JP2022024249A - Scandium recovery method - Google Patents

Abstract

To provide a method for recovering scandium of a high purity through effectively reducing an impurity grade of obtained oxalic acid scandium as well as suppressing variation of the impurity grade.SOLUTION: A method for recovering scandium from acidic solution (scandium-containing solution) containing scandium and an impurity metal element, includes a step of conducting an oxalic acid oxidation treatment through a reverse addition method of adding a scandium-containing solution to an oxalic acid solution housed in a container so as to obtain oxalic acid scandium. In the step, reaction temperature in the oxalic acid oxidation treatment is 20°C to 35°C.SELECTED DRAWING: Figure 3

Description

The present invention relates to a method for recovering scandium. More specifically, the present invention relates to a method for recovering scandium, which selectively recovers scandium from an acidic sulfuric acid solution containing impurities.

Scandium is known to be extremely useful as an additive element for aluminum alloys and as an electrolyte for fuel cells. However, it has not been widely used because of its low production volume and high cost.

Scandium has a particularly small ionic radius among rare earth elements, and is rarely present in ordinary rare earth minerals. Instead, it is known to be widely present in trace amounts in oxide ores of aluminum, tin, tungsten, zirconium, iron, nickel and the like.

In recent years, an HPAL process has been put into practical use in which nickel oxide ore is charged into a pressurized container together with sulfuric acid and heated to a high temperature to solid-liquid separation into a nickel-containing leachate and a leachate residue. A neutralizing agent is added to the leachate obtained by the HPAL process to separate impurities, and a sulfurizing agent is further added to recover nickel as nickel sulfide. Then, by treating the recovered nickel sulfide in an existing nickel smelting process, nickel salt compounds such as electric nickel, nickel sulfate, and nickel chloride can be obtained.

When the HPAL process as described above is used, the scandium contained in the nickel oxide ore is leached together with nickel and contained in the leachate, for example, as shown in Patent Document 1. Then, when a neutralizing agent is added to the leachate to separate impurities and then a sulfide agent is added, nickel is recovered as nickel sulfide, and scandium does not form sulfide and is an acidic solution after addition of the sulfide agent (sulfuric acid). Included in acidic solution). Thus, it is also known that nickel and scandium can be effectively separated by using the HPAL process.

However, the scandium concentration in the sulfuric acid acidic solution is dilute (several tens of mg / L), and other impurities such as iron and aluminum are contained in a much larger amount.

Therefore, in order to concentrate and purify scandium, a method of selectively recovering and concentrating scandium by an adsorption method using an ion exchange resin or a solvent extraction method is used. After that, in order to further improve the scandium quality, an alkali is added to the concentrated scandium solution to cause a crystallization reaction to form a hydroxide, or oxalic acid is added to crystallize the oxalic acid. It is recovered by processing such as analysis.

For example, among the above-mentioned methods, the method of crystallizing scandium as a hydroxide has a problem that it is difficult to selectively separate scandium because various impurity metals are contained in the starting liquid. be. Further, since the obtained hydroxide is in the form of a gel, the solid-liquid separation treatment such as filtration takes time, and the handleability is poor and the productivity is inferior.

Therefore, as a method for selectively recovering scandium, as described above, a crystallization reaction using oxalic acid ((COOH) ₂ ) (hereinafter referred to as “oxalic acid”) is often used.

As a method of shu oxidation, for example, there is a method as shown in Patent Document 2. That is, scandium is extracted from the scandium-containing solution by solvent extraction, and the back extract is crystallized as scandium oxalate using oxalic acid to separate and purify the scandium. Regarding the treatment of shu oxidation, specifically, an oxidizing agent such as hydrogen peroxide is added to an acidic solution containing scandium or iron as an impurity to control the redox potential (ORP) of the acidic solution within a certain range. While suppressing the precipitation formation of iron (II) oxalate, a oxalic acid solution is added to recover scandium in the form of oxalate oxide.

In the above-mentioned treatment, most of the acidic solutions containing scandium and iron contain iron in the form of divalent ions, and when iron oxide is carried out as it is, the solubility of iron (II) oxide produced. Due to its small size (solubility in water: 0.022 g / 100 g), iron (II) oxalate precipitates due to the oxalic acid reaction.

Therefore, in order to prevent the precipitation of iron (II) oxalate, an oxidizing agent is added to oxidize the ORP of the acidic solution to about 700 mV with a silver / silver chloride electrode as a reference electrode and maintain the divalent value. A method of oxidizing iron ions to trivalent iron ions is used. Since iron (III) oxalate, which is produced by shu oxidation of trivalent iron ions, has high solubility, it is possible to generate scandium oxalate while preventing the precipitation of iron (II) oxalate. ..

Further, as a further method in the shu oxidation step, for example, Patent Document 3 is a method of recovering scandium in the form of high-purity scandium oxide from a solution containing scandium and iron. Patent Document 3 discloses a method of adding a scandium-sulfuric acid acidic solution to a oxalic acid solution (hereinafter referred to as "reverse addition method") in order to reduce the amount of oxalic acid added and save the space for industrial equipment. There is.

In this Patent Document 3, the back addition method is carried out by oxalic acid oxidation, the pH of the solution containing scandium and iron is adjusted to the range of −0.5 or more and less than 1, and then the pH-adjusted scandium-containing solution is prepared. It is also disclosed to obtain scandium oxalate by adding it to a oxalic acid solution. By doing so, it is possible to prevent the precipitation of iron (II) oxalate without adding an oxidizing agent such as hydrogen peroxide, and further, it is possible to prevent the precipitation of impurities even when the concentration of impurities in the solution is high. ..

However, there is a problem that the quality of the recovered product obtained by the reverse addition method may vary, resulting in an increase in the quality of impurities and a spec-out of the final quality.

Japanese Unexamined Patent Publication No. 2000-313928 Japanese Unexamined Patent Publication No. 2014-12901 Japanese Unexamined Patent Publication No. 2016-141839

The present invention has been proposed in view of such circumstances, and is obtained in a scandium recovery method including a step of obtaining scandium oxalate by a scandium oxidation treatment from a scandium-containing solution containing an impurity metal element. It is an object of the present invention to provide a method capable of recovering high-purity scandium by effectively reducing the impurity grade of Scandium and suppressing the variation of the impurity grade.

As a result of repeated diligent studies, the present inventor performed the sucrose oxidation treatment by a reverse addition method in which a scandium-containing solution is added to the oxalic acid solution in the sucrose oxidation treatment step, and at that time, the reaction temperature of the sulphate oxidation reaction was specified. We have found that the above-mentioned problems can be solved by adjusting and maintaining the above range, and have completed the present invention.

(1) The first invention of the present invention is a method for recovering scandium from an acidic solution (scandium-containing solution) containing scandium and an impurity metal element, wherein the scandium is contained in the oxalic acid solution contained in the container. It is a scandium recovery method including a step of obtaining scandium oxalate by performing a scandium oxidation treatment by a reverse addition method of adding a solution, and in the step, the reaction temperature in the oxalate oxidation treatment is set to 20 ° C. or higher and 35 ° C. or lower. ..

(2) In the second invention of the present invention, in the first invention, the scandium-containing solution contains at least one selected from the group consisting of iron, nickel, and manganese as the impurity metal element. , Scandium recovery method.

(3) The third invention of the present invention is the first or second invention, wherein the scandium-containing solution is produced by adding a sulfurizing agent to a leachate obtained by leaching nickel oxide ore with sulfuric acid. This is a method for recovering scandium, which is a solution after separating sulfides.

(4) In the fourth aspect of the present invention, in any one of the first to third inventions, in the step, the pH of the scandium-containing solution is adjusted to a range of −0.5 or more and less than 1.0. This is a scandium recovery method for performing the pH oxidation treatment.

(5) The fifth aspect of the present invention is the method for recovering scandium in any one of the first to fourth inventions, wherein no oxidizing agent is added to the scandium-containing solution to be subjected to the shu oxidation treatment.

INDUSTRIAL APPLICABILITY According to the present invention, it is possible to provide a method capable of effectively reducing the impurity grade of the obtained scandium oxalate, suppressing the variation in the impurity grade, and recovering high-purity scandium.

It is a flow chart which shows an example of the flow of the wet smelting process of nickel oxide ore. It is a flow chart which shows an example of the flow of the ion exchange process performed by the ion exchange reaction using a chelate resin. The flow chart of the shu oxidation treatment is shown. It is a graph when the relationship between the reaction temperature and Ni grade in the oxalic acid treatment in Test Example 1 to Test Example 16 is compared with two kinds of oxalic acid equivalents. It is a graph when the relationship between the reaction temperature and Mn grade in the oxalic acid treatment in Test Example 1 to Test Example 16 is compared with two kinds of oxalic acid equivalents. It is a graph when the relationship between the reaction temperature and Fe grade in the oxalic acid treatment in Test Example 1 to Test Example 16 is compared with two kinds of oxalic acid equivalents.

Hereinafter, a specific embodiment of the present invention (hereinafter, referred to as “the present embodiment”) will be described in detail. The present invention is not limited to the following embodiments, and various modifications can be made without changing the gist of the present invention. Further, in the present specification, the notation "X to Y" (X and Y are arbitrary numerical values) means "X or more and Y or less".

≪1. Overview ≫
The method for recovering scandium according to the present embodiment is a method for recovering scandium from an acidic solution containing scandium and an impurity metal element (hereinafter, also referred to as "scandium-containing solution").

Specifically, this method for recovering scandium includes a step of subjecting a scandium-containing solution containing scandium and an impurity metal element to a scandium-oxidizing treatment that causes a reaction to oxidize scandium with oxalic acid. In particular, in the scandium recovery method according to the present embodiment, as the oxalic acid treatment, a scandium-containing solution is added to the oxalic acid solution contained in the container, which is a so-called "reverse addition" method to obtain scandium oxalate. ..

As a scandium-containing solution containing an impurity metal element to be subjected to the shu oxidation treatment, a solution obtained by sulphurizing the leachate obtained by high-pressure acid leaching (HPAL) treatment on nickel oxide ore to separate nickel (post-sulfurized liquid). Can be used. Further, the post-sulfurized liquid may be further subjected to an ion exchange treatment and / or a solvent extraction treatment to separate impurities into a concentrated scandium solution, and the concentrated solution may be used. In the HPAL process, nickel is converted to sulfur by sulfurization treatment, while scandium can remain in the solution, and nickel and scandium can be effectively separated.

The scandium recovery method according to the present embodiment is characterized in that the reaction temperature is adjusted to a specific range to cause a succulent oxidation reaction in the step of performing the sulphate oxidation treatment by the back addition method. Specifically, the shu oxidation reaction is caused by setting the reaction temperature in the shu oxidation treatment to 20 ° C. or higher and 35 ° C. or lower.

According to such a method, the impurity metal element contained in the scandium-containing solution can be suppressed from becoming a precipitate as an oxalate, and the impurity grade contained in the obtained scandium oxalate crystal can be effectively reduced. In addition, it is possible to suppress variations in the impurity grade in scandium oxalate, and it is possible to stably obtain high-purity scandium oxalate.

In addition, for example, by roasting the crystals of scandium oxalate obtained by subjecting such a scandium oxide treatment, it can be recovered in the form of scandium oxide.

≪2. Scandium recovery method ≫
Hereinafter, the scandium recovery method according to the present embodiment will be described in more detail.

<2-1. Wet smelting process of nickel oxide ore ＞
In the method for recovering scandium according to the present embodiment, as described above, as a solution containing scandium and an impurity metal element (scandium-containing solution), a leachate obtained by high-pressure acid leaching treatment of nickel oxide ore is used. A solution after separating nickel as a sulfide (post-sulfide solution) can be used. Further, it is also possible to use a solution from which impurity components have been removed by performing an ion exchange treatment or a solvent extraction treatment on the after sulfidation liquid.

These scandium-containing solutions contain impurity metal elements such as iron (Fe), manganese (Mn), aluminum (Al), chromium (Cr), and magnesium (Mg). In addition, nickel (Ni) that has not been separated as a sulfide may also be contained as an impurity.

In the following, first, a hydrometallurgical process of nickel oxide ore for obtaining a scandium-containing solution as a starting material will be described.

FIG. 1 is a flow chart showing the flow of the hydrometallurgical process of nickel oxide ore. The hydrometallurgical process of nickel oxide ore consists of a leaching step S11 in which the nickel oxide ore is leached with sulfuric acid under high temperature and high pressure to obtain a leaching slurry, and a solid-liquid separation step S12 in which the leaching slurry is solid-liquid separated into a leachate and a leachate residue. S13, a neutralization step S13 in which a neutralizing agent is added to the leachate to obtain a neutralized starch containing impurities and a post-neutralizing liquid, and a sulfurizing agent is added to the post-neutralizing liquid to obtain nickel sulfide and a post-sulfurized liquid. It has a sulfurization step S14 for obtaining the above.

(1) Leaching step In the leaching step S11, for example, using a high-temperature pressure vessel (autoclave) or the like, sulfuric acid is added to a slurry of nickel oxide ore and high-pressure steam and high-pressure air are supplied to a temperature of 240 ° C to 260 ° C. It is a step of performing a stirring treatment below to generate a leachate slurry composed of a leachate containing nickel and a leachate residue containing hematite. Scandium is contained in the leachate together with nickel.

Here, examples of the nickel oxide ore include so-called laterite ores such as limonite ore and saprolite ore. The nickel content of the laterite ore is usually 0.8 to 2.5% by weight, and is contained as a hydroxide or a siliceous earth (magnesium silicate) mineral. In addition, these nickel oxide ores contain scandium.

(2) Solid-Liquid Separation Step In the solid-liquid separation step S12, the leachate slurry generated in the above-mentioned leachation step S11 is washed in multiple stages to separate the leachate containing nickel and cobalt from the leachate residue which is hematite. Is.

In the solid-liquid separation step S12, the leachate slurry is mixed with the cleaning liquid, and then the solid-liquid separation treatment is performed using a solid-liquid separation device such as a thickener. Specifically, the slurry is first diluted with a washing liquid, and then the leachate residue in the slurry is concentrated as a thickener sediment. Thereby, the nickel content adhering to the leachate residue can be reduced according to the degree of dilution thereof. In actual operation, thickeners with such functions are used in multiple stages.

(3) Neutralization Step The neutralization step S13 is a step of adding a neutralizing agent to the leachate to adjust the pH to obtain a neutralized starch containing an impurity element and a neutralized liquid. By the neutralization treatment in the neutralization step S13, valuable metals such as nickel, cobalt, and scandium are contained in the neutralized liquid, and most of the impurities such as aluminum become neutralized starch.

In the neutralization step S13, known neutralizing agents can be used, and examples thereof include limestone, slaked lime, and sodium hydroxide. Further, in the neutralization treatment, it is preferable to adjust the pH to the range of 1 to 4 while suppressing the oxidation of the separated leachate, and it is more preferable to adjust the pH to the range of 1.5 to 2.5. preferable. If the pH is less than 1, neutralization may be insufficient and the neutralized starch and the neutralized liquid may not be separated. On the other hand, when the pH exceeds 4, not only impurities such as aluminum but also valuable metals such as scandium and nickel may be contained in the neutralized starch.

(4) Sulfurization Step The sulfurization step S14 is a step of adding a sulfurizing agent to the neutralized liquid obtained in the neutralization step S13 to obtain nickel sulfide and a post-sulfurized liquid. By the sulfurization treatment in the sulfurization step S14, nickel, cobalt, zinc and the like are recovered as sulfurized substances, and scandium and the like remain in the after sulfidation liquid. Therefore, nickel and scandium can be effectively separated by the sulfurization treatment in such a hydrometallurgical process.

Specifically, in the sulfurization step S14, a sulfurizing agent such as hydrogen sulfide gas, sodium sulfide, and sodium hydride sulfide is supplied to the obtained after-neutralization liquid to provide a sulfide containing nickel having a small impurity component (sulfide). Nickel sulfide) and a post-sulfurization liquid containing scandium and the like are produced by stabilizing the nickel concentration at a low level.

In the sulfurization treatment in the sulfurization step S14, the nickel sulfide slurry is separated and separated using a sedimentation separator such as a thickener, and the nickel sulfide is separated and recovered from the bottom of the thickener, while the after-sulfurization liquid, which is an aqueous solution component, overflows. Let me collect it.

In the scandium recovery method according to the present embodiment, for example, the post-sulfidation solution, which is an acidic sulfuric acid solution obtained through each step in the hydrometallurgical process of nickel oxide ore as described above, is recovered and used as a starting material. be able to. Further, a solution obtained by subjecting the after-sulfurized liquid to an ion exchange treatment and a solvent extraction treatment, which will be described later, can be used as a starting material. The scandium recovery method produces scandium oxide from such a solution.

<2-2. Ion exchange treatment, solvent extraction treatment>
In the method for recovering scandium according to the present embodiment, as described above, as a scandium-containing solution, an ion exchange treatment and a solvent are applied to the post-sulfurized liquid obtained through the hydrometallurgical step of the wet smelting process of nickel oxide ore. The solution obtained by subjecting the extraction treatment can be used. By subjecting the post-sulfidation liquid to an ion exchange treatment and / or a solvent extraction treatment in this way, impurities in the solution can be separated and removed to concentrate scandium.

Hereinafter, the ion exchange treatment and the solvent extraction treatment will be described. Although the solvent extraction treatment is described by taking as an example a mode in which the eluent obtained through the ion exchange treatment is treated, it is possible to perform only the solvent extraction treatment without performing the ion exchange treatment. good.

(1) Ion exchange treatment The post-sulfidation liquid contains aluminum, chromium and the like as impurities. For this reason, when recovering scandium in the solution as scandium oxide, it is preferable to remove these impurities and concentrate the scandium. Examples of the method for concentrating scandium include a method by ion exchange treatment using a chelate resin.

FIG. 2 is a flow chart showing an example of the flow of an ion exchange process performed by an ion exchange reaction using a chelate resin. In addition, FIG. 2 also shows the flow until the scandium eluent obtained by the ion exchange treatment is subjected to the solvent extraction treatment. In the ion exchange treatment, the post-sulfidation liquid obtained through the sulfurization step S14 (FIG. 1) in the hydrometallurgical process of nickel oxide ore is brought into contact with the chelate resin, and the scandium in the post-sulfidation liquid is adsorbed on the chelate resin. To obtain a scandium (Sc) eluent.

The mode (each step) of the ion exchange treatment is not particularly limited, but as shown in FIG. 2, for example, an adsorption step S21 in which the post-sulfurized liquid is brought into contact with the chelate resin to adsorb scandium to the chelate resin, and sulfuric acid is added to the chelate resin. The aluminum removal step S22 for removing the aluminum adsorbed on the chelate resin by contacting the chelate resin, the scandium elution step S23 for obtaining the scandium eluent by contacting sulfuric acid with the chelate resin that has undergone the aluminum removal step S22, and the scandium elution step S23. An example thereof includes a chrome removing step S24 in which sulfuric acid is brought into contact with the chelate resin and the chrome adsorbed on the chelate resin is removed in the adsorption step S21.

[Adsorption process]
In the adsorption step S21, the after-sulfidated liquid is brought into contact with the chelate resin to adsorb scandium to the chelate resin. The type of chelate resin is not particularly limited, and for example, a resin having iminodiacetic acid as a functional group can be used.

[Aluminum removal process]
In the aluminum removal step S22, sulfuric acid of 0.1 N or less is brought into contact with the chelate resin adsorbed with scandium in the adsorption step S21 to remove the aluminum adsorbed on the chelate resin. When removing aluminum, it is preferable to maintain the pH in the range of 1 or more and 2.5 or less, and it is more preferable to maintain the pH in the range of 1.5 or more and 2.0 or less.

[Scandium elution process]
In the scandium elution step S23, sulfuric acid of 0.3N or more and less than 3N is brought into contact with the chelate resin that has undergone the aluminum removal step S22 to obtain a scandium eluent. When obtaining the scandium eluate, the normality of sulfuric acid used in the eluent is preferably maintained in the range of 0.3N or more and less than 3N, and more preferably maintained in the range of 0.5N or more and less than 2N.

[Chromium removal process]
In the chromium removing step S24, sulfuric acid of 3N or more is brought into contact with the chelate resin that has undergone the scandium elution step S23 to remove chromium adsorbed on the chelate resin. When the normality of sulfuric acid used in the eluent is less than 3N when removing chromium, it is not preferable because chromium is not properly removed from the chelate resin.

By such an ion exchange treatment, impurities such as aluminum and chromium are removed, and a scandium-enriched scandium eluent can be obtained. By repeating the same ion exchange treatment on the obtained scandium eluate again, the concentration of the scandium eluent can be increased. As for the number of repetitions, the concentration of recovered scandium increases as the number of repetitions increases, but the degree of increase in the concentration of recovered scandium decreases even if the number of repetitions is too large, so it is industrially about 8 times or less. preferable.

(2) Solvent Extraction Treatment In the solvent extraction treatment, the scandium (Sc) eluent obtained through the above-mentioned ion exchange treatment is brought into contact with a predetermined extractant to extract scandium.

The extractant used for solvent extraction is not particularly limited, and an amine-based extractant, a phosphoric acid-based extractant, or the like can be used. Further, depending on the type of the extractant, the scandium to be extracted can be extracted in an organic solvent containing the extractant, or the extractant can selectively extract the impurity component and the scandium is contained in the extraction residue. It can be made to remain. For example, when an amine-based extractant is used, since it is an extractant having low selectivity with scandium, impurity components are selectively extracted in an organic solvent, and scandium is concentrated in the extraction residue.

The mode (each step) of the solvent extraction treatment is not particularly limited, but the extraction step S31 and the extraction step S31 in which the scandium eluent and the extractant are mixed to extract impurities and then separated into an organic solvent and a drawing residue containing scandium. The scrubbing step S32, in which a hydrochloric acid solution or a sulfuric acid solution is mixed with the organic solvent after extraction to separate a trace amount of scandium contained in the organic solvent after extraction, and the back extraction starting solution is mixed with the organic solvent after washing, and the organic solvent is used after washing. An example thereof includes a back extraction step S33 in which impurities are back-extracted to obtain a back-extract solution. By performing the solvent extraction treatment in this way, the purity of scandium contained in the scandium eluent can be further increased.

[Extraction process]
In the extraction step S31, a scandium-containing solution and an organic solvent containing an extractant are mixed, impurities are selectively extracted into the organic solvent, and the organic solvent containing the impurities and the scandium-concentrated extract residue liquid. And get.

As the extractant, for example, an amine-based extractant is used. As the amine-based extractant, products such as PrimeneJM-T, which is a primary amine, LA-1, which is a secondary amine, TNOA (Tri-n-octylamine), which is a tertiary amine, and TIOA (Tri-i-octylamine). An amine-based extractant known by the name can be used.

At the time of extraction, it is preferable to dilute an extractant such as an amine-based extractant with a hydrocarbon-based organic solvent or the like before use. The concentration of the extractant in the organic solvent is not particularly limited, but is preferably about 1% by volume or more and 10% by volume or less, particularly 5 volumes, in consideration of phase separation during extraction and back extraction described later. It is more preferably about%. The volume ratio of the organic solvent to the scandium-containing solution at the time of extraction is not particularly limited, but the amount of the organic solvent mol is about 0.01 times or more and 0.1 times or less with respect to the amount of metal in the scandium-containing solution. Is preferable.

[Scrubbing (cleaning) process]
In the extraction step S31, when scandium is slightly coexisted in the organic solvent obtained by extracting impurities from the scandium-containing solution, the obtained extract is subjected to the organic solvent (organic phase) before back extraction. It is preferable to perform a scrubbing (washing) treatment to separate the scandium into an aqueous phase and recover it from the extractant (scrubbing step S32). By providing the scrubbing step S32 to wash the organic solvent and separating a small amount of scandium extracted by the extractant, scandium can be separated into the washing liquid, and the scandium recovery rate can be further increased. ..

As the solution (washing solution) used for scrubbing, a sulfuric acid solution, a hydrochloric acid solution, or the like can be used. Further, it is also possible to use water to which soluble chloride or sulfate is added. Specifically, when a sulfuric acid solution is used as the cleaning solution, it is preferable to use a solution having a concentration range of 1.0 mol / L or more and 3.0 mol / L or less.

Since the number of cleaning stages (number of times) depends on the type and concentration of the impurity element, it can be appropriately changed depending on each extractant and extraction conditions. For example, when the phase ratio O / A of the organic phase (O) and the aqueous phase (A) is O / A = 1, the number of stages is about 3 to 5, and the scandium extracted in the organic solvent is detected by the analyzer. It can be separated to less than the lower limit.

[Reverse extraction process]
In the back extraction step S33, impurities are back extracted from the organic solvent from which the impurities have been extracted in the extraction step S31. Specifically, in the back extraction step S33, a back extraction solution (back extraction starting solution) is added to an organic solvent containing an extractant and mixed to cause a reaction opposite to the extraction process in the extraction step S31. The impurities are back-extracted to obtain a liquid after back-extraction containing the impurities.

The concentration of the solution containing carbonate, which is a back-extraction solution, is preferably about 0.5 mol / L or more and 2 mol / L or less from the viewpoint of suppressing excessive use.

When the organic solvent containing the extractant is subjected to the scrubbing treatment in the scrubbing step S32, the back-extraction treatment is similarly performed by adding the back-extraction solution to the scrubbing extractant and mixing it. It can be performed.

The extractant after adding a carbonate solution such as sodium carbonate to the extractant after extraction or the extractant after scrubbing in this way and performing a back-extraction treatment to separate impurities is again in the extraction step S31. It can be repeatedly used as an extractant used in the extraction process.

<2-3. Shu oxidation treatment>
The scandium recovery method according to the present embodiment includes a step of subjecting a scandium-containing solution to an oxalate treatment to convert scandium into an oxalate (scandium oxalate). Specifically, a scandium-containing solution, which is a back extract obtained through the above-mentioned solvent extraction treatment, is used to perform a scandium oxidation treatment for forming scandium oxalate crystals. As described above, by converting scandium into oxalate by the oxalate oxidation treatment, handling properties such as filterability can be improved, and scandium can be efficiently recovered.

The scandium-containing solution obtained through the solvent extraction treatment is a solution in which most of the impurity metal elements have been removed by the above-mentioned ion exchange treatment or solvent extraction treatment to concentrate scandium. However, it contains a certain amount of impurity metal elements that were not removed by these treatments (see the composition of the Shu oxidation starting solution shown in Table 1 in Examples described later). Specifically, examples of the impurity metal element include at least iron, nickel, manganese, aluminum, chromium, magnesium and the like.

Here, as the method of the shu oxidation treatment, the so-called "reverse addition" method is used. Specifically, the scandium-containing solution is gradually added to the oxalic acid solution contained in a predetermined container to precipitate and generate solid crystals of scandium oxalate. According to the shu oxidation treatment based on such a back addition method, iron shu oxidation, which is an impurity metal element, is performed without adding an oxidizing agent such as hydrogen peroxide to adjust the redox potential (ORP). Can be suppressed and the formation of iron (II) oxalate precipitates can be prevented.

The reaction temperature is set to a specific range, specifically, 20 ° C. or higher and 35 ° C. or lower in the shu oxidation treatment by the reverse addition method. Further, it is preferably 20 ° C. or higher and 30 ° C. or lower, and more preferably 23 ° C. or higher and 30 ° C. or lower.

In the conventional oxalic acid treatment, it is common to add an oxalic acid solution to a scandium-containing solution, that is, a so-called "normal addition" method (standard addition method), and the reaction temperature thereof is also a matter of course. However, in the oxalic acid treatment, although scandium oxalate can be preferentially generated to suppress the precipitation of impurity metal elements, the quality of impurities in the obtained scandium oxalate varies depending on the treatment conditions. It was easy to occur, and it was not possible to stably obtain scandium oxalate with the specified specifications.

In the oxalate oxidation treatment, metal elements other than scandium, which is a rare earth element, also react with oxalic acid to form a complex, but impurity metal elements with low complex stability are adsorbed on the precipitate of scandium oxalate and co-precipitate. .. It is considered that the stability of such a complex depends not only on the type of the metal element but also on the conditions of the oxalic acid treatment, which causes variations in the impurity grade in the obtained scandium oxalate.

In the present embodiment, as described above, a scandium-containing solution is added to the oxalic acid solution contained in a predetermined container to cause a oxalic acid reaction, and the oxalic acid treatment is carried out by a "reverse addition" method. The reaction temperature at this time is set to 20 ° C. or higher and 35 ° C. or lower. This makes it possible to suppress the oxalate formation of the impurity metal element contained in the scandium-containing solution and effectively reduce the impurity grade contained in the scandium oxalate crystal. In addition, it is possible to suppress variations in the quality of impurities contained in the crystals regardless of the conditions of the shu oxidation treatment. In particular, among the impurity metal elements contained in the scandium-containing solution, the variation in quality of iron (Fe), nickel (Ni), and manganese (Mn) can be effectively suppressed.

The mechanism by which the variation in impurity grade in scandium oxalate can be suppressed by setting the reaction temperature within a specific range is unknown, but the number of hydrated water changes depending on the temperature in the oxalate oxidation reaction, which affects the solubility of impurities. It is possible that it is giving.

According to such a method of oxalate oxidation treatment, scandium oxalate containing scandium with high purity and stable impurity-containing specifications can be obtained, and by roasting the scandium oxalate, high quality can be obtained. Scandium oxide can be obtained.

FIG. 3 shows a flow chart of the shu oxidation treatment. As described above, the present embodiment is characterized in that the reaction temperature is set to 20 ° C. or higher and 35 ° C. or lower during the oxalate oxidation treatment by the back addition method. Specifically, in the oxalic acid treatment, a temperature adjusting step S41 for adjusting the temperature of the scandium-containing solution and a scandium oxalate crystal by adding the temperature-adjusted solution (starting solution of oxalic acid) to the oxalic acid solution contained in the container. It has a crystallization step S42 for precipitating. The obtained scandium oxalate crystals can be recovered by passing through the filtration / cleaning step S43 in which the filtration / cleaning treatment is performed.

Further, it is preferable to adjust the pH of the scandium-containing solution to a range of −0.5 or more and 1.0 or less prior to the treatment in the crystallization step S42. That is, although not shown in FIG. 3, a pH adjusting step is provided to adjust the pH of the scandium-containing solution to be treated in the crystallization step S42 in advance within the above range. As a result, the solubility of iron (II) oxalate and the like can be increased, and the precipitation formation of impurities can be more effectively suppressed without using an expensive oxidizing agent or the like, and scandium with higher purity can be recovered. be able to. The pH of the scandium-containing solution may be adjusted before or after the temperature adjustment step S41, or may be performed at the same timing as the temperature adjustment.

(Temperature adjustment process)
In the temperature adjusting step S41, the temperature of the scandium-containing solution to be subjected to the shu oxidation treatment is adjusted to 20 ° C. or higher and 35 ° C. or lower, preferably 20 ° C. or higher and 30 ° C. or lower, and more preferably 23 ° C. or higher and 30 ° C. or lower. As described above, the temperature of the scandium-containing solution is adjusted to a range of 20 ° C. or higher and 35 ° C. or lower, and the temperature is maintained to cause a reaction in the next crystallization step S42 to obtain scandium oxalate crystals. It is possible to reduce the contained impurity grade and suppress the variation in the impurity grade.

The method for adjusting the temperature of the scandium-containing solution is not particularly limited, and the temperature can be adjusted by using, for example, a heater or the like.

Further, as described above, in the oxalic acid treatment, since the scandium-containing solution is gradually added to the oxalic acid solution contained in the container to cause the oxalic acid reaction, the oxalic acid solution used for the oxalic acid treatment is previously prepared. It is preferable to adjust the temperature to a range of 20 ° C. or higher and 35 ° C. or lower, and maintain the temperature for reaction. Thereby, the reaction temperature can be appropriately maintained in the range of 20 ° C. or higher and 35 ° C. or lower, and the variation in the impurity grade in the obtained scandium oxalate can be more effectively suppressed.

(Crystalization process)
In the crystallization step S42, the reaction temperature is set to 20 ° C. or higher and 35 ° C. or lower, and a scandium-containing solution (starting solution for oxalic acid) is added to the oxalic acid solution to perform a oxalic acid treatment to cause a reaction to oxidize scandium. , Obtain scandium oxalate (crystals of scandium oxalate).

Regarding the reaction temperature of the oxalic acid reaction, if the reaction temperature is higher than 35 ° C., the impurities grade in the obtained scandium oxalate varies. Further, if the reaction temperature is less than 20 ° C., the reaction rate may decrease, and the solubility of the oxalate may decrease, causing a problem that the oxalate precipitates in an unfavorable place such as a supply pipe.

As described above, the oxalic acid solution is contained in a reaction vessel, and a scandium-containing solution is added to the oxalic acid solution to cause a reaction by a "reverse addition" method. The amount of the oxalic acid solution is preferably at least 1.05 times or more, more preferably 2.0 times or more the equivalent amount required for precipitating scandium in the scandium-containing solution as an oxalate. preferable. If the amount used is less than 1.05 times the required equivalent, it may not be possible to effectively recover the entire amount of scandium.

Further, as the oxalic acid solution, it is preferable to use a solution having its pH adjusted to the range of −0.5 or more and 1.0 or less. In particular, when adjusting the pH of the scandium-containing solution to the range of -0.5 or more and 1.0 or less, the pH of the oxalic acid solution can also be adjusted to further reduce the impurity grade, resulting in a high pH. Pure scandium can be recovered.

In the above-mentioned example, the scandium-containing solution is adjusted to a temperature of 20 ° C. or higher and 35 ° C. or lower in advance, and the reaction temperature in the crystallization step S42 is set to 20 ° C. or higher and 35 ° C. or lower while maintaining the temperature. I explained, but it is not limited to this. That is, the reaction temperature when the scandium-containing solution is added to the oxalic acid solution to cause a reaction may be maintained in the range of 20 ° C. or higher and 35 ° C. or lower.

<2-4. Generation of scandium oxide (roasting)>
In the present embodiment, scandium oxide is obtained by roasting the crystals of scandium oxalate obtained by performing the oxalate oxidation treatment as described above.

The roasting treatment is a treatment in which the scandium oxalate crystals obtained by the oxalic acid oxidation treatment are washed with water, dried, and then roasted. By undergoing this roasting treatment, scandium can be recovered as scandium oxide.

In particular, in the present embodiment, since the reaction is caused by setting the reaction temperature in the above-mentioned oxalic acid oxidation treatment within a specific range, the impurity grade of the scandium oxalate to be produced is effectively reduced, and the impurity grade is reduced. Variations are also suppressed. Therefore, by roasting such scandium oxalate, it is possible to obtain scandium oxide containing high-purity scandium in which the impurity grade is reduced and the variation in the impurity grade is suppressed.

The conditions for the roasting treatment are not particularly limited, but for example, they may be placed in a tube furnace and heated at about 900 ° C. for about 2 hours. Industrially, it is preferable to use a continuous furnace such as a rotary kiln because drying and roasting can be performed by the same device.

Hereinafter, the present invention will be described in more detail with reference to Examples and Comparative Examples of the present invention. The present invention is not limited to the following examples.

(Hydrometallurgy process of nickel oxide ore)
Nickel oxide ore was leached with sulfuric acid using an autoclave, and slaked lime was added to the obtained leachate to neutralize it. Then, a sulfurizing agent was added to the obtained neutralized liquid to cause a sulfurization reaction, and nickel, cobalt and the like were separated as sulfides to obtain a scandium-containing post-sulfurized liquid.

(Ion exchange treatment, neutralization treatment)
Next, the obtained post-sulfurized solution is subjected to ion exchange treatment using a chelate resin to separate impurities in the solution, and an eluent containing scandium eluted from the chelate resin (scandium eluent) is obtained. rice field. Then, a neutralizing agent was added to the scandium eluent to form a scandium hydroxide precipitate.

(Solvent extraction treatment)
Next, sulfuric acid is added to the precipitate of scandium hydroxide and dissolved again to obtain a solution (scandium solution), which is then subjected to solvent extraction treatment using an amine-based extractant and extracted. As the residual liquid, most of the impurities were removed and purified, and a scandium solution (scandium-containing solution) in which scandium was concentrated was obtained.

(Shu oxidation treatment)
Next, using the obtained scandium-containing solution, a oxalate oxidation treatment was performed using scandium in the solution as an oxalate.

Specifically, sulfuric acid is added to the scandium-containing solution to adjust the pH to 0.28, and water is further added until the scandium concentration in the solution reaches about 4.5 g / L to dilute the solution. , Scandium oxidation starting solution was prepared. 500 ml of Shu oxidation starting solution was prepared for each test under the conditions shown in Tables 1 and 2 below. The pH was adjusted under the same temperature conditions as the reaction temperature (reaction temperature) of each test. The redox potential (ORP) of the scandium-containing solution was 500 mV to 560 mV with a silver / silver chloride electrode as a standard electrode.

Further, as the oxalic acid solution used for the oxalic acid treatment, a solution in which 100 g of oxalic acid was dissolved per 1 L of the liquid volume was prepared.

In the oxalic acid treatment, a oxalic acid solution in an amount of 183 ml, which is 2.7 equivalents, or 344 ml, which is 5.1 equivalents, with respect to scandium contained in the scandium used in each test is contained in a container. An initial solution of shu oxidation (scandium-containing solution) was added to the oxalic acid solution at a flow rate of 2.3 ml / min and reacted. The temperature (reaction temperature) at the time of the reaction is set at room temperature (23 ° C.), 30 ° C., 35 ° C., 42 ° C., or 50 ° C. for each test, and the oxalic acid solution is used as the starting solution for oxalic acid. The temperature was maintained from the start of addition to the end of stirring for 1 hour.

Table 1 below shows the test conditions for the equivalent of the oxalic acid solution and the reaction temperature in each test, and the analysis results of the concentration of the metal component contained in the scandium-containing solution (starting solution of oxalic acid) used for the oxalic acid treatment. As shown in Table 1, it can be seen that the scandium-containing solution contains various impurity metal elements.

After the stirring was completed, the mixture was allowed to stand to precipitate the crystallized scandium oxalate. Then, the supernatant was taken until the remaining liquid in the container was 150 ml, and the washing operation of adding 150 ml of pure water and stirring and washing was repeated twice. Each cleaning operation was performed under the same temperature conditions as the temperature at the time of adding oxalic acid (reaction temperature).

Next, after washing, the whole amount was filtered using a suction filtration device and a membrane filter having a pore size of 0.45 μm, and crystals of scandium oxalate were separated. Further, the separated crystals were put into 140 ml of pure water so as to have a slurry concentration of about 50 g / L, and repulp washing was repeated twice.

After washing the repulp, the whole amount was filtered using the same suction filtration device and a membrane filter, and scandium oxalate crystals were recovered. Then, the obtained scandium oxalate crystals were dried overnight in an air dryer at a temperature of 105 ° C., and the dried crystals were analyzed by the ICP atomic absorption spectrophotometric method to confirm the impurity grade.

Table 2 below shows the analysis results of the impurity grade of scandium oxalate obtained in Test Examples 1 to 16.

As shown in Table 2, in Test Examples 1 to 10 in which the reaction temperature during the oxalis oxidation treatment was in the range of 20 ° C. or higher and 35 ° C. or lower, Test Examples 11 to 16 in which the reaction temperature was higher than 35 ° C. In addition to being able to effectively reduce the impurity grade, it was possible to suppress variations in the impurity grade even if there were differences in other conditions such as oxalic acid equivalent under the same reaction temperature conditions. In Test Examples 11 to 16, not only the effect of reducing the impurity grade was inferior, but also the impurity grade varied due to the difference in the oxalic acid equivalent conditions under the same reaction temperature conditions.

In order to confirm the variation in the impurity grade contained in the obtained scandium oxalate, in Table 3 below, in all 16 examples of Test Examples 1 to 16, the impurity metal elements were particularly Ni, Mn, Fe, and so on. And when focusing on the grade of Al, the relationship between the reaction temperature, the oxalic acid equivalent and the impurity grade was summarized. Further, FIGS. 4 to 6 show two types (2.) of the relationship between the Ni grade (FIG. 4), the Mn grade (FIG. 5), the Fe grade (FIG. 6) and the reaction temperature, respectively, based on Table 3 below. It is a graph figure when comparing with the oxalic acid equivalent of 7 equivalents, 5.1 equivalents).

As can be seen from the graphs of FIGS. 4 to 6, when the oxalic acid treatment is performed in the range of the reaction temperature of 20 ° C. or higher and 35 ° C. or lower, the oxalic acid equivalent becomes an impurity product regardless of the conditions. There was no variation and the quality was low. On the other hand, under the condition that the reaction temperature exceeds 35 ° C., it can be clearly seen that the impurity grade varies due to the difference in oxalic acid equivalent.

Claims (5)

A method for recovering scandium from an acidic solution (scandium-containing solution) containing scandium and an impurity metal element.
Including a step of obtaining scandium oxalate by performing a oxalic acid treatment by a reverse addition method in which the scandium-containing solution is added to the oxalic acid solution contained in a container.
In the step, the reaction temperature in the oxalate oxidation treatment is set to 20 ° C. or higher and 35 ° C. or lower.
Scandium recovery method. The scandium-containing solution contains at least one selected from the group consisting of iron, nickel, and manganese as the impurity metal element.
The scandium recovery method according to claim 1. The scandium-containing solution is a solution after separating the sulfide produced by adding a sulfide agent to the leachate obtained by leaching nickel oxide ore with sulfuric acid.
The scandium recovery method according to claim 1 or 2. In the step, the pH of the scandium-containing solution is adjusted to a range of −0.5 or more and less than 1.0, and the shu oxidation treatment is performed.
The scandium recovery method according to any one of claims 1 to 3. No oxidizing agent is added to the scandium-containing solution to be subjected to the shu oxidation treatment.
The scandium recovery method according to any one of claims 1 to 4.

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