Method for reducing yield of tetravalent cerium in rare earth chloride extraction and separation

Abstract

The invention belongs to the technical field of rare earth extraction and separation, and particularly relates to a method for reducing the yield of tetravalent cerium in rare earth chloride extraction and separation. The method comprises the following steps: in the extraction separation process, stirring and mixing a water phase and an organic phase, carrying out phase separation in a clarifying chamber, overflowing the water phase to a stirring chamber of a previous stage through a spiral pipe, overflowing the organic phase to a next stage, and realizing separation of rare earth elements through multi-stage series connection, the water phase outlet of the spiral pipe has an optimized diameter and an optimized distance between the water phase outlet of the spiral pipe and the extraction tank body, and the water phase outlet of the spiral pipe is provided with an upper blocking device. According to the method for reducing the yield of tetravalent cerium in rare earth chloride extraction and separation, the purity of a separated product is improved, the content of impurity cerium chloride is reduced, the improved technology avoids formation of crystals on the inner wall of the extraction box body, and the quality of rare earth chloride obtained through extraction and separation is controlled. The rare earth chloride is mixed rare earth chloride.

Description

Technical Field

[0001] The invention belongs to the technical field of rare earth extraction and separation, and in particular relates to a method for reducing the amount of tetravalent cerium produced in the extraction and separation of rare earth chloride. Background Art

[0002] As an important source of rare earth elements, rare earth chloride has a wide range of applications in metallurgy, electronics, magnetic materials and other fields. However, in the extraction and separation process of rare earth chloride, the generation of tetravalent cerium has always been a difficult problem to solve. The presence of tetravalent cerium not only reduces the purity of the product, but also increases the difficulty and cost of subsequent processing.

[0003] Traditionally, there are two main reasons for the generation of tetravalent cerium: one is that the raw materials contain tetravalent cerium; the other is that part of the cerium is oxidized to tetravalent cerium during the extraction and separation process. The former can be controlled by strictly testing the quality of the raw materials. However, the latter has not been effectively solved due to its complex mechanism of generation.

[0004] During the extraction and separation process, the chlorinated rare earth liquid is usually carried out under weak acidic conditions. Under these conditions, cerium will be oxidized by oxygen in the air to form tetravalent cerium. Although the rare earth industry has realized this problem and tried to reduce the production of tetravalent cerium by adding reducing agents, this method cannot fundamentally solve the problem. At the same time, the addition of reducing agents will not only increase production costs, but also reduce the organic phase, introduce new impurities, and affect the purity of the product.

[0005] Further research has found that the generation of tetravalent cerium is closely related to the design of the extraction tank and the operating conditions during the production process. During the extraction process, the aqueous phase and the organic phase are stirred and mixed, and then separated in the clarification chamber. The aqueous phase overflows to the stirring chamber of the previous stage through the spiral tube, while the organic phase overflows to the next stage. In this process, when the aqueous phase passes through the spiral tube, it will splash onto the wall of the extraction tank around the spiral tube. Over time, due to the evaporation of water and the volatilization of hydrochloric acid, rare earth chloride crystals will form on the tank wall. The cerium in these crystals is more easily oxidized by oxygen in the air to form tetravalent cerium. After being washed by the aqueous phase, these tetravalent cerium will re-enter the extraction system, resulting in excessive cerium content in subsequent products.

[0006] Therefore, how to reduce and avoid the production of tetravalent cerium in the extraction process from the source has become an urgent problem to be solved in the rare earth industry. Summary of the invention

[0007] The technical problem to be solved by the present invention is to overcome the above-mentioned defects of the prior art, provide a method for reducing the amount of tetravalent cerium produced in the extraction and separation of rare earth chloride, and reduce the content of cerium in the extracted products of praseodymium chloride, neodymium chloride, praseodymium-neodymium chloride, and samarium-europium-gadolinium chloride. The improved technology avoids the formation of crystals on the inner wall of the extraction box body, and the quality of the product after extraction and separation is controlled. The rare earth chloride is a mixed rare earth chloride.

[0008] The method for reducing the amount of tetravalent cerium produced in the extraction and separation of rare earth chloride described in the present invention is as follows: during the extraction and separation process, the aqueous phase and the organic phase are stirred and mixed, and the phases are separated in the clarification chamber. The aqueous phase overflows to the stirring chamber of the previous stage through the spiral tube, and the organic phase overflows to the next stage. The separation between rare earth elements is achieved through multi-stage series connection. The spiral tube aqueous phase outlet has an optimized diameter and a distance from the extraction tank body, and the spiral tube aqueous phase outlet is provided with an upper blocking device. The splashing of the aqueous phase after outflow is controlled, so that the feed liquid flows out of the spiral tube and flows along the outer wall of the spiral tube to the extraction box body below, thereby avoiding the crystallization of the feed liquid in the extraction box body. The upper blocking device can be made of plastic or stainless steel, and is in the shape of an inverted U-shaped cover.

[0009] Preferably, the distance between the outer wall of the spiral tube and the inner wall of the extraction box body is 0.5-4 times the outer diameter of the spiral tube.

[0010] Preferably, the distance between the outer wall of the spiral tube and the inner wall of the extraction box body is 1-3 times the outer diameter of the spiral tube, so that the overflow water phase flows directly into the water phase below along the spiral tube, reducing the area of ​​the water phase splashing onto the inner wall of the extraction box body.

[0011] Preferably, the inner diameter of the spiral tube is 50-400 mm, and the outflow speed of the water phase is controlled to be less than 0.2 m / s, thereby reducing the splashing of the water phase out of the spiral tube and preventing the liquid from adhering to the extraction box body and crystallizing, thereby causing the cerium to be oxidized by contact with air.

[0012] Further preferably, the inner diameter of the spiral tube is 100-400 mm, and the outflow speed of the water phase is controlled to be less than 0.15 m / s.

[0013] More preferably, the inner diameter of the spiral tube is 200-400 mm, and the outflow velocity of the water phase is controlled to be less than 0.10 m / s.

[0014] Preferably, the upper blocking device is made of plastic or stainless steel and is in the shape of an inverted U-shaped cover.

[0015] Further preferably, the upper blocking device is bonded or welded to the spiral tube.

[0016] Preferably, the distance between the water phase liquid level of the extraction box body and the water phase outlet of the spiral tube is controlled to be less than 6 cm, which is achieved by adjusting the vertical height of the spiral tube in the extraction box body. In the actual production process, the height of the spiral tube can be controlled to control the distance between the upper liquid level of the water phase flowing out of the spiral tube and the upper end surface of the spiral tube to be less than 6 cm to reduce and avoid water phase splashing.

[0017] Further preferably, the distance between the water phase liquid surface of the extraction box body and the water phase outlet of the spiral tube is controlled to be 3 cm, which is achieved by adjusting the vertical height of the spiral tube in the extraction box body.

[0018] Further preferably, the distance between the water phase liquid surface of the extraction box body and the water phase outlet of the spiral tube is controlled to be 2 cm, which is achieved by adjusting the vertical height of the spiral tube in the extraction box body.

[0019] In the extraction and separation process, the aqueous phase and the organic phase are stirred and mixed, and the phases are separated in the clarification chamber. The aqueous phase overflows to the stirring chamber of the previous stage through the spiral tube, and the organic phase overflows to the next stage. The separation between the rare earth elements is achieved through multi-stage series connection. In this process, before the improvement, when the aqueous phase overflows through the spiral tube, it will splash onto the extraction tank wall around the spiral tube. As time goes by, due to the dissolution of water and the volatilization of hydrochloric acid, rare earth chloride crystals will be formed on the tank wall. The acidity of this part of crystals is significantly lower than the acidity of the aqueous phase in the extraction system. The cerium contained is more easily oxidized to tetravalent cerium by air. This part of crystals is taken away by the sputtered aqueous phase. After re-entering the aqueous phase, the tetravalent cerium enters the extraction phase again. The tetravalent cerium forms colloidal particles and moves to the rear stage of the extraction under the entrainment of the organic phase, resulting in a high content of cerium in the rare earth oxide. After the improvement of the present invention, the overflow of the aqueous phase through the spiral tube and splashing onto the extraction tank wall is reduced and avoided, and the crystals formed on the extraction tank wall are avoided, thereby reducing the possibility of cerium being oxidized by air.

[0020] In the actual rare earth chloride extraction process, the industry generally believes that tetravalent cerium is formed by oxidation of cerium in the feed liquid by air during the reaction of the tetravalent cerium colloidal particles peptized in the raw material and the reaction of the organic phase and the aqueous phase during the stirring and mixing extraction. In practice, the present invention finds that the rare earth chloride feed liquid containing cerium, when flowing through the spiral tube of the tank body during the extraction process, is splashed onto the wall of the extraction tank and crystallized on the wall of the extraction tank. As time goes by, the cerium in the crystals is oxidized by oxygen in the air to form tetravalent cerium. After being washed by the aqueous phase, part of it is brought into the extraction system and enters the rare earth chloride, causing the tetravalent cerium to move to the back of the extraction tank, affecting the purity of the extracted and separated products of praseodymium chloride, neodymium chloride, praseodymium-neodymium chloride, and samarium-europium-gadolinium chloride.

[0021] Compared with the prior art, the present invention has the following beneficial effects: (1) The method of reducing the amount of tetravalent cerium produced in the extraction and separation of rare earth chlorides of the present invention effectively reduces the production of tetravalent cerium in the extraction process caused by the prior art, reduces the content of cerium in the extraction products praseodymium chloride, neodymium chloride, praseodymium-neodymium chloride, and samarium-europium-gadolinium chloride, and improves the purity of the products.

[0022] (2) The method of reducing the amount of tetravalent cerium produced in the extraction and separation of rare earth chlorides of the present invention significantly reduces the amount of tetravalent cerium produced in the extraction and separation process of rare earth chlorides, thereby reducing the amount of reagents added in the extraction process for reducing tetravalent cerium by more than half, thereby improving the purity of the extraction and separation product. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 It is a schematic structural diagram of the extraction box of the present invention.

[0024] In the figure: 1. extraction box body; 2. upper blocking device; 3. spiral tube; 4. water phase; 5. water phase outlet of spiral tube. DETAILED DESCRIPTION

[0025] The present invention will be further described below in conjunction with specific embodiments.

[0026] The raw materials and additives used in the following examples and comparative examples are all commercially available products.

[0027] The structure of the extraction box of the present invention is as follows Figure 1 As shown, a spiral tube 3 is provided in the middle part of the inner part of the extraction box body 1, and there is a water phase 4 in the spiral tube 3 and the extraction box body 1. A spiral tube water phase outlet 5 is provided on the spiral tube 3, and the water phase 4 in the spiral tube 3 overflows into the extraction box body 1 from here. An upper blocking device 2 is provided just above the spiral tube water phase outlet 5 to prevent the water phase from splashing onto the inner wall of the extraction box body 1.

[0028] Example 1 The method for reducing the generation of tetravalent cerium in the extraction and separation of rare earth chlorides: in the extraction tank body and the subsequent extraction tank body in which the neodymium and samarium groups produce the praseodymium-neodymium chloride products during the extraction and separation process, the distance between the outer wall of the spiral tube 3 and the inner wall of the extraction box body 1 is 1.1 times the outer diameter of the spiral tube 3; the spiral tube 3 is provided with a spiral tube water phase outlet 5, and the spiral tube water phase outlet 5 is provided with an upper blocking device 2. The aqueous phase and the organic phase are stirred and mixed, and separated in the clarification chamber, the aqueous phase overflows to the stirring chamber of the previous stage through the spiral tube, and the organic phase overflows to the next stage, and the rare earth elements are separated by multiple stages in series to obtain the praseodymium-neodymium chloride product.

[0029] The inner diameter of the spiral tube 3 is 150 mm, and the outflow speed of the water phase is controlled to be 0.17 m / s.

[0030] The upper blocking device 2 is made of PVC and is an inverted U-shaped cover.

[0031] The upper blocking device 2 is welded on the spiral tube 3 .

[0032] The distance between the water phase surface of the extraction box body 1 and the water phase outlet 5 of the spiral tube is controlled to be 3 cm, which is achieved by adjusting the vertical height of the spiral tube 3 in the extraction box body 1.

[0033] Example 2 The method for reducing the production of tetravalent cerium in the extraction and separation of rare earth chlorides: during the extraction and separation process, samarium europium gadolinium chloride products are produced from the neodymium and samarium groups; in all tanks in the extraction section and the washing section, the distance between the outer wall of the spiral tube 3 and the inner wall of the extraction box body 1 is 2.5 times the outer diameter of the spiral tube 3; the spiral tube 3 is provided with a spiral tube water phase outlet 5, and the spiral tube water phase outlet 5 is provided with an upper blocking device 2, and the samarium europium gadolinium chloride products are obtained after extraction and separation.

[0034] The inner diameter of the spiral tube 3 is 200 mm, and the outflow speed of the water phase is controlled to be 0.1 m / s.

[0035] The upper blocking device 2 is made of PP plastic and is an inverted U-shaped cover.

[0036] The upper blocking device 2 is bonded to the spiral tube 3 .

[0037] The distance between the water phase surface of the extraction box body 1 and the water phase outlet 5 of the spiral tube is controlled to be 2 cm, which is achieved by adjusting the vertical height of the spiral tube 3 in the extraction box body 1.

[0038] Example 3 The method for reducing the generation of tetravalent cerium in the extraction and separation of rare earth chloride: in the praseodymium-neodymium grouping during the extraction and separation process, in all tanks in the extraction section and the washing section, the distance between the outer wall of the spiral tube 3 and the inner wall of the extraction box body 1 is twice the outer diameter of the spiral tube 3; the spiral tube 3 is provided with a spiral tube water phase outlet 5, and the spiral tube water phase outlet 5 is provided with an upper blocking device 2. After extraction and separation, a neodymium chloride product is produced.

[0039] The inner diameter of the spiral tube 3 is 100 mm, and the outflow speed of the water phase is controlled to be 0.13 m / s.

[0040] The upper blocking device 2 is made of PE and is an inverted U-shaped cover.

[0041] The upper blocking device 2 is bonded to the spiral tube 3 .

[0042] The distance between the water phase surface of the extraction box body 1 and the water phase outlet 5 of the spiral tube is controlled to be 4 cm, which is achieved by adjusting the vertical height of the spiral tube 3 in the extraction box body 1.

[0043] Example 4 The method for reducing the amount of tetravalent cerium produced in the extraction and separation of rare earth chlorides: in the extraction and separation process, the distance between the outer wall of the spiral tube 3 and the inner wall of the extraction box body 1 is 4 times the outer diameter of the spiral tube 3; the spiral tube 3 is provided with a spiral tube water phase outlet 5, and the spiral tube water phase outlet 5 is provided with an upper blocking device 2. After linkage extraction, praseodymium-neodymium chloride and samarium-europium-gadolinium chloride products are produced.

[0044] The inner diameter of the spiral tube 3 is 125 mm, and the outflow speed of the water phase is controlled to be 0.11 m / s.

[0045] The upper blocking device 2 is made of stainless steel and is an inverted U-shaped cover.

[0046] The upper blocking device 2 is welded on the spiral tube 3 .

[0047] The distance between the water phase surface of the extraction box body 1 and the water phase outlet 5 of the spiral tube is controlled to be 1 cm, which is achieved by adjusting the vertical height of the spiral tube 3 in the extraction box body 1.

[0048] Example 5 The method for reducing the amount of tetravalent cerium produced in the extraction and separation of rare earth chlorides: in the extraction and separation process, the distance between the outer wall of the spiral tube 3 and the inner wall of the extraction box body 1 is 3 times the outer diameter of the spiral tube 3; the spiral tube 3 is provided with a spiral tube water phase outlet 5, and the spiral tube water phase outlet 5 is provided with an upper blocking device 2. After linkage extraction, praseodymium-neodymium chloride and samarium-europium-gadolinium chloride products are produced.

[0049] The inner diameter of the spiral tube 3 is 80 mm, and the outflow speed of the water phase is controlled to be 0.12 m / s.

[0050] The upper blocking device 2 is made of PVC plastic and is an inverted U-shaped cover.

[0051] The upper blocking device 2 is welded to the spiral tube 3 by plastic welding.

[0052] The distance between the water phase surface of the extraction box body 1 and the water phase outlet 5 of the spiral tube is controlled to be 5 cm, which is achieved by adjusting the vertical height of the spiral tube 3 in the extraction box body 1.

[0053] Example 6 The method for reducing the amount of tetravalent cerium produced in the extraction and separation of rare earth chloride: in the extraction and separation process, the distance between the outer wall of the spiral tube 3 and the inner wall of the extraction box body 1 is 3 times the outer diameter of the spiral tube 3; the spiral tube 3 is provided with a spiral tube water phase outlet 5, and the spiral tube water phase outlet 5 is provided with an upper blocking device 2. The aqueous phase and the organic phase are stirred and mixed, and separated in the clarification chamber. The aqueous phase overflows to the stirring chamber of the previous stage through the spiral tube, and the organic phase overflows to the next stage. The separation between rare earth elements is achieved through multi-stage series connection. To verify the effect, 5% hydrogen peroxide is added as a reducing agent for tetravalent cerium in the 10th stage before the last stage of the rare earth chloride washing section, and the daily amount of hydrogen peroxide is counted. After linkage extraction, praseodymium-neodymium chloride and samarium-europium-gadolinium chloride products are produced.

[0054] The inner diameter of the spiral tube 3 is 80 mm, and the outflow speed of the water phase is controlled to be 0.12 m / s.

[0055] The upper blocking device 2 is made of PVC plastic and is an inverted U-shaped cover.

[0056] The upper blocking device 2 is welded to the spiral tube 3 by plastic welding.

[0057] The distance between the water phase surface of the extraction box body 1 and the water phase outlet 5 of the spiral tube is controlled to be 5 cm, which is achieved by adjusting the vertical height of the spiral tube 3 in the extraction box body 1.

[0058] Comparative Example 1 This comparative example is the same as Example 5, except that during the extraction and separation process, the height of the spiral tube 3 in the extraction box is not controlled, so that the liquid level of the outflowing feed liquid is 6.5 cm above the upper end surface of the spiral tube.

[0059] Comparative Example 2 This comparative example is the same as Example 1, except that the distance between the outer wall of the spiral tube 3 and the inner wall of the extraction box body 1 is controlled to be 0.4 times the outer diameter of the spiral tube 3 .

[0060] Comparative Example 3 This comparative example is the same as Example 3, except that the outflow velocity of the water phase is controlled to be 0.28 m / s.

[0061] Comparative Example 4 This comparative example is the same as Example 6, except that the spiral tube water phase outlet 5 is not provided with a blocking device 2. The inner diameter of the spiral tube 3 is 50 mm, and the water phase outflow speed is controlled to be 0.31 m / s.

[0062] The effect was tested by using the cerium content in the products prepared in the above examples and comparative examples. The lower the cerium content, the less tetravalent cerium is produced during the extraction and separation process, and the more obvious the effect is. The test results are shown in Table 1. ∑CeO2 / TREO / % indicates the percentage of the total rare earth oxides of the impurity cerium oxide in the product. Hydrogen peroxide can reduce the tetravalent cerium present in the extraction production line. Under the condition of the same product quality, that is, the same cerium oxide content in the same product, the more hydrogen peroxide is used, the more tetravalent cerium is produced.

[0063] Table 1 Test results

Claims

1. A method for reducing the amount of tetravalent cerium produced in the extraction and separation of rare earth chloride, characterized in that: During the extraction and separation process, the aqueous phase and the organic phase are stirred and mixed, and then separated in the clarification chamber. The aqueous phase overflows to the stirring chamber of the previous stage through the spiral tube (3), and the organic phase overflows to the next stage. The separation of the rare earth elements is achieved through multiple stages in series. The spiral tube (3) is provided with a spiral tube aqueous phase outlet (5), and the spiral tube aqueous phase outlet (5) is provided with an upper blocking device (2); The distance between the outer wall of the spiral tube (3) and the inner wall of the extraction box body (1) is 0.5-4 times the outer diameter of the spiral tube (3); The inner diameter of the spiral tube (3) is 50-400 mm, and the outflow speed of the water phase is controlled to be less than 0.2 m / s.

2. The method for reducing the amount of tetravalent cerium produced in the extraction and separation of rare earth chloride according to claim 1, characterized in that: The distance between the outer wall of the spiral tube (3) and the inner wall of the extraction box body (1) is 1 to 3 times the outer diameter of the spiral tube (3).

3. The method for reducing the amount of tetravalent cerium produced in the extraction and separation of rare earth chloride according to claim 1, characterized in that: The inner diameter of the spiral tube (3) is 100-400 mm, and the outflow speed of the water phase is controlled to be less than 0.15 m / s.

4. The method for reducing the amount of tetravalent cerium produced in the extraction and separation of rare earth chloride according to claim 1, characterized in that: The inner diameter of the spiral tube (3) is 200-400 mm, and the outflow speed of the water phase is controlled to be less than 0.10 m / s.

5. The method for reducing the amount of tetravalent cerium produced in the extraction and separation of rare earth chloride according to claim 1, characterized in that: The upper blocking device (2) is made of plastic or stainless steel and has an inverted U shape.

6. The method for reducing the amount of tetravalent cerium produced in the extraction and separation of rare earth chloride according to claim 1, characterized in that: The distance between the water phase liquid surface of the extraction box body (1) and the water phase outlet (5) of the spiral tube is controlled to be less than 6 cm.

7. The method for reducing the amount of tetravalent cerium produced in the extraction and separation of rare earth chloride according to claim 6, characterized in that: The distance between the water phase liquid surface of the extraction box body (1) and the water phase outlet (5) of the spiral tube is controlled to be 3 cm.

8. The method for reducing the amount of tetravalent cerium produced in the extraction and separation of rare earth chloride according to claim 6, characterized in that: The distance between the water phase liquid surface of the extraction box body (1) and the water phase outlet (5) of the spiral tube is controlled to be 2 cm.

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