JP5929294B2 - Tantalum recovery method - Google Patents

Description

  The present invention relates to a tantalum recovery method.

  In recent years, attention has been paid to effective use of limited resources, and a method for collecting and reusing various resources is required. In particular, rare metals are rarely produced, and it is difficult to purify them, so that stable supply is difficult, and a method of collecting and reusing them is eagerly desired.

  By the way, among rare metals, tantalum is a metal that has a wide range of uses and is excellent in corrosion resistance and heat resistance. In particular, tantalum oxide films are widely used as capacitors because they have rectifying characteristics. This capacitor is used in various electronic devices such as mobile phones, smartphones, and notebook computers, and it is expected that the demand will increase further due to the recent increase in electronic devices. In addition, lithium tantalate single crystal wafers are used as surface acoustic wave filters for removing noise in mobile communication terminals such as mobile phones and smartphones, and the demand is explosively increasing as the mobile communication terminal market expands. .

  Under such circumstances, a method for recovering tantalum from oil-containing sludge containing a metal such as tantalum is known. For example, Patent Document 1 discloses that an oil component is dried and evaporated from oil-containing sludge at a high temperature (150 to 300 ° C.), suspended or dissolved in water or an organic solvent, slurried by aging, and concentrated (about 50 mass percent A tantalum recovery method for obtaining a tantalum raw material suitable for efficient production of various products by dissolving the slurry using hydrofluoric acid as described above is described.

JP 2002-346596 A

  However, in such a tantalum recovery method, there is a risk of ignition or the like because it is kept under high temperature conditions in the step of drying and evaporating sludge containing oil in the recovery step. In addition, since a high concentration of hydrofluoric acid is used, there are problems of using a high concentration of highly toxic chemicals and a high environmental load of waste liquid. In addition, such a tantalum recovery method has a problem that it takes a long time to recover.

  The present invention has been made in view of such problems, and provides a tantalum recovery method capable of recovering tantalum from oil-containing sludge in a short time and in a high yield under conditions of low risk and environmental load. The main purpose.

  In order to achieve the above-mentioned main object, the present inventors removed a part of iron by washing with sludge containing lithium tantalate, iron and oil by hydrothermal treatment and then washing with organic acid. As a result, deiron sludge was obtained. A solution containing tantalum was eluted from the deiron sludge by hydrothermal treatment, and an alkali solution was added to the solution to precipitate a salt containing tantalum in the solution to collect tantalum. By doing so, it was found that high-purity tantalum can be recovered from the oil-containing sludge in a high yield without using a drying step under high temperature conditions or an organic solvent with a high environmental load, and the present invention has been completed.

That is, the tantalum recovery method of the present invention is
In a tantalum recovery method for recovering tantalum from sludge containing lithium tantalate, iron and oil,
An oil removal step of removing a part of the oil from the sludge containing tantalum, iron and oil by hydrothermal treatment;
Washing the sludge that has undergone the oil removal step with an organic acid, and removing iron from the iron removal step;
An elution step of eluting a solution containing tantalum from the sludge that has undergone the iron removal step by hydrothermal treatment in the presence of hydrofluoric acid ,
A recovery step of adding an alkaline solution to the solution obtained in the elution step to precipitate and recover a salt containing tantalum;
Is included.

  The tantalum recovery method of the present invention may include an oil primary removal step of removing a part of the oil from the sludge before the oil removal step. In this way, most of the oil contained in the oil-containing sludge can be removed before the oil removal step.

  In the tantalum recovery method of the present invention, as the organic acid used in the iron removal step, for example, sulfonic acid or carboxylic acid may be used, and carboxylic acid is preferable. This is because carboxylic acid has a lower environmental load than sulfonic acid, and therefore can reduce the environmental load during tantalum recovery. As the carboxylic acid, for example, acetic acid, lactic acid, oxalic acid, citric acid and the like can be used, and citric acid is preferable. This is because citric acid is industrially inexpensive and can be mass-produced, and has little toxicity to the human body.

In the tantalum recovery method of the present invention, the iron removal step is performed by replacing the sludge that has undergone the oil removal step with the organic acid, and hydrogen fluoride of 1% (w / v) to 5% (w / v) It may be a step of removing a part of iron by washing with an acid aqueous solution. In this case, tantalum can be recovered with high safety and reduced environmental burden as compared with the case of using a high concentration hydrofluoric acid aqueous solution. At this time, the concentration of the hydrofluoric acid aqueous solution is more preferably 3% (w / v).

  In the tantalum recovery method of the present invention, the alkali solution used in the elution step is preferably an aqueous sodium hydroxide solution. This is because it is industrially inexpensive and can be mass-produced as compared with an aqueous ammonia solution.

In the tantalum recovery method of the present invention, the oil removal step is a step of removing a part of oil from sludge containing tantalum, iron and oil by hydrothermal treatment in the presence of hydrogen peroxide water instead of the hydrothermal treatment. may I Oh. In this way, hydrothermal treatment can be performed at a lower temperature than when no hydrogen peroxide solution is added, which contributes to energy efficiency.

  In the tantalum recovery method of the present invention, the recovery step includes adding an alkaline solution to the solution obtained in the elution step, and then adding a cationic polymer flocculant to precipitate and collect tantalum. Also good. At this time, as the cationic polymer flocculant, for example, polymethacrylate is preferable. This is because by adding the polymethacrylic acid ester, the precipitate aggregates, and the process time required for the recovery process can be shortened.

  According to the tantalum recovery method of the present invention, high-concentration tantalum can be produced in a high yield, safe, and environmentally friendly without performing high-risk high-temperature dry evaporation or dissolution treatment with high-concentration hydrofluoric acid. Tantalum can be recovered by reducing Such tantalum recovery is possible because the oil content can be sufficiently removed from the oil-containing sludge by performing the hydrothermal treatment in the oil removal step, and the oil-containing sludge by performing the hydrothermal treatment in the elution step. The inventors think that this is because it is possible to elute even when oil remains in the oil.

  Next, a tantalum recovery method for recovering tantalum from oil-containing sludge containing tantalum, which is an example of an embodiment of the present invention, will be briefly described. The tantalum recovery method of the present invention mainly comprises an oil removal step of hydrothermally treating oil-containing sludge containing tantalum, a deironing step of washing the oil-containing sludge subjected to hydrothermal treatment in the oil removal step with an organic acid, An elution step of hydrothermally treating the solid material obtained in the iron step, and a recovery step of adding an alkaline solution to the solution obtained in the elution step.

(1) Oil content removal process In the oil content removal process, the oil-containing raw material containing lithium tantalate (hereinafter referred to as "LT") was allowed to stand on a wire mesh on which filter paper was placed. At this time, the time for standing on the wire mesh is preferably 3 days or more and 14 days or less, and more preferably 5 days or more and 10 days or less with respect to 25 kg of the oil-containing raw material. Less than 3 days is not preferable because the oil cannot be sufficiently removed, and the oil is sufficiently removed in 14 days. Therefore, it is not necessary to leave it for a longer period than 14 days. By doing so, much of the oil being reduced is dripped below the wire mesh.

  Next, the solid remaining on the filter paper was hydrothermally treated to obtain a solid. At this time, the temperature for performing the hydrothermal treatment is preferably 100 ° C. or higher and 250 ° C. or lower, and more preferably 130 ° C. or higher and 220 ° C. or lower. Moreover, as time to perform a hydrothermal treatment, 30 minutes or more and 10 hours or less are preferable, and 1 hour or more and 6 hours or less are more preferable.

(2) Deironing step The solid obtained in the oil removal step was put into an aqueous solution containing an organic acid warmed at about 50 ° C and stirred, and then filtered to obtain a solid on the filter paper. This solid was repeatedly washed with water until the pH was in the range of 6.0 to 7.0 and dried to obtain a dry solid.

  As the organic acid used here, for example, sulfonic acid or carboxylic acid may be used, and carboxylic acid is preferable. Since carboxylic acid has a lower environmental load than sulfonic acid, it is preferable because the environmental load during tantalum recovery can be reduced. As the carboxylic acid, for example, acetic acid, lactic acid, oxalic acid, citric acid and the like can be used, and citric acid is preferable. This is because citric acid is industrially inexpensive and can be mass-produced, and has little toxicity to the human body.

  In addition, an acid such as hydrochloric acid, sulfuric acid, or nitric acid may be used instead of the organic acid, and preferably hydrochloric acid or nitric acid may be used. Hydrochloric acid and nitric acid are preferable because they do not contain sulfur (elemental sulfur), and therefore the possibility of redissolving tantalum hydroxide when the tantalum hydroxide is recovered can be reduced.

  Further, when citric acid is used as the organic acid, the temperature is preferably 30 ° C. or higher and 80 ° C. or lower, and more preferably 40 ° C. or higher and 70 ° C. or lower. In addition, the amount of citric acid is preferably 20 g or more and 250 g or less, more preferably 40 g or more and 200 g or less with respect to 6 liters of warm water.

(3) Elution process 3 liters of 3% (w / v) hydrofluoric acid aqueous solution was added to 300 g of the dry solid obtained in the iron removal process, hydrothermally treated, and separated into a solid and a filtrate. This solid was repeatedly washed with water until the pH was in the range of 6.0 to 7.0, and the washing solution and the filtrate were collected as a mixed solution. The inventors believe that during this hydrothermal reaction, LT and hydrofluoric acid contained in the dry solid were eluted into the solution (filtrate and washing solution) by the reaction represented by the following formula (2). .

  At this time, the ratio of the dry solid to the hydrofluoric acid aqueous solution is preferably 100 g or more and 600 g or less, for example, with respect to 3 liters of 3% (w / v) hydrofluoric acid aqueous solution. 200 g or more and 400 g or less is more preferable. Even if the weight of the dry solid is less than 100 g, LT can be eluted, but the weight of LT that can be eluted with respect to the hydrofluoric acid aqueous solution may be reduced, which is not efficient. On the other hand, even if the weight of the dry solid is more than 600 g, LT can be eluted, but LT in the dry solid may not be sufficiently eluted. Becomes lower. Moreover, as temperature which performs a hydrothermal treatment, 100 degreeC or more and 250 degrees C or less are preferable, and 130 degreeC or more and 220 degrees C or less are more preferable. Moreover, as time to perform a hydrothermal treatment, 30 minutes or more and 10 hours or less are preferable, and 1 hour or more and 6 hours or less are more preferable.

  The concentration of the hydrofluoric acid aqueous solution at this time is not limited to 3% (w / v), but preferably 0.5% (w / v) to 7% (w / v). % (W / v) or more and 5% (w / v) or less is preferable. This is because the environmental load increases as the concentration of hydrofluoric acid increases.

(4) Recovery step An alkali was added to the mixed solution obtained in the elution step until the pH reached 9.0, and the mixture was allowed to stand to obtain a white precipitate. The operation of discarding the supernatant, dispersing the white precipitate and allowing to stand is repeated until the pH of the supernatant is about 7.0, and the white precipitate is filtered and dried to recover a white solid containing tantalum. did. The inventors consider that the main component of the white solid is tantalum hydroxide, and the reaction at this time is not clear, but is considered to be a reaction represented by the following formula (2).

  The alkali used here may be, for example, a 25% (w / w) aqueous sodium hydroxide solution or a 25% (w / w) aqueous ammonia solution. The concentration of the aqueous sodium hydroxide solution is not limited to 25% (w / w), and may be 3% (w / w) or more and 40% (w / w) or less, and 5% (w / W) or more and 40% (w / w) or less. Further, the pH of the mixed solution at this time is not limited to 9.0, and may be 7.5 or more and 11 or less, or may be 8.0 or more and 11 or less.

  Next, an example of the tantalum recovery method of the present invention will be described by dividing it into four steps: (1) oil removal step, (2) deironing step, (3) elution step, and (4) recovery step.

(1) Oil content removing step First, 100 kg of sludge containing LT processing waste was used as a raw material. This sludge contains 1400 liters of oil (grinding oil), 2000 kg of SiC abrasive grains, 500 to 800 kg of LT, and 100 kg of wire scrap (iron). 25 kg of this sludge was placed on a wire net having a filter paper on the upper surface and allowed to stand for one week. By so doing, most of the oil can be dropped below the wire mesh and much of the oil in the sludge can be removed. 400 g of the sludge after standing still enough until there is no oil remaining on the sludge is taken and placed in a 5 liter hydrothermal vessel with a stirring mechanism (OML-5, OML Labtech Co., Ltd.), 3 liters Was added and sealed, and hydrothermal treatment was performed at a temperature of 150 ° C. for 2 hours. In this hydrothermal treatment, the internal pressure at 150 ° C. was 0.46 MPa. After hydrothermal treatment, the container was naturally cooled until the temperature in the container reached 90 ° C., and then forcedly cooled to room temperature to recover the solid and liquid in the container. The liquid collected here was filtered, and the solid matter containing LT remaining on the filter paper was collected as oil-removed sludge. At this time, the ratio of oil contained in the oil removal sludge (hereinafter referred to as “oil content”) was measured and found to be 3.6% (w / w).

Here, the method for measuring the oil content will be described in detail. When measuring the amount of oil, put an appropriate amount of the target sample in a magnetic crucible whose weight (W ₀ ) has been measured in advance, weigh the crucible with the target sample in it, and obtain the total weight (W ₁ ) It was. Next, the crucible containing the target sample was placed in an electric furnace and baked at 700 ° C. for 1 hour. Next, after removing the crucible from the electric furnace and cooling it to room temperature in the desiccator, the weight of the crucible was measured to obtain the weight after firing (W ₂ ). Finally, these weights were applied to the following formula (1) to calculate the oil content (W). In the following, the oil content was measured in the same manner.

(2) Deironing step The oil removal sludge obtained in the oil removal step was placed in 6 liters of warm water heated to about 50 ° C., 100 g of citric acid was added with stirring, and the mixture was held for 6 hours. By doing so, iron contained in the oil-removed sludge reacts with citric acid, and iron is removed as iron citrate. After 6 hours, the solid component containing LT was filtered off, washed repeatedly with water until the pH was in the range of 6.0 to 7.0, and dried to obtain 16.6 kg of deiron-dried solid. Obtained. At this time, when the amount of oil contained in the deiron-dried solid was measured, it was 3.6% (w / w).

(3) Elution step 500 g of the deiron-free dried solid obtained in the iron removal step is weighed and placed in a 5 liter hydrothermal vessel with a stirring mechanism (OML-5, manufactured by OM Lab Tech Co., Ltd.). w / v) Hydrofluoric acid aqueous solution was added and sealed, and hydrothermal treatment was performed at a temperature of 150 ° C. for 6 hours. In this hydrothermal treatment, the maximum pressure during the treatment was 0.48 MPa. After the hydrothermal treatment, the temperature in the container was naturally cooled to 90 ° C., then forcedly cooled to room temperature, and then filtered into a filtrate and a solid material in which LT was dissolved. This solid was repeatedly washed with water until the pH was in the range of 6.0 to 7.0, and a mixed solution containing LT in which the washed water and the filtrate were mixed was obtained. At this time, since SiC contained in the deiron-dried solid does not react with hydrofluoric acid, it remains mainly in the solid, whereas LT reacted with hydrofluoric acid and dissolved in the solution. The inventors are thinking.

(4) Recovery step Water (6 liters) is added to the mixed solution (6 liters) obtained in the elution step, and 25% (w / v) sodium hydroxide aqueous solution is added while stirring until the pH reaches 9.0. did. At this time, a white precipitate was precipitated from around pH 7.0. Stirring was stopped when the pH of the solution was 9.0, and the solution was allowed to stand to sufficiently settle the white precipitate, and the supernatant was removed. Subsequently, an operation of changing to a 25% (w / v) aqueous sodium hydroxide solution and washing with 6 liters of water, allowing the precipitate to settle, and removing the supernatant is performed until the pH of the supernatant reaches 7.0. After repeating, the white precipitate was filtered off and dried to recover a white solid containing tantalum.

(5) Component analysis Fluorescent X-ray analyzer (Rigaku) for each of the deiron dry solid obtained in the iron removal step, the washed solid obtained in the elution step and the white solid obtained in the recovery step. Elemental analysis was performed using a product number: ZSX-101s. The results obtained at this time are shown in Table 1 below.

  From the measurement results of the deiron-dried solid in Table 1, it is clear that 0.4% iron element is contained in the de-iron dry solid. Since sludge contained wire scrap (iron), it can be said that it was sufficiently removed by the iron removal process. Moreover, from the measurement result of tantalum in Table 1, it is clear that the proportion of tantalum, which was 30.9% in the deiron-dried solid, is reduced to 2.23% in the solid. . From this, it can be said that 28.67% of tantalum could be eluted in the elution step by hydrothermal treatment. Furthermore, from the measurement result of the white solid in Table 1, it is clear that 90.3% of tantalum is contained in the white solid and tantalum is contained in the white solid with high purity. From this, it can be said that this tantalum recovery method was able to recover high-purity tantalum from oil-containing sludge without using a high-risk high-temperature drying step and high-concentration hydrofluoric acid with a high environmental load. .

  Subsequently, another example of the tantalum recovery method of the present invention will be described by dividing it into four steps: (1) oil removal step, (2) deironing step, (3) elution step, and (4) recovery step.

(1) Oil removal step The oil removal step of Example 1 except that 3 liters of water added during the hydrothermal treatment of Example 1 was changed to 3 liters of 3% (w / v) hydrogen peroxide solution. In the same manner as described above, an oil removing sludge was obtained. At this time, in the hydrothermal treatment, the internal pressure at 150 ° C. was 4 MPa. The amount of oil contained in the oil removal sludge was measured and found to be 1.7% (w / w).

(2) Deironing step In the same manner as in the deironing step of Example 1, 16.2 kg of deironed and dried iron free solid was obtained. At this time, when the amount of oil contained in the deiron-dried solid was measured, it was 1.7% (w / w).

(3) Elution process It carried out similarly to the elution process of Example 1, and collect | recovered the mixed solution containing a solid substance and LT. The maximum pressure during hydrothermal treatment was 0.47 MPa.

(4) Recovery step In the same manner as in the recovery step of Example 1, a white solid was obtained.

(5) Component analysis Next, in the same manner as in Example 1, each of the deiron-dried solid obtained in the deiron process, the solid obtained in the elution process, and the white solid obtained in the recovery process. Component analysis was performed. The results obtained at this time are shown in Table 2 below.

  From the measurement results of the deiron-dried solid in Table 2, it is clear that 0.48% iron element is contained in the de-iron dry solid. Since sludge contained wire scrap (iron), it can be said that it was sufficiently removed by the iron removal process. Moreover, from the measurement result of tantalum in Table 2, it is clear that the ratio of tantalum, which was 30.6% in the deiron-dried solid, is reduced to 2.43% in the solid. . From this, it can be said that 28.17% of tantalum could be eluted in the elution step by hydrothermal treatment. Furthermore, from the measurement result of the white solid in Table 2, it is clear that 93.2% of tantalum is contained in the white solid and tantalum is contained in the white solid with high purity. From this, it can be said that this tantalum recovery method was able to recover high-purity tantalum from oil-containing sludge without using a high-risk high-temperature drying step and high-concentration hydrofluoric acid with a high environmental load. .

  Subsequently, another example of the tantalum recovery method of the present invention will be described by dividing it into four steps: (1) oil removal step, (2) deironing step, (3) elution step, and (4) recovery step.

(1) Oil content removal process In the same manner as in Example 1, 100 kg to 25 kg of sludge was placed on a wire net having filter paper placed on the upper surface, and allowed to stand for one week. By so doing, most of the oil can be dropped below the wire mesh and much of the oil in the sludge can be removed. 400 g of the sludge after standing still enough until there is no oil remaining on the sludge is taken and placed in a 5 liter hydrothermal vessel with a stirring mechanism (OML-5, OML Labtech Co., Ltd.), 3 liters 3% (w / v) of hydrogen peroxide was added and sealed, followed by hydrothermal treatment at 150 ° C. for 2 hours. At this time, the valve at the top of the container was released from room temperature to 100 ° C. so that the internal pressure did not increase, and the valve was closed and sealed from 100 ° C. The internal pressure at 150 ° C. was 0.42 MPa. After hydrothermal treatment, the container was naturally cooled until the temperature in the container reached 90 ° C., and then forcedly cooled to room temperature to recover the solid and liquid in the container. The liquid collected here was filtered, and the solid matter containing LT remaining on the filter paper was collected as oil-removed sludge. At this time, when the amount of oil contained in the oil removal sludge was measured, it was 1.42% (w / w).

(2) Deironing step In the same manner as in the deironing step of Example 1, 16.4 kg of deironed and dried iron free solid was obtained. At this time, when the amount of oil contained in the deiron-dried solid was measured, it was 1.42% (w / w).

(3) Elution process It carried out similarly to the elution process of Example 1, and collect | recovered the mixed solution containing a solid substance and LT. The maximum pressure during hydrothermal treatment was 0.46 MPa.

(4) Recovery step In the same manner as in the recovery step of Example 1, a white solid was obtained.

(5) Component analysis Next, in the same manner as in Example 1, each of the deiron-dried solid obtained in the deiron process, the solid obtained in the elution process, and the white solid obtained in the recovery process. Component analysis was performed. The results obtained at this time are shown in Table 3 below.

  From the measurement results of the deiron-dried solid in Table 3, it is clear that 0.45% iron element is contained in the de-iron dry solid. Since sludge contained wire scrap (iron), it can be said that iron was sufficiently removed by the deironing process. Moreover, from the measurement result of tantalum in Table 3, it is clear that the proportion of tantalum, which was 25.4% in the deiron-dried dry solid, is reduced to 2.07% in the solid. . From this, it can be said that 23.47% of tantalum could be eluted in the elution step by hydrothermal treatment. Furthermore, from the measurement result of the white solid in Table 3, it is clear that 96.1% of tantalum is contained in the white solid, and tantalum is contained in the white solid with high purity. From this, it can be said that this tantalum recovery method was able to recover high-purity tantalum from oil-containing sludge without using a high-risk high-temperature drying step and high-concentration hydrofluoric acid with a high environmental load. .

Comparative Example 1

  Subsequently, a comparative example for comparison with the tantalum recovery method of the present invention is divided into four steps: (1) pretreatment step, (2) firing step, (3) elution step, and (4) recovery step. To do.

(1) Pretreatment step First, in the same manner as in Example 1, 25 kg of sludge was placed on a wire net having a filter paper placed on the upper surface and allowed to stand for one week. By so doing, most of the oil can be dropped below the wire mesh and much of the oil in the sludge can be removed. 4 kg of the sludge that has been allowed to stand until there is no oil remaining on the sludge is taken, poured into 60 liters of warm water heated to 50 ° C., stirred, and a surfactant (eg, alkyl A suitable amount of amine oxide) was added, and the mixture was further stirred for 24 hours and filtered to obtain an intermediate.

  Next, the intermediate was put into 60 liters of warm water heated to 50 ° C., 300 g of concentrated sulfuric acid was added with stirring, and the mixture was further stirred for 8 hours. After stirring for 8 hours, filtration and washing with water were repeated to obtain an oil removing sludge. The dry weight of the oil-removed sludge was measured and found to be 2.2 kg. The amount of oil contained in the oil removal sludge was measured and found to be 3.45% (w / w).

(2) Firing step The oil-removed sludge was placed on an alumina shelf, placed in a firing furnace, and fired at 700 ° C for 1 hour to obtain a deiron-dried solid. The weight of the deiron-dried solid was measured and found to be 2 kg. Moreover, it was 0.97% (w / w) when the amount of oil contained in a deiron removal dry solid was measured.

(3) Elution step 300 g of the deiron-dried solid obtained in the firing step was weighed, placed in 3 liters of 55% hydrofluoric acid, and stirred for 5 days. After stirring for 5 days, the filtrate was separated into a filtrate in which LT was dissolved and a solid substance. Next, this solid was repeatedly washed with water until the pH was in the range of 6.0 to 7.0, and a mixed solution containing LT in which the washed water and the filtrate were mixed was obtained.

(4) Recovery step In the same manner as in the recovery step of Example 1, a white solid was obtained.

(5) Component analysis Next, in the same manner as in Example 1, each of the deiron-dried solid obtained in the firing step, the solid obtained in the elution step, and the white solid obtained in the recovery step, Component analysis was performed. The results obtained at this time are shown in Table 4 below.

  From the measurement results of the deiron-dried solid in Table 4, it is clear that 0.23% iron element is contained in the de-iron dry solid. Since sludge contained wire scrap (iron), it can be said that iron was sufficiently removed in the pretreatment process. Moreover, from the measurement result of tantalum in Table 4, it is clear that the ratio of tantalum, which was 23.2% in the deiron-dried dry solid, is reduced to 6.43% in the solid. . From this, it can be said that 16.77% of tantalum could be eluted in the elution process using high concentration (55%) hydrofluoric acid. However, the measurement result of the white solid in Table 4 clearly shows that the white solid contains only 4.1% of tantalum and the white solid contains almost no tantalum. . From this, it can be said that the tantalum recovery method of Comparative Example 1 cannot recover tantalum with high purity.

Comparative Example 2

  Subsequently, another comparative example for comparison with the tantalum recovery method of the present invention is divided into four steps: (1) pretreatment step, (2) firing step, (3) elution step, and (4) recovery step. I will explain.

(1) Pretreatment step In the same manner as in Comparative Example 1, an oil removing sludge was obtained. The amount of oil contained in the oil removal sludge was measured and found to be 3.45% (w / w).

(2) Firing step In the same manner as in Comparative Example 1, a deiron-dried solid was obtained. The amount of oil contained in this deiron-dried solid was measured and found to be 0.97% (w / w).

(3) Elution step A solid was obtained in the same manner as in Comparative Example 1, except that 3 liters of 55% hydrofluoric acid was changed to 3 liters of 3% hydrofluoric acid.

(4) Recovery step A white solid was obtained in the same manner as in Example 1 except that a white precipitate was formed as soon as the aqueous sodium hydroxide solution was added.

(4) Component analysis Next, in the same manner as in Example 1, each of the deiron-dried solid obtained in the pretreatment step, the solid obtained in the elution step, and the white solid obtained in the recovery step. Component analysis was performed. The results obtained at this time are shown in Table 5 below.

  From the measurement results of the deiron-dried solid in Table 5, it is clear that the iron-free dry solid contains only 0.23% of iron element. Since sludge contained wire scrap (iron), it can be said that iron was sufficiently removed in the pretreatment process. Moreover, from the measurement result of tantalum in Table 5, the ratio of tantalum that was 23.2% in the deiron-dried solid was 20.7% in the solid, and tantalum was sufficiently eluted in the elution process. It is clear that it was not done. Furthermore, from the measurement result of the white solid in Table 5, it is clear that only 63.3% of tantalum is contained in the white solid, and the tantalum contained in the white solid is small. From this, it can be said that the tantalum recovery method of Comparative Example 2 cannot recover tantalum with high purity.

Comparative Example 3

  Subsequently, another comparative example for comparison with the tantalum recovery method of the present invention will be described. The tantalum recovery method of Comparative Example 3 was the same as Comparative Example 1 except that the firing step was not performed. Each thing was obtained. At this time, when the amount of oil contained in the solid 132 was measured, it was 7.8% (w / w). Moreover, about each, component analysis was performed by the method similar to Example 1, and the result obtained at this time is shown in the following Table 6.

  From the measurement results of the deiron-dried solid in Table 6, it is clear that 0.25% iron element is contained in the de-iron dry solid. Since sludge contained wire scrap (iron), it can be said that iron was sufficiently removed in the pretreatment process. Moreover, from the measurement result of tantalum in Table 6, the ratio of tantalum which was 27% in the deiron-dried solid was 24.4% in the solid, and tantalum was sufficiently eluted in the elution step. Clearly not. Furthermore, from the measurement result of the white solid in Table 6, it is clear that the white solid contains only 2.5% of tantalum and the tantalum contained in the white solid is small. From this, it can be said that the tantalum recovery method of Comparative Example 3 cannot recover tantalum with high purity.

Next, for each of Examples 1 to 3 and Comparative Examples 1 to 3, the elution rate of tantalum, the purity of recovered tantalum, and the process time required to recover tantalum were calculated, and the respective oil content In addition, the results are shown in Table 7 below. The tantalum elution rate (W _Ta ) was calculated by applying the following equation (2), where Wa is the mass percent of tantalum in the deiron-dried solid and Wa is the mass percent of tantalum in the solid. Further, the purity of tantalum was calculated by using the mass percentage of tantalum in the white solid, and the process time was calculated by adding the times for each process time.

  Comparing the results of Examples 1 to 3 and the results of Comparative Examples 1 to 3, by using the tantalum recovery method of this example, high-purity tantalum of 90% or more is obtained in a high yield of 90% or more. And it can collect | recover in half or less process time compared with Comparative Examples 1-3. At this time, neither a high-risk high-temperature drying process nor high-concentration hydrofluoric acid with high environmental load is used.

  Moreover, when Example 1 is compared with Example 2 and Example 3, compared with Example 1, the amount of oil in Example 2 and Example 3 is reduced, and the purity of the recovered tantalum is increased. Is clear. From this, it can be said that by adding hydrogen peroxide water in the oil removing step, the oil could be removed more than in the case of water. Further, since the purity of tantalum is increased by reducing the amount of oil, the inventors consider that tantalum having higher purity can be recovered by reducing the amount of oil before the dissolution treatment step. ing.

  Furthermore, when Examples 1 to 3 and Comparative Example 3 are compared, it is clear that Examples 1 to 3 have less oil than Comparative Example 3. From this, it can be said that the oil content can be sufficiently reduced by the oil removal process using hydrothermal treatment without performing the firing process performed in Comparative Example 1 and Comparative Example 2. In the firing process of Comparative Example 1 and Comparative Example 2, there is a risk of ignition etc. by firing a solid containing oil at a high temperature, but it is safer than performing the firing process by performing the oil removing process. It can be said that oil can be removed.

  Furthermore, when Comparative Example 1 and Comparative Example 2 were compared, Comparative Example 1 was able to recover 72.2% of tantalum, whereas Comparative Example 2 was recovering only 10.8% of tantalum. I couldn't. From this, it can be said that the conventional tantalum recovery method cannot recover tantalum at a high recovery rate unless high concentration hydrofluoric acid is used. On the other hand, comparing this result with the results of Examples 1 to 3, it is clear that in Examples 1 to 3, tantalum could be recovered at a higher recovery rate than in Comparative Examples 1 to 3. From this, it can be said that tantalum acid could be recovered at a high recovery rate without using chemicals with high risk of hydrofluoric acid and high environmental load.

  As shown in the above-described embodiment, the present invention can be used as a rare metal recovery field, particularly as a tantalum recovery method.

Claims (8)

In a tantalum recovery method for recovering tantalum from sludge containing lithium tantalate, iron and oil,
An oil removal step of removing a part of the oil from the sludge containing tantalum, iron and oil by hydrothermal treatment;
Washing the sludge that has undergone the oil removal step with an organic acid, and removing iron from the iron removal step;
An elution step of eluting a solution containing tantalum from the sludge that has undergone the iron removal step by hydrothermal treatment in the presence of hydrofluoric acid ,
A recovery step of adding an alkaline solution to the solution obtained in the elution step to precipitate and recover a salt containing tantalum;
including,
Tantalum recovery method. The organic acid is a carboxylic acid,
The tantalum recovery method according to claim 1 . The carboxylic acid is citric acid.
The tantalum recovery method according to claim 2 . In the iron removal step, the sludge that has undergone the oil removal step is washed with an aqueous hydrofluoric acid solution of 1% (w / v) or more and 5% (w / v) or less , instead of the organic acid, Is a step of removing a part of
The tantalum recovery method according to claim 1 . The alkaline solution is an aqueous sodium hydroxide solution.
The tantalum recovery method according to any one of claims 1 to 4 . The oil removal step is a step of removing a part of oil from sludge containing tantalum, iron and oil by hydrothermal treatment in the presence of hydrogen peroxide water instead of the hydrothermal treatment.
The tantalum recovery method according to any one of claims 1 to 5 . In the recovery step, after adding an alkaline solution to the solution obtained in the elution step, a cationic polymer flocculant is added, and tantalum is precipitated and recovered.
The tantalum recovery method according to any one of claims 1 to 6 . The cationic polymer flocculant is polymethacrylate.
The tantalum recovery method according to claim 7 .