Method for recovering scandium, method for producing scandium oxide, and method for ion exchange treatment

Abstract

To provide, in relation to a method for recovering scandium through ion exchange treatment using a chelate resin from an acidic solution containing scandium and chromium, a method for efficiently removing chromium remaining in the chelate resin and productively and efficiently recovering scandium.　The present invention is a method for recovering scandium from an acidic solution containing scandium and chromium, the method comprising an ion exchange treatment step including a step for causing scandium in an acidic solution to be adsorbed on a chelate resin, a step for eluting scandium from the chelate resin, and a step for bringing a sulfuric acid solution into contact with the chelate resin and removing chromium adsorbed on the chelate resin, scandium being recovered from the obtained scandium eluate. In the ion exchange treatment step, a sulfuric acid solution having a temperature of 32°C or higher is brought into contact with the chelate resin in the chromium removal step to remove chromium, and the chelate resin after chromium has been removed is used repeatedly.

Description

Scandium recovery method, scandium oxide production method, and ion exchange treatment method

[0001] The present invention relates to a method for recovering scandium, a method for producing scandium oxide from scandium recovered by the recovery method, and an ion exchange treatment method applied to the method for recovering scandium.

[0002] Scandium (Sc) is extremely useful as an additive for high-strength aluminum alloys and as an electrode material for fuel cells, but its use has been limited due to its low production volume and high cost.

[0003] Nickel oxide ores, such as laterite and limonite, are known to contain trace amounts of scandium. However, because nickel oxide ores have a low nickel content, there has been a problem in that recovering nickel is costly. For this reason, nickel oxide ores have only been used for purposes other than pyrometallurgy, where they are melted at high temperatures in a furnace to obtain ferronickel, an alloy of iron and nickel, which can then be used as a raw material for stainless steel.

[0004] However, when nickel oxide ore is processed using a pyrometallurgical process, scandium is separated from nickel, but is distributed together with many impurities into the slag, which is a chemically stable form, making it technically difficult to recover scandium at a high purity. For this reason, there has been little research into industrial methods for recovering scandium from nickel oxide ore.

[0005] However, in recent years, a high pressure acid leach (HPAL) process has been put into industrial use, in which nickel oxide ore is charged into a pressurized vessel together with a sulfuric acid solution and heated to a high temperature of about 240°C to 260°C to perform solid-liquid separation into a nickel-containing leach solution and a leach residue (see, for example, Patent Document 1).

[0006] In the HPAL process, a neutralizing agent is added to the leachate obtained by leaching to separate impurities, and then a sulfiding agent is added to recover nickel as nickel sulfide. The recovered nickel sulfide can then be processed in an existing nickel smelting process to obtain nickel salt compounds such as electrolytic nickel and nickel sulfate solution.

[0007] When such an HPAL process is used, scandium contained in nickel oxide ore is contained in the leachate together with nickel. Then, a neutralizing agent is added to the obtained leachate to separate impurities, and then a sulfiding agent is added to perform sulfidation treatment. Nickel is recovered as nickel sulfide, while scandium is contained in the acidic solution (post-sulfidation solution) after the addition of the sulfiding agent. Therefore, by using the HPAL process, nickel and scandium can be effectively separated.

[0008] However, the scandium separated by the HPAL process is dilute and contains a variety of impurities, so further purification is required to separate the scandium from the impurities and concentrate and recover it. For example, Patent Document 2 proposes a method using a chelating resin as a purification method.

[0009] Specifically, the method disclosed in Patent Document 2 involves first selectively leaching nickel and scandium from nickel oxide ore in an acidic aqueous solution under high temperature and pressure in an oxidizing atmosphere to obtain an acidic solution, then adjusting the pH of the acidic solution to a range of 2 to 4 and selectively precipitating and recovering nickel as sulfide using a sulfiding agent, then contacting the resulting solution after nickel recovery (post-sulfidation liquid) with a chelating resin to adsorb scandium, washing the chelating resin with dilute acid, and then contacting the chelating resin with a strong acid after washing to elute scandium.

[0010] Nickel oxide ore is known to contain impurities such as iron, aluminum, chromium, manganese, and magnesium, although the types and amounts of these impurities vary depending on the region where it is produced.

[0011] In particular, chromium contained in nickel oxide ore behaves similarly to scandium and is easily adsorbed by chelating resin, but is difficult to elute unless a sulfuric acid solution with a higher concentration is used than when eluting scandium.

[0012] Therefore, Patent Document 3 discloses a method of eluting chromium from a chelating resin using a sulfuric acid solution having a higher concentration than the sulfuric acid solution used to elute scandium.

[0013] Specifically, Patent Document 3 discloses a scandium recovery method including an ion exchange step in which a post-sulfurization solution obtained by hydrometallurgy using a nickel oxide ore containing scandium, aluminum, and chromium is subjected to an ion exchange treatment using a chelating resin. The ion exchange step includes an adsorption step in which the post-sulfurization solution is brought into contact with the chelating resin to adsorb scandium onto the chelating resin, a scandium elution step in which a sulfuric acid solution of 0.3 N or more but less than 3 N is brought into contact with the chelating resin to obtain a scandium eluate, and a chromium removal step in which a sulfuric acid solution of 3 N or more is brought into contact with the chelating resin that has been subjected to the scandium elution step to remove the chromium adsorbed onto the chelating resin.

[0014] That is, the method disclosed in Patent Document 3 involves adsorbing the impurity element chromium together with scandium onto a chelating resin, and utilizing the difference in concentration of the sulfuric acid solution used for elution, eluting only scandium from the chelating resin while chromium remains adsorbed onto the chelating resin, thereby separating it from chromium.

[0015] In view of this situation, Patent Document 4 proposes a method of increasing the amount of scandium recovered by bringing an acidic solution containing scandium and chromium into contact with a chelating resin at a predetermined temperature to reduce the amount of chromium adsorbed.

[0016] However, no method has been provided for efficiently eluting accumulated chromium and recovering a large amount of scandium when a chelating resin is repeatedly used.

[0017] Japanese Patent Application Laid-Open No. 3-173725 Japanese Patent Application Laid-Open No. 9-194211 Japanese Patent Application Laid-Open No. 2014-218719 Japanese Patent Application Laid-Open No. 2021-050378

[0018] The present invention has been proposed in view of the above circumstances, and has as its object to provide a method for recovering scandium from an acidic solution containing at least scandium and chromium via ion exchange treatment using a chelating resin, which method can efficiently remove chromium remaining in the chelating resin after scandium has been eluted with the acidic solution, thereby enabling productive and efficient recovery of scandium.

[0019] The present inventors have conducted extensive research to solve the above-mentioned problems, and as a result, have found that in an ion exchange process in which an acidic solution containing at least scandium and chromium is brought into contact with a chelating resin to obtain a solution in which scandium is concentrated, the chromium adsorbed on the chelating resin can be efficiently eluted and removed by bringing the chelating resin, after eluting the scandium, into contact with a sulfuric acid solution maintained at a predetermined temperature, and as a result, a larger amount of scandium can be adsorbed and recovered by the chelating resin after removing the chromium, which led to the completion of the present invention.

[0020] (1) A first aspect of the present invention is a method for recovering scandium from an acidic solution containing at least scandium and chromium, the method comprising: an ion exchange treatment step including an adsorption step of bringing the acidic solution into contact with a chelating resin to adsorb scandium in the acidic solution onto the chelating resin; an elution step of eluting scandium from the chelating resin to obtain a scandium eluate; and a chromium removal step of bringing a sulfuric acid solution into contact with the chelating resin to remove chromium adsorbed onto the chelating resin, wherein scandium is recovered from the scandium eluate obtained in the ion exchange treatment step. In the ion exchange treatment step, in the chromium removal step, the temperature of the sulfuric acid solution is maintained at 32°C or higher and the sulfuric acid solution is brought into contact with the chelating resin to remove chromium, and the chelating resin from which chromium has been removed in the chromium removal step is repeatedly used in the adsorption step.

[0021] (2) A second aspect of the present invention is the method for recovering scandium according to the first aspect, wherein, in the chromium removal step, the temperature of the sulfuric acid solution is maintained in the range of 32°C or higher and 80°C or lower, and the sulfuric acid solution is brought into contact with the chelating resin.

[0022] (3) A third aspect of the present invention is a method for recovering scandium according to the first or second aspect of the present invention, wherein the chelating resin is a resin having iminodiacetic acid as a functional group.

[0023] (4) A fourth aspect of the present invention is a method for recovering scandium according to any one of the first to third aspects, wherein the acidic solution is a solution obtained by subjecting nickel oxide ore to leaching treatment with a sulfuric acid solution, and adding a sulfiding agent to the obtained leachate to separate nickel sulfide.

[0024] (5) A fifth aspect of the present invention is a method for producing scandium oxide from scandium recovered by the scandium recovery method according to any one of the first to fourth aspects, comprising producing a precipitate containing scandium from the scandium eluate and roasting the precipitate containing scandium to produce scandium oxide.

[0025] (6) A sixth aspect of the present invention is an ion exchange treatment method for obtaining a solution in which scandium is concentrated by subjecting an acidic solution containing at least scandium and chromium to ion exchange treatment using a chelating resin, the method comprising: an adsorption step of bringing the acidic solution into contact with a chelating resin to adsorb scandium in the acidic solution onto the chelating resin; an elution step of eluting scandium from the chelating resin to obtain a scandium eluate; and a chromium removal step of bringing a sulfuric acid solution into contact with the chelating resin to remove chromium adsorbed onto the chelating resin, wherein the chelating resin from which chromium has been removed in the chromium removal step is repeatedly used in the adsorption step, and in the chromium removal step, the temperature of the sulfuric acid solution is maintained at 32°C or higher and the sulfuric acid solution is brought into contact with the chelating resin to remove chromium.

[0026] According to the present invention, in a process for recovering scandium from an acidic solution containing at least scandium and chromium through ion exchange treatment using a chelating resin, chromium can be efficiently and effectively removed from the chelating resin after scandium has been eluted.

[0027] This makes it possible to prevent a decrease in the amount of scandium adsorbed onto the chelating resin even when the chelating resin is used repeatedly, and as a result, the scandium concentration in the scandium eluate obtained by elution from the chelating resin can be increased, making it possible to recover high-purity scandium and increase the amount of scandium recovered.

[0028] 1 is a process diagram showing an example of the flow of a scandium recovery method. 2 is a graph showing the results of elution time and chromium elution rate when a treatment for eluting and removing chromium from a chelating resin is performed using a sulfuric acid solution at a liquid temperature of 30° C. 3 is a graph showing the results of elution time and chromium elution rate when a treatment for eluting and removing chromium from a chelating resin is performed using a sulfuric acid solution at a liquid temperature of 60° C.

[0029] Specific embodiments of the present invention (hereinafter referred to as "present embodiments") will be described in detail below, but the present invention is not limited to the following embodiments and can be implemented with appropriate modifications within the scope of the present invention. In this specification, the expression "X to Y" (X and Y are arbitrary numerical values) means "at least X and at most Y."

[0030] The method for recovering scandium according to this embodiment is a method for recovering scandium from an acidic solution containing at least scandium (Sc) and chromium (Cr). For example, the acidic solution may be a solution obtained by subjecting nickel oxide ore to leaching with a sulfuric acid solution, and then adding a sulfiding agent to the resulting leachate to separate nickel sulfide.

[0031] The scandium recovery method according to this embodiment includes an ion exchange treatment step of contacting an acidic solution with a chelating resin to adsorb scandium in the acidic solution onto the chelating resin, and then eluting the scandium from the chelating resin to obtain an eluate (scandium eluate) containing concentrated scandium. This scandium recovery method recovers scandium from the scandium eluate obtained in the ion exchange treatment step.

[0032] Specifically, the ion exchange treatment process includes an adsorption process in which scandium in an acidic solution is adsorbed onto a chelating resin by contacting the acidic solution with the chelating resin, an elution process in which scandium is eluted from the chelating resin to obtain a scandium eluate, and a chromium removal process in which chromium adsorbed onto the chelating resin is removed by contacting the chelating resin with a sulfuric acid solution. In the ion exchange treatment process, the chelating resin from which chromium has been removed in the chromium removal process is repeatedly used in the adsorption process.

[0033] The chromium removal step in the ion exchange treatment step is characterized in that the temperature of the sulfuric acid solution is maintained at 32° C. or higher and the sulfuric acid solution is brought into contact with a chelating resin to remove chromium. Preferably, the temperature of the sulfuric acid solution is maintained at 32° C. or higher and 80° C. or lower and the sulfuric acid solution is brought into contact with the chelating resin.

[0034] In this manner, in the scandium recovery method according to the present embodiment, in the chromium removal step in the ion exchange treatment using a chelating resin, when chromium is eluted and removed from the chelating resin with a sulfuric acid solution, the temperature of the sulfuric acid solution is maintained within a specific temperature range during contact. This improves the elution rate (removal rate) of chromium adsorbed on the chelating resin, and effectively reduces the amount of chromium accumulated on the chelating resin after the chromium removal step.

[0035] As a result, even when the chelating resin is repeatedly used, the amount of scandium adsorbed onto the chelating resin can be prevented from decreasing, the scandium concentration in the resulting scandium eluate can be increased, the purity of the recovered scandium can be improved, and the amount of recovered scandium can be increased.

[0036] 1 is a process diagram showing an example of the flow of a scandium recovery method. In this example, scandium is recovered from a post-sulfidation solution, which is an acidic solution obtained through a hydrometallurgical process of nickel oxide ore. The post-sulfidation solution contains at least scandium and chromium.

[0037] 1, the scandium recovery method includes a hydrometallurgical treatment step S1 in which nickel oxide ore is subjected to a hydrometallurgical process to produce nickel sulfide and a post-sulfidation solution, an ion exchange treatment step S2 in which the acidic solution obtained from the hydrometallurgical treatment step S1 is subjected to an ion exchange treatment to obtain a scandium eluate, and a scandium recovery step S3 in which scandium is recovered from the scandium eluate. The method may also include a re-adsorption treatment step S4 in which the scandium eluate is re-adsorbed onto a chelating resin.

[0038] (1) Hydrometallurgical Treatment Step As the acidic solution containing scandium to be treated for scandium recovery, as described above, a solution obtained through hydrometallurgical treatment of nickel oxide ore, such as an acidic sulfuric acid solution obtained by leaching nickel oxide ore with a sulfuric acid solution, can be used.

[0039] Specifically, the acidic solution containing scandium can be a post-sulfurization solution obtained by a hydrometallurgical treatment step S1 including a leaching step S11 in which nickel oxide ore is leached with a sulfuric acid solution under high temperature and pressure to obtain a leachate, a neutralization step S12 in which a neutralizing agent is added to the leachate to obtain a neutralized precipitate containing impurities and a post-neutralization solution, and a sulfurization step S13 in which a sulfurizing agent is added to the post-neutralization solution to obtain nickel sulfide and a post-sulfurization solution. The flow of the hydrometallurgical treatment step S1 will be briefly described below.

[0040] (Leaching Step) The leaching step S11 is a step in which a sulfuric acid solution is added to a slurry of nickel oxide ore using, for example, a high-temperature pressurized vessel (autoclave), and the mixture is stirred at a temperature of 240° C. to 260° C. to produce a leached slurry containing a leachate and a leach residue. The treatment in the leaching step S11 may be carried out in accordance with a conventionally known HPAL process.

[0041] Nickel oxide ores include so-called laterite ores such as limonite ore and saprolite ore. The nickel content of laterite ore is usually 0.8% by mass to 2.5% by mass, and is contained as hydroxide or magnesia (magnesium silicate) mineral. These nickel oxide ores also contain scandium.

[0042] In the leaching step S11, the resulting leaching slurry, which is made up of the leachate and leaching residue, is washed and subjected to solid-liquid separation into a leachate containing nickel, cobalt, scandium, etc. and a leaching residue mainly containing hematite. The solid-liquid separation treatment can be carried out, for example, by mixing the leaching slurry with a washing liquid and then using a flocculant supplied from a flocculant supply facility or the like, using solid-liquid separation equipment such as a thickener.

[0043] (Neutralization step) In the neutralization step S12, a neutralizing agent is added to the obtained leachate to adjust the pH, thereby obtaining a neutralized precipitate containing impurity elements and a neutralized solution. As a result of the neutralization treatment in the neutralization step S12, valuable metals such as nickel, cobalt, and scandium are contained in the neutralized solution, and most of the impurities such as iron and aluminum are converted into a neutralized precipitate.

[0044] As the neutralizing agent, conventionally known ones can be used, such as calcium carbonate, slaked lime, and sodium hydroxide.

[0045] (Sulfurization Step) The sulfurization step S13 is a step of adding a sulfurizing agent to the neutralized solution obtained in the neutralization step S12 to obtain nickel sulfide and a sulfurized solution. By the sulfurization treatment in the sulfurization step S13, nickel, cobalt, zinc, etc. become sulfides, and scandium is contained in the sulfurized solution.

[0046] Specifically, in the sulfurization step S13, a sulfurizing agent such as hydrogen sulfide gas, sodium sulfide, or sodium hydrosulfide is added to the obtained neutralized solution to produce a sulfide containing nickel and cobalt with few impurity components (hereinafter also simply referred to as "nickel sulfide") and a sulfurized solution containing scandium in which the nickel concentration is stabilized at a low level.

[0047] In the sulfurization treatment in the sulfurization step S13, the slurry containing nickel sulfide is subjected to a sedimentation treatment using a sedimentation device such as a thickener, and the nickel sulfide is separated and recovered from the bottom of the thickener. On the other hand, the post-sulfurization liquid, which is an aqueous solution component and contains scandium, is allowed to overflow and recovered.

[0048] In the method for recovering scandium, the post-sulfidation liquid obtained through each step of the nickel oxide ore hydrometallurgical treatment step S1 as described above can be used as an acidic solution containing at least scandium and chromium, which is to be subjected to the scandium recovery treatment.

[0049] (2) Ion Exchange Treatment Step The ion exchange treatment step S2 is a step of performing an ion exchange treatment using a chelating resin (ion exchange resin) on the post-sulfurization solution obtained through the hydrometallurgical treatment step S1. In the ion exchange treatment step S2, a scandium eluate in which scandium is concentrated can be obtained.

[0050] The post-sulfurization solution, which is an acidic solution containing scandium, contains, in addition to scandium, impurities such as chromium and aluminum that remain in the solution without being sulfurized during the sulfurization treatment in the above-mentioned sulfurization step S13. For this reason, when recovering scandium from the post-sulfurization solution, it is preferable to first remove the impurities contained in the post-sulfurization solution to concentrate the scandium.

[0051] The ion exchange treatment step S2 can be exemplified by an adsorption step S21 in which the post-sulfurization liquid is brought into contact with a chelating resin to adsorb scandium; an aluminum removal step S22 in which the chelating resin that has adsorbed scandium is brought into contact with a sulfuric acid solution of a predetermined normality to remove aluminum; a scandium elution step S23 in which the chelating resin is brought into contact with a sulfuric acid solution of a predetermined normality to obtain a scandium eluate; and a chromium removal step S24 in which the chelating resin is brought into contact with a sulfuric acid solution of a predetermined normality to remove chromium adsorbed to the chelating resin.

[0052] The type of chelating resin used in the ion exchange treatment is not particularly limited. For example, chelating resins having iminodiacetic acid, polyamine, or methylglucamine as functional groups can be used. Such chelating resins can enhance the adsorption selectivity for scandium. Among these, chelating resins having iminodiacetic acid as a functional group are preferred because they have particularly high adsorption selectivity for scandium.

[0053] In the ion exchange treatment step S2, the chelating resin from which chromium has been removed in the chromium removal step S24 is repeatedly used in the adsorption step S21.

[0054] In the adsorption step S21, for example, a column is filled with a chelating resin, and the post-sulfuration solution, which is an acidic solution, is passed through the column to bring the acidic solution into contact with the chelating resin, thereby adsorbing scandium in the solution onto the chelating resin. As described above, for example, a resin having iminodiacetic acid as a functional group can be used as the chelating resin.

[0055] When recovering scandium from the post-sulfurization solution obtained through the hydrometallurgical treatment step S1 by the HPAL process as described above, the temperature of the post-sulfurization solution at the time of passing it through the chelating resin is generally about 60° C. to 80° C. This is because the pressure leaching in the hydrometallurgical treatment step S1 (the treatment in the leaching step S11) is carried out at a high temperature of about 240° C. to 250° C., and by maintaining the solubility in the solution as high as possible, the equipment can be made compact.

[0056] As described above, in the ion exchange treatment step S2, the chelating resin from which chromium has been removed in the chromium removal step S24 is repeatedly used in the adsorption step S21. The adsorption rate (scandium adsorption rate) when scandium in an acidic solution is adsorbed onto the chelating resin in the adsorption step S21 depends on the amount of chromium accumulated in the chelating resin after repeated use. For example, a new resin with no adsorption of chromium can adsorb almost 100% of the scandium in the solution. However, as chromium accumulates on the chelating resin with repeated use, the adsorption of scandium is suppressed, and the adsorption rate gradually decreases.

[0057] Therefore, in order to effectively recover scandium remaining in the solution after adsorption, an adsorption treatment involving contact with multiple chelating resins can be performed, thereby increasing the amount of scandium recovered. For example, if the scandium adsorption rate of the chelating resin in the first column (first-stage column) is 60% and the scandium adsorption rate of the chelating resin in the next column (second-stage column) is 75%, it is possible to adsorb 90% of the scandium in the solution onto the chelating resin. By combining multiple chelating resins in this way, more scandium can be recovered efficiently.

[0058] However, as mentioned above, the scandium adsorption rate depends on the amount of chromium accumulated on the chelating resin when it is repeatedly used, and the accumulation of chromium on the chelating resin is greatly affected by the efficiency of chromium removal in the chromium removal step 24, which will be described later. Therefore, in the method according to this embodiment, when chromium is eluted and removed from the chelating resin with a sulfuric acid solution, the temperature of the sulfuric acid solution is maintained within a specific temperature range during contact, thereby making it possible to improve the efficiency of removal of chromium adsorbed on the chelating resin. Details will be described later.

[0059] In the aluminum removal step S22, the chelating resin that has adsorbed scandium in the adsorption step S21 is contacted with a sulfuric acid solution of less than 0.3 N to remove the aluminum adsorbed on the chelating resin. When the aluminum is removed from the chelating resin with the sulfuric acid solution, a solution in which the aluminum has been eluted (aluminum eluate) is recovered.

[0060] When removing aluminum, the pH of the sulfuric acid solution brought into contact with the chelating resin is preferably maintained in the range of 1.0 to 2.5, more preferably in the range of 1.5 to 2.0. By maintaining the pH of the sulfuric acid solution at 1.0 or higher, scandium adsorbed to the chelating resin becomes difficult to remove. Furthermore, by maintaining the pH of the sulfuric acid solution at 2.5 or lower, aluminum can be efficiently removed from the chelating resin. Therefore, the normality of the sulfuric acid solution is preferably 0.1N or higher but less than 0.3N, more preferably 0.1N to 0.2N.

[0061] (Scandium elution step) In the scandium elution step S23, the chelating resin from which aluminum has been removed is contacted with a sulfuric acid solution of 0.3 N or more and less than 3.0 N to elute scandium from the chelating resin, thereby obtaining a scandium eluate, which is a solution in which scandium is concentrated.

[0062] When obtaining a scandium eluent, it is preferable to maintain the normality of the sulfuric acid solution used as the eluent (solution for elution) in the range of 0.3 N or more and less than 3.0 N, and more preferably in the range of 0.5 N to 2.0 N. By setting the normality to less than 3.0 N, it is possible to suppress the elution of chromium adsorbed on the chelating resin, and to reduce the amount of chromium contaminating the scandium eluent. Furthermore, by setting the normality to 0.3 N or more, it is possible to efficiently elute scandium from the chelating resin.

[0063] The scandium eluate obtained from the scandium elution step S23 may be repeatedly used, i.e., the obtained scandium eluate may be brought into contact with the chelating resin again to repeat the scandium elution step S23 (purification of the scandium eluate). This makes it possible to further increase the concentration of scandium contained in the scandium eluate.

[0064] In the chromium removal step S24, a sulfuric acid solution is brought into contact with the chelating resin from which scandium has been eluted in the scandium elution step S23, thereby removing chromium, which is an impurity adsorbed on the chelating resin. After the chromium is removed from the chelating resin by contact with the sulfuric acid solution, a solution in which chromium has been eluted (chromium eluate) is recovered.

[0065] 2 shows a graph of the elution time and chromium elution rate (removal rate) when the chelating resin was contacted with two types of sulfuric acid solutions, 5N and 3N normalities, at a solution temperature of 30°C in a treatment for eluting and removing chromium adsorbed to the chelating resin with a sulfuric acid solution. Also, FIG. 3 shows a graph of the elution time and chromium elution rate when the sulfuric acid solution temperature was 60°C, unlike the test in FIG. 2. The chromium elution rate is calculated using the following formula: Chromium elution rate (%) = (amount of chromium in resin before elution - amount of chromium in resin after elution) / amount of chromium in resin before elution × 100

[0066] As shown in the graph of Fig. 2, it is understood that the chromium elution rate depends on the normality of the sulfuric acid solution when the liquid temperature of the sulfuric acid solution is in the low temperature range of about 30°C. On the other hand, as shown in the graph of Fig. 3, it is understood that by setting the liquid temperature of the sulfuric acid solution in the high temperature range, it is possible to improve the elution time and the chromium elution rate regardless of the normality of the sulfuric acid solution.

[0067] That is, as a result of research by the present inventors, it was found that the elution rate (removal rate) and elution time of chromium adsorbed on a chelating resin depend on the temperature of the sulfuric acid solution used for elution.

[0068] Therefore, in the scandium recovery method according to the present embodiment, in the chromium removal step S24, the temperature of the sulfuric acid solution is maintained at 32° C. or higher, and the sulfuric acid solution is brought into contact with a chelating resin to remove chromium. Preferably, the temperature of the sulfuric acid solution is maintained at 32° C. or higher and 80° C. or lower, and the sulfuric acid solution is brought into contact with the chelating resin.

[0069] In this way, by maintaining the temperature of the sulfuric acid solution used to elute and remove chromium from the chelating resin at a specific temperature or higher, the elution rate (removal rate) of chromium can be improved, and the amount of chromium accumulated in the chelating resin after the chromium removal step S24 can be effectively reduced. Furthermore, since the amount of chromium remaining in the chelating resin can be suppressed, when the chelating resin after chromium removal is repeatedly used in the adsorption step S21, the amount of scandium adsorbed can be maintained at a stable high level.

[0070] Furthermore, since the amount of chromium accumulated in the chelating resin can be reduced, the chelating resin can be used repeatedly in a stable manner, and the process of recovering scandium can be carried out more economically.

[0071] Regarding the temperature of the sulfuric acid solution for eluting and removing chromium, as described above, by setting the temperature of the sulfuric acid solution to 32° C. or higher, chromium can be efficiently and effectively removed with an appropriate amount of sulfuric acid. The temperature of the sulfuric acid solution is preferably set to 35° C. or higher, more preferably 40° C. or higher, even more preferably 45° C. or higher, and particularly preferably 50° C. or higher. Thus, the higher the temperature of the sulfuric acid solution, the more efficiently chromium can be removed.

[0072] On the other hand, from the viewpoint of continuous and effective use of a general chelating resin over a long period of time, the temperature of the sulfuric acid solution brought into contact with the chelating resin is preferably 80°C or less, and more preferably 70°C or less.

[0073] It should be noted that, within the temperature range of the sulfuric acid solution described above, a more appropriate temperature range is preferably determined depending on the type of chelating resin. For example, when a chelating resin that is less susceptible to deterioration due to temperature is used, it is preferable to maintain the temperature in the range of 50°C to 70°C for treatment in order to further enhance the chromium removal efficiency. Furthermore, when a chelating resin having iminodiacetic acid as a functional group is used, for example, by maintaining the temperature in the range of 35°C to 50°C for treatment, chromium can be removed with high removal efficiency while maintaining the long life of the chelating resin.

[0074] The normality of the sulfuric acid solution is not particularly limited, but is preferably 3.0 N or more, and more preferably 5.0 N or more. By setting the normality of the sulfuric acid solution to 3.0 N or more, chromium tends to be appropriately removed from the chelating resin, and by setting the normality to 5.0 N or more, chromium can be removed more efficiently in a short time.

[0075] (Iron Removal Step) Although not shown, an iron removal step for removing iron, which is an impurity, may be performed prior to the aluminum removal step S22. The post-sulfurization solution may contain iron derived from the nickel oxide ore used as the raw material. In such a case, from the viewpoint of reducing the impurities and increasing the scandium concentration in the scandium eluate, it is preferable to perform the iron removal step to remove iron adsorbed to the chelating resin.

[0076] Specifically, in the iron removal step, a sulfuric acid solution having a normality lower than that of the sulfuric acid solution used in the aluminum removal step S22 is brought into contact with the chelating resin to remove iron adsorbed to the chelating resin. When removing iron, it is preferable to maintain the pH of the sulfuric acid solution in the range of 1.0 to 3.0. By setting the pH of the sulfuric acid solution to 1.0 or higher, it becomes difficult to remove scandium adsorbed to the chelating resin. Furthermore, by setting the pH of the sulfuric acid solution to 3.0 or lower, iron can be efficiently removed from the chelating resin.

[0077] (3) Scandium Recovery Step The scandium recovery step S3 is a step of recovering scandium from the scandium eluate obtained through the ion exchange treatment step S2. For example, scandium can be recovered in the form of scandium oxide. Therefore, this method can be defined as a method for producing scandium oxide using scandium recovered from the scandium eluate.

[0078] The treatment method in the scandium recovery step S3 is not particularly limited, and any known method can be used. For example, a method of adding an alkali to the scandium eluate to perform a neutralization treatment and recovering scandium as a precipitate of scandium hydroxide, or a method of adding oxalic acid to the scandium eluate to recover scandium as a precipitate of oxalate (oxalation treatment) can be used. Among these, the method using the oxalation treatment can more effectively separate impurities.

[0079] Specifically, in the recovery method using oxalation, oxalic acid is added to a scandium eluent to form a scandium oxalate precipitate, which is then dried and roasted to form scandium oxide, which is then recovered. Alternatively, in the oxalation treatment, the scandium oxalate precipitate may be formed by adding the scandium eluent to a reaction vessel containing an oxalic acid solution.

[0080] The roasting treatment is a process in which the scandium oxalate precipitate obtained by the oxalation treatment is washed with water, dried, and then roasted. Through this roasting treatment, scandium can be recovered as highly pure scandium oxide. The roasting conditions are not particularly limited, but for example, the precipitate may be placed in a tubular furnace and heated at approximately 900°C for approximately two hours.

[0081] As described above, in the scandium recovery step S3, a precipitate containing scandium is produced from the scandium eluate obtained through the ion exchange treatment step S2, and then the resulting precipitate containing scandium is roasted to produce scandium oxide.

[0082] Although not shown, prior to the scandium recovery step S3, the scandium eluate obtained through the ion exchange treatment step S2 may be subjected to a solvent extraction treatment (solvent extraction step). By performing the solvent extraction treatment in this manner, impurities contained in the scandium eluate can be selectively extracted into an organic solvent containing an extractant, for example, thereby purifying the scandium eluate and obtaining a solution in which scandium is concentrated (extraction residue).

[0083] (4) Re-adsorption treatment step Furthermore, a re-adsorption treatment may be performed to re-adsorb the scandium eluate obtained through the ion exchange treatment step S2 onto a chelating resin, thereby recovering a larger amount of scandium (re-adsorption treatment step S4).

[0084] Specifically, the scandium eluate is treated to re-adsorb onto the chelating resin by, for example, adding a neutralizing agent to the scandium eluate to adjust the pH to a range of 2.0 to 4.0, preferably 2.7 to 3.3, followed by adding a reducing agent. Sulfuric acid solution is then added to adjust the pH to a range of 1.0 to 2.5, preferably 1.7 to 2.3. The solution after adjusting the pH in this manner (pH-adjusted solution) is then used to again undergo the ion exchange treatment step S2 (adsorption step S21, aluminum removal step S22, scandium elution step S23).

[0085] The scandium eluate thus obtained is subjected to pH adjustment, and the pH-adjusted solution is then subjected to the ion exchange treatment step S2 again to be re-adsorbed onto the chelating resin, thereby further improving the quality of the recovered scandium. Furthermore, the cost of chemicals and the scale of facilities required for separating scandium from the scandium eluate can be reduced.

[0086] As the neutralizing agent, a conventionally known agent can be used, for example, calcium carbonate, etc. As the reducing agent, a conventionally known agent can be used, for example, a sulfiding agent such as hydrogen sulfide gas or sodium sulfide, sulfur dioxide gas, hydrazine, metallic iron, etc.

[0087] The reducing agent is preferably added so that the oxidation-reduction potential (ORP) is maintained in a range of more than 200 mV and less than 300 mV, with a silver / silver chloride electrode as the reference electrode. For example, when a sulfiding agent is used as the reducing agent, setting the oxidation-reduction potential to 200 mV or more prevents sulfur from being precipitated as a fine solid, prevents clogging of the filter cloth during the filtration process after sulfidation, and enables good solid-liquid separation. Furthermore, when the solution is passed through the chelating resin again, clogging or uneven liquid flow may occur in the column, which may result in the inability to pass the solution uniformly. Furthermore, for all reducing agents, setting the oxidation-reduction potential to 300 mV or less can prevent residual iron ions and the like from being adsorbed onto the chelating resin and inhibiting the adsorption of scandium.

[0088] Furthermore, when re-adsorbing the scandium eluate onto the chelating resin, the chelating resin may be reused from an already used chelating resin, or a new chelating resin may be used. From the viewpoint of preventing impurity contamination, it is preferable to reuse the chelating resin recovered through the chromium removal step S24 or to use a new chelating resin. In particular, reusing the chelating resin recovered through the chromium removal step S24 not only prevents impurity contamination but also reduces the amount of chelating resin used.

[0089] The present invention will be explained in more detail below by showing examples, but the present invention is not limited to the following examples in any way.

[0090] Test Example 1: Verification of the temperature of the sulfuric acid solution in the chromium removal treatment Nickel oxide ore was subjected to a hydrometallurgical treatment based on the HPAL process to recover nickel, and the resulting acidic solution, a post-sulfurization solution, was brought into contact with a chelating resin having iminodiacetic acid as a functional group, and an ion exchange treatment was carried out in which scandium in the post-sulfurization solution was adsorbed onto the chelating resin. The post-sulfurization solution contained at least scandium and chromium.

[0091] Specifically, first, 330 mL of the post-sulfurization liquid was passed through a column packed with 15 mL of chelating resin, thereby adsorbing scandium in the post-sulfurization liquid onto the chelating resin (adsorption treatment).

[0092] Next, a sulfuric acid solution having a normality of 0.5 N was passed through the chelating resin on which scandium was adsorbed to bring the solution into contact with the chelating resin, thereby eluting scandium from the chelating resin (elution treatment). As a result, a scandium eluate in which scandium was concentrated was obtained.

[0093] After the scandium was eluted, a treatment was carried out to elute and remove chromium from the chelating resin using a sulfuric acid solution having a normality of 5N (chromium removal treatment).

[0094] Furthermore, after elution of chromium, the chelating resin was washed with pure water to remove the sulfuric acid solution remaining in the resin (washing treatment), and the chelating resin was repeatedly used in the adsorption step.

[0095] This cycle of adsorption, elution, chromium removal, and cleaning was repeated five times, and the scandium adsorption rate in the fifth cycle of adsorption was measured. The chromium elution rate (removal rate) in the fourth cycle of chromium removal was also measured.

[0096] The scandium adsorption rate was calculated using the following formula [1]. A scandium adsorption rate of 75% in this test, which was simply conducted using one column, was used as the standard for pass / fail in industrial operation. Scandium adsorption rate (%) = (amount of scandium in the solution after sulfurization - amount of scandium in the solution after adsorption) / amount of scandium in the solution after sulfurization × 100 ... formula [1]

[0097] Scandium in the solution was measured by optical emission spectroscopy (ICP-OES) using an Agilent 5100 (manufactured by Agilent Technologies Ltd.).

[0098] The chromium elution rate (removal rate) from the chelating resin was calculated using the following formula [2]. A chromium elution rate of 20% was set as the standard for pass / fail in industrial operations. Chromium elution rate (%) = (amount of chromium in resin before elution - amount of chromium in resin after elution) / amount of chromium in resin before elution × 100 ... formula [2]

[0099] Example 1 In Example 1, the temperature of the obtained post-sulfurization liquid was adjusted and maintained at 60°C, and 330 mL of the post-sulfurization liquid was passed through 15 mL of a chelating resin having iminodiacetic acid as a functional group to bring the resin into contact with the resin, thereby adsorbing scandium in the post-sulfurization liquid.

[0100] After the adsorption treatment, scandium was eluted from the chelating resin using a 0.5N sulfuric acid solution.

[0101] After the elution of scandium, chromium was eluted and removed from the chelating resin using a sulfuric acid solution with a normality of 5N. In Example 1, the temperature of the sulfuric acid solution was adjusted to and maintained at 46°C while the solution was brought into contact with the chelating resin. The chelating resin from which chromium had been removed was washed and then repeatedly used for the adsorption treatment.

[0102] This treatment was repeated, and the scandium adsorption rate after the fifth cycle was measured to be 90%. The chromium elution rate after the fourth cycle of chromium removal treatment was measured to be 46%.

[0103] Example 2 In Example 2, the procedure was the same as in Example 1, except that after scandium was eluted, the temperature of the 5N sulfuric acid solution was adjusted and maintained at 68°C and brought into contact with the chelating resin, and chromium was eluted and removed from the chelating resin.

[0104] As a result, the scandium adsorption rate after the fifth cycle was 99%, meaning that scandium was almost completely adsorbed. Furthermore, the chromium elution rate measured after the fourth cycle of chromium removal treatment was 95%.

[0105] Example 3 In Example 3, the procedure was the same as in Example 1, except that after scandium was eluted, the temperature of the 5N sulfuric acid solution was adjusted and maintained at 34°C and brought into contact with the chelating resin, and chromium was eluted and removed from the chelating resin.

[0106] As a result, the scandium adsorption rate after the fifth cycle was 78%, and the chromium elution rate measured after the fourth cycle of chromium removal treatment was 30%.

[0107] Example 4 In Example 4, the procedure was the same as in Example 1, except that after scandium was eluted, the temperature of a 5N sulfuric acid solution was adjusted and maintained at 55°C and brought into contact with the chelating resin, and chromium was eluted and removed from the chelating resin.

[0108] As a result, the scandium adsorption rate after the fifth cycle was 95%. Furthermore, the chromium elution rate measured after the fourth cycle of chromium removal treatment was 77%. [Example 5] In Example 5, the same procedures as in Example 1 were carried out, except that after scandium elution, the temperature of the 3N sulfuric acid solution was adjusted and maintained at 55°C and brought into contact with the chelating resin, and chromium was eluted and removed from the chelating resin.

[0109] As a result, the scandium adsorption rate after the fifth cycle was 75%, and the chromium elution rate measured after the fourth cycle of chromium removal treatment was 25%.

[0110] Comparative Example 1 Comparative Example 1 was carried out in the same manner as in Example 1, except that after scandium was eluted, the temperature of a 5N sulfuric acid solution was adjusted and maintained at 30°C and brought into contact with a chelating resin, and chromium was eluted and removed from the chelating resin.

[0111] As a result, the scandium adsorption rate after the fifth cycle was 70%, which was significantly lower than those of Examples 1 to 5 and fell below the pass / fail criterion. In addition, the chromium elution rate measured after the chromium removal treatment in the fourth cycle was 18%, which fell below the pass / fail criterion.

[0112] Test Example 2: Verification of Lifespan of Chelate Resin After Chromium Removal Treatment Next, the lifespan of the chelating resin in the chromium removal process was examined. Specifically, the lifespan of the chelating resin in each Experimental Example and Comparative Example 1 was evaluated relative to the lifespan of the chelating resin in Comparative Example 1, which had the longest usable lifespan, set at 100.

[0113] In Comparative Example 2, the procedure was the same as in Example 1, except that after scandium was eluted, the temperature of the 5N sulfuric acid solution was adjusted and maintained at 85°C and brought into contact with the chelating resin, and chromium was eluted and removed from the chelating resin.

[0114] As a result, the scandium recovery rate after the fifth cycle was 99%, and the life of the chelating resin was 20. Although the scandium adsorption rate and chromium elution rate were both very high at 99%, the life was shorter than in Examples 1 to 5, and it was found that this method is not economical for industrial use.

[0115] The following Table 1 summarizes the treatment conditions, scandium (Sc) adsorption rate, chromium (Cr) elution rate, and test results regarding the life of the chelating resin for the Examples and Comparative Examples. Based on the results of the Examples and Comparative Examples, Fig. 4 shows a graph of the relationship between the temperature (elution temperature) of the sulfuric acid solution used in the chromium removal treatment and the Sc adsorption rate, Fig. 5 shows a graph of the relationship between the elution temperature and the Cr elution rate, and Fig. 6 shows a graph of the relationship between the elution temperature and the life of the chelating resin.

[0116]

Claims

1. A method for recovering scandium from an acidic solution containing at least scandium and chromium, comprising: an ion exchange treatment step including an adsorption step of bringing the acidic solution into contact with a chelating resin to adsorb scandium in the acidic solution onto the chelating resin; an elution step of eluting scandium from the chelating resin to obtain a scandium eluate; and a chromium removal step of bringing the chelating resin into contact with a sulfuric acid solution to remove chromium adsorbed to the chelating resin, wherein scandium is recovered from the scandium eluate obtained in the ion exchange treatment step, and in the ion exchange treatment step, the temperature of the sulfuric acid solution is maintained at 32°C or higher and the sulfuric acid solution is brought into contact with the chelating resin to remove chromium, and the chelating resin from which chromium has been removed in the chromium removal step is repeatedly used in the adsorption step.

2. The method for recovering scandium according to claim 1, wherein in the chromium removal step, the temperature of the sulfuric acid solution is maintained in the range of 32°C or higher and 80°C or lower, and the sulfuric acid solution is brought into contact with the chelating resin.

3. The method for recovering scandium according to claim 1 or 2, wherein the chelating resin is a resin having iminodiacetic acid as a functional group.

4. The method for recovering scandium according to claim 1 or 2, wherein the acidic solution is a solution obtained by subjecting nickel oxide ore to leaching treatment with a sulfuric acid solution, and adding a sulfurizing agent to the resulting leachate to separate nickel sulfide.

5. A method for producing scandium oxide from scandium recovered by the scandium recovery method according to claim 1, comprising the steps of: generating a precipitate containing scandium from the scandium eluate; and producing scandium oxide by roasting the precipitate containing scandium.

6. An ion exchange treatment method for obtaining a solution in which scandium is concentrated by subjecting an acidic solution containing at least scandium and chromium to an ion exchange treatment using a chelating resin, the ion exchange treatment method comprising: an adsorption step of bringing the acidic solution into contact with a chelating resin to adsorb scandium in the acidic solution onto the chelating resin; an elution step of eluting scandium from the chelating resin to obtain a scandium eluate; and a chromium removal step of bringing the chelating resin into contact with a sulfuric acid solution to remove chromium adsorbed to the chelating resin, the chelating resin from which chromium has been removed in the chromium removal step being repeatedly used in the adsorption step, and in the chromium removal step, the temperature of the sulfuric acid solution is maintained at 32°C or higher and the sulfuric acid solution is brought into contact with the chelating resin to remove chromium.

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