JP7311349B2 - Scandium recovery method - Google Patents

Description

The present disclosure relates to a method of recovering scandium (Sc).

Sc is a rare metal used in various applications. Examples of applications include metal halide lamps, aluminum alloy additives, additives for laser single crystals, and Lewis acid catalysts.

Ti, Fe and Cu can be purified from titanium ores, iron ores and copper ores, respectively. However, unlike these metals, there are no ores rich in Sc. In practice, as an example, Sc is recovered from the residue after the target metal component (that is, Ni or Ti) is extracted from nickel ore or titanium ore. However, the amount of Sc contained in the residue is very small and there are many impurities. Therefore, various measures are required to extract Sc.

Patent Document 1 (Japanese Patent Application Laid-Open No. 2000-313928) discloses a method for recovering Sc from nickel-containing ores. More specifically, the document discloses performing multiple neutralization steps to adjust the pH after leaching Sc from the ore.

Patent Literature 2 (International Publication No. 2016/031699) discloses leaching Sc from a titanium ore-derived residue and adjusting the pH in multiple steps. This discloses precipitating other metal elements while maintaining the dissolved state of Sc, or vice versa.

JP-A-2000-313928 WO2016/031699

However, even conventional scandium generation techniques cannot completely eliminate impurities, and impurities such as alkali metals, transition metals, and rare earths may still be contained in large amounts, and there is still room for investigation.

Therefore, the present disclosure provides a scandium recovery method capable of reducing impurities.

In one aspect of the embodiment of the present invention, a water washing step of washing solids containing scandium hydroxide with water, and adjusting the pH of the aqueous solution containing the solids after washing to 2.0 to 5.0 to leach Sc a separation step of separating the leachate obtained in the leaching step into a residue and a solution; and a precipitation step of precipitating Sc in the solution.

According to the present disclosure, a scandium recovery method capable of reducing impurities can be provided.

In one embodiment, the relationship between Sc dissolution and pH in solids comprising scandium hydroxide is shown. FIG. 2(a) shows an example of a graph showing the relationship between the pH of the Sc solution before the precipitation step and the precipitation rate of scandium oxalate, and FIG. 2(b) shows an example in which oxalic acid was added to the Sc solution. An example of a graph showing the relationship between subsequent pH and scandium oxalate precipitation rate is shown. 4 is a graph showing an example of the relationship between the pH of solids containing scandium hydroxide at the end of a water washing step and the Sc loss rate to the washing liquid.

Specific embodiments for carrying out the invention of the present disclosure will be described below. The following discussion is intended to facilitate understanding of the invention of this disclosure. it is not intended to limit the scope of the invention.

1. Overview A method according to an embodiment of the present invention relates to a method for recovering Sc and includes at least the following steps.
- A step of washing the solids containing scandium hydroxide with water - A step of adjusting the pH of the aqueous solution containing the washed solids to 2.0 to 5.0 to leach Sc - The leachate obtained in the above step is Step of separating into solution and step of precipitating Sc in the solution The above method will be described in detail below.

2. raw materials
A solid substance containing scandium hydroxide is used as an object (raw material) for Sc recovery. The solid matter contains various impurities in addition to scandium hydroxide. For example, the impurity elements contained in the solid matter include Si, P, Cl, Na, Ca, Al, Ti, Fe, Cu, Nb, Zr, Hf, and the like. Typically, the solid containing scandium hydroxide may contain 0.1% or more (preferably 0.1% or more and 1.0% or less) of Ti.

In one embodiment, a solid containing scandium hydroxide can be obtained through the following steps.
a step of solvent extraction of Sc from a solution containing Sc;
- Obtaining scandium hydroxide by back-extracting Sc with NaOH

For example, in the step of extracting Sc with a solvent, a mixed solvent of D2EHPA (Bis(2-ethylhexyl) phosphate) and TBP (tributyl phosphate) can be added to the solution containing Sc. As a result, Sc can be moved to the oil phase side, while some elements other than Sc (for example, Nb, Cr, etc.) can be left in the water phase side (the liquid after Sc extraction).

After this, NaOH can be added to the oil phase side to perform Sc back extraction. As a result, Sc exists in the aqueous phase in the form of scandium hydroxide. If necessary, HCl or NaCl may be added to the oil phase to which Sc has migrated to perform scrubbing before back extraction. This makes it possible to reduce the contamination of Ti, Fe, V, Th, and the like.

Impurities can be reduced to some extent through the step of solvent-extracting Sc and the step of back-extracting Sc as described above. However, impurities still remain in the solid matter containing scandium hydroxide that has migrated to the aqueous phase side due to back extraction. Therefore, there is still room for improving the purity of Sc.

In a preferred embodiment, the solution containing Sc to be solvent extracted may be derived from ores. Examples of ores include nickel-containing ores and titanium-containing ores. Taking an ore containing titanium as an example, titanium tetrachloride is produced by chlorinating the ore. After the chlorination reaction, titanium leaves the ore in the form of titanium tetrachloride, resulting in a residue. The residue contains rare metals such as Sc. The residue can be recovered and the Sc can be leached from the residue with an acidic solution. After leaching, Sc can be precipitated. The Sc-containing leachate can then be subjected to solvent extraction as described above.

In the above-mentioned Patent Document 2, the Sc solution after leaching from the ore (in other words, the Sc solution before the solvent extraction operation) is adjusted to a specific pH, thereby increasing the purity of Sc. disclosed to raise On the other hand, the method in one embodiment of the present disclosure adjusts the pH in processing the solid matter containing scandium hydroxide obtained in the step after the solvent extraction described above. In general, Sc exists in various compound forms during Sc leaching from solids and in Sc solutions after leaching. Patent document 2 discloses the optimum pH according to various compound forms regarding Sc. On the other hand, in the method of one embodiment of the present disclosure, Sc is in the form of scandium hydroxide, and the optimum pH is adopted for that form.

A scandium hydroxide slurry is obtained through the step of solvent-extracting Sc and the step of back-extracting Sc. By properly performing the back extraction, the oil and the scandium hydroxide slurry can be efficiently separated. By separating the separated slurry and oil and subjecting the slurry to solid-liquid separation such as filtration, a solid containing scandium hydroxide suitable for the treatment according to the present embodiment can be obtained.

3. Water washing process
The solid matter containing scandium hydroxide is washed with water. This can remove some impurities (eg NaOH). In a more preferred embodiment, the pH of the solution used for washing with water is more than 5.0 and 7.0 or less, more preferably more than 5.0 and 6.0 or less, more preferably in the range of 5.5 to 6.0. adjust to Although the method for adjusting the pH is not particularly limited, typically hydrochloric acid can be used. By washing with water in the above pH range, it is possible to remove impurities, particularly rare earth elements, especially light rare earth elements such as La, Ce, and Pr, while preventing dissolution of scandium hydroxide.

After washing with water, the solids containing scandium hydroxide are treated in the leaching process described in the next section. If necessary, after washing with water, the solid matter containing scandium hydroxide may be filtered and dried.

4. Leaching process
After washing with water, the solid containing scandium hydroxide is subjected to a leaching treatment to make Sc leached into the solution. The pH of the solution during leaching is 2.0-5.0, preferably 2.0-4.5, more preferably 3.5-4.5. If the pH exceeds 5.0, the Sc leaching rate may decrease. If the pH is less than 2.0, the leaching rate of Sc is good, but impurities other than Sc (eg, Ti, Fe, etc.) may be leached. Although the pH adjustment method is not particularly limited, hydrochloric acid can be preferably used. When hydrochloric acid is used, the presence of Cl is preferable in that it does not adversely affect the subsequent step of metallizing Sc during recovery. Moreover, by using hydrochloric acid, the possibility of contamination by impurities caused by the solution for adjusting the pH can be reduced as compared with the case of using sulfuric acid containing sulfur S or the like.

5. Separation process
The leaching solution obtained by the leaching step in the preceding paragraph is separated into a residue and a solution (hereinafter also referred to as "Sc solution") by solid-liquid separation such as filtration. The Sc solution obtained by the separation step is subjected to the precipitation treatment described in the next section.

6. Precipitation process
In the precipitation step, a process of precipitating Sc from the Sc solution is performed. Sc can be recovered by recovering the precipitate. In a preferred embodiment, specific pH conditions can promote the precipitation of Sc. More specifically, the pH of the Sc solution before the precipitation step is preferably 0 to 4.0, more preferably 1.0 to 3.0. If the pH exceeds 4.0, the Sc precipitation rate decreases. If the pH is less than 0, the solubility of the scandium carboxylate, which will be described later, increases, resulting in a decrease in the precipitation rate of Sc. Although the method for adjusting the pH is not particularly limited, typically hydrochloric acid can be used.

In a preferred embodiment, a carboxylic acid can be added to the Sc solution when precipitating Sc. A preferred example of carboxylic acid is oxalic acid. Addition of a carboxylic acid (especially oxalic acid) can promote the formation of a precipitate between Sc and the carboxylic acid (eg scandium oxalate).

The amount of carboxylic acid (preferably oxalic acid) to be added is not particularly limited, but it is 1 equivalent or more, preferably 2.4 equivalent or more, relative to Sc. If it is less than 1 equivalent, there will be insufficient carboxylic acid to form a precipitate with Sc. In addition, if it is 2.4 equivalents or more, precipitation of other impurity elements can be suppressed. As the concentration of the carboxylic acid to be added is increased, the effect of reducing impurities in the recovered Sc can be obtained. Although the upper limit of the amount of the carboxylic acid to be added is not limited to the following, it can typically be 4 equivalents or less.

7. others
After the precipitation step, the precipitate can be collected by filtration. The precipitate can then be calcined and finally recovered in the form of Sc ₂ O ₃ .

Examples are set forth below to further facilitate understanding of the present disclosure. These, like the above embodiments, are not intended to limit the scope of the invention.

For the elements contained in the sample, GDMS (Glow Discharge Mass Spectrometry) method (manufactured by VG Scientific, VG-9000) and ICP-OES (Incudtivity Coupled Plasma Optical Emission Spectrometer) method (manufactured by Seiko Instruments Inc. , SPS3100). GDMS analysis values are values obtained by excluding gas components (H, C, N, O) and calculating the grade of each element based on the matrix component Sc. In other words, it can be said that the quality is almost the same as when considered as scandium metal.

(Example 1)
Sc was leached from the residue derived from titanium ore (residue after chlorination reaction). D2EHPA was then added to the Sc leachate for solvent extraction. Further, NaOH was added and back extraction was performed to separate the oil and the scandium hydroxide slurry, and the scandium hydroxide slurry was separated from the oil. By filtering this scandium hydroxide slurry, a solid containing scandium hydroxide (and impurities) was obtained.

Thereafter, the solid containing scandium hydroxide was washed with water while adjusting the pH to 6.0. Adjustment of pH was performed using hydrochloric acid. After washing, it was filtered with a membrane filter and the solid matter remaining on the filter was dried.

GDMS analysis was performed on the solid matter. The results were as follows.

Next, 0.6 g of the solid was added to 30 ml of distilled water, and hydrochloric acid was added to adjust the pH to a range of about 0.5 to about 5.0, thereby leaching Sc from the solid. After that, it was filtered with a membrane filter to remove the residue. The Sc concentration in the filtrate in which Sc was dissolved (Sc solution) was analyzed by ICP-OES. Next, the Sc leaching rate was calculated based on the amount of Sc originally contained in the solid matter. The results are shown in FIG. A generally high leaching rate can be achieved in any pH range of the Sc solution from 0.5 to 5.0, and a leaching rate close to 100% can be achieved particularly at pH 3.5 to 4.5. I understand.

(Example 2)
Of the Sc solutions obtained in Example 1, 2.4 equivalents of oxalic acid were added to the Sc solutions other than those having a relatively low leaching rate of pH 4.9 to form a precipitate of scandium oxalate. The amount of Sc contained in the Sc solution was analyzed by ICP-OES, and the precipitation rate was calculated based on the amount of the solution before and after precipitation and the Sc concentration. The relationship between the Sc solution pH and the Sc precipitation rate before adding oxalic acid is shown in FIG. 2(a), and the relationship between the Sc solution pH and the Sc precipitation rate after precipitate formation is shown in FIG. 2(b). .

A high precipitation rate could be achieved in any pH range. In particular, in the pH range of 0 to 4.0 of the Sc solution before adding oxalic acid, a Sc precipitation rate close to 100% could be achieved.

(Example 3)
Of the Sc solution obtained in Example 1, the leaching solution in which Sc was leached at pH 4.0 was filtered with a membrane filter to remove residues, thereby obtaining an Sc solution. Next, 1.2 or 2.4 equivalents of oxalic acid was added to the Sc solution to form a precipitate of scandium oxalate. GDMS analysis was performed on the amounts of various impurities contained in the precipitate.

As shown in Table 2, the content of impurities after precipitation tended to decrease compared to the content of impurities in the raw material. In addition, for some elements, the content of impurities tended to decrease as the equivalent of oxalic acid increased.

(Example 4)
The solid matter containing scandium hydroxide obtained in Example 1 was poured into distilled water and washed with water while adjusting the pH by adding hydrochloric acid so that the pH ranged from 4.0 to 6.0. The Sc concentration contained in the washing liquid after washing was analyzed by ICP-OES, and the Sc loss rate to the washing liquid was calculated based on the amount of liquid before and after washing and the Sc concentration. The results are shown in FIG.

When the pH during washing was in the range of 5.0 or more (pH 5.0 to 6.0), the Sc loss rate to the washing liquid was low, and was almost 0% especially at pH 5.5 to 6.0. On the other hand, at pH 4.0, which is lower than pH 5.0, the Sc loss rate was confirmed to be about 50%.

Specific embodiments of the present disclosure have been described above. The above embodiments are only specific examples of the invention of the present disclosure, and the scope of the present invention is not limited to the above embodiments. For example, technical features disclosed in one of the above embodiments may be applied to other embodiments. Also, unless otherwise stated, for a particular method, some steps may be interchanged with other steps, and additional steps may be added between two particular steps. The scope of the invention is defined by the claims.

Claims (7)

a water washing step of washing the solid matter containing scandium hydroxide with water while adjusting the pH to 5.0 to 6.0 ;
a leaching step of leaching Sc by adjusting the pH of the aqueous solution containing the solids after washing to 2.0 to less than 5.0;
a separation step of separating the leaching solution obtained in the leaching step into a residue and a solution;
and a precipitation step of precipitating Sc in the solution. 2. The method for recovering scandium according to claim 1, wherein the washing step includes adjusting the pH of the solution used for washing to higher than 5.0 and lower than or equal to 7.0. 3. The method for recovering scandium according to claim 1, wherein the solution after the separation step and before the precipitation step has a pH of 0 to 4.0. The method for recovering scandium according to any one of claims 1 to 3, wherein the precipitation step includes adding a carboxylic acid to the solution. 5. The method for recovering scandium according to claim 4, wherein the carboxylic acid is oxalic acid. Before the water washing step,
Solvent extracting Sc from a solution containing Sc;
The method for recovering scandium according to any one of claims 1 to 5, further comprising the step of obtaining the scandium hydroxide by back-extracting Sc. The method for recovering scandium according to any one of claims 1 to 6, comprising adding hydrochloric acid in the leaching step.