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

Abstract

To provide a method for recovering scandium through ion exchange treatment using chelate resin an acidic solution containing scandium and chromium, the method enabling efficient removal of chromium remaining in the chelate resin, and enabling productive and efficient recovery of scandium.SOLUTION: A method for recovering scandium from acidic solution containing scandium and chromium is provided, including an ion exchange treatment step including a step of causing a chelate resin to adsorb the scandium in the acidic solution, a step of eluting the scandium from the chelate resin, a step of bringing a sulfuric acid solution into contact with the chelate resin and removing the chromium adsorbed to the chelate resin, and the method causes the scandium to be recovered from the obtained scandium eluent. In the chromium removal step in the ion exchange treatment step, the chelate resin is brought into contact with sulfuric acid solution at a temperature of 32°C or higher and consequently the chromium is removed, and the chelate resin after the chromium has been removed is repeatedly used.SELECTED DRAWING: Figure 3

Description

[Technical field]

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

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

[0003] It is known that nickel oxide ores, such as laterite ore and limonite ore, contain trace amounts of scandium. However, nickel oxide ores have a low nickel content, so there is a problem that it is costly to recover nickel. Therefore, it could not be used for anything other than obtaining ferronickel, an alloy of iron and nickel, by subjecting it to dry smelting at high temperatures in a furnace, and using it 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 high-purity scandium. For this reason, very little research has been done on industrial methods for recovering scandium contained in nickel oxide ore.

[0005] However, in recent years, a high pressure acid leach (HPAL) process has been industrially put into practical use, in which nickel oxide ore is placed in 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 leachate 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 the leaching process to separate impurities, and then a sulfurizing 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 sulfurizing agent is added to perform sulfurization treatment, whereby nickel is recovered as nickel sulfide, while scandium is contained in the acidic solution (post-sulfurization solution) after the addition of the sulfurizing 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 wide variety of impurities, so further purification is required to concentrate and recover the scandium by separating it from the impurities. 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 high 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 a sulfide by using a sulfiding agent. Next, the resulting solution after nickel recovery (post-sulfidation liquid) is brought into contact with a chelating resin to adsorb scandium, the chelating resin is washed with a dilute acid, and after washing, the chelating resin is brought into contact with a strong acid to elute scandium.

[0010] Nickel oxide ore is known to contain impurities such as iron, aluminum, chromium, manganese, and magnesium, although the type and amount of 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 more concentrated sulfuric acid solution 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 for eluting scandium.

[0013] Specifically, Patent Document 3 discloses a method for recovering scandium, which includes an ion exchange process using a chelating resin to perform an ion exchange process on a post-sulfurization liquid obtained by hydrometallurgy processing using nickel oxide ore containing scandium, aluminum, and chromium as a raw material. The ion exchange process includes an adsorption process in which the post-sulfurization liquid is brought into contact with a chelating resin to adsorb scandium onto the chelating resin, a scandium elution process in which a sulfuric acid solution of 0.3N or more but less than 3N is brought into contact with the chelating resin to obtain a scandium eluate, and a chromium removal process in which a sulfuric acid solution of 3N or more is brought into contact with the chelating resin that has been subjected to the scandium elution process 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 contacting an acidic solution containing scandium and chromium 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 the chelating resin is repeatedly used. [Prior art documents] [Patent documents]

[0017] [Patent Document 1] Japanese Patent Application Publication No. 3-173725 [Patent Document 2] Japanese Patent Application Publication No. 9-194211 [Patent Document 3] JP 2014-218719 A [Patent Document 4] JP 2021-050378 A Summary of the Invention [Problem to be solved by the invention]

[0018] The present invention has been proposed in view of the above circumstances, and has an 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 can efficiently remove chromium remaining in the chelating resin after scandium is eluted with the acidic solution, thereby enabling scandium to be recovered productively and efficiently. [Means for solving the problem]

[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 from which scandium has been eluted into contact with a sulfuric acid solution maintained at a predetermined temperature, and thus the chelating resin from which chromium has been removed can adsorb and recover a larger amount of scandium, leading 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. 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 a method for recovering scandium according to the first aspect of the present invention, 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 of the present invention, wherein the acidic solution is a solution obtained by subjecting nickel oxide ore to a leaching treatment with a sulfuric acid solution, and adding a sulfurizing 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 any one of the first to fourth methods for recovering scandium, comprising generating 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 an ion exchange treatment using a chelating resin, the ion exchange treatment method 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 onto 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. Effect of the Invention

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

[0028] [Figure 1] FIG. 1 is a process diagram showing an example of the flow of a method for recovering scandium. [Diagram 2] 1 is a graph showing the results of the elution time and the elution rate of chromium when a treatment for eluting and removing chromium from a chelating resin was performed using a sulfuric acid solution at a liquid temperature of 30° C. [Diagram 3] 1 is a graph showing the results of the elution time and the chromium elution rate when a treatment for eluting and removing chromium from a chelating resin was performed using a sulfuric acid solution at a liquid temperature of 60° C. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0029] A specific embodiment of the present invention (hereinafter, referred to as "the present embodiment") will be described in detail below, but the present invention is not limited to the following embodiment, 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 numbers) means "X or more and Y or less."

[0030] The method for recovering scandium according to the present 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 treatment with a sulfuric acid solution, and adding a sulfurizing agent to the resulting leachate to separate nickel sulfide.

[0031] The method for recovering scandium according to the present embodiment includes an ion exchange process in which an acidic solution is brought into contact with a chelating resin to adsorb scandium in the acidic solution onto the chelating resin, and then the scandium is eluted from the chelating resin to obtain an eluate (scandium eluate) in which scandium is concentrated. This method for recovering scandium includes recovering scandium from the scandium eluate obtained in the ion exchange process.

[0032] Specifically, the ion exchange treatment process includes an adsorption process in which the acidic solution is brought into contact with a chelating resin to adsorb scandium in the acidic solution onto 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 the chelating resin is brought into contact with a sulfuric acid solution to remove chromium adsorbed onto the chelating resin. 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] In the chromium removal step in the ion exchange treatment process, 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 a chelating resin.

[0034] In this manner, in the method for recovering scandium 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 makes it possible to improve the elution rate (removal rate) of chromium adsorbed to the chelating resin, and effectively reduce the amount of chromium accumulated in the chelating resin after the chromium removal step.

[0035] As a result, even when the chelating resin is repeatedly used, it is possible to prevent a decrease in the amount of scandium adsorbed to the chelating resin, and it is possible to increase the concentration of scandium in the resulting scandium eluate. In addition, it is possible to improve the purity of the recovered scandium, and further to increase the amount of recovered scandium.

[0036] Fig. 1 is a process diagram showing an example of the flow of a method for recovering scandium. In this example, a post-sulfurization liquid, which is an acidic solution obtained through a hydrometallurgical process of nickel oxide ore, is used to recover scandium from the post-sulfurization liquid. Note that the post-sulfurization liquid contains at least scandium and chromium.

[0037] 1, the method for recovering scandium includes a hydrometallurgical process S1 for producing nickel sulfide and a post-sulfurization solution by carrying out a hydrometallurgical process of nickel oxide ore, an ion exchange process S2 for obtaining a scandium eluate by performing an ion exchange process on the acidic solution obtained from the hydrometallurgical process S1, and a scandium recovery process S3 for recovering scandium from the scandium eluate. The method may also include a re-adsorption process S4 for re-adsorbing the scandium eluate onto a chelating resin.

[0038] (1) Hydrometallurgical processing As the acidic solution containing scandium to be treated for scandium recovery, as described above, a solution obtained through a hydrometallurgical treatment of nickel oxide ore, such as a 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 processing step S1 including a leaching step S1 in which nickel oxide ore is leached with a sulfuric acid solution under high temperature and high 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 processing step S1 will be briefly described below.

[0040] (Leaching process) 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 leaching slurry consisting of a leachate and a leach residue. The treatment in the leaching step S11 may be performed according to 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. In addition, these nickel oxide ores contain scandium.

[0042] In the leaching step S11, the leaching slurry consisting of the obtained leachate and leach residue is washed and separated into a leachate containing nickel, cobalt, scandium, etc. and a leachate residue mainly containing hematite. The solid-liquid separation process can be carried out, for example, by mixing the leachate slurry with a washing liquid, and then using a flocculant supplied from a flocculant supplying facility or the like, using solid-liquid separation equipment such as a thickener.

[0043] (neutralization process) In the neutralization step S12, a neutralizing agent is added to the obtained leachate to adjust the pH, and a neutralized precipitate containing impurity elements and a neutralized liquid are obtained. By the neutralization treatment in the neutralization step S12, valuable metals such as nickel, cobalt, and scandium are contained in the neutralized liquid, and most of the impurities including iron and aluminum become the neutralized precipitate.

[0044] As the neutralizing agent, a conventionally known agent can be used, and examples thereof include calcium carbonate, slaked lime, and sodium hydroxide.

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

[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 liquid to produce a sulfide containing nickel and cobalt with few impurity components (hereinafter also simply referred to as "nickel sulfide") and a sulfurized liquid containing scandium with the nickel concentration stabilized at a low level.

[0047] In the sulfurization step S13, the slurry containing nickel sulfide is subjected to a sedimentation separation 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 is recovered.

[0048] In the method for recovering scandium, the post-sulfurization liquid obtained through each step of the hydrometallurgical treatment process S1 of nickel oxide ore 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 process 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 liquid 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 liquid, 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 liquid, it is preferable to first remove the impurities contained in the post-sulfurization liquid to concentrate scandium.

[0051] The ion exchange treatment step S2 can include, for example, 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 a functional group can be used, and such chelating resins can increase the adsorption selectivity of scandium. Among them, chelating resins having iminodiacetic acid as a functional group are particularly preferred because they have 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] (Adsorption process) In the adsorption step S21, for example, a column is filled with a chelating resin, and the post-sulfurization 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 liquid obtained through the hydrometallurgical treatment step S1 by the HPAL process as described above, the temperature of the post-sulfurization liquid 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 (treatment in the leaching step S11) is carried out at a high temperature of about 240° C. to 250° C., and the equipment can be made compact by maintaining the solubility in the solution as high as possible.

[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 the acidic solution is adsorbed by the chelating resin in the adsorption step S21 depends on the amount of chromium accumulated in the chelating resin that is repeatedly used. For example, a new resin that has no adsorption of chromium can adsorb almost 100% of the scandium in the solution, but as chromium accumulates in the chelating resin through repeated use, the adsorption of scandium is suppressed and the adsorption rate gradually decreases.

[0057] Therefore, in order to effectively recover the scandium remaining in the solution after adsorption, an adsorption process is performed in which the solution is brought into contact with multiple chelating resins, 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%, then 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 in the chelating resin used repeatedly, and the accumulation of chromium in the chelating resin is greatly affected by the efficiency of chromium removal in the chromium removal step 24 described later. Therefore, in the method according to the present embodiment, when chromium is eluted and removed from the chelating resin with a sulfuric acid solution, the contact is performed while the temperature of the sulfuric acid solution is maintained within a specific temperature range, which makes it possible to improve the efficiency of removing chromium adsorbed on the chelating resin. Details will be described later.

[0059] (Aluminum removal process) 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 0.3N 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 to be contacted 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 making the pH of the sulfuric acid solution 1.0 or more, the scandium adsorbed on the chelating resin is difficult to remove. In addition, by making the pH of the sulfuric acid solution 2.5 or less, aluminum can be efficiently removed from the chelating resin. Therefore, the normality of the sulfuric acid solution is preferably 0.1N or more and less than 0.3N, more preferably 0.1N to 0.2N.

[0061] (Scandium elution process) 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 0.3N or more and less than 3.0N, and more preferably in the range of 0.5N to 2.0N. By setting the normality to less than 3.0N, it is possible to suppress the elution of chromium adsorbed on the chelating resin, and it is possible to reduce the amount of chromium mixed into the scandium eluent. In addition, by setting the normality to 0.3N 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, that is, the obtained scandium eluate may be brought into contact with the chelating resin again to repeatedly perform 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] (Chromium removal process) In the chromium removal step S24, the chelating resin from which scandium has been eluted in the scandium elution step S23 is contacted with a sulfuric acid solution to remove chromium, an impurity adsorbed on the chelating resin. When chromium is removed from the chelating resin by contacting it with the sulfuric acid solution, a solution from which chromium has been eluted (chromium eluate) is collected.

[0065] Here, Fig. 2 shows a graph of the elution time and chromium elution rate (removal rate) when the chelating resin is contacted with two types of sulfuric acid solutions, 5N and 3N in normality, at a liquid temperature of 30°C in a process for eluting and removing chromium adsorbed on the chelating resin with a sulfuric acid solution. Fig. 3 shows a graph of the elution time and chromium elution rate when the sulfuric acid solution temperature is set to 60°C, unlike the test in Fig. 2. The chromium elution rate is calculated by the following formula. Chromium elution rate (%) = (amount of chromium in the resin before elution - amount of chromium in the resin after elution) ÷ amount of chromium in the resin before elution × 100

[0066] As shown in the graph of Figure 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 Figure 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 to 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 for eluting and removing 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 removing chromium is repeatedly used in the adsorption step S21, the amount of scandium adsorbed can be stably maintained at a 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 for 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 set to 40° C. or higher, even more preferably set to 45° C. or higher, and particularly preferably set to 50° C. or higher. In this way, the higher the temperature of the sulfuric acid solution, the higher the efficiency of removing chromium can be.

[0072] On the other hand, from the viewpoint of using a general chelating resin continuously and effectively for 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] In addition, in the above-mentioned temperature range of the sulfuric acid solution, it is preferable to determine a more appropriate temperature range depending on the type of chelating resin. For example, when a chelating resin that is less deteriorated by temperature is used, it is preferable to maintain the temperature in the range of 50°C to 70°C from the viewpoint of further increasing the chromium removal efficiency. In addition, when a chelating resin having iminodiacetic acid as a functional group is used, it is preferable to maintain the temperature in the range of 35°C to 50°C for the treatment, so that 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 process) Furthermore, although not shown, an iron removal step for removing iron, which is an impurity, may be provided prior to the above-mentioned aluminum removal step S22. The post-sulfurization liquid 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 elution liquid, it is preferable to provide an iron removal step to remove the 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 the 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 the scandium adsorbed to the chelating resin. In addition, by setting the pH of the sulfuric acid solution to 3.0 or lower, the iron can be efficiently removed from the chelating resin.

[0077] (3) Scandium recovery process 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, it 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 recovering scandium as a precipitate of scandium hydroxide by adding an alkali to the scandium eluent and performing a neutralization treatment, or a method of recovering scandium as a precipitate of oxalate by adding oxalic acid to the scandium eluent (oxalation treatment) can be used. Among these, the method using the oxalation treatment can separate impurities more effectively.

[0079] Specifically, in the recovery method using oxalation treatment, oxalic acid is added to a scandium eluent to generate a precipitate of scandium oxalate, which is then dried and roasted to form scandium oxide and recovered. Note that in the oxalation treatment, the scandium eluent may be added to a reaction tank containing an oxalic acid solution to generate a precipitate of scandium oxalate.

[0080] The roasting process is a process in which the precipitate of scandium oxalate obtained by the oxalation process is washed with water, dried, and then roasted. Through this roasting process, 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 about 900°C for about 2 hours.

[0081] In this way, 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, for example, impurities contained in the scandium eluate can be selectively extracted into an organic solvent containing an extractant, thereby purifying the scandium eluate and obtaining a solution in which scandium is concentrated (extraction residue).

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

[0084] Specifically, the treatment of the scandium eluate for re-adsorbing the chelating resin may be, for example, by 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, and then adding a reducing agent. Thereafter, a sulfuric acid solution is added to adjust the pH to a range of 1.0 to 2.5, preferably 1.7 to 2.3. The solution after the pH adjustment in this way (pH-adjusted solution) is used again to perform the treatment in the ion exchange treatment step S2 (adsorption step S21, aluminum removal step S22, scandium elution step S23).

[0085] In this way, the pH of the resulting scandium eluate is adjusted, and the pH-adjusted solution is subjected to the ion exchange treatment step S2 repeatedly to be re-adsorbed by the chelating resin, thereby further improving the quality of the recovered scandium. Also, 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 sulfurizing agent is used as the reducing agent, the oxidation-reduction potential is set to 200 mV or more to prevent sulfur from being precipitated as fine solids derived from the added sulfurizing agent, and to prevent clogging of the filter cloth in the filtration process after sulfurization, thereby enabling good solid-liquid separation. In addition, when the liquid is passed through the chelating resin again, clogging or a bias in the liquid flow may occur in the column, which may cause the liquid to not pass through uniformly. In addition, in all reducing agents, the oxidation-reduction potential is set to 300 mV or less to prevent residual iron ions, etc. from being adsorbed on the chelating resin and inhibiting the adsorption of scandium.

[0088] In addition, when re-adsorbing the scandium eluent to the chelating resin, the chelating resin may be one that has already been used, 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, if the chelating resin recovered through the chromium removal step S24 is reused, not only can impurity contamination be prevented, but the amount of chelating resin used can also be reduced. EXAMPLES

[0089] The present invention will be described in more detail below with reference to 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 process> Nickel oxide ore was subjected to hydrometallurgical treatment based on the HPAL process to recover nickel, and the resulting acidic post-sulfurization solution was used to contact 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. Note that 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 with a normality of 0.5N was passed through the chelating resin to which scandium had been adsorbed, to contact the chelating resin and elute scandium from the chelating resin (elution treatment). This produced a scandium eluate in which scandium was concentrated.

[0093] After the elution of scandium, 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 washing was repeated five times, and the scandium adsorption rate in the fifth cycle of the adsorption was measured. The chromium elution rate (removal rate) in the fourth cycle of the 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 (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 pass / fail standard for industrial operation. Chromium elution rate (%) = (amount of chromium in the resin before elution - amount of chromium in the resin after elution) ÷ amount of chromium in the 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 and 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%, while 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 the elution of scandium, 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 in the fifth cycle was 99%, which means that scandium was almost completely adsorbed. 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 the elution of scandium, 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 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 the elution of scandium, the temperature of the 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%, and the chromium elution rate after the fourth cycle of chromium removal treatment was 77%. [Example 5] In Example 5, the procedure was the same as in Example 1, except that after the elution of scandium, 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 after the fourth cycle of chromium removal treatment was 25%.

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

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

[0112] <Test Example 2: Verification of the lifespan of chelating resin after chromium removal treatment> Next, the life of the chelating resin in the chromium removal process was examined. Specifically, the life of the chelating resin in each experimental example and Comparative Example 1 was evaluated relatively, with the life of the chelating resin in Comparative Example 1, which had the longest life, set as 100.

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

[0114] As a result, the scandium recovery rate in 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 it is not economical for industrial use.

[0115] The following Table 1 shows the test results for the treatment conditions, scandium (Sc) adsorption rate, chromium (Cr) elution rate, and life of the chelating resin in 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 liquid 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] [Table 1]

Claims

1. A method for recovering scandium from an acidic solution containing at least scandium and chromium, comprising the steps of: an adsorption step of contacting the acidic solution 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; a chromium removal step of contacting the chelating resin with a sulfuric acid solution to remove chromium adsorbed on the chelating resin; and recovering scandium 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; The chelating resin from which chromium has been removed in the chromium removal step is repeatedly used in the adsorption step. How to recover scandium.

2. In the chromium removal step, the temperature of the sulfuric acid solution is maintained in a range of 32° C. or more and 80° C. or less, and the sulfuric acid solution is brought into contact with the chelating resin.

2. The method for recovering scandium according to claim 1.

3. The chelating resin is a resin having iminodiacetic acid as a functional group.

3. The method for recovering scandium according to claim 1 or 2.

4. The acidic solution is a solution obtained by subjecting nickel oxide ore to a leaching treatment using a sulfuric acid solution, and adding a sulfurizing agent to the resulting leachate to separate nickel sulfide.

3. The method for recovering scandium according to claim 1 or 2.

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

6. An ion exchange treatment method for obtaining a solution in which scandium is concentrated by performing an ion exchange treatment using a chelating resin on an acidic solution containing at least scandium and chromium, comprising the steps of: an adsorption step of contacting the acidic solution 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; a chromium removal step of contacting the chelating resin with a sulfuric acid solution to remove chromium adsorbed on the chelating resin, The chelating resin from which chromium has been removed in the chromium removal step is repeatedly used in the adsorption 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. Ion exchange treatment method.

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