Method for preparing rare earth oxide from rare earth ore by nitric acid method

Abstract

The invention provides a method for preparing rare earth oxide from rare earth ore through a nitric acid method, and relates to the technical field of metallurgy and chemical engineering. S2, carrying out acid leaching on the pretreated rare earth ore; s3, neutralizing excessive nitric acid; s4, removing phosphorus; s5, further impurity removal; s6, extracting and separating; and S7, obtaining the micron-scale or nano-scale rare earth oxide. The method solves the problem that a large amount of gypsum solid waste is piled up in a sulfuric acid method, mineral smelting is free of waste water and waste gas, and the method is environmentally friendly. The materials used in the invention are common industrial products, are easy to purchase and are low in price; the whole process is short in flow, low in cost, wide in raw material source, low in energy consumption, easy to scale and easy to realize industrialization.

Description

Technical Field

[0001] The invention relates to the technical field of metallurgy and chemical engineering, and in particular to a method for preparing rare earth oxides, in particular micron or nanometer rare earth oxides, by using a rare earth ore nitric acid method. Background Art

[0002] Rare earths are known as the "gold" of industry and are an important strategic resource in my country. The current method of using fluorocarbon cerium ore, monazite or mixed rare earth ores is to beneficiate them before smelting. However, some ores cannot obtain good technical and economic indicators through beneficiation. They are currently unusable and in a stockpiled state, and urgently need to be developed. Moreover, beneficiation will produce tailings, which not only reduces the recovery rate of rare earth elements, but also contains many valuable elements such as rare earths, Fe, F, Nb, Sc, Ca, Mg, etc. that have not been utilized. The rare earth concentrate obtained by mineral processing is mainly smelted by the sulfuric acid method. The sulfuric acid roasting process produces a large amount of waste gas containing S and F. The process and equipment for recovering S and F are complicated. In addition, the sulfuric acid method inevitably produces a large amount of gypsum solid waste, and the storage and treatment causes waste of land resources and environmental pollution. At the same time, Ca resources are not utilized; although the alkaline method for treating rare earth concentrate does not produce harmful gases and has a small amount of waste slag, it is relatively environmentally friendly, but it has high requirements on the grade of the concentrate, the reaction time of the decomposition process is long, the operation process is discontinuous, the amount of NaOH is large, and the economic cost is relatively high; whether it is the sulfuric acid method or the alkaline method, the hydrochloric acid system is used to extract rare earths. Hydrochloric acid is highly corrosive and has high requirements on equipment materials.

[0003] Among rare earth products, micron-sized rare earth oxides (such as lanthanum oxide and cerium oxide) are usually cheaper. If they can be made into nano-sized rare earth oxides, their value can be increased several times. Currently, the main methods for preparing nano-sized rare earth oxides are: first, use sulfuric acid method, hydrochloric acid method, and alkali method to prepare micron-sized rare earth oxides, then dissolve in nitric acid to prepare nitrate rare earth precursors, and then use combustion method, flame spray pyrolysis method, precipitation method and other processes to produce nano-sized rare earth oxides. The process is complicated and lengthy. If nitric acid can be used throughout the process to separate and extract minerals, the refining process will be greatly shortened.

[0004] The prior art discloses a method for low-temperature pretreatment of concentrated sulfuric acid roasting and decomposing high-grade mixed rare earth concentrate. Although this method can achieve low energy consumption and high recovery rate of mixed rare earth concentrate decomposition, it requires rare earth grade REO ≥ 58%, and the best rare earth grade REO ≥ 65%, which is not suitable for low-grade rare earth ores. The prior art discloses a method for separating calcium ions from rare earth transformation calcium-magnesium sulfate rare earth solution by extraction. The method uses calcium-magnesium sulfate rare earth solution as raw material, and prepares Ca into calcium sulfate and Mg into magnesium sulfate after extraction and crystallization. Although it solves the technical problem that wastewater is difficult to treat in the existing extraction method for separating rare earth transformation, due to the use of traditional sulfuric acid method, Ca can only be converted into low-value calcium sulfate, and even become solid waste accumulation, which cannot fundamentally solve the waste of Ca resources and gypsum solid waste problems. The prior art also discloses cerium dioxide nanomaterials and their preparation methods and applications. This invention can synthesize cerium dioxide nanowires by hydrothermal method, but firstly, cerium nitrate hexahydrate needs to be prepared as raw material, and the overall process route is relatively long. Summary of the invention

[0005] The purpose of the present invention is to provide a method for preparing rare earth oxides, especially micron or nanometer, especially nanometer rare earth oxides, by a nitric acid method, which is used to solve the many shortcomings of the existing mineral-type rare earth ore smelting process that are difficult to solve and cannot be ignored. The present invention is applicable to rare earth concentrates, some rare earth ores and tailings, and has strong adaptability and wide sources of raw materials. The method can obtain rare earth nitrates, micron and nanometer rare earth oxides, calcium carbonate and magnesium oxide, which is not only applicable to a variety of mineral-type rare earth ores, but also improves the recovery rate of rare earth elements, realizes the comprehensive recovery of a variety of valuable elements, and can solve the pollution problem of gypsum solid waste from the source. The auxiliary materials are low in price, a variety of auxiliary materials are recycled, and the equipment is less corrosive, which greatly reduces the production cost, and the product has high added value, realizing the maximum utilization of resources. The method of the present invention can prevent the generation of "new tailings" from the source, solve the problem of large-scale storage of gypsum solid waste generated by the sulfuric acid method, and solve the problem of rare earth ore storage occupying land area and causing soil pollution and water pollution. The mineral smelting process does not generate waste water or waste gas, and the amount of solid waste is greatly reduced. In addition, the process does not use hydrochloric acid, which is more friendly to the equipment and the process is environmentally friendly and pollution-free. This process can produce rare earth nitrate products and nano-rare earth oxides in a shorter process, greatly reducing fixed investment and operating costs. Specifically:

[0006] A method for preparing rare earth oxides by nitric acid method comprises the following steps:

[0007] S1: Drying, crushing and classifying the rare earth ore, mixing the obtained rare earth ore powder with the additive and then roasting (or directly roasting without the additive), cooling the ore powder after roasting with the additive and then grinding, washing and filtering, to obtain the pretreated rare earth ore and fluorine-containing by-products. At this time, the pretreated rare earth ore is divided into two parts, one part is used for step S2, and the other part is used for step S3.

[0008] S2: The rare earth ore after pretreatment is pulped, and then excess nitric acid is added to the pulp for acid leaching. After the reaction is completed, the solid-liquid mixture is filtered and washed to obtain leaching solution 1 and leaching residue 1. In S2, an excess of nitric acid must be used to leach out some of the Ce and Pr elements that are oxidized during calcination. If the amount of nitric acid in S2 is reduced, a large amount of Ce and Pr will remain in the leaching residue. Even if the leaching residue is returned to S2, the acidity is insufficient and some Ce and Pr are difficult to leach.

[0009] S3: Mix the leaching solution 1 and the pretreated rare earth ore to neutralize the excess residual nitric acid in the leaching solution 1. After the reaction is completed, the solid-liquid mixture is filtered and washed to obtain the leaching solution 2 and the leaching residue 2. The leaching residue 2 is an intermediate and can continue to be leached using excess nitric acid.

[0010] S4: Add an iron source to the above-obtained leaching solution 2, stir for reaction, and then filter and wash to obtain a ferric phosphate dihydrate precipitate and a leaching solution after dephosphorization.

[0011] S5: The pH of the above-obtained post-phosphorus removal leaching solution is adjusted using magnesium oxide, and the solution is neutralized and filtered to obtain iron-thorium slag and post-impurity removal leaching solution.

[0012] S6: extracting and separating the impurity-removed leaching solution to obtain a single rare earth nitrate and a leaching solution after rare earth extraction.

[0013] S7: The single rare earth nitrate obtained in S6 is subjected to one-stage or multi-stage pyrolysis (after pyrolysis, rare earth oxides and nitrogen oxide gas are obtained, and the obtained nitrogen oxide gas is sent to a nitric acid absorption and regeneration device to obtain regenerated nitric acid) to obtain micron-sized rare earth oxides; or the single rare earth nitrate obtained in S6 can be used to prepare nano rare earth oxides (average particle size ≤ 500nm) by industrialized methods such as combustion method, flame spray pyrolysis method, precipitation method, etc. The present invention uses the nitric acid method to leaching rare earth ores to prepare rare earth nitrates faster and more conveniently, and can greatly shorten the process flow of preparing nano rare earth oxides as a whole. At the same time, the nitric acid can still be recycled when preparing nano rare earth oxides in the present invention.

[0014] S8: If the extractant in S6 is saponified with magnesium oxide or magnesium bicarbonate, ammonia evaporation is not required; when the extractant in S6 is saponified with ammonia water or ammonia gas, the pH of the rare earth extraction solution obtained in S6 is adjusted with magnesium oxide and then stripped and ammonia evaporated. The evaporated ammonia gas is condensed to prepare ammonia water, which can be recycled for extractant saponification. The liquid after ammonia evaporation is mainly a mixture of calcium and magnesium nitrates, and the main chemical equation is:

[0015] 2NH4NO3+MgO+H2O=Mg(NO3)2+2NH3.H2O

[0016] NH3.H2O= NH3↑+H2O

[0017] S9: The calcium-magnesium nitrate mixture obtained in S8 can be carbonized with carbon dioxide to obtain the Ca therein, and light calcium carbonate product and magnesium nitrate solution can be obtained after solid-liquid separation. The magnesium nitrate solution can be concentrated and frozen and crystallized to obtain magnesium nitrate crystals. The magnesium nitrate crystals can be thermally decomposed to obtain magnesium oxide and nitric acid, and both the magnesium oxide and the nitric acid can be recycled.

[0018] In the present invention, preferably, in step S1, the rare earth ore is fluorocarbon cerium ore, monazite or mixed rare earth ore, REO 0.5%~80%, and the particle size of the rare earth ore powder after crushing and grading is 80~150 mesh; the auxiliary agent used in the pretreatment stage is one or more of calcium carbonate, calcium oxide, sodium hydroxide, sodium carbonate, sodium bicarbonate, etc., and the obtained fluorine-containing by-product is CaF2 or NaF, the roasting temperature is 800~1000℃, the roasting time is 1~3h, the mass ratio of rare earth ore powder to auxiliary agent is 1:1~3:1, and when the ore powder is washed after roasting, the liquid-solid ratio is 5:1~10:1.

[0019] Preferably, in step S2, the liquid-to-solid ratio of the pulping is 2:1-4:1, the amount of nitric acid added is 300%-400% of the theoretical molar amount of nitric acid required for the reaction, the concentration of nitric acid is 40wt%-70wt%, the acid leaching reaction time is 1-3h, and the acid leaching reaction temperature is 70-95°C.

[0020] Preferably, in step S3, when neutralizing the residual acid, the liquid-to-solid ratio of the leaching solution 1 to the pretreated rare earth ore is 2:1-5:1, the reaction time for neutralizing the residual acid is 2-4 hours, and the reaction temperature is 60-90°C.

[0021] Preferably, in step S4, the iron source used for dephosphorization is one or more of iron powder, ferric nitrate, and iron oxide, the amount of iron source added is 100-150% of the theoretical amount, the reaction temperature is 80-130° C., and the reaction time is 1-3 h.

[0022] Preferably, in step S5, the pH of the post-phosphorus removal leaching solution is adjusted to 3-5 using magnesium oxide, the neutralization and impurity removal reaction time is 30 min-2 h, and the reaction temperature is 20-40°C.

[0023] Preferably, in step S6, the extractant is one or more of P204, P507, TBP, P350, and N263, the diluent is kerosene or alcohol, and the extractant is saponified using one or more of ammonia water, ammonia gas, magnesium oxide, and magnesium bicarbonate.

[0024] Preferably, in step S7, the pyrolysis method of the one-stage or multi-stage pyrolysis includes one or more methods of calcination pyrolysis, suspension roasting pyrolysis, atomization pyrolysis, etc.; the temperature of calcination pyrolysis is 500-1100° C., and the pyrolysis time is 3-6 hours.

[0025] Preferably, when ammonia water or ammonia gas is used as the saponifying extractant in S6, the stripping and evaporating ammonia in step S8 is carried out in an ammonia evaporation tower, the pH of the post-rare earth extraction leaching solution is adjusted to 10-12 using magnesium oxide, the pressure of the stripping and evaporating ammonia is 0.03-0.06 MPa, and the temperature is 80-100°C.

[0026] Preferably, in step S9, carbon dioxide is introduced to react until the pH of the calcium magnesium nitrate mixed solution is 7-7.5, and the reaction temperature is 20-40°C; the pyrolysis method of the magnesium nitrate crystals in S9 is the same as the pyrolysis method of the rare earth nitrate in S7, the pyrolysis temperature is 600-800°C, and the pyrolysis time is 4-6h.

[0027] The method of the present invention can prepare rare earth nitrates and (nano) rare earth oxides with a shorter process flow, has strong adaptability to raw materials, avoids rare earth losses caused by ore dressing, greatly improves the utilization rate of rare earth elements, and can also realize the recycling of other valuable elements; in the present invention, a variety of raw and auxiliary materials are recycled, no waste water and waste gas are generated, and the generation of gypsum solid waste is avoided from the source, and the acid leaching residue is small, the amount of solid waste is greatly reduced, and the use of hydrochloric acid is not used to reduce equipment corrosion, and the cost is significantly reduced. The materials used in the present invention are all common industrial products, easy to purchase and cheap; the entire process is short, low cost, wide source of raw materials, low energy consumption, easy to scale and industrialize.

[0028] The technical solution of the present invention has the following beneficial effects:

[0029] (1) The present invention eliminates the generation of a large amount of gypsum solid waste in the traditional sulfuric acid process from the source, is environmentally friendly, and utilizes Ca resources to make products.

[0030] (2) The process of preparing rare earth nitrate and nano rare earth oxides is greatly shortened, the production cost is reduced, and the product value is higher.

[0031] (3) This process is applicable to rare earth ores of different grades, and has strong raw material adaptability and a wide range of sources.

[0032] (4) The acids and alkalis used in the process (such as nitric acid, magnesium oxide, and ammonia water) can be recycled and regenerated, reducing the purchase of auxiliary materials and lowering direct processing costs. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] In order to more clearly illustrate the technical solutions in the embodiments of the present invention, the following briefly introduces the drawings required for use in the description of the embodiments. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without creative work.

[0034] Figure 1 The present invention is a process flow chart of the method for preparing (nano) rare earth oxides by the rare earth ore nitric acid method. DETAILED DESCRIPTION

[0035] In order to make the purpose, technical solution and advantages of the present invention more clear, the technical solution of the present invention will be described in detail below with reference to the accompanying drawings and specific embodiments.

[0036] The analysis results of the components of the rare earth ore raw materials used in the following examples are shown in Tables 1 to 3.

[0037] Table 1 Analysis results of various components of a rare earth concentrate

[0038]

[0039] Table 2 Analysis results of components of a rare earth tailings

[0040]

[0041] Table 3 Analysis results of various components of a rare earth ore

[0042]

[0043] Example 1

[0044] like Figure 1 As shown, a method for preparing (nano) rare earth oxides by nitric acid method specifically comprises the following steps:

[0045] S1: Dry and crush a rare earth concentrate in Table 1 to a particle size of about 100 mesh, mix the rare earth ore powder with the additive at a mass ratio of 1.67:1, calcine at 850°C for 1h, grind the ore powder after cooling, wash and filter at a liquid-to-solid ratio of 5:1, and obtain the pretreated rare earth ore.

[0046] S2: water and the pretreated rare earth ore are slurried at a liquid-to-solid ratio of 2:1, and then a theoretical amount of 335% nitric acid (60wt%) is added to the slurry for acid leaching at 90°C for 1 hour. After the reaction is completed, the solid-liquid mixture obtained is filtered and washed to obtain an leaching solution 1 and a leaching residue 1.

[0047] S3: Mix the leaching solution 1 and the pretreated rare earth ore in a liquid-to-solid ratio of 3:1, stir and react at 25°C for 2 hours, filter and wash after the reaction to obtain leaching solution 2 and leaching residue 2. The leaching residue 2 is an intermediate and can continue to be leached using excess nitric acid.

[0048] S4: Add 105% of the theoretical amount of ferric nitrate to the leaching solution 2, add a small amount of seed crystals, react at 115° C. for 2 h, filter and wash to obtain the dephosphorized leaching solution and ferric phosphate dihydrate.

[0049] S5: The pH value of the above-obtained post-phosphorus removal leaching solution is adjusted to 4.5 using magnesium oxide, the reaction time is 1 hour, the reaction temperature is 25° C., and the iron-thorium slag and the post-impurity removal leaching solution are obtained after neutralization and filtration.

[0050] S6: The impurity-removed leaching solution is extracted and separated using P507 (kerosene is used as a diluent) saponified with ammonia water to obtain a single rare earth nitrate and a leaching solution after rare earth extraction.

[0051] S7: atomizing and pyrolyzing the cerium nitrate obtained in S6 to prepare micron-sized cerium oxide, the pyrolysis temperature is 600° C., and the pyrolysis time is 5 hours.

[0052] S8: The rare earth extraction solution obtained in S6 is adjusted to pH 11 using magnesium oxide, and then transferred to an ammonia evaporation tower for stripping and ammonia evaporation at a pressure of 0.04 MPa and a temperature of 90°C. The evaporated ammonia gas is condensed to prepare ammonia water, which can be recycled for saponification of the extractant. The liquid after ammonia evaporation is mainly a mixture of calcium and magnesium nitrates.

[0053] S9: introducing carbon dioxide into the calcium magnesium nitrate mixed solution obtained in S8 until the pH of the slurry is 7.5 and the reaction temperature is 25°C; concentrating and crystallizing the filtrate (magnesium nitrate solution) to obtain magnesium nitrate crystals, and atomizing and pyrolyzing the magnesium nitrate crystals to prepare micron-sized magnesium oxide at a pyrolysis temperature of 700°C and a pyrolysis time of 5 hours.

[0054] In this embodiment, the leaching rates of the main rare earth elements are all above 98%, and the slag rate is only 2%; the obtained micron-grade cerium oxide meets the GB / T 4155-2012 standard, with an average particle size of 4.1 μm, a content of 99.52%, and a cerium recovery rate of 92.86%; the content of calcium carbonate is 98.81%, and the calcium recovery rate is 94.69%; the content of magnesium oxide is 95.36%, and the magnesium recovery rate is 91.10%; the content of ferric phosphate dihydrate is 97.11%, and the phosphorus recovery rate is 98.37%.

[0055] Example 2

[0056] A method for preparing (nano) rare earth oxides by nitric acid method is implemented according to the method described in Example 1, except that:

[0057] In step S7, the cerium nitrate obtained in S6 is used to prepare nano-scale cerium oxide by a precipitation method. Ammonia water is added to the cerium nitrate aqueous solution to adjust the pH of the solution until cerium hydroxide is precipitated. The precipitate is separated, washed, dried, and calcined at 600°C to obtain CeO2 microspheres.

[0058] The remaining experimental parameters are the same as those in Example 1.

[0059] The nano-cerium oxide obtained in this embodiment meets the GB / T 38061-2019 standard, has an average particle size of 59 nm, a content of 99.37%, and a cerium recovery rate of 91.20%; the content of calcium carbonate is 98.12%, and the calcium recovery rate is 95.25%; the content of magnesium oxide is 95.58%, and the magnesium recovery rate is 92.34%; the content of ferric phosphate dihydrate is 97.16%, and the phosphorus recovery rate is 98.08%.

[0060] Example 3

[0061] A method for preparing (nano) rare earth oxides by nitric acid method is implemented according to the method described in Example 1, except that:

[0062] In step S1, the raw material used is a rare earth tailing in Table 2. After the rare earth tailing is dried, crushed and classified, it is directly calcined at 900° C. for 2 h without mixing with an additive to obtain a pretreated rare earth ore.

[0063] In step S2, water and the pretreated rare earth ore are slurried at a liquid-to-solid ratio of 2:1, and then 130% of the theoretical amount of nitric acid (60wt%) is added to the slurry for acid leaching at 90°C for 3 hours. After the reaction is completed, the solid-liquid mixture obtained is filtered and washed to obtain an leaching solution 1 and a leaching residue 1.

[0064] In step S3, the leaching solution 1 and the pretreated rare earth ore are mixed at a liquid-to-solid ratio of 3:1, and stirred for reaction at 25°C for 2 hours. After the reaction is completed, the leaching solution 2 and the leaching residue 2 are obtained by filtering and washing. The leaching residue 2 is an intermediate and can continue to be leached using excess nitric acid.

[0065] The subsequent experimental parameters are the same as those in Example 1.

[0066] The micron-grade cerium oxide obtained in this embodiment meets the GB / T 4155-2012 standard, has an average particle size of 3.5 μm, a content of 99.57%, and a cerium recovery rate of 91.08%; the content of calcium carbonate is 98.15%, and the calcium recovery rate is 95.21%; the content of magnesium oxide is 95.63%, and the magnesium recovery rate is 92.05%; the content of ferric phosphate dihydrate is 97.09%, and the phosphorus recovery rate is 98.15%.

[0067] Example 4

[0068] A method for preparing (nano) rare earth oxides by nitric acid method is implemented according to the method described in Example 1, except that:

[0069] In step S1, the rare earth concentrate powder in Table 1 is mixed with an additive in a mass ratio of 3:1, calcined, washed with water, and filtered to obtain a pretreated rare earth ore.

[0070] The remaining experimental parameters are the same as those in Example 1.

[0071] The micron-sized cerium oxide obtained in this embodiment meets the GB / T 4155-2012 standard, has an average particle size of 4.2 μm, a content of 99.49%, and a cerium recovery rate of 63.46%; the content of calcium carbonate is 98.11%, and the calcium recovery rate is 93.25%; the content of magnesium oxide is 95.50%, and the magnesium recovery rate is 93.13%; the content of ferric phosphate dihydrate is 97.15%, and the phosphorus recovery rate is 81.06%.

[0072] Example 5

[0073] A method for preparing (nano) rare earth oxides by nitric acid method is implemented according to the method described in Example 1, except that:

[0074] In step S2, after slurrying the water and the pretreated rare earth ore, 150% of the theoretical amount of nitric acid (60wt%) is added to the slurry for acid leaching for 1 hour. After the reaction is completed, the solid-liquid mixture obtained is filtered and washed to obtain leaching solution 1 and leaching residue 1.

[0075] The remaining experimental parameters are the same as those in Example 1.

[0076] The micron-sized cerium oxide obtained in this embodiment meets the GB / T 4155-2012 standard, has an average particle size of 4.6 μm, a content of 99.37%, and a cerium recovery rate of 37.99%; the content of calcium carbonate is 98.05%, and the calcium recovery rate is 91.86%; the content of magnesium oxide is 95.61%, and the magnesium recovery rate is 91.22%; the content of ferric phosphate dihydrate is 97.06%, and the phosphorus recovery rate is 43.28%.

[0077] The above is only a specific embodiment of the present invention, but the protection scope of the present invention is not limited thereto. Any person skilled in the art who is familiar with the technical field can easily think of changes or substitutions within the technical scope disclosed by the present invention, which should be included in the protection scope of the present invention. Therefore, the protection scope of the present invention should be based on the protection scope of the claims.

Claims

1. A method for preparing rare earth oxides by nitric acid method, characterized in that: include: S1: drying, crushing and classifying the rare earth ore, roasting, crushing and washing the obtained rare earth ore powder to obtain the pretreated rare earth ore and fluorine-containing byproducts; S2: pulping a portion of the pretreated rare earth ore, then adding excess nitric acid to the pulp for acid leaching, filtering and washing the solid-liquid mixture obtained after the reaction to obtain a leaching solution 1 and a leaching residue 1; S3: mixing the leaching solution 1 with another part of the pretreated rare earth ore, filtering and washing the solid-liquid mixture obtained after the reaction to obtain the leaching solution 2 and the leaching residue 2, and returning the leaching residue 2 to S2 for acid leaching; S4: adding an iron source to the leaching solution 2, filtering and washing after the reaction to obtain an iron phosphate precipitate and a leaching solution after dephosphorization; S5: adjusting the pH of the post-phosphorus removal leaching solution with magnesium oxide, neutralizing and filtering to obtain iron-thorium slag and post-impurity removal leaching solution; S6: extracting and separating the impurity-removed leaching solution to obtain a single rare earth nitrate and a leaching solution after rare earth extraction; S7: pyrolyzing the single rare earth nitrate obtained in S6 to obtain micron-sized rare earth oxides; or preparing nano rare earth oxides from the single rare earth nitrate obtained in S6 by one or more methods selected from the group consisting of combustion, flame spray pyrolysis, and precipitation.

2. The method according to claim 1, characterized in that The method further comprises S8: when the extractant used in S6 is saponified with ammonia water or ammonia gas, the pH of the rare earth extraction leaching solution obtained in S6 is adjusted with magnesium oxide, and then the ammonia is stripped and evaporated, and the ammonia is circulated for saponification of the extractant.

3. The method according to claim 2, characterized in that The method further comprises S9: introducing carbon dioxide into the liquid phase remaining after stripping and distilling ammonia in S8, obtaining a light calcium carbonate product and a magnesium nitrate solution after solid-liquid separation, concentrating the magnesium nitrate solution and freezing and crystallizing it to obtain magnesium nitrate crystals, thermally decomposing the magnesium nitrate crystals to obtain magnesium oxide and nitric acid, and recycling the magnesium oxide and nitric acid.

4. The method according to claim 1 is characterized in that the rare earth ore in S1 is at least one selected from bastnaesite, monazite, and mixed rare earth ore, REO is 0.5%~80%, and the particle size of the rare earth ore powder after crushing and grading is 80~150 mesh; the roasting temperature is 800~1000℃, the roasting time is 1~3h, and when the ore powder is washed after roasting, the liquid-to-solid ratio is 5:1~10:1, and the obtained fluorine-containing by-product is CaF2 or NaF.

5. The method according to claim 1 is characterized in that the liquid-to-solid ratio of pulping in S2 is 2:1~4:1, the amount of nitric acid added is 300%~400% of the theoretical molar amount of nitric acid required for the reaction, the concentration of nitric acid is 40wt%~70wt%, the acid leaching reaction time is 1~3h, and the acid leaching reaction temperature is 70~95°C.

6. The method according to claim 1 is characterized in that, in S3, when neutralizing the residual acid, the liquid-to-solid ratio of the leaching solution 1 to the pretreated rare earth ore is 2:1-5:1, the reaction time for neutralizing the residual acid is 2-4 hours, and the reaction temperature is 60-90°C.

7. The method according to claim 1, characterized in that: The iron source used in the phosphorus removal in S4 is one or more of iron powder, iron nitrate, and iron oxide, the amount of the iron source added is 100-150% of the theoretical amount, the reaction temperature is 80-130°C, and the reaction time is 1-3h; In S5, the pH of the post-phosphorus removal solution is adjusted to 3-5 using magnesium oxide, the neutralization and impurity removal reaction time is 30min-2h, and the reaction temperature is 20-40℃; The extractant in S6 is selected from one or more of P204, P507, TBP, P350, and N263, the diluent is kerosene or alcohol, and the extractant is saponified using one or more of ammonia water, ammonia gas, magnesium oxide, and magnesium bicarbonate.

8. The method according to claim 1, characterized in that: The pyrolysis method in S7 is selected from one or more of calcination pyrolysis, suspension roasting pyrolysis, and atomization pyrolysis; the calcination pyrolysis temperature is 500-1100° C., and the pyrolysis time is 3-6 hours.

9. The method according to claim 2, characterized in that: In S8, the stripping and evaporating of ammonia is carried out in an ammonia evaporation tower, and the pH of the leaching solution after rare earth extraction is adjusted to 10-12 using magnesium oxide. The pressure of the stripping and evaporating of ammonia is 0.03-0.06 MPa, and the temperature is 80-100°C.

10. The method according to claim 3, characterized in that carbon dioxide is introduced into S9 to react until the pH of the calcium magnesium nitrate mixed solution is 7-7.5, and the reaction temperature is 20-40°C; the pyrolysis method of the magnesium nitrate crystals in S9 is the same as the pyrolysis method of the rare earth nitrate in S7, the pyrolysis temperature is 600-800°C, and the pyrolysis time is 4-6h.

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