JP5454735B2 - Scandium separation and purification method - Google Patents

Description

  The present invention relates to a method for separating and purifying scandium, and more specifically, scandium is separated and purified using a solvent extraction method from a scandium-containing solution obtained by leaching from an ore or intermediate containing scandium. The present invention relates to a method for separating and purifying scandium.

  Since scandium has a particularly small ionic radius among rare earth elements, it rarely exists in ordinary rare earth minerals, and is widely present in oxide ores such as aluminum, tin, tungsten, zirconium, iron, and nickel. .

  Since scandium has a low basicity due to its small ionic radius, a strong acid is required for its dissolution. Therefore, since there are many types of coexisting elements that dissolve simultaneously and the concentration thereof is high, it is not easy to separate and purify scandium contained in an aqueous solution.

  As a typical separation method, for example, an organic solvent using an acidic alkyl phosphate such as a trade name PC-88A (main component: 2-ethylhexyl phosphonate 2-ethylhexyl) as described in Patent Document 1 as an extractant. A solvent extraction method using the above is known. Specifically, the organic solvent and an aqueous solution containing scandium are mixed, and coexisting elements such as scandium and iron, aluminum, calcium, yttrium are extracted into the organic solvent, and then a hydrochloric acid solution having a concentration of 4 to 9 mol / l In addition to washing with an organic solvent, elements other than scandium are separated and removed, and finally an aqueous sodium hydroxide solution is added to the organic solvent to separate scandium from the organic solvent in the form of hydroxide. is there.

  However, in the method of Patent Document 1, scandium cannot be back-extracted as an aqueous solution, and scandium hydroxide is separated from the organic solvent as a solid rubber-like or gel-like precipitate. For this reason, the solid-liquid separation of the solvent and scandium hydroxide becomes difficult, and there is a problem that scandium hydroxide is contaminated by the solvent, particularly phosphorus. Furthermore, since a considerable part of the extractant dissolves in water as a sodium salt each time back extraction is performed, a recovery process from the aqueous phase after back extraction is also required. If this recovery process is not performed, the COD value of the wastewater will rise significantly, resulting in environmental problems.

  Further, when zirconium is contained in a solution containing scandium, since scandium and zirconium have similar extraction characteristics, scandium produced by this method has a problem that a lot of zirconium is contained and the quality is lowered.

  Further, in the industrial aspect, as described above, solid rubbery to gel-like precipitates are precipitated and separated, so that separation and purification operations by continuous extraction operations such as a mixer settler cannot be performed, and the reverse It is necessary to proceed with a complicated batch operation every extraction, which is disadvantageous in terms of labor and cost.

  Regarding the extractant, an acidic phosphate ester having an alkylcyclohexyl group instead of the usual 2-ethylhexyl group as its alkyl chain has also been devised (see, for example, Patent Document 2). However, with this extractant, although the separation factor for the impurity element due to steric hindrance changes, the strong chemical bonding force for scandium does not change, and thus the above-mentioned problems cannot be solved.

  On the other hand, it is also conceivable to use the acidic alkyl phosphate ester as an adsorbent in a form supported on a resin, not by a solvent extraction method.

  For example, in Patent Document 3, 2-ethylhexylphosphonic acid, di (2-ethylhexyl) phosphonic acid, tributyl phosphate, and the like are supported on a resin, an inorganic strong acid aqueous solution such as hydrochloric acid, nitric acid, and sulfuric acid, and an organic acid such as acetic acid and monochloroacetic acid. A method of developing with an aqueous solution is disclosed.

  For example, Patent Document 4 discloses a method in which scandium is adsorbed by a resin impregnated with an alkylphosphonic acid ester or an alkylphosphoric acid ester, and then scandium is eluted together with an extractant with an organic solvent.

  However, in the methods of Patent Documents 3 and 4, in addition to the difficulty in elution of scandium from the resin, scandium forms a solid with an extractant and a polymer on the resin surface even in the process of adsorbing scandium. Therefore, there is a problem that scandium itself inhibits diffusion to the whole extractant as the adsorption proceeds.

  In addition, as a method for solving the problems in the case where the above-described phosphoric acid ester is used, for example, a method using lipophilic aminocarboxylic acids as described in Patent Document 5 is known.

  Since aminocarboxylic acids with weak acidity have a weak affinity for scandium, back extraction is characterized by being easier than acidic phosphate esters. However, on the contrary, since the binding force with chromium (III), iron (III) ions, etc., which has a high complex stability constant with aminocarboxylic acid, becomes stronger, in a solution containing these impurities, impurities accumulate in the solvent. As a result, the extractability of scandium gradually decreases. Moreover, since the hydrophilicity is structurally strong, there is a problem that an elution loss into an aqueous solution increases.

  Thus, a method capable of efficiently separating and purifying scandium has not yet been found.

JP 09-291320 A Japanese Patent Laid-Open No. 04-36373 JP-A-01-108119 Japanese Patent Laid-Open No. 01-246328 Japanese Patent Laid-Open No. 04-74711

  Therefore, the present invention has been proposed in view of such a situation, from the aqueous solution containing scandium, while ensuring the separability (selectivity) between scandium and impurity elements, improving the back-extractability, It is an object of the present invention to provide a method for separating and purifying scandium that can efficiently separate and purify scandium from a scandium-containing solution.

  The inventors of the present invention have made extensive studies to achieve the above-described object. As a result, scandium is selectively extracted by subjecting a solution containing scandium to an extraction process using an organic solvent containing trioctylphosphine oxide (TOPO), which is a solvating type extractant, as an extractant. It has been found that the back extractability can be enhanced while being able to.

  That is, in the method for separating and purifying scandium according to the present invention, an aqueous solution containing scandium and an organic solvent containing trioctylphosphine oxide having a concentration of 5 v / v% or more and 20 v / v% or less are mixed, and scandium is mixed in the organic solvent. After the extraction step to extract, the above organic solvent and a back extraction starting solution containing at least one of water, hydrochloric acid, sulfuric acid, and oxalic acid, and back extraction of scandium from the organic solvent and back extraction A back extraction step for obtaining a liquid.

  Here, the organic solvent from which scandium has been extracted in the extraction step is a hydrochloric acid solution having a concentration of 2.0 mol / l or more and 9.0 mol / l or less, or 3.5 mol / l or more and 9.0 mol / l or less. It is preferable to further have a scrubbing step of separating impurities by mixing with a sulfuric acid solution having a concentration.

  In addition, when a hydrochloric acid solution or a sulfuric acid solution is used as the back extraction starting solution in the back extraction step, it is preferable to use a hydrochloric acid solution of less than 2.0 mol / l or a sulfuric acid solution of less than 3.5 mol / l.

  In addition, when an oxalic acid solution is used as a back extraction start solution in the back extraction step, an oxalic acid solution having a concentration of 0.1 mol / l or more and less than 1.0 mol / l is used as a back extraction start solution, and scandium oxalate crystals Get.

  In addition, in the back extraction step, when one or more of water, hydrochloric acid solution, and sulfuric acid solution is used as the back extraction starting solution, oxalic acid is added to the back extracted solution obtained by back extracting scandium. It is preferable to add a crystallization step to obtain scandium oxalate crystals.

  When zirconium is contained in the aqueous solution containing scandium, prior to the extraction step, the aqueous solution and an organic solvent containing tenoyltrifluoroacetone are mixed to extract zirconium into the organic solvent. It is preferable to separate them.

  According to the present invention, scandium can be selectively extracted and the back extractability can be enhanced, and scandium can be separated and purified from the scandium-containing solution at a high back extraction rate. Thereby, the amount of scandium retained in the process system without being back-extracted can be reduced, and the yield of scandium can be increased.

  Also, since scandium can be back-extracted in the form of an aqueous solution with high fluidity, for example, separation and purification operations can be carried out by continuous extraction operations, facilitating equipment continuation and high-speed operation, and equipment costs. In addition, labor saving can be achieved.

It is process drawing which shows the flow of the separation and purification method which isolate | separates and refines scandium from a scandium containing solution, and the flow of the manufacturing method of scandium oxide using the separation and purification method. 4 is a graph showing the relationship between the number of cleanings in the cleaning process of Example 1 and the impurity metal concentration in the cleaning liquid. It is a graph which shows the relationship between the frequency | count of back extraction in the back extraction process of Example 1, and each metal element density | concentration in the liquid after back extraction. It is a graph which shows the relationship between the density | concentration of the hydrochloric acid solution (cleaning liquid) used for a washing | cleaning process, and the scandium (Sc) density | concentration in a washing | cleaning liquid. It is a graph which shows the relationship between the density | concentration of the sulfuric acid solution (cleaning liquid) used for a cleaning process, and the scandium (Sc) density | concentration in a cleaning liquid.

Hereinafter, the scandium separation and purification method according to the present invention will be described in detail in the following order. Note that the present invention is not limited to the following embodiments, and can be appropriately changed without changing the gist of the present invention.
1. 1. Outline of the present invention 2. Scandium separation and purification method 2-1. Extraction process 2-2. Scrubbing process (cleaning process)
2-3. Back extraction process 2-4. Crystallization step 2-5. Summary 3. 3. Method for producing scandium oxide Example

<< 1. Outline of the present invention >>
The method for separating and purifying scandium according to the present invention is a method for selectively extracting and purifying scandium from an aqueous solution obtained by leaching an ore or intermediate containing scandium with an acid solution or the like.

  Specifically, in this separation and purification method, an aqueous solution containing scandium and an organic solvent containing trioctylphosphine oxide (hereinafter also referred to as “TOPO” as appropriate) are mixed to extract scandium into the organic phase, The organic solvent is mixed with a back-extraction starting solution containing any one or more of water, hydrochloric acid, sulfuric acid, and oxalic acid, and scandium is back-extracted from the organic phase to separate scandium.

  In the method for separating and purifying scandium according to the present invention, it is important to use an organic solvent containing trioctylphosphine oxide in the extraction step and mix an aqueous solution containing scandium with this organic solvent.

  Although details will be described later, trioctylphosphine oxide used as an extractant is a solvate-type extractant, and is extracted only with an affinity with a scandium compound and does not form a chemical bond. Moreover, extraction and back extraction can be easily controlled by controlling the ionic strength of the solution. Therefore, as in the case of extraction with an acidic extractant or the like, a strong chemical bond is formed, so that a rubber-like or gel-like solid is precipitated in the liquid after back extraction, thereby hindering the fluidity of the organic phase and the aqueous phase. In other words, back extraction can be performed with high fluidity in the form of an aqueous solution, and back extraction can be improved.

  Therefore, according to this separation and purification method, the amount of scandium remaining in the process system without being back-extracted can be reduced, and scandium can be separated and purified in a high yield from a solution containing scandium. . In addition, since the back extraction can be performed with high fluidity, continuous extraction operation is possible and high-speed operation is facilitated, so the processing equipment is compact and labor-saving in terms of equipment and cost. Can be realized.

  Hereinafter, specific embodiments of the method for separating and purifying scandium according to the present invention (hereinafter referred to as “this embodiment”) will be described in more detail for each step.

≪2. Scandium separation and purification method >>
As shown in the process diagram of FIG. 1, the scandium separation and purification method according to the present embodiment mixes an aqueous solution containing scandium and an organic solvent containing trioctylphosphine oxide (TOPO), and scandium is mixed into the organic solvent. The extraction process to extract, the organic solvent, and the back-extraction starting solution containing one or more of water, hydrochloric acid, sulfuric acid, and oxalic acid are mixed, and back-extracted liquid is obtained by back-extracting scandium from the organic solvent. And a back-extraction step.

  In this separation and purification method, after extracting scandium with an organic solvent containing trioctylphosphine oxide in the extraction step, the organic solvent is mixed with a hydrochloric acid solution or sulfuric acid solution having a predetermined concentration before back-extracting it. You may make it provide the scrubbing process of making it wash | clean. Thereby, the impurity element coexisting in the solution to be treated and extracted together with scandium in the organic solvent can be separated and removed into the aqueous phase, and the purity of the obtained scandium compound can be further increased.

  Furthermore, in the back extraction step, when back extraction processing is performed using a back extraction starting solution containing any of water, hydrochloric acid, and sulfuric acid, oxalic acid is added to the back extracted liquid obtained by back extraction. A crystallization step of adding and forming scandium oxalate crystals may be provided. Thereby, scandium can be separated and recovered as hardly soluble oxalate.

  Hereinafter, each process will be described more specifically.

<2-1. Extraction process>
In the extraction process, an aqueous solution (scandium-containing solution) containing scandium obtained by leaching ore or an intermediate containing scandium with an acid solution such as hydrochloric acid or sulfuric acid, and an organic solvent containing an extractant Mixing is performed, and a solvent extraction process for selectively extracting scandium into an organic solvent is performed.

  In this extraction step, an organic solvent containing a solvating type extracting agent (solvating extractant) is used for extracting and separating scandium by a solvent extraction method. Specifically, trioctyl phosphine oxide (TOPO) is used as an extractant.

  Here, it is conceivable to use an acidic extractant as an extractant used for the extraction and separation of scandium. An acidic extractant is an extractant that extracts metal ions by replacing -H of the extractant with cations such as scandium ions to form metal salts. However, this acidic extractant is strongly chemically bonded to metal ions, and back extraction cannot be performed unless the bond is broken. For example, when a phosphoric acid-based extractant such as an acidic phosphate is used as the acidic extractant, the selectivity for scandium increases due to the extremely strong affinity between phosphoric acid and scandium, but it is difficult to break the bond. (For example, see the following reaction formula (1).) As a result, a rubber-like or gel-like solid is precipitated, the fluidity of the organic phase or the aqueous phase is deteriorated, and an effective and efficient back extraction process becomes difficult. Moreover, in order to cut | disconnect the strong coupling | bonding, it is necessary to process by adding alkalis, such as sodium hydroxide, separately, for example.

3H-R + ScCl ₃ + 3NaOH
→ Sc—R ₃ + 3NaCl + 3H ₂ O (1)
(In the formula, HR represents an acidic extractant.)

  In addition, in order to improve the back extractability, the use of a carboxylic acid having a weak binding force with metal ions as an acidic extractant can improve the back extractability, but it does not contain phosphoric acid, so it is selective for scandium. Can not be used as a purification medium.

  On the other hand, a solvating type extractant is an extractant that has a functional group having an affinity for a molecular metal compound that is not ionized in the molecule and performs extraction by affinity with the metal compound. In this way, in the solvation-type extractant, since it is extracted by binding with a scandium compound only with an affinity and does not form a chemical bond, the fluidity of the solution after back extraction is improved and the back extraction can be easily performed.

  In addition, the solvation-type extractant can promote the extraction reaction by promoting solvation by increasing the ionic strength in the aqueous phase, and can promote the reverse extraction reaction by decreasing the ionic strength. Therefore, extraction and back-extraction can be easily controlled by controlling the ionic strength based on adjustment of the salt concentration in the solution.

  In more detail in this regard, generally, when a metal compound is dissolved in water, water molecules are surrounded and stabilized (hydrated) in each of the cation and the anion, so that a solvated extractant is included in that state. It is difficult to incorporate a metal compound into the organic solvent. However, when salts that are easily dissolved in water are dissolved in the solution, that is, when the ionic strength is increased, the water molecules in the aqueous solution are hydrated one after another to the ions constituting the salts, and finally free water ( There is almost no free water). As a result, the metal compound cannot be hydrated, and the proportion of the metal compound existing as a molecule increases, and as a result, the metal compound is extracted with the solvating side extractant. On the other hand, when the solvating-type extractant comes into contact with an aqueous solution or water whose ionic strength is lower than the extracted conditions, ions constituting the metal compound are hydrated and stabilized, so that they remain in the organic solvent. As a result, the back extraction reaction proceeds. Thus, by using the solvating type extractant, the reaction of extraction and back-extraction can be freely controlled by adjusting the salt concentration of the solution and controlling the ionic strength.

  As this solvating-type extractant, there are phosphorus-based and non-phosphorus-based extractants. However, in view of the high selectivity with scandium that is the object of separation and purification, solvated extractants containing phosphorus are particularly suitable. Yes. Among them, it is preferable to use trioctylphosphine oxide (TOPO) from the viewpoint that scandium can be extracted and back-extracted more effectively.

  The following reaction formula (2) shows an extraction reaction formula using TOPO as an extractant. As shown in this reaction formula (2), a scandium compound is only added with affinity to the extractant, and the extractant is extracted by a reaction that does not involve formation of a chemical bond.

3TOPO + ScCl ₃ → ScCl ₃ · 3TOPO (2)

  As the trioctyl phosphine oxide used as the extracting agent, various trialkyl phosphine oxides having different alkyl chains exist, and any of them can be suitably used.

  Trioctylphosphine oxide has a melting point of about 60 ° C. and is solid at room temperature. For this reason, in the extraction process, it is diluted with, for example, a hydrocarbon-based organic solvent. Even if the extractant is called trioctylphosphine oxide, some kinds of similar structures with different alkyl chains are liquid at room temperature, and dilution is not always necessary when the liquid is liquid. .

  Although it does not specifically limit as a density | concentration in the organic solvent of trioctyl phosphine oxide, It is preferable to set it as 5 v / v% or more and 20 v / v% or less. For example, when the concentration of TOPO in the organic solvent is 5 v / v%, Sc is about 1.8 g / l, and when the concentration is 40 v / v%, Sc is 11.4 g. / L. Thus, the extraction capability increases as the concentration of TOPO in the organic solvent increases, but the amount of scandium extracted per volume of TOPO decreases. Accordingly, in consideration of phase separation during extraction and back extraction, the concentration of TOPO in the organic solvent is preferably 5 v / v% or more and 20 v / v% or less, particularly about 10 v / v%. It is more preferable. Although the solubility varies depending on the type of hydrocarbon of the organic solvent, a concentration of about 40 v / v% is almost the upper limit at around room temperature of 25 ° C.

  The scandium-containing solution used as the stock solution is not particularly limited, and any liquid aqueous solution can be used. As described above, the higher the ionic strength of the scandium-containing solution, the more the solvation by TOPO is promoted. Therefore, it becomes advantageous for extraction. That is, in order to advance the solvation reaction, it is important that the compound to be extracted is molecular, and in order to suppress the dissociation of the compound, it is possible to maintain a high salt concentration and increase the ionic strength. preferable.

  For this reason, it is particularly preferable to use a scandium-containing solution composed of a 2.0 mol / l or more hydrochloric acid solution or a 3.5 mol / l or more sulfuric acid solution, similarly to the concentration of the scrubbing liquid described later. Thereby, the extraction effect of scandium can be enhanced. Even in the case of performing extraction using a solution having a concentration lower than these, there is no practical problem if the number of extraction stages is two or more.

<2-2. Scrubbing process (cleaning process)>
TOPO, which is an extractant used in the extraction process described above, has high selectivity for impurities that coexist in the solution. However, when a large excess of impurity elements coexists in the scandium-containing solution in addition to the scandium to be extracted, scrubbing for the organic solvent (organic phase) after extracting scandium and before back-extracting it ( It is preferable to remove the impurity element from the extractant by separating the impurity element into an aqueous phase.

  Thus, by providing the scrubbing step and washing the organic solvent to remove the impurity element, the purity of the scandium compound obtained through each step described later can be further increased.

  As a solution (cleaning solution) used for scrubbing, a hydrochloric acid solution or a sulfuric acid solution can be used. Although scrubbing can be performed using a nitric acid solution, it is not preferable because oxidative deterioration of TOPO as an extractant is promoted. Further, water-soluble chlorides and sulfates can be used in place of the hydrochloric acid solution and the sulfuric acid solution. However, for example, use of alkali metal salts may cause new impurities, which is not preferable in terms of highly purifying scandium.

  The concentration of the cleaning solution used for scrubbing is preferably 2.0 mol / l or more and 9.0 mol / l or less when a hydrochloric acid solution is used, and 3.5 mol / l or more and 9.0 mol / l when a sulfuric acid solution is used. The following concentration range is preferable.

  Here, when scandium in hydrochloric acid solution or sulfuric acid solution is extracted using TOPO, the extraction effect is maximized when the concentration is 6.5 mol / l for hydrochloric acid solution and 7.0 mol / l for sulfuric acid solution. There is a tendency that the amount of scandium that cannot be extracted and remains in the stock solution gradually increases as it goes away from the range. As described above, when the ionic strength of the aqueous solution is increased, the proportion of the metal compound existing as a molecule increases and the solvation side extractant is extracted. This is probably because another reaction occurs in which the metal stabilizes by forming complex ions in an aqueous solution.

  For this reason, in the scrubbing step, it is preferable to wash the solvent using a hydrochloric acid solution or a sulfuric acid solution having a concentration in the above-described range (see also the examination on the acid concentration dependency in Example 2 below). . Thereby, even the scandium extracted together with the metal impurities by washing with the organic solvent can be prevented from being back-extracted and removed by washing, and loss can be suppressed. In addition, when the hydrochloric acid solution and the sulfuric acid solution are compared, it is more preferable to use the hydrochloric acid solution in that the loss concentration can be kept low.

  As the number of washing steps (number of times), for example, when the phase ratio of the organic phase (O) and the aqueous phase (A) is O / A = 1/1, depending on the type and concentration of the impurity element, 3 to 5 steps. With this number of stages, almost all elements other than zirconium described later can be separated to below the detection limit of the analyzer.

<2-3. Back extraction process>
In the back extraction step, scandium is back-extracted from the organic solvent from which scandium has been extracted through the extraction step, or from the organic solvent from which scandium has been extracted and then removed through the scrubbing step.

  In this back extraction step, water or a low-concentration acid solution is mixed with the organic solvent as a back extraction solution (back extraction start solution), thereby causing the reverse reaction of the above reaction formula (2). Thus, scandium is back-extracted to obtain a post-back-extraction solution containing scandium.

  Here, as described above, in the extraction of scandium, the extraction rate increases as the acid concentration of the solution increases. This means that in terms of scandium back extraction, the back extraction rate decreases as the acid concentration increases. Therefore, from the viewpoint of the back extraction rate, it is most advantageous to perform the back extraction process using water. However, if the ionic strength of the aqueous phase is extremely reduced, phase separation from the organic phase may be poor, which may cause emulsion generation. For this reason, it is practically preferable to perform the back extraction treatment using a solution (acid solution) containing a slight amount of acid as the back extraction start solution.

  As the acid solution, a hydrochloric acid solution or a sulfuric acid solution can be used. In the case of the hydrochloric acid solution, the concentration is preferably less than 2.0 mol / l, and in the case of the sulfuric acid solution, the concentration is preferably less than 3.5 mol / l. In particular, when a hydrochloric acid solution is used, the concentration range is preferably about 0.05 mol / l or more and 0.3 mol / l or less.

  In addition, an oxalic acid solution can also be used as a back extraction starting solution, similar to the hydrochloric acid solution and sulfuric acid solution described above. When an oxalic acid solution is mixed and allowed to act on an organic solvent from which scandium has been extracted, as shown in the following reaction formula (3), crystals of scandium oxalate are generated and recovered without passing through the crystallization step described later. can do.

2ScCl ₃ · 3TOPO + 3H ₂ C ₂ O ₄
→ Sc ₂ (C ₂ O ₄ ) 3 + 3TOPO + 6HCl (3)

  Moreover, since the back extraction reaction using the oxalic acid solution as the back extraction starting solution is not a reversible reaction, it is more than the back extraction process by the back reaction of the above reaction formula (2) performed using a hydrochloric acid solution or a sulfuric acid solution. The back extraction reaction can be allowed to proceed completely, and the back extraction rate can be further increased.

  When the oxalic acid solution is used as the back extraction starting solution, the concentration of the oxalic acid solution is not particularly limited, but is preferably 0.1 mol / l or more and less than 1.0 mol / l. If the concentration is less than 0.1 mol / l, the back extraction force is too weak, and scandium oxalate may not be produced effectively. On the other hand, the solubility of oxalic acid itself in water is not large, and the upper limit is around 1 mol / l, and even if the concentration is higher than that, it only settles as crystals.

  The amount of oxalic acid solution used, that is, the amount of oxalic acid solution for back-extracting scandium and producing scandium oxalate crystals, is calculated with respect to the amount of scandium extracted and contained in the organic solvent. It is preferable that the amount is 1 equivalent or more. Thereby, the extracted scandium can be reliably converted into scandium oxalate crystals.

  As described above, in the back extraction reaction using the oxalic acid solution, a solid crystal of scandium oxalate is precipitated, which may have an influence on the back extractability. However, since this solid crystal is hydrophilic, it is extracted with an organic extractant and then an organic solvent (organic) is added as in the conventional method in which rubber-to-gel solid scandium hydroxide is produced and back-extracted. High fluidity can be maintained without interfering with phase separation between the phase) and the aqueous phase. Therefore, by mixing the mixture with an organic solvent in the back extraction process, the solid crystals of scandium are distributed to the aqueous phase and quickly settle to the bottom of the aqueous phase, so that they can be easily separated and recovered. it can.

  The back extraction start solution may be a solution containing any one of the above-described water, hydrochloric acid, sulfuric acid, and oxalic acid, or a solution containing any two or more of them together. Good.

<2-4. Crystallization process>
As described above, extraction is performed using an organic solvent containing trioctylphosphine oxide, and the obtained organic solvent is mixed with a back-extraction starting solution containing one or more of water, hydrochloric acid, sulfuric acid, and oxalic acid. By back extraction, scandium can be separated and purified with high fluidity in the form of an aqueous solution.

  Here, with respect to scandium contained in the liquid after back extraction obtained in the back extraction step described above, it is preferable to recover the scandium as a solid crystal. Thereby, the scandium in the solution after back extraction can be concentrated to further enhance the purification effect, and the recovery efficiency can be increased.

  Therefore, in the present embodiment, a crystallization step of obtaining a scandium solid crystal from the back-extracted solution obtained in the above-described back extraction step can be provided.

  In the crystallization step, oxalic acid is added to the back-extracted solution obtained by back-extracting scandium using any one or more of water, hydrochloric acid solution, and sulfuric acid solution as the back-extraction starting solution in the back-extraction step described above. Addition to obtain scandium oxalate crystals.

  As described above, in the crystallization step, when back extraction is performed using an oxalic acid solution as a back extraction start solution in the back extraction step, crystals are generated and recovered in the back extraction process. Because it can, it becomes unnecessary. Therefore, in the back extraction step, when a back extraction process is performed using any one or more of water, hydrochloric acid solution, and sulfuric acid solution, a solid crystal of scandium is generated and recovered by the crystallization step.

  As a method for producing scandium solid crystals from the liquid after back extraction containing scandium, it is possible to use a general method for producing rare earth salts, in which oxalic acid is added and separated as a poorly soluble oxalate. preferable. Like other rare earth elements, scandium also forms slightly soluble crystals. At the same time, most other impurity elements form complexes with oxalic acid and remain in the mother liquor, so a further purification effect is expected. And a higher purity scandium compound can be produced.

  The amount of oxalic acid added is preferably an amount that is 1 equivalent or more in terms of the amount of scandium contained in the solution after back extraction. Thereby, the back-extracted scandium can be reliably converted into scandium oxalate crystals.

<2-5. Summary>
As described above, in the scandium separation and purification method according to the present embodiment, scandium is extracted by mixing a scandium-containing solution and an organic solvent containing trioctylphosphine oxide, and the organic solvent, water, hydrochloric acid are extracted. Then, the mixture is mixed with a back-extraction starting solution containing one or more of sulfuric acid and oxalic acid to back-extract scandium.

  According to such a separation and purification method, as in the case of extraction with a conventional acidic extractant or the like, a strong chemical bond is formed, and a rubber-like or gel-like solid precipitates in the liquid after back extraction, and the organic phase. In addition, it does not hinder the fluidity of the aqueous phase, can be back-extracted with high fluidity in the form of an aqueous solution, and can improve the back-extractability.

  As a result, the amount of scandium remaining in the process system without being back-extracted is reduced, and scandium can be separated and purified from the scandium-containing solution at a high back-extraction rate. In addition, since the back extraction can be performed with high fluidity, continuous extraction operation is possible and high-speed operation is facilitated, so the processing equipment is compact and labor-saving in terms of equipment and cost. Can be realized.

  In addition, since the extraction and back-extraction can be easily controlled by controlling the ionic strength of the solution, the back-extraction rate can be adjusted by adjusting the concentration of the acid solution used as the back-extraction starting solution to a predetermined range. The loss of scandium to be separated and purified can be reduced.

  Furthermore, after the scandium is extracted, an impurity element can be effectively removed by providing a step of washing the organic solvent with a hydrochloric acid solution or a sulfuric acid solution having a predetermined concentration, thereby improving the purity of the scandium compound. Can be increased.

  By the way, in the scandium-containing solution that is the solution to be processed (stock solution) of the separation and purification method described above, zirconium having a chemical property similar to that of scandium often often coexists. When a solution in which such zirconium coexists is used as a processing target, there is a possibility that the zirconium cannot be sufficiently separated by the separation and purification method described above.

  Therefore, when zirconium coexists in the scandium-containing solution to be treated, it is preferable to provide a pre-extraction step for extracting and separating zirconium in the solution prior to the extraction step in the above-described scandium separation and purification method.

  In this pre-extraction step, a scandium-containing solution in which zirconium coexists is mixed with an organic solvent containing tenoyltrifluoroacetone (hereinafter also referred to as “TAA” where appropriate), and zirconium is extracted into the organic solvent. Separate.

  Zirconium tends to form an anionic complex more than scandium. Therefore, separation as an anion was examined, and as a type of extraction agent suitable for anion extraction, tenoyltrifluoroacetone, which is a kind of beta diketone, has particularly high extraction and separation characteristics of zirconium, and scandium is hardly extracted. I found out.

  Tenoyltrifluoroacetone is a solid at room temperature like trioctylphosphine oxide (TOPO), so it is diluted with a hydrocarbon solvent to a concentration range of about 50 g / l to 100 g / l. Are preferably used.

  In the pre-extraction step, it is preferable to extract zirconium with an organic solvent containing TAA and then perform back extraction, and repeat these operations several times. However, the zirconium quality in the scandium-containing solution is, for example, higher than that of scandium. When the level is as low as about 100 ppm or less, only the extraction operation can be repeated without performing the back extraction operation every time.

≪3. Method for producing scandium oxide >>
Scandium oxide can be produced using scandium separated and purified from a scandium-containing solution by the scandium separation and purification method described above.

  Specifically, a method for producing scandium oxide includes an extraction step of mixing scandium-containing solution and an organic solvent containing trioctylphosphine oxide (TOPO) to extract scandium in the organic solvent, the organic solvent, water, Mixing with a back-extraction starting solution containing at least one of hydrochloric acid, sulfuric acid, and oxalic acid, back-extracting the scandium from an organic solvent to obtain a back-extracted solution, and water in the back-extraction step. In the case of back-extraction using a back-extraction starting solution containing one or more of hydrochloric acid, sulfuric acid, sulfuric acid, oxalic acid is added to the obtained back-extracted solution to obtain scandium oxalate crystals And a pyrolysis step of obtaining scandium oxide by heating and pyrolyzing the obtained scandium oxalate.

  In this scandium oxide production method, the extraction step and the back extraction step are the same as those in the above-described scandium separation and purification method, and thus the description thereof is omitted. Similarly, in the crystallization step, when back extraction is performed using a back extraction starting solution containing one or more of water, hydrochloric acid, and sulfuric acid in the back extraction step, The solid crystals of scandium oxalate are produced and recovered by adding oxalic acid to the solution. In addition, when back extraction is performed using an oxalic acid solution as a back extraction start solution in the back extraction step, scandium oxalate crystals are obtained along with the back extraction process, and are collected.

  In this method for producing scandium oxide, after recovering the solid crystals of scandium oxalate, the scandium oxalate is heated and subjected to a thermal decomposition (firing) treatment to obtain a scandium oxide oxide (oxidation step). (Scandium conversion step). Thereby, it can convert into the form which can utilize scandium easily.

  The treatment conditions in the pyrolysis step are not particularly limited. For example, a solid crystal of scandium oxalate obtained by crystallization in a pyrolysis furnace such as a tubular furnace is charged, and 700 ° C. to 900 ° C. in an oxygen atmosphere. It can be performed under a temperature condition of about ℃ or less.

  In such a method for producing scandium oxide, scandium can be selectively extracted from a scandium-containing solution using an organic solvent containing trioctylphosphine oxide, and back extraction can be performed with high fluidity. Therefore, scandium oxide can be obtained with high yield from the scandium-containing solution that is the stock solution. Further, the obtained scandium oxide has a low impurity element quality and becomes a high-purity compound.

<< 4. Examples >>
Examples of the present invention will be described below, but the present invention is not limited to the following examples.

[Example 1]
(1) Extraction step Scandium (Sc) -containing solution (stock solution) 103L having the composition shown in Table 1 below and trioctylphosphine oxide (TOPO) (made by Hokuko Chemical Co., Ltd.) as a solvent Shellsol A (made by Shell Chemicals) Then, 2.6 L of an organic solvent dissolved at a concentration of 13 v / v% was stirred for 60 minutes and mixed to obtain an extracted organic phase containing scandium. Note that the scandium concentration in the extraction residual liquid was less than 0.1 mg / l, and the extraction rate was 99.8% or more.

(2) Scrubbing process (cleaning process)
Next, the scandium-containing organic solvent (extracted organic phase) obtained in the extraction step is mixed using a hydrochloric acid solution having a concentration of 6.5 mol / l so that the phase ratio is O / A = 1/1. And washed by stirring for 10 minutes. Thereafter, the aqueous phase was separated, and the organic phase was again mixed with a new hydrochloric acid solution having a concentration of 6.5 mol / l and washed, and the aqueous phase was similarly separated. Such washing operation was repeated 3 times in total.

  Here, FIG. 2 shows the relationship between the number of times of cleaning with respect to the organic solvent and the metal quality (impurity metal concentration) in the cleaning liquid.

  As shown in FIG. 2, it can be understood that the impurity metal concentration to be eluted can be removed to a level of 0.001 g / l or less by washing the extracted organic phase three times. On the other hand, scandium remains at a loss of the order of 0.01 g / l, and it can be seen that only impurities can be effectively removed without separating scandium extracted into an organic solvent into an aqueous phase.

(3) Back extraction step Next, the organic phase after washing is adjusted to a phase ratio of O / A = 1/1 using a hydrochloric acid solution having a concentration of 1% (about 0.3 mol / l). After mixing and stirring for 20 minutes, scandium was back extracted into the aqueous phase. Thereafter, the mixture was allowed to stand to separate the aqueous phase, and again mixed with a fresh hydrochloric acid solution having a concentration of 1% to separate the aqueous phase. Such back extraction operation was repeated three times.

  FIG. 3 shows the relationship between the number of back extraction operations and the concentration of each metal element in the aqueous phase in the back extract.

  The total amount of scandium in the liquid after three back extractions (the liquid after back extraction) was 98.3% of the amount contained in the stock solution, indicating that almost all of the scandium was extracted. Further, as shown in FIG. 3, nickel (Ni) present at a high concentration as an impurity was contained about 1% with respect to scandium, but all other impurity elements could be reduced to less than 0.1 mg / l. I understand that.

(4) Scandium oxide conversion step Oxalic acid / dihydration that is twice the calculated amount of scandium contained in the liquid after extraction by combining the three liquids after back extraction by the back extraction operation described above. 18 g of the product (Mitsubishi Gas Co., Ltd.) was dissolved and stirred for 60 minutes to produce a white crystalline precipitate of scandium oxalate. The produced white crystalline precipitate was filtered by suction, washed with 500 ml of pure water, and dried at 105 ° C. for 8 hours.

  Subsequently, the dried oxalate was transferred to a high-purity magnesia boat and placed in a quartz tube tube furnace, and air was sent at a flow rate of 2 L / min and oxidized by heat decomposition at 850 ° C. for 2 hours. Scandium was produced. Thereafter, the obtained scandium oxide was cooled to room temperature and taken out, and the metal quality contained in the oxide was analyzed by emission spectroscopy. The analysis results are shown in Table 2 below.

  As shown in Table 2, all major impurity elements can be separated to less than 1 ppm, and other elements detected by emission spectroscopic analysis are 4 ppm for iron (Fe), calcium (Ca), and magnesium, respectively. (Mg), antimony (Sb), and silicon (Si) were all less than 1 ppm, and high-quality scandium oxide comparable to 5N purity was obtained.

[Example 2: Acid concentration dependence of Sc extraction and back extraction]
100 L of an aqueous chloride solution containing 0.11 g / l of scandium and 220 g / l of nickel and 6.7 L of an organic solvent in which TOPO was diluted with the solvent Shellsol A to 10% by volume were mixed and stirred for 10 minutes. Scandium was extracted into the organic phase. The phase ratio O / A is 1/15.

  Next, 50 ml of the obtained organic phase is taken out and extracted by mixing in a separatory funnel with various concentrations of hydrochloric acid solution or sulfuric acid solution so that the phase ratio is O / A = 1/1. The organic phase was washed. 4 and 5 show the relationship between the concentration of each acid solution and the dissolved scandium concentration.

  As shown in FIG. 4, when washed with a hydrochloric acid solution, the elution loss of scandium increases rapidly under conditions of a concentration of less than 2.0 mol / l or more than 9.0 mol / l. Also, as shown in FIG. 5, when washed with a sulfuric acid solution, the scandium elution loss similarly increases under conditions of a concentration of less than 3.5 mol / l or greater than 9.0 mol / l.

  From this, it can be seen that a concentration of less than 2.0 mol / l for a hydrochloric acid solution and a concentration of less than 3.5 mol / l for a sulfuric acid solution are suitable acid concentrations for the back extraction process.

[Example 3: Treatment of stock solution coexisting with zirconium (Zr)]
(1) Zirconium removal process (Zr extraction process)
125 g of a raw material having the composition shown in Table 3 below containing zirconium (Zr) was mixed with 600 ml of a hydrochloric acid solution having a concentration of 11.5 mol / l and stirred for 30 minutes to completely dissolve. Next, 400 ml each of a 11.5 mol / l hydrochloric acid solution and pure water are added to the dissolved solution (stock solution) for dilution, and further, tenoyltrifluoroacetone (TTA) is contained at a concentration of 50 g / l. 400 ml of solvent Shellsol A solution was added and mixed with stirring for 10 minutes to extract and separate zirconium in the stock solution. In addition, all elements other than the elements shown in Table 3 were below the lower limit of detection by emission spectroscopy.

(2) Sc extraction step to washing step 1.75 L of hydrochloric acid solution having a concentration of 11.5 mol / l and 2.25 L of water are further added to the extraction residual liquid after the removal of zirconium in the dezircination step in (1) above. Then, a solvent Shellsol A20L containing TOPO at a ratio of 20 v / v% was mixed and stirred for 1 hour to extract scandium.

  Next, 5 L of 6.5 mol / l hydrochloric acid was mixed with the obtained extracted organic phase and stirred for 1 hour to perform a washing treatment, and the metal impurities in the organic solvent were washed and separated into the aqueous phase.

(3) Back extraction step to oxide production step In the extracted organic phase after washing, 343 g of oxalic acid dihydrate (1 equivalent in terms of the amount of scandium in the extracted organic phase) was dissolved in 5 L of water. An aqueous solution (0.5 mol / l) was added and stirred for 60 minutes, and scandium was back-extracted as scandium oxalate crystals. The obtained crystals were sucked from the bottom of the aqueous phase, and after suction filtration, washed successively with 300 ml of ethanol and 500 ml of water. The crystal after washing was dried at 105 ° C. for 8 hours.

  The dried crystals were pyrolyzed under the same conditions as in Example 1 to produce scandium oxide. Thereafter, the obtained scandium oxide was cooled to room temperature and taken out, and the metal quality contained in the oxide was analyzed by emission spectroscopy. The analysis results are shown in Table 4 below.

  As shown in Table 4, all impurity elements including zirconium could be reduced to less than 1 ppm, and high-purity scandium oxide with few impurities could be obtained. All the elements other than those shown in Table 4 were below the lower limit of detection by emission spectroscopy.

Claims (7)

An extraction step in which an aqueous solution containing scandium and an organic solvent containing trioctylphosphine oxide having a concentration of 5 v / v% or more and 20 v / v% or less are mixed to extract scandium into the organic solvent;
A back extraction step of mixing the organic solvent and a back extraction starting solution containing one or more of water, hydrochloric acid, sulfuric acid, and oxalic acid, and back-extracting scandium from the organic solvent to obtain a back-extracted solution A method for separating and purifying scandium, comprising:   The organic solvent from which scandium has been extracted in the extraction step is a hydrochloric acid solution having a concentration of 2.0 mol / l to 9.0 mol / l, or sulfuric acid having a concentration of 3.5 mol / l to 9.0 mol / l. 2. The method for separating and purifying scandium according to claim 1, further comprising a scrubbing step of separating impurities by mixing with a solution.   3. The separation and purification of scandium according to claim 1, wherein in the back extraction step, a hydrochloric acid solution of less than 2.0 mol / l or a sulfuric acid solution of less than 3.5 mol / l is used as a back extraction starting solution. Method.   3. The scandium oxalate crystal according to claim 1, wherein, in the back extraction step, a scandium oxalate crystal is obtained using an oxalic acid solution of 0.1 mol / l or more and less than 1.0 mol / l as a back extraction start solution. Separation and purification method.   In the back extraction step, oxalic acid is added to the back-extracted solution obtained by back-extracting scandium using any one or more of water, hydrochloric acid solution and sulfuric acid solution as the back-extraction starting solution, and scandium oxalate is added. The method for separating and purifying scandium according to any one of claims 1 to 3, further comprising a crystallization step of obtaining a crystal of   When zirconium is contained in the aqueous solution containing scandium, prior to the extraction step, the aqueous solution and an organic solvent containing thenoyltrifluoroacetone are mixed and the zirconium is extracted into the organic solvent and separated. The method for separating and purifying scandium according to any one of claims 1 to 5, wherein: An extraction step in which an aqueous solution containing scandium and an organic solvent containing trioctylphosphine oxide having a concentration of 5 v / v% or more and 20 v / v% or less are mixed to extract scandium into the organic solvent;
A back extraction step of mixing the organic solvent and a back extraction starting solution containing one or more of water, hydrochloric acid, sulfuric acid, and oxalic acid, and back-extracting scandium from the organic solvent to obtain a back-extracted solution When,
When back extraction is performed using a back extraction starting solution containing one or more of water, hydrochloric acid, and sulfuric acid in the back extraction step, oxalic acid is added to the resulting back extracted solution, and oxalic acid is added. A crystallization step for obtaining scandium crystals;
And a thermal decomposition step of obtaining the scandium oxide by heating and thermally decomposing the obtained scandium oxalate.

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