JP5362292B2 - Production method of Schwertmannite - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To produce high purity shwertmannite in short period of time and in high yield. <P>SOLUTION: A method for producing shwertmannite includes a heating step of heating an aqueous solution of Fe<SB>2</SB>(SO<SB>4</SB>)<SB>3</SB>-nH<SB>2</SB>O (n: an integer of 1-50) to 60-95&deg;C, and a deposition step of depositing shwertmannite by adding a pH adjuster comprising an alkali metal-containing weakly basic salt to the heated aqueous solution so that the aqueous solution is adjusted to pH 1.6-2.5. The weakly basic salt is preferably an alkali metal carbonate and the alkali metal carbonate is preferably at least one of NaHCO<SB>3</SB>and Na<SB>2</SB>CO<SB>3</SB>. <P>COPYRIGHT: (C)2010,JPO&amp;INPIT

Description

  The present invention relates to a method for producing Schwertmannite. The Schwertmannite produced by the present invention can be suitably used when removing these harmful ions from waste liquid containing harmful ions such as chromate ions, phosphate ions and fluoride ions.

_{Schwertmannite} is a metastable mineral having the composition formula of Fe ₈ O ₈ (OH) _8-2x (SO ₄ ) _x , and it is _suitable for specific ions including harmful ions such as chromate ions and phosphate ions. It exhibits interesting chemical properties such as high adsorption capacity.

  In order to industrially use such a Schwbertmannite as a catalyst or a chemical adsorption material, a production method capable of mass-producing high-purity Schwbertmannite at a low cost is required.

As a method for producing Schwertmannite, a method is known in which FeCl ₃ or Fe (NO ₃ ) ₃ is reacted with Na ₂ SO ₄ or CaSO _{4 at} a temperature of about 60 ° C. to deposit Schwertmannite. . However, the Schwertmannite obtained by this method contains about 50% of an impurity salt. In addition, since the impurity salt is molecularly bonded to Schwertmannite, it is difficult to separate and remove the impurity salt.

As another manufacturing method of Schwertmannite, urea ((NH ₂ ) ₂ CO) is added to an aqueous solution of Fe ₂ (SO ₄ ) ₃ .nH ₂ O heated to about 60 to 95 ° C. for about ₂ to 4 hours. A method is also known in which the pH of the aqueous solution is finally increased to about 2 to 6 to deposit Schwbertmannite (for example, see Non-Patent Document 1). However, this method has a problem that the yield of the obtained schbertmanite is low. For example, when 170 g of urea is reacted with 30 g of Fe ₂ (SO ₄ ) ₃ .nH ₂ O, only 5 g of Schwertmannite can be obtained.

Furthermore, as another manufacturing method for Schwertmannite, iron-containing sulfuric acid acidic water, which is industrial wastewater or anti-waste water having a pH of 3 or less, is selected from alkaline earth metal-based materials and iron-based materials having reactivity with sulfuric acid acidic water. There is also known a method of precipitating schwertmannite by treating with at least one solid pH adjusting material and maintaining the pH at 2.5 to 4 in the presence of iron-oxidizing bacteria (for example, see Patent Document 1). .
Materials Research Bulletin, Vol.34, No.6, pp.905-914, 1999, “UNIFORM PARTICLES WITH A LARGE SURFACE AREA FORMED BY HYDROLYSIS OF Fe2 (SO4) 3 WITH UREA”, Jan Subrt, Jaroslav Bohacek, Vaclav Stengl, Tomas Grygar, and Peter Bezdicka Japanese Patent Laid-Open No. 2005-22937

  This invention is made | formed in view of the said situation, and it aims at providing the manufacturing method which can manufacture highly purified schwertmannite in a short time and a high yield.

The manufacturing method of the Schwermannite of the present invention that solves the above problems includes a heating step of heating an aqueous solution of Fe ₂ (SO ₄ ) ₃ .nH ₂ O (n: integer of 1 to 50) to 60 to 95 ° C., A precipitation step of adding a pH adjuster comprising an alkali metal-containing weak basic salt to the aqueous solution so that the pH of the heated aqueous solution is 1.6 to 2.5, and precipitating Schwertmannite; It is characterized by having.

  According to the method for producing a Schwermannite of the present invention, as shown in the examples described later, a highly pure Schwermanite can be obtained in a short time and in a high yield. The reason for this can be considered as follows.

  That is, since a weak basic salt is used as a pH adjuster, the increase in pH due to the addition of the pH adjuster becomes relatively gradual. This moderate increase in pH is considered to realize stable precipitation of schwertmannite. Moreover, in the manufacturing method of the Schwertmannite of this invention, since the weakly basic salt as a pH adjuster contains an alkali metal, these alkali metal ions may show a catalytic effect in the synthesis of Schwertmannite. Therefore, according to the method for producing a Schwbertmannite of the present invention, a high-purity Schwbertmannite can be synthesized in a short time. For example, alkaline earth metal ions do not show a catalytic effect in the synthesis of Schwertmannite.

The weak basic salt is preferably an alkali metal carbonate. The alkali metal carbonate is preferably at least one of NaHCO ₃ and Na ₂ CO ₃ .

  Therefore, according to the manufacturing method of the Schwbertmannite of the present invention, high-purity Schwbertmannite can be obtained in a short time and with a high yield. It becomes possible to do.

  The manufacturing method of the Schwertmannite of this invention is equipped with the heating process and the precipitation process.

In the heating step, an aqueous solution of Fe ₂ (SO ₄ ) ₃ .nH ₂ O (n: an integer of 1 to 50) is heated to 60 to 95 ° C. The number of n in ferric sulfate n-hydrate is not particularly limited, and may be 1 to 10, or may exceed 10. The number of n in the ferric n hydrate _sulfate, Fe _{2 (SO 4)} 3 · nH _{2 Fe} at O solution of 2 _{(SO 4)} only affects the ₃ concentrations, the synthesis of schwertmannite Has no effect.

  When the heating temperature in the heating step exceeds 95 ° C., the reaction efficiency decreases due to evaporation of the reaction solution, and when it is less than 60 ° C., the synthesis of Schwertmannite becomes impossible. This heating temperature is preferably 65 to 80 ° C. from the viewpoint of realizing stable precipitation of schwertmannite.

The pH of the aqueous solution of Fe ₂ (SO ₄ ) ₃ · nH ₂ O is predicted to be in the range of 0.001 to 1 regardless of the concentration of Fe ₂ (SO ₄ ) ₃ · nH ₂ O in the aqueous solution. It is predicted to be about 0.1 to 0.9. It is considered that the pH of the aqueous solution of Fe ₂ (SO ₄ ) ₃ · nH ₂ O does not affect the synthesis of Schwertmannite.

In the precipitation step, a pH adjusting agent made of an alkali metal-containing weak basic salt is added to the aqueous solution so that the pH of the heated aqueous solution becomes 1.6 to 2.5, thereby precipitating Schwertmannite. . PH adjustment at this time _can be performed by adjusting the amount of addition of Fe _{2 (SO 4)} pH adjusting agent for 3 · nH ₂ O aqueous solution. If the pH of the aqueous solution after the addition of the pH adjuster is out of the range of 1.6 to 2.5, it is difficult to stably deposit schbertmannite. Specifically, if the pH of the aqueous solution after the addition of the pH adjuster is less than 1.6, synthesis of Schwertmannite becomes impossible, and if it exceeds 2.5, impurities increase. Therefore, this pH is preferably 1.7 to 2 from the viewpoint of realizing stable precipitation of schwertmannite.

The alkali metal-containing weakly basic salt as the pH adjuster is preferably an alkali metal carbonate. The alkali metal carbonate that can be used in the present invention, carbonates potassium KHCO ₃ and _K 2 CO _3, and the like can be mentioned carbonates of sodium NaHCO ₃ and _Na 2 CO _3, NaHCO ₃ And at least one of Na ₂ CO ₃ is preferred. If it is sodium carbonate, the reaction products will be only Schwertmannite and water by selecting appropriate conditions. Only one or both of NaHCO ₃ and Na ₂ CO ₃ may be used.

  The addition rate of the pH adjuster is preferably 5 to 20 g / min, and more preferably 6 to 15 g / min. If the addition rate of the pH adjusting agent is too fast, stable precipitation of schwertmannite becomes difficult, and if it is too slow, productivity is lowered.

  The shape and size of the pH adjuster are not particularly limited, but it is preferable to use a powdery pH adjuster from the viewpoint of realizing stable precipitation of Schwertmannite.

  The Schwertmannite precipitated in the precipitation step is washed with ion exchange water or the like, filtered, dried, and pulverized as necessary.

Example 1
Schwertmannite was produced by the production method of Example 1 shown below.

<Heating process>
Commercially available Fe ₂ (SO ₄ ) ₃ · nH ₂ O (trade name “EXTRA PURE REAGENT, Code 19529-75 500 g, Iron (III) Sulfate n-Hydrate, Iron sulfate (III) n hydrate, Nacalai Tesque shares Prepared by the company).

Then, 20 g of Fe ₂ (SO ₄ ) ₃ .nH ₂ O and 200 g of water were mixed to obtain 220 g of a 100 g / L Fe ₂ (SO ₄ ) ₃ .nH ₂ O aqueous solution. The pH of this aqueous solution of Fe ₂ (SO ₄ ) ₃ .nH ₂ O was 0.8.

In addition, NaHCO ₃ powder was prepared as a pH adjuster.

Then, the _Fe 2 _{(SO 4)} by heating the 3 · nH ₂ O aqueous solution, the temperature was raised over a period of about 10 minutes to a temperature of 70 ° C. from room temperature, and then held at that temperature for 10 minutes.

<Precipitation process>
Thereafter, 18 g of NaHCO ₃ powder was added to the aqueous solution while being heated to a temperature of 70 ° C. at an addition rate of about 9 g / min. The amount of NaHCO ₃ powder added to Fe ₂ (SO ₄ ) ₃ .nH ₂ O at this time was NaHCO ₃ powder / Fe ₂ (SO ₄ ) ₃ .nH ₂ O = 0.9 in terms of mass ratio.

  In this precipitation step, it took about 2 minutes to add the pH adjuster. The pH of the aqueous solution at the time when the addition of the pH adjuster was completed was 2.0. And when addition of this pH adjuster was completed, a large amount of schwertmannite had precipitated in aqueous solution.

<Washing, filtration, drying, powdering process>
The Schwertmannite obtained in the precipitation step was washed with ion exchange water and filtered. Then, after drying at about 45 ° C., it was pulverized.

  The amount of Schwertmannite thus obtained was 7 g.

  Here, after the addition of the pH adjusting agent was completed (the pH of the aqueous solution became 2.0), the case where the subsequent washing process was performed immediately, and the addition of the pH adjusting agent was completed (the pH of the aqueous solution was 2). After that, the amount of Schbertmannite deposited was not different between the case where it was kept for several minutes and the subsequent washing step was performed.

  The time of the precipitation process in Example 1 was about 2 minutes, and a large amount of Schwertmannite could be precipitated in an extremely short time.

Moreover, in Example 1, 1 mol of Schwermanite could be obtained from 4 mol of Fe ₂ (SO ₄ ) ₃ .nH ₂ O, and the yield was 100%.

  Furthermore, in Example 1, since all the deposits precipitated in the precipitation step were Schbertmanite, it was not necessary to separate and remove impurities from the precipitates.

(Comparative Example 1)
Schwertmannite was produced by the production method of Comparative Example 1 shown below.

<Heating process>
As in Example 1, commercially available Fe ₂ (SO ₄ ) ₃ · nH ₂ O (trade name “EXTRA PURE REAGENT, Code 19529-75 500 g, Iron (III) Sulfate n-Hydrate, Iron (III) sulfate n water” Japanese product, manufactured by Nacalai Tesque Co., Ltd.) was prepared.

Then, 20 g of Fe ₂ (SO ₄ ) ₃ .nH ₂ O and 200 g of water were mixed to prepare a 100 / L Fe ₂ (SO ₄ ) ₃ .nH ₂ O aqueous solution 220 g. The pH of this aqueous solution of Fe ₂ (SO ₄ ) ₃ .nH ₂ O was 0.8.

  As a pH adjuster, 170 g of urea and 500 g of water were mixed to prepare 670 g of a 340 g / L urea aqueous solution.

Then, the _Fe 2 _{(SO 4)} by heating the 3 · nH ₂ O aqueous solution, the temperature was raised over a period of about 10 minutes to a temperature of 70 ° C. from room temperature, and then held at that temperature for 10 minutes.

<Precipitation process>
Thereafter, the urea aqueous solution was added to the aqueous solution that had been heated to a temperature of 70 ° C. The amount of urea aqueous solution added to Fe ₂ (SO ₄ ) ₃ · nH ₂ O at this time was (NH ₂ ) ₂ CO / Fe ₂ (SO ₄ ) ₃ · nH ₂ O = 170/20 in mass ratio. . The time required for adding the pH adjuster was about 2 hours. The pH of the aqueous solution at the time when the addition of the pH adjuster was completed was 2.

  By the addition of this pH adjuster, Schwertmannite was precipitated in the aqueous solution.

<Washing, filtration, drying, powdering process>
The Schwertmannite obtained in the precipitation step was washed with ion exchange water and filtered. Then, after drying at about 45 ° C., it was pulverized.

  The amount of Schwertmannite thus obtained was 5 g.

  In Comparative Example 1, the precipitation process took about 2 hours, a large amount of pH adjusting agent was required, and the amount of Schwbertmannite obtained was only 5 g.

(Evaluation 1)
The X-ray diffractometer was used for XRD analysis of the Schwertmannite obtained in Example 1 and Comparative Example 1. FIG. 1 shows the XRD analysis results of the Schwermanite obtained in Example 1, and FIG. 2 shows the XRD analysis results of the Schwermanite obtained in Comparative Example 1.

  1 and 2, the schbertmanite obtained in Example 1 and Comparative Example 1 was pure with no impurities.

(Evaluation 2)
The amount of Cr absorbed was examined for the Schwermannite obtained in Example 1 and Comparative Example 1. First, Schwertmannite was added at a rate of addition of 1 g / L to a K ₂ Cr ₂ O ₇ solution having an initial Cr concentration of 200 ppm and stirred for 50 minutes. And about the solution after filtering solid content with a paper filter, the Cr density | concentration in a liquid was measured using the inductively coupled plasma atomic emission spectrometer (ICP) (SII (Seiko Instruments Inc) SPS 7800). . And the Cr absorption amount was computed from the measurement result.

Further, the P absorption amount was examined for the Schwermannite obtained in Example 1 and Comparative Example 1. First, Schwertmannite was added to the KH ₂ PO ₄ solution having an initial P concentration of 80 ppm at an addition rate of 1 g / L and stirred for 50 minutes. And about the solution after filtering and removing solid content with a paper filter, the P density | concentration in a liquid was measured using the photometer (mobile laboratory photometer, LASA 30- "Germany"). In this measurement, a filter for a wavelength of 800 nm was used. The amount of P absorption was calculated from the measurement result.

  These results are summarized in Table 1.

  From Table 1, with respect to both Cr ions and P ions, the Schwbertmannite obtained in Example 1 exhibited higher absorption performance than the Schwertmannite obtained in Comparative Example 1.

(Evaluation 3)
Reaction time in the precipitation step of Example 1 (elapsed time after adding NaHCO ₃ powder to Fe ₂ (SO ₄ ) ₃ .nH ₂ O aqueous solution), pH and redox potential (ORP: Oxidation- The relationship with Reduction Potential was investigated.

  The pH and redox potential of the aqueous solution were measured with a pH meter (MM-60R, manufactured by Toa DKK Corporation).

The relationship between reaction time and pH is shown in FIG. 3, and the relationship between reaction time and redox potential is shown in FIG. The pH of the aqueous solution rose from pH 0.8 before addition to pH 2 until about 2 minutes had elapsed after the addition of NaHCO ₃ powder, and remained almost at pH 2 thereafter. In addition, the redox potential of the aqueous solution decreased with time. From these results, it was confirmed that in 2 to 3 minutes, the pH became approximately 2 and the oxidation-reduction potential became 1 V or less, so that Schwbertmannite was precipitated.

(Example 2)
The same production method as in Example 1 was carried out except that Na ₂ CO ₃ powder was used instead of NaHCO ₃ powder as a pH adjuster.

  As a result, as in Example 1, a large amount of Schwbertmannite could be precipitated in an extremely short time.

  In the precipitation step of Example 2, the time taken to add the pH adjuster was about 2 minutes. The pH of the aqueous solution at the time when the addition of the pH adjuster was completed was 1.7. And when addition of this pH adjuster was completed, a large amount of schwertmannite had precipitated in aqueous solution.

Moreover, in Example 2, 1 mol of Schwermanite could be obtained from 4 mol of Fe ₂ (SO ₄ ) ₃ .nH ₂ O, and the yield was 100%.

  Furthermore, in Example 2, since all the deposits precipitated in the precipitation step were Schbertmanite, it was not necessary to separate and remove impurities from the precipitates.

(Comparative Example 2)
As the pH adjuster, Schwartmannite was tried to be produced by the same production method as in Example 1 except that CaCO ₃ powder, which is an alkaline earth metal carbonate, was used instead of NaHCO ₃ powder.

However, in Comparative Example 2 in which CaCO ₃ powder was used as a pH adjuster, no Schwermannite was deposited.

(Evaluation 4)
XRD analysis was performed on the Schwertmannite obtained in Example 2 and the product obtained in Comparative Example 2 using an X-ray diffractometer. FIG. 5 shows the results of XRD analysis of the Schwertmannite obtained in Example 2, and FIG. 6 shows the results of XRD analysis of the product obtained in Comparative Example 2.

  As shown in FIG. 5, the schwertmannite obtained in Example 2 was pure with no impurities. On the other hand, it can be seen from FIG. 6 that the product obtained in Comparative Example 2 is not Schwbertmannite.

(Evaluation 5)
The relationship between the reaction time in the precipitation step of Example 2 (elapsed time after adding Na ₂ CO ₃ powder to the Fe ₂ (SO ₄ ) ₃ .nH ₂ O aqueous solution) and the pH of this aqueous solution was examined.

Similarly, the relationship between the reaction time in the precipitation process of Comparative Example 2 (elapsed time since the addition of Ca ₂ CO ₃ powder to the Fe ₂ (SO ₄ ) ₃ .nH ₂ O aqueous solution) and the pH of this aqueous solution is shown. Examined.

  The relationship between the reaction time and pH in Example 2 is shown in FIG. 7, and the relationship between the reaction time and pH in Comparative Example 2 is shown in FIG. From FIG. 7, it was confirmed that in Example 2, Schwbertmannite was generated near pH2. Further, from FIG. 8, it was confirmed that in Comparative Example 2, impurities other than Schwermannite were generated over a long period of time at a pH of 1.5 or less, and the vicinity of pH 2 suitable for the generation of Schwertmannite passed instantaneously.

It is a figure which shows the XRD analysis result of the Schwertmannite obtained in Example 1. It is a figure which shows the XRD analysis result of the Schwertmannite obtained by the comparative example 1. It is a figure which shows the relationship between the reaction time in the precipitation process of Example 1, and pH of aqueous solution. It is a figure which shows the relationship between the reaction time in the precipitation process of Example 1, and the oxidation-reduction potential of aqueous solution. It is a figure which shows the XRD analysis result of the Schwertmannite obtained in Example 2. It is a figure which shows the XRD analysis result of the product obtained in the comparative example 2. It is a figure which shows the relationship between the reaction time in the precipitation process of Example 2, and pH of aqueous solution. It is a figure which shows the relationship between the reaction time in the precipitation process of the comparative example 2, and pH of aqueous solution.

Claims (3)

A heating step of heating an aqueous solution of Fe ₂ (SO ₄ ) ₃ .nH ₂ O (n: an integer of 1 to 50) to 60 to 95 ° C .;
A precipitation step of adding a pH adjuster comprising an alkali metal-containing weak basic salt to the aqueous solution so that the pH of the heated aqueous solution is 1.6 to 2.5, and precipitating Schwertmannite; The manufacturing method of the Schwertmannite characterized by the above-mentioned.   The method for producing a Schwertmannite according to claim 1, wherein the weakly basic salt is an alkali metal carbonate. The method for producing a Schwertmannite according to claim 2, wherein the alkali metal carbonate is at least one of NaHCO ₃ and Na ₂ CO ₃ .

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