A method for double-layer pelletizing 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 pellets of mixed rare earth concentrate. The method comprises the following steps: uniformly mixing the Bayan Obo mixed rare earth concentrate with a sodiumizing agent and a binder A, then pelletizing the mixture, and subjecting the pellets to a first layer of solidification to obtain core pellets; spraying a binder B on the surface of the core pellets to wet the core pellets, thereby obtaining wet pellets; uniformly mixing the Bayan Obo mixed rare earth concentrate, water, and binder B, and then placing the wet pellets in a pelletizing machine for pressing to obtain green pellets; subjecting the green pellets to a second layer of solidification to obtain solidified pellets, which are the raw materials for the subsequent roasting and decomposition process. The present invention combines the pelletizing and pelletizing processes to prepare double-layer pellets, which can effectively alleviate the "ringing" phenomenon of the rotary kiln during the traditional sodiumizing roasting and decomposition process, and does not introduce other impurities during the reaction process, thus providing a possibility for the industrialization of the sodiumizing roasting and decomposition process of mixed rare earth concentrate.

Description

Technical Field

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

[0002] As researchers delve deeper into rare earth minerals, they are playing a vital role in national defense, aerospace, agricultural production, petroleum catalysis, steel alloys, and other fields. Their applications are rapidly expanding. "The Middle East has oil, China has rare earths." Rare earths, considered a strategic mineral resource, are ranked first in the world in reserves, production, and exports. The Bayan Obo Mine boasts the world's largest rare earth reserves, accounting for 83% of my country's total, making it a key production site. Rare earth ore primarily occurs as a mixture of bastnaesite and monazite, characterized by abundance, poor quality, mixed quality, and fineness, making it difficult to select and smelt.

[0003] With the increasing depletion of rare earth resources and the increasing efforts in environmental protection, the high-consumption and high-pollution concentrated sulfuric acid roasting method and the high-consumption liquid alkali decomposition method are difficult to adapt to the current environmentally friendly and resource-saving industrial production concept. Therefore, the development of a green, environmentally friendly and economically reasonable rare earth smelting process has become an urgent task.

[0004] In fact, sodium roasting is a relatively clean smelting process for decomposing Bayan Obo mixed rare earth concentrate. Due to its advantages such as no waste gas generation, low alkaline wastewater generation, and low treatment costs, many researchers have conducted in-depth research on it in recent years, but none of them have achieved industrial application. This is mainly because ring formation will appear on the inner wall of the rotary kiln during the sodium roasting process, resulting in a reduction in volume. For example, in 1963, my country began to study the use of Na2CO3 to roast Bayan Obo mixed rare earth concentrate. Subsequently, many institutions such as the Changchun Institute of Applied Chemistry, Baotou Iron and Steel Metallurgical Research Institute, Nonferrous Metals Research Institute, and Baotou Rare Earth Research Institute conducted detailed research on this process, and even carried out kilogram-level semi-industrial production in rotary kilns. However, due to the serious ring formation in the rotary kiln, the equipment could not operate normally, resulting in the process not being applied to industrial production to date. Therefore, whether the problem of ring formation in the rotary kiln can be overcome is the key to whether the sodium roasting method can be applied to industrial production. The present invention proposes a method for preparing high-strength mixed rare earth concentrate double-layer pellets. The method uses a rare earth mineral in the outer layer that does not react with the inner wall to cover the sodium-forming agent that is bound to the mineral in the inner layer, thereby avoiding contact between the sodium-forming agent and the inner wall. This method completely solves the problem of rotary kiln ring formation during the sodium-forming roasting and decomposition process, and can provide certain reference value for the decomposition of other minerals. Summary of the Invention

[0005] In view of this, the purpose of the present invention is to provide a method for double-layer pelletizing 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 ​​sintering pellets and proposes a technical idea of ​​preparing ball cores by mixing the Bayan Obo mixed rare earth concentrate with a sodium agent and a binder A. The prepared ball cores are moistened and then subjected to secondary ball making and solidification for reproduction to prepare high-strength mixed rare earth concentrate double-layer pellets, thereby solving the problem of "ringing" in the rotary kiln.

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

[0008] A method for preparing mixed rare earth concentrate double-layer pellets specifically 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 evenly distributes the sodium-forming agent, Bayan Obo mixed rare earth concentrate and binder A, and brings them into close contact, thereby achieving effective decomposition of rare earth minerals while ensuring bonding strength.

[0011] (2) pelletizing: placing the mixture obtained in step (1) in a pelletizing plate for pelletizing to obtain pellets with a diameter of 20 mm to 40 mm;

[0012] The purpose of this step is to prepare the mixed material into pellets with consistent properties through the pelletizing disk.

[0013] (3) First layer solidification: solidifying the pellets obtained in step (2) to obtain a core;

[0014] Through curing, the core can have a certain compressive strength and provide suitable mechanical properties for the next step of bonding mineral powder.

[0015] (4) Wetting: preparing a solution of a water-soluble binder B and spraying it onto the surface of the core to wet it, thereby obtaining a wetted pellet;

[0016] By evenly spraying adhesive B on the surface of the core, the surface of the core has a certain degree of adhesiveness, providing more bonding sites for the second layer of mixture.

[0017] (5) Mixing and ball pressing: The wet pellets obtained in step (4) are placed in a ball press, and a mixture of rare earth concentrate, water, and binder B is added and ball pressed to obtain green balls with a diameter of 30 mm to 50 mm;

[0018] By evenly distributing the rare earth concentrate and binder to ensure the bonding strength, and coating the surface of the wet pellets with a layer of rare earth concentrate, the problem of rotary kiln ring formation during the sodium roasting and decomposition process caused by the contact between the sodium agent inside the pellets and the inner wall of the rotary kiln is fundamentally solved.

[0019] (6) Second stage solidification: solidify the green pellets obtained in step (5) to obtain solidified pellets.

[0020] The purpose of this operation step is to give the green balls a certain compressive strength through solidification, so as to provide them with suitable mechanical properties for application in industrial production practice.

[0021] Optionally, in step (1), the Bayan Obo mixed rare earth concentrate is a mixed ore of one or more of monazite, fluorocarbon cerium ore or roasted ore after roasting and decomposition of rare earth minerals, and the rare earth grade is ≥50%.

[0022] Optionally, the added amount of the binder A is 1.0-2.0% of the weight of the Bayan Obo mixed rare earth concentrate, and the added amount of the sodium agent is 20-30% of the weight of the Bayan Obo mixed rare earth concentrate.

[0023] 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 polyacrylate, lignin, sodium sulfonate, dextrin, and sodium carboxymethyl cellulose, or any mixture thereof.

[0024] Optionally, the curing temperature in step (3) is 40° C. to 70° C., and the curing time is 1.0 h to 2.0 h.

[0025] Optionally, the binder B is at least one of sodium carboxymethyl cellulose and polyethylene oxide.

[0026] Furthermore, the water-soluble binder B is prepared into a solution with a concentration of 1% to 5%, and the amount of the binder B added is 5% to 10% of the mass of the core.

[0027] Optionally, the rare earth concentrate is a mixed ore of one or more of monazite, bastnaesite, and mixed rare earth ores, and the rare earth grade is ≥50%.

[0028] Furthermore, in step (5), the amount of binder B added is 5% to 10% of the weight of the rare earth concentrate, the amount of water added is 5% to 10% of the weight of the rare earth concentrate, and the ball pressing pressure is 7 MPa to 11 MPa.

[0029] Furthermore, the curing temperature in step (5) is 60° C. to 160° C., and the curing time is 0.5 h to 2.0 h.

[0030] 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 pellet provided by the present invention has the following excellent effects:

[0031] 1) The mixed rare earth concentrate double-layer pellets prepared by the present invention not only have strong compressive strength, but also can solve the problem of "ringing" in the rotary kiln, so that the method of decomposing rare earth concentrate by sodium roasting can be applied to industrial production.

[0032] 2) Since the binder selected in the present invention is an organic substance, it decomposes at high temperature to produce water, carbon dioxide and sodium carbonate, which has little effect on the separation and purification of rare earth products.

[0033] 3) The sodium-forming agent consumption in the present invention is low, the amount of binder added is small, the production cost can be reduced, and the method is suitable for industrial production. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] 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.

[0035] Figure 1 This is a flow chart of the preparation process of the mixed rare earth concentrate double-layer pellets described in the present invention.

[0036] Figure 2 This is a schematic structural diagram of the mixed rare earth concentrate double-layer pellets of the present invention. DETAILED DESCRIPTION

[0037] 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.

[0038] The embodiment of the present invention discloses a method for preparing mixed rare earth concentrate double-layer pellets.

[0039] 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.

[0040] Process parameter optimization experiment:

[0041] (1) Optimization of process parameters for binder A

[0042] As mentioned earlier, the amount of binder A added is a critical parameter in this process. Selecting the appropriate amount can reduce production costs while providing good pellet performance. The effect of binder A addition on the compressive strength and drop times of the pellet cores was investigated under a pressure of 7 MPa, as shown in Table 1. It can be seen that within the addition range of 1.0% to 2.0%, the compressive strength of the pellet cores remains stable between 500 N / piece and 900 N / piece, and the drop times range from 2 to 6.

[0043] Table 1 Effect of binder A addition on the compressive strength and drop times of the core

[0044]

[0045] (2) Optimization of process parameters for binder B

[0046] As mentioned above, the amount of binder B added determines whether the second layer of the pellets can adhere the mixed rare earth concentrate to the surface, thus insulating the inner layer of pellets. The effect of binder B addition on the compressive strength and drop rate of green pellets was investigated under a pressure of 7 MPa, as shown in Table 2. Increasing the amount of binder B added increases both the compressive strength and drop rate of the pellets.

[0047] Table 2 Effect of binder B addition on green ball compressive strength and falling times

[0048]

[0049] Therefore, considering the above, the addition amount of binder A is selected to be 1.0-2.0%, and the addition amount of binder B is selected to be 5-10%.

[0050] (III) Optimization of secondary curing process parameters

[0051] Pellet curing is a key step in this process, effectively improving the compressive strength of the pellets. Therefore, the selection of curing conditions is crucial. While ensuring high compressive strength and a high number of pellet drops, minimizing the curing temperature and time is crucial. To this end, we conducted further research on optimizing curing conditions.

[0052] Table 3 shows the effect of curing temperature on the compressive strength and drop times of the pellets. To fully consider the effect of curing temperature on the compressive strength of the pellets, a double-layer pellet was prepared using a pressure of 7 MPa, a binder A content of 1.4%, a binder B content of 10%, and a curing time of 30 minutes. All other conditions remained the same, and the results are shown in Table 3. Curing temperature has a significant impact on the compressive strength of the pellets. At the same curing time, higher temperatures result in lower moisture content and higher compressive strength.

[0053] Table 4 shows the effect of curing time on the compressive strength and number of drops of the pellets. To fully explore the relationship between curing time and compressive strength, double-layer pellets were prepared at a pressure of 7 MPa, 1.4% binder A, 10% binder B, and a curing temperature of 140°C. Curing at the same temperature significantly affects the compressive strength of the pellets. As curing time increases, the compressive strength increases as more moisture evaporates from the pellets.

[0054] Table 3 Effect of curing temperature on compressive strength and falling times of cured pellets

[0055]

[0056]

[0057] Table 4 Effect of curing time on compressive strength and falling times of cured pellets

[0058]

[0059] Therefore, considering the above, the curing temperature is selected to be 60-160°C and the curing time is 0.5-2.0h.

[0060] The technical solution of the present invention will be further described below in conjunction with specific embodiments.

[0061] Example 1

[0062] A method for preparing high-strength mixed rare earth concentrate double-layer pellets comprises the following steps:

[0063] (1) Take 10g of Bayan Obo mixed rare earth concentrate, 0.12g of sodium polyacrylate, and 2g of Na2CO3 and mix them evenly to obtain a mixed material for later use;

[0064] (2) placing the mixture obtained in step (1) in a pelletizing plate to form pellets to prepare 20 mm pellets;

[0065] (3) placing the pellets from step (2) in a drying oven at 50°C for 1 hour to obtain pellet cores;

[0066] (4) Wetting: Prepare a 2% solution of water-soluble sodium carboxymethyl cellulose and spray it on the surface of the core to wet it and obtain wet pellets;

[0067] (5) placing the wet pellets obtained in step (4) in a pelletizing machine, adding a mixture of 10 g of rare earth concentrate, 0.5 g of water, and 0.6 g of sodium carboxymethyl cellulose, and pelletizing at a pressure of 8 MPa to obtain green pellets with a diameter of 30 mm;

[0068] (6) The obtained green balls are solidified at a temperature of 90°C for 1 hour to obtain solidified pellets.

[0069] The compressive strength of the obtained solidified pellets is 1473N / piece.

[0070] Example 2

[0071] A method for preparing high-strength mixed rare earth concentrate double-layer pellets comprises the following steps:

[0072] (1) Take 10g of Bayan Obo mixed rare earth concentrate, 0.14g of sodium polyacrylate, and 2.5g of Na2CO3 and mix them evenly to obtain a mixed material for later use;

[0073] (2) placing the mixture obtained in step (1) in a pelletizing plate to form pellets to prepare 30 mm pellets;

[0074] (3) placing the pellets from step (2) in a drying oven at 60°C for 1 hour to obtain pellet cores;

[0075] (4) Wetting: Prepare a 3% solution of water-soluble sodium carboxymethyl cellulose and spray it on the surface of the core to wet it and obtain wet pellets;

[0076] (5) placing the wet pellets obtained in step (4) in a pellet press, adding a mixture of 10 g of rare earth concentrate, 0.6 g of water, and 0.7 g of sodium carboxymethyl cellulose, and pelletizing at a pressure of 8 MPa to obtain green pellets with a diameter of 40 mm;

[0077] (6) The obtained green balls are solidified for 1 hour at a temperature of 100°C to obtain solidified pellets.

[0078] The compressive strength of the obtained solidified pellets is 1547N / piece.

[0079] Example 3

[0080] A method for preparing high-strength mixed rare earth concentrate double-layer pellets comprises the following steps:

[0081] (1) Take 10g of Bayan Obo mixed rare earth concentrate, 0.16g of sodium polyacrylate, and 3g of Na2CO3 and mix them evenly to obtain a mixed material for later use;

[0082] (2) placing the mixture obtained in step (1) in a pelletizing plate to form pellets to prepare 40 mm pellets;

[0083] (3) placing the pellets from step (2) in a drying oven at 70°C for 1 hour to obtain pellet cores;

[0084] (4) Wetting: Prepare a 4% solution of water-soluble sodium carboxymethyl cellulose and spray it on the surface of the core to wet it and obtain wet pellets;

[0085] (5) placing the wet pellets obtained in step (4) in a pelletizing machine, adding a mixture of 10 g of rare earth concentrate, 0.7 g of water, and 0.8 g of sodium carboxymethyl cellulose, and pelletizing at a pressure of 8 MPa to obtain green pellets with a diameter of 50 mm;

[0086] (6) The obtained green balls are solidified at a temperature of 110° C. for 1 h to obtain solidified pellets.

[0087] The compressive strength of the obtained solidified pellets is 1750N / piece.

[0088] Comparative Example 1

[0089] A method for preparing high-strength mixed rare earth concentrate double-layer pellets comprises the following steps:

[0090] (1) Take 10g of Bayan Obo mixed rare earth concentrate, 0.05g of sodium polyacrylate, and 3g of Na2CO3 and mix them evenly to obtain a mixed material for later use;

[0091] (2) placing the mixture obtained in step (1) in a pelletizing plate to form pellets to prepare 40 mm pellets;

[0092] (3) placing the pellets from step (2) in a drying oven at 70°C for 1 hour to obtain pellet cores;

[0093] (4) Wetting: Prepare a 2% solution of water-soluble sodium carboxymethyl cellulose and spray it on the surface of the core to wet it and obtain wet pellets;

[0094] (5) placing the wet pellets obtained in step (4) in a pelletizing machine, adding a mixture of 10 g of rare earth concentrate, 0.7 g of water, and 0.2 g of sodium carboxymethyl cellulose, and pelletizing at a pressure of 8 MPa to obtain green pellets with a diameter of 50 mm;

[0095] (6) The obtained green balls are solidified at a temperature of 110° C. for 1 h to obtain solidified pellets.

[0096] The compressive strength of the obtained solidified pellets is 932N / piece.

[0097] Comparative Example 2

[0098] A method for preparing high-strength mixed rare earth concentrate double-layer pellets comprises the following steps:

[0099] (1) Take 10g of Bayan Obo mixed rare earth concentrate, 0.08g of sodium polyacrylate, and 3g of Na2CO3 and mix them evenly to obtain a mixed material for later use;

[0100] (2) placing the mixture obtained in step (1) in a pelletizing plate to form pellets to prepare 40 mm pellets;

[0101] (3) placing the pellets from step (2) in a drying oven at 70°C for 1 hour to obtain pellet cores;

[0102] (4) Wetting: Prepare a 2% solution of water-soluble sodium carboxymethyl cellulose and spray it on the surface of the core to wet it and obtain wet pellets;

[0103] (5) placing the wet pellets obtained in step (4) in a pelletizing machine, adding a mixture of 10 g of rare earth concentrate, 0.4 g of water, and 0.8 g of sodium carboxymethyl cellulose, and pelletizing at a pressure of 8 MPa to obtain green pellets with a diameter of 50 mm;

[0104] (6) The obtained green balls are solidified at a temperature of 110° C. for 1 h to obtain solidified pellets.

[0105] The compressive strength of the obtained solidified pellets is 1023N / piece.

[0106] It can be seen from Example 3 and Comparative Examples 1 and 2 that, under the same process conditions, when the amount of binder A and binder B is reduced, the compressive strength of the pellets will be significantly reduced, making it impossible to meet the requirements of industrial production.

[0107] 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 mixed rare earth concentrate double-layer pellets, characterized in that: The method comprises the following steps: (1) Mixing: Evenly mix the Bayan Obo mixed rare earth concentrate, binder A, and sodiumizing agent to obtain a mixture for standby use, wherein the amount of the binder A added is 1.0-2.0% by weight of the Bayan Obo mixed rare earth concentrate, the sodiumizing agent is 20-30% by weight of the Bayan Obo mixed rare earth concentrate, and the sodiumizing agent is a mixture of one or more of NaOH, Na2CO3, KOH, and K2CO3, and the binder A is one of sodium polyacrylate, lignin, sodium sulfonate, dextrin, and sodium carboxymethyl cellulose, or any mixture thereof; (2) pelletizing: placing the mixture obtained in step (1) in a pelletizing plate for pelletizing to obtain pellets with a diameter of 20 mm to 40 mm; (3) First layer curing: curing the pellets obtained in step (2) at a curing temperature of 40°C to 70°C for 1.0h to 2.0h to obtain a core; (4) Wetting: preparing a solution of a water-soluble binder B in an amount of 5% to 10% of the mass of the core, spraying the solution onto the surface of the core to wet the core, and obtaining wet pellets. The binder B is at least one of sodium carboxymethyl cellulose and polyethylene oxide. (5) Mixing and ball pressing: The wet pellets obtained in step (4) are placed in a ball press, and a mixture of rare earth concentrate, water, and binder B is added for ball pressing. The amount of binder B added is 5% to 10% by weight of the rare earth concentrate, and the amount of water added is 5% to 10% by weight of the rare earth concentrate. The ball pressing pressure is 7 MPa to 11 MPa, and green balls with a diameter of 30 mm to 50 mm are obtained. (6) Second stage solidification: solidify the green pellets obtained in step (5) at a solidification temperature of 60°C to 160°C for 0.5h to 2.0h to obtain solidified pellets.

2. The method for preparing a mixed rare earth concentrate double-layer 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 a roasted ore after rare earth minerals are roasted and decomposed, and the rare earth grade is ≥50%.

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

4. The method for preparing double-layer pellets of mixed rare earth concentrate according to claim 1, characterized in that: The rare earth concentrate is a mixed ore of monazite and bastnaesite, and the rare earth grade is ≥50%.

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