Patent Document 1, selenium, arsenic, and chromium are added to an iron oxide mineral called _{Schwertmannite} [composition formula: Fe ₈ O ₈ (OH) _8-2x (SO ₄ ) _x ; 1 ≦ x ≦ 1.75]. Adsorption methods have been proposed.

JP 2005-95732 A

  As a result of intensive studies by the present inventors, the Schwertmannite described in Patent Document 1 inherently contains sulfate ions, so that it is necessary to replace the sulfate ions in order to sufficiently adsorb the target anions. It was thought that there was. In addition, since the binding force of sulfate ions is relatively strong, it has been found that the efficiency of adsorbing the target anion to Schwertmannite is not necessarily high.

Therefore, the present inventors have examined various minerals exhibiting better adsorption efficiency, and found that akaganeite is useful. However, there is a problem that a method for synthesizing akaganeate with good yield on an industrial scale is not yet known.
In addition, since akaganate easily adsorbs anions, when akaganate is introduced into an aqueous solution in which sulfate ions coexist with the anions to be treated, adsorption of the anions other than sulfate ions to the akaganate is not effective. There was a problem that was hindered by ions.

  The present invention provides a method for producing akaganate capable of easily synthesizing akaganate with high yield, and an anion adsorption method using this akaganate.

[1] A first step of dissolving iron chloride (III) and barium hydroxide in water, generating akaganeate in the obtained aqueous solution, and obtaining a first reaction solution containing the akaganeate, A manufacturing method of akaganate.
[2] The method for producing an akaganate according to [1], wherein the first step generates akaganate by setting the pH of the aqueous solution to less than 7.
[3] The first step is a step in which the molar ratio of Fe ³⁺ produced by iron (III) chloride and OH ⁻ produced by barium hydroxide is 1: 1 to 1: 3. The manufacturing method of the akaganeate as described in [1] or [2] characterized by these.
[4] The first step is a step of producing akaganeate by setting the pH of the aqueous solution to less than 4, and then adjusting the pH of the first reaction solution to pH 4 or more and pH 6 or less, The method for producing akaganate according to any one of [1] to [3], further comprising a second step of aggregating akaganate and recovering akaganate.
[5] The first reaction liquid obtained by the method for producing an akaganeate according to any one of [1] to [3] is used as a liquid to be treated containing sulfate ions and anions of inorganic compounds other than sulfate ions. An anion adsorption method comprising mixing and obtaining the mixed solution to produce barium sulfate in the mixed solution and adsorbing an anion of an inorganic compound other than the sulfate ion to the akaganeate.

  According to the method for producing akaganate of the present invention, akaganate can be produced simply and with good yield. In addition, according to the anion adsorption method of the present invention, the amount of anion of an inorganic compound other than sulfate ion to akaganeate can be increased in an aqueous solution in which anion of an inorganic compound other than sulfate ion and sulfate ion coexists. .

It is an adsorption isotherm of the selenate ion in three types of iron oxide minerals. It is a schematic diagram showing the tunnel structure of an akaganate.

《Akaganate Manufacturing Method》
[First step]
According to the first aspect of the present invention, there is provided a method for producing akaganate, wherein iron chloride (III) and barium hydroxide are dissolved in water, akaganate is produced in the resulting aqueous solution, and a first reaction solution containing the akaganate is obtained. One step.

  By dissolving iron (III) chloride and barium hydroxide in water, ions ionized in the aqueous solution react spontaneously to produce akaganate. More specifically, hydroxide ions are generated when barium hydroxide is dissolved in water. The hydroxide ions and iron ions react in an acidic aqueous solution in which a large amount of chloride ions are dissolved, thereby producing akaganeate.

  In order to promote the formation reaction of akaganeate, the aqueous solution (first reaction solution) may be heated to about 40 to 100 ° C.

In the first step, it is preferable to produce akaganeate by setting the pH of the aqueous solution to less than 7. The pH of the aqueous solution is preferably less than 7, more preferably less than 4, and still more preferably 1 to 3.
If the pH is less than 7, akaganeate is easily produced in the presence of chloride ions.
When the pH is less than 4, particularly when the pH is 3 or less, akaganeate can be produced in a high yield in the presence of chloride ions. In addition, although akaganate is easily formed even at pH 4 to 6, if it is within this pH range, the akaganate being produced may aggregate and unreacted iron chloride (III) or barium hydroxide may be taken in. . On the other hand, when the pH is alkaline, there is a high possibility that iron oxide minerals having different structures (for example, goethite, scumite, etc.) are generated.

  Adjustment of the pH of the first reaction solution when producing akaganeate may be performed before adding at least one of iron (III) chloride and barium hydroxide to the reaction solution, or both are dissolved in the reaction solution. It may be done later. However, if the pH of the first reaction solution in which both are dissolved is left in an alkaline state, iron oxide minerals other than akaganate may be generated. Therefore, it is preferable to adjust the pH of the first reaction solution to be acidic and maintain the acidic pH immediately after dissolving the both, or before or during dissolution of the at least one.

  The method of adjusting the pH of the first reaction solution is preferably a method of dropping hydrochloric acid. If hydrochloric acid is used, it is possible to prevent an anion (for example, sulfate ion) other than chloride ions useful for the production of akaganate from being added to the reaction solution, and to prevent the anion from adsorbing to the akaganate. It is also preferable to adjust and maintain the pH of the first reaction solution using sodium hydroxide.

The amount of iron (III) chloride dissolved when preparing the aqueous solution is not particularly limited, and can be, for example, 0.01 to 3 mol / L. Similarly, the amount of barium hydroxide dissolved when preparing the aqueous solution is not particularly limited, and can be, for example, 0.01 to 3 mol / L.
When preparing the aqueous solution, the order of dissolving iron (III) chloride and barium hydroxide is not particularly limited, but in order to maintain the pH of the aqueous solution acidic, iron (III) chloride may be dissolved first. desirable.

In the first reaction liquid of the first step, the molar ratio of Fe ³⁺ produced by iron (III) chloride and OH ⁻ produced by barium hydroxide is 1: 1 to 1: 3. Preferably, it is 1: 1.5 to 1: 2.5, more preferably 1: 1.8 to 1: 2.2. Theoretically, a molar ratio of 1: 2 is most preferred.
When the molar ratio is in the above range close to 1: 2, the positive charge amount of Fe ³⁺ in the first reaction liquid and the negative charge amount of OH ⁻ are in a suitable balance for the production of akaganate, and iron chloride Almost all of Fe ³⁺ derived from (III) can be consumed in the reaction, and akaganate can be easily produced in high yield.

  Specifically, for example, in a 1 L aqueous solution in which 0.1 mol of barium hydroxide is dissolved, the concentration of hydroxide ions generated in the aqueous solution is set to 0. It is considered to be about 08 to 0.1 mol / L. Based on this, the concentration of iron (III) chloride is preferably 1/3 to 1 times the concentration of 0.08 to 0.1 mol / L, and more preferably 1/2 to 1 times the concentration.

Considering the above comprehensively, in the first reaction liquid in the first step, the molar ratio of iron (III) chloride to barium hydroxide is preferably 2: 1 to 2: 3.
When the molar ratio is within the above range, the charge balance between Fe ³⁺ and OH ^{− in} the first reaction solution becomes good, and akaganate can be easily produced in a high yield.

[Second step]
In the first step, the akaganate is produced by setting the pH of the aqueous solution to less than 4, and then the pH of the first reaction solution obtained in the first step is adjusted to 4 or more to pH 6 or less, whereby It is preferable to perform a second step of agglomerating and collecting akaganate.
Here, as a method for adjusting the pH of the reaction solution to 4 or more and pH 6 or less, a method of adding barium hydroxide to the reaction solution and adding it is preferable. By using barium hydroxide, it is possible to prevent extra anions (for example, sulfate ions, etc.) from being mixed into the reaction solution and adsorbed on the akaganate.
It is preferable to perform a 2nd process at the temperature range which does not prevent aggregation, for example at 10-40 degreeC.

(Estimated reaction time)
The completion of the akaganeate formation reaction in the first step can be determined empirically based on the fact that the aqueous solution (first reaction solution) has changed from dark brown to reddish brown. In addition, when the akaganates aggregate in the second step, the viscosity of the first reaction liquid increases, so that the degree of viscosity can be determined as the degree of aggregation.
Usually, the required time required for each process is as follows.
The time required for the reaction to complete after the start of the reaction in the first step is, for example, about 3 to 5 minutes at 10 to 25 ° C. Next, the time required for adding barium hydroxide in the second step, adjusting the pH and aggregating the akaganeate is, for example, about 5 to 10 minutes at 10 to 25 ° C.

Examples of the method for recovering akaganeate include known precipitation methods and filtration methods. It is preferable to flocculate the akaganeate in advance because recovery becomes easy.
The collected red akaganate can be dried and stored until use.
The form of the dried akaganeate obtained by filtration is usually a clay-like lump, and can be pulverized into a powder by a mortar or the like.

  According to the method for producing akaganate of the present invention, when the yield when all of the iron ions added as iron (III) is converted to akaganate is 100% on a molar basis, for example, the yield is 90 to 99. % Can be obtained by collecting red akaganate.

Akaganeite (Akaganeite) obtained by the production method described above is an iron oxide mineral represented by the chemical composition β-Fe ³⁺ (O (OH, Cl)). The crystal system is monoclinic, and the crystallographic data of space group I2 / m, unit cell: a = 10.600, b = 3.0339, c = 10.513, β = 90.24 ° are academic. It is described in a paper “Post JE, Buchwald VF, American Mineralogist, 76 (1991) p.272-277, Crystal structure refinement of akaganeite”. It is also described that the crystal structure of akaganeate clarified in this paper has a tunnel structure that retains chloride ions, and a hydroxyl group is pushed out from the tunnel wall toward the center.
FIG. 2 is a diagram schematically showing the tunnel structure. In the figure, gray circles represent oxygen atoms, white circles represent hydrogen atoms, the circle at the center of the octahedron represents iron atoms, and the black circles in the tunnel represent the same occupation ratio (50 :)).

  The akaganeate obtained by the above production method is suitable for use as an adsorbent that adsorbs anions in an aqueous solution. Hereinafter, an example of the anion adsorption method will be described.

<Anion adsorption method>
(First embodiment)
In the first embodiment of the anion adsorption method, a solution containing an anion of an inorganic compound (hereinafter sometimes referred to as a liquid to be treated) is brought into contact with akaganate to adsorb the anion onto the akaganate. It is.

  Examples of the inorganic compound include inorganic compounds containing inorganic elements such as selenium, arsenic, chromium, fluorine, sulfur, and phosphorus. Specific examples include selenium, arsenic, chromium oxo acid, hydrofluoric acid (hydrofluoric acid), sulfuric acid, phosphoric acid, and the like.

The inorganic compound is preferably an oxo acid, more preferably an oxo acid of the inorganic element, from the viewpoint of exhibiting a high adsorptive power to akaganate.
Here, the oxo acid is an inorganic compound in which a hydroxyl group (—OH) and an oxo group (═O) are bonded to one inorganic atom, and a proton of the hydroxyl group can be eliminated. Oxo acid can be an oxo acid ion from which the proton is eliminated in water.

Examples of the oxo acid, from the viewpoint of showing a high adsorption force Akaganeito, oxoacids of selenium is preferred as the oxoacid ions of selenium, selenium ion (SeO 4 ^_2-), selenate hydrogen ions (HSeO ₄ ^-) , Selenite ions (SeO ₃ ²⁻ ), and hydrogen selenite ions (HSeO ₃ ⁻ ).

  One type of anion of the inorganic compound contained in the treatment target liquid may be used, or two or more types may be used.

  The method of bringing akaganate into contact with the treatment target liquid is not particularly limited, for example, a method of adding and stirring the akaganate powder to the treatment target liquid, a method of adding and stirring a suspension containing akaganate to the treatment target liquid, For example, a method may be used in which the liquid to be treated is poured over the akaganate held by the holding member.

  In this embodiment, when the treatment target liquid is brought into contact with akaganate, it is considered that the anions contained in the treatment target liquid are trapped and adsorbed by the tunnel structure of the akaganate. It is unclear whether or not chloride ions pre-existing in the tunnel structure need to be replaced by the anions due to this adsorption, but in any case, the anions are sufficiently adsorbed by the akaganeate. This is clear from the experiment described later.

The pH of the liquid to be treated when the liquid to be treated and akaganate are brought into contact is preferably 10 or less, more preferably 2 or more and 9 or less, further preferably 3 or more and 7 or less, and particularly preferably 4 or more and 6 or less.
When the pH of the solution to be treated during treatment is 9 or less, the decomposition of akaganate can be prevented, and the adsorption power of the target anion by akaganate can be increased.
The lower the pH of the solution to be treated during treatment, the more protons that bind to the hydroxyl groups facing the center of the tunnel structure of akaganeate. As a result, the tunnel structure can be prevented from being negatively charged, and the target anion can be more easily adsorbed in the tunnel structure. Therefore, from the viewpoint of increasing the target anion adsorptive power, the pH of the liquid to be treated during treatment is preferably pH 2 to 5, more preferably pH 2 to 4, and still more preferably pH 2 to 3.
It is preferable that the pH of the solution to be treated during treatment is 4 or more and 6 or less from the viewpoint of easy aggregation of akaganates and easy recovery of akaganates.
The method for adjusting the pH of the liquid to be treated is not particularly limited, and examples thereof include a method of adding hydrochloric acid, sodium hydroxide, and barium hydroxide.

The temperature of the liquid to be treated when the liquid to be treated and akaganate are brought into contact with each other is not particularly limited, and is preferably, for example, 4 to 60 ° C, more preferably 15 to 50 ° C, and further preferably 30 to 40 ° C.
When the temperature is within the above range, the adsorption force of the target anion by akaganate can be enhanced. When the temperature is at least the lower limit of the above temperature range, the diffusion rate of the target anion in the liquid to be treated is increased, and the efficiency of adsorbing in contact with the akaganeate is further increased. When the temperature is not more than the upper limit of the above temperature range, it is possible to further reduce the desorption of the anion once adsorbed from the akaganeate.

There is no particular limitation on the amount of akaganeate in contact with the treatment target liquid relative to the content of the target anion contained in the treatment target liquid, and the target anion can be sufficiently adsorbed empirically by conducting a preliminary experiment. Can be set to the confirmed amount.
Usually, if the amount of akaganeate added is increased, the amount of anions that can be adsorbed also increases. For example, the amount of inorganic oxoacid ions adsorbed by akaganeate is 0.3 to 0.5 mol / kg.

When an adsorption method in which akaganate powder is added to the liquid to be treated and stirred is used, the akaganate having adsorbed the anions can be recovered from the liquid to be treated.
Examples of the method for recovering the akaganeate powder from the liquid to be treated include a precipitation method and a filtration method. Examples of the precipitation method include, for example, a method in which the liquid to be treated is allowed to settle, a method in which a sulfuric acid band, PAC, a polymer flocculant, etc. are added to the liquid to be treated for aggregation, and a pH of the liquid to be treated. For example, a method of agglomerating akaganeates by adjusting to 4-6.

  It is also possible to employ an adsorption method in which akaganeate powder is packed in a column and a liquid to be treated containing a target anion flows into this column. In this case, it is possible to obtain the processing target liquid from which the target anion is adsorbed and the target anion is removed from the column.

  In the anion adsorption method of the first embodiment described above, an anion adsorbent having akaganeate as the main component of the adsorbent can be used. Here, “main component” means a component having the largest adsorption amount when the adsorption amount of the target anion between the components of the adsorbent is compared. This anion adsorbent may further have a holding member for holding an adsorbent (akaganate).

  As the shape of the akaganeate as the adsorbent, for example, a shape such as powder, gravel, lump, or plate can be easily used. The powdered akaganate obtained by chemical synthesis may be used as an adsorbent as it is, or may be formed into a larger shape by binding this powder. As a method for binding powdered akaganate, for example, a known method used when forming a porous body (for example, electrode, deodorant) by binding carbon particles with a polymer is adopted. can do. In addition, a lump obtained by pressing or sintering may be used as it is, or the lump may be formed by crushing or cutting the lump to an appropriate size. The akaganeate suspension in which akaganeates of these shapes are dispersed in a solvent such as water can be used as the adsorbent.

  Examples of the holding member include containers, columns (cylinders), baskets, nets, and the like that hold akaganate inside. Also, a holding member capable of fixing akaganate to the outer surface can be adopted, and for example, a form in which akaganate is fixed to the surface of the plate material can be mentioned.

(Second embodiment)
In the second embodiment of the anion adsorption method according to the present invention, the first reaction liquid obtained by the method for producing an akaganeate of the first aspect described above is treated with sulfate ions and anions of inorganic compounds other than sulfate ions. In this method, barium sulfate is produced in the mixed solution by mixing with the liquid and obtaining the mixed solution, and the anion of the inorganic compound other than the sulfate ion is adsorbed on the akaganeate.

  In the first reaction solution, barium ions derived from the barium salt used for the production of akaganeate are dissolved. Therefore, the mixed solution contains at least akaganate and barium ions. The shape of the akaganeate is considered to be at least a few nanometers.

When this mixed solution is mixed with the liquid to be treated, barium ions and sulfate ions, which have a faster diffusion rate than the particulate akaganate, are bound first to produce barium sulfate. Since barium sulfate has extremely low solubility in water, barium sulfate precipitates in the mixed solution, and the mixed solution becomes cloudy. As a result, the sulfate ion concentration in the mixed solution is reduced.
On the other hand, the akaganeate in the mixed solution can easily adsorb anions other than sulfate ions without being hindered by sulfate ions having a reduced concentration.

  Examples of the inorganic compound other than sulfate ions include the inorganic compounds exemplified in the anion adsorption method of the first embodiment.

The amount of barium ions contained in the first reaction liquid to be mixed is preferably 80 parts by mole or more, more preferably 100 parts by mole or more with respect to 100 parts by weight of the amount of sulfate ions contained in the liquid to be treated. More preferably, it is 150 mol parts mol parts or more.
When it is at least the lower limit of the above range, barium sulfate can be easily formed, and the sulfate ion concentration in the mixed solution can be sufficiently reduced. The upper limit of the above range is not particularly limited, and may be, for example, about 200 parts by mole.

  The method for mixing the liquid to be treated and the first reaction liquid is not particularly limited, and the first reaction liquid may be added gradually or all at once to the liquid to be treated. The liquid to be treated may be added gradually or all at once.

The pH of the mixed solution is preferably 10 or less, more preferably 2 or more, 9 or less, further preferably 3 or more and 7 or less, and more preferably 4 or more and 6 for the same reason as in the case of the anion adsorption method of the first embodiment described above. The following are particularly preferred:
The method for adjusting the pH of the mixed solution to the above-mentioned preferred range is not particularly limited. For example, (1) after mixing the liquid to be treated and the first reaction solution, hydrochloric acid, sodium hydroxide, A method of adding barium hydroxide or the like; (2) adding hydrochloric acid, sodium hydroxide, barium hydroxide or the like to at least one of the liquid to be treated and the first reaction liquid, and adjusting the pH in advance to the above-mentioned prior to mixing; The method of adjusting to a range, etc. are mentioned.

  The temperature of the mixed solution is preferably 4 to 60 ° C, more preferably 15 to 50 ° C, and still more preferably 30 to 40 ° C, for the same reason as in the case of the anion adsorption method of the first embodiment described above. .

  With respect to the content of anions of inorganic compounds other than the sulfate ions contained in the liquid to be treated, the amount of akaganate in contact with the liquid to be treated is not particularly limited. What is necessary is just to set to the quantity which confirmed that ion can fully adsorb | suck.

  The akaganeate adsorbing the anions in the mixed solution can be recovered from the mixed solution together with the precipitation of barium sulfate. As a specific method, the precipitation method, the filtration method, etc. which were illustrated with the anion adsorption method of 1st embodiment mentioned above are mentioned.

(Synthesis of akaganate)
To 1 L of 0.2 mol / L iron (III) chloride aqueous solution, 0.4 L / L sodium hydroxide (1 L) was added, and while stirring gently for 5 minutes, about pH 2 aqueous solution (Fe ³⁺ : OH ⁻ = about 1: 2) Akaganate was produced. Next, sodium hydroxide was further added to the suspension containing the produced akaganeate, adjusted to pH 4 to 5, and agglomerated with each other while gently stirring for 5 minutes. Aggregated akaganeate was collected by filtration to obtain a dried clay-like akaganeto lump. The akaganeate, which was crushed in a mortar and made into powder, was used in the following experiment.
When the yield when all of the iron ions added as iron (III) chloride became akaganate was assumed to be 100% on a molar basis, the akaganate was recovered and obtained at a yield of 95%.
When the synthesized akaganate was analyzed by XRD, a peak indicating akaganate was confirmed.

[Test Example 1]
A sodium selenate aqueous solution (pH 9) containing 10 mg / L of selenium was prepared. The following experimental procedure was performed using the akaganeate obtained by the above synthesis.
(1) 0.015, 0.025, 0.05, 0.1, 0.2, 0.5, 1.0 (unit: w) is added to the above-described aqueous solution containing selenate ions. / W%) at each concentration. After the aqueous solution adjusted to pH 6 was stirred at 20 ° C. for 1 hour, akaganeate was precipitated, the supernatant was recovered, and the selenate ion concentration was determined according to “67. Method ".
(2) Green last was added to the aqueous solution containing selenate ions so as to have a weight ratio of 0.15 w / w% to 1.0 w / w%. After the aqueous solution at pH 6 was stirred at 20 ° C. for 1 hour, green last was precipitated, the supernatant was collected, and the selenate ion concentration was measured by the above method.
(3) To the above aqueous solution containing selenate ions, Schwertmannite is added to 0.015, 0.025, 0.05, 0.1, 0.2, 0.5, 1.0 (unit: w / w). %) At each concentration. After the aqueous solution adjusted to pH 6 was stirred at 20 ° C. for 1 hour, Schwertmannite was precipitated, the supernatant was collected, and the selenate ion concentration was measured by the above method.
By the above experiment, adsorption isotherms for selenate ions in iron oxide minerals of akaganeate, green last, and schbertmanite were obtained (FIG. 1).
From the results shown in FIG. 1, it is clear that the iron oxide mineral whose dissolved selenate ion equilibrium concentration is not more than the environmental standard (0.01 mg / L) is only akaganate, and its adsorption amount is the highest.

(Synthesis of akaganeate 2)
To 1 L of 1.05 mol / L iron (III) chloride aqueous solution, 1 L of 1.05 mol / L barium hydroxide was added, and while stirring gently for 5 minutes, about pH 2 aqueous solution (Fe ³⁺ : OH ⁻ = about 1: 2) Akaganate was produced. Next, 1.05 mol / L of barium hydroxide is further added to the suspension containing the produced akaganate, and the reaction is performed almost completely so that iron (III) chloride does not remain, and the produced akaganate is dispersed. A reaction solution was obtained.
A portion of the synthesized akaganate was collected and analyzed by XRD, and a peak indicating akaganate was confirmed.

[Example 1]
A liquid to be treated containing sodium selenate 0.21 mg / L and sulfuric acid 1200 mg / L was prepared and adjusted to pH 9.
Three 2.5 L of the liquids to be treated were prepared, and 45 ml, 67 ml, and 89 ml of the reaction liquid obtained in the above (Akaganate synthesis 2) were added to each liquid to be treated and mixed liquid (pH 6) Got. When this mixed solution was gently shaken, turbidity considered to be barium sulfate immediately occurred.
After continuously shaking for 5 minutes, the mixture was filtered with a 0.45 μm filter. As a result, the sulfate ion concentration in each filtrate was reduced to 0.5 mg / L for all the mixed solutions to which the reaction solution containing akaganate was added, and the selenate ion concentration was also reduced to 0.001 mg / L. It was. Each ion concentration was measured by ICP emission spectroscopic analysis as described above.
From the above results, it was confirmed that the barium ions contained in the reaction solution reacted with sulfate ions to generate barium sulfate precipitates, and the remaining sulfate ions and selenate ions were adsorbed by akaganate. .

[Comparative Example 1]
A suspension containing akaganeate was obtained in the same manner as above (Synthesis 1 of akaganeate). At this time, the final molar ratio represented by sodium hydroxide / iron (III) chloride used for the production of akaganeate was 2.5.
When the above suspension containing no barium ions was added to each liquid to be treated in the same manner as in Example 1, turbidity derived from sulfate did not occur.
After continuously shaking for 5 minutes, the mixed solution (pH 6) was filtered with a 0.45 μm filter. As a result, when measured by ICP emission spectroscopic analysis, the sulfate ion concentration in each filtrate was 1100 to 1150 mg / L for all the mixed solutions to which the suspension containing akaganeate was added. The concentration was 0.17-0.20 mg / L.
The reason why the degree of reduction of each ion was smaller than in Example 1 was that the above suspension did not contain barium ions, and most of the akaganeate was consumed by sulfate ions, and akaganeate contained selenate ions. It is thought that it was not able to adsorb.

  From the results of Example 1 and Comparative Example 1, the reaction solution of akaganeate produced using barium hydroxide was mixed with the liquid to be treated containing sulfate ions and selenate ions, so that the purpose was not hindered by sulfate ions. It is clear that the selenate ion can be recovered by adsorbing to akaganeate.

  The configurations and combinations thereof in the embodiments described above are examples, and additions, omissions, substitutions, and other modifications of known configurations are possible without departing from the spirit of the present invention.

  The present invention can be widely applied to uses for purifying contaminated water containing heavy metals such as selenium, arsenic, and chromium.

Claims (5)

  A first step of producing akaganate, comprising dissolving iron (III) chloride and barium hydroxide in water, producing akaganate in the resulting aqueous solution, and obtaining a first reaction solution containing the akaganate. Method.   The method for producing akaganate according to claim 1, wherein in the first step, akaganate is produced by setting the pH of the aqueous solution to less than 7. The first step is a step in which the molar ratio of Fe ³⁺ produced by iron (III) chloride and OH ⁻ produced by barium hydroxide is 1: 1 to 1: 3. The manufacturing method of the akaganeate of Claim 1 or 2. The first step is a step of generating akaganate by setting the pH of the aqueous solution to less than 4.
Next, by adjusting the pH of the first reaction liquid to pH 4 or more and pH 6 or less, the second reaction step comprises aggregating akaganate and recovering akaganate. The manufacturing method of the akaganeate of one term.   The said 1st reaction liquid obtained by the manufacturing method of the akaganeate as described in any one of Claims 1-3 is mixed with the to-be-processed liquid containing the anion of inorganic compounds other than a sulfate ion and a sulfate ion, The mixing An anion adsorption method characterized in that barium sulfate is generated in the mixed solution by obtaining a liquid, and an anion of an inorganic compound other than the sulfate ion is adsorbed on the akaganate.