WO2003102254A1

WO2003102254A1 - Method of metal recovery

Info

Publication number: WO2003102254A1
Application number: PCT/JP2003/007085
Authority: WO
Inventors: Norio Moriya; Hisashi Matsukawa
Original assignee: Cabot Supermetals K.K.
Priority date: 2002-06-04
Filing date: 2003-06-04
Publication date: 2003-12-11
Also published as: JP4245899B2; JP2004060047A; AU2003242042A1; CN1659294A; CN100471968C

Abstract

A method by which tantalum compounds and niobium compounds dissolved in water such as a liquid detergent are insolubilized and recovered. An aqueous solution containing tantalum compounds and/or niobium compounds dissolved therein is regulated so as to have a pH and an oxidation-reduction potential E which satisfy E<60×(10-pH) to thereby insolubilize the tantalum compounds and/or niobium compounds. The tantalum compounds and/or niobium compounds thus insolubilized are recovered through a membrane treatment. Thus, the metal compounds can be more effectively recovered. This method is especially suitable for use in the treatment of a wastewater generated in the production of a tantalum powder or niobium powder through the reduction of a raw tantalum compound and/or raw niobium compound in a diluting salt.

Description

Description Metal recovery method Technical field

The present invention relates to a method for insolubilizing and recovering a tantalum compound and a niobium compound having high solubility in water. Background art

Solid electrolytic capacitors with anode electrodes formed of

Due to its low ESR and high capacity, it has rapidly spread as a component for mobile phones and personal computers. Also, niobium, which is an element of the same family as tantalum, is cheaper than tantalum, and the dielectric constant of niobium oxide is large. The anode electrode is formed by sintering a tantalum powder and a niobium powder into a porous sintered body, and subjecting the porous sintered body to chemical oxidation. As described above, the tantalum powder and niobium powder used as the anode electrode raw material are obtained by mixing raw material compounds such as tantalum salt and niobium salt with molten dilute salts such as KC1, NaCl, KF and eutectic salts thereof. After the reduction reaction is completed, the reaction melt is cooled, and the obtained agglomerates are washed to remove dilute salts and the like.

Here, the agglomerates are washed sequentially with water, with an acid such as hydrofluoric acid, and with hydrogen peroxide and nitric acid. However, when the agglomerates are washed in this manner, there is a problem that a part of tantalum and niobium is dissolved in the washing solution in the form of a compound which is easily dissolved in water, and is discarded together with the washing solution.

In addition, no method for effectively recovering such dissolved tantalum or niobium compounds has been found so far. Only a study focused on the pH of the liquid has been made (for example, see Japanese Patent Application Laid-Open No. 2002-80915). 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 insolubilizing and recovering an evening compound and a niobium compound dissolved in water such as a washing liquid. Disclosure of the invention

As a result of intensive studies, the present inventors have found that the above problems can be solved by appropriately controlling the oxidation-reduction potential and pH of an aqueous solution in which tantalum or niobium is dissolved. It was completed.

In the method for recovering a metal according to the present invention, the tantalum compound is adjusted by adjusting the pH and the oxidation-reduction potential E of an aqueous solution in which the compound and the compound are dissolved so as to satisfy the following formula (1). And / or a step of insolubilizing the niobium compound.

E <60 X (10-pH) (1)

(In the equation (1), the unit of E is [mV].)

More preferably, 11 is adjusted to 1 or less, and the oxidation-reduction potential E is adjusted to 40 OmV or less. Alternatively, adjust the pH to 6.5-9.0.

Preferably, the method further comprises a step of separating and recovering the insolubilized tantalum compound and / or niobium compound by membrane treatment.

The utility of the metal recovery method of the present invention is particularly exhibited when the aqueous solution contains hydrogen peroxide. BEST MODE FOR CARRYING OUT THE INVENTION

Hereinafter, the present invention will be described in detail.

The method for recovering a metal according to the present invention comprises a step of insolubilizing the tantalum compound and / or the niobium compound by adjusting the pH and the oxidation-reduction potential of the aqueous solution in which the tantalum compound and / or the niobium compound are dissolved. Having. Here, the aqueous solution in which the tantalum compound and the z or niobium compound are dissolved is not particularly limited, but the wastewater generated in the step of manufacturing the tantalum powder by reducing the tantalum raw material compound in a dilute salt is exemplified. Of recovering tantalum from coal. First, a method for producing a tantalum powder by reducing a tantalum raw material compound in a dilute salt will be described.

Examples of tantalum raw material compounds include potassium fluoride salts such as K ₂ TaF ₇ and the like, chlorides such as nanta pentachloride and lower tantalum chloride, and halides such as iodide and bromide. These starting compounds are dissolved in a diluted salt composed of KCl, NaCl, KF and their eutectic salts heated to a temperature of about 800 to 900 and mixed with alkali metals such as sodium, magnesium, and calcium. It is fed together with earth metal and a reducing agent such as hydride to perform a reduction reaction. Here, the raw material and the reducing agent may be charged at once, or may be added in small amounts alternately, and there is no particular limitation. The reduction reaction is usually performed with stirring.

For example, when K ₂ TaF ₇ is used as a raw material and sodium is used as a reducing agent, the reduction reaction that proceeds here is represented by the following equation (2).

K ₂ TaF ₇ + 5Na → 2KF + 5NaF + Ta (2) After the completion of such a reduction reaction, the mixture of diluted salts and reaction products in the molten state, that is, the reaction melt is cooled, The obtained agglomerates are washed to remove dilute salts and the like, and purified to obtain a tantalum powder. Here, taking as an example the case where the reduction reaction is the reaction represented by the above formula (2) and KC 1 is used as a diluting salt, the obtained agglomerate is the target product In addition, it contains KC 1 as a dilute salt, KF and NaF as by-products, and small amounts of K ₂ TaF ₇ and Na as unreacted residues. So, Tanyu In order to remove as much as possible other elements than possible, and to make the surface state of the tantalum powder as smooth as possible and to reduce the amount of impurities, it is usual to first wash with water, and then use an acid such as hydrofluoric acid. Perform cleaning. Then, cleaning with a hydrogen peroxide solution and nitric acid is performed.

As a result, three types of wastewater will be generated as wastewater generated by such cleaning: cleaning with water, cleaning with an acid such as hydrofluoric acid, and cleaning with a hydrogen peroxide solution and nitric acid. In this case, the wastewater generated by washing with water (hereinafter referred to as the first wastewater) contains only diluting salts (KC1) and by-products (KF and NaF), which are highly soluble in water, and mainly dissolves them. Therefore, tantalum or tantalum compounds dissolve in trace amounts of less than 1 O ppm.

On the other hand, wastewater generated by washing with an acid such as hydrofluoric acid (hereinafter referred to as “second wastewater”) has high solubility due to the reaction of fluorine in hydrofluoric acid with a part of tantalum and potassium derived from dilute salt. by such _₂ T a F ₂ 〇 _4, K ₃ T A_〇 ₂ F ₄ is generated, these melts, in a state in which tantalum is relatively large dissolved about 500 ppm in terms of metal.

Also, wastewater generated by washing with hydrogen peroxide and nitric acid (hereinafter referred to as “third wastewater”) is considered to be due to oxidation of tantalum to form water-soluble compounds. About 1500 ppm of tantalum compound is dissolved. Hereinafter, a method for insolubilizing a tantalum compound in the third wastewater having a high solubility of tantalum among the first to third wastewaters will be described.

First, the pH and the oxidation-reduction potential E are adjusted so that the pH and the oxidation-reduction potential E of the third wastewater satisfy the following expression (1). However, in Equation (1), the unit of E is [mV].

E <6 OX (10 -pH) (1)

As long as the pH and redox potential E satisfy Equation (1), any pH and redox potential Even at redox potential E, at least 95% or more of the tantalum compounds dissolved in the third wastewater can be insolubilized. However, since the third effluent is usually acidic with a pH of 1 or less, even if the pH is not increased by adding an alkaline aqueous solution, for example, when the pH is 1, the formula (1) ), The redox potential E is set to less than 540 mV. For example, when the pH is 0.5, the redox potential E is also set to less than 57 OmV from the equation (1) to obtain the tantalum dissolved in the third wastewater. At least 95% or more of the compound can be easily insolubilized. More preferably, when the pH is 1 or less, most of the dissolved tantalum compounds are easily insolubilized by adjusting the oxidation-reduction potential E to 40 OmV or less, and more preferably to 35 OmV or less. be able to. Here, in order to lower the oxidation-reduction potential E, for example, various reducing agents such as iron (III) chloride, sodium sulfite (Na ₂ S ₃ ), and hydrogen chloride may be appropriately added. By adding an appropriate amount of the reducing agent in this way, the oxidation-reduction potential E of the third waste liquid can be reduced from around 60 OmV before adjustment to a desired value. By adjusting only the oxidation-reduction potential E so as to satisfy the expression (1) while keeping the third waste liquid in an acidic state, at least 95% of the dissolved tantalum compound can be obtained. % Or more can be easily insolubilized.However, by setting the third waste liquid to pH 6.5 to 9, the liquid becomes stable and insolubilization can be performed stably, and it is handled near the neutral region. Therefore, the pH is adjusted to 6.5 to 9.0 by appropriately adding an alkaline aqueous solution such as sodium hydroxide, and then the oxidation-reduction potential E is adjusted to satisfy the expression (1). Is also good. Instead of adding sodium hydroxide or the like, an alkaline waste liquid generated in another process may be used.

In this case, when the pH is adjusted to 6.5 to 9.0, about 30 to 50% of the water-soluble tantalum compound in the third wastewater becomes insoluble. Then, by adding the above-mentioned reducing agent, for example, when the pH is 7, the oxidation-reduction potential E is set to less than 18 OmV according to the equation (1). For example, when the pH is 9, the oxidation-reduction potential E is also obtained from the equation (1). E to 6 OmV When the content is less than 90%, at least 95% or more of the dissolved tantalum compound can be easily insolubilized. Further, even when the third waste liquid has an alkaline property in which the pH exceeds 9.0, as long as the pH and the oxidation-reduction potential E satisfy the formula (1), insolubilization is possible. Thus, irrespective of the pH value, by adjusting the oxidation-reduction potential E according to the pH so that the relationship with the oxidation-reduction potential E satisfies the equation (1), the solution can be dissolved in the third wastewater It can insolubilize at least 95% or more of the unraveled tantalum compound, and reduce the solubility of tantalum in the third wastewater to about 10 ppm or less. Although the form of the tantalum compound formed by insolubilization is not clear, it can be assumed that it is a tantalum pentoxide or a hydroxide that dissolves only a trace amount in water. Usually, most of the insolubilized tantalum compound is present in the third wastewater as suspended matter having a particle size of about 0.3 to 10 / m. Therefore, it is appropriately separated and collected. The method of separating and recovering such tantalum compounds may be sedimentation separation using thickener, foam separation using a surfactant, or centrifugation.However, according to membrane treatment, the separation efficiency should be close to 100%. Is preferred. The membrane used here can be appropriately selected, but is preferably a Teflon (registered trademark) -based or polyethylene-based membrane having excellent chemical resistance and a pore diameter of 0.03 m or less. As such a membrane, for example, a hollow fiber membrane (product name: UMF-212WFA, pore size: 0.03 m) manufactured by Mitsubishi Rayon Co., Ltd. can be exemplified. In particular, tantalum has a large specific gravity, and its compound also has a large sedimentation property. Therefore, such membrane treatment and sedimentation separation may be used in combination. By using both membrane treatment and sedimentation separation, the load on the membrane can be reduced, and the frequency of washing and replacing the membrane can be reduced. In that case, it is preferable to use an upward sulfur total filtration system. According to such a method, the tantalum compound dissolved in the washing liquid such as the third wastewater can be easily insolubilized and recovered, and these can be effectively reused. It is possible to improve the productivity of a process for manufacturing or using a hologram. In the above description, the method of recovering metal is to reduce the tantalum raw material compound in dilute salt to insolubilize and recover the tantalum compound in the third wastewater generated when manufacturing tantalum powder. However, the same applies to the case of producing niobium powder. That is, the method can be suitably applied to the case where the niobium raw material compound is reduced in a dilute salt to insolubilize the niobium compound in the third wastewater generated when producing niobium powder. The niobium raw material _{_{compounds, K 2 N b F 6,}} K 2 N b F 7 potassium fluoride salt such as, niobium pentachloride, chloride such as lower niobium chloride, and halides such as iodide, odor products . In particular, in the case of niobium, a niobium fluoride such as potassium fluoroniobate can be used as the niobium raw material compound. Further, as an aqueous solution to be insolubilized in such a recovery method, tantalum powder is used. It is not limited to wastewater for producing niobium or niobium powder, and may be any aqueous solution in which a tantalum compound and / or a diobium compound is dissolved. As described above, according to such a metal recovery method, the pH and the oxidation-reduction potential E of the aqueous solution in which the nantalum compound and Z or the niobium compound are dissolved are determined so that these have the relationship of the formula (1). Process to insolubilize the tantalum compound and / or niobium compound, and can be recovered at a high rate, so that these compounds can be reused to produce or use It is possible to improve the productivity of the process. In addition, in such a method, it is not necessary to limit the range of pH, and at any pH, insolubilization can be performed only by adjusting the oxidation-reduction potential E accordingly. Since no operation such as neutralization is required, the work is simple and the work efficiency is excellent. 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 heated to about 870 and in a molten state, and a reduction reaction was performed. Here, the tantalum raw material compound K ₂ TaF ₇ was used, 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 the second wastewater. Further, the substrate was washed with 1.5% hydrogen peroxide and 9% nitric acid. The wastewater obtained here is the third wastewater. When the first wastewater was analyzed by ICP, the first wastewater contained 610 ppm of tantalum and Z or a tantalum compound in terms of metal, of which 10 t less than pm.

Analysis of the second wastewater by ICP revealed that the second wastewater contained 14800 ppm of tantalum or a tantalum compound in terms of metal, of which 14320 ppm was dissolved. A 20% NaOH aqueous solution was added to the second wastewater to adjust 1 from 1.0 to 7.5, and the dissolved tantalum and / or tantalum compound precipitated and dissolved tantalum And the Z or tantalum compounds dropped below 10 Ppm. Analysis of the third wastewater by ICP revealed that the third wastewater contained 780 ppm of tantalum or a tantalum compound, of which 770 ppm was dissolved. Therefore, a 20% Na〇H aqueous solution (A) was added to this third wastewater as a pH adjusting solution to adjust the pH from below 1.0 to 7.5, and as a redox potential adjusting solution. The redox potential was adjusted from 600 mV to 1 O OmV by adding a ₃₀ % NaHS03 aqueous solution (B). As a result, dissolved tantalum and / or tantalum compounds were precipitated, and dissolved tantalum and / or tantalum compounds were reduced to less than 10 ppm. Next, the first wastewater, the second wastewater whose pH was adjusted as described above, and the third wastewater whose pH and oxidation-reduction potential were adjusted were mixed, and were collected by membrane treatment. The membrane used here was a hollow fiber membrane (product name: UMF-20 12WFA, pore size 0.03 mm) manufactured by Mitsubishi Rayon Co., Ltd. It was used in the form of a hollow fiber membrane unit.

In this way, 95% of the tantalum and / or tantalum compounds initially contained in the first, second and third wastewater could be recovered (metal equivalent). The above is summarized in Table 1.

[Examples 2 and 3]

The first wastewater and the second wastewater were treated in the same manner as in Example 1.

On the other hand, by changing the amount of the pH adjustment liquid and the oxidation-reduction potential adjustment liquid added to the third wastewater,

The third wastewater was treated in the same manner as in Example 1 except that the pH and the oxidation-reduction potential of the third wastewater were set to the values shown in Table 1.

Then, the first wastewater, the second wastewater, and the third wastewater are mixed in the same manner as in the first embodiment.

This was recovered by membrane treatment. As a result, it was possible to recover 95% of the evening and / or tantalum compounds contained in the first, second and third wastewater (metal conversion).

[Comparative Examples 1-2]

This was recovered by membrane treatment. However, as shown in Table 1, only a small percentage of the evening and / or evening compounds contained in the first, second, and third wastewater could be recovered (metal Conversion).

(table 1 ) Example Example Example Comparative example Comparative example

1 2 3 1 2 Adjusted pH 7.5 8 8 7.5 1 0 Adjusted pH

1 00 80 60 250 60 Third waste liquid Redox potential (mV)

Ta and or

95 95 95 1 0 40 Recovery rate of Ta compound (%)

[Examples 4 to 13]

On the other hand, the pH and the oxidation-reduction potential of the third wastewater are shown in Tables 2 and 3, without adding the pH-adjustment liquid to the third wastewater, and adding only the oxidation-reduction potential adjustment liquid while appropriately changing the amount. Except for the values, the third wastewater was treated in the same manner as in Example 1.

This was recovered by membrane treatment. As a result, it was possible to recover 99% of tantalum and Z or tantalum compounds contained in the first, second and third wastewaters (metal equivalent).

[Comparative Example 3]

On the other hand, except that the pH adjustment liquid was not added to the third wastewater but only a small amount of the oxidation-reduction potential adjustment liquid was added to adjust the pH and redox potential of the third wastewater to the values shown in Table 3, The third wastewater was treated in the same manner as in Example 1.

This was recovered by membrane treatment. However, as shown in Table 3, only a small percentage of the evening tar and / or evening compounds contained in the first, second and third wastewaters was recovered (metal Conversion). (Table 2)

(Table 3)

[Example 14]

On the other hand, except that the amounts of the pH adjusting solution and the oxidation-reduction potential adjusting solution added to the third wastewater were changed to adjust the pH and the oxidation-reduction potential of the third wastewater to the values shown in Table 3, Similarly, the third wastewater was treated.

Then, the first wastewater, the second wastewater, and the third wastewater were mixed in the same manner as in the example, and collected by membrane treatment. As a result, it was possible to recover 99% of the tantalum and / or tantalum compounds contained in the first, second and third wastewater at first (metal conversion).

From this result, it was clarified that pH can be recovered even as an alkaline solution. Industrial applicability

As described above, according to the recovery method of the present invention, a tantalum compound and a niobium compound having high solubility in water can be insolubilized only by changing the oxidation-reduction potential under an arbitrary pH, and can be recovered at a high rate. As a result, these compounds, which have often been discarded, can be reused, and the productivity of processes that produce or use tantalum or niobium can be improved.

Claims

The scope of the claims

1. A step of adjusting the pH and the oxidation-reduction potential E of the aqueous solution in which the tantalum compound and / or the niobium compound is dissolved so as to satisfy the following formula (1) to insolubilize the tantalum compound and / or the niobium compound. A metal recovery method characterized by the following.

E 6 6 OX (10-ρΗ) (1)

(In equation (1), the unit of E is [mV].)

2. The method according to claim 1, wherein the pH is adjusted to 1 or less and the oxidation-reduction potential E is adjusted to 40 OmV or less.

3. The method for recovering metal according to claim 1, wherein the pH is adjusted to 6.5 to 9.0.

4. The method for recovering a metal according to claim 1, further comprising a step of separating and recovering the insolubilized tantalum compound and Z or niobium compound by membrane treatment.

5. The method for recovering a metal according to claim 1, wherein the aqueous solution contains hydrogen peroxide.

6. A metal characterized by using evening water or niobium recovered by the metal recovery method according to any one of claims 1 to 5.