A method for preparing cerium carbonate by continuous precipitation and crystallization

Abstract

The present invention provides a method for preparing cerium carbonate by continuous precipitation and crystallization, and relates to the technical field of hydrometallurgy. The present invention applies a sieve plate tower reactor to carbonate precipitation of rare earths, and the shear rate and shear stress in the sieve plate tower reactor are distributed relatively evenly within the entire flow field, and the particle size and quality stability and consistency of the rare earth carbonate precipitation crystallization can be ensured as much as possible under the premise of ensuring the two-phase mass transfer efficiency, thereby improving the product quality; the present invention adopts a sieve plate tower reactor to realize reaction-washing synchronously, greatly shortening the production time and improving the production efficiency; thanks to the tower-type continuous structure of the sieve plate tower reactor, the parameters of each level in the tower are consistent and stable, and the circulating water temperature and the inlet and outlet valve positions can realize full automatic control, reducing human errors and low operating difficulty, thereby improving its safety. The method provided by the present invention is used to prepare cerium carbonate, and the product quality is good and the production efficiency is high.

Description

Technical Field

[0001] The invention relates to the technical field of hydrometallurgy, and in particular to a method for preparing cerium carbonate through continuous precipitation and crystallization. Background Art

[0002] Rare earth oxides have unique physical and chemical properties and are widely used in emerging fields such as electronics, new energy, and environmental protection. Rare earth oxides can be obtained by high-temperature calcination of rare earth carbonates, and the physical and chemical properties of the products are closely related to the physical and chemical properties of rare earth carbonates. Precipitation is an important method for preparing rare earth carbonates, so in recent years, research on precipitation and crystallization technology of rare earth carbonate has emerged in an endless stream.

[0003] At present, the industry still uses the method of intermittent operation in a stirred reactor with cerium chloride as the cerium source and ammonium bicarbonate as the precipitant to prepare cerium carbonate products. The use of a mechanical stirring device can easily cause a large number of crystals to break due to the strong shearing effect of the external mechanical force, and easily produce a large number of crystal nuclei (secondary nucleation); at the same time, there are concentration gradients and "dead zones" in the stirred reactor equipment, resulting in poor quality consistency and stability of cerium carbonate produced by intermittent stirred reactors, resulting in a lack of core competitiveness of the product. In addition, the production efficiency of cerium carbonate products prepared by traditional stirred reactors is low. In each production cycle, it is necessary to go through the steps of transferring out cerium carbonate and filtering and eluting, which undoubtedly increases the time cost. Summary of the invention

[0004] In view of this, the object of the present invention is to provide a method for preparing cerium carbonate by continuous precipitation and crystallization. The method provided by the present invention can ensure the stability and consistency of the particle size and quality of rare earth carbonate precipitation and crystallization, improve the quality of cerium carbonate products, and have high production efficiency.

[0005] In order to achieve the above-mentioned object of the invention, the present invention provides the following technical solutions:

[0006] The present invention provides a method for preparing cerium carbonate by continuous precipitation and crystallization, comprising the following steps:

[0007] A first cerium chloride solution and cerium carbonate seed crystals are added from the top of a sieve plate tower reactor, wherein the first cerium chloride solution is used as a reaction bottom liquid; the sieve plate tower reactor comprises a reaction zone and a settling and washing zone from top to bottom, wherein the reaction zone is provided with a plurality of sieve plates arranged side by side at equal intervals from top to bottom, the settling and washing zone is provided with a wash water inlet and a discharge port, and a heat exchange jacket is provided on the wall of the sieve plate tower reactor;

[0008] The sieve plate tower reactor is heated to a stable temperature by passing hot circulating water through the heat exchange jacket, and then the second cerium chloride solution is continuously added from the top of the sieve plate tower reactor into the reaction zone, and at the same time, the first ammonium bicarbonate solution, the second ammonium bicarbonate solution and the third ammonium bicarbonate solution are continuously added from three different heights from top to bottom, respectively, wherein the feeding points of the first ammonium bicarbonate solution, the second ammonium bicarbonate solution and the third ammonium bicarbonate solution are respectively located at a distance of 2 to 9 baffle plates downward from the feeding point of the second cerium chloride solution, wherein the distance of 1 baffle plate is the spacing between adjacent sieve plates in the reaction zone;

[0009] The feed liquid flowing out of the reaction zone enters the sedimentation washing zone and is washed by the washing water introduced from the washing water inlet;

[0010] When the volume of the solution in the sieve plate tower reactor accounts for 60-80% of the total volume of the sieve plate tower reactor, the discharge port is opened to discharge the water-containing crystals;

[0011] The water-containing crystals are filtered and dried in sequence to obtain cerium carbonate.

[0012] Preferably, the concentration of the first cerium chloride solution is 0.2-0.8 mol / L, and the amount of the first cerium chloride solution added is 5-15% of the volume of the reaction zone.

[0013] Preferably, the usage ratio of the first cerium chloride solution and the cerium carbonate seed crystals is (1.5-3.5) L: (50-300) g.

[0014] Preferably, the temperature of the hot circulating water is 45-60° C., and the flow rate is 100-150 mL / min.

[0015] Preferably, the concentration of the second cerium chloride solution is 1.6 mol / L, and the concentrations of the first ammonium bicarbonate solution, the second ammonium bicarbonate solution and the third ammonium bicarbonate solution are all 2.15 mol / L.

[0016] Preferably, the feed flow rate of the second cerium chloride solution is 10-40 mL / min.

[0017] Preferably, the feed flow rate of the first ammonium bicarbonate solution is 15-30 mL / min, the feed flow rate of the second ammonium bicarbonate solution is 10-20 mL / min, and the feed flow rate of the third ammonium bicarbonate solution is 5-15 mL / min.

[0018] Preferably, the ratio of the feed flow rate of the second cerium chloride solution to the total feed flow rate of the first ammonium bicarbonate solution, the second ammonium bicarbonate solution and the third ammonium bicarbonate solution is 1:(1.5-3).

[0019] Preferably, the feed flow rate of the wash water is 10-30 mL / min.

[0020] Preferably, the drying temperature is 60-105° C. and the drying time is 2-8 hours.

[0021] The present invention provides a method for preparing cerium carbonate by continuous precipitation and crystallization. Compared with the prior art, the present invention has the following beneficial effects:

[0022] (1) Improving product quality: The present invention applies a sieve plate tower reactor to the carbonate precipitation of rare earth. The shear rate and shear stress in the sieve plate tower reactor are relatively uniformly distributed in the entire flow field. Under the premise of ensuring the two-phase mass transfer efficiency, the particle size and quality of the rare earth carbonate precipitation crystals can be ensured to the greatest extent possible, thereby improving product quality.

[0023] (2) Improved production efficiency: In the preparation of cerium carbonate products by traditional stirred reactors, the cerium carbonate needs to be transferred out and filtered and washed in each production cycle. The sieve plate tower reactor used in the present invention can achieve simultaneous reaction and washing, greatly shortening the production time and improving the production efficiency.

[0024] (3) Better operability: Thanks to the tower continuous structure of the sieve plate tower reactor, the parameters of each level in the tower are consistent and stable, and the circulating water temperature and inlet and outlet valve positions can be fully automatically controlled, which reduces human errors and reduces the difficulty of operation, thereby improving its safety.

[0025] The results of the embodiment show that the total recovery rate of rare earth is 99.2-99.3% when cerium carbonate is prepared by the method of the present invention, and the particle size of the cerium carbonate product is D 50 The particle size is 30~32.5μm, the chloride content in the cerium carbonate product is 200~260ppm, and the total mass content of rare earth is 48.2~52%. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 is a schematic diagram of the structure of the sieve plate tower reactor in the present invention, Figure 1 In the figure, 1-reaction zone, 1-1-sieve plate, 2-sedimentation washing zone, 2-1-wash water inlet, 2-2-discharge port, 3-heat exchange jacket, 4-feeding point of the first cerium chloride solution and the second cerium chloride solution, 5-feeding point of the first ammonium bicarbonate solution, 6-feeding point of the second ammonium bicarbonate solution, 7-feeding point of the third ammonium bicarbonate solution. DETAILED DESCRIPTION

[0027] The present invention provides a method for preparing cerium carbonate by continuous precipitation and crystallization, comprising the following steps:

[0028] A first cerium chloride solution and cerium carbonate seed crystals are added from the top of a sieve plate tower reactor, wherein the first cerium chloride solution is used as a reaction bottom liquid; the sieve plate tower reactor comprises a reaction zone and a settling and washing zone from top to bottom, wherein the reaction zone is provided with a plurality of sieve plates arranged side by side at equal intervals from top to bottom, the settling and washing zone is provided with a wash water inlet and a discharge port, and a heat exchange jacket is provided on the wall of the sieve plate tower reactor;

[0029] The sieve plate tower reactor is heated to a stable temperature by passing hot circulating water through the heat exchange jacket, and then the second cerium chloride solution is continuously added from the top of the sieve plate tower reactor into the reaction zone, and at the same time, the first ammonium bicarbonate solution, the second ammonium bicarbonate solution and the third ammonium bicarbonate solution are continuously added from three different heights from top to bottom, respectively, wherein the feeding points of the first ammonium bicarbonate solution, the second ammonium bicarbonate solution and the third ammonium bicarbonate solution are respectively located at a distance of 2 to 9 baffle plates downward from the feeding point of the second cerium chloride solution, wherein the distance of 1 baffle plate is the spacing between adjacent sieve plates in the reaction zone;

[0030] The feed liquid flowing out of the reaction zone enters the sedimentation washing zone and is washed by the washing water introduced from the washing water inlet;

[0031] When the volume of the solution in the sieve plate tower reactor accounts for 60-80% of the total volume of the sieve plate tower reactor, the discharge port is opened to discharge the water-containing crystals;

[0032] The water-containing crystals are filtered and dried in sequence to obtain cerium carbonate.

[0033] In the present invention, a first cerium chloride solution and cerium carbonate seed crystals are added from the top of a sieve plate tower reactor, wherein the first cerium chloride solution is used as a reaction bottom liquid.

[0034] In the present invention, the structure of the sieve plate tower reactor is as follows Figure 1 shown.

[0035] In the present invention, the sieve plate tower reactor comprises a reaction zone 1 and a settling and washing zone 2 from top to bottom, the reaction zone 1 is provided with a plurality of sieve plates 1-1 arranged side by side at equal intervals from top to bottom, the settling and washing zone 2 is provided with a wash water inlet 2-1 and a discharge port 2-2, and the wall of the sieve plate tower reactor is provided with a heat exchange jacket 3. The present invention has no special requirements on the source of the sieve plate tower reactor, and commercially available products well known to those skilled in the art can be used; in the embodiment of the present invention, the aperture of the sieve plate is preferably 3-9 mm, the total number of sieve plates is preferably 20-30, the spacing between the sieve plates is preferably 50-250 mm, the top sieve plate is preferably separated from the top of the sieve plate tower reactor by 1-2 baffle plates, and the distance between the bottom sieve plate and the bottom of the sieve plate tower reactor is preferably 1 / 5-1 / 2 of the tower body, and more preferably 3 / 10-2 / 5. In the present invention, the wash water inlet 2-1 is preferably arranged at the lower part of the settling washing zone 2, and the discharge port 2-2 is preferably arranged at the bottom of the settling washing zone 2. In the present invention, the heat exchange jacket 3 is used to introduce circulating water.

[0036] In the present invention, the concentration of the first cerium chloride solution is preferably 0.2-0.8 mol / L, and may be 0.2, 0.3, 0.4, 0.5, 0.6, 0.7 or 0.8 mol / L. The amount of the first cerium chloride solution added is preferably 5-15% of the volume of the reaction zone, and more preferably 7-13%. In the present invention, the particle size D of the cerium carbonate seed crystals is 50 Preferably, it is 30 to 32.5 μm. In the present invention, the dosage ratio of the first cerium chloride solution and the cerium carbonate seed crystals is preferably (1.5 to 3.5) L: (50 to 300) g, and more preferably (1.5 to 3.5) L: (60 to 180) g. In the present invention, the first cerium chloride solution and the cerium carbonate seed crystals finally enter the settling and washing zone of the sieve plate tower reactor.

[0037] After adding the first cerium chloride solution and the cerium carbonate seed crystals, the present invention passes hot circulating water through the heat exchange jacket to heat the sieve plate tower reactor until the temperature is stable, and then continuously adds the second cerium chloride solution from the top of the sieve plate tower reactor into the reaction zone, and simultaneously continuously adds the first ammonium bicarbonate solution, the second ammonium bicarbonate solution and the third ammonium bicarbonate solution from three different heights from top to bottom.

[0038] In the present invention, the temperature of the hot circulating water is preferably 45-60°C, and may be 45, 48, 50, 55 or 60°C, and the flow rate is preferably 100-150 mL / min, and may be 100, 120 or 150 mL / min. In the present invention, the temperature of the hot circulating water is preferably achieved by a circulating water heating device, and the circulating water heating device is preferably an electric heating working mode, and a temperature control system is provided therein.

[0039] In the present invention, the concentration of the second cerium chloride solution is preferably 1.6 mol / L; the concentrations of the first ammonium bicarbonate solution, the second ammonium bicarbonate solution and the third ammonium bicarbonate solution are preferably 2.15 mol / L, and the first ammonium bicarbonate solution, the second ammonium bicarbonate solution and the third ammonium bicarbonate solution are used as precipitants. In the present invention, the feed points of the first ammonium bicarbonate solution, the second ammonium bicarbonate solution and the third ammonium bicarbonate solution are respectively located at a distance of 2 to 9 baffle plates downward from the feed point of the second cerium chloride solution, wherein the distance of 1 baffle plate is the distance between adjacent sieve plates in the reaction zone. In the present invention, the feed point of the first ammonium bicarbonate solution is preferably located at a distance of 2 to 3.5 baffles downward from the feed point of the second cerium chloride solution (i.e., the top of the sieve plate tower reactor), which can be 2, 3 or 3.5 baffles; the feed point of the second ammonium bicarbonate solution is preferably located at a distance of 3.5 to 5 baffles downward from the feed point of the second cerium chloride solution, which can be 3.5 or 5 baffles; the feed point of the third ammonium bicarbonate solution is preferably located at a distance of 6 to 9 baffles downward from the feed point of the second cerium chloride solution, which can be 6, 6.5, 8 or 9 baffles. In the present invention, the first ammonium bicarbonate solution, the second ammonium bicarbonate solution and the third ammonium bicarbonate solution are specifically transported to the corresponding feed points through pipelines.

[0040] In the present invention, the feed rate of the second cerium chloride solution is preferably 10-40 mL / min, which can be 10, 15, 20, 25, 30, 35 or 40 mL / min; the feed rate of the first ammonium bicarbonate solution is preferably 15-30 mL / min, which can be 15, 18, 20, 25, 28 or 30 mL / min, the feed rate of the second ammonium bicarbonate solution is preferably 10-20 mL / min, which can be 10, 12.5, 15, 17, 18 or 20 mL / min, and the feed rate of the third ammonium bicarbonate solution is preferably 5-15 mL / min, which can be 5, 7, 10, 12 or 15 mL / min. In the present invention, the flow rates of the first ammonium bicarbonate solution, the second ammonium bicarbonate solution and the third ammonium bicarbonate solution are preferably reduced in sequence. In the present invention, the ratio of the feed flow rate of the second cerium chloride solution to the total feed flow rate of the first ammonium bicarbonate solution, the second ammonium bicarbonate solution and the third ammonium bicarbonate solution is preferably 1:(1.5-3), more preferably 1:(1.8-2.8). In the present invention, the second cerium chloride solution, the first ammonium bicarbonate solution, the second ammonium bicarbonate solution and the third ammonium bicarbonate solution are preferably added by a flow pump.

[0041] In the present invention, the second cerium chloride solution is added to the sieve plate tower reactor from the top of the tower to form a continuous phase; the first ammonium bicarbonate solution, the second ammonium bicarbonate solution and the third ammonium bicarbonate solution are continuously injected into the reactor from three heights, and the small holes on the sieve plate in the reactor are used to form dispersed droplets that flow downward through the sieve plate.

[0042] In the reaction zone, the second cerium chloride solution and the first ammonium bicarbonate solution, the second ammonium bicarbonate solution, and the third ammonium bicarbonate solution react as follows: 2CeCl3+ 6NH4HCO3= Ce2(CO3)3+ 6NH4Cl + 3H2O + 3CO2. During the operation of the reaction zone, each sieve plate in the reaction zone preferably reciprocates up and down within a small range, and the movement amplitude is preferably 20-60% of the distance of one baffle plate, and more preferably 30-50%.

[0043] The feed liquid flowing out of the reaction zone enters the sedimentation washing zone and is washed by the wash water introduced from the wash water inlet. In the present invention, the feed liquid flowing out of the reaction zone includes cerium carbonate generated by the reaction and unreacted feed liquid, wherein the cerium carbonate generated by the reaction gradually grows under the induction of the cerium carbonate seeds in the sedimentation washing zone, and the unreacted ammonium bicarbonate can continue to react with the reaction bottom liquid. In the sedimentation washing zone, washing is carried out while settling. In the present invention, the wash water is preferably deionized water, and the wash water is preferably introduced through a flow pump. The feed flow rate of the wash water is preferably 10~30mL / min, which can be 10, 12, 15, 20, 30mL / min; the wash water washes the cerium carbonate crystals in the feed liquid. In the sieve plate tower reactor, reaction and washing can be carried out simultaneously, avoiding the transfer of cerium carbonate and improving production efficiency.

[0044] When the volume of the solution in the sieve plate tower reactor accounts for 60-80% of the total volume of the sieve plate tower reactor, the discharge port is opened to discharge the washed water-containing crystals. In the present invention, the volume of the solution in the sieve plate tower reactor may account for 60%, 65%, 70% or 80% of the total volume of the sieve plate tower reactor. In the present invention, when the discharge port is opened, the opening size of the discharge port is controlled to achieve a constant volume of the solution in the reactor and achieve dynamic equilibrium.

[0045] After obtaining the hydrous crystals, the present invention sequentially filters and dries the hydrous crystals to obtain cerium carbonate. In the present invention, the drying temperature is preferably 60-105° C., more preferably 70-100° C., the time is preferably 2-8 hours, more preferably 3-5 hours; the drying is preferably performed in an oven.

[0046] The present invention uses a sieve plate tower reactor for the rare earth hydrometallurgy and rare earth carbonate precipitation process to prepare cerium carbonate. The shear rate and shear stress in the sieve plate tower reactor are evenly distributed in the entire flow field. By adjusting the parameters of the sieve plate tower reactor, the mixing characteristics of the slurry in the reactor can be effectively controlled to ensure efficient mixing and achieve precise control of the crystal particle size of the rare earth carbonate precipitation. At the same time, the water consumption in the rare earth hydrometallurgy process is greatly reduced, and the production efficiency is improved.

[0047] In order to further illustrate the present invention, the method for preparing cerium carbonate by continuous precipitation crystallization provided by the present invention is described in detail below with reference to examples, but they should not be construed as limiting the scope of protection of the present invention.

[0048] The structure of the sieve plate tower reactor used in each embodiment is as follows: Figure 1 As shown, it includes a reaction zone 1 and a sedimentation washing zone 2, wherein the reaction zone 1 is provided with a plurality of sieve plates 1-1 which are arranged side by side with equal spacing from top to bottom, the sedimentation washing zone 2 is provided with a wash water inlet 2-1 and a discharge port 2-2, and the wall of the sieve plate tower reactor is provided with a heat exchange jacket 3 for introducing circulating water; wherein the aperture of the sieve plate is 4 mm, the total number of the sieve plates is 23, the spacing between the sieve plates is 91 mm, the uppermost sieve plate is separated from the top of the sieve plate tower reactor by 2 baffle plates, and the distance between the lowermost sieve plate and the bottom of the sieve plate tower reactor is 2 / 5 of the tower body.

[0049] Example 1

[0050] Add 2L (7.07% of the volume of the reaction zone) of 0.3mol / L cerium chloride solution as the reaction bottom liquid from the top of the sieve plate tower reactor, and add 80g of cerium carbonate (particle size D 50 31.65μm) as seed crystals. Turn on the circulating water heating device, the circulating water flow rate is 100mL / min, and the circulating water temperature is 48℃. After the temperature of the sieve plate tower reactor reaches stability, 1.6mol / L cerium chloride solution is filled into the sieve plate tower reactor from the top of the tower through a flow pump at a flow rate of 15mL / min to form a continuous phase; a precipitant ammonium bicarbonate solution with a concentration of 2.15mol / L is continuously injected into the sieve plate tower reactor from 3.5, 5, and 6.5 baffle distances downward from the cerium chloride feed point (1 baffle distance is the spacing between adjacent sieve plates) at flow rates of 18mL / min, 12.5mL / min, and 7mL / min, respectively, and flows downward through the sieve plate. Each sieve plate reciprocates up and down in a small range, and the movement amplitude is 30% of the distance of 1 baffle plate; deionized water is injected into the reactor from the wash water inlet at a flow rate of 15mL / min through a flow pump to wash the cerium carbonate crystals. When the volume of the solution in the reactor accounts for 80% of the total volume of the reactor, the discharge port at the bottom of the reactor is opened to allow the washed water-containing crystals to flow out. The obtained solid is filtered and placed in an oven at 80°C to dry for 4 hours to obtain a cerium carbonate product.

[0051] By analyzing the input cerium chloride and the output cerium carbonate product, the total recovery rate of rare earth was calculated to be 99.2%. The cerium carbonate product was tested and the particle size of the cerium carbonate product was D 50 The particle size is 32 μm, the chloride content in cerium carbonate is 260 ppm, and the total mass content of rare earth cerium is 52%.

[0052] Example 2

[0053] Add 3.5L (12.38% of the volume of the reaction zone) of 0.5mol / L cerium chloride solution as the reaction bottom liquid from the top of the sieve plate tower reactor, and add 180g of cerium carbonate (particle size D 50 32.27μm) as seed crystals. Turn on the circulating water heating device, the circulating water flow rate is 120mL / min, and the circulating water temperature is 55℃. After the temperature of the sieve plate tower reactor reaches stability, the 1.6mol / L cerium chloride solution is filled into the sieve plate tower reactor from the top of the tower through a flow pump at a flow rate of 20mL / min to form a continuous phase; the precipitant ammonium bicarbonate solution with a concentration of 2.15mol / L is continuously injected into the sieve plate tower reactor from 2, 3.5, and 6 baffle distances downward from the cerium chloride feed point (1 baffle distance is the spacing between adjacent sieve plates) at flow rates of 25mL / min, 18mL / min, and 12mL / min, respectively, and flows downward through the sieve plate. Each sieve plate reciprocates up and down in a small range, and the movement amplitude is 40% of the distance of 1 baffle plate; deionized water is injected into the reactor from the wash water inlet at a flow rate of 12mL / min through a flow pump to wash the cerium carbonate crystals. When the volume of the solution in the reactor accounts for 70% of the total volume of the reactor, the discharge port at the bottom of the reactor is opened to allow the washed water-containing crystals to flow out. The obtained solid is filtered and placed in an oven at 100°C to dry for 3 hours to obtain a cerium carbonate product.

[0054] By analyzing the input cerium chloride and the output cerium carbonate product, the total recovery rate of rare earth was calculated to be 99.3%. The cerium carbonate product was tested and the particle size of the cerium carbonate product was D 50 The particle size is 30μm, the chloride content in cerium carbonate is 225ppm, and the total mass content of rare earth cerium is 48.2%.

[0055] Example 3

[0056] Add 1.5L (5.31% of the volume of the reaction zone) of 0.2mol / L cerium chloride solution as the reaction bottom liquid from the top of the sieve plate tower reactor, and add 60g of cerium carbonate (particle size D 5030.81μm) as seed crystals. Turn on the circulating water heating device, the circulating water flow rate is 150mL / min, and the circulating water temperature is 50℃. After the temperature of the sieve plate tower reactor reaches stability, 1.6mol / L cerium chloride solution is filled into the sieve plate tower reactor from the top of the tower through a flow pump at a flow rate of 30mL / min to form a continuous phase; a precipitant ammonium bicarbonate solution with a concentration of 2.15mol / L is continuously injected into the sieve plate tower reactor from 3, 5, and 8 baffles below the cerium chloride feed point (1 baffle distance is the spacing between adjacent sieve plates) at flow rates of 28mL / min, 17mL / min, and 10mL / min, respectively, and flows downward through the sieve plate. Each sieve plate reciprocates up and down in a small range, and the movement amplitude is 50% of the distance of 1 baffle; deionized water is injected into the reactor from the wash water inlet at a flow rate of 20mL / min through a flow pump to wash the cerium carbonate crystals. When the volume of the solution in the reactor accounts for 65% of the total volume of the reactor, the discharge port at the bottom of the reactor is opened to allow the washed water-containing crystals to flow out. The solid obtained after filtration is placed in an oven and dried at 70°C for 5 hours to obtain a cerium carbonate product.

[0057] By analyzing the input cerium chloride and the output cerium carbonate product, the total recovery rate of rare earth was calculated to be 99.2%. The cerium carbonate product was tested and the particle size of the cerium carbonate product was D 50 The particle size is 32.5 μm, the chloride content in cerium carbonate is 200 ppm, and the total mass content of rare earth cerium is 51.8%.

[0058] Comparative Example 1

[0059] Add 2L (7.07% of the volume of the reaction zone) of 0.3mol / L cerium chloride solution as the reaction bottom liquid from the top of the sieve plate tower reactor, and add 80g of cerium carbonate (particle size D 50 31.65μm) as seed crystals. Turn on the circulating water heating device, the circulating water flow rate is 100mL / min, and the circulating water temperature is 48℃. After the temperature of the sieve plate tower reactor reaches stability, the 1.6mol / L cerium chloride solution is filled into the sieve plate tower reactor from the top of the tower through a flow pump at a flow rate of 15mL / min to form a continuous phase; the precipitant ammonium bicarbonate solution with a concentration of 2.15mol / L is continuously injected into the sieve plate tower reactor from 3.5, 5, and 6.5 baffle distances downward from the cerium chloride feed point (1 baffle distance is the spacing between adjacent sieve plates) at flow rates of 32mL / min, 25mL / min, and 18mL / min, respectively, and flows downward through the sieve plate. Each sieve plate reciprocates up and down in a small range, and the movement amplitude is 30% of the distance of 1 baffle plate; deionized water is injected into the reactor from the wash water inlet at a flow rate of 15mL / min through a flow pump to wash the cerium carbonate crystals. When the volume of the solution in the reactor accounts for 80% of the total volume of the reactor, open the discharge port at the bottom of the reactor.

[0060] Compared with Example 1, Comparative Example 1 only changed the ratio of the feed flow rate of the cerium chloride solution to the total feed flow rate of the ammonium bicarbonate solution. During the reaction process, small flocculent particles were gradually generated, and an emulsion-like liquid appeared, which made it difficult for the cerium carbonate crystals to settle, and the cerium carbonate product was not successfully obtained.

[0061] Comparative Example 2

[0062] Add 2L (7.07% of the volume of the reaction zone) of 0.3mol / L cerium chloride solution as the reaction bottom liquid from the top of the sieve plate tower reactor, and add 80g of cerium carbonate (particle size D 50 31.65μm) as seed crystals. Turn on the circulating water heating device, the circulating water flow rate is 100mL / min, and the circulating water temperature is 48℃. After the temperature of the sieve plate tower reactor reaches stability, 1.6mol / L cerium chloride solution is filled into the sieve plate tower reactor from the top of the tower through a flow pump at a flow rate of 15mL / min to form a continuous phase; a precipitant ammonium bicarbonate solution with a concentration of 2.15mol / L is continuously injected into the sieve plate tower reactor from 8, 10, and 13 baffles below the cerium chloride feed point (1 baffle distance is the spacing between adjacent sieve plates) at flow rates of 18mL / min, 12.5mL / min, and 7mL / min, respectively, and flows downward through the sieve plate. Each sieve plate reciprocates up and down in a small range, and the movement amplitude is 30% of the distance of 1 baffle; deionized water is injected into the reactor from the wash water inlet at a flow rate of 15mL / min through a flow pump to wash the cerium carbonate crystals. When the volume of the solution in the reactor accounts for 80% of the total volume of the reactor, the discharge port at the bottom of the reactor is opened to allow the washed water-containing crystals to flow out. The obtained solid is filtered and placed in an oven at 80°C for 4 h to obtain a cerium carbonate product.

[0063] By analyzing the input cerium chloride and the output cerium carbonate product, the total recovery rate of rare earth was calculated to be 67.3%. The cerium carbonate product was tested and the particle size of the cerium carbonate product was D 50 The particle size is 30 μm, the chloride content in cerium carbonate is 295 ppm, and the total mass content of rare earth cerium is 50.5%.

[0064] Compared with Example 1, Comparative Example 2 only changes the feeding position of the precipitant ammonium bicarbonate solution. The feeding position of the ammonium bicarbonate solution is too low, resulting in insufficient reaction between the cerium chloride solution and the ammonium bicarbonate solution and a low total recovery rate of rare earths.

[0065] The above description is only a preferred embodiment of the present invention and does not limit the present invention in any form. 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, and these improvements and modifications should also be regarded as the protection scope of the present invention.

Claims

1. A method for preparing cerium carbonate by continuous precipitation and crystallization, characterized in that: The following steps are involved: A first cerium chloride solution and cerium carbonate seed crystals are added from the top of a sieve plate tower reactor, wherein the first cerium chloride solution is used as a reaction bottom liquid; the sieve plate tower reactor comprises a reaction zone and a settling and washing zone from top to bottom, wherein the reaction zone is provided with a plurality of sieve plates arranged side by side at equal intervals from top to bottom, the settling and washing zone is provided with a wash water inlet and a discharge port, and a heat exchange jacket is provided on the wall of the sieve plate tower reactor; The sieve plate tower reactor is heated to a stable temperature by passing hot circulating water through the heat exchange jacket, and then the second cerium chloride solution is continuously added from the top of the sieve plate tower reactor into the reaction zone, and at the same time, the first ammonium bicarbonate solution, the second ammonium bicarbonate solution and the third ammonium bicarbonate solution are continuously added from three different heights from top to bottom, respectively, wherein the feeding points of the first ammonium bicarbonate solution, the second ammonium bicarbonate solution and the third ammonium bicarbonate solution are respectively located at a distance of 2 to 9 baffle plates downward from the feeding point of the second cerium chloride solution, wherein the distance of 1 baffle plate is the reverse The spacing between adjacent sieve plates in the response zone; the feed rate of the second cerium chloride solution is 10-40 mL / min; the feed rate of the first ammonium bicarbonate solution is 15-30 mL / min, the feed rate of the second ammonium bicarbonate solution is 10-20 mL / min, and the feed rate of the third ammonium bicarbonate solution is 5-15 mL / min; the ratio of the feed rate of the second cerium chloride solution to the total feed rate of the first ammonium bicarbonate solution, the second ammonium bicarbonate solution and the third ammonium bicarbonate solution is 1:(1.5-3); The feed liquid flowing out of the reaction zone enters the sedimentation washing zone and is washed by the washing water introduced from the washing water inlet; When the volume of the solution in the sieve plate tower reactor accounts for 60-80% of the total volume of the sieve plate tower reactor, the discharge port is opened to discharge the water-containing crystals; The water-containing crystals are filtered and dried in sequence to obtain cerium carbonate.

2. The method according to claim 1, characterized in that: The concentration of the first cerium chloride solution is 0.2-0.8 mol / L, and the amount of the first cerium chloride solution added is 5-15% of the volume of the reaction zone.

3. The method according to claim 1 or 2, characterized in that: The dosage ratio of the first cerium chloride solution and the cerium carbonate seed crystals is (1.5-3.5) L: (50-300) g.

4. The method according to claim 1, characterized in that: The temperature of the hot circulating water is 45-60°C, and the flow rate is 100-150 mL / min.

5. The method according to claim 1, characterized in that: The concentration of the second cerium chloride solution is 1.6 mol / L, and the concentrations of the first ammonium bicarbonate solution, the second ammonium bicarbonate solution and the third ammonium bicarbonate solution are all 2.15 mol / L.

6. The method according to claim 1, characterized in that The feed flow rate of the wash water is 10-30 mL / min.

7. The method according to claim 1, characterized in that The drying temperature is 60-105° C. and the drying time is 2-8 hours.

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