Method for reducing the production amount of cerium(IV) in the extraction and separation of rare earth chlorides

Abstract

The present invention belongs to the technical field of rare earth extraction and separation, and particularly relates to a method for reducing the generation amount of tetravalent cerium in the extraction and separation of rare earth chlorides. The method for reducing the generation amount of tetravalent cerium in the extraction and separation of rare earth chlorides according to the present invention: during the extraction and separation process, the aqueous phase and the organic phase are stirred and mixed, 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 separation between rare earth elements is achieved through multi-stage series connection. The aqueous phase outlet of the spiral tube has an optimized diameter and a distance from the extraction tank body, and an upper blocking device is arranged at the aqueous phase outlet of the spiral tube. The method for reducing the generation amount of tetravalent cerium in the extraction and separation of rare earth chlorides provided by the present invention can improve the purity of the separated product, reduce the content of impurity cerium chloride, and the improved technology avoids the formation of crystallization on the inner wall of the extraction tank body, and the quality of the extracted and separated rare earth chlorides is controlled. The rare earth chloride is mixed rare earth chloride.

Description

Technical Field

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

[0002] Rare earth chlorides, as an important source of rare earth elements, have wide applications in fields such as metallurgy, electronics, and magnetic materials. However, in the process of extraction and separation of rare earth chlorides, the generation of tetravalent cerium has always been a difficult problem to solve. The existence of tetravalent cerium not only reduces the purity of the product but also increases the difficulty and cost of subsequent treatment.

[0003] Traditional views hold that the generation of tetravalent cerium mainly has two reasons: one is that the raw materials themselves contain tetravalent cerium; the other is that during the extraction and separation process, part of the cerium is oxidized to tetravalent. For the former, it can be controlled by strictly detecting the quality of the raw materials. However, for the latter, due to its complex generation mechanism, it has not been effectively solved.

[0004] During the extraction and separation process, the rare earth chloride feed solution is usually carried out under weakly acidic conditions. Under this condition, cerium will be oxidized by the oxygen in the air to form tetravalent cerium. Although the rare earth industry has realized this problem and tried to reduce the generation of tetravalent cerium by adding reducing agents, this method cannot fundamentally solve the problem. At the same time, the addition of reducing agents not only increases the production cost but also reduces the organic phase and introduces new impurities, affecting 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, after the aqueous phase and the organic phase are stirred and mixed, they are 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. During this process, when the aqueous phase passes through the spiral tube, it will splash onto the extraction tank wall 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 the oxygen in the air to form tetravalent cerium. After being washed by the aqueous phase, these tetravalent ceriums will re-enter the extraction system, resulting in the over-standard cerium content in the subsequent product.

[0006] Therefore, how to reduce and avoid the generation 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 existing in the prior art, and to provide a method for reducing the generation amount of tetravalent cerium in the extraction and separation of rare earth chlorides, so as to reduce the cerium content in the extraction products such as 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 extraction and separation products is controlled. The rare earth chloride described is mixed rare earth chloride.

[0008] The method for reducing the generation amount of tetravalent cerium in the extraction and separation of rare earth chlorides according to the present invention: during the extraction and separation process, the aqueous phase and the organic phase are stirred and mixed, 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 separation between rare earth elements is achieved through multi-stage series connection. The water phase outlet of the spiral tube has an optimized diameter and a distance from the extraction tank body, and an upper blocking device is arranged at the water phase outlet of the spiral tube. The splashing after the aqueous phase flows out is controlled, so that the liquid material flows along the outer wall of the spiral tube to the inner body of the lower extraction box after flowing out of the spiral tube, avoiding the crystallization of the liquid material on the inner body of the extraction box. The upper blocking device can be made of plastic or stainless steel, and its shape is 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. The overflowing aqueous phase directly flows into the lower aqueous phase along the spiral tube, reducing the area where the aqueous phase splashes onto the inner wall of the extraction box body.

[0011] Preferably, the inner diameter of the spiral tube is 50 - 400 mm, and the flow rate of the aqueous phase flowing out is controlled to be less than 0.2 m / s. Thereby reducing the splashing generated when the aqueous phase flows out of the spiral tube, avoiding the crystallization and precipitation of the liquid material adhering to the inner body of the extraction box, and thus preventing cerium from contacting with air and being oxidized.

[0012] Further preferably, the inner diameter of the spiral tube is 100 - 400 mm, and the flow rate of the aqueous phase flowing out is controlled to be less than 0.15 m / s.

[0013] Even more preferably, the inner diameter of the spiral tube is 200 - 400 mm, and the flow rate of the aqueous phase flowing out is controlled to be less than 0.10 m / s.

[0014] Preferably, the upper blocking device is made of plastic or stainless steel, and its shape is 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 aqueous phase liquid level in the extraction tank body and the aqueous phase outlet of the spiral tube is controlled to be < 6 cm, which is achieved by adjusting the vertical height of the spiral tube in the extraction tank body. In the actual production process, the height of the spiral tube can be controlled to make the distance between the upper liquid level of the aqueous phase flowing out of the spiral tube and the upper end face of the spiral tube less than 6 cm to reduce and avoid the splashing of the aqueous phase.

[0017] More preferably, the distance between the aqueous phase liquid level in the extraction tank body and the aqueous 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 tank body.

[0018] More preferably, the distance between the aqueous phase liquid level in the extraction tank body and the aqueous 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 tank body.

[0019] In the extraction and separation process, the aqueous phase and the organic phase are stirred and mixed, 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, realizing the separation between rare earth elements through multi-stage series connection. In this process, before the improvement, when the aqueous phase overflowed and entered through the spiral tube, it would splash onto the extraction tank wall around the spiral tube. As time went by, due to the dissolution of water and the volatilization of hydrochloric acid, rare earth chloride crystals would form on the tank wall. The acidity of this part of the crystals was significantly lower than that of the aqueous phase in the extraction system, and cerium contained in it was more easily oxidized by air to tetravalent cerium. This part of the crystals was carried away by the splashed aqueous phase and re-entered the aqueous phase. After the tetravalent cerium re-entered the extraction phase, it formed colloidal particles and moved towards the latter stage of 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 splashing of the aqueous phase onto the extraction tank wall through the spiral tube overflow was reduced and avoided, and the formation of crystals on the extraction tank wall was avoided, thus reducing the possibility of cerium being oxidized by air.

[0020] In the actual extraction process of rare earth chloride, it is generally considered in the industry that tetravalent cerium is formed due to the colloidal particles of tetravalent cerium solubilized in the raw materials and the oxidation of cerium in the feed liquid by air during the stirring and mixing of the extraction organic phase and the aqueous phase. However, in practice, the present invention has found that when the rare earth chloride feed liquid containing cerium flows through the spiral tube of the tank body during the extraction process, it splashes onto the extraction tank wall and crystallizes out on the extraction tank wall. As time goes by, 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, resulting in the movement of tetravalent cerium towards the latter stages of the extraction tank and affecting the purity of the extraction separation products such as praseodymium chloride, neodymium chloride, praseodymium-neodymium chloride, and samarium-europium-gadolinium chloride.

[0021] Compared with the prior art, the beneficial effects of the present invention are:

[0022] (1)The method for reducing the generation amount of tetravalent cerium in the extraction and separation of rare earth chlorides of the present invention effectively reduces the generation of tetravalent cerium in the extraction process caused by the prior art, reduces the cerium content in the extraction products such as praseodymium chloride, neodymium chloride, praseodymium-neodymium chloride, and samarium-europium-gadolinium chloride, and improves the purity of the products.

[0023] (2)In the method for reducing the generation amount of tetravalent cerium in the extraction and separation of rare earth chlorides of the present invention, the generation amount of tetravalent cerium in the extraction and separation process of rare earth chlorides is significantly reduced, so that the dosage of the reagent for reducing tetravalent cerium added in the extraction process is reduced by more than half, and the purity of the extraction and separation products is improved. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 It is a schematic structural diagram of the extraction box body of the present invention.

[0025] In the figure: 1. Main body of the extraction box body; 2. Upper blocking device; 3. Spiral tube; 4. Aqueous phase; 5. Aqueous phase outlet of the spiral tube. DETAILED DESCRIPTION OF THE INVENTION

[0026] The present invention will be further described below in conjunction with specific embodiments.

[0027] The raw materials and auxiliaries used in the following examples and comparative examples are all commercially available products.

[0028] The structure of the extraction box body described in the present invention is as Figure 1 shown. An intermediate part inside the main body 1 of the extraction box body is provided with a spiral tube 3. There is an aqueous phase 4 both inside the spiral tube 3 and inside the main body 1 of the extraction box body. The spiral tube 3 is provided with an aqueous phase outlet 5 of the spiral tube. The aqueous phase 4 inside the spiral tube 3 overflows into the main body 1 of the extraction box body from here. An upper blocking device 2 is provided directly above the aqueous phase outlet 5 of the spiral tube, which serves to block the splashing of the aqueous phase onto the inner wall of the main body 1 of the extraction box body.

[0029] Example 1

[0030] The method for reducing the generation of tetravalent cerium in the extraction and separation of rare earth chlorides: In the extraction tank body for producing praseodymium-neodymium chloride product during the neodymium-samarium grouping and the subsequent extraction tank body in the extraction and separation process, the distance between the outer wall of the spiral tube 3 and the inner wall of the main body 1 of the extraction box body is 1.1 times the outer diameter of the spiral tube 3; the spiral tube 3 is provided with an aqueous phase outlet 5 of the spiral tube, and an upper blocking device 2 is provided at the aqueous phase outlet 5 of the spiral tube. The aqueous phase and the organic phase are stirred and mixed, phase-separated in the clarification chamber, the aqueous phase overflows through the spiral tube to the stirring chamber of the previous stage, and the organic phase overflows to the next stage, and the separation between rare earth elements is achieved through multi-stage series connection to obtain praseodymium-neodymium chloride product.

[0031] The inner diameter of the spiral tube 3 is 150 mm, and the outflow speed of the aqueous phase is controlled to be 0.17 m / s.

[0032] The upper blocking device 2 is made of PVC and is an inverted U-shaped cover body.

[0033] The upper blocking device 2 is welded to the spiral tube 3.

[0034] The distance between the aqueous phase liquid level of the extraction box body 1 and the aqueous 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.

[0035] Example 2

[0036] The method for reducing the generation of tetravalent cerium in the extraction and separation of rare earth chlorides: During the extraction and separation process, in the production of samarium europium gadolinium chloride products in the neodymium samarium grouping, 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 an aqueous phase outlet 5 of the spiral tube, and the aqueous phase outlet 5 of the spiral tube is provided with an upper blocking device 2. After extraction and separation, samarium europium gadolinium chloride products are obtained.

[0037] The inner diameter of the spiral tube 3 is 200 mm, and the aqueous phase outflow rate is controlled to be 0.1 m / s.

[0038] The upper blocking device 2 is made of PP plastic and is an inverted U-shaped cover body.

[0039] The upper blocking device 2 is bonded to the spiral tube 3.

[0040] The distance between the aqueous phase liquid level of the extraction box body 1 and the aqueous 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.

[0041] Example 3

[0042] The method for reducing the generation of tetravalent cerium in the extraction and separation of rare earth chlorides: During the extraction and separation process, in the praseodymium neodymium grouping, 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 times the outer diameter of the spiral tube 3; the spiral tube 3 is provided with an aqueous phase outlet 5 of the spiral tube, and the aqueous phase outlet 5 of the spiral tube is provided with an upper blocking device 2. After extraction and separation, neodymium chloride products are produced.

[0043] The inner diameter of the spiral tube 3 is 100 mm, and the aqueous phase outflow rate is controlled to be 0.13 m / s.

[0044] The upper blocking device 2 is made of PE and is an inverted U-shaped cover body.

[0045] The upper blocking device 2 is bonded to the spiral tube 3.

[0046] The distance between the aqueous phase liquid level of the extraction box body 1 and the aqueous 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.

[0047] Example 4

[0048] The method for reducing the generation amount of tetravalent cerium in the extraction and separation of rare earth chlorides: 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 4 times the outer diameter of the spiral tube 3; a spiral tube aqueous phase outlet 5 is provided on the spiral tube 3, and an upper blocking device 2 is provided at the spiral tube aqueous phase outlet 5. Praseodymium-neodymium chloride and samarium-europium-gadolinium chloride products are produced through linked extraction.

[0049] The inner diameter of the spiral tube 3 is 125 mm, and the aqueous phase outflow speed is controlled to be 0.11 m / s.

[0050] The upper blocking device 2 is made of stainless steel and is an inverted U-shaped cover body.

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

[0052] The distance between the aqueous phase liquid level of the extraction box body 1 and the aqueous 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.

[0053] Example 5

[0054] The method for reducing the generation amount of tetravalent cerium in the extraction and separation of rare earth chlorides: 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 3 times the outer diameter of the spiral tube 3; a spiral tube aqueous phase outlet 5 is provided on the spiral tube 3, and an upper blocking device 2 is provided at the spiral tube aqueous phase outlet 5. Praseodymium-neodymium chloride and samarium-europium-gadolinium chloride products are produced through linked extraction.

[0055] The inner diameter of the spiral tube 3 is 80 mm, and the aqueous phase outflow speed is controlled to be 0.12 m / s.

[0056] The upper blocking device 2 is made of PVC plastic and is an inverted U-shaped cover body.

[0057] The upper blocking device 2 is welded to the spiral tube 3 by plastic welding.

[0058] The distance between the aqueous phase liquid level of the extraction box body 1 and the aqueous 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.

[0059] Example 6

[0060] Method for reducing the generation amount of tetravalent cerium in the extraction and separation of rare earth chlorides: During the extraction and separation process, the distance between the outer wall of the described spiral tube 3 and the inner wall of the extraction box body 1 is 3 times the outer diameter of the spiral tube 3; a spiral tube aqueous phase outlet 5 is provided on the spiral tube 3, and an upper blocking device 2 is provided at the spiral tube aqueous phase outlet 5. The aqueous phase and the organic phase are stirred and mixed, phase-separated in the clarification chamber, the aqueous phase overflows through the spiral tube to the stirring chamber of the previous stage, and the organic phase overflows to the next stage, and the separation between rare earth elements is achieved through multi-stage series connection. To verify the effect, hydrogen peroxide with a concentration of 5% is added as a reducing agent for tetravalent cerium at the 10th stage before the last stage of the rare earth chloride washing section, and the daily consumption of hydrogen peroxide is counted. Praseodymium-neodymium chloride and samarium-europium-gadolinium chloride products are produced through linked extraction.

[0061] The inner diameter of the described spiral tube 3 is 80 mm, and the flow rate of the aqueous phase is controlled to be 0.12 m / s.

[0062] The material of the described upper blocking device 2 is PVC plastic and is an inverted U-shaped cover body.

[0063] The described upper blocking device 2 is welded to the spiral tube 3 by plastic welding.

[0064] The distance between the aqueous phase liquid level of the extraction box body 1 and the spiral tube aqueous phase outlet 5 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.

[0065] Comparative Example 1

[0066] This comparative example is the same as Example 5, and the difference is that during the extraction and separation process, the height of the spiral tube 3 in the extraction box is not controlled, and the height of the upper liquid level of the discharged liquid is 6.5 cm above the upper end face of the spiral tube.

[0067] Comparative Example 2

[0068] This comparative example is the same as Example 1, and the difference is 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.

[0069] Comparative Example 3

[0070] This comparative example is the same as Example 3, and the difference is that the flow rate of the aqueous phase is controlled to be 0.28 m / s.

[0071] Comparative Example 4

[0072] This comparative example is the same as Example 6, and the difference is that the blocking device 2 is not provided at the spiral tube aqueous phase outlet 5 adopted. The inner diameter of the spiral tube 3 is 50 mm, and the flow rate of the aqueous phase is controlled to be 0.31 m / s.

[0073] The cerium content in the products prepared with the above examples and comparative examples was used to examine the effect. The lower the cerium content, the less tetravalent cerium is generated during the extraction and separation process, and the more obvious the effect is. The test results are shown in Table 1. ∑CeO 2 / T REO / % represents the percentage of total rare earth oxides of cerium oxide impurities in the product. Hydrogen peroxide can reduce the tetravalent cerium present in the extraction production line. Under the same product quality, that is, when the cerium oxide content in the same product is equivalent, the more hydrogen peroxide is used, the more tetravalent cerium is generated.

[0074] Table 1 Test Results

[0075]

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; 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.

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 3 cm.

7. 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 2 cm.

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