Method for continuously preparing low-impurity rare earth carbonate by using mixed precipitant

Abstract

The invention provides a method for continuously preparing low-impurity rare earth carbonate by using a mixed precipitator, and belongs to the technical field of hydrometallurgy. The method comprises the following steps: 1, adding a rare earth solution and a mixed precipitator solution into a first-stage reactor in a parallel flow feeding manner, and carrying out a heat preservation reaction to obtain reaction slurry; 2, the reaction slurry overflows from the first-stage reactor to a second-stage reactor, and when the volume of the overflowed reaction slurry is larger than or equal to 10% of the volume of the second-stage reactor, the step 1 is repeated in the second-stage reactor; and repeating the step 2 until a heat preservation reaction is carried out in the nth-stage reactor, and collecting the precipitate in the nth-stage reactor. According to the method provided by the invention, the key problem that system anions such as Cl <-> and NO3 <-> are retained in rare earth carbonate in manners of wrapping, adsorption or chemical bonding and the like is solved, and the low-impurity dilute carbonate with the content of Cl <-> and NO3 <-> of less than or equal to 50ppm in a microscopic multi-pore structure is obtained.

Description

Technical Field

[0001] The invention relates to the technical field of hydrometallurgy, and in particular to a method for continuously preparing low-impurity rare earth carbonate by using a mixed precipitant. Background Art

[0002] High purification of rare earth raw materials is an important support for realizing the rare earth power strategy. In the process of synthesizing rare earth carbonates and oxides from rare earth solutions, anions in the rare earth solution system will inevitably be introduced, which will directly affect the preparation and quality of back-end functional materials. For example, chlorine can cause catalyst poisoning, high temperature decomposition of hydrogen chloride corrodes the technical (alloy) matrix material, and nitrate ions will release nitrogen oxides after thermal decomposition, causing corrosion or environmental pollution.

[0003] Impurities in rare earth carbonate and rare earth oxide (Cl - 、NO3 - ) is mainly retained in rare earth products in the form of surface adsorption, encapsulation or basic salts. Impurities adsorbed on the surface can be removed by washing with a large amount of clean water. Impurities in the form of encapsulation and basic salts must be comprehensively regulated by optimizing the crystal structure and controlling the reaction limit. In existing industrial production, there are three main ways to prepare low-impurity rare earth products in batches: First, homogeneous precipitation of low-concentration rare earth solutions is used to control the encapsulation form by controlling the extremely low ammonium salt concentration of the reaction system. The second is to dissolve high-impurity rare earth carbonate in nitric acid and then precipitate it, and the precipitate is burned to obtain low-impurity rare earth oxide. The third is to obtain low-impurity products by high-temperature conversion and crystal reconstruction of rare earth carbonate.

[0004] At present, in order to achieve low-carbon production, the existing technology generally adopts the mixed precipitation technology of ammonium bicarbonate and ammonia water to prepare low-impurity rare earth products, but the Cl - The content is about 400-600ppm. Especially in the mixed precipitation technology of ammonium bicarbonate and ammonia water, when the ratio of ammonia water to ammonium bicarbonate is increased from 4:6, the ammonia water provides OH - As the ion concentration increases, it is very easy to form basic salts such as RE(OH)2Cl and RE2(OH)5NO3, which will lead to a significant increase in the impurity content of the product. - In a high-concentration mixed precipitation system, the core technical challenge is to effectively control the product microstructure to avoid encapsulation and to control the reaction limit to avoid the formation of basic salts. The core equipment challenge is how to transform the complex fine control process into engineering technology and realize continuous production.

[0005] CN107746976 A discloses a method for preparing rare earth carbonate using a high concentration precipitant, wherein ammonium bicarbonate and ammonia water are used as mixed precipitants, and a single tank reaction takes 3 to 9 hours, the reaction time is too long, and the efficiency is low; the generated rare earth carbonate product has the morphology of solid flakes stacked in an irregular state, and Cl- The content is 400-600ppm.

[0006] CN104891550A discloses a method for preparing cerium dioxide by using a mixed precipitant, wherein a mixed precipitant solution of 2.0 to 5.5 mol / L is prepared by mixing ammonium bicarbonate and ammonia water in a molar ratio of 55 to 25:45 to 75 with a cerium chloride solution at 50 to 70°C to prepare a mixed precipitate mainly composed of basic cerium carbonate and supplemented by cerium carbonate and cerium hydroxide. The precipitate prepared by this method is a mixture and the basic salt content is difficult to control. The product Cl - The impurity content is more than 1000ppm.

[0007] CN103276440B discloses a method for processing low-chloride rare earth carbonate, which can reduce the chloride content of the product by 50%, but still leaves a large amount of chloride. The method uses multiple warm water washings in combination with multiple burning processes, and adds pure water before burning to remove the chloride content in the rare earth carbonate product. Multiple warm water washings will increase water consumption to form low-concentration wastewater, and multiple burnings will make the industrialization cost extremely high.

[0008] CN110372027A discloses a method for precipitating low-chloride lutetium oxide in a chloride system, wherein a lutetium chloride feed solution is mixed with nitric acid and then precipitated with an oxalic acid precipitant. The method adds an oxalic acid precipitant, which is costly, and the addition of nitric acid results in the formation of mixed wastewater of nitrate, chloride and oxalic acid, which is difficult to treat.

[0009] CN103708525B discloses a method for producing high bulk density fine-grained low-chloride rare earth carbonate and oxide, which uses an alkaline solution to treat rare earth carbonate to transform it into a fine-grained low-chloride basic rare earth carbonate, so that the entrained chloride is released and removed. However, due to the finer particle size of the product, solid-liquid separation becomes difficult, and the chloride content of the product basic rare earth carbonate is still above 160ppm. At the same time, the rare earth carbonate needs to be treated twice to reduce the chloride, which is not suitable for industrial production. Summary of the invention

[0010] In view of this, the object of the present invention is to provide a method for continuously preparing low-impurity rare earth carbonate using a mixed precipitant. The method provided by the present invention solves the problem of Cl - 、NO3 - The key problem of the anion system being retained in the rare earth carbonate by means of encapsulation, adsorption or chemical bonding is to obtain the Cl - 、NO3 - Low impurity rare earth carbonate content ≤50ppm.

[0011] In order to achieve the above object, the present invention provides the following technical solution: a method for continuously preparing low-impurity rare earth carbonate using a mixed precipitant, comprising the following steps:

[0012] Step 1. adding the rare earth solution and the mixed precipitant solution into the first-stage reactor by a co-current feeding method for heat preservation reaction to obtain a reaction slurry;

[0013] Step 2. The reaction slurry overflows from the first-stage reactor to the second-stage reactor. When the volume of the overflowed reaction slurry is greater than or equal to 10% of the volume of the second-stage reactor, step 1 is repeated in the second-stage reactor;

[0014] Step 3. Repeat step 2 until the heat preservation reaction is carried out in the n-stage reactor, and collect the precipitate in the n-stage reactor to obtain low-impurity rare earth carbonate;

[0015] The first-stage reactor to the n-stage reactor are each independently provided with a rare earth solution feed inlet and a mixed precipitant solution feed inlet.

[0016] In some embodiments of the present invention, the rare earth solution includes a single rare earth chloride solution, a mixed rare earth chloride solution, a single rare earth nitrate solution or a mixed rare earth nitrate solution; the concentration of the rare earth solution is 100-350 g / L in terms of REO.

[0017] In some embodiments of the present invention, the mixed precipitant solution contains CO3 2- and OH - ; The CO3 2- The concentration of CO3 is 1.5-3.5 mol / L; 2- and OH - The molar ratio = 1:(0-1).

[0018] In some embodiments of the present invention, the mixed precipitant solution is at least two of ammonia water, ammonium bicarbonate solution, ammonium carbonate solution, sodium hydroxide solution and sodium carbonate solution, and the mixed precipitant solution contains CO3 2- .

[0019] In some embodiments of the present invention, during the parallel flow feeding process, the flow rate of the mixed precipitant is: the time for the reactor to be filled with liquid is controlled to be greater than or equal to 4 hours and less than or equal to 8 hours, and the feeding is maintained at a uniform speed.

[0020] In the actual application process, the volume of the first-stage reactor to the n-stage reactor remains consistent. When the first-stage reactor is fed for the first time, the first-stage reactor is filled from empty to full, and the time for the liquid in the first-stage reactor to be filled is controlled to be greater than or equal to 4h and less than or equal to 8h, and the flow rate is kept to feed at a uniform rate; the second-stage reactor to the n-stage reactor are all kept at the same flow rate for uniform feeding. The present invention controls the feed rate of the feed by controlling the feeding time of each batch of materials, and keeps the feed at a uniform rate during feeding. If the flow rate is too fast, the reaction is insufficient, the crystal particles are small, and it is not easy to filter; if the reaction is too slow and wastes time, for economic benefits, the present invention preferably has the flow rate as the above parameters.

[0021] In some embodiments of the present invention, during the co-current feeding process, the relative flow rates of the rare earth solution and the mixed precipitant solution are: 2- :OH - The molar ratio is 1:(0-1), the concentration of the rare earth solution is 2 mol / L in terms of REO, and CO3 2- When the concentration of the rare earth solution in the mixed precipitant solution is 1.5-3.5 mol / L, during the parallel flow feeding process of the first stage reactor, the relative flow rate of the rare earth solution and the mixed precipitant solution is 1:(2.0-2.4), during the parallel flow feeding process from the second stage reactor to the n-1 stage reactor, the relative flow rate of the rare earth solution and the mixed precipitant solution is 1:(1.8-2.2), and during the parallel flow feeding process of the nth stage reactor, the relative flow rate of the rare earth solution and the mixed precipitant solution is 1:(2.2-2.5).

[0022] In the present invention, the flow rate and relative flow rate of the rare earth solution and the mixed precipitant solution are controlled so that the total dripping time of the rare earth solution and the mixed precipitant solution is ≥4h, wherein the feed flow rate in the first-stage reactor is slower, the feed flow rate from the second-stage reactor to the n-1-stage reactor is faster, and the feed flow rate in the n-stage reactor is slower.

[0023] In some embodiments of the present invention, during the co-current feeding process, the relative flow rates of the rare earth solution and the mixed precipitant are: 2 - :OH- molar ratio is 1:0, REO in rare earth solution is 2 mol / L, CO3 in mixed precipitant solution 2-When it is 1.5-3.5 mol / L, during the co-flow feeding process of the first-stage reactor, the relative flow rate of the rare earth solution and the mixed precipitant solution is 1:(2.2-2.4), during the co-flow feeding process from the second-stage reactor to the n-1-stage reactor, the relative flow rate of the rare earth solution and the mixed precipitant solution is 1:(2-2.2), and during the co-flow feeding process of the n-stage reactor, the relative flow rate of the rare earth solution and the mixed precipitant solution is 1:(2.4-2.5).

[0024] In some embodiments of the present invention, during the co-current feeding process, the relative flow rates of the rare earth solution and the mixed precipitant are: 2- :OH - The molar ratio is 1:1, REO in the rare earth solution is 2 mol / L, CO3 in the mixed precipitant solution 2- When the concentration of the rare earth solution in the mixed precipitant solution is 1.5-3.5 mol / L, during the co-flow feeding process of the first-stage reactor, the relative flow rate of the rare earth solution and the mixed precipitant solution is 1:(2.0-2.2), during the co-flow feeding process from the second-stage reactor to the n-1-stage reactor, the relative flow rate of the rare earth solution and the mixed precipitant solution is 1:(1.8-2), and during the co-flow feeding process of the n-stage reactor, the relative flow rate of the rare earth solution and the mixed precipitant solution is 1:(2.2-2.3).

[0025] In some embodiments of the present invention, in the first to nth stage reactors, the RE in the bottom liquid 3+ With CO3 2- The effective molar ratio of RE participating in the rare earth carbonate reaction 3+ and CO3 2- The molar ratio of the reaction system to the reaction system is 1:(1.3-1.8); the pH value of the reaction system in the first to n-1 reactors is 5.6-6.2, and the pH value of the reaction system in the n-1 reactor is 6.5-7.0. In the present invention, the bottom liquid is the part of the reaction slurry other than the rare earth carbonate solid.

[0026] In some embodiments of the present invention, in the reaction system from the first stage reactor to the nth stage reactor, the concentration of ammonium salt (or other supernatant salt) in the bottom liquid is ≤60 g / L, preferably ≤40 g / L.

[0027] In some embodiments of the present invention, water is further added into the first-stage reactor as a bottom liquid; the volume of the water is 10% of the volume of the first-stage reactor.

[0028] In some embodiments of the present invention, the first-stage reactor further comprises adding seed crystals, wherein the seed crystals are rare earth carbonates having a porous spherical structure.

[0029] In some embodiments of the present invention, the temperature of the insulation reaction is 30-70°C.

[0030] The present invention controls the concentration, relative flow rate, flow rate and other factors of the rare earth solution and the mixed precipitant solution in each reactor during the feeding process to control the bottom liquid RE 3+ With effective CO3 2- molar ratio and pH value of the reaction system in the first reactor to the nth reactor to prepare low-impurity rare earth carbonate; when the rare earth solution is a single rare earth chloride solution or a mixed rare earth chloride solution, Cl in the low-impurity rare earth carbonate - When the rare earth solution is a single rare earth nitrate solution or a mixed rare earth nitrate solution, the low-impurity rare earth carbonate NO3 - Content ≤50ppm.

[0031] The low-chloride rare earth carbonate produced by the process of the present invention is used as a precursor. Any products such as low-impurity rare earth oxides, low-impurity rare earth basic carbonates, low-impurity rare earth carbonate oxides, low-impurity rare earth fluorides, low-impurity fluoride oxides, low-impurity rare earth phosphates, etc. obtained through calcination, fluorination, acid dissolution and other processes all fall within the scope of this patent.

[0032] The present invention discloses the following technical effects:

[0033] The present invention uses different proportions of mixed precipitants to have the following advantages: First, it inhibits HCO3 - Release H + Neutralize another HCO3 - , forming CO2 emissions and effective CO3 2- , achieving carbon reduction at the source; secondly, effectively improving the solubility and concentration of the precipitant, thereby increasing the concentration of the wastewater, and achieving carbon reduction at the source from the perspective of wastewater concentration; thirdly, with the OH in the mixed precipitant - As the concentration increases, the proportion of stable basic salts such as RE(OH)2Cl and RE2(OH)5NO3 formed increases. The present invention effectively controls and avoids the formation of basic salts, thereby realizing the preparation of low-impurity rare earth carbonate by mixed precipitants.

[0034] The present invention uses a high-concentration rare earth solution and a high-concentration mixed precipitant to prepare low-impurity high-purity rare earth carbonate, thereby improving equipment production capacity, increasing wastewater concentration, reducing labor intensity, and obtaining a low-impurity product with a small amount of washing water.

[0035] The present invention refines, differentiates and finely controls each stage of the rare earth carbonate nucleation / crystallization / growth process through continuous production, effectively optimizes the nucleation and growth of the crystallization process and inhibits the formation of rare earth basic carbonate, thus solving the problem of Cl - 、NO3- The key problem of retaining anions in rare earth carbonate by means of encapsulation, adsorption or chemical bonding has been solved, which has improved product quality and achieved continuous production.

[0036] The present invention solves the technical problem of continuous synthesis of low-impurity rare earth carbonate by mixed precipitation in high-concentration solution system. It realizes continuous low-carbon synthesis, improves production efficiency, improves product quality, and expands the rare earth solution system by comprehensively regulating various factors according to the principle of impurity introduction of different rare earth solution systems. BRIEF DESCRIPTION OF THE DRAWINGS

[0037] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0038] Figure 1 This is a SEM image of the low-impurity rare earth carbonate prepared in Example 2 of the present invention. DETAILED DESCRIPTION

[0039] Various exemplary embodiments of the present invention will now be described in detail. This detailed description should not be considered as limiting the present invention, but should be understood as a more detailed description of certain aspects, features, and embodiments of the present invention.

[0040] It should be understood that the terms described in the present invention are only for describing a particular embodiment and are not intended to limit the present invention. In addition, for the numerical range in the present invention, it should be understood that each intermediate value between the upper and lower limits of the scope is also specifically disclosed. The intermediate value in any stated value or stated range, and each smaller range between any other stated value or intermediate value in the described range is also included in the present invention. The upper and lower limits of these smaller ranges can be independently included or excluded in the scope.

[0041] Unless otherwise indicated, all technical and scientific terms used herein have the same meanings as those generally understood by those skilled in the art. Although the present invention describes only preferred methods and materials, any methods and materials similar or equivalent to those described herein may also be used in the implementation or testing of the present invention. All documents mentioned in this specification are incorporated by reference to disclose and describe the methods and / or materials associated with the documents. In the event of a conflict with any incorporated document, the content of this specification shall prevail.

[0042] It will be apparent to those skilled in the art that various modifications and variations may be made to the specific embodiments of the present invention description without departing from the scope or spirit of the present invention. Other embodiments derived from the present invention description will be apparent to those skilled in the art. The present invention description and examples are exemplary only.

[0043] The words “include,” “including,” “have,” “contain,” etc. used in this document are open-ended terms, meaning including but not limited to.

[0044] In order to better understand the present invention, the content of the present invention is further explained below in conjunction with the embodiments, but the content of the present invention is not limited to the following embodiments.

[0045] Unless otherwise specified, the raw materials and reagents used in the examples can be obtained through commercial channels.

[0046] The seed crystals used in Example 1 are rare earth carbonate with a porous spherical structure precipitated after the rare earth solution and the mixed precipitant solution in Example 1 are mixed and reacted. The preparation method of the seed crystals used in Examples 2 to 6 is the same as the preparation method of the seed crystals used in Example 1.

[0047] In the embodiment, the first to nth reactors are independently provided with a rare earth solution feed port and a mixed precipitant solution feed port. In the embodiment 1-6, the volume of the first to nth reactors is 5L.

[0048] Example 1

[0049] Step 1. Prepare 1.8 mol / L praseodymium-neodymium chloride rare earth solution (in terms of REO) and a mixed precipitant solution (molar ratio of ammonium bicarbonate to aqueous ammonia = 1:0.8, 3.8 mol / L), and add them to the first-stage reactor in parallel and keep them at 30°C for reaction. Seed crystals are added to the first-stage reactor in advance, and water is added as a bottom liquid. The amount of water used is 10% of the volume of the first-stage reactor.

[0050] Step 2. The reaction slurry overflows from the first-stage reactor into the second-stage reactor. When the volume of the overflowed reaction slurry reaches 10% of the volume of the second-stage reactor, step 1 is repeated in the second-stage reactor.

[0051] Step 3. Repeat step 2 until the reaction is carried out in the fifth-stage reactor at a temperature of 30° C., and collect the precipitate in the fifth-stage reactor to obtain low-impurity rare earth carbonate.

[0052] Wherein, while feeding from the second to the fifth reactors, water is replenished to make the concentration of ammonium salt in the bottom liquid of the second to the fifth reactors to be 55 g / L.

[0053] In the parallel flow feeding process, the relative flow rate of the rare earth solution and the mixed precipitant solution in the parallel flow feeding process of the first stage reactor is 1:2.2, the relative flow rate of the rare earth solution and the mixed precipitant solution in the parallel flow feeding process of the second to fourth stage reactors is 1:2.3, and the relative flow rate of the rare earth solution and the mixed precipitant solution in the parallel flow feeding process of the fifth stage reactor is 1:2.5. The time from empty to full in the first stage reactor is 6 hours, and the flow rate is kept uniformly fed. The second to nth stage reactors are all kept uniformly fed at this flow rate. In the first to fifth stage reactors, the RE in the rare earth solution in the bottom liquid 3+ CO3 in mixed precipitant solution 2- The effective binding molar ratio is 1:1.3. The pH value of the reaction system in the first to fourth reactors is 5.8, and the pH value of the reaction system in the fifth reactor is 7.0 to ensure complete precipitation of the rare earth. The filtration and washing process uses pure water for washing, and the washing water temperature is 90°C to obtain low-impurity rare earth carbonate. The obtained rare earth carbonate contains Cl - The content is 48ppm.

[0054] Example 2

[0055] Step 1. Prepare 1.85 mol / L lanthanum chloride cerium rare earth solution (calculated as REO) and a mixed precipitant solution (molar ratio of ammonium bicarbonate to ammonia water = 1:0.65, 3.8 mol / L), and add them to the first stage reactor in parallel and keep them at 50°C for reaction. Seed crystals are added to the first stage reactor in advance, and water is added as the bottom liquid. The amount of water used is 10% of the volume of the first stage reactor.

[0056] Step 2. The reaction slurry overflows from the first-stage reactor into the second-stage reactor. When the volume of the overflowed reaction slurry reaches 10% of the volume of the second-stage reactor, step 1 is repeated in the second-stage reactor.

[0057] Step 3. Repeat step 2 until the reaction is carried out at 50° C. in the fifth-stage reactor, and collect the precipitate in the fifth-stage reactor to obtain low-impurity rare earth carbonate.

[0058] Wherein, while feeding from the second stage reactor to the fifth stage reactor, water is replenished to make the concentration of ammonium salt in the bottom liquid of the second stage reactor to the fifth stage reactor be 46 g / L.

[0059] In the parallel flow feeding process, the relative flow rate of the rare earth solution and the mixed precipitant solution is 1:2.25 in the parallel flow feeding process of the first reactor, the relative flow rate of the rare earth solution and the mixed precipitant solution is 1:2.32 in the parallel flow feeding process of the second to fourth reactors, and the relative flow rate of the rare earth solution and the mixed precipitant solution is 1:2.4 in the parallel flow feeding process of the fifth reactor. The time from empty to full in the first reactor is 4h, and the flow rate is kept uniformly fed. The second to nth reactors are all fed uniformly at this flow rate. In the first to fifth reactors, the RE in the rare earth solution in the bottom liquid 3+ CO3 in mixed precipitant solution 2- The effective binding molar ratio is 1:1.7. The pH value of the reaction system in the first to fourth reactors is 5.9, and the pH value of the reaction system in the fifth reactor is 7.0 to ensure complete precipitation of the rare earth. The filtration and washing process uses pure water for washing, and the washing water temperature is 90°C to obtain low-impurity rare earth carbonate. The obtained rare earth carbonate contains Cl - The content is 49ppm.

[0060] Depend on Figure 1 It can be seen that by controlling the conditions during the precipitation reaction, spherical particles with a porous structure were prepared, which reduced the Cl - , so that the Cl in the form of entrainment and adsorption - Can be effectively removed during the washing process.

[0061] Example 3

[0062] Step 1. Prepare 1.9 mol / L lanthanum chloride cerium rare earth solution (in terms of REO) and a mixed precipitant solution (sodium bicarbonate to sodium hydroxide molar ratio = 1:0.43, 3 mol / L), and add them to the first stage reactor in parallel and keep them at 40°C for reaction. Seed crystals are added to the first stage reactor in advance, and water is added as the bottom liquid. The amount of water used is 10% of the volume of the first stage reactor.

[0063] Step 2. The reaction slurry overflows from the first-stage reactor into the second-stage reactor. When the volume of the overflowed reaction slurry reaches 10% of the volume of the second-stage reactor, step 1 is repeated in the second-stage reactor.

[0064] Step 3. Repeat step 2 until the reaction is carried out in the fifth-stage reactor at a temperature of 40° C., and collect the precipitate in the fifth-stage reactor to obtain low-impurity rare earth carbonate.

[0065] While feeding from the second to fifth stage reactors, water is replenished to make the concentration of ammonium salt in the bottom liquid of the second to fifth stage reactors to be 38 g / L.

[0066] In the parallel flow feeding process, the relative flow rate of the rare earth solution and the mixed precipitant solution in the first reactor is 1:2.4, the relative flow rate of the rare earth solution and the mixed precipitant solution in the second to fourth reactors is 1:2.2, and the relative flow rate of the rare earth solution and the mixed precipitant solution in the fifth reactor is 1:2.5. The time from empty to full in the first reactor is 6 hours, and the flow rate is kept uniform. The second reactor to the nth reactor are all fed at a uniform rate. In the first reactor to the fifth reactor, the RE in the rare earth solution in the bottom liquid 3+ CO3 in mixed precipitant solution 2- The effective binding molar ratio is 1:1.5. The pH value of the reaction system in the first to fourth reactors is 5.8, and the pH value of the reaction system in the fifth reactor is 6.8 to ensure complete precipitation of the rare earth. The filtration and washing process uses pure water for washing, and the washing water temperature is 70°C to obtain low-impurity rare earth carbonate. The obtained rare earth carbonate contains Cl - The content is 33ppm.

[0067] Example 4

[0068] Step 1. Prepare 1.7 mol / L lanthanum cerium rare earth nitrate solution (in terms of REO) and a mixed precipitant solution (sodium bicarbonate to ammonia water molar ratio = 1:0.5, 3 mol / L), and add them to the first-stage reactor in parallel and keep them at 60°C for reaction. Seed crystals are added to the first-stage reactor in advance, and water is added as the bottom liquid. The amount of water used is 10% of the volume of the first-stage reactor.

[0069] Step 2. The reaction slurry overflows from the first-stage reactor to the second-stage reactor. When the volume of the overflowed reaction slurry reaches 10% of the volume of the second-stage reactor, step 1 is repeated in the second-stage reactor.

[0070] Step 3. Repeat step 2 until the reaction is carried out in the fifth-stage reactor at a temperature of 60° C., and collect the precipitate in the fifth-stage reactor to obtain low-impurity rare earth carbonate.

[0071] Wherein, while feeding from the second to fifth stage reactors, water is replenished to make the concentration of ammonium salt in the bottom liquid of the second to fifth stage reactors to be 20 g / L.

[0072] In the parallel flow feeding process, the relative flow rate of the rare earth solution and the mixed precipitant solution in the parallel flow feeding process of the first stage reactor is 1:2.4, the relative flow rate of the rare earth solution and the mixed precipitant solution in the parallel flow feeding process of the second to fourth stage reactors is 1:2.1, and the relative flow rate of the rare earth solution and the mixed precipitant solution in the parallel flow feeding process of the fifth stage reactor is 1:2.4. The time from empty to full in the first stage reactor is 7h, and the flow rate is kept uniformly fed. The second to nth stage reactors are all fed uniformly at this flow rate. In the first to fifth stage reactors, the RE in the rare earth solution in the bottom liquid 3+ CO3 in mixed precipitant solution 2- The effective binding molar ratio is 1:1.8. In the first to fourth reactors, the pH value of the reaction system is 6. In the fifth reactor, the pH value of the reaction system is 6.7 to ensure complete precipitation of the rare earth. The filtration and washing process uses pure water for washing at a temperature of 70°C to obtain low-impurity rare earth carbonate. The obtained rare earth carbonate contains Cl - The content is 40ppm.

[0073] Example 5

[0074] Step 1. Prepare 1.8 mol / L praseodymium-neodymium rare earth nitrate solution (in terms of REO) and a mixed precipitant solution (molar ratio of ammonium bicarbonate to aqueous ammonia = 1:0.8, 3.6 mol / L), and add them to the first-stage reactor in parallel and keep them at 30°C for reaction. Seed crystals are added to the first-stage reactor in advance, and water is added as a bottom liquid. The amount of water used is 10% of the volume of the first-stage reactor.

[0075] Step 2. The reaction slurry overflows from the first-stage reactor into the second-stage reactor. When the volume of the overflowed reaction slurry reaches 10% of the volume of the second-stage reactor, step 1 is repeated in the second-stage reactor.

[0076] Step 3. Repeat step 2 until the reaction is carried out in the fifth-stage reactor at a temperature of 30° C., and collect the precipitate in the fifth-stage reactor to obtain low-impurity rare earth carbonate.

[0077] Wherein, while feeding from the second to fifth stage reactors, water is replenished to make the concentration of ammonium salt in the bottom liquid of the second to fifth stage reactors to be 20 g / L.

[0078] In the parallel flow feeding process, the relative flow rate of the rare earth solution and the mixed precipitant solution in the first reactor is 1:2.4, the relative flow rate of the rare earth solution and the mixed precipitant solution in the second to fourth reactors is 1:2.1, and the relative flow rate of the rare earth solution and the mixed precipitant solution in the fifth reactor is 1:2.4. The time from empty to full in the first reactor is 4 hours, and the flow rate is kept uniform. The second to nth reactors are fed uniformly at this flow rate. In the first to fifth reactors, the RE in the rare earth solution in the bottom liquid 3+ CO3 in mixed precipitant solution 2- The effective binding molar ratio is 1:1.6. The pH value of the reaction system in the first to fourth reactors is 5.6, and the pH value of the reaction system in the fifth reactor is 6.8 to ensure complete precipitation of the rare earth. The filtration and washing process uses pure water for washing, and the washing water temperature is 20°C to obtain low-impurity rare earth carbonate. The obtained rare earth carbonate contains Cl - The content is 52ppm.

[0079] Example 6

[0080] Step 1. Use cerium carbonate with a chloride content of 650ppm, dissolve it with nitric acid to prepare a 1.7mol / L cerium chloride rare earth solution (in terms of REO) and a mixed precipitant solution (molar ratio of ammonium bicarbonate to ammonia water = 1:0.58, 3.2mol / L), and add them to the first-stage reactor and keep them at 55°C for reaction. Seed crystals are added to the first-stage reactor in advance, and water is added as a bottom liquid. The amount of water used is 10% of the volume of the first-stage reactor.

[0081] Step 2. The reaction slurry overflows from the first-stage reactor into the second-stage reactor. When the volume of the overflowed reaction slurry reaches 10% of the volume of the second-stage reactor, step 1 is repeated in the second-stage reactor.

[0082] Step 3. Repeat step 2 until the reaction is carried out at 55° C. in the fifth-stage reactor, and collect the precipitate in the fifth-stage reactor to obtain low-impurity rare earth carbonate.

[0083] While feeding from the second to fifth stage reactors, water is replenished to make the concentration of ammonium salt in the bottom liquid of the second to fifth stage reactors to be 15 g / L.

[0084] In the parallel flow feeding process, the relative flow rate of the rare earth solution and the mixed precipitant solution in the first reactor is 1:2, the relative flow rate of the rare earth solution and the mixed precipitant solution in the second to fourth reactors is 1:1.8, and the relative flow rate of the rare earth solution and the mixed precipitant solution in the fifth reactor is 1:2.2. The time from empty to full in the first reactor is 8 hours, and the flow rate is kept uniform. The second reactor to the nth reactor are all fed at a uniform rate. In the first reactor to the fifth reactor, the RE in the rare earth solution in the bottom liquid 3+ CO3 in mixed precipitant solution 2- The effective binding molar ratio is 1:1.8. The pH value of the reaction system in the first to fourth reactors is 5.8, and the pH value of the reaction system in the fifth reactor is 7 to ensure complete precipitation of the rare earth. The filtration and washing process uses pure water for washing, and the washing water temperature is 70°C to obtain low-impurity rare earth carbonate. The obtained rare earth carbonate contains Cl - The content is 32ppm.

[0085] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principle of the present invention. These improvements and modifications should also be regarded as the scope of protection of the present invention.

Claims

1. A method for continuously preparing low-impurity rare earth carbonate using a mixed precipitant, characterized in that: The following steps are involved: Step 1. adding the rare earth solution and the mixed precipitant solution into the first-stage reactor by a co-current feeding method for heat preservation reaction to obtain a reaction slurry; Step 2. The reaction slurry overflows from the first-stage reactor to the second-stage reactor. When the volume of the overflowed reaction slurry is greater than or equal to 10% of the volume of the second-stage reactor, step 1 is repeated in the second-stage reactor; Step 3. Repeat step 2 until the heat preservation reaction is carried out in the n-stage reactor, and collect the precipitate in the n-stage reactor to obtain low-impurity rare earth carbonate; The first-stage reactor to the n-stage reactor are each independently provided with a rare earth solution feed inlet and a mixed precipitant solution feed inlet.

2. The method for continuously preparing low-impurity rare earth carbonate using a mixed precipitant according to claim 1, characterized in that: The rare earth solution includes a single rare earth chloride solution, a mixed rare earth chloride solution, a single rare earth nitrate solution or a mixed rare earth nitrate solution; the concentration of the rare earth solution is 100-350 g / L in terms of REO.

3. The method for continuously preparing low-impurity rare earth carbonate using a mixed precipitant according to claim 1, characterized in that: The mixed precipitant solution contains CO3 2- and OH - ; The CO3 2- The concentration of CO3 is 1.5-3.5 mol / L; 2- and OH - The molar ratio = 1:(0-1).

4. The method for continuously preparing low-impurity rare earth carbonate using a mixed precipitant according to claim 3, characterized in that: The mixed precipitant solution is at least two of ammonia water, ammonium bicarbonate solution, ammonium carbonate solution, sodium hydroxide solution and sodium carbonate solution, and the mixed precipitant solution contains CO3 2- .

5. The method for continuously preparing low-impurity rare earth carbonate using a mixed precipitant according to claim 1, characterized in that: During the parallel feeding process, the flow rate of the mixed precipitant is: the time for the reaction kettle to be filled with liquid is controlled to be greater than or equal to 4 hours and less than or equal to 8 hours, and the feeding is maintained at a uniform speed.

6. The method for continuously preparing low-impurity rare earth carbonate using a mixed precipitant according to claim 1, characterized in that: In the co-current feeding process, the relative flow rate of the rare earth solution and the mixed precipitant solution is: 2- :OH - The molar ratio is 1:(0-1), the concentration of the rare earth solution is 2 mol / L in terms of REO, and CO3 2- When the concentration of the rare earth solution in the mixed precipitant solution is 1.5-3.5 mol / L, during the parallel flow feeding process of the first stage reactor, the relative flow rate of the rare earth solution and the mixed precipitant solution is 1:(2.0-2.4), during the parallel flow feeding process from the second stage reactor to the n-1 stage reactor, the relative flow rate of the rare earth solution and the mixed precipitant solution is 1:(1.8-2.2), and during the parallel flow feeding process of the nth stage reactor, the relative flow rate of the rare earth solution and the mixed precipitant solution is 1:(2.2-2.5).

7. The method for continuously preparing low-impurity rare earth carbonate using a mixed precipitant according to claim 1, characterized in that: In the first stage reactor to the nth stage reactor, RE in the bottom liquid 3+ With CO3 2- The effective binding molar ratio is 1:(1.3-1.8); in the first-stage reactor to the n-1-stage reactor, the pH value of the reaction system is 5.6-6.2, and in the n-stage reactor, the pH value of the reaction system is 6.5-7.

0.

8. The method for continuously preparing low-impurity rare earth carbonate using a mixed precipitant according to claim 1, characterized in that: The temperature of the heat preservation reaction is 30-70°C.

Images