JP5983526B2 - Recovery method for heavy rare earth elements - Google Patents

Description

  The present invention relates to a method for recovering heavy rare earth elements.

  Rare earth elements are used in various applications. Specifically, for example, it is used as a raw material for a negative electrode agent for nickel-metal hydride batteries, for which demand has been increasing in recent years. In addition, they are also used as additives for magnets mounted on motors, abrasives for glass substrates used in liquid crystal panels and hard disk drives, and the like.

  As described above, rare earth elements are essential components for manufacturing automobiles and electronic devices, and in particular, in the automobile industry, they are applied to hybrid cars and electric cars equipped with drive motors and secondary batteries. The transition is progressing and its importance is increasing.

  However, the procurement of rare earth elements currently depends almost entirely on imports, and it is desired to establish a method for efficiently recovering rare earth elements from wastes of these products efficiently and at a high recovery rate. .

  As a method for recovering rare earth elements, a wet method for recovering waste from an aqueous solution in which an acid such as mineral acid is dissolved is generally known, and there are a solvent extraction method and a precipitation method.

  Specifically, when the rare earth elements are separated from each other and separated into each element, precise separation by a solvent extraction method is often used (for example, see Patent Document 1). However, since rare earth elements have similar chemical properties, the solvent extraction apparatus requires a large number of stages. In addition, since an organic solvent is used, facilities that take fire into consideration are required. Furthermore, since the COD (chemical oxygen demand) in the wastewater rises, the cost tends to increase, for example, the wastewater treatment needs to be strengthened.

  On the other hand, when recovering as a rare earth mixture such as misch metal, precipitation methods that can be recovered at low cost without the need to separate the contained rare earth elements from each other are easy to use industrially. In this precipitation method, precipitation is performed by adding succinic acid and recovery is performed (for example, see Patent Document 2), or precipitation is formed by forming a sulfate double salt of rare earth sulfate and alkali sulfate. How to do is known.

  However, in the case of the oxalic acid precipitation method, the COD in the wastewater becomes high, and the cost of the wastewater treatment tends to increase as in the solvent extraction method described above.

  On the other hand, the sulfate double salt precipitation method uses light rare earth elements such as scandium (Sc), lanthanum (La), cerium (Ce), praseodymium (Pr), neodymium (Nd), promethium (Pm), and samarium (Sm). Unlike the case of recovery by oxalic acid precipitation, COD in the waste water is not increased. Therefore, the cost of waste water treatment is advantageous as compared with the wet recovery method by the oxalic acid precipitation method.

  However, in this sulfate double salt precipitation method, yttrium (Y), europium (Eu), gadolinium (Gd), terbium (Tb), dysprosium (Dy), holmium (Ho), erbium (Er), thulium (Tm), It has been difficult to effectively recover heavy rare earth elements such as ytterbium (Yb) and lutetium (Lu).

  This is because the sulfate double salt produced by the alkali sulfate has a property that the solubility decreases as the concentration of the alkali sulfate in the solution increases. This is because the solubility tends to be higher than that of the sulfate double salt. Therefore, in the above-described sulfate double salt precipitation method, separation is performed by utilizing the difference in solubility between light rare earth elements and heavy rare earth elements.

  In the conventional sulfate double salt precipitation methods, since the heavy rare earth element remains in the solution and cannot be recovered, it is necessary to separately collect the heavy rare earth element remaining in the solution after the light rare earth element is recovered. As a result, when recovering heavy rare earth elements, not only a separate process is required, but also costs increase or the recovery rate of heavy rare earth elements decreases, resulting in an efficient and high recovery rate. It was difficult to recover.

  As a means for solving such problems of the conventional method, a method of efficiently coprecipitation of heavy rare earth elements with light rare earth elements by adding a rare earth sulfate double salt precipitate as a seed crystal has also been proposed. (For example, refer to Patent Document 3).

  However, this method requires strict control of the amount of seed crystals for each reaction batch. That is, if the addition amount of the seed crystal is insufficient, the coprecipitation effect cannot be obtained. On the other hand, if the addition amount is excessive, the energy consumption of the stirrer increases or the time required for filtering the precipitate increases. Even when the amount of seed crystals is strictly controlled, it is difficult to stably produce coprecipitation of heavy rare earth elements, and it is not easy to stabilize separation efficiency, quality, cost, etc. It was.

Japanese Patent Application Laid-Open No. 07-026336 JP 09-217133 A JP 2012-229483 A

  Then, this invention is proposed in view of such a situation, and it aims at providing the collection | recovery method of the heavy rare earth element which can collect | recover heavy heavy rare earth elements stably.

  As a result of intensive studies to achieve the above-mentioned object, the present inventors have found that the variation in the separation performance of heavy rare earth elements is correlated with the variation in the content of light rare earth elements in the raw material, and the reaction It has been found that heavy rare earth elements can be stably coprecipitated and recovered by setting the total concentration of light rare earth elements in the liquid to a predetermined concentration or more.

That is, the method for recovering heavy rare earth elements according to the present invention includes adding an alkali metal sulfate or a solution containing an alkali metal sulfate to a rare earth element-containing solution containing a heavy rare earth element and a light rare earth element. In the method of recovering heavy rare earth elements by producing a sulfate double salt precipitate, a rare earth element sulfate double salt precipitate is added as a seed crystal to the rare earth element-containing solution, and the concentration of light rare earth elements in the seed crystal is 26 g. / L or more, and controlled so that the sum of the concentration of light rare earth elements in the seed crystal and the concentration of light rare earth elements in the rare earth element-containing solution is 28 g / L or more. To do.

  According to the present invention, since the heavy rare earth element can be stably coprecipitated in the light rare earth element sulfate double salt, the separation efficiency of the heavy rare earth element from the rare earth element-containing solution is kept stable. Thus, heavy rare earth elements can be recovered at a high recovery rate.

It is a graph showing the relationship of the density | concentration of the heavy rare earth element (Y) in the filtrate after reaction with respect to the density | concentration of the light rare earth element (La + Ce) in a rare earth element (RE) reaction liquid.

  Hereinafter, a specific embodiment of the heavy rare earth element recovery method according to the present invention (hereinafter referred to as “the present embodiment”) will be described in detail. Note that the present invention is not limited to the following embodiments, and various modifications can be made without departing from the gist of the present invention.

  The method for recovering heavy rare earth elements according to the present embodiment uses a solution containing heavy rare earth elements and light rare earth elements (hereinafter also referred to as “rare earth element-containing solution”) as a target solution (raw material solution). On the other hand, it is a method for recovering heavy rare earth elements by adding alkali metal sulfate or a solution containing alkali metal sulfate to generate a sulfate double salt precipitate of rare earth elements.

  As described above, the target rare earth element-containing solution is a solution containing heavy rare earth elements and light rare earth elements, and is a solution made of a mineral acid such as sulfuric acid or hydrochloric acid. Specifically, as this solution, for example, a leachate obtained by leaching a scrap product containing heavy rare earth elements and light rare earth elements with a mineral acid such as sulfuric acid or hydrochloric acid can be used. . Although the pH conditions of a solution are not specifically limited, It is preferable to adjust pH to 1-2 with a mineral acid.

  The heavy rare earth element contained in the rare earth element-containing solution and to be collected is not particularly limited. For example, yttrium (Y), europium (Eu), gadolinium (Gd), terbium (Tb), Examples include dysprosium (Dy), holmium (Ho), erbium (Er), thulium (Tm), ytterbium (Yb), and lutetium (Lu).

  Further, the light rare earth element contained in the solution together with the heavy rare earth element described above is not particularly limited, and for example, scandium (Sc), lanthanum (La), cerium (Ce), praseodymium (Pr), neodymium. (Nd), promethium (Pm), samarium (Sm) and the like.

  In the present embodiment, an alkali metal sulfate or a solution containing an alkali metal sulfate is added to the rare earth element-containing solution described above and stirred. Then, in the solution, a rare earth element sulfate double salt formation reaction occurs.

  The solubility of the light rare earth element sulfate double salt is lower than the solubility of the heavy rare earth element sulfate double salt. Therefore, when an alkali metal sulfate or a solution containing an alkali metal sulfate is added to the rare earth element-containing solution and reacted, first, a light rare earth element sulfate double salt formation reaction occurs and the light rare earth element sulfate complex is first produced. A salt precipitate is formed, and then the heavy rare earth element is co-precipitated in the sulfated double salt precipitate of the light rare earth element. At this time, in the present embodiment, in addition to the addition of the alkali metal sulfate or a solution containing the alkali metal sulfate, a rare earth element sulfate double salt precipitate is added as a seed crystal. Thereby, coprecipitation of heavy rare earth elements can be promoted.

  In this way, the heavy rare earth element is co-precipitated in the sulfate double salt precipitate formed for the light rare earth element contained in the solution, so that the coprecipitated heavy rare earth element is collected together with the light rare earth element. can do. Also, at that time, by adding a rare earth sulfate sulfate precipitate as a seed crystal, a coprecipitation reaction of the heavy rare earth element with the seed crystal can be caused, so that the heavy rare earth element can be more efficiently added. It can be recovered as a precipitate.

  Here, the alkali metal sulfate to be added is not particularly limited, but sodium sulfate, potassium sulfate and the like can be used. Alternatively, a solution containing an alkali metal sulfate such as sodium sulfate or potassium sulfate can be used. Among these alkali metal sulfates, sodium sulfate or a solution containing sodium sulfate is preferably used from the viewpoint of high convenience such as good operability.

  The addition amount of the alkali metal sulfate is not particularly limited, but the sulfate ion concentration is preferably 27 g / L or more, and more preferably 54 g / L or more. . Thereby, the heavy rare earth element which exists in a solution can be efficiently made into a coprecipitate, and it can collect | recover with a high recovery rate. Further, with respect to the upper limit of the amount of alkali metal sulfate added, even if it is added to the solution so that the sulfate ion concentration is higher than 100 g / L, the recovery rate of heavy rare earth elements is not further improved. Therefore, from the viewpoint of economic efficiency, the addition amount of alkali metal sulfate is preferably 27 g / L or more and 100 g / L or less as the sulfate ion concentration, and 54 g / L or more and 100 g / L. It is more preferable to add so that it may become the following.

  In the present embodiment, the alkali metal sulfate is not limited to the rare earth element-containing solution, but an ammonium sulfate salt or an amine sulfate salt is added to cause a sulfate double salt formation reaction. Also good. Thus, even when ammonium sulfate salt, amine sulfate salt, or the like is used, by adding the sulfate ion concentration to the above-mentioned concentration, the heavy rare earth element can be effectively combined with the sulfate precipitation of the light rare earth element. It can be recovered by sinking.

  By the way, the present inventors have found that the fluctuation of the separation performance of heavy rare earth elements is large in a plant that has been operating in a state where the concentration of light rare earth elements in the sulfate double salt precipitate added as a seed crystal is fixed. Confirmed and investigated the cause. As a result, it was found that the separation performance of heavy rare earth elements is not related to factors such as temperature, but has a correlation with fluctuations in the content of light rare earth elements in the raw material (rare earth element-containing solution).

  That is, it is possible to expect coprecipitation of heavy rare earth elements in the light rare earth element sulfate double salt contained in the seed crystal and raw material, and even if the seed crystal amount is fixed, the light rare earth element contained in the raw material must be small. As a result, it was found that the amount of light rare earth element sulfate double salt precipitation was relatively small, and the coprecipitation effect of heavy rare earth element was so weak.

  FIG. 1 shows the concentration of light rare earth elements (La + Ce) in the rare earth element (RE) reaction solution, that is, the total concentration of light rare earth elements contained in the rare earth element-containing solution and the seed crystal. The graph showing the relationship of the density | concentration of a heavy rare earth element (Y) is shown. As shown in the graph of FIG. 1, the total concentration of light rare earth elements including seed crystals in the reaction solution and the concentration of heavy rare earth elements remaining in the filtrate after the reaction have a negative correlation. It was found that heavy rare earth elements cannot be sufficiently separated unless the concentration of rare earth elements is increased.

  Thus, in order to stabilize the separation performance of heavy rare earth elements, it is important to ensure a sufficient amount of light rare earth elements in the entire reaction batch. Therefore, in the method for recovering heavy rare earth elements according to the present embodiment, a rare earth element-containing sulfuric acid double salt precipitate is added as a seed crystal to the rare earth element-containing solution, and the light in the seed crystal (from the seed crystal) is added. The total concentration of the rare earth element and the concentration of the light rare earth element in the rare earth element-containing solution (derived from the raw material) is controlled to be equal to or higher than a predetermined value so as to cause a sulfate double salt formation reaction.

  Specifically, in this heavy rare earth element recovery method, the total concentration of the light rare earth element in the seed crystal and the light rare earth element in the rare earth element-containing solution of the raw material is controlled to be 28 g / L or more, A sulfuric acid double salt formation reaction is caused to occur.

  Thus, by controlling the total concentration of the light rare earth elements derived from the seed crystals and the light rare earth elements derived from the raw materials to be 28 g / L or more, sulfuric acid of the light rare earth elements that are the basis for coprecipitation of the heavy rare earth elements A sufficient amount of double salt precipitation can be ensured, and heavy rare earth elements can be stably coprecipitated and separated from the solution. Thus, the heavy rare earth element can be effectively recovered at a high recovery rate without causing the heavy rare earth element to remain in the solution (in the filtrate).

  In addition, since the heavy rare earth element can be stably coprecipitated in this way, not only the separation efficiency of the heavy rare earth element, but also the quality of the recovered heavy rare earth element, further, the separation and recovery cost, etc. can be stabilized. it can. Furthermore, since the labor and cost of separately collecting the light rare earth element after collecting the light rare earth element as in the prior art are unnecessary, the heavy rare earth element can be efficiently recovered.

  Regarding the concentration of the light rare earth element in the reaction solution, the concentration of the light rare earth element in the seed crystal is made larger than the concentration of the light rare earth element in the rare earth element-containing solution, and the total concentration is 28 g / L or more. It is preferable to do. Thereby, the coprecipitation effect | action of the heavy rare earth element based on a seed crystal can be improved more effectively.

  Further, it is more preferable to control the total concentration of light rare earth elements in the rare earth element-containing solution to be 28 g / L or more after setting the concentration of light rare earth elements in the seed crystal to 26 g / L or more. . Thereby, the fluctuation | variation of content of the light rare earth element contained in the rare earth element containing solution of a raw material can be absorbed, and a heavy rare earth element can be coprecipitated and isolate | separated more stably.

  The upper limit of the total concentration of the light rare earth element in the seed crystal and the light rare earth element in the rare earth element-containing solution is not particularly limited, but is preferably 40 g / L or less. Even if the total concentration exceeds 40 g / L, the coprecipitation effect of heavy rare earth elements (recovery rate of heavy rare earth elements) is not improved further, which causes a decrease in efficiency. Accordingly, the total concentration of the light rare earth element in the seed crystal and the light rare earth element in the rare earth element-containing solution is preferably in the range of 28 g / L to 40 g / L.

  The light rare earth element concentration management method (operation method) is not particularly limited. For example, the light rare earth element concentration (content) in the rare earth element-containing solution (raw material) to be treated, The concentration of light rare earth elements (content) is determined by weighing and analysis, and the amount charged into the reaction tank is determined based on this, and the total concentration of light rare earth elements derived from raw materials and seed crystals is managed. can do.

  As described above, the seed crystal to be added is a sulfate double salt precipitation of rare earth elements. As this precipitate, for example, it was recovered by solid-liquid separation in the previous (1 batch) heavy rare earth element recovery process. All or part of the sulfate double salt precipitation can be used repeatedly. Moreover, you may make it use the sulfate double salt precipitation which consists only of light rare earth elements.

  Further, the amount of seed crystal added is not particularly limited as long as the total concentration of the seed crystal-derived and raw material-derived light rare earth elements can be controlled within the predetermined range described above. As a specific example, the amount of liquid at the time of coprecipitation of heavy rare earth elements, that is, the final liquid amount, can be 25 g / L or more in terms of slurry concentration.

  Regarding the upper limit of the seed crystal addition amount, even if the seed crystal is added so that the slurry concentration exceeds 100 g / L, the coprecipitation effect of the heavy rare earth element is not further improved. This addition amount corresponds to about 30 g / L in terms of the concentration of the light rare earth element derived from the seed crystal, and is an amount corresponding to about 40 g / L together with the concentration of the light rare earth element derived from the raw material. When the seed crystal is added so that the slurry concentration exceeds 100 g / L, as described above, not only the coprecipitation effect is improved, but also the agitator power is wasted or the stirring effect is increased. This may lead to a decrease in the operating efficiency, resulting in a decrease in operational efficiency.

  The timing for adding the seed crystal is not particularly limited, and any stage before the addition of the alkali metal sulfate, at the same time as the addition of the alkali metal sulfate, or after the addition of the alkali metal sulfate. You may make it carry out.

  The temperature condition of the rare earth element-containing solution is not particularly limited. However, the residual heavy rare earth element concentration in the solution after the reaction with the alkali metal sulfate and the temperature of the solution have a negative correlation. Therefore, it is preferable to make it react in the solution of high temperature. Thereby, heavy rare earth elements can be recovered more effectively and efficiently. Specifically, the temperature condition of the solution is preferably 55 ° C. or higher. By setting the temperature of the solution to 55 ° C. or higher, the heavy rare earth element in the solution can be quickly recovered with a higher recovery rate. On the other hand, setting the temperature of the solution to 100 ° C. or higher increases the cost of heat sources and capital investment, and is not practical from an industrial viewpoint. Therefore, the temperature condition is preferably 55 ° C. or higher and 100 ° C. or lower.

  Moreover, in this heavy rare earth element recovery method, as described above, it is preferable to carry out a stirring operation after adding an alkali metal sulfate or a solution containing an alkali metal sulfate. By performing the stirring operation, the coprecipitation can be promoted to the precipitation of a light rare earth element of a heavy rare earth element into a sulfate double salt.

  The stirring operation method is not particularly limited. For example, the stirring operation can be performed by a method using a stirrer equipped with a stirring blade, a method using various mills such as a ball mill and a bead mill. Further, the stirring time can be appropriately set according to the concentration of the rare earth element in the rare earth element-containing solution, but for example, stirring for 20 minutes or more is preferable, and stirring for 60 minutes or more is more preferable.

  As described above in detail, in the heavy rare earth element recovery method according to the present embodiment, the separation performance of heavy rare earth elements has a correlation with the total concentration of light rare earth elements in the reaction solution, The total concentration of the light rare earth element in the seed crystal and the light rare earth element in the rare earth element-containing solution is controlled to be 28 g / L or more so as to cause a sulfate double salt formation reaction. According to such a method, since the heavy rare earth element can be stably co-precipitated in the sulfuric acid double salt precipitation of the light rare earth element, the separation efficiency of the heavy rare earth element from the rare earth element-containing solution is stabilized. The heavy rare earth elements can be recovered at a high recovery rate.

  In particular, this heavy rare earth element recovery method is intended for a leachate obtained by leaching a used product containing heavy rare earth elements such as batteries and electronic equipment with sulfuric acid or the like (as a rare earth element-containing solution). ), A method that can be applied when recovering heavy rare earth elements from the leachate. Thereby, heavy rare earth elements can be recovered from a used battery or the like at a high recovery rate without performing a complicated process at a low cost.

  Specific examples and comparative examples to which the present invention is applied will be described below, but the present invention is not limited to these examples and comparative examples.

Example 1
The test was performed using a solution (rare earth element-containing solution) containing lanthanum (La) and cerium (Ce) as light rare earth elements and yttrium (Y) as heavy rare earth elements. Specifically, as the rare earth element-containing solution, a sulfuric acid solution 140L having a lanthanum concentration of 15 g / L, a cerium concentration of 7.5 g / L, and an yttrium concentration of 1.1 g / L is used. Adjusted to 1-2. Then, a solution 140L having a sodium sulfate concentration of 180 g / L was prepared in advance in the reaction vessel, and the above-mentioned rare earth element-containing solution was added thereto. Thereafter, the temperature of the solution was maintained at 60 ° C.

  Next, 20 kg of a rare earth element sulfate double salt precipitate was added to the reaction vessel as a seed crystal. The amount of lanthanum and cerium contained in this seed crystal was 4.3 kg. Thereafter, the rare earth element-containing solution was maintained at 60 ° C. for 3 hours to form a rare earth element sulfate double salt precipitate to prepare 270 L of a rare earth element sulfate double salt slurry.

  Then, the filtrate was obtained by performing a solid-liquid separation process with respect to the created slurry.

  When the yttrium concentration in the obtained filtrate was measured, it was as low as 0.02 g / L, and yttrium, which is a heavy rare earth element, could be separated from the rare earth element-containing solution with a high yield.

(Comparative Example 1)
As the rare earth element-containing solution, a sulfuric acid solution 140L having a lanthanum concentration of 7.5 g / L, a cerium concentration of 3.5 g / L, and an yttrium concentration of 0.61 g / L is used. Adjusted. And like Example 1, the liquid 140L of sodium sulfate concentration 180g / L was prepared in the reaction tank beforehand, and the above-mentioned rare earth element containing solution was added to this. Moreover, the temperature of the solution at the time of reaction was maintained so that it might become 60 degreeC.

  Next, 20 kg of a rare earth element sulfate double salt precipitate was added to the reaction vessel as a seed crystal. This seed crystal contained 4.4 kg of lanthanum and cerium. Thereafter, the rare earth element-containing solution was maintained at 60 ° C. for 3 hours to form a rare earth element sulfate double salt precipitate to prepare 280 L of a rare earth element sulfate double salt slurry.

  Then, the filtrate was obtained by performing a solid-liquid separation process with respect to the created slurry.

  When the yttrium concentration in the obtained filtrate was measured, it remained at a high rate of 0.15 g / L, and the separation performance of heavy rare earth elements was insufficient.

  Table 1 below summarizes the concentrations of the light rare earth elements derived from the raw materials (in the rare earth element-containing solution) used in Example 1 and Comparative Example 1, and the concentrations of the light rare earth elements derived from the seed crystals (in the seed crystals). In addition, the measurement results of the concentration of yttrium (heavy rare earth element) in the filtrate obtained by solid-liquid separation are shown.

  Thus, even if the concentration of the light rare earth elements derived from the seed crystal is the same, the concentration of the light rare earth elements in the reaction solution is smaller than the predetermined ratio due to the low concentration of the light rare earth elements derived from the raw material, It was found that heavy rare earth elements cannot be stably coprecipitated and separated. And from the result of the above-mentioned Example 1, since the total concentration of the light rare earth elements derived from the raw material and the seed crystal in the reaction solution is 28 g / L or more, the effect is hardly left in the obtained filtrate. In particular, it was found that heavy rare earth elements can be separated and recovered.

Claims (1)

By adding a solution containing alkali metal sulfate or alkali metal sulfate to a rare earth element-containing solution containing heavy rare earth elements and light rare earth elements, a rare earth element sulfate double salt precipitate is generated to recover heavy rare earth elements. In the method
A rare earth element sulfate double salt precipitate is added as a seed crystal to the rare earth element-containing solution, and the concentration of the light rare earth element in the seed crystal is set to 26 g / L or more . A method for recovering heavy rare earth elements, wherein the concentration is controlled so that the total concentration of light rare earth elements in the rare earth element-containing solution is 28 g / L or more.

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