JP5699988B2 - Recovery method of rare earth elements - Google Patents

Description

  The present invention relates to a method for recovering a rare earth element, and more particularly, when recovering a rare earth element as a sulfate double salt precipitate, by using a part of the sulfate double salt precipitate efficiently as a seed crystal, high recovery is achieved. The present invention relates to a method for recovering rare earth elements that makes it possible to recover rare earth elements at a high rate.

  Rare earth elements are physically unique because their electron configuration is different from normal elements, and materials such as hydrogen storage alloys, secondary battery materials, optical glass, powerful rare earth magnets, phosphors, and abrasives It is used as.

  In particular, in recent years, rare earth-nickel alloys have been used in large quantities as a negative electrode material for nickel metal hydride batteries because they have a high hydrogen storage capacity. It is getting higher.

  However, since there is a current situation that almost all rare earths are imported, and molded products such as nickel metal hydride batteries have a long life, it is desirable to establish a method for efficiently recovering expensive rare earth elements from these scrap products. ing.

  As a method for collecting rare earth elements, a wet method is generally known in which scraps containing rare earth elements are recovered from an aqueous solution in which acids such as mineral acids are dissolved. Among them, there are a plurality of rare earth elements contained. However, when it is not necessary to separate them from each other, a precipitation method that can be recovered at low cost is easy to use industrially.

  Examples of the precipitation method include an oxalic acid precipitation method (see, for example, Patent Document 1) that is recovered as an oxalic acid precipitation, and a sulfuric acid double salt precipitation method that generates and recovers a sulfate double salt precipitate with a rare earth sulfate and an alkali sulfate. is there. In particular, this sulfate double salt precipitation method is known as a relatively inexpensive method.

  In the sulfate double salt precipitation method, heavy rare earth elements may remain in the solution among the rare earth elements. In this case, it is efficient to add the rare earth sulfate sulfate precipitate as a seed crystal. Has been found to be recoverable. For example, by repeatedly using sulfate double salt precipitates extracted with a filter press as seed crystals, it is confirmed that rare earth elements can be recovered at a high recovery rate without generating precipitates by another method. (See, for example, the specification of Japanese Patent Application No. 2011-176780 filed by the present applicant).

  However, once the total amount of sulfate double salt precipitates has been recovered with a filter press, etc., the work of weighing the rare earth deposits to give the prescribed slurry concentration and putting them into the reaction tank is an increase in the size of the filter press. The larger the is, the more it is related to heavy objects and requires more work. In addition, there is a possibility that the liquid may be scattered when a weighed amount of the precipitate is put into the solution, so that there is a problem that the operation is dangerous.

JP 09-217133 A

  Therefore, the present invention has been proposed in view of the conventional situation as described above, and when collecting rare earth elements by the sulfate double salt precipitation method, the sulfate double salt precipitate is taken into account and charged into the reaction vessel. Providing a method capable of recovering rare earth elements by using a desired amount of sulfate double salt precipitate as a seed crystal efficiently and with high safety, without the need for complicated handling The purpose is to do.

  As a result of intensive studies to achieve the above-mentioned object, the present inventors have found that a solution containing a predetermined amount of a sulfate double salt precipitate in a state where the solution after completion of the sulfate double salt formation reaction is stirred. Remains in the upper tank, and settles and removes the supernatant, so there is no need for complicated handling, and a heavy rare earth sulfate double salt precipitate is used as a seed crystal for efficient and high safety Thus, the present invention was completed.

  That is, the method for recovering a rare earth element according to the present invention includes the step of adding an alkali metal sulfate to a solution containing a rare earth element contained in a reaction vessel in the presence of a seed crystal to form a sulfate double salt of the rare earth element. In the method for recovering rare earth elements, in which a reaction is caused to form and recover the sulfate double salt precipitate of the rare earth element, after the completion of the sulfate double salt formation reaction, the resulting solution is stirred so that the sulfate double salt precipitate does not settle Then, the solution other than the solution containing a predetermined amount of sulfate double salt precipitate is recovered by passing it through a solid-liquid separator, and the solution containing the predetermined amount of sulfate double salt precipitate is statically placed in the reaction vessel. To settling the sulfate double salt precipitate, and then draining the supernatant to leave the sulfate double salt precipitate in the reaction vessel, and the sulfate double salt precipitate left in the reaction vessel. In the state of coexisting as a seed crystal, a solution containing rare earth elements Houses, and performs double sulfate generation reaction by adding an alkali metal sulfate.

  According to the present invention, complicated handling is not required, and a sulfated double salt precipitate of a rare earth element, which is a heavy material, can be efficiently used as a seed crystal with high safety and high. It makes it possible to recover rare earth elements with a recovery rate.

It is a graph which shows transition of the residual density | concentration in the solution of rare earth elements (Y) with respect to the retention time of a rare earth element containing solution in the sulfate double salt production | generation reaction in the case of coexisting the seed crystal of three types of different slurry density | concentrations. It is the graph evaluated about the settling property after leaving the solution (slurry) containing the sulfate double salt precipitate made into the stirring state to stand. It is the figure which showed typically about the method of attracting | sucking and extracting a supernatant liquid with the liquid removal nozzle which can raise / lower. It is the figure which showed typically about the method of extracting the supernatant liquid through the liquid extraction port provided with two or more in the height direction of the reaction tank.

Hereinafter, the rare earth element recovery method according to the present invention will be described in detail in the following order with reference to the drawings. 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.
1. About the present invention 2. Rare earth element recovery by sulfuric acid double salt formation reaction Rare earth element recovery method (use of sulfate double salt precipitate as seed crystal)
3-1. Recovery of formed sulfate double salt precipitate of rare earth element 3-2. Settling of the remaining sulfate double salt precipitate 3-3. 3. Double salt formation reaction in the presence of double salt precipitate 4. Application to other valuable metal recovery methods Example

<< 1. About the present invention >>
The method for recovering a rare earth element according to the present invention causes a sulfate double salt formation reaction by adding an alkali metal sulfate to a solution containing a rare earth element (hereinafter also referred to as a “rare earth element-containing solution”). The element is recovered as a hardly soluble sulfate double salt precipitate (hereinafter also simply referred to as “precipitate”).

  In the recovery of rare earth elements by this sulfuric acid double salt formation reaction, a part of the formed sulfuric acid double salt precipitate is repeatedly made to coexist in the solution as a seed crystal, thereby forming a rare earth element sulfate double salt precipitate. It becomes possible to promote.

  In the rare earth element recovery method according to the present invention, the sulfate double salt precipitate formed after the sulfate double salt formation reaction of the rare earth element is completed in coexisting the sulfate double salt precipitate as a seed crystal in the solution. In the state where a predetermined amount of the sulfate double salt precipitate is left in the reaction vessel and the residue is coexisted as a seed crystal, the sulfate double salt for the novel rare earth element-containing solution is recovered. Perform the production reaction.

  That is, in this rare earth element recovery method, first, after the rare earth element sulfate double salt formation reaction is completed, the obtained solution (slurry) is brought into a stirring state in which the sulfate double salt precipitate does not settle, and a predetermined amount of sulfate double salt is obtained. A portion other than the solution containing the precipitate is passed through a solid-liquid separator and collected. Next, the solution containing the predetermined amount of the sulfate double salt precipitate is allowed to stand in the reaction vessel to settle the sulfate double salt precipitate, and then the supernatant is removed to remove the sulfate double salt precipitate in the reaction vessel. To remain. Then, in the state where the sulfate double salt precipitate left in the reaction tank is coexisted as a seed crystal, a rare earth element-containing solution is accommodated, and an alkali metal sulfate is added to perform a sulfate double salt generation reaction.

  According to such a method, after collecting the entire amount of the sulfate double salt precipitate formed by the sulfate double salt formation reaction, weigh out a predetermined amount of precipitate used as a seed crystal, and add it again to the reaction vessel. Thus, it is not necessary to perform a complicated operation requiring much labor, and a very efficient recovery process can be performed. In addition, since it is not necessary to introduce a precipitate as a seed crystal into the reaction vessel in which the solution is accommodated, there is no danger due to scattering of the liquid at the time of addition.

  Hereinafter, a specific embodiment of the rare earth element recovery method according to the present invention (hereinafter referred to as “the present embodiment”) will be described in more detail for each process.

≪2. Recovery process of rare earth elements by sulfuric acid double salt formation reaction >>
First, in the rare earth element recovery method according to the present embodiment, a rare earth element recovery process by a sulfate double salt generation reaction for a solution containing a rare earth element will be described.

  As described above, the rare earth element recovery treatment by the sulfate double salt formation reaction causes the sulfate double salt formation reaction to occur by adding and stirring the alkali metal sulfate to the rare earth element-containing solution, and the rare earth element in the solution is removed. It is separated and recovered as a sulfate double salt precipitate. At this time, in the rare earth element recovery process, a predetermined amount of the formed sulfate double salt precipitate is allowed to coexist in the solution as a seed crystal, and then a reaction is caused.

  The rare earth element-containing solution to be collected is a solution made of a mineral acid such as sulfuric acid or hydrochloric acid containing a rare earth element. As this solution, for example, a leachate obtained by leaching a scrap product containing a rare earth element such as a battery or an electronic device with a mineral acid such as sulfuric acid or hydrochloric acid can be used. In addition, although it does not specifically limit as pH of this solution, It is preferable to adjust to pH 1-2 about with a mineral acid.

  The rare earth element contained in the solution is not particularly limited, and yttrium (Y), europium (Eu), gadolinium (Gd), terbium (Tb), dysprosium (Dy), holmium (Ho), erbium ( Er), thulium (Tm), heavy rare earth elements such as ytterbium (Yb), lutetium (Lu), scandium (Sc), lanthanum (La), cerium (Ce), praseodymium (Pr), neodymium (Nd), promethium ( Pm) and light rare earth elements such as samarium (Sm) can be mentioned.

  The addition amount of the alkali metal sulfate that is added to the rare earth element-containing solution to cause the sulfate double salt formation reaction is not particularly limited, but it is preferably added so that the sulfate ion concentration is 27 g / l or more, and 54 g It is more preferable to add so that it becomes more than / l. Thus, by adding the alkali metal sulfate so that the sulfate ion concentration is preferably 27 g / l or more, more preferably 54 g / l or more, the coprecipitate of heavy rare earth elements and light rare earth elements can be efficiently produced. Thus, heavy rare earth elements that are difficult to be formed into precipitates can be collectively converted into precipitates effectively, and the rare earth elements can be recovered at a high recovery rate. In addition, as an upper limit of addition amount, it is preferable to set it as 100 g / l or less as a sulfate ion density | concentration from a viewpoint of economical efficiency.

Further, as the alkali metal sulfate to be added is not particularly limited, for example, sodium sulfate _(Na 2 _SO 4), can be used such as potassium sulfate _(K 2 SO _4). Among these, it is preferable to use sodium sulfate from the viewpoint of high convenience such as good operability. Further, the alkali metal sulfate is not limited to adding a solid one, and an aqueous solution containing an alkali metal sulfate adjusted to have a predetermined addition amount may be added.

≪3. Rare earth element recovery method (use of sulfate double salt precipitate as seed crystal) >>
Here, as described above, in the rare earth element recovery process by the sulfuric acid double salt formation reaction, the rare earth element sulfate double salt precipitate formed together with the addition of the alkali metal sulfate to the rare earth element-containing solution. The reaction is carried out in the state of coexisting as a seed crystal. As a result, the formation of the precipitate of the rare earth element can be more effectively promoted, the rare earth element remaining in the solution can be effectively reduced, and the rare earth element can be recovered at a high recovery rate.

  Conventionally, when using the formed sulfate double salt precipitate as a seed crystal, the required amount as a seed crystal is estimated from the recovered sulfate double salt precipitate and added to the reaction vessel. It was. However, the operation of introducing such a well-defined sediment into the reaction vessel is a matter related to the heavy load, so that the larger the operation scale, the more labor is required. There was also a danger of the solution splashing.

  Therefore, in the rare earth element recovery method according to the present embodiment, first, after completion of the rare earth element sulfate double salt formation reaction, the obtained solution (slurry) is in a stirring state in which the sulfate double salt precipitate does not settle, A portion other than the solution containing a predetermined amount of a sulfate double salt precipitate is passed through a solid-liquid separator and recovered. Next, the solution containing the predetermined amount of the sulfate double salt precipitate is allowed to stand in the reaction vessel to settle the sulfate double salt precipitate, and then the supernatant is removed to remove the sulfate double salt precipitate in the reaction vessel. To remain. Then, in the state where the sulfate double salt precipitate left in the reaction tank is coexisted as a seed crystal, a rare earth element-containing solution is accommodated, and an alkali metal sulfate is added to perform a sulfate double salt generation reaction. Each process will be specifically described below.

<3-1. Recovery of formed rare earth sulfate sulfate precipitate>
First, after completion of the sulfate double salt formation reaction of the rare earth element, a solution (slurry) containing the sulfate double salt precipitate is put in a stirring state in which the sulfate double salt precipitate does not settle, and a predetermined amount of the sulfate double salt precipitate is included. The remaining solution is passed through a solid-liquid separator and collected.

  This treatment is a treatment for recovering a sulfate double salt precipitate of a rare earth element obtained by a sulfate double salt formation reaction by adding an alkali metal sulfate. In this embodiment, in collecting the sulfate double salt precipitate, the total amount formed is not recovered, but a solution containing a predetermined amount of the sulfate double salt precipitate is left in the reaction tank, and the rest is recovered. To do.

  When the rare earth element sulfate double salt precipitate is formed by the sulfate double salt formation reaction, the precipitate gradually precipitates in the reaction tank as the reaction proceeds. Therefore, when collecting the sulfate double salt precipitate, the solution obtained in the reaction vessel is set in a stirring state in which the sulfate double salt precipitate does not settle so that the precipitate is uniformly dispersed in the slurry. Then, under this stirring state, a portion other than the solution containing a predetermined amount of the sulfate double salt precipitate is passed through the solid-liquid separator and recovered.

  In this way, by uniformly dispersing the precipitate with the solution in which the sulfate double salt precipitate after the sulfate double salt formation reaction is formed being stirred, the amount of the precipitate to be left as a seed crystal as described later is simplified. It can be grasped as the amount of solution. In other words, since the precipitate is uniformly dispersed in the solution, the amount of the precipitate can be converted into the amount of the solution, and the desired amount of the precipitate to coexist as a seed crystal and a new precipitate after the reaction are added. From a ratio relationship with the total amount of precipitates later, a predetermined ratio of the total amount of the solution obtained after the reaction can be determined as a solution containing a desired amount of precipitates. Then, simply leave the solution at a predetermined ratio as a seed crystal, and leave it as a solution containing a precipitate, and transfer the other solution to a solid-liquid separation device. A sufficient amount of precipitate can remain in the reaction vessel.

  Regarding the stirring of the solution after the sulfate double salt formation reaction, the stirring strength is not particularly limited, but a uniform slurry is maintained in a state where the formed sulfate double salt precipitate does not settle in the solution. Stir with sufficient strength to achieve a state. When the stirring strength is too weak, the sedimentation rate of the precipitate increases, so that the amount of the collected precipitate increases and the desired amount of sulfate double salt precipitate cannot be left.

  As for the stirring strength, the optimum strength differs depending on various factors such as the concentration and composition of the slurry, the shape of the stirring blade, the amount of the solution in the reaction tank, the shape of the reaction tank, etc. What is necessary is just to set suitably based on the grade which can maintain the state which a sediment does not settle.

  Further, the stirring method is not particularly limited as long as it can be a stirring state in which the sulfate double salt precipitate does not settle using a known stirring device.

  When the solution after the sulfate double salt formation reaction is in a stirring state, next, a solution other than the solution containing a predetermined amount of the sulfate double salt precipitate is passed through the solid-liquid separation device. The rare earth element sulfate double salt precipitate contained in the solution is recovered by solid-liquid separation. By doing in this way, the rare earth elements contained in the solution passed through the solid-liquid separator are recovered as a sulfate double salt precipitate.

  Here, in the present embodiment, a solution other than the solution containing a predetermined amount of sulfate double salt precipitate is passed through the solid-liquid separator out of all the solutions in a stirred state, and a predetermined amount of sulfuric acid is added. It is important to leave the solution containing the double salt precipitate in the reaction vessel.

  “Solution containing a predetermined amount of sulfate double salt precipitate” means that it is desired to remain in the reaction tank in order to act as a seed crystal in the next recovery process of rare earth elements by the sulfate double salt formation reaction. Solution containing a quantity of sulfate double salt precipitate.

  The amount of the sulfate double salt precipitate that remains as a seed crystal is not particularly limited, but the rare earth element-containing solution that is contained in the reaction vessel and is subject to recovery treatment has a slurry concentration of 25 g / in the initial reaction. It is preferable to leave an amount of 1 or more, and it is more preferable to leave an amount of about 50 g / l.

  FIG. 1 shows a rare earth element (yttrium (Y)) with respect to the retention time (80 ° C.) of a rare earth element-containing solution in a sulfuric acid double salt formation reaction in the case where seed crystals of three different slurry concentrations (early reaction) coexist. It is a graph which shows transition of the density | concentration in solution (residual density | concentration). As can be seen from the graph of FIG. 1, the presence of a seed crystal having a slurry concentration of 25 g / l in the solution can effectively reduce the residual concentration of rare earth elements over time. It can be seen that if it is 50 g / l, almost all rare earth elements can be converted into sulfate double salt precipitates in a short time of about 1 hour. Although not shown, in the absence of seed crystals (slurry concentration 0 g / l), 0.19 g / l of rare earth element remained in the solution even after 3 hours.

  From this, a sulfate double salt precipitate having an amount of slurry concentration of preferably 25 g / l or more, more preferably about 50 g / l, is allowed to coexist in the reaction vessel with respect to the rare earth element-containing solution to be collected. In order to start the reaction, the solution containing the precipitate corresponding to the amount is left in the reaction tank, and the other solution is passed through the solid-liquid separator and collected. As described above, the sulfate double salt precipitate as a seed crystal has an effect of an extremely short reaction time of about 1 hour even at a slurry concentration of 50 g / l. On the other hand, as the slurry concentration increases, the effect of shortening the reaction time decreases, and the time required for settling described later may increase. Therefore, the upper limit of the slurry concentration of the sulfate double salt precipitate as a seed crystal is, for example, 100 g / l or less, preferably 75 g / l or less.

  Here, a calculation example of the amount of the solution remaining in the reaction tank and the amount of the solution to be passed through the other solid-liquid separator is shown below.

For example, 140 L of a rare earth element-containing solution is accommodated in a medium-scale reaction tank, 140 L of a solution of sodium sulfate (Na ₂ SO ₄ ), which is an alkali metal sulfate, dissolved in a predetermined concentration is added and mixed, and the solution It is assumed that the sulfate double salt formation reaction is performed in the presence of 50 g / l of a rare earth element sulfate double salt precipitate as a seed crystal.

  In the case of this reaction condition, the amount of seed crystal added is (140 L + 140 L) × 50 g / l = 14,000 g [dry] (14 kg [dry]). Then, assuming that the water content of the sulfate double salt precipitate recovered by the treatment in this reaction tank is about 30%, considering the water content, the amount of seed crystals added is 14 kg / (100-30) × 100 = 20 kg [wet]. That is, 20 kg [wet] is desirable as the amount of the sulfate double salt precipitate as a seed crystal.

  Next, when the sulfate double salt formation reaction is caused in the state where the added amount of the precipitate coexists as a seed crystal, a precipitate newly formed by the reaction is added to the coexisting 20 kg [wet] precipitate. The amount 8 kg [wet] (calculated based on the composition of the solution to be treated) is added, and the amount of precipitate after the reaction is 28 kg [wet].

  As described above, in order to allow seed crystals to coexist at a slurry concentration of 50 g / l, it is necessary to leave 20 kg [wet] of precipitate, so the amount of precipitate to be extracted after the reaction is completed, that is, solid-liquid separation. The amount of precipitate to be recovered by solid-liquid separation in the apparatus is 8 kg [wet], and the amount is about 1/3 of the entire precipitate after the reaction (8 kg [wet] / 28 kg [wet] × 100≈29 %).

  In the present embodiment, as described above, when a solution other than a solution containing a predetermined amount of sulfate double salt precipitate is passed through the solid-liquid separator, the solution after the reaction is subjected to strong stirring. The slurry is in a uniformly dispersed state (stirring state). Therefore, about 1/3 of the solution after completion of the sulfate double salt formation reaction is passed through the solid-liquid separator, and the remaining about 2/3 contains a predetermined amount of sulfate double salt precipitate. It is possible to leave the 20 kg [wet] sulfate double salt precipitate calculated as described above as a seed crystal in the reaction tank.

  The above-described calculation example is an example. In determining the amount of the solution to be retained and the amount of the solution to be recovered through the solid-liquid separator, for example, the scale of the reaction tank to be used and the target of the rare earth element recovery process It is preferable to calculate appropriately according to the composition of the rare earth element-containing solution (the amount of the rare earth element contained), the desired slurry concentration of the seed crystal, and the like.

  The solid-liquid separation device used for recovering the sulfate double salt precipitate is not particularly limited, and for example, a known device such as a filter press, a screw press, or a centrifugal separator can be used. Among these, it is preferable to use a filter press in that solid-liquid separation can be performed with higher efficiency.

  In addition, when transferring the slurry containing the formed sulfate double salt precipitate to the solid-liquid separator, it can be transferred by suction using, for example, a pump via a pipe connected to the reaction tank. . In addition, an extraction port that can be controlled to be opened and closed by a valve may be provided in the lower part of the reaction tank, and transferred to the solid-liquid separation device via the extraction port. Thus, even when a predetermined amount is withdrawn from the lower part of the reaction tank, since the solution is transferred after being stirred, there is no concern that the precipitate will be discharged beyond the desired amount.

  In addition, when transferring to a solid-liquid separator, a liquid level meter such as a float type level meter or an ultrasonic level meter is provided in the reaction tank, and the liquid level of the solution in the reaction tank is monitored and transferred accurately. You may be able to grasp it.

<3-2. Settling of residual sulfate double salt precipitate>
Next, let the solution containing a predetermined amount of sulfate double salt precipitate left in the reaction vessel stand and hold for a predetermined time to precipitate the sulfate double salt precipitate, and then the sulfate double salt precipitate settles. The supernatant obtained by separation is withdrawn, and a sulfate double salt precipitate is left in the reaction vessel.

  In the above-described pre-process, the solution containing a predetermined amount of sulfate double salt precipitate to be coexisted as a seed crystal in a state where the solution after the sulfate double salt formation reaction is stirred is not transferred to the solid-liquid separation device. It remains inside. Therefore, the reaction tank contains an aqueous solution together with a precipitate that becomes a seed crystal. Therefore, in this step, the precipitate is settled (settling) by allowing the solution containing the sulfate double salt precipitate remaining in the reaction vessel to stand and hold for a predetermined time.

  FIG. 2 is a graph showing an evaluation of settling properties after allowing a solution (slurry) containing a sulfate double salt precipitate in a stirred state to stand. As shown in the graph of FIG. 2, it can be seen that the retention time (settling time) of the slurry becomes longer, the sedimentation depth becomes larger, and the sulfate double salt precipitate effectively settles. In the sedimentation of this sediment, since the coarsening of the sediment particles that settle is also contributing, it is considered that the sedimentation depth increases as the holding time elapses.

  Thus, after the solution containing a predetermined amount of the sulfate double salt precipitate is left in the reaction vessel, the solution is left to stand for a predetermined time, whereby the sulfate double salt precipitate in the solution is gradually It settles and deposits at the bottom of the reaction vessel, and the solution becomes a clear liquid. And if sediment is settled in this way, next, only the clarified liquid (supernatant liquid) which exists in upper part will be extracted, and a sulfuric acid double salt precipitate will be made to remain in a reaction tank.

  Here, the method for extracting the supernatant liquid in the reaction tank is not particularly limited including the apparatus to be used, and only the supernatant liquid is extracted to leave the sulfate double salt precipitate in the reaction tank. Any method can be used. At this time, it is preferable to extract only the supernatant so that the precipitated sulfate double salt precipitate does not roll up into the supernatant.

  As an example of a method of extracting the supernatant, for example, as shown in FIG. 3, a liquid discharge nozzle 20 that can be raised and lowered from above the reaction tank 10A is inserted, and the sulfate double salt precipitate 11 is obtained by sedimentation. There is a method in which the liquid discharge nozzle 20 is lowered to a height level at which the supernatant liquid 12 can be sucked, and the supernatant liquid 12 is sucked and extracted through the liquid discharge nozzle 20 by a pump or the like.

  Further, as another example of the method for extracting the supernatant, as shown in FIG. 4, for example, valves 30a, 30b, 30c (hereinafter referred to as 30) in the height direction of the wall surface of the reaction vessel 10B. A plurality of liquid discharge ports 31a, 31b, 31c (hereinafter referred to as 31) that can be controlled by extraction are provided, and the liquid discharge port 31 up to the liquid level of the supernatant 12 to be finally extracted is provided. A method of withdrawing the supernatant 12 by opening all the valves 30 is available.

  In addition, when extracting the supernatant liquid, a liquid level meter such as a float type level meter or an ultrasonic level meter is provided in the reaction tank so that it can be extracted with higher accuracy. You may make it extract while monitoring.

  In addition, there is a possibility that a sulfate double salt precipitate is partially mixed in the extracted supernatant. Therefore, also from the viewpoint of improving the recovery rate of rare earth elements, it is preferable to pass the extracted supernatant through a solid-liquid separation device such as a filter press to recover the mixed sulfate double salt precipitate. For this reason, it is more preferable from the viewpoint of operational efficiency that the apparatus used for extracting the supernatant liquid described above is configured so as to allow continuous liquid passage through a solid-liquid separation apparatus such as a filter press.

  When the supernatant is extracted after the sulfate double salt precipitate is settled in this manner, a thick precipitate consisting almost of the sulfate double salt precipitate is left in the reaction vessel. This residual sulfate double salt precipitate is contained in the solution that remains without being passed through the solid-liquid separator, and is desired for use as a seed crystal calculated as described above. Amount of precipitate.

<3-3. Sulfate double salt formation reaction in the presence of double sulfate precipitate>
When the sulfate double salt precipitate is left in the reaction tank as described above, a new rare earth element-containing solution to be recovered is accommodated in the reaction tank, and the sulfate double salt precipitate left in the reaction tank is seeded. Under the condition of coexisting as crystals, an alkali metal sulfate is added to carry out a sulfate double salt formation reaction.

  The sulfate double salt precipitate remaining in the reaction tank is left as a slurry concentration, for example, 25 g / l or more as a seed concentration during the sulfate double salt formation reaction by the above-described operation. Precipitation of rare earth elements can be promoted by performing a sulfate double salt generation reaction on a rare earth element-containing solution to be newly treated in the coexistence state. Thereby, the rare earth element can be recovered at a high recovery rate.

  In addition, about the sulfuric acid double salt production | generation reaction of rare earth elements, said 2. The details are the same as those described in detail in FIG.

  As described above in detail, the rare earth element recovery method according to the present embodiment provides a rare earth element in the presence of a sulfate double salt precipitate of a rare earth element as a seed crystal for the purpose of efficiently recovering and removing the rare earth element. After completion of the elemental sulfate double salt formation reaction, the resulting solution is stirred and the formed sulfate double salt precipitate is recovered, while a predetermined amount of the sulfate double salt precipitate is contained in the reaction vessel. To remain. Then, a sulfuric acid double salt generation reaction is performed on the novel rare earth element-containing solution in a state where the residual component coexists as a seed crystal.

  According to such a method, after collecting the entire amount of the precipitate with a solid-liquid separator such as a filter press as in the past, the necessary amount to be used as a seed crystal is taken into consideration and returned to the reaction tank again. Therefore, a heavy precipitate can be efficiently used as a seed crystal, and rare earth elements can be recovered at a high recovery rate. Further, there is no danger that the solution will be scattered at the time of charging, as in the case of charging and adding again to the reaction vessel after taking out the dose, and the processing can be performed with high safety.

<< 4. Application to other valuable metal recovery methods >>
In the embodiment described above, the process of recovering the rare earth element by the sulfate double salt formation reaction in the presence of the seed crystal has been described as an example, but the recovery process of other valuable metals as the precipitate in the presence of the seed crystal is described. It can also be applied effectively in

  Specifically, for example, in sulfuric acid solution or hydrochloric acid solution containing valuable metals such as nickel (Ni), cobalt (Co), lithium (Li), copper (Cu), zinc (Zn), lead (Pb) The present invention can also be suitably used in a recovery processing method in which a predetermined agent is added to cause a valuable metal precipitate formation reaction in a state in which the valuable metal precipitate coexists as a seed crystal. In such a valuable metal recovery process, the obtained precipitate can be efficiently used as a seed crystal by the same method as described above, and the valuable metal can be recovered at a high recovery rate.

  That is, first, after completion of the valuable metal precipitate formation reaction, the obtained solution is brought into a stirring state in which the valuable metal precipitate does not settle, and the liquid other than the solution containing the predetermined amount of precipitate is solid-liquid. Pass through the separator and collect. Next, the solution containing the predetermined amount of precipitate is allowed to stand in the reaction vessel to settle the precipitate, and then the supernatant is extracted to leave the precipitate in the reaction vessel. And the solution containing valuable metals is accommodated in the state which made the deposit which remained in the reaction tank coexisted as a seed crystal, and the precipitate production | generation reaction of the valuable metals is performed.

≪5. Examples >>
Specific examples to which the present invention is applied will be described below, but the present invention is not limited to these examples.

[Example 1: Examination of residual method of sulfate double salt precipitate as seed crystal]
140 L of a sulfuric acid solution (rare earth element solution) having a pH of 1 in which the rare earth elements whose analytical values are shown in Table 1 below are dissolved and 140 L of an aqueous solution containing sodium sulfate at a concentration of 180 g / l are added to the reaction tank. did. Then, the temperature of the solution was raised to 60 ° C. and held for 3 hours with stirring to cause a rare earth element sulfate double salt formation reaction, whereby the rare earth element in the solution was converted into a sulfate double salt precipitate.

  Here, in order to contain the sulfate double salt precipitate as a seed crystal so that the slurry concentration at the initial stage of the reaction is 50 g / l, the average moisture content of the formed rare earth element sulfate double salt precipitate is about 30%. In consideration, it is necessary to leave about 20 kg [wet] in the reaction vessel. Under this condition, when a sulfate double salt formation reaction is caused to the rare earth element solution of the analysis values shown in Table 1 above, the sulfate complex compound recovered including the seed crystal is calculated from the composition of the rare earth element solution. The amount of salt precipitate is about 28 kg [wet]. That is, about 1/3 of the amount of precipitate obtained is the amount of precipitate newly formed.

  Therefore, the solution obtained after the completion of the sulfuric acid double salt formation reaction is vigorously stirred using a stirrer so that the precipitate in the solution is uniformly dispersed without being settled (stirring state). Then, 1/3 of the solution obtained by the filter press was withdrawn, and 2/3 was left in the reaction vessel. Specifically, when the liquid volume in the reaction tank is 280 liters, the liquid level in the height direction of the reaction tank is about 65 cm. Therefore, it is determined that it is necessary to extract a 22 cm level solution as 1/3 of the solution. The solution was fed to the filter press until the measured value of the float type liquid level meter provided in the reaction vessel was changed from 65 cm to 43 cm.

  When the amount of the rare earth element sulfate double salt precipitate separated by the filter press was collected and confirmed, it was 9.0 kg [wet]. For confirmation, the slurry remaining in the reaction vessel was passed through a filter press, and the rare earth sulfate double salt precipitate was collected and measured to find 19.28 kg [wet]. . From this, the ratio of the amount of the precipitate to be retained is 68.2% with respect to the target 66.7% (about 1/3), and it is confirmed that the target amount of the precipitate can be left in the reaction vessel. It was.

[Example 2: Recovery of rare earth elements]
In Example 1 described above, it was shown that a substantially double amount of sulfate double-salt precipitate could be left. Therefore, in Example 2, a specific rare earth element recovery process was performed as follows.

  To the reaction tank, 140 L of a sulfuric acid solution in which a rare earth element having an analytical value shown in Table 1 as in Example 1 was dissolved and 140 L of an aqueous solution containing sodium sulfate at a concentration of 180 g / l were added to make 280 L. Then, the temperature of the solution was raised to 60 ° C. and held for 3 hours with stirring to cause a rare earth element sulfate double salt formation reaction, whereby the rare earth element in the solution was converted to a sulfate double salt precipitate.

  Next, the solution in the reaction vessel obtained after completion of the reaction was vigorously stirred with a stirrer, and the measured value of the float type liquid level meter was changed from 65 cm to 43 cm while maintaining the state where the precipitate did not settle and was uniformly dispersed. The solution was fed to the filter press until The portion passed through the filter press was subjected to solid-liquid separation treatment to collect rare earth elements as sulfate double salt precipitates.

  Next, stirring of the solution in the reaction vessel was stopped, and a settling time of 1 hour was provided to precipitate the precipitate in the solution. After settling, insert a liquid removal nozzle that can be raised and lowered from the upper part of the reaction tank, remove the upper clarified liquid (supernatant liquid) while visually checking it, and pass it through the filter press. Only the elemental sulfate double salt precipitate remained.

  Then, with the rare earth element sulfate double salt precipitate remaining in the reaction tank, 140 L of a sulfuric acid solution (rare earth element solution having analytical values shown in Table 1) in which the rare earth element was dissolved was charged into the reaction tank, Further, 140 L of a solution containing alkali metal sulfate was added. Then, the temperature of the solution was raised to 60 ° C. and held for 3 hours with stirring to generate a rare earth element sulfate double salt formation reaction, and the rare earth element in the solution was converted to a sulfate double salt precipitate.

  After the treatment, a filtrate was obtained by subjecting the resulting solution to solid-liquid separation treatment. Table 2 shows analytical values obtained by analyzing the concentration of yttrium (Y) in the filtrate by ICP.

[Reference example: Conventional seed crystal addition example]
To the reaction vessel, 140 L of a sulfuric acid solution in which the same rare earth element as in Example 1 was dissolved and 140 L of an aqueous solution containing sodium sulfate at a concentration of 180 g / l were added to make 280 L. In order to add a rare earth element sulfate double salt precipitate as a seed crystal to this solution, 19.3 kg [wet] of the sulfate double salt precipitate recovered by the filter press was weighed and the reaction vessel in which the solution was accommodated I put it in. Then, the temperature of the solution was raised to 60 ° C. and held for 3 hours with stirring to generate a rare earth element sulfate double salt formation reaction, and the rare earth element in the solution was converted to a sulfate double salt precipitate.

  After the treatment, a filtrate was obtained by subjecting the resulting solution to solid-liquid separation treatment. Table 2 shows analytical values obtained by analyzing the concentration of yttrium (Y) in the filtrate by ICP.

  As shown in Table 2, in the method of Example 2 in which the sulfate double salt precipitate remained in the reaction vessel, the Y concentration in the solution after the treatment was 0.01 g / l. This is the case where a seed crystal is added by a method of taking a predetermined amount after recovering the entire amount of the sulfate double salt precipitate with a solid-liquid separator such as a filter press as in the past, and returning it to the solution again. The concentration was almost the same, and the rare earth elements could be recovered with a very high recovery rate. That is, it can be seen that the residual sulfate double salt precipitate could be used effectively as a seed crystal.

  And in the method implemented in such Example 2, compared with the case where the deposit which weighed in like the conventional example is thrown in and added to a solution, it does not take the effort of carrying a heavy load, etc. There was no concern that the solution would scatter when the precipitate was added to the tank.

  As is clear from the above, in the process of adding a rare earth sulfate sulfate precipitate as a seed crystal for the purpose of efficiently recovering and removing rare earth elements, the precipitate recovered by a solid-liquid separator such as a filter press is added. Efficient and high safety of rare earth elements by improving the slurry extraction method and leaving a predetermined amount of rare earth deposits in the reaction tank without needing to take the required amount of material and re-entering the reaction tank It can be recovered by sex. This method can be suitably used for a wide range of techniques for recovering valuable metals by repeatedly using a precipitate as a seed crystal, and its industrial utility value is extremely high.

Claims (5)

Alkali metal sulfate is added to the solution containing the rare earth element contained in the reaction vessel in the presence of seed crystals to cause a sulfate double salt formation reaction of the rare earth element, and the sulfate double salt precipitation of the rare earth element In the method for collecting rare earth elements to form and recover the product,
After completion of the sulfuric acid double salt formation reaction, the obtained solution is brought into a stirring state in which the sulfuric acid double salt precipitate does not settle, and a solution other than a solution containing a predetermined amount of the sulfuric acid double salt precipitate is passed through a solid-liquid separator. Recovered,
The solution containing the predetermined amount of the sulfate double salt precipitate is allowed to stand in the reaction vessel to settle the sulfate double salt precipitate, and then the supernatant is removed to remove the sulfate double salt precipitate from the reaction vessel. Left in,
In the state where the sulfate double salt precipitate left in the reaction vessel coexists as a seed crystal, a solution containing a rare earth element is accommodated, and an alkali metal sulfate is added to perform a sulfate double salt formation reaction. A method for recovering rare earth elements.   2. The method for recovering rare earth elements according to claim 1, wherein the sulfate double salt precipitate as a seed crystal is allowed to coexist so that the slurry concentration at the initial stage of the reaction is 25 g / l or more.   3. The method for recovering a rare earth element according to claim 1 or 2, wherein a liquid discharge nozzle capable of ascending / descending is inserted from above the reaction tank, and the supernatant liquid is extracted by suction through the liquid discharge nozzle.   A plurality of liquid outlets provided with valves in the height direction of the reaction tank are provided, the valves of the plurality of liquid outlets are opened according to the liquid level of the supernatant liquid, and the liquid outlets are connected via the liquid outlets. The method for recovering rare earth elements according to claim 1 or 2, wherein the supernatant is extracted. In the method for recovering a valuable metal, the solution containing the valuable metal contained in the reaction vessel is caused to generate and recover a precipitate formation reaction of the valuable metal in a state where seed crystals coexist.
After completion of the valuable metal precipitate formation reaction, the obtained solution is stirred so that the valuable metal precipitate does not settle, and the solution other than the solution containing a predetermined amount of precipitate is passed through the solid-liquid separator. Recovered
In the reaction vessel, the solution containing the predetermined amount of the precipitate is allowed to stand to settle the precipitate, and then the supernatant is removed to leave the precipitate in the reaction vessel.
Collecting a solution containing a valuable metal in a state where the precipitate remaining in the reaction vessel coexists as a seed crystal, and performing a precipitate formation reaction of the valuable metal. Method.

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