Method for decomposing monazite at low temperature

Abstract

The invention provides a method for decomposing monazite at low temperature, and relates to the technical field of crossing of metallurgy and chemical industry. The method for decomposing the monazite at the low temperature comprises the steps of grading and roasting treatment, washing and filtering treatment, acid leaching treatment, reduction treatment, P and Fe removal treatment and extraction separation treatment. According to the method, the leaching rate of main rare earth elements, the recovery rate of the rare earth elements, the removal rate of P and Fe and the like are synergistically improved creatively through mixed roasting, washing, filtering, pulping, stirring leaching, reducing agent reduction, iron source adding and neutralizing agent neutralization of monazite mineral powder and auxiliaries; the method is high in resource utilization rate, low in production cost, short in process, easy to operate and high in efficiency, thereby being suitable for large-scale industrial production.

Description

Technical Field

[0001] The invention relates to the technical field of the intersection of metallurgy and chemical industry, and in particular to a method for decomposing monazite at low temperature. Background Art

[0002] Monazite is a rare earth phosphate, one of the important rare earth minerals, and the earliest rare earth mineral to be used in industry. Monazite is mainly light rare earth, but the content of medium and heavy rare earth is higher than that of mixed light rare earth ores. Before the development of ionic rare earth ores, it was the main source of medium and heavy rare earths in my country.

[0003] At present, the more mature industrial production processes of monazite include caustic soda leaching and sulfuric acid roasting. The caustic soda leaching method uses about 50% sodium hydroxide solution to decompose monazite at 140-160℃ for 5-18h, converting the rare earth into insoluble rare earth hydroxide. After separating and washing the rare earth hydroxide, it is dissolved in hydrochloric acid. The filter cake left after the dissolution can also be completely dissolved in hydrochloric acid.

[0004] Although the above-mentioned monazite treatment process can convert phosphorus in monazite into trisodium phosphate products, and the overall utilization rate of rare earths is also relatively high, it also has many technical disadvantages: 1) The monazite leaching process is complicated and lengthy, and needs to go through alkali conversion-hydrochloric acid partial dissolution-hydrochloric acid full dissolution, with too much solid-liquid conversion; 2) The grade requirements for monazite concentrate are relatively high. When the content of impurities such as silicon and titanium in the concentrate is relatively high, the viscosity of the reaction system increases during alkali conversion, resulting in dirt agglomeration on the wall and bottom of the reaction pot, or making it difficult for the gas produced by decomposition to dissipate, resulting in "swelling" and "bubbling" phenomena; 3) The product after alkali decomposition is a very concentrated slurry, and solid-liquid separation is difficult; 4) The concentration of strong alkali during alkali decomposition is high, the reaction temperature is high, the reaction time is long, and the material requirements for equipment are relatively high, which increases the construction and maintenance costs.

[0005] The sulfuric acid roasting method uses concentrated sulfuric acid to react monazite concentrate at 200-300℃ for 2-4 hours. Although this method has slightly lower requirements for the concentrate grade, it will produce a large amount of harmful gases such as fluorine and sulfur during production.

[0006] Chinese patent CN111020242A discloses a process for smelting and separating uranium, thorium and rare earth from monazite concentrate. The method is to prepare rare earth chloride, trisodium phosphate, uranium products and thorium hydroxide by crushing, alkali decomposition, hydrochloric acid dissolution, and complete dissolution of slag hydrochloric acid. Although the recovery rate of valuable resources such as uranium, thorium and rare earth is greater than 95%, this process requires three treatments to completely dissolve the rare earth elements in the monazite concentrate, multiple solid-liquid conversions, and the mineral dissolution process is complicated and cumbersome; the quality requirements of monazite concentrate are high, and the decomposition conditions of high-concentration and long-term strong alkaline solution are relatively harsh. Chinese patent CN115818694A discloses a method for treating monazite, mixing monazite with high-concentration sulfuric acid, heating and reacting, and the P2O5 decomposition rate is greater than 99.5%; although this process reduces the decomposition temperature of monazite, it is not suitable for low-grade monazite ore. The same is true for Chinese patent CN103103349A, which is aimed at high-grade concentrates. Fluorine complexes will be produced during the acid-base combined process, and the recovery rate of rare earth elements by heating decomposition is not high.

[0007] Chinese patent CN105441674A discloses a method for comprehensive recovery of phosphorus and rare earth from monazite-containing phosphate ore, which uses phosphoric acid to leach the monazite-containing phosphate ore to separate apatite from monazite, and then uses sulfuric acid to strengthen roasting the obtained monazite slag, and also needs to add fluorine-containing compounds and iron-containing compounds to strengthen roasting at 250-500°C. Obviously, this process is relatively complicated, and fluorine and sulfuric acid are roasted at high temperatures, which has high requirements on equipment materials.

[0008] Chinese patent CN109735706A discloses a method for treating monazite using a two-stage hot alkali decomposition process. This method abandons the traditional method of acid-base mixed leaching and multiple acid treatments, and adopts a two-stage method of grinding leaching and stirring leaching to treat monazite materials. However, it is aimed at monazite concentrate with REO50-65%, which is obviously a high-grade monazite ore and is not suitable for low-grade monazite ore. Chinese patent CN117144159A discloses a method for reconstructing monazite phosphate rare earth phases with liquid alkali, which is obtained by controlling the liquid-solid ratio of alkali solution and monazite powder, ultrasonic vibration and stirring, and long-term reaction after solid-liquid separation; the recovery of rare earth elements is not considered, and it is also aimed at high-grade concentrate, which is also not suitable for low-grade monazite ore.

[0009] Chinese patent CN114231740A discloses a method for decomposing monazite using composite microorganisms. The monazite concentrate is decomposed by composite microorganisms through two-step leaching, using waste from industrial and agricultural production as an energy source. The organic acid produced can be decomposed by microorganisms in nature, which has little impact on the environment. The organic acids produced are all weak acids, which reduces the loss of equipment and has no environmental pollution. Although it belongs to green metallurgy, the decomposition efficiency is not high and the recovery efficiency of rare earth elements is low.

[0010] In summary, the current monazite treatment process has many shortcomings that are difficult to solve and cannot be ignored. Therefore, it is necessary to develop a new low-cost, green, and short-process monazite treatment process that overcomes the above-mentioned defects. Summary of the invention

[0011] In order to solve the technical problems existing in the prior art of monazite treatment process, such as multiple acid and / or alkali solid-liquid conversions, complicated mineral dissolution process, high quality requirements for monazite concentrate, difficulty in alkali decomposition, acid decomposition corrosion of reactor walls, low removal rate of impurities such as phosphorus and iron, low recovery rate of rare earth elements, long process flow, and high cost, the embodiment of the present invention provides a low-cost, green, and short-process method for low-temperature decomposition of monazite. The technical solution is as follows:

[0012] A method for low-temperature decomposition of monazite, the method for low-temperature decomposition of monazite comprising the following steps:

[0013] S1, classification and roasting treatment: drying the monazite concentrate, crushing and classifying it to obtain graded ore powder; mixing the graded ore powder with an additive and then roasting it to obtain a roasted material;

[0014] S2, washing and filtering treatment: washing and filtering the roasted material in S1 to obtain F-containing washing water and pre-treated rare earth ore;

[0015] S3, acid leaching treatment: pulping the pretreated rare earth ore obtained in S2, adding an acid solution, and stirring and leaching at normal temperature and pressure. After the leaching is completed, filtering is performed to obtain a rare earth acid leaching solution, and the filter residue is washed to obtain a leaching residue;

[0016] S4, reduction treatment: adding a reducing agent to the rare earth acid leaching solution of S3, and stirring the mixture to react, thereby obtaining a reduced rare earth leaching solution;

[0017] S5, P and Fe removal treatment: adding an iron source and a neutralizer to the reduced rare earth leaching solution of S4, stirring the reaction, adjusting the pH of the reduced rare earth leaching solution, and then filtering to obtain a leaching solution after impurities are removed;

[0018] S6, extraction and separation treatment: extract and separate the impurity-removed leaching solution of S5 to obtain a single rare earth salt, which is used to prepare a single rare earth oxide.

[0019] Optionally, in S1, the REO of the monazite concentrate is 20-75%, and the particle size of the rare earth ore powder after crushing and grading is 100-400 mesh; the auxiliary agent used during calcination is one or more of sodium bicarbonate, sodium carbonate, calcium oxide, calcium nitrate, calcium chloride, calcium fluoride, sodium fluoride and other sodium-containing, calcium-containing, and fluorine-containing compounds.

[0020] Optionally, the particle size of the rare earth ore powder after crushing and classification is 250-300 mesh.

[0021] Optionally, in S1, the mass ratio of the graded mineral powder to the additive is 1:0.3-1:1, the roasting temperature is 500-1200°C, and the roasting time is 0.5-5h.

[0022] Optionally, in S2, the liquid-to-solid ratio of the washing process is 2:1-10:1, and washing is continued for multiple times until the pH of the washing water is 7-8, the washing time is 10min-3h, and the washing temperature is 50-100°C; the F-containing washing water mainly contains elements such as P, F, and S. After pretreatment, the rare earth elements in the rare earth ore are increased by 0.2-7% compared with monazite concentrate, and the P content is reduced by 1-10% compared with monazite concentrate.

[0023] Optionally, in S2, the liquid-to-solid ratio of the washing process is 3:1-6:1, and washing is continued for multiple times until the pH of the washing water is 7-8. The washing time is 30min-1h, and the washing temperature is 70-90°C; the F-containing washing water mainly contains elements such as P, F, and S. After pretreatment, the rare earth elements in the rare earth ore are increased by 0.5-7% compared with monazite concentrate, and the P content is reduced by 2-10% compared with monazite concentrate.

[0024] Optionally, in S3, the liquid-to-solid ratio of pulping is 1:2-5:1, the acid solution is nitric acid, hydrochloric acid or sulfuric acid, the amount added is 100-500% of the molar amount of acid required to participate in the reaction, the acid leaching reaction time is 1-6h, and the acid leaching reaction temperature is 50-100°C; the liquid-to-solid ratio of the filter residue washing is 2:1-6:1, the washing time is 20min-2h, and the washing temperature is 50-100°C; the leaching rate of the main rare earth elements treated by acid leaching is 50.0-100%, and the residue rate is 5.0-45.0%.

[0025] Optionally, in S3, the liquid-to-solid ratio of pulping is 2:1-5:1, the acid solution is nitric acid, hydrochloric acid or sulfuric acid, the amount added is 300-450% of the molar amount of acid required for the reaction, the acid leaching reaction time is 1-3h, and the acid leaching reaction temperature is 70-90°C; the liquid-to-solid ratio of the filter residue washing is 3:1-5:1, the washing time is 30min-1h, and the washing temperature is 70-90°C; the leaching rate of the main rare earth elements treated by acid leaching is 80.0-100%, and the residue rate is 5.0-15.0%.

[0026] Optionally, in S4, the reducing agent is one or more of hydrogen peroxide and thiourea, the amount of reducing agent added is 0.5-5% of the raw material, the reduction reaction time is 20min-2h, the reaction temperature is 10-60°C; the reduction rate of the tetravalent cerium treated by reduction is 60.0-100%.

[0027] Optionally, in S4, the reducing agent is one or more of hydrogen peroxide and thiourea, the amount of reducing agent added is 1-3% of the raw material, the reduction reaction time is 30min-1h, the reaction temperature is 30-50°C; the reduction rate of the tetravalent cerium treated by reduction is 80.0-100%.

[0028] Optionally, in S5, the iron source is one or more of ferric nitrate, ferric chloride, ferric sulfate, and iron powder, the neutralizer is one or more of magnesium oxide and calcium oxide, the amount of iron source added is 50-200% of the theoretical amount of iron phosphate generated, the pH of the rare earth leaching solution is adjusted to 0.5-6 using the neutralizer, the neutralization and impurity removal reaction time is 30min-5h, and the reaction temperature is 10-60°C; the removal rates of P and Fe in the P and Fe removal treatment are 70.0-100% and 90.0-100%, respectively.

[0029] Optionally, in S5, the iron source is one or more of ferric nitrate, ferric chloride, ferric sulfate, and iron powder, the neutralizer is one or more of magnesium oxide and calcium oxide, the amount of iron source added is 70-120% of the theoretical amount of iron phosphate generated, the pH of the rare earth leaching solution is adjusted to 2-4 using the neutralizer, the neutralization and impurity removal reaction time is 2-4h, and the reaction temperature is 30-50°C; the removal rates of P and Fe in the P and Fe removal treatment are 90.0-100% and 95.0-100%, respectively.

[0030] Optionally, in S6, the extractant for extraction and separation treatment is one or more of P204, P507, TBP, P350, N263, N235 and other commonly used rare earth extractants, the diluent is kerosene or alcohol, and the extractant is saponified with ammonia water.

[0031] Optionally, in S6, the single rare earth oxide includes micron rare earth oxide and nano rare earth oxide with an average particle size of ≤500nm; wherein the average particle size of the micron rare earth oxide is 1-10μm, the content is 98.0-100%, and the rare earth recovery rate is 90.0-99.99%; the content of the nano rare earth oxide with an average particle size of ≤500nm is 98.0-100%, and the rare earth recovery rate is 90.0-99.99%.

[0032] Optionally, in S6, micron rare earth oxides are prepared by one-stage or multi-stage pyrolysis, and nano rare earth oxides with an average particle size of ≤500 nm are prepared by combustion, flame spray pyrolysis or precipitation, or other industrialized methods.

[0033] Compared with the prior art, the above technical solution has at least the following beneficial effects:

[0034] The above scheme, the present invention proposes a method for low-temperature decomposition of monazite, which can solve the technical problems existing in the prior art monazite treatment process, such as multiple acid and / or alkali solid-liquid conversions, complex and cumbersome mineral dissolution process, high quality requirements for monazite concentrate, difficulty in alkali decomposition, acid decomposition corrosion of reactor walls, low removal rate of impurities such as phosphorus and iron, low recovery rate of rare earth elements, long process flow, and high cost.

[0035] The method of the present invention achieves a leaching rate of more than 95% for main rare earth elements, a recovery rate of more than 90% for rare earth elements, and a removal rate of more than 99% for P and Fe through the mixed roasting, washing, filtering, beating, stirring leaching, reducing agent reduction, adding iron source, and neutralizing with a neutralizing agent of monazite ore powder and an auxiliary agent.

[0036] The invention is a brand-new process for decomposing monazite, which is applicable to monazite concentrates of different grades, especially to low-grade monazite concentrates of 20-40% which are difficult to adapt to in the prior art. It broadens the source of raw materials, reduces the cost of raw materials, and promotes the industrialization process of monazite decomposition.

[0037] The method of the present invention greatly simplifies the dissolution process of rare earth elements in monazite concentrate, including technical advantages such as no use of strong alkali, less solid-liquid conversion times, strong operability, and no waste water and waste gas generation in the overall mineral smelting. It is green and environmentally friendly, and only acid can be used to decompose monazite at normal temperature and pressure, with low requirements for leaching equipment; and the acid can be recycled.

[0038] The method of the present invention can produce single acid earth products and micron-level and nano-level rare earth oxides through low-cost, green and short processes, greatly reducing investment and equipment maintenance costs. This process provides new ideas and new processes for the treatment and development of monazite, and provides a demonstration for the comprehensive utilization of monazite. The existing technologies are not simply combined, such as combining microbial decomposition and multiple alkaline dissolution, but the advantages and disadvantages of the existing technologies are fully considered, and the technical prejudice is overcome to obtain the method of the present invention.

[0039] The method of the present invention can obtain rare earth nitrates, rare earth chlorides, and nanometer or micron rare earth oxides, and is not only suitable for low-, medium-, and high-grade monazite concentrates, but also greatly simplifies the leaching process of the monazite concentrate. The leaching temperature is low, the time is short, and the requirements for equipment materials are relatively low, which greatly reduces the production cost. In addition, the method has a wide variety of products and a high market added value, which is conducive to large-scale industrial production and popularization.

[0040] In summary, compared with other traditional methods, the method of the present invention creatively improves the leaching rate of major rare earth elements, the recovery rate of rare earth elements, the removal rate of P and Fe and other properties through mixed roasting, washing, filtering, pulping, stirring leaching, reducing agent reduction, iron source, and neutralization by neutralizing agent of monazite ore powder and additives; and has high resource utilization, low production cost, short process, easy operation, and high efficiency, so it is suitable for large-scale industrial production. BRIEF DESCRIPTION OF THE DRAWINGS

[0041] 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.

[0042] Figure 1 The present invention is a process flow chart of a method for low-temperature decomposition of monazite. DETAILED DESCRIPTION

[0043] The technical solution of the present invention is described below in conjunction with the accompanying drawings.

[0044] In the embodiments of the present invention, words such as "exemplarily" and "for example" are used to indicate examples, illustrations or explanations. Any embodiment or design described as "example" in the present invention should not be interpreted as being more preferred or more advantageous than other embodiments or designs. Specifically, the use of the word "example" is intended to present the concept in a specific way. In addition, in the embodiments of the present invention, the meaning expressed by "and / or" can be both, or it can be either of the two.

[0045] In the embodiments of the present invention, "image" and "picture" can sometimes be used interchangeably. It should be noted that when the difference between them is not emphasized, the meanings they want to express are the same. "of", "corresponding" and "corresponding" can sometimes be used interchangeably. It should be noted that when the difference between them is not emphasized, the meanings they want to express are the same.

[0046] In the embodiments of the present invention, sometimes a subscript such as W1 may be written as a non-subscript such as W1. When the difference is not emphasized, the meanings to be expressed are consistent.

[0047] In order to make the technical problems, technical solutions and advantages to be solved by the present invention more clear, a detailed description will be given below with reference to the accompanying drawings and specific embodiments.

[0048] A method for low-temperature decomposition of monazite, the method for low-temperature decomposition of monazite combined with Figure 1 Follow these steps:

[0049] S1, classification and roasting treatment: drying the monazite concentrate, crushing and classifying it to obtain graded ore powder; mixing the graded ore powder with an additive and then roasting it to obtain a roasted material;

[0050] S2, washing and filtering treatment: washing and filtering the roasted material in S1 to obtain F-containing washing water and pre-treated rare earth ore;

[0051] S3, acid leaching treatment: pulping the pretreated rare earth ore obtained in S2, adding an acid solution, and stirring and leaching at normal temperature and pressure. After the leaching is completed, filtering is performed to obtain a rare earth acid leaching solution, and the filter residue is washed to obtain a leaching residue;

[0052] S4, reduction treatment: adding a reducing agent to the rare earth acid leaching solution of S3, and stirring the mixture to react, thereby obtaining a reduced rare earth leaching solution;

[0053] S5, P and Fe removal treatment: adding an iron source and a neutralizer to the reduced rare earth leaching solution of S4, stirring the reaction, adjusting the pH of the reduced rare earth leaching solution, and then filtering to obtain a leaching solution after impurities are removed;

[0054] S6, extraction and separation treatment: extract and separate the impurity-removed leaching solution of S5 to obtain a single rare earth salt, which is used to prepare a single rare earth oxide.

[0055] In particular, in S1, the REO of the monazite concentrate is 20-75%, and the particle size of the rare earth ore powder after crushing and grading is 100-400 mesh; the auxiliary agent used during calcination is one or more of sodium bicarbonate, sodium carbonate, calcium oxide, calcium nitrate, calcium chloride, calcium fluoride, sodium fluoride and other sodium-containing, calcium-containing, and fluorine-containing compounds.

[0056] In particular, the particle size of the rare earth ore powder after crushing and classification is 250-300 mesh.

[0057] In particular, in S1, the mass ratio of the graded mineral powder to the additive is 1:0.3-1:1, the roasting temperature is 500-1200°C, and the roasting time is 0.5-5h.

[0058] In particular, in S2, the liquid-to-solid ratio of the washing process is 2:1-10:1, and washing is continued for multiple times until the pH of the washing water is 7-8. The washing time is 10min-3h, and the washing temperature is 50-100°C; the F-containing washing water mainly contains elements such as P, F, and S. After pretreatment, the rare earth elements in the rare earth ore are increased by 0.2-7% compared with monazite concentrate, and the P content is reduced by 1-10% compared with monazite concentrate.

[0059] In particular, in S2, the liquid-to-solid ratio of the washing process is 3:1-6:1, and washing is continued for multiple times until the pH of the washing water is 7-8. The washing time is 30min-1h, and the washing temperature is 70-90°C; the F-containing washing water mainly contains elements such as P, F, and S. After pretreatment, the rare earth elements in the rare earth ore are increased by 0.5-7% compared with monazite concentrate, and the P content is reduced by 2-10% compared with monazite concentrate.

[0060] In particular, in S3, the liquid-to-solid ratio of pulping is 1:2-5:1, the acid solution is nitric acid, hydrochloric acid or sulfuric acid, the amount added is 100-500% of the molar amount of acid required for the reaction, the acid leaching reaction time is 1-6h, and the acid leaching reaction temperature is 50-100°C; the liquid-to-solid ratio of the filter residue washing is 2:1-6:1, the washing time is 20min-2h, and the washing temperature is 50-100°C; the leaching rate of the main rare earth elements treated by acid leaching is 50.0-100%, and the residue rate is 5.0-45.0%.

[0061] In particular, in S3, the liquid-to-solid ratio of pulping is 2:1-5:1, the acid solution is nitric acid, hydrochloric acid or sulfuric acid, the amount added is 300-450% of the molar amount of acid required for the reaction, the acid leaching reaction time is 1-3h, and the acid leaching reaction temperature is 70-90°C; the liquid-to-solid ratio of the filter residue washing is 3:1-5:1, the washing time is 30min-1h, and the washing temperature is 70-90°C; the leaching rate of the main rare earth elements treated by acid leaching is 80.0-100%, and the residue rate is 5.0-15.0%.

[0062] In particular, in S4, the reducing agent is one or more of hydrogen peroxide and thiourea, the amount of the reducing agent added is 0.5-5% of the raw material, the reduction reaction time is 20min-2h, the reaction temperature is 10-60°C; the reduction rate of the tetravalent cerium treated by reduction is 60.0-100%.

[0063] In particular, in S4, the reducing agent is one or more of hydrogen peroxide and thiourea, the amount of reducing agent added is 1-3% of the raw material, the reduction reaction time is 30min-1h, and the reaction temperature is 30-50°C; the reduction rate of the tetravalent cerium treated by reduction is 80.0-100%.

[0064] In particular, in S5, the iron source is one or more of ferric nitrate, ferric chloride, ferric sulfate, and iron powder, the neutralizer is one or more of magnesium oxide and calcium oxide, the amount of the iron source added is 50-200% of the theoretical amount of iron phosphate generated, the pH of the rare earth leaching solution is adjusted to 0.5-6 using the neutralizer, the neutralization and impurity removal reaction time is 30min-5h, and the reaction temperature is 10-60°C; the removal rates of P and Fe in the removal treatment are 70.0-100% and 90.0-100%, respectively.

[0065] In particular, in S5, the iron source is one or more of ferric nitrate, ferric chloride, ferric sulfate, and iron powder, the neutralizer is one or more of magnesium oxide and calcium oxide, the amount of the iron source added is 70-120% of the theoretical amount of iron phosphate generated, the pH of the rare earth leaching solution is adjusted to 2-4 using the neutralizer, the neutralization and impurity removal reaction time is 2-4h, and the reaction temperature is 30-50°C; the removal rates of P and Fe in the removal treatment are 90.0-100% and 95.0-100%, respectively.

[0066] In particular, in S6, the extractant for the extraction and separation treatment is one or more of P204, P507, TBP, P350, N263, N235 and other commonly used rare earth extractants, the diluent is kerosene or alcohol, and the extractant is saponified using ammonia water.

[0067] In particular, in S6, the single rare earth oxide includes micron rare earth oxide and nano rare earth oxide with an average particle size of ≤500nm; among them, the average particle size of the micron rare earth oxide is 1-10μm, the content is 98.0-100%, and the rare earth recovery rate is 90.0-99.99%; the content of the nano rare earth oxide with an average particle size of ≤500nm is 98.0-100%, and the rare earth recovery rate is 90.0-99.99%.

[0068] In particular, in S6, micron rare earth oxides are prepared by one-stage or multi-stage pyrolysis, and nano rare earth oxides with an average particle size of ≤500 nm are prepared by combustion, flame spray pyrolysis or precipitation and other industrialized methods.

[0069] Example 1

[0070] A method for low-temperature decomposition of monazite, wherein the composition of monazite is 63.4wt.%, REO, 11.87wt.%, P, 1.65wt.%, Si, 0.93wt.%, Ca, 0.35wt.%, Fe, 0.26wt.%, Zr, 0.29wt.%, Pb, 0.26wt.%, Na, 0.15wt.%, and the rest are unavoidable impurities; the method for low-temperature decomposition of monazite comprises the following steps:

[0071] S1, classification and roasting treatment: drying the monazite concentrate, crushing and classifying it into 300 mesh ore powder, and obtaining graded ore powder; mixing the graded ore powder with a mixed auxiliary agent of sodium bicarbonate, sodium carbonate and sodium fluoride at a mass ratio of 1:0.7, roasting at 850°C for 2h, and obtaining a roasted material;

[0072] S2, washing and filtering treatment: the calcined material in S1 is washed and filtered, the liquid-to-solid ratio of the washing process is 3:1, and the washing is continued for multiple times until the pH of the washing water is 7.7, the washing time is 30 minutes, and the washing temperature is 90°C; F-containing washing water and pre-treated rare earth ore are obtained; wherein, the contents of each component in the F-containing washing water are P 8.72g / L, F 0.89g / L, and the contents of each component in the pre-treated rare earth ore are REO 69.70wt.%, P 5.19wt.%, Si 0.96wt.%, Ca 0.91wt.%, Fe0.39wt.%, Zr 0.31wt.%, Pb 0.30wt.%, Na 0.29wt.%, Ti 0.16wt.%;

[0073] S3, acid leaching treatment: the pretreated rare earth ore obtained in S2 is pulped, and the liquid-to-solid ratio of the pulping is 2:1; nitric acid solution is added, and the amount added is 400% of the molar amount of acid required for the reaction, the acid leaching reaction time is 2h, the acid leaching reaction temperature is 90°C, and the leaching is carried out under stirring at normal temperature and pressure. After the leaching is completed, the rare earth nitric acid leaching solution is obtained by suction filtration, the liquid-to-solid ratio of the filter residue washing is 4:1, the washing time is 30min, the washing temperature is 90°C, and the filter residue is washed to obtain the leached residue; wherein, the leaching rate of the main rare earth elements treated by acid leaching is 96.6%, and the residue rate is 11.6%;

[0074] S4, reduction treatment: adding thiourea reducing agent to the rare earth acid leaching solution of S3, and stirring for reaction, the amount of reducing agent added is 2% of the raw material, the reduction reaction time is 40 minutes, and the reaction temperature is 40°C; obtaining the reduced rare earth leaching solution; wherein the reduction rate of tetravalent cerium treated by reduction is 97.3%;

[0075] S5, P and Fe removal treatment: add iron source of ferric nitrate nonahydrate and neutralizer of magnesium oxide to the rare earth leaching solution after reduction of S4, the amount of iron source added is 100% of the theoretical amount of iron phosphate generated, and stir to react, the pH of the rare earth leaching solution is adjusted to 2.5 using the neutralizer, the neutralization and impurity removal reaction time is 2.5h, the reaction temperature is 40°C, and the pH of the rare earth leaching solution after reduction is adjusted and then filtered to obtain the impurity-removed leaching solution; wherein, the removal rates of P and Fe in the P and Fe removal treatment are 99.5% and 99.1%, respectively;

[0076] S6, extraction and separation treatment: extract and separate the impurity-removed leaching liquid of S5, the extractant of the extraction and separation treatment is P507, the diluent is kerosene, the extractant is saponified with ammonia water to obtain a single rare earth nitrate, and the single rare earth nitrate is flame spray pyrolyzed to prepare a single nano rare earth oxide.

[0077] In S6, the content of nano rare earth oxides with an average particle size of 52 nm is 99.2%, and the rare earth recovery rate is 92.50%.

[0078] Comparative Example 1

[0079] A method for low-temperature decomposition of monazite, wherein the composition of monazite is 63.4wt.%, REO, 11.87wt.%, P, 1.65wt.%, Si, 0.93wt.%, Ca, 0.35wt.%, Fe, 0.26wt.%, Zr, 0.29wt.%, Pb, 0.26wt.%, Na, 0.15wt.%, and the rest are unavoidable impurities; the method for low-temperature decomposition of monazite comprises the following steps:

[0080] S1, classification and roasting treatment: drying the monazite concentrate, crushing and classifying it into 300 mesh ore powder to obtain graded ore powder; roasting at 850° C. for 2 h to obtain a roasted material;

[0081] S2, washing and filtering treatment: washing and filtering the calcined material in S1, the liquid-solid ratio of the washing process is 3:1, washing is continued for multiple times until the pH of the washing water is 7.7, the washing time is 30 minutes, and the washing temperature is 90°C; obtaining F-containing washing water and pretreated rare earth ore; wherein, the contents of each component in the F-containing washing water are P 0.12g / L, F 0.03g / L, and the contents of each component in the pretreated rare earth ore are REO 63.61wt.%, P 11.84wt.%, Si 1.66wt.%, Ca 0.93wt.%, Fe0.36wt.%, Zr 0.25wt.%, Pb 0.30wt.%, Na 0.23wt.%, Ti 0.16wt.%;

[0082] S3, acid leaching treatment: the pretreated rare earth ore obtained in S2 is pulped, and the liquid-to-solid ratio of the pulping is 2:1; a nitric acid solution is added, and the amount added is 400% of the molar amount of acid required for the reaction, the acid leaching reaction time is 2 hours, the acid leaching reaction temperature is 90°C, and the leaching is carried out under stirring at normal temperature and pressure. After the leaching is completed, the rare earth nitric acid leaching solution is obtained by suction filtration, the liquid-to-solid ratio of the filter residue washing is 4:1, the washing time is 30 minutes, the washing temperature is 90°C, and the filter residue is washed to obtain the leached residue; wherein, the leaching rate of the main rare earth elements treated by acid leaching is 49.3%, and the residue rate is 59.6%;

[0083] S4, reduction treatment: adding thiourea reducing agent to the rare earth acid leaching solution of S3, and stirring for reaction, the amount of reducing agent added is 2% of the raw material, the reduction reaction time is 40 minutes, and the reaction temperature is 40°C; obtaining the reduced rare earth leaching solution; wherein the reduction rate of tetravalent cerium treated by reduction is 97.0%;

[0084] S5, P and Fe removal treatment: add iron source of ferric nitrate nonahydrate and neutralizer of magnesium oxide to the rare earth leaching solution after reduction of S4, the amount of iron source added is 100% of the theoretical amount of iron phosphate generated, and stir to react, the pH of the rare earth leaching solution is adjusted to 2.5 using the neutralizer, the neutralization and impurity removal reaction time is 2.5h, the reaction temperature is 40°C, and the pH of the rare earth leaching solution after reduction is adjusted and then filtered to obtain the impurity-removed leaching solution; wherein, the removal rates of P and Fe in the P and Fe removal treatment are 99.7% and 99.2%, respectively;

[0085] S6, extraction and separation treatment: extract and separate the impurity-removed leaching liquid of S5, the extractant of the extraction and separation treatment is P507, the diluent is kerosene, the extractant is saponified with ammonia water to obtain a single rare earth nitrate, and the single rare earth nitrate is prepared into a single nano rare earth oxide by flame spray pyrolysis.

[0086] In S6, the content of nano rare earth oxides with an average particle size of 60 nm is 99.0%, and the rare earth recovery rate is 38.50%.

[0087] Example 2

[0088] A method for low-temperature decomposition of monazite, wherein the composition of monazite is 63.4wt.%, REO, 11.87wt.%, P, 1.65wt.%, Si, 0.93wt.%, Ca, 0.35wt.%, Fe, 0.26wt.%, Zr, 0.29wt.%, Pb, 0.26wt.%, Na, 0.15wt.%, and the rest are unavoidable impurities; the method for low-temperature decomposition of monazite comprises the following steps:

[0089] S1. Classification and roasting treatment: drying the monazite concentrate, crushing and classifying it into 300 mesh ore powder to obtain graded ore powder; mixing the graded ore powder with a mixed auxiliary agent of calcium oxide, calcium nitrate, calcium chloride and calcium fluoride at a mass ratio of 1:0.7, roasting at 850°C for 2h to obtain a roasted material;

[0090] S2, washing and filtering treatment: washing and filtering the calcined material in S1, the liquid-solid ratio of the washing process is 3:1, washing is continued for multiple times until the pH of the washing water is 7.7, the washing time is 30 minutes, and the washing temperature is 90°C; obtaining F-containing washing water and pretreated rare earth ore; wherein, the contents of each component in the F-containing washing water are P 8.44g / L, F 0.69g / L, and the contents of each component in the pretreated rare earth ore are REO 69.68wt.%, P 5.37wt.%, Si 0.99wt.%, Ca 0.89wt.%, Fe0.36wt.%, Zr 0.30wt.%, Pb 0.31wt.%, Na 0.25wt.%, Ti 0.17wt.%;

[0091] S3, acid leaching treatment: the pretreated rare earth ore obtained in S2 is pulped, and the liquid-to-solid ratio of the pulping is 2:1; hydrochloric acid solution is added, and the amount added is 400% of the molar amount of acid required for the reaction, the acid leaching reaction time is 2h, the acid leaching reaction temperature is 90°C, and the leaching is carried out under stirring at normal temperature and pressure. After the leaching is completed, the rare earth nitric acid leaching solution is obtained by suction filtration, the liquid-to-solid ratio of the filter residue washing is 4:1, the washing time is 30min, the washing temperature is 90°C, and the filter residue is washed to obtain the leached residue; wherein, the leaching rate of the main rare earth elements treated by acid leaching is 95.7%, and the residue rate is 12.2%;

[0092] S4, reduction treatment: adding thiourea reducing agent to the rare earth acid leaching solution of S3, and stirring for reaction, the amount of reducing agent added is 2% of the raw material, the reduction reaction time is 40 minutes, and the reaction temperature is 40°C; obtaining the reduced rare earth leaching solution; wherein the reduction rate of tetravalent cerium treated by reduction is 97.1%;

[0093] S5, P and Fe removal treatment: add an iron source of ferric chloride and a neutralizer of magnesium oxide to the rare earth leaching solution after reduction of S4, the amount of the iron source added is 100% of the theoretical amount of iron phosphate generated, and stir to react, the pH of the rare earth leaching solution is adjusted to 2.5 using a neutralizer, the neutralization and impurity removal reaction time is 2.5h, the reaction temperature is 40°C, and the pH of the rare earth leaching solution after reduction is adjusted and then filtered to obtain a leaching solution after impurities are removed; wherein, the removal rates of P and Fe in the P and Fe removal treatment are 99.4% and 99.2%, respectively;

[0094] S6, extraction and separation treatment: the impurity-removed leaching liquid of S5 is subjected to extraction and separation, the extractant for the extraction and separation treatment is P507, the diluent is kerosene, the extractant is saponified with ammonia water to obtain a single rare earth chloride, the single rare earth chloride is precipitated with oxalic acid, and then calcined at high temperature to obtain a micron-sized single rare earth oxide.

[0095] In S6, the content of micron-sized single rare earth oxides with an average particle size of 4.3 μm is 99.1%, and the rare earth recovery rate is 92.20%.

[0096] Comparative Example 2

[0097] A method for low-temperature decomposition of monazite, wherein the composition of monazite is 63.4wt.%, REO, 11.87wt.%, P, 1.65wt.%, Si, 0.93wt.%, Ca, 0.35wt.%, Fe, 0.26wt.%, Zr, 0.29wt.%, Pb, 0.26wt.%, Na, 0.15wt.%, and the rest are unavoidable impurities; the method for low-temperature decomposition of monazite comprises the following steps:

[0098] S1. Classification and roasting treatment: After drying the monazite concentrate, crush and classify it into 300 mesh ore powder to obtain graded ore powder; the graded ore powder is mixed with a mixed auxiliary agent of calcium oxide, calcium nitrate, calcium chloride and calcium fluoride at a mass ratio of 1:0.2 and roasted at 850° C. for 2 hours to obtain a roasted material;

[0099] S2, washing and filtering treatment: washing and filtering the calcined material in S1, the liquid-solid ratio of the washing process is 3:1, washing is continued for multiple times until the pH of the washing water is 7.7, the washing time is 30 minutes, and the washing temperature is 90°C; obtaining F-containing washing water and pre-treated rare earth ore; wherein, the contents of each component in the F-containing washing water are P 2.73g / L, F 0.18g / L, and the contents of each component in the pre-treated rare earth ore are REO 65.6wt.%, P 9.04wt.%, Si 1.30wt.%, Ca 0.94wt.%, Fe 0.34wt.%, Zr 0.28wt.%, Pb 0.30wt.%, Na 0.26wt.%, Ti 0.16wt.%;

[0100] S3, acid leaching treatment: the pretreated rare earth ore obtained in S2 is pulped, and the liquid-to-solid ratio of the pulping is 2:1; hydrochloric acid solution is added, and the amount added is 400% of the molar amount of acid required for the reaction, the acid leaching reaction time is 2h, the acid leaching reaction temperature is 90°C, and the leaching is carried out under stirring at normal temperature and pressure. After the leaching is completed, the rare earth nitric acid leaching solution is obtained by suction filtration, the liquid-to-solid ratio of the filter residue washing is 4:1, the washing time is 30min, the washing temperature is 90°C, and the filter residue is washed to obtain the leached residue; wherein, the leaching rate of the main rare earth elements treated by acid leaching is 71.4%, and the residue rate is 42.8%;

[0101] S4, reduction treatment: adding thiourea reducing agent to the rare earth acid leaching solution of S3, and stirring for reaction, the amount of reducing agent added is 2% of the raw material, the reduction reaction time is 40 minutes, and the reaction temperature is 40°C; obtaining the reduced rare earth leaching solution; wherein the reduction rate of tetravalent cerium treated by reduction is 97.4%;

[0102] S5, P and Fe removal treatment: add an iron source of ferric chloride and a neutralizer of magnesium oxide to the rare earth leaching solution after reduction of S4, the amount of the iron source added is 100% of the theoretical amount of iron phosphate generated, and stir to react, the pH of the rare earth leaching solution is adjusted to 2.5 using a neutralizer, the neutralization and impurity removal reaction time is 2.5h, the reaction temperature is 40°C, and the pH of the rare earth leaching solution after reduction is adjusted and then filtered to obtain a leaching solution after impurities are removed; wherein, the removal rates of P and Fe in the P and Fe removal treatment are 99.3% and 99.7%, respectively;

[0103] S6, extraction and separation treatment: the impurity-removed leaching liquid of S5 is subjected to extraction and separation, the extractant for the extraction and separation treatment is P507, the diluent is kerosene, the extractant is saponified with ammonia water to obtain a single rare earth chloride, the single rare earth chloride is precipitated with oxalic acid, and then calcined at high temperature to obtain a micron-sized single rare earth oxide.

[0104] In S6, the content of micron-sized single rare earth oxides with an average particle size of 4.6 μm is 99.2%, and the rare earth recovery rate is 62.7%.

[0105] Comparative Example 3

[0106] A method for low-temperature decomposition of monazite, wherein the composition of monazite is 63.4wt.%, REO, 11.87wt.%, P, 1.65wt.%, Si, 0.93wt.%, Ca, 0.35wt.%, Fe, 0.26wt.%, Zr, 0.29wt.%, Pb, 0.26wt.%, Na, 0.15wt.%, and the rest are unavoidable impurities; the method for low-temperature decomposition of monazite comprises the following steps:

[0107] S1, classification and roasting treatment: drying the monazite concentrate, crushing and classifying it into 300 mesh ore powder, and obtaining graded ore powder; mixing the graded ore powder with a mixed auxiliary agent of sodium bicarbonate, sodium carbonate and sodium fluoride at a mass ratio of 1:0.7, roasting at 850°C for 2h, and obtaining a roasted material;

[0108] S2, washing and filtering treatment: the calcined material in S1 is washed and filtered, the liquid-to-solid ratio of the washing process is 3:1, and the washing is continued for multiple times until the pH of the washing water is 7.7, the washing time is 30 minutes, and the washing temperature is 90°C; F-containing washing water and pre-treated rare earth ore are obtained; wherein, the contents of each component in the F-containing washing water are P 7.90g / L, F 0.73g / L, and the contents of each component in the pre-treated rare earth ore are REO 69.25wt.%, P 5.44wt.%, Si 1.03wt.%, Ca 0.95wt.%, Fe 0.38wt.%, Zr 0.28wt.%, Pb 0.29wt.%, Na 0.27wt.%, Ti 0.14wt.%;

[0109] S3, acid leaching treatment: the pretreated rare earth ore obtained in S2 is pulped, and the liquid-to-solid ratio of the pulping is 2:1; nitric acid solution is added, and the amount added is 90% of the molar amount of acid required for the reaction, the acid leaching reaction time is 2h, the acid leaching reaction temperature is 90°C, and the leaching is stirred at normal temperature and pressure. After the leaching is completed, the rare earth nitric acid leaching solution is obtained by suction filtration, the liquid-to-solid ratio of the filter residue washing is 4:1, the washing time is 30min, the washing temperature is 90°C, and the filter residue is washed to obtain the leached residue; wherein, the leaching rate of the main rare earth elements treated by acid leaching is 48.6%, and the residue rate is 69.1%;

[0110] S4, reduction treatment: adding thiourea reducing agent to the rare earth acid leaching solution of S3, and stirring for reaction, the amount of reducing agent added is 2% of the raw material, the reduction reaction time is 40 minutes, and the reaction temperature is 40°C; obtaining the reduced rare earth leaching solution; wherein the reduction rate of tetravalent cerium treated by reduction is 98.1%;

[0111] S5, P and Fe removal treatment: add iron source of ferric nitrate nonahydrate and neutralizer of magnesium oxide to the rare earth leaching solution after reduction of S4, the amount of iron source added is 100% of the theoretical amount of generated iron phosphate, and stir to react, the pH of the rare earth leaching solution is adjusted to 2.5 using the neutralizer, the neutralization and impurity removal reaction time is 2.5h, the reaction temperature is 40°C, and the pH of the rare earth leaching solution after reduction is adjusted and then filtered to obtain the impurity-removed leaching solution; wherein, the removal rates of P and Fe in the P and Fe removal treatment are 99.6% and 99.2%, respectively;

[0112] S6, extraction and separation treatment: extract and separate the impurity-removed leaching liquid of S5, the extractant of the extraction and separation treatment is P507, the diluent is kerosene, the extractant is saponified with ammonia water to obtain a single rare earth nitrate, and the single rare earth nitrate is flame spray pyrolyzed to prepare a single nano rare earth oxide.

[0113] In S6, the content of nano-scale single rare earth oxides with an average particle size of 68nm is 99.3%, and the rare earth recovery rate is 36.9%.

[0114] Example 3

[0115] A method for low-temperature decomposition of monazite, wherein the composition of monazite is REO 23.43wt.%, P 4.85wt.%, Si 9.55wt.%, Ca 3.57wt.%, Fe 4.41wt.%, Zr 4.92wt.%, Pb 0.34wt.%, Na 0.40wt.%, Ti 4.73wt.%, and the rest are unavoidable impurities; the method for low-temperature decomposition of monazite comprises the following steps:

[0116] S1. Classification and roasting treatment: drying the monazite concentrate, crushing and classifying it into 250 mesh ore powder to obtain graded ore powder; mixing the graded ore powder with a mixed auxiliary agent of sodium bicarbonate, sodium carbonate, calcium oxide, calcium nitrate, calcium chloride, calcium fluoride and sodium fluoride at a mass ratio of 1:0.3, roasting at 700°C for 2h to obtain a roasted material;

[0117] S2, washing and filtering treatment: the calcined material in S1 is washed and filtered, the liquid-to-solid ratio of the washing process is 6:1, and the washing is continued for multiple times until the pH of the washing water is 7-8, the washing time is 1 hour, and the washing temperature is 60°C; F-containing washing water and pre-treated rare earth ore are obtained; wherein, the contents of each component in the F-containing washing water are P 2.61g / L, F 0.25g / L, and the contents of each component in the pre-treated rare earth ore are REO 26.17wt.%, P 2.36wt.%, Si 8.83wt.%, Ca 3.72wt.%, Fe 4.99wt.%, Zr5.05wt.%, Pb 0.31wt.%, Na 0.39wt.%, Ti 4.86wt.%;

[0118] S3, acid leaching treatment: the pretreated rare earth ore obtained in S2 is pulped, and the liquid-to-solid ratio of the pulping is 4:1; nitric acid solution is added, and the amount added is 350% of the molar amount of acid required for the reaction, the acid leaching reaction time is 3h, the acid leaching reaction temperature is 75°C, and the leaching is stirred at normal temperature and pressure. After the leaching is completed, the rare earth acid leaching liquid is obtained by suction filtration, the liquid-to-solid ratio of the filter residue washing is 5:1, the washing time is 1h, the washing temperature is 80°C, and the filter residue is washed to obtain the leached residue; wherein, the leaching rate of the main rare earth elements treated by acid leaching is 95.17%, and the residue rate is 32.75%;

[0119] S4, reduction treatment: adding hydrogen peroxide reducing agent to the rare earth acid leaching solution of S3, and stirring for reaction, the amount of reducing agent added is 5% of the raw material, the reduction reaction time is 2h, and the reaction temperature is 60°C; obtaining the reduced rare earth leaching solution; wherein the reduction rate of tetravalent cerium treated by reduction is 97.58%;

[0120] S5, P and Fe removal treatment: add an iron source of ferric nitrate and a neutralizer of magnesium oxide to the rare earth leaching solution after reduction of S4, the amount of the iron source added is 55% of the theoretical amount of iron phosphate generated, and stir to react, the pH of the rare earth leaching solution is adjusted to 1.0 using a neutralizer, the neutralization and impurity removal reaction time is 4 hours, the reaction temperature is 20°C, and the pH of the rare earth leaching solution after reduction is adjusted and then filtered to obtain a leaching solution after impurities are removed; wherein, the removal rates of P and Fe in the P and Fe removal treatment are 99.79% and 97.27%, respectively;

[0121] S6, extraction and separation treatment: extract and separate the impurity-removed leaching liquid of S5, the extractant of the extraction and separation treatment is P204, the diluent is kerosene, the extractant is saponified with ammonia water to obtain a single rare earth nitrate, and the single rare earth nitrate is flame spray pyrolyzed to prepare a single nano rare earth oxide.

[0122] In S6, the content of nano-scale single rare earth oxides with an average particle size of 54 nm is 99.5%, and the rare earth recovery rate is 91.9%.

[0123] Example 4

[0124] A method for low-temperature decomposition of monazite, wherein the composition of monazite is REO 41.77wt.%, P 8.10wt.%, Si 5.02wt.%, Ca 1.88wt.%, Fe 2.05wt.%, Zr 3.08wt.%, Pb 0.25wt.%, Na 0.37wt.%, Ti 3.71wt.%, and the rest are unavoidable impurities; the method for low-temperature decomposition of monazite comprises the following steps:

[0125] S1. Classification and roasting treatment: drying the monazite concentrate, crushing and classifying it into 250 mesh ore powder to obtain graded ore powder; mixing the graded ore powder with a mixed auxiliary agent of sodium bicarbonate, sodium carbonate, calcium oxide, calcium nitrate, calcium chloride, calcium fluoride and sodium fluoride at a mass ratio of 1:0.45, roasting at 1100° C. for 0.5 h to obtain a roasted material;

[0126] S2, washing and filtering treatment: washing and filtering the calcined material in S1, the liquid-to-solid ratio of the washing process is 4:1, washing is continued for multiple times until the pH of the washing water is 7-8, the washing time is 30 minutes, and the washing temperature is 70°C; obtaining F-containing washing water and pre-treated rare earth ore; wherein, the contents of each component in the F-containing washing water are P 4.59g / L, F 0.51g / L, and the contents of each component in the pre-treated rare earth ore are REO 44.69wt.%, P 5.13wt.%, Si 4.70wt.%, Ca 2.08wt.%, Fe2.35wt.%, Zr 3.41wt.%, Pb 0.28wt.%, Na 0.37wt.%, Ti 4.02wt.%;

[0127] S3, acid leaching treatment: the pretreated rare earth ore obtained in S2 is pulped, and the liquid-to-solid ratio of the pulping is 4:1; nitric acid solution is added, and the amount added is 450% of the molar amount of acid required for the reaction, the acid leaching reaction time is 5 hours, the acid leaching reaction temperature is 95°C, and the leaching is stirred at room temperature and pressure. After the leaching is completed, the rare earth acid leaching liquid is obtained by suction filtration, the liquid-to-solid ratio of the filter residue washing is 2:1, the washing time is 1 hour, the washing temperature is 50°C, and the filter residue is washed to obtain the leached residue; wherein, the leaching rate of the main rare earth elements treated by acid leaching is 94.81%, and the residue rate is 24.35%;

[0128] S4, reduction treatment: adding a reducing agent of hydrogen peroxide to the rare earth acid leaching solution of S3, and stirring for reaction, the amount of reducing agent added is 5% of the raw material, the reduction reaction time is 30 minutes, and the reaction temperature is 20°C; obtaining a rare earth leaching solution after reduction; wherein the reduction rate of tetravalent cerium after reduction treatment is 97.37%;

[0129] S5, P and Fe removal treatment: add ferric nitrate, an iron source, and a neutralizer of calcium oxide to the rare earth leaching solution after reduction of S4, the amount of the iron source added is 80% of the theoretical amount of iron phosphate generated, and stir to react, the pH of the rare earth leaching solution is adjusted to 1.5 using a neutralizer, the neutralization and impurity removal reaction time is 3h, the reaction temperature is 30°C, and the pH of the rare earth leaching solution after reduction is adjusted and then filtered to obtain the impurity-removed leaching solution; wherein, the removal rates of P and Fe in the P and Fe removal treatment are 99.81% and 97.36%, respectively;

[0130] S6, extraction and separation treatment: extract and separate the impurity-removed leaching liquid of S5, the extractant of the extraction and separation treatment is N235, the diluent is ethanol, the extractant is saponified with ammonia water to obtain a single rare earth nitrate, and the single rare earth nitrate is flame spray pyrolyzed to prepare a single nano rare earth oxide.

[0131] In S6, the content of nano-micron single rare earth oxides with an average particle size of 47nm is 99.1%, and the rare earth recovery rate is 90.56%.

[0132] In summary, by comparing the embodiments with the comparative examples, it can be found that as long as appropriate experimental parameters (such as the amount of additives, the amount of nitric acid, etc.) are selected and the process route is followed, micron, nanometer and rare earth oxides can be prepared from monazite concentrates of different grades.

[0133] The above scheme, the present invention proposes a method for low-temperature decomposition of monazite, which can solve the technical problems existing in the prior art monazite treatment process, such as multiple acid and / or alkali solid-liquid conversions, complex and cumbersome mineral dissolution process, high quality requirements for monazite concentrate, difficulty in alkali decomposition, acid decomposition corrosion of reactor walls, low removal rate of impurities such as phosphorus and iron, low recovery rate of rare earth elements, long process flow, and high cost.

[0134] The method of the present invention achieves a leaching rate of more than 95% for main rare earth elements, a recovery rate of more than 90% for rare earth elements, and a removal rate of more than 99% for P and Fe through the mixed roasting, washing, filtering, beating, stirring leaching, reducing agent reduction, adding iron source, and neutralizing with a neutralizing agent of monazite ore powder and an auxiliary agent.

[0135] The invention is a brand-new process for decomposing monazite, which is applicable to monazite concentrates of different grades, especially to low-grade monazite concentrates of 20-40% which are difficult to adapt to in the prior art. It broadens the source of raw materials, reduces the cost of raw materials, and promotes the industrialization process of monazite decomposition.

[0136] The method of the present invention greatly simplifies the dissolution process of rare earth elements in monazite concentrate, including technical advantages such as no use of strong alkali, less solid-liquid conversion times, strong operability, and no waste water and waste gas generation in the overall mineral smelting. It is green and environmentally friendly, and only acid can be used to decompose monazite at normal temperature and pressure, with low requirements for leaching equipment; and the acid can be recycled.

[0137] The method of the present invention can produce single acid earth products and micron-level and nano-level rare earth oxides through low-cost, green and short processes, greatly reducing investment and equipment maintenance costs. This process provides new ideas and new processes for the treatment and development of monazite, and provides a demonstration for the comprehensive utilization of monazite. The existing technologies are not simply combined, such as combining microbial decomposition and multiple alkaline dissolution, but the advantages and disadvantages of the existing technologies are fully considered, and the technical prejudice is overcome to obtain the method of the present invention.

[0138] The method of the present invention can obtain rare earth nitrates, rare earth chlorides, and nanometer or micron rare earth oxides, and is not only suitable for low-, medium-, and high-grade monazite concentrates, but also greatly simplifies the leaching process of the monazite concentrate. The leaching temperature is low, the time is short, and the requirements for equipment materials are relatively low, which greatly reduces the production cost. In addition, the method has a wide variety of products and a high market added value, which is conducive to large-scale industrial production and popularization.

[0139] In summary, compared with other traditional methods, the method of the present invention creatively improves the leaching rate of major rare earth elements, the recovery rate of rare earth elements, the removal rate of P and Fe and other properties through mixed roasting, washing, filtering, pulping, stirring leaching, reducing agent reduction, iron source, and neutralization by neutralizing agent of monazite ore powder and additives; and has high resource utilization, low production cost, short process, easy operation, and high efficiency, so it is suitable for large-scale industrial production.

[0140] It should be understood that the term "and / or" in this article is only a description of the association relationship of associated objects, indicating that there can be three relationships. For example, A and / or B can represent: A exists alone, A and B exist at the same time, and B exists alone. A and B can be singular or plural. In addition, the character " / " in this article generally indicates that the associated objects before and after are in an "or" relationship, but it may also indicate an "and / or" relationship. Please refer to the context for specific understanding.

[0141] In the present invention, "at least one" means one or more, and "plurality" means two or more. "At least one of the following" or similar expressions refers to any combination of these items, including any combination of single items or plural items. For example, at least one of a, b, or c can be represented by: a, b, c, ab, ac, bc, or abc, where a, b, and c can be single or multiple.

[0142] It should be understood that in various embodiments of the present invention, the size of the serial numbers of the above-mentioned processes does not mean the order of execution. The execution order of each process should be determined by its function and internal logic, and should not constitute any limitation on the implementation process of the embodiments of the present invention.

[0143] 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 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 low temperature decomposition of monazite, characterized in that: The method for low temperature decomposition of monazite comprises the following steps: S1, classification and roasting treatment: drying the monazite concentrate, crushing and classifying it to obtain graded ore powder; mixing the graded ore powder with an additive and then roasting it to obtain a roasted material; S2, washing and filtering treatment: washing and filtering the roasted material in S1 to obtain F-containing washing water and pre-treated rare earth ore; S3, acid leaching treatment: pulping the pretreated rare earth ore obtained in S2, adding an acid solution, and stirring and leaching at normal temperature and pressure. After the leaching is completed, filtering is performed to obtain a rare earth acid leaching solution, and the filter residue is washed to obtain a leaching residue; S4, reduction treatment: adding a reducing agent to the rare earth acid leaching solution of S3, and stirring the mixture to react, thereby obtaining a reduced rare earth leaching solution; S5, P and Fe removal treatment: adding an iron source and a neutralizer to the reduced rare earth leaching solution of S4, stirring the reaction, adjusting the pH of the reduced rare earth leaching solution, and then filtering to obtain a leaching solution after impurities are removed; S6, extraction and separation treatment: extract and separate the impurity-removed leaching solution of S5 to obtain a single rare earth salt, which is used to prepare a single rare earth oxide.

2. The method for low-temperature decomposition of monazite according to claim 1, characterized in that: In S1, the REO content of the monazite concentrate is 20-75%, and the particle size of the rare earth ore powder after crushing and grading is 100-400 meshes; the auxiliary agent used during calcination is one or more of sodium bicarbonate, sodium carbonate, calcium oxide, calcium nitrate, calcium chloride, calcium fluoride, sodium fluoride and other sodium-containing, calcium-containing, and fluorine-containing compounds.

3. The method for low-temperature decomposition of monazite according to claim 1, characterized in that: In S1, the mass ratio of the graded mineral powder to the additive is 1:0.3-1:1, the roasting temperature is 500-1200°C, and the roasting time is 0.5-5h.

4. The method for low-temperature decomposition of monazite according to claim 1, characterized in that: In S2, the liquid-to-solid ratio of the washing process is 2:1-10:1, and washing is continued for multiple times until the pH of the washing water is 7-8. The washing time is 10min-3h, and the washing temperature is 50-100°C; the F-containing washing water mainly contains P, F, and S elements. After pretreatment, the rare earth elements in the rare earth ore are increased by 0.2-7% compared with monazite concentrate, and the P content is reduced by 1-10% compared with monazite concentrate.

5. The method for low-temperature decomposition of monazite according to claim 1, characterized in that: In S3, the liquid-to-solid ratio of pulping is 1:2-5:1, the acid solution is nitric acid, hydrochloric acid or sulfuric acid, the amount added is 100-500% of the molar amount of acid required for the reaction, the acid leaching reaction time is 1-6h, and the acid leaching reaction temperature is 50-100°C; the liquid-to-solid ratio of filter residue washing is 2:1-6:1, the washing time is 20min-2h, and the washing temperature is 50-100°C; the leaching rate of the main rare earth elements treated by acid leaching is 50.0-100%, and the residue rate is 5.0-45.0%.

6. The method for low-temperature decomposition of monazite according to claim 1, characterized in that: In S4, the reducing agent is one or more of hydrogen peroxide and thiourea, the amount of reducing agent added is 0.5-5% of the raw material, the reduction reaction time is 20min-2h, the reaction temperature is 10-60°C; the reduction rate of tetravalent cerium treated by reduction is 60.0-100%.

7. The method for low-temperature decomposition of monazite according to claim 1, characterized in that: In S5, the iron source is one or more of ferric nitrate, ferric chloride, ferric sulfate, and iron powder, the neutralizer is one or more of magnesium oxide and calcium oxide, the amount of iron source added is 50-200% of the theoretical amount of iron phosphate generated, the pH of the rare earth leaching solution is adjusted to 0.5-6 using the neutralizer, the neutralization and impurity removal reaction time is 30min-5h, and the reaction temperature is 10-60°C; the removal rates of P and Fe in the P and Fe removal treatment are 70.0-100% and 90.0-100%, respectively.

8. The method for low temperature decomposition of monazite according to claim 1, characterized in that: In S6, the extractant for extraction and separation treatment is one or more of P204, P507, TBP, P350, N263, N235 and other commonly used rare earth extractants, the diluent is kerosene or alcohol, and the extractant is saponified with ammonia water.

9. The method for low-temperature decomposition of monazite according to claim 1, characterized in that: In S6, single rare earth oxides include micron rare earth oxides and nano rare earth oxides with an average particle size of ≤500nm; among them, the average particle size of the micron rare earth oxides is 1-10μm, the content is 98.0-100%, and the rare earth recovery rate is 90.0-99.99%; the content of the nano rare earth oxides with an average particle size of ≤500nm is 98.0-100%, and the rare earth recovery rate is 90.0-99.99%.

10. The method for low temperature decomposition of monazite according to claim 9, characterized in that: In S6, micron rare earth oxides are prepared by one-stage or multi-stage pyrolysis, and nano rare earth oxides with an average particle size of ≤500nm are prepared by combustion, flame spray pyrolysis or precipitation and other industrialized methods.

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