JP3303066B2 - How to purify scandium - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for purifying scandium, and more particularly to a method for effectively removing impurities such as uranium and thorium contained in crude scandium.

[0002]

2. Description of the Related Art Scandium (Sc) is an element that is expected to be widely used as a raw material for catalysts, phosphors, and superconducting materials. Further, when scandium is added to aluminum in an amount of about 0.01 to 1%, its strength is improved. Therefore, it is recently used as a gate electrode material and a wiring material of a semiconductor in addition to an aluminum-based target material. Scandium is contained in the crust at about 25 ppm, but single ore containing high concentrations is small in type and yield,
It is mainly obtained from uranium or tungsten refining residues. As a method for selectively separating and recovering scandium from such scouring residue, a solvent extraction method using an organic phosphorus compound such as tributyl phosphate (JP-A-59-164)
No. 538) and an adsorption method using a chelating resin (Japanese Patent Laid-Open No. 1-1081)
No. 18) and a method of adsorbing scandium or the like on a cation exchange resin and then eluting only scandium with a chelating agent (Japanese Patent Application Laid-Open No. 1-502976).

However, leaching residues or tungsten leaching residues in uranium ore generally contain a considerable amount of uranium (U) and / or thorium (Th). In particular, thorium has a chemical behavior similar to that of scandium, and is generally used. Separation is difficult with a manual operation. For example, among the above-mentioned conventional methods, the solvent extraction method has low selectivity to scandium, so multi-step operation is required to obtain high-purity scandium, and a large amount of an organic phosphorus solvent is used. , And considerable thorium remains after multiple extractions. The method of adsorbing and recovering scandium using a chelating resin (Japanese Patent Laid-Open No. 1-108118)
After a scandium-containing solution such as a tungsten leaching residue is treated with ether, it is brought into contact with a specific chelating resin, and after selectively adsorbing scandium, an eluent is passed through the resin to release the adsorbed scandium. No consideration is given to the separation of thorium that is inevitably adsorbed together with the thorium.

A method using a cation exchange resin (Japanese Patent Application Laid-Open No. 1-502976) discloses a method in which a scandium-containing liquid is passed through a cation exchange resin to adsorb the scandium to the resin, and thorium which is inevitably adsorbed together with the scandium is removed. After separation, a specific eluent is passed through the resin to separate it, leaving thorium on the resin to selectively elute scandium from the resin.However, this method also reduces thorium etc. to a level of several ppm. This is the limit, and in particular, trying to recover 90% or more of scandium results in thorium contamination of several hundred ppm or more. In fact, when analyzing commercially available 4N-class scandium oxide, several to several tens of ppm of uranium and thorium are detected. Therefore, when a highly integrated circuit is manufactured using scandium obtained by these methods as an aluminum-based target material, there is a concern that radiation emitted from uranium or thorium as an impurity in scandium may cause malfunction of the circuit. There is. Further, the method using a chelate resin and a cation exchange resin is a method in which scandium is adsorbed on the resin, and in order to purify and recover scandium, a step of further eluting scandium from the resin is required. It takes time.

[0005]

SUMMARY OF THE INVENTION The present invention provides a substantially simple operation of a scandium to a level at which impurities in the scandium do not cause circuit malfunction even when used in an aluminum target for a semiconductor circuit. It is an object of the present invention to provide a purification method for removing impurity uranium and thorium.

[0006]

The present inventors have studied the chemical behavior of scandium, thorium and uranium in the acidic region, and found that by adding an appropriate acid to a solution containing these elements, thorium and thorium, which are impurities, were added. They found that it was possible to selectively convert uranium to anions, and succeeded in obtaining high-purity scandium by adsorbing these impurities on an anion exchange resin. ADVANTAGE OF THE INVENTION According to this invention, the scandium which reduced the impurity concentration of thorium and uranium to the ppb level which is orders of magnitude lower than the conventional method which adsorbs scandium to a specific resin can be obtained.

That is, according to the present invention, there is provided a method for purifying scandium having the following constitution. (1) Dissolving crude scandium in nitric acid having a concentration of 4N or more, bringing the nitric acid solution into contact with an anion exchange resin, adsorbing the thorium as an impurity dissolved in the liquid onto the resin, and removing the thorium from the scandium solution. A method for purifying scandium, which is a feature. (2) The purification method according to (1), wherein nitric acid having a normality of 5 to 9N is used. (3) The purification method according to the above (1) or (2), wherein an anion exchange resin is used in a volume ratio of 10% or more with respect to the amount of the processing solution. (4) When uranium is contained together with thorium in the crude scandium, (a) after separating and removing thorium from the crude scandium by the method of claim 1, a scandium precipitate is recovered from the scandium solution, and the precipitate is added to hydrochloric acid. Dissolve and contact this hydrochloric acid solution with an anion exchange resin to remove uranium dissolved in the solution from the scandium solution by adsorbing to the resin, or (b) dissolve crude scandium in hydrochloric acid, Is brought into contact with an anion exchange resin, uranium dissolved in the solution is adsorbed to the resin and removed from the scandium solution. Then, a scandium precipitate is recovered from the scandium solution and dissolved in nitric acid having a concentration of 4 N or more. A method for purifying scandium, wherein thorium is separated and removed by the method of claim 1. (5) After bringing the scandium solution into contact with an anion exchange resin to remove thorium or uranium as impurities, adjust the pH of the solution, and then add oxalic acid or hydrofluoric acid to convert the scandium in the solution to oxalate or hydrofluoric acid. The method for purifying scandium according to any one of (1) to (4), wherein the precipitate is precipitated as a compound, and the precipitate is collected, washed, dried, and fired to produce high-purity scandium oxide. (6) After removing the impurities thorium or uranium by bringing the scandium solution into contact with an anion exchange resin, adjusting the pH of the solution, adding ammonium carbonate to precipitate the scandium in the solution as scandium carbonate, and recovering the precipitate. The method for purifying scandium according to any one of the above (1) to (4).

[0008]

FIG. 1 shows an outline of the purification method of the present invention. As shown in the figure, the method of the present invention uses crude scandium oxide as a raw material, (1) dissolving crude scandium in nitric acid, and contacting this with an anion exchange resin to remove thorium dissolved in the liquid; (2) a step of converting the scandium solution into a hydrochloric acid solution and contacting the solution with an anion exchange resin to remove uranium dissolved in the solution; and (3) removing thorium or uranium, and then removing scandium. A recovery step of producing a soluble salt, recovering the same, washing and baking to obtain purified scandium. The uranium removal step is necessary when crude scandium as a raw material contains uranium, and uranium can be removed to some extent in the recovery step, so that the above (2) can be omitted.
Further, the step (2) may be performed prior to the step (1).

The crude scandium to be treated is not particularly limited, and the present invention can be applied to crude scandium obtained from ore leaching residue. Typical examples include scandium oxide obtained from alkali leaching residue of iron-manganese heavy stone concentrate in tungsten refining or acid leaching residue in uranium refining. Preliminary purification is preferably performed by known means to reduce the concentration of impurities containing uranium and thorium to about 10 ppm in advance.

(1) Thorium Removal Step In the method of the present invention, the above-mentioned crude scandium is dissolved in nitric acid having a concentration of 4 N or more, and then contacted with an anion exchange resin. In a nitric acid solution, thorium forms an anion complex, whereas scandium does not form an anion complex.Thus, when this scandium nitrate solution is passed through an anion exchange resin, scandium remains in the solution, but thorium does not. Since it is adsorbed by the anion exchange resin, it can be separated from scandium. When sulfuric acid or hydrochloric acid is used instead of nitric acid, the effect of the present invention is not exhibited. In other words, when crude scandium is dissolved in sulfuric acid, scandium,
Since all of thorium forms an anion complex, both are adsorbed on the anion exchange resin, and thorium cannot be separated from scandium. On the other hand, when crude scandium is dissolved in hydrochloric acid, neither scandium nor thorium forms an anion complex, so that both pass through the anion exchange resin and thorium cannot be separated from scandium. On the other hand, when dissolved in a nitric acid solution, as described above, thorium forms an anion complex, but scandium does not form an anion complex. Only thorium is selectively adsorbed on the anion exchange resin and separated from scandium.

The scandium nitrate solution has a nitric acid concentration of 4 N or more, preferably 5 to 9 N. Nitric acid concentration is 4N
If it is less than uranium or thorium which is not adsorbed when the treatment liquid is passed through the anion exchange resin, the effect of removing these impurities is reduced. If the nitric acid concentration is 5N or more, the removal rate of thorium is remarkably improved, and the thorium content in the recovered scandium can be suppressed to about 30 ppb or less. On the other hand, if the nitric acid concentration exceeds 9 N, the rate of adsorption of thorium on the anion exchange resin decreases, which is not preferable. The liquid temperature of the nitric acid solution is not particularly limited, and may be any liquid temperature depending on processing conditions such as the type of anion exchange resin.

The contact between the scandium nitrate solution and the anion exchange resin is typically carried out by passing a nitric acid solution through a column filled with the resin, but is not necessarily limited to this method. Also, the shape of the resin is not particularly limited,
Various shapes such as a fiber shape, a sheet shape, and a tube shape can be used. Generally, a resin packed in a column or a column with a granular resin having a particle size of about 0.35 to 0.5 mm can be suitably used. When using a column or column, adjust the flow rate so that breakthrough does not occur. Although it depends on the scandium concentration and nitric acid concentration, it is generally 1/10 of the processing solution.
It is preferable to use a resin having a (volume ratio) or more. As the anion exchange resin, those effective under strongly acidic conditions, for example, those having a quaternary ammonium group are preferably used. Examples of such an anion exchange resin include a resin having the following structure. By this ion exchange treatment, the thorium concentration in the effluent is reduced to several tens of ppb or less.

[0013]

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(2) Uranium Removal Step When crude scandium contains uranium, uranium as an impurity can be removed by the following treatment steps. The uranium removal step can be performed before or after the thorium removal step. Specifically, 3N or more hydrochloric acid is added to the scandium-containing liquid to form a hydrochloric acid solution, which is then contacted with an anion exchange resin. In a hydrochloric acid solution, uranium forms an anion complex, whereas scandium does not form an anion complex.Thus, when this scandium hydrochloric acid solution is passed through an anion exchange resin, scandium remains in the solution, but uranium does not. Since it is adsorbed by the anion exchange resin, it can be separated from scandium. The type and amount of the anion exchange resin used in this step are the same as those in the above-described thorium removal step. By this ion exchange treatment, the uranium concentration in the effluent is reduced to several hundred ppb or less.

(3) Step of Recovering Purified Scandium Purified scandium is prepared by adding ammonia water or the like to the effluent that has undergone the above-mentioned ion exchange treatment, adjusting the pH of the solution, and then adding oxalic acid or hydrofluoric acid and stirring. When oxalic acid is used, the pH of the effluent is preferably about 1 to 2;
Add 5-1 N oxalic acid solution. When hydrofluoric acid is used, the pH of the effluent is preferably 3 or less, and a hydrofluoric acid solution of an equivalent amount or more is added. As a result, scandium in the liquid precipitates as oxalate or fluoride, which is hardly soluble in water, and is collected by filtration, washed with ethanol or the like, dried, and calcined at about 800 ° C. to reduce scandium oxide. obtain.

When the crude scandium contains uranium, uranium is also removed by this process of forming a hardly soluble salt. That is, uranium forms a complex with oxalate ions or fluorine ions, most of which remain in solution.
However, since uranium is not sufficiently removed by one precipitation, it is preferable to carry out the ion exchange step (2) or to perform reprecipitation before this step. After the precipitate is formed, the precipitate may be dissolved in hydrochloric acid and reprecipitated through the ion exchange step (2). These methods can ultimately reduce the uranium concentration to about 30 ppb or less. The anion exchange resin adsorbing thorium or uranium can be regenerated by flowing hydrochloric acid having a concentration of about 3N or less. The eluted thorium or uranium is treated according to a conventional method, and collected if necessary.

The purified scandium is recovered by adding ammonia water or the like to the effluent that has undergone the above-mentioned ion exchange treatment.
After adjusting H, ammonium carbonate may be added to precipitate purified scandium in the liquid as scandium carbonate, and the precipitate may be collected. The carbonate ion forms a complex with uranium similarly to the oxalate ion or the fluorine ion, and exists in the solution. On the other hand, scandium also forms a complex with carbonic acid, and this complex decomposes in about 30 minutes when heated to 60 to 70 ° C., resulting in precipitation of scandium carbonate, which can be separated from uranium in the liquid. Since carbonic acid is a weak acid, if the pH is low, it is decomposed into carbon dioxide gas and water and does not produce a carbonate. Therefore, the pH is adjusted to 1-2 by adding aqueous ammonia to a scandium nitrate solution that has undergone ion exchange. Since the scandium carbonate precipitate dissolves easily when the pH is lowered in the nitric acid solution, a purified scandium nitric acid solution can be easily obtained. Therefore, the drying and firing steps can be omitted as compared with the recovery method of recovering and firing hardly soluble scandium oxalate or scandium fluoride, and the entire purification process can be simplified.

[0018]

Examples and Comparative Examples Hereinafter, the present invention will be described in more detail with reference to Examples and Comparative Examples. Note that the present embodiment does not limit the scope of the present invention.

Examples 1 to 4 and Comparative Example 1 7.65 g of crude scandium oxide obtained by treating the acid leaching residue in uranium scouring was put into nitric acid having a normality of 2.5 to 7.5 N and completely dissolved. A scandium nitrate solution was obtained (Sc concentration: 40-50 g / l, impurity concentration U: 0.5 ppm, Th: 0.5
ppm). On the other hand, an ion exchange column packed with 10 g of an anion exchange resin (Taiyaion SA10A manufactured by Mitsubishi Chemical Corporation, 32 to 42 mesh) was prepared, and 4% caustic soda was passed through the column.
Washed deionized water was passed through the anionic groups substantially all OH ^- and, the nitric acid solution was passed through the column at a flow rate of 1 ml / min to the ion exchange column. Purified ammonia water was added to 100 ml of the effluent to adjust the pH to 1, and then 250 ml of an aqueous oxalic acid solution (concentration: 1N) was added with stirring to form a precipitate of scandium oxalate, which was collected by filtration and washed with ethanol. After drying at 120 ° C. for 15 hours and further firing at 800 ° C. for 1 hour, 7.21 g of scandium oxide powder was obtained.

FIG. 2 shows the relationship between the concentration of thorium contained in the scandium oxide and the concentration of nitric acid. As shown in the figure, the sample with a nitric acid concentration of 2.7N (Comparative Example 1) has a high thorium concentration of 3000 ppb, whereas the sample with a nitric acid concentration of 4N (Example 1) has a thorium concentration of 500 ppb, 5N and 7N, 7N. In the case of the 0.5 N sample (Examples 2 to 4), the thorium concentration was below the detection limit (30 ppb), and was significantly reduced.

Examples 5 to 9 The column of Example 1 in which a scandium nitrate solution (Sc concentration: 50 g / l, nitric acid concentration: 6.68 N) obtained in the same manner as in Example 1 was packed with an anion exchange resin (column diameter) 1.27 for φ10cm)
After passing the solution at a linear speed of cm / min, scandium oxide powder was obtained in the same manner as in Example 1. FIG. 3 shows the relationship between the concentration of thorium in the scandium oxide and the amount of the scandium nitrate solution treated in the column. As shown in FIG. 3, a sample having a treatment liquid (ml) / resin (ml) of 10 or less (Example 5)
Nos. To 7) have a thorium concentration of 30 ppb or less, and are particularly excellent in removing effect.

Example 10 The steps from the preparation of the scandium nitrate solution to the contact with the anion exchange resin were carried out in the same manner as in Example 1, and 20 ml of a hydrofluoric acid aqueous solution (concentration: 50%) was added to the effluent with stirring.
The precipitate was added to form a precipitate of scandium fluoride, which was collected by filtration, dried at 250 ° C. for 15 hours, and further dried at 800 ° C.
Calcination was performed for 1 hour at ℃ to obtain 6.9 g of scandium oxide powder. The concentration of uranium remaining in this powder was 200 ppb, and thorium was below the detection limit.

Example 11 4.5 g of scandium oxide obtained in the same manner as in Example 1
Was redissolved in 60 ml of 5N hydrochloric acid. Next, this solution was passed through a column filled with the same anion exchange resin as in Example 1, and 3.8 g of scandium oxide powder was obtained in the same manner as in Example 1. Thorium and uranium remaining in this powder were below the detection limit.

Example 12 7.65 g of crude scandium oxide powder as in Example 1
Was dissolved in 100 ml of 5N hydrochloric acid, and this solution was passed through a column packed with the same anion exchange resin as in Example 1, and the effluent was treated as in Example 1 to obtain 7.35 g of scandium oxide. I got Thorium and uranium remaining in this powder were below the detection limit.

Example 13 7.11 g of scandium oxide obtained in the same manner as in Example 1
Was dissolved in 7N nitric acid, purified ammonia was added, the pH was adjusted, oxalic acid or hydrofluoric acid was added to reprecipitate, and the same treatment as in Example 1 was performed to obtain 6.88 g of scandium oxide. Thorium and uranium remaining in this powder were below the detection limit.

Example 14 Scandium nitrate solution (30 ml) obtained in the same manner as in Example 1
Then, purified ammonia was added thereto, and after adjusting the pH, a solution prepared by dissolving 15 g of ammonium carbonate in 100 ml of water was added. The mixture was kept at 70 ° C. for 30 minutes with stirring to produce a precipitate of scandium carbonate, which was collected by filtration and collected at 120 ° C. After drying for 15 hours, it was further baked at 800 ° C. for 1 hour to obtain 2 g of scandium oxide powder. The concentration of uranium remaining in this powder is 20
0 ppb and thorium was 3000 ppb.

Example 15 Scandium nitrate solution (30 ml) obtained in the same manner as in Example 1
After adjusting the pH by adding purified ammonia, a solution prepared by dissolving 15 g of ammonium carbonate in 100 ml of water was added, and the mixture was kept at 70 ° C. for 30 minutes with stirring to produce a precipitate of scandium carbonate, which was collected by filtration. Then, a small amount of nitric acid was added to this, and it was easily dissolved. After the pH of the solution was adjusted again, a solution prepared by dissolving 15 g of ammonium carbonate in 100 ml of water was added, and the mixture was maintained at 70 ° C. for 30 minutes with stirring to form a precipitate of scandium carbonate.
After drying at 15 ° C. for 15 hours, it was calcined at 800 ° C. for 1 hour to obtain 1.94 g of scandium oxide powder. The concentration of uranium remaining in this powder is below the detection limit, and the thorium concentration is 900
ppb.

Example 16 After the steps from the preparation of the scandium nitrate solution to the contact with the anion exchange resin were performed in the same manner as in Example 1, purified ammonia was added to the effluent, and the pH was adjusted. Was dissolved in 100 ml of water, and the mixture was kept at 70 ° C. for 30 minutes with stirring to form a precipitate of scandium carbonate, which was collected by filtration. Then, a small amount of nitric acid was added to this, and it was easily dissolved. After adjusting the pH of this solution again, 6.8 g of scandium oxide was obtained as an oxalate in the same manner as in Example 1. The concentrations of thorium and uranium remaining in this powder were below the detection limit.

Comparative Example 2 A scandium oxide powder (7.22 g) was obtained in the same manner as in Example 1 except that 5N hydrochloric acid was used in place of nitric acid.
The uranium concentration remaining in this powder was below the detection limit, but the thorium concentration was 4000 ppb, indicating a high thorium concentration.

The following table shows the residual concentrations of uranium and thorium as impurities in the scandium oxides obtained in Examples 3, 10 to 12 and Comparative Example 2.

[Table 1] U (ppb) in oxidized Sc Th (ppb) in oxidized Sc Example 3 300 Detection limit (30 ppb) or less Example 10 200 Same as above Example 11 Detection limit (30 ppb) Same as above Example 12 Same as above Example 13 Same as above Comparative Example 2 Same as above 4000

As shown by these results, the purification method of the present invention has a high removal effect on both uranium and thorium impurities. In particular, Examples 13 and 1 in which reprecipitation was performed
6. In Examples 11 and 12 after the treatment with hydrochloric acid, the concentrations of both uranium and thorium are below the detection limit, and high-purity scandium can be obtained. Also, as shown in Comparative Example 2, when hydrochloric acid was used instead of nitric acid, there was no thorium removal effect, while uranium was removed in the same manner as when nitric acid was used. That is, thorium is not converted to an anion by hydrochloric acid, while uranium is converted to an anion by hydrochloric acid and adsorbed and removed. This is also confirmed by the following experiment.

Experimental Example 1 The same crude scandium as in Example 1 was dissolved in 7N nitric acid, sulfuric acid and hydrochloric acid, respectively, and passed through an anion exchange column under the same conditions as in Example 1. Table 2 shows the analysis results of the element contents in scandium oxide obtained from the column effluent.

[Table 2] Type of acid Sc recovery rate U concentration Th concentration Hydrochloric acid (HCl 94.4% <30 ppb 4 ppm Sulfuric acid (H2SO4) not recovered --- Nitric acid (HNO3) 93.9% 1 ppm <30 ppb

As shown in the results, when sulfuric acid is used as the acid, scandium is adsorbed on the anion exchange resin together with uranium and thorium, and these cannot be effectively separated. However, when nitric acid is used as the acid of the solution, only scandium passes through the anion exchange resin without forming complex ions, so that thorium in scandium can be effectively removed. The use of nitric acid to form uranium complex ions is not always sufficient, but some separation is possible.
On the other hand, when hydrochloric acid is used, scandium and thorium pass through the anion exchange resin without forming complex ions, so that uranium in scandium can be selectively removed.

[0034]

The refining method of the present invention is excellent in the removal rate of thorium and uranium remaining in crude scandium, and the obtained purified scandium is used in fields where low radioactivity is strictly required, such as semiconductor wiring materials. be able to. Also, unlike the conventional method using a special solvent for solvent extraction or a chelating agent, the treatment process is simple, so that thorium and uranium can be separated and removed from scandium at low cost. In addition, the chemicals and resins used are easy to process and regenerate, so they are economical and minimize the environmental impact of the practice of the invention.

[Brief description of the drawings]

FIG. 1 is a process chart showing an outline of the method of the present invention.

FIG. 2 is a graph showing the relationship between nitric acid concentration and Th concentration.

FIG. 3 is a graph showing a relationship between a processing solution amount and a Th concentration.

Claims (6)

(57) [Claims] A crude scandium is dissolved in nitric acid having a concentration of 4N or more. The nitric acid solution is brought into contact with an anion exchange resin, and thorium, an impurity dissolved in the solution, is adsorbed by the resin and removed from the scandium solution. A method for purifying scandium, comprising: 2. The method according to claim 1, wherein the normality is 5 to 9 N nitric acid.
Purification method described in 1. 3. The purification method according to claim 1, wherein an anion exchange resin is used in a volume ratio of 10% or more with respect to the amount of the processing solution. 4. When the crude scandium contains uranium together with thorium, (a) after separating and removing thorium from the crude scandium by the method of claim 1, a scandium precipitate is recovered from the scandium solution;
This is dissolved in hydrochloric acid, this hydrochloric acid solution is brought into contact with an anion exchange resin, and uranium dissolved in the solution is adsorbed on the resin and removed from the scandium solution, or (ii) crude scandium is dissolved in hydrochloric acid. After bringing the hydrochloric acid solution into contact with an anion exchange resin and adsorbing uranium dissolved in the solution to remove the uranium from the scandium solution, the scandium precipitate is recovered from the scandium solution, and the concentration of the scandium precipitate is 4N or more. 2. A method for purifying scandium, wherein the scandium is dissolved in nitric acid, and thorium is separated and removed by the method of claim 1. 5. A scandium solution is brought into contact with an anion exchange resin to remove impurities such as thorium and uranium. After adjusting the pH of the solution, oxalic acid or hydrofluoric acid is added to convert the scandium in the solution to oxalate. The method for purifying scandium according to any one of claims 1 to 4, wherein the precipitate is precipitated as a fluoride, and the precipitate is recovered, washed, dried, and fired to produce high-purity scandium oxide. 6. The scandium solution is brought into contact with an anion exchange resin to remove impurities such as thorium and uranium. After adjusting the pH of the solution, ammonium carbonate is added to precipitate the scandium in the solution as scandium carbonate.
The method for purifying scandium according to claim 1, wherein the precipitate is recovered.