WO2004018369A1

WO2004018369A1 - Method of recovering fluorine

Info

Publication number: WO2004018369A1
Application number: PCT/JP2003/010450
Authority: WO
Inventors: Norio Moriya
Original assignee: Cabot Supermetals K.K.
Priority date: 2002-08-20
Filing date: 2003-08-19
Publication date: 2004-03-04
Also published as: JP2004074041A; AU2003262247A1

Abstract

A method of recovering fluorine wherein calcium fluoride of relatively large grain diameter exhibiting high filtration performance at membrane treatment can be formed. Recovery of fluorine is accomplished by mixing an aqueous solution having fluorine dissolved therein with calcium carbonate and/or calcium sulfate to thereby form calcium fluoride. Calcium fluoride of desired grain diameter can be formed by appropriately selecting the grain diameter of calcium carbonate and calcium sulfate mixed, so that calcium fluoride of relatively large grain diameter exhibiting high filtration performance can be formed and thus membrane treatment can be efficiently performed, thereby enabling reducing the concentration of fluoride contained in waste water, etc.

Description

Description Fluorine recovery method Technical field

The present invention relates to a method for recovering fluorine dissolved in wastewater or the like.

This application is based on Japanese Patent Application No. 2002-239392, the contents of which are incorporated herein. Background art

Solid electrolytic capacitors with anode electrodes made of tantalum are small, have low ESR, and have high capacitance, and have rapidly become popular as components for mobile phones and personal computers. Also, niobium, which is a homologous element to tantalum, is cheaper than tantalum, and the dielectric constant of niobium oxide is high.

Thus tantalum powder and niobium powder used as Anodo electrode material is usually a fluoride potassium salts, such as _{_{K 2 T a F 7, K}} 2 N b F 6, K 2 N b F 7, melting diluted It is obtained by reacting with a reducing agent such as sodium in a salt, cooling the reaction melt after completion of the reduction reaction, and washing the obtained agglomerate to remove dilute salts and the like. For example, the K ₂ T a F ₇ as fluoride potassium © unsalted, when using sodium as the reducing agent, the reduction reaction is represented by the following formula (1), the waste water generated by washing the agglomerates Has dissolved fluorine.

K ₂ T a F ₇ + 5 N a → 2 KF + 5 N a F + T a… (1)

As a method for treating such wastewater, a method is generally used in which a calcium compound is added to the wastewater to precipitate calcium fluoride, and the calcium fluoride is recovered by membrane treatment. However, in such a method, the generated calcium fluoride is very fine, and it often takes a long time for the membrane treatment or the membrane is clogged, and thus there is a problem in the filterability. Disclosure of the invention

The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a method for recovering fluorine, which is capable of easily generating calcium fluoride having a relatively large particle diameter and good filterability in membrane treatment. And

The first method for recovering fluorine is a method for recovering fluorine by mixing an aqueous solution in which fluorine is dissolved and calcium carbonate to generate calcium fluoride. The calcium carbonate has a particle size of 5 It is characterized by using particles of ~ 5 μμπι.

Further, the number of moles of the fluorine and (M _F), the ratio M _{C a} / 2M _F of Karushiu moles of beam and (M _{C a)} in the calcium carbonate, 1. be 2 to 2.0 range Is preferred.

The second method for recovering fluorine is characterized by recovering fluorine by mixing an aqueous solution in which fluorine is dissolved and calcium sulfate to generate calcium fluoride.

As the calcium sulfate, particles having a particle size of 5 to 5 μπι are preferably used.

Further, the number of moles of the fluorine and (M _F), the ratio M _{C a} Z 2M _F of Karushiu moles of beam and (M _{C a)} in the calcium sulfate, 1. be 2 to 2.0 range Is preferred. BRIEF DESCRIPTION OF THE FIGURES

Figure 1 shows the ratio of fluorine to calcium

5 is a graph in which the residual fluorine concentration is plotted with respect to FIG.

FIG. 2 is a graph showing a change in the residual fluorine concentration with respect to the stirring time. BEST MODE FOR CARRYING OUT THE INVENTION

Hereinafter, the present invention will be described in detail.

In the method for recovering fluorine of the present invention, an aqueous solution in which fluorine is dissolved and calcium sulfate and / or calcium carbonate are mixed to form hardly soluble calcium fluoride. By doing so, it recovers fluorine.

Here, the aqueous solution in which fluorine is dissolved is not particularly limited, and includes wastewater generated in various manufacturing industries.For example, a potassium fluoride of tantalum is reduced in a dilute salt to be used in a capacitor. Wastewater generated in the process of manufacturing tantalum powder can be mentioned.

In the process of manufacturing the tantalum powder, first, K ₂ T a tantalum of full Tsu of potassium © beam salts F _7, etc., 8 00-9 00 is heated to about ° C in a molten state KC 1, N a Into a dilute salt consisting of Cl, KF and their eutectic salts, etc., together with an alkali metal such as sodium, magnesium, calcium, etc., together with a reducing agent such as an alkaline earth metal, or a hydride of these, is subjected to reduction reaction I do. Here, the potassium fluoride salt of tantalum and the reducing agent may be charged all at once or alternately little by little. The reduction reaction is usually performed with stirring.

Here, for example, when K ₂ TaF ₇ is used as a raw material and sodium is used as a reducing agent, a progressing reduction reaction is represented by the following equation (1).

K ₂ T a F ₇ + 5 N a → 2 KF + 5 N a F + T a (1)

After the completion of the reduction reaction, a mixture of the diluted salt and the reaction product in a molten state, that is, the reaction melt is cooled, and the obtained agglomerate is washed to remove and purify the diluted salt and the like. Thereby, a tantalum powder can be obtained.

If the reduction reaction is a reaction represented by the above formula (1), and KC 1 is used as a diluting salt, the obtained agglomerate is composed of the target product tantalum and the diluting salt. and KC 1 is a KF and N a F a by-product, and thus containing a small amount of K ₂ T a F ₇ and N a is the unreacted residue. Here, to remove as much as possible other substances than tantalum, and to smooth the surface of the tantalum powder and reduce the amount of impurities, usually, first, washing with water is performed, and then acid such as hydrofluoric acid is used. Cleaning is performed, and finally, cleaning with hydrogen peroxide and nitric acid is performed.

As a result, three types of wastewater are generated as wastewater generated by such washing: washing with water, washing with an acid such as hydrofluoric acid, and washing with a hydrogen peroxide solution and nitric acid.

In this case, wastewater generated by washing with water (hereinafter referred to as first wastewater) includes water Fluorine is contained at a concentration of about 10 to 300 ppm because by-products (KF and NaF) as well as diluted salts (KC 1) having high solubility in water are dissolved. In this case, if KF is used as the diluting salt, the fluorine concentration in the first wastewater may be higher. -Waste water generated by washing with acid such as hydrofluoric acid (hereinafter referred to as “second waste water”) reacts with fluorine in hydrofluoric acid, a part of tantalum, and the reaction rim from dilute salts to produce water. by such _{_{_{K 2 T a F 2 0 4}}} , K 3 T a 0 2 F 4 which forms is dissolved, contains fluorine in a concentration of about 1 0 0~ 2 0 000 ppm.

Thus, the first wastewater and the second wastewater generated in the process of manufacturing tantalum powder contain relatively high concentrations of fluorine derived from raw materials, by-products, and dilute salts. Wastewater generated by washing with aqueous hydrogen peroxide and nitric acid (hereinafter referred to as “third wastewater”) contains almost no fluorine. Here, p pm is based on mass.

By mixing the first wastewater and the second wastewater having a high concentration of fluorine with calcium carbonate and / or calcium sulfate, hardly soluble calcium fluoride is generated. Then, by recovering the calcium fluoride by a membrane treatment or the like, the concentration of fluorine remaining in the wastewater can be reduced.

The calcium carbonate and calcium sulfate used here may be added directly to the wastewater in the form of particles, or may be added in the form of a slurry previously dispersed in water.

The particle size of calcium carbonate and calcium sulfate is preferably in the range of 5 to 5 μπι. When calcium carbonate and calcium sulfate having such a particle size are used, the particle size of the generated calcium fluoride is 5 to 50 μπι, which is almost the same as that of the used calcium carbonate and calcium sulfate. Excellent filtration properties, such as less clogging of the membrane during recovery and shorter time.

The reason why the particle size of the generated calcium fluoride is substantially the same as the particle size of the calcium carbonate and calcium sulfate used can be explained as follows. That is, both calcium carbonate and calcium sulfate have very low solubility in water. On the other hand, slightly dissolved calcium ions and fluoride ions The reaction rate of the reaction represented by the following formula (2) is large. Thus, when waste water in which fluorine is dissolved is mixed with calcium carbonate and calcium or calcium sulfate, a small amount of dissolved calcium ion immediately reacts with fluorine ion to form hardly soluble calcium fluoride. This shifts the equilibrium of the solution, causing the calcium carbonate and calcium sulfate particles to slightly dissolve again from their surface. It is considered that the calcium ions generated by the dissolution immediately react with the fluorine ions on the particle surface to again generate insoluble calcium fluoride.

C a ^{2 +} + 2 F- → C a F ₂

As described above, calcium carbonate and calcium sulfate have low solubility and a high dissolution rate, while the reaction between calcium ions and fluoride ions is fast, so that the formation of calcium fluoride takes place on the surface of the calcium carbonate and calcium sulfate particles. As a result, the particle size of the finally obtained calcium fluoride is considered to be almost the same as the particle size of the calcium carbonate and calcium sulfate originally used. Here, if the particle size of the calcium carbonate and calcium sulfate used is less than 5 μπι, the particle size of the generated calcium fluoride also becomes small, and as a result, the filterability by membrane treatment tends to decrease. On the other hand, when the particle size exceeds 5 μππι, the formation rate of calcium fluoride becomes extremely slow, and the efficiency tends to decrease.

In addition, here, the number of moles of fluorine is dissolved with (M _F), the ratio M _{C a} / 2M _F with calcium carbonate Oyo Pi moles of calcium in the calcium sulfate (M _{C a)} is 1.2 It is preferable to mix calcium carbonate and calcium sulfate with an aqueous solution such as wastewater in which fluorine is dissolved so as to be in the range of 2.0 to 2.0. The M _Ca Z 2M _F is 1. less than 2, the rate of formation of calcium fluoride tends to be slower. On the other hand, the use of excess calcium and calcium sulfate carbonate exceeding M _{C a} / 2M _F force S 2. 0, the recovery effect of the fluorine does not change much. Ratio M _Ca Z 2M _F is 1. 2 2. in the range of 0, such that the use of an excess of calcium carbonate and sulfate Karushiu Ku, a short time it is possible to produce calcium fluoride, as a result However, the remaining fluorine concentration can be effectively reduced to tens to hundreds of ppm.

As the calcium sulfate, anhydrous (C a S_〇 _4), hydrate (C a S 0 ₄ ' 0

6

_{1/2 H 2 0, C} a S 0 4 · 2 H 2 0) , but can be used, but low solubility in water at near-equipped room temperature Among these, the dissolution rate is high C a S 0 ₄ preferable. The mixing of the aqueous solution in which fluorine is dissolved with calcium carbonate and calcium sulfate may be performed continuously or in a batch system, but the batch system is more effective in reducing the fluorine concentration. it can.

Further, the generated calcium fluoride may be recovered by a method such as coagulation separation, centrifugation, sedimentation, or the like, but is preferably performed by a membrane treatment using a hollow fiber membrane, a filter press, or the like. .

As described above, according to such a method for recovering fluorine, calcium carbonate and calcium sulfate having extremely low solubility in water are used as the calcium compound. Therefore, the formation reaction of calcium fluoride is performed using calcium carbonate and calcium sulfate. On the surface of the particles. Therefore, the particle size of the obtained calcium fluoride is controlled to be substantially the same as the particle size of the calcium carbonate and sulfated calcium used, and by appropriately selecting the particle size of the calcium carbonate and calcium sulfate used, the desired particle size is obtained. A diameter of calcium fluoride can be produced. According to such a method, calcium fluoride having a relatively large particle size and excellent filterability can be easily generated, so that the recovery by membrane treatment is performed in a short time to effectively reduce the fluorine concentration in the wastewater. Can be reduced.

(Example)

Hereinafter, the present invention will be described specifically with reference to examples.

(Example 1)

The tantalum raw material compound was charged together with a reducing agent into a diluted salt that was heated to about 870 ° C and was in a molten state, and a reduction reaction was performed. Here, K ₂ Ta F ₇ was used as a tantalum raw material compound, KF was used as a diluting salt, and Na was used as a reducing agent.

After the completion of the reduction reaction, the reaction melt in a molten state was cooled, and the obtained agglomerates were first washed with water. The wastewater obtained here is designated as the first wastewater. Then, it was washed with 3% hydrofluoric acid. The wastewater obtained here is designated as the second wastewater. Further, it was washed with 1.5% hydrogen peroxide and 9% nitric acid. The wastewater obtained here is the third wastewater.

The concentration of fluorine dissolved in the first wastewater and the second wastewater is JISK-0102 According to the analysis, they were 100 ppm and 2000 ppm, respectively. The concentration of fluorine dissolved in the third wastewater was 50 ppm.

The mixed wastewater 2 L (fluorine concentration 100000 Op pm) obtained by mixing the first wastewater and the second wastewater and the average particle diameter (particle diameter of the cumulative mass 50%) 38.7 7.1μπι C a S_〇 ₄ is mixed with slurries 0. 7 L dispersed in water, calcium fluoride rollers and stirred for 10 minutes at room temperature to precipitate.

At this time, the ratio 2M _F number of moles of fluorine (M _F) the moles of calcium in calcium sulfate and (M _{C a)} was 1.5.

Next, when the mixed wastewater on which calcium fluoride was precipitated was subjected to membrane treatment using a filter having an aperture of 0.45 μπι, membrane treatment could be performed smoothly without clogging.

The average particle size of the obtained calcium fluoride (cumulative mass 50% of the particle diameter) is 4 2. Ο Ομηι, an average particle diameter of the same order of C a S Ο ₄ used.

Further, when the obtained filtrate was analyzed by JISK-0102, the concentration of dissolved fluorine was 20 ppm, and fluorine could be recovered at a recovery rate of 99.8%.

Was further calculated filtered resistivity α during filtration, a [m / kg] is 1 0 ^{1 1} O over da one, was excellent in filterability.

(Examples 2 to 20)

Except that the number of moles of fluorine (M _F) and C a S 0 moles of calcium in ₄ (M _{C a)} and the ratio M _{C a} / 2M _F of was varied in the same manner as in Example 1, fluorinated Calcium was deposited, and the mixed wastewater was subjected to membrane treatment. The obtained filtrate was similarly analyzed as in Example 1, the relationship between the ratio M _{C a} / 2M _F and the fluorine concentration in the filtrate (the residual fluorine concentration), shown in Figure 1 together with the results of Example 1 Was.

(Examples 21 to 22)

The average particle size of C a S_〇 ₄ using (cumulative mass 50% particle size), in Example 2 1 1 8. 9 5μηι, except for using 5. 74 μπι Example 2 2 Example 1 Calcium fluoride was precipitated in the same manner as described above, and the mixed wastewater was subjected to membrane treatment, but was smoothly performed without clogging. T / JP2003 / 010450

8

The average particle size (particle size at a cumulative mass of 50%) of the obtained calcium fluoride was 20.2 μηι in Example 21 and 8.1 μηι in Example 22. a The average particle size of SO ₄ was almost the same.

(Comparative Example 1)

Except that the average particle size in place of the C a S_〇 ₄ (cumulative mass 50% particle size) was used nitrate Cal Shiumu of 5 0Myupaiiota in the same manner as in Example 1, to precipitate calcium fluoride, then the mixture The wastewater was subjected to membrane treatment, and the obtained filtrate was analyzed in the same manner as in Example 1.

However, the average particle size of the obtained calcium fluoride (particle size at a cumulative mass of 50%) was as fine as 0.2 μπι, and the film treatment required a long time. Further, when the filtration specific resistance α at the time of filtration was calculated, a [m / kg] was in the order of 10 ¹³ .

(Comparative Example 2)

Except C a S 0 ₄ average particle size in place of (cumulative mass 50% particle size) was used 5 0Myuiotaita chloride Cal Shiumu in the same manner as in Example 1, to precipitate calcium fluoride, followed by the The mixed wastewater was subjected to membrane treatment, and the obtained filtrate was analyzed in the same manner as in Example 1.

However, the average particle size of the obtained calcium fluoride (particle size at a cumulative mass of 50%) was as fine as 0.7 μπι, and the film treatment required a long time. Further, when the filtration specific resistance α at the time of filtration was calculated, a [m / kg] was in the order of 10 ¹³ . The filtration specific resistance a is defined by Ruth's filtration theory: R = ac V / A. Here, R: cake filtration resistance, c: cake mass per unit, V: filtration flow rate, A: filtration area, indicating the ease of filtration of the slurry.

(Examples 23 to 28)

Mixing the waste water obtained by mixing the first and Wastewater a second wastewater, C a S 0 ₄ while varying the agitation time and distributed slurry in water, the residual fluorine concentration in the filtrate at each agitation time Was measured. The ratio M _{C a} Z2M _F number of moles of fluorine (M _F) and the number of moles of calcium that put the calcium sulfate and (M _Ca) is 1.1 at 1.0, Example 24 in Example 2 3 It was 1.2 in Example 25, 1.3 in Example 26, 1.4 in Example 27, and 1.5 in Example 28. The time course for the stirring time of the residual fluorine concentration in each M _Ca Z 2M _F shown in FIG.

From the above results, when using calcium sulfate (C a S_〇 _4), Ki de be generated substantially calcium fluoride having an average particle diameter substantially equal to that of sulfuric acid calcium used, also be carried out smoothly filtered Was completed. Further, M _{C a} / 2M _F is 1.1 to 2.0, more in the range of 1.2 to 2.0, it became clear that it is the this to particular reduced effectively residual fluorine concentration.

Incidentally, if using calcium carbonate in place of calcium sulfate (C a S_〇 _4), it can be made live calcium fluoride having an average particle diameter of approximately the same as the calcium carbonate used, M _{C a} / 2M _F is 1.1 to 2.0, more in the range of 1.1 to 2.0, it could be particularly reduced effectively residual fluorine concentration. Industrial applicability

As described above, according to the recovery method of the present invention, calcium carbonate and / or calcium sulfate having extremely low solubility in water is used as the calcium compound. By appropriately selecting, calcium fluoride having a desired particle size can be generated. In other words, according to such a method, calcium fluoride having a relatively large particle size and excellent filterability can be easily produced. The concentration of fluorine dissolved in the metal can be effectively reduced.

Claims

The scope of the claims .

1. A method for recovering fluorine, comprising: mixing an aqueous solution in which fluorine is dissolved and calcium carbonate to generate calcium fluoride, thereby recovering fluorine.

A method for recovering fluorine, wherein the calcium carbonate is particles having a particle size of 5 to 5 μμπι.

2. The method for recovering fluorine according to claim 1, wherein

The moles of the fluorine (M _F), the ratio M _Ca Z 2M _F of molar number of calcium and (M _Ca) in the calcium carbonate, from 1.2 to 2. Fluorine recovered method ranges from 0 .

3. A method for recovering fluorine, comprising: mixing an aqueous solution in which fluorine is dissolved with calcium sulfate to generate calcium fluoride, thereby recovering fluorine.

4. The method for recovering fluorine according to claim 3, wherein the calcium sulfate is particles having a particle diameter of 5 to 5 μμπι.

5. The method for recovering fluorine according to claim 3, wherein a ratio M _Ca // 2M _F between the number of moles of fluorine (モル_F ) and the number of moles of calcium in the calcium sulfate (M _{C a} ) is satisfied. The method of recovering fluorine, which is in the range of 1.2 to 2.0.

6. A fluorine recovery method according to claim 4, the number of moles of the fluorine and (M _F), the ratio M _Ca Z2M _F number of moles of calcium and (M _Ca) in the calcium sulfate, 1. A method for recovering fluorine in the range of 2 to 2.0.