A method for double-layer solidification pelletization of mixed rare earth concentrate

Abstract

The present invention belongs to the field of rare earth hydrometallurgy and relates to a method for preparing double-layer solidified pellets of mixed rare earth concentrate. The mixed rare earth concentrate of Bayan Obo is uniformly mixed with a sodiumizing agent and a binder A to obtain a mixture; the mixture is then placed in a pelletizing machine for pelletizing to obtain pellets; the binder B is sprayed on the surface of the pellets to wet the surface of the pellets to obtain wetted pellets; the wetted pellets are placed in mineral powder for bonding, and after screening, powder-bonded pellets are obtained; the powder-bonded pellets are solidified to obtain solidified pellets, which are the raw materials for the subsequent roasting and decomposition process. The present invention, combined with production practice, can effectively alleviate the "ringing" phenomenon of the rotary kiln during the traditional sodiumizing roasting and decomposition process, and no other impurities are introduced during the reaction process, making it a relatively clean smelting process.

Description

Technical Field

[0001] The invention belongs to the field of rare earth hydrometallurgy and relates to a method for preparing double-layer solidified pellets of mixed rare earth concentrate. Background Art

[0002] Rare earth elements, a crucial strategic resource, are widely used in the manufacture of a variety of high-tech materials with diverse properties due to their unique electronic structure. Currently, 90% of global rare earth production comes from China, making its rare earth production capacity significantly influential in the development of the global rare earth industry. China boasts abundant and diverse rare earth resources. After decades of development, China has established three major production bases for medium and heavy rare earths in five southern provinces, represented by Baotou in Inner Mongolia and Liangshan in Sichuan, and Ganzhou in Jiangxi. These bases possess comprehensive mining, smelting, and separation technologies, as well as equipment manufacturing and materials processing systems. Bayan Obo's rare earth reserves account for over 83% of China's total rare earth reserves, ranking first in the world and serving as my country's primary production base for light rare earths. Bayan Obo's rare earth deposits are primarily composed of bastnaesite and monazite. Due to their close intercalation, severe intergrowth, and vastly different chemical properties, these minerals are considered difficult to select and smelt.

[0003] So far, the main processing technologies for Bayan Obo mixed rare earth concentrate are concentrated sulfuric acid roasting method and liquid alkali decomposition method. However, the concentrated sulfuric acid roasting method and liquid alkali decomposition method still have some shortcomings in environmental pollution or production costs. As the efforts to protect the ecological environment gradually increase, these shortcomings have become technical bottlenecks restricting the development of the process itself. Therefore, it is an urgent need to develop a clean and efficient Bayan Obo mixed rare earth concentrate processing technology.

[0004] Researchers have conducted extensive research on the clean extraction of Bayan Obo mixed rare earth concentrate. Sodium carbonate roasting is a relatively clean smelting process, producing neither significant acidic waste gas nor alkaline wastewater treatment. Furthermore, Na2CO3 is cheaper than the NaOH used in the liquid caustic soda method, offering significant environmental and price advantages. Consequently, researchers have conducted extensive research on this process. Publicly available data indicates that my country began researching the use of Na2CO3 for roasting Bayan Obo mixed rare earth concentrate in 1963. Subsequently, several institutions, including the Changchun Institute of Applied Chemistry, the Baotou Iron and Steel Metallurgical Research Institute, the General Research Institute of Nonferrous Metals, and the Baotou Rare Earth Research Institute, conducted detailed research on the process, even conducting kilogram-scale semi-industrial production in rotary kilns. Initially, all indicators performed well, but as the reaction progressed, the rotary kiln developed severe ringing, causing the equipment to malfunction. Consequently, the process has not yet been adopted for industrial production. Therefore, addressing this issue of ringing in the rotary kiln is crucial for the proper operation of the Na2CO3 roasting method. However, for many years, no relevant literature has explored this issue. Summary of the Invention

[0005] In view of this, the object of the present invention is to provide a method for preparing double-layer solidified pellets of mixed rare earth concentrate to solve the technical problems existing in the above-mentioned prior art.

[0006] Specifically, the present invention draws on the technical idea of ​​producing pellets in the steel industry, and proposes a technical idea of ​​mixing the Bayan Obo mixed rare earth concentrate with a sodium agent and a binder A to form pellets. The obtained pellets are then subjected to powder bonding and solidification, thereby greatly alleviating the "ringing" problem of the rotary kiln.

[0007] In order to achieve the above object, the present invention provides the following technical solutions:

[0008] A method for preparing double-layer solidified pellets of mixed rare earth concentrate comprises the following steps:

[0009] (1) Mixing: Evenly mix the Bayan Obo mixed rare earth concentrate, binder A, and sodium agent to obtain a mixture, which is then set aside;

[0010] This step of evenly mixing the Bayan Obo mixed rare earth concentrate, binder A, and sodium agent has two main purposes: 1. ensuring that the sodium agent is in full contact with the Bayan Obo mixed rare earth concentrate to ensure the decomposition rate of the rare earth mineral; 2. ensuring that the binder A is evenly distributed so that the materials can stick together.

[0011] (2) pelletizing: placing the mixture obtained in step (1) in a pelletizing machine for pelletizing to obtain pellets with a diameter of 1 cm to 4 cm;

[0012] The purpose of this step is to prepare pellets of appropriate size using a pellet press so that the pellets have certain mechanical strength and appropriate thermal decomposition properties.

[0013] (3) Infiltration: Prepare a solution of the water-soluble binder B and spray it onto the surface of the pellets to obtain infiltrated pellets;

[0014] By spraying the binder B on the surface of the pellets, the surface of the pellets has a certain adhesive property, thereby providing the possibility of powder sticking to the surface of the pellets in the next step.

[0015] (4) powder bonding and screening: placing the impregnated pellets obtained in step (3) in mineral powder for powder bonding, and obtaining powder-bonded pellets after screening;

[0016] By sticking rare earth minerals on the surface of the impregnated pellets, the contact between the exposed Na2CO3 on the surface of the pellets or the generated complex salts and the furnace wall can be fundamentally prevented. At the same time, since the sticky substances are rare earth minerals, other impurities will not be introduced. And according to multiple data, pure rare earth minerals will not show "ringing" phenomenon during high-temperature decomposition. Therefore, double-layer pellets can avoid the occurrence of "ringing" problems to the greatest extent.

[0017] (5) solidification: solidifying the powder pellets obtained in step (4) to obtain solidified pellets.

[0018] The purpose of this operation step is to provide the powder pellets with a certain compressive strength through solidification, so as to provide them with suitable mechanical properties for application in industrial production practice.

[0019] Optionally, in step (1), the Bayan Obo mixed rare earth concentrate is a mixed ore of one or more of monazite, bastnaesite, xenotime, and ionic rare earth ores.

[0020] Alternatively, the Bayan Obo mixed rare earth concentrate is a roasted ore obtained by roasting and decomposing rare earth minerals, and the rare earth grade is ≥50%.

[0021] Optionally, the added amount of the binder A is 10-20% of the weight of the Bayan Obo mixed rare earth concentrate, and the added amount of the sodium agent is 10-30% of the weight of the Bayan Obo mixed rare earth concentrate.

[0022] Furthermore, the sodiumizing agent is a mixture of one or more of NaOH, Na2CO3, KOH, and K2CO3, and the binder A is one of sodium carboxymethyl cellulose, polyethylene oxide, sodium polyacrylate, starch, dextrin, and lignin, or any mixture thereof.

[0023] Optionally, the binder B is one of water glass, phenolic resin, epoxy resin, melamine formaldehyde resin, sodium polyacrylate, starch, dextrin, lignin, or any mixture thereof.

[0024] Furthermore, the water-soluble binder B is prepared into a solution with a concentration of 5% to 10%, and the amount of the binder B added is 0.5% to 20% of the mass of the pellets.

[0025] Optionally, the mineral powder is a mixture of one or more of monazite, bastnaesite, xenotime, and ionic rare earth ores, and the rare earth grade is ≥50%.

[0026] Optionally, the curing temperature in step (5) is 40° C. to 100° C., and the curing time is 0.5 h to 2.0 h.

[0027] Furthermore, the curing equipment in step (5) includes a microwave reactor, a muffle furnace or a drying oven.

[0028] It can be seen from the above technical solution that, compared with the prior art, the method for preparing a mixed rare earth concentrate double-layer solidified pellet provided by the present invention has the following excellent effects:

[0029] 1) The present invention first mixes the Bayan Obo mixed rare earth concentrate with a sodium agent and a binder to form pellets, and then smelts the prepared pellets, which can greatly alleviate the occurrence of the "ringing" phenomenon, providing another feasible way for the clean extraction of the Bayan Obo mixed rare earth concentrate.

[0030] 2) In the present invention, since the selected binder is an organic matter, it will volatilize during the solidification and subsequent pellet roasting and decomposition process, and has little effect on the purification and refining of rare earth resources.

[0031] 3) The outermost layer of the pellets prepared by the present invention is rare earth mineral powder, which can block the contact between the sodium-forming agent and the furnace wall and will not introduce other non-rare earth impurities. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are merely embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on the provided drawings without paying any creative work.

[0033] Figure 1 This is a flow chart of the preparation process of the mixed rare earth concentrate double-layer solidified pellets of the present invention.

[0034] Figure 2 This is a schematic diagram of the double-layer solidified pellets of the mixed rare earth concentrate according to the present invention. DETAILED DESCRIPTION

[0035] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the embodiments of the present invention and the accompanying drawings. Obviously, the embodiments described are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of the present invention.

[0036] The embodiment of the present invention discloses a method for preparing mixed rare earth concentrate double-layer solidified pellets.

[0037] For a better understanding of the present invention, the present invention is further specifically described below through the following examples, but it should not be understood as limiting the present invention. Some non-essential improvements and adjustments made by those skilled in the art based on the above invention content are also considered to fall within the scope of protection of the present invention.

[0038] Process parameter optimization experiment:

[0039] (1) Optimization of process parameters for binder A

[0040] The amount of binder A added plays a significant role in the compressive strength of the pellets. Therefore, selecting the appropriate addition level not only reduces production costs but also ensures superior pellet performance. The relationship between binder A addition and pellet performance was investigated under a pressure of 8 MPa, as shown in Table 1. As the amount of binder A increased, the compressive strength and the number of drops from a height of 0.5 m increased. The compressive strength of the pellets stabilized between 1000 N / pellet and 1500 N / pellet, while the number of drops ranged from 16 to 25. Both properties were optimal at a 16% addition level.

[0041] Table 1 Effect of binder A addition on pellet performance

[0042]

[0043] (2) Optimization of process parameters for binder B

[0044] As mentioned above, the amount of binder B added determines whether the second layer of the pellet can bond the mixed rare earth concentrate to the surface and play an insulating role for the inner layer of the pellet.

[0045] Under a pressure of 8 MPa, the relationship between the amount of binder B added and the performance was explored, as shown in Table 2. It can be seen that as the amount of binder B added increases, the compressive strength and the number of pellet drops also increase. The compressive strength of the pellets stabilizes between 500 N / pellet and 1400 N / pellet, and the number of drops (0.5 m) ranges from 2 to 19. Both properties of the pellets reach their optimum when the binder B addition is 14%.

[0046] Table 2 Effect of binder B addition on pellet performance

[0047]

[0048] Therefore, considering the above, the addition amount of binder A is selected to be 10-20%, and the addition amount of binder B is selected to be 5-20%.

[0049] (3) Optimization of curing process parameters

[0050] Pellet curing is a key process in this invention, effectively improving the compressive strength of the pellets. Therefore, the selection of curing conditions is crucial. While ensuring high compressive strength, minimizing the curing temperature and time is crucial. To this end, we conducted further research on the selection of curing conditions.

[0051] Table 3 shows the effect of curing temperature on pellet performance. To fully explore the effect of curing temperature on pellet compressive strength, a double-layer pellet was prepared using a pressure of 8 MPa, 10% binder A, and 15% binder B. The curing time was 20 minutes. The results of the study, with other conditions remaining the same, are shown in Table 3. It can be seen that the increase in compressive strength of the pellets with increasing temperature is relatively low. This is mainly due to the short curing time, which prevents the pellets from being completely dried, resulting in a high internal moisture content and a soft pellet with low strength. Within the scope of the present invention, the compressive strength of the pellets is stable between 200 N / pellet and 900 N / pellet. The number of drops ranges from 2 to 5, and the pellets exhibit high performance at 100°C.

[0052] Table 4 shows the effect of curing time on pellet performance. To fully explore the effect of curing time on pellet compressive strength, double-layer pellets were prepared at a pressure of 8 MPa, 10% binder A, 15% binder B, and a curing temperature of 100°C. As curing time increased, the compressive strength of the pellets significantly improved. Within the scope of the present invention, the compressive strength of the pellets remained stable at 1300 N / pellet to 1600 N / pellet, with a drop rate of 18 to 27 times, demonstrating excellent performance and meeting industrial production standards.

[0053] Table 3 Effect of curing temperature on pellet performance

[0054]

[0055] Table 4 Effect of solidification time on pellet performance

[0056]

[0057] Therefore, based on the above considerations, the curing temperature is selected to be 40-100°C and the curing time is 0.5-2.0h.

[0058] The technical solution of the present invention will be further described below in conjunction with specific embodiments.

[0059] Example 1

[0060] A method for preparing mixed rare earth concentrate double-layer solidified pellets comprises the following steps:

[0061] (1) Take 10g of Bayan Obo mixed rare earth concentrate, 0.5g of sodium polyacrylate, and 2.5g of Na2CO3 and mix them evenly to obtain a mixture for standby use;

[0062] (2) placing the mixture obtained in step (1) in a pelletizing machine for pelletizing, selecting a pressure of 8 Pa and a pressing time of 30 min to obtain pellets with a diameter of 3 cm;

[0063] (3) preparing a 10% solution of water-soluble sodium polyacrylate and spraying it on the surface of the pellets to soak them. The spraying amount is 4% of the pellet weight to obtain soaked pellets.

[0064] (4) placing the soaked pellets in mineral powder for bonding for 20 min, and obtaining bonded pellets after sieving;

[0065] (5) The obtained sticky powder pellets are solidified at a curing temperature of 100° C. for 30 min to obtain solidified pellets.

[0066] The compressive strength of the obtained solidified pellets is 561N / piece.

[0067] Example 2

[0068] A method for preparing mixed rare earth concentrate double-layer solidified pellets comprises the following steps:

[0069] (1) Take 10g of Bayan Obo mixed rare earth concentrate, 0.5g of sodium polyacrylate, and 3g of Na2CO3 and mix them evenly to obtain a mixture for standby use;

[0070] (2) placing the mixture obtained in step (1) in a pelletizing machine for pelletizing, selecting a pressure of 8 Pa and a pressing time of 30 min to obtain pellets with a diameter of 3 cm;

[0071] (3) preparing a 10% solution of water-soluble sodium polyacrylate and spraying it on the surface of the pellets to soak them. The spraying amount is 4% of the pellet weight to obtain soaked pellets.

[0072] (4) placing the soaked pellets in mineral powder for bonding for 20 min, and obtaining bonded pellets after sieving;

[0073] (5) The obtained sticky powder pellets are solidified at a curing temperature of 100° C. for 30 min to obtain solidified pellets.

[0074] The compressive strength of the obtained solidified pellets is 1753N / piece.

[0075] Example 3

[0076] A method for preparing mixed rare earth concentrate double-layer solidified pellets comprises the following steps:

[0077] (1) 10 g of Bayan Obo mixed rare earth concentrate, 1 g of sodium polyacrylate, and 10 g of Na2CO3 were mixed to obtain a mixture for standby use;

[0078] (2) placing the mixture obtained in step (1) in a pelletizing machine for pelletizing, selecting a pressure of 8 Pa and a pressing time of 30 min to obtain pellets with a diameter of 3 cm;

[0079] (3) preparing a 10% solution of water-soluble sodium polyacrylate and spraying it on the surface of the pellets to soak them. The spraying amount is 4% of the pellet weight to obtain soaked pellets.

[0080] (4) placing the soaked pellets in mineral powder for bonding for 20 min, and obtaining bonded pellets after sieving;

[0081] (5) The obtained sticky powder pellets are solidified at a curing temperature of 100° C. for 30 min to obtain solidified pellets.

[0082] The compressive strength of the obtained solidified pellets is 800N / piece.

[0083] Example 4

[0084] A method for preparing mixed rare earth concentrate double-layer solidified pellets comprises the following steps:

[0085] (1) Take 10g of Bayan Obo mixed rare earth concentrate, 1.5g of sodium polyacrylate, and 10g of Na2CO3 and mix them evenly to obtain a mixture for standby use;

[0086] (2) placing the mixture obtained in step (1) in a pelletizing machine for pelletizing, selecting a pressure of 8 Pa and a pressing time of 30 min to obtain pellets with a diameter of 3 cm;

[0087] (3) preparing a 10% solution of water-soluble sodium polyacrylate and spraying it on the surface of the pellets to soak them. The spraying amount is 4% of the pellet weight to obtain soaked pellets.

[0088] (4) placing the soaked pellets in mineral powder for bonding for 20 min, and obtaining bonded pellets after sieving;

[0089] (5) The obtained sticky powder pellets are solidified at a curing temperature of 100° C. for 30 min to obtain solidified pellets.

[0090] The compressive strength of the obtained solidified pellets is 764N / piece.

[0091] Comparative Example

[0092] In both Comparative Examples 1 and 2, the amount of adhesive A added was 2.0 g. The amount of NaCO added was 4.5 g in Comparative Example 1, and 5.0 g in Comparative Example 2. The experimental preparation process still required mixing, pelletizing, impregnation, powder bonding, and curing. The relevant parameters were designed according to Example 3. The compressive strength of the resulting cured pellets is shown in Table 1.

[0093] As shown in Table 1, when excessive amounts of binder and sodium carbonate were used to prepare pellets, the compressive strength of the pellets was low, far below the production standard. However, within the scope of the present invention, the compressive strength was high, particularly in Example 2, where the compressive strength of the pellets reached 1753 N / piece, achieving high pellet performance.

[0094] It can be seen from the examples and comparative examples 1 and 2 that, under the same process conditions, when the dosage of binder A and binder Na2CO3 is high, the compressive strength of the pellets is significantly reduced and cannot meet the requirements of industrial production. This is because excessive addition of the binder will form a sticky form inside, making it impossible to compact the pellets during the pressing process, thereby reducing the compressive strength of the pellets.

[0095] Table 1

[0096] Amount of binder A added <![CDATA[Amount of Na2CO3 added]]> Compressive strength of solidified pellets Example 1 0.5g 2.5g 561N / each Example 2 0.5g 3g 1753N / each Example 3 1.5g 3.5g 800N / piece Example 4 1.5g 4.0g 764N / each Comparative Example 1 2.0 4.5g 459N / each Comparative Example 2 2.0 5.0g 444N / each

[0097] The above description of the disclosed embodiments will enable one skilled in the art to implement or use the present invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the present invention. Therefore, the present invention is not limited to the embodiments shown herein but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A method for preparing double-layer solidified pellets of mixed rare earth concentrate, characterized in that: The method comprises the following steps: (1) Mixing: Evenly mix the Bayan Obo mixed rare earth concentrate, binder A, and sodium-forming agent to obtain a mixture for standby use; the amount of the binder A added is 10-20% of the weight of the Bayan Obo mixed rare earth concentrate, the sodium-forming agent is 10-30% of the weight of the Bayan Obo mixed rare earth concentrate, the sodium-forming agent is a mixture of one or more of NaOH, Na2CO3, KOH, and K2CO3, and the binder A is one of sodium carboxymethyl cellulose, polyethylene oxide, sodium polyacrylate, starch, dextrin, and lignin, or any mixture thereof; (2) pelletizing: placing the mixture obtained in step (1) in a pelletizing machine for pelletizing to obtain pellets with a diameter of 1 cm to 4 cm; (3) Infiltration: a water-soluble binder B is prepared into a solution and sprayed onto the surface of the pellets to obtain infiltrated pellets. The binder B is one of phenolic resin, epoxy resin, melamine formaldehyde resin, sodium polyacrylate, starch, dextrin, and lignin, or any mixture thereof. The amount of the binder B added is 5% to 20% of the mass of the pellets. (4) powder bonding and screening: placing the impregnated pellets obtained in step (3) in mineral powder for bonding, and obtaining powder-bonded pellets after screening, wherein the mineral powder is a mixed ore of one or more of monazite, bastnaesite, xenotime, and ionic rare earth ore; (5) Curing: Curing the powder pellets obtained in step (4) at a curing temperature of 40° C. to 100° C. for 0.5 h to 2.0 h to obtain cured pellets.

2. The method for preparing a mixed rare earth concentrate double-layer solidified pellet according to claim 1, characterized in that: In step (1), the Bayan Obo mixed rare earth concentrate is a mixed ore of monazite and fluorocarbon cerium ore, or the Bayan Obo mixed rare earth concentrate is a roasted ore after rare earth minerals are roasted and decomposed, and the rare earth grade of the Bayan Obo mixed rare earth concentrate is ≥50%.

3. The method for preparing a mixed rare earth concentrate double-layer solidified pellet according to claim 1, characterized in that: In the step (3), the water-soluble binder B is prepared into a solution with a concentration of 5% to 10%.

4. The method for preparing double-layer solidified pellets of mixed rare earth concentrate according to claim 1, characterized in that: The rare earth grade of the mineral powder in step (4) is ≥50%.

5. The method for preparing double-layer solidified pellets of mixed rare earth concentrate according to claim 1, characterized in that: The curing equipment in step (5) includes a microwave reactor, a muffle furnace or a drying oven.

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