Segmented calcination process for preparing praseodymium neodymium oxide

Abstract

The invention belongs to the technical field of praseodymium neodymium oxide preparation, and particularly relates to a segmented calcination process for preparing praseodymium neodymium oxide. The technology is carried out in a rotary furnace and comprises the following steps that praseodymium neodymium carbonate, NH4Cl and Al2O3 are mixed and then fed into the rotary furnace from the kiln tail, meanwhile, oxygen flowing reversely is introduced into the rotary furnace from the kiln head, the oxygen and materials moving from the kiln tail to the kiln head are mixed and react, and finally a praseodymium neodymium oxide product is obtained at a discharge port of the kiln head; the interior of the rotary furnace is sequentially divided into a first preheating section, a second decomposition section, a third dechlorination section and a fourth cooling section from the kiln tail to the kiln head, and carbon monoxide is introduced into the second decomposition section to participate in the decomposition reaction. Through dynamic gradient temperature field optimization and gas-solid countercurrent mass transfer reinforcement, the energy consumption is reduced, and the operation stability of equipment is improved; meanwhile, according to the process, the reaction process is accurately regulated and controlled through segmented temperature control, the total amount of praseodymium neodymium oxide rare earth is increased, and the stability and acid solubility of the product are enhanced.

Description

Technical Field

[0001] The invention belongs to the technical field of praseodymium-neodymium oxide preparation, and in particular relates to a staged calcination process for preparing praseodymium-neodymium oxide. Background Art

[0002] As a key raw material for high-performance permanent magnet materials for new energy vehicle drive motors, the optimization of its preparation process is crucial to improving product performance and reducing production costs. At present, the industry mainly uses tunnel kilns, push-plate kilns or roller kilns for calcination, relying on the combustion of fossil fuels (such as coal, diesel, and gas) to provide heat. However, the existing technology has the following significant defects: 1) High energy consumption: The traditional process relies on high-temperature flame horizontal heat transfer, with low heat utilization, high electricity consumption and natural gas consumption per ton of product, and a large proportion of the overall energy consumption cost; 2) Unstable product quality: During the calcination process in a fixed bed or rotary kiln, the material is prone to agglomeration, resulting in uneven heating and incomplete calcination. Cl in the product - 、SO4 2- The residual impurities such as carbon dioxide and carbon dioxide exceed the standard, thereby reducing the total amount of rare earth products; 3) Poor environmental protection: the exhaust gas treatment is not sufficient, the particulate matter emission is high, and the rare earth dust escapes, causing waste of resources and environmental pollution; 4) Low equipment reliability: the ring formation rate on the inner wall of the rotary kiln is fast, and frequent shutdowns are required for cleaning, and the continuous operation cycle is short, which seriously affects production efficiency.

[0003] The above problems limit the large-scale and efficient preparation of praseodymium neodymium oxide. Therefore, there is an urgent need for a new roasting process that is energy-saving, high-purity, environmentally friendly and has stable equipment to solve the problems in the prior art. Summary of the invention

[0004] In view of the shortcomings of the prior art, the purpose of the present invention is to provide a staged calcination process for preparing praseodymium-neodymium oxide, which reduces energy consumption and improves equipment operation stability through dynamic gradient temperature field optimization and gas-solid countercurrent mass transfer enhancement. At the same time, the process accurately controls the reaction process through staged temperature control, increases the total amount of praseodymium-neodymium oxide rare earth, and enhances the acid solubility of the product.

[0005] The technical solution adopted by the present invention is as follows: The stepwise calcination process for preparing praseodymium-neodymium oxide is carried out in a rotary kiln and specifically comprises the following steps: PrNd carbonate, NH4Cl and Al2O3 are mixed in weight proportions of 88-92 parts, 6-8 parts and 0.02-0.03 parts, and then fed into a rotary kiln from the kiln tail. Meanwhile, oxygen is introduced into the rotary kiln from the kiln head in a reverse flow to react with the materials moving from the kiln tail to the kiln head, and finally a praseodymium-neodymium oxide product is obtained at the kiln head discharge port. The rotary kiln is divided into a first preheating section, a second decomposition section, a third dechlorination section and a fourth cooling section from the kiln tail to the kiln head, wherein carbon monoxide is introduced into the second decomposition section to participate in the decomposition reaction; The reaction conditions of each process section are as follows: the temperature of the first preheating section is 320-500°C, and the total residence time is 50-60min; the temperature of the second decomposition section is 500-650°C, and the total residence time is 80-90min; the temperature of the third dechlorination section is 650-950°C, and the total residence time is 60-70min; the temperature of the fourth cooling section is 950-300°C, and the total residence time is 50-60min.

[0006] The rotation speed of the rotary kiln is 1-1.5 r / min, the helical angle of the guide plate is 40-44°, and the axial moving speed of the material is 0.8 m / h.

[0007] The air flow velocity of the oxygen and carbon monoxide is 1.8-2.2 m / s, and the Reynolds number Re>3500.

[0008] The method for preparing praseodymium neodymium carbonate comprises the following steps: The rare earth ore is sequentially subjected to acid dissolution and extraction separation to obtain a praseodymium-neodymium chloride solution; carbonate is added to the praseodymium-neodymium chloride solution for neutralization reaction to generate praseodymium-neodymium carbonate, wherein the rare earth oxide content is ≥45%.

[0009] Preferably, the method for preparing praseodymium neodymium carbonate comprises the following steps: (1) Using fluorocarbon cerium ore or monazite as raw material, after crushing and grinding, sieving through a 200-mesh screen to obtain a powder, mixing the powder with hydrochloric acid for acid dissolution reaction, the acid dissolution conditions are: acid concentration 6-10 mol / L, temperature 60-90°C, reaction time 2-4h, to obtain a rare earth leachate containing praseodymium and neodymium. Subsequently, the leachate is extracted and separated by solvent extraction: using P507 or P204 as an extractant, adjusting the solution pH to 2.0-4.0, removing impurities such as calcium and iron through extraction, and obtaining a praseodymium-neodymium chloride solution, wherein the molar ratio of praseodymium to neodymium can be controlled in the range of 1:9 to 9:1; (2) diluting the above-mentioned praseodymium-neodymium chloride solution to a rare earth oxide (REO) concentration of 50-150 g / L, heating to 40-60°C and continuously stirring, slowly adding a carbonate solution as a precipitant to the praseodymium-neodymium chloride solution for neutralization reaction, reacting for 3-4 hours, and controlling the pH value at the end point of the reaction to be 6.5-7.5 to generate a pink praseodymium-neodymium carbonate precipitate, the main component of which is (PrNd)2(CO3)3; (3) The praseodymium-neodymium carbonate precipitate is washed 3-5 times with deionized water, and then dried at 80-120° C. for 0.5-1 h to obtain an industrial-grade praseodymium-neodymium carbonate solid, and its rare earth oxide (REO) content is determined by the calcination method to be ≥45%.

[0010] The D50 particle size of the praseodymium-neodymium carbonate is 30-40 μm, the particle size of NH4Cl is 80-200 mesh, and the specific surface area of ​​Al2O3 is 8-20 m2 / g.

[0011] The oxygen concentrations in the first preheating section, the second decomposition section, the third dechlorination section and the fourth cooling section are 8-10 vol%, 12-14 vol%, 20-23 vol% and 19-21 vol% respectively.

[0012] The carbon monoxide concentration in the second decomposition stage is 0.3-0.5 vol%.

[0013] The concentration of water vapor in the third dechlorination stage is 1.2-1.5 vol%.

[0014] The tail gas generated by the rotary kiln is processed in sequence by a bag filter, an SCR denitration system and a water spray absorption tower.

[0015] The filtering accuracy of the bag filter is 0.1 μm, and the filter material is PTFE coating; the catalyst used in the SCR denitration system is V2O5-WO3 / TiO2 type catalyst, and the denitration efficiency is ≥85%.

[0016] The water spray absorption tower adopts aqueous solution circulation absorption, and after absorption, the absorption liquid is separated into solid and liquid, the obtained aqueous solution is circulated and used, and the solid material is recovered to the production line.

[0017] The rotary kiln cylinder adopts a structural design of a 310S stainless steel substrate with a composite Al2O3 coating on the surface. The coating has a porosity of ≤2%, ensuring the anti-oxidation and corrosion resistance of the cylinder in a high temperature environment. The maximum tolerable temperature can reach 1100°C.

[0018] The burner of the rotary kiln is equipped with a multi-stage swirl low-nitrogen combustion device, which realizes the combustion process of nitrogen oxides (NO x ) is effectively suppressed, and its emission concentration is ≤100mg / Nm 3 .

[0019] The temperature measurement system of the rotary kiln integrates an infrared non-contact temperature measurement module and a thermocouple contact sensing unit to form a composite temperature monitoring network, which can provide real-time feedback on temperature fluctuations in each process section of the furnace, and the overall temperature measurement accuracy is controlled within ±3°C.

[0020] The stepwise calcination process for preparing praseodymium-neodymium oxide described in the present invention has the following reaction mechanism: The first preheating stage: praseodymium neodymium carbonate ((PrNd)2(CO3)3·nH2O) is initially dehydrated in an oxygen atmosphere to generate basic carbonate (PrNd)2O(CO3)2·H2O. The reaction process is as follows: (PrNd)2(CO3)3·nH2O→(PrNd)2O(CO3)2·H2O+CO2↑+(n-1)H2O↑.

[0021] The second decomposition stage: carbon monoxide reacts with (PrNd)2O(CO3)2·H2O to promote the decomposition of carbonate into (PrNd)2O3. At the same time, NH4Cl decomposes to generate HCl gas. Al2O3 acts as an inert carrier to inhibit sintering. On the contrary, it can reduce the original roasting temperature under normal product quality. The reaction process is as follows: (PrNd)2O(CO3)3·H2O+CO→(PrNd)2O3+4CO2↑+H2O.

[0022] The third dechlorination stage: water vapor and residual Cl in (PrNd)2O3 - The reaction generates HCl gas, which further reduces the residual chloride ions. The reaction process is: Cl - + H2O →HCl↑+OH - .

[0023] The fourth cooling stage: The product is slowly cooled in an oxygen-rich environment to stabilize the crystal structure and form praseodymium-neodymium oxide with a high rare earth content.

[0024] Compared with the prior art, the present invention has the following beneficial effects: (1) The staged calcination process for preparing praseodymium-neodymium oxide described in the present invention greatly reduces the overall energy consumption of the process through dynamic gradient temperature field optimization and gas-solid countercurrent mass transfer enhancement, while improving the equipment operation stability and reducing the frequency of shutdown maintenance. The equipment operation cycle can reach 600 hours, and the daily output of a single furnace can reach 9 tons, realizing continuous and efficient production; (2) The staged calcination process for preparing praseodymium-neodymium oxide described in the present invention can precisely control the reaction process by staged temperature control, effectively increase the total amount of praseodymium-neodymium oxide rare earth, suppress impurity residues, improve the stability of the crystal structure, and thus enhance the acid solubility of the final product; (3) The staged calcination process for preparing praseodymium-neodymium oxide described in the present invention adopts a three-stage closed-loop tail gas purification system, which significantly reduces particulate matter and nitrogen oxide emissions and realizes green and clean production. DETAILED DESCRIPTION

[0025] The present invention is further described below with reference to the embodiments, but they do not limit the implementation of the present invention.

[0026] The raw materials used in the examples and comparative examples are conventional commercially available raw materials unless otherwise specified, and the process methods used in the examples and comparative examples are conventional methods in the art unless otherwise specified.

[0027] Some of the raw materials used in the examples and comparative examples are described as follows: The D50 particle size of the praseodymium-neodymium carbonate is 35±5 μm, and the preparation method thereof comprises the following steps: (1) Using fluorocarbon cerium ore as raw material, after crushing and grinding, sieving through a 200-mesh screen to obtain a powder, mixing the powder with hydrochloric acid for acid dissolution reaction, with a solid-liquid ratio of 1:3, and the acid dissolution conditions are: acid concentration 8 mol / L, temperature 80°C, reaction time 3h, to obtain a rare earth leachate containing praseodymium and neodymium. Subsequently, the leachate is extracted and separated by solvent extraction: using P507 as an extractant, adjusting the solution pH to 2.0, removing impurities such as calcium and iron through extraction, and obtaining a praseodymium-neodymium chloride solution, wherein the praseodymium-neodymium molar ratio is controlled at 1:3; (2) Dilute the above praseodymium-neodymium chloride solution with water to a rare earth oxide (REO) concentration of 84 g / L, heat to 42°C and continue stirring. Slowly add 2.7 mol / L ammonium bicarbonate solution as a precipitant to the praseodymium-neodymium chloride solution for neutralization reaction for 3 hours. The pH value at the end of the reaction is controlled to be 6.5 to generate a pink praseodymium-neodymium carbonate precipitate, the main component of which is (PrNd)2(CO3)3; (3) The praseodymium-neodymium carbonate precipitate was washed three times with deionized water and then dried at 80°C for 0.5 h to obtain an industrial-grade praseodymium-neodymium carbonate solid. The rare earth oxide (REO) content of the solid was determined to be 48% by the calcination method.

[0028] The particle size of the NH4Cl is 140±60 mesh.

[0029] The specific surface area of ​​Al2O3 is 14±6m 2 / g.

[0030] Example 1 The stepwise calcination process for preparing praseodymium-neodymium oxide is carried out in a rotary kiln and specifically comprises the following steps: PrNd carbonate, NH4Cl and Al2O3 were mixed in proportions of 88, 8 and 0.02 by weight and then fed into a rotary kiln from the kiln tail. At the same time, oxygen with a countercurrent flow rate of 1.8 m / s was introduced from the kiln head into the rotary kiln to react with the materials moving from the kiln tail to the kiln head. Finally, praseodymium-neodymium oxide products were obtained at the kiln head discharge port. The tail gas generated by the rotary kiln was treated in turn by a bag filter, an SCR denitration system and a water spray absorption tower. The final particulate matter emission was 2.3 mg / m 3 .

[0031] The rotation speed of the rotary kiln is 1 r / min, the helical angle of the guide plate is 40°, and the axial moving speed of the material is 0.8 m / h.

[0032] The rotary kiln is divided into the first preheating section, the second decomposition section, the third dechlorination section and the fourth cooling section from the kiln tail to the kiln head. In the second decomposition section, a counter-flow of carbon monoxide with a gas flow velocity of 1.8 m / s is introduced to participate in the decomposition reaction.

[0033] The reaction conditions of each process section are as follows: the total residence time of the first preheating section is 60 min, the temperature is increased from 320°C to 500°C, and the oxygen concentration is 9±1 vol%; the total residence time of the second decomposition section is 80 min, the temperature is increased from 500°C to 650°C, the oxygen concentration is 13±1 vol%, and the carbon monoxide concentration is 0.4±0.1 vol%; the total residence time of the third dechlorination section is 70 min, the temperature is increased from 650°C to 950°C, the oxygen concentration is 21±1 vol%, and the water vapor concentration is 1.3±0.1 vol%; the total residence time of the fourth cooling section is 60 min, and the temperature is reduced from 950°C to 300°C.

[0034] Example 2 The stepwise calcination process for preparing praseodymium-neodymium oxide is carried out in a rotary kiln and specifically comprises the following steps: PrNd carbonate, NH4Cl and Al2O3 were mixed in proportions of 90, 7 and 0.03 by weight and then fed into a rotary kiln from the kiln tail. At the same time, oxygen with a countercurrent flow rate of 2 m / s was introduced from the kiln head into the rotary kiln to react with the materials moving from the kiln tail to the kiln head. Finally, praseodymium-neodymium oxide products were obtained at the kiln head discharge port. The tail gas generated by the rotary kiln was treated in turn by a bag filter, an SCR denitration system and a water spray absorption tower. The final particulate matter emission was 2.3 mg / m 3 .

[0035] The rotation speed of the rotary kiln is 1.2 r / min, the helical angle of the guide plate is 42°, and the axial moving speed of the material is 0.8 m / h.

[0036] The rotary kiln is divided into the first preheating section, the second decomposition section, the third dechlorination section and the fourth cooling section from the kiln tail to the kiln head. In the second decomposition section, a counter-flow of carbon monoxide with a gas flow velocity of 2m / s is introduced to participate in the decomposition reaction.

[0037] The reaction conditions of each process section are as follows: the total residence time of the first preheating section is 50 min, the temperature is increased from 320°C to 500°C, and the oxygen concentration is 9±1 vol%; the total residence time of the second decomposition section is 90 min, the temperature is increased from 500°C to 650°C, the oxygen concentration is 13±1 vol%, and the carbon monoxide concentration is 0.4±0.1 vol%; the total residence time of the third dechlorination section is 60 min, the temperature is increased from 650°C to 950°C, the oxygen concentration is 21±1 vol%, and the water vapor concentration is 1.3±0.1 vol%; the total residence time of the fourth cooling section is 50 min, and the temperature is reduced from 950°C to 300°C.

[0038] Example 3 The stepwise calcination process for preparing praseodymium-neodymium oxide is carried out in a rotary kiln and specifically comprises the following steps: PrNd carbonate, NH4Cl and Al2O3 were mixed in weight proportions of 92 parts, 6 parts and 0.03 parts respectively, and then fed into the rotary kiln from the kiln tail. At the same time, oxygen with a countercurrent flow rate of 2.2 m / s was introduced from the kiln head into the rotary kiln to react with the materials moving from the kiln tail to the kiln head. Finally, PrNd oxide products were obtained at the kiln head discharge port. The tail gas generated by the rotary kiln was treated in turn by bag filter, SCR denitration system and water spray absorption tower. The final particulate matter emission was 2.1 mg / m 3 .

[0039] The rotation speed of the rotary kiln is 1.5 r / min, the helical angle of the guide plate is 44°, and the axial moving speed of the material is 0.8 m / h.

[0040] The rotary kiln is divided into the first preheating section, the second decomposition section, the third dechlorination section and the fourth cooling section from the kiln tail to the kiln head. In the second decomposition section, a counter-flow of carbon monoxide with a gas flow velocity of 2.2 m / s is introduced to participate in the decomposition reaction.

[0041] The reaction conditions of each process section are as follows: the total residence time of the first preheating section is 60 min, the temperature is increased from 320°C to 500°C, and the oxygen concentration is 9±1 vol%; the total residence time of the second decomposition section is 90 min, the temperature is increased from 500°C to 650°C, the oxygen concentration is 13±1 vol%, and the carbon monoxide concentration is 0.4±0.1 vol%; the total residence time of the third dechlorination section is 60 min, the temperature is increased from 650°C to 950°C, the oxygen concentration is 21±1 vol%, and the water vapor concentration is 1.3±0.1 vol%; the total residence time of the fourth cooling section is 50 min, and the temperature is reduced from 950°C to 300°C.

[0042] Comparative Example 1 The difference from Example 1 is that 88 parts by weight of praseodymium neodymium carbonate and 8 parts by weight of NH4Cl are used as raw materials, and Al2O3 is not added. The rest is the same as Example 1.

[0043] Comparative Example 2 The difference from Example 1 is that SiO2 of equal weight is used to replace Al2O3, and the rest is the same as Example 1.

[0044] Calculate the electricity consumption per ton of product (kWh / tREO) and the natural gas consumption per ton of product (m 3 / tREO), and the results are shown in Table 1.

[0045] The properties of the praseodymium-neodymium oxides prepared in Examples 1-3 and Comparative Examples 1-2 were tested respectively, and the testing methods were as follows: Total amount of rare earth (%): praseodymium-neodymium oxide was roasted in a muffle furnace at a temperature of 950°C for 1 h. The mass before and after roasting was weighed, and the loss on ignition was calculated by the formula: (mass of material before roasting - mass of material after roasting) / mass before roasting × 100%; the total amount of rare earth was calculated by the formula: (99.99% - loss on ignition) × 100%; Specific surface area (m 2 / g): tested by specific surface area and pore size analyzer; Acid solubility (%): Weigh 0.5 g of calcined praseodymium neodymium oxide and dissolve it in 10 mL of 68% nitric acid. After dissolving for 20 minutes, filter out the insoluble matter, weigh the insoluble matter after drying (g), and calculate the acid solubility. The calculation formula is: (0.5-mass of the insoluble matter after drying) / 0.5×100%.

[0046] Chlorine mass fraction (%): Tested in accordance with GB / T 12690.9-2003.

[0047] The calculation results are shown in Table 1.

[0048] Table 1 Data results

[0049] It can be seen from the test data in Table 1 that the staged calcination process used to prepare praseodymium-neodymium oxide in Examples 1-3 has low energy consumption through staged temperature control and the synergistic effect of Al2O3, and the total amount of rare earth in the prepared praseodymium-neodymium oxide product is ≥99.4%.

[0050] In Comparative Example 1, due to the lack of addition of Al2O3, the calcination was incomplete, ring formation was obvious, the electricity consumption per ton of product and the natural gas consumption per ton of product increased, the total amount of rare earth products decreased, and the acid solubility was significantly reduced.

[0051] In Comparative Example 2, due to the use of SiO2 instead of Al2O3, the temperature in the rotary furnace drops rapidly during the actual production process. In order to maintain the reaction temperature in the rotary furnace, the feed rate needs to be reduced, resulting in an extension of the production cycle, which in turn significantly increases the electricity consumption per ton of product and the natural gas consumption per ton of product.

Claims

1. A staged calcination process for preparing praseodymium-neodymium oxide, characterized in that: The process is carried out in a rotary kiln and specifically includes the following steps: PrNd carbonate, NH4Cl and Al2O3 are mixed in weight proportions of 88-92 parts, 6-8 parts and 0.02-0.03 parts, and then fed into a rotary kiln from the kiln tail. Meanwhile, oxygen is introduced into the rotary kiln from the kiln head in a reverse flow to react with the materials moving from the kiln tail to the kiln head, and finally a praseodymium-neodymium oxide product is obtained at the kiln head discharge port. The rotary kiln is divided into a first preheating section, a second decomposition section, a third dechlorination section and a fourth cooling section from the kiln tail to the kiln head, wherein carbon monoxide is introduced into the second decomposition section to participate in the decomposition reaction; The reaction conditions of each process section are as follows: the temperature of the first preheating section is 320-500°C, and the total residence time is 50-60min; the temperature of the second decomposition section is 500-650°C, and the total residence time is 80-90min; the temperature of the third dechlorination section is 650-950°C, and the total residence time is 60-70min; the temperature of the fourth cooling section is 950-300°C, and the total residence time is 50-60min.

2. The staged calcination process for preparing praseodymium-neodymium oxide according to claim 1, characterized in that: The rotating speed of the rotary kiln is 1-1.5 r / min, and the helical angle of the guide plate is 40-44°.

3. The stepwise calcination process for preparing praseodymium-neodymium oxide according to claim 1, characterized in that: The air flow velocity of the oxygen and carbon monoxide is 1.8-2.2 m / s.

4. The staged calcination process for preparing praseodymium-neodymium oxide according to claim 1, characterized in that: The method for preparing praseodymium neodymium carbonate comprises the following steps: The rare earth ore is sequentially subjected to acid dissolution and extraction separation to obtain a praseodymium-neodymium chloride solution; carbonate is added to the praseodymium-neodymium chloride solution for neutralization reaction to generate praseodymium-neodymium carbonate, wherein the rare earth oxide content is ≥45%.

5. The staged calcination process for preparing praseodymium-neodymium oxide according to claim 1, characterized in that: The D50 particle size of the praseodymium-neodymium carbonate is 30-40 μm, the particle size of NH4Cl is 80-200 mesh, and the specific surface area of ​​Al2O3 is 8-20 m 2 / g.

6. The staged calcination process for preparing praseodymium-neodymium oxide according to claim 1, characterized in that: The oxygen concentrations in the first preheating section, the second decomposition section, the third dechlorination section and the fourth cooling section are 8-10 vol%, 12-14 vol%, 20-23 vol% and 19-21 vol% respectively.

7. The staged calcination process for preparing praseodymium-neodymium oxide according to claim 1, characterized in that: The carbon monoxide concentration in the second decomposition stage is 0.3-0.5 vol%.

8. The staged calcination process for preparing praseodymium-neodymium oxide according to claim 1, characterized in that: The concentration of water vapor in the third dechlorination section is 1.2-1.5 vol%.

9. The staged calcination process for preparing praseodymium-neodymium oxide according to claim 1, characterized in that: The tail gas generated by the rotary kiln is processed in sequence by a bag filter, an SCR denitration system and a water spray absorption tower.

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