A method for recovering fluorine, phosphorus and rare earths by two-step alkali decomposition of mixed rare earth concentrate after hydrochloric acid leaching

Abstract

This invention belongs to the field of rare earth concentrate processing technology, specifically relating to a method for recovering fluoride, phosphorus, and rare earth elements from mixed rare earth concentrate through hydrochloric acid leaching and a two-step alkaline decomposition. The method comprises the following steps: mixing hydrochloric acid with the mixed rare earth concentrate and reacting to leach, yielding an acid-leached mixed ore and an acidic rare earth chloride solution; stirring the acid-leached mixed ore with sodium hydroxide solution A, heating to react, washing with water, and filtering to obtain a first-step alkali cake and a first-step alkali solution; concentrating the first-step alkali solution to obtain sodium fluoride; stirring the first-step alkali cake with sodium hydroxide solution B to obtain a second-step alkali cake and a second-step alkali solution; processing the second-step alkali solution to obtain trisodium phosphate dodecahydrate; and adding the second-step alkali cake to the acidic rare earth chloride solution to obtain a rare earth chloride feed solution. The method for recovering fluoride, phosphorus, and rare earth elements from mixed rare earth concentrate through hydrochloric acid leaching and a two-step alkaline decomposition provided by this invention has the advantages of low production cost, low waste generation, simple operation, and high recovery rates of rare earth elements and fluoride / phosphorus.

Description

Technical Field

[0001] This invention belongs to the field of rare earth concentrate processing technology, specifically relating to a method for recovering fluorine, phosphorus and rare earths by hydrochloric acid leaching and two-step alkaline decomposition of mixed rare earth concentrate. Background Technology

[0002] The Bayan Obo rare earth mine in Baotou is a mixed rare earth mine, with rare earth elements occurring in bastnaesite and monazite respectively. The proportion of bastnaesite and monazite in the raw ore mined at different times is not fixed.

[0003] Currently, the main methods for large-scale processing of rare earth deposits in Baotou's Bayan Obo mine are concentrated sulfuric acid high-temperature roasting and traditional caustic soda decomposition. The concentrated sulfuric acid high-temperature roasting process is simple and efficient, with a rare earth recovery rate of over 94%. However, to achieve this high recovery rate, the amount of sulfuric acid added is far greater than the theoretical amount. A large amount of sulfuric acid decomposes into SO2 and SO3 at high temperatures, and the phosphorus (F) in the minerals also reacts with the sulfuric acid to form HF, resulting in a large amount of highly polluting exhaust gas that is complex and costly to treat. Furthermore, the phosphorus in the minerals is roasted with sulfuric acid to form pyrophosphate, wasting phosphorus resources. Simultaneously, the amount of tailings generated during production is also substantial, leading to high solid waste disposal costs. The caustic soda decomposition process is characterized by mild reaction conditions and does not produce highly polluting exhaust gas, but it generates a large amount of wastewater and solid waste, resulting in higher overall treatment costs.

[0004] Patent CN102251106A discloses a method for alkaline decomposition of Baotou rare earth concentrate, which uses hydrochloric acid to remove calcium, followed by alkaline hydrolysis and acid dissolution to obtain a rare earth chloride solution. This method is simple, has a short process, and produces little pollution, allowing for the recovery of resources such as phosphorus and fluorine (F). However, the recovered fluorine and phosphorus are a mixture with low market value; furthermore, the overall production of caustic soda flakes has a high unit consumption.

[0005] Patent CN106978531A discloses a method for the combined acid-base decomposition of mixed rare earth concentrates. This method involves mixing a mixed rare earth concentrate with REO≥50%, CaO≤12%, and SiO2≤1.5% with concentrated sulfuric acid, followed by roasting at 120-180℃. The roasting product is then leached with water to obtain a mixed water leaching residue of calcium sulfate and monazite. The calcium sulfate and monazite are separated using gravity separation, and the monazite is then decomposed with alkali. While this method achieves comprehensive recovery of fluorine and phosphorus resources and recycling of alkali washing wastewater, the low-temperature roasting process easily causes ring formation in the rotary kiln. Furthermore, the small amount of sulfuric acid increases the difficulty of controlling the decomposition of fluorocarbon cerium ore. Gravity separation also yields some radioactive calcium sulfate waste residue, resulting in the loss of fine-grained rare earth elements that are ultimately unrecoverable.

[0006] Patent CN103103349A discloses a method for the combined acid-base low-temperature decomposition of rare earth concentrate from Bayan Obo. The method involves using AlCl3 as a complexing agent to leach rare earth concentrate with a rare earth oxide content greater than 65% using hydrochloric acid, followed by the addition of Na2SO4 to convert the rare earth elements in the leachate into RENa(SO4)2 precipitate. Rare earth sodium sulfate double salt and monazite slag are then decomposed using an alkaline method. Although no harmful waste gas is produced, the alkaline wastewater has a complex composition, making the recovery of valuable elements difficult and resulting in high production costs.

[0007] Patent CN109536746A discloses a method for the cyclic slurry decomposition of low-calcium, high-grade mixed rare earth concentrate. The method involves mixing a mixed rare earth concentrate with REO ≥ 62% and CaO ≤ 3% in a specific ratio with a sulfuric acid solution, followed by heating and slurry reaction. This primarily decomposes fluorine-containing minerals, and the tail gas is absorbed to form a fluorosilicone mixed acid byproduct. After the reaction, the acid leaching residue is leached with water to dissolve calcium sulfate and rare earth sulfate in the leaching solution. After neutralization and impurity removal, the leaching solution forms phosphorus-iron-thorium slag. The leaching solution is replenished with sulfuric acid and recycled to treat new ore. Concentrated alkali solution is used to decompose the leaching residue and phosphorus-iron-thorium slag, and the alkaline wastewater is crystallized to recover sodium phosphate for recycling. While this method effectively improves the separation efficiency of fluorine and phosphorus, during the sulfuric acid slurry process, Si element escapes along with F as SiF4 gas, resulting in a long and costly process for F element recovery. Furthermore, the numerous steps in the overall process for recovering rare earth from the concentrate lead to large investments in production equipment and a large land area.

[0008] Patent CN102277483A discloses a new method for preparing rare earth chlorides from Bayan Obo rare earth concentrate. For a mixed rare earth concentrate of bastnaesite and monazite with REO grade of 60-68%, an oxidative roasting-hydrochloric acid preferential dissolution-sub-molten salt alkaline decomposition process is adopted. After sub-molten salt alkaline decomposition, fluorine and phosphorus can be effectively concentrated in the alkaline solution, but subsequent fluorine and phosphorus separation is relatively difficult.

[0009] Patents CN103045851A and CN105132682A both combine oxidative roasting with alkaline decomposition processes to treat Baotou mixed rare earth concentrate. Utilizing the non-reducing nature of sulfuric acid, all rare earth elements are leached out during roasting, causing tetravalent cerium in the leachate to form complexes with fluorine and phosphorus. These complexes are then separated through extraction to produce a mixed product of cerium fluoride and cerium phosphate. While this technology effectively reduces alkali consumption during alkaline decomposition, it still faces challenges in treating mixed sodium salt wastewater and in developing applications for mixed cerium rare earth salts. Summary of the Invention

[0010] The technical problem to be solved by the present invention is to overcome the above-mentioned defects of the prior art and to provide a method for the hydrochloric acid leaching and two-step alkaline decomposition of mixed rare earth concentrate to recover fluorine, phosphorus and rare earth. It has the advantages of low production cost, low amount of waste generated, simple operation, high rare earth recovery rate and comprehensive utilization of valuable elements. It realizes the efficient and green extraction of rare earth from Baotou mixed rare earth concentrate and the resource utilization of valuable elements such as fluorine and phosphorus, and produces high-quality rare earth chloride, trisodium phosphate dodecahydrate and sodium fluoride products.

[0011] The method for recovering fluoride, phosphorus, and rare earth elements from mixed rare earth concentrate by hydrochloric acid leaching and two-step alkaline decomposition according to the present invention includes the following steps:

[0012] (1) Mix hydrochloric acid with mixed rare earth concentrate and leach under heat and pressure to obtain acid-leached mixed ore and acidic rare earth chloride solution;

[0013] (2) Stir the acid-leached mixed ore with sodium hydroxide solution A evenly, heat and keep warm to react. After the reaction is completed, add water to wash and filter to obtain one-step alkali cake and one-step alkali solution. The one-step alkali solution is concentrated to obtain sodium fluoride and one-step alkali water.

[0014] (3) Stir the first-step alkali cake and sodium hydroxide solution B evenly, heat and keep warm to react. After the reaction is completed, filter to obtain the second-step alkali cake and the second-step alkali solution. The second-step alkali solution is purified and cooled to crystallize to obtain trisodium phosphate dodecahydrate. The alkali solution is further concentrated to obtain the second-step alkali water, which is reused in the sodium hydroxide solution B of this step. The concentrated condensate is returned to the second-step alkali cake for water washing and recycling. The second-step alkali cake is washed with water, and the washing water is returned to dilute the alkali decomposition slurry.

[0015] (4) After the two-step alkali cake is washed with water, it is added to the acidic rare earth chloride solution in step (1), heated and kept warm for reaction. After the reaction is completed, it is filtered, and the filtrate is purified to obtain rare earth chloride solution.

[0016] The mixed rare earth concentrate contains 45% to 70% REO, 4% to 9% F, and 3% to 7% P.

[0017] The hydrochloric acid used in step (1) is industrial hydrochloric acid, added at a ratio of 1:1.8 to 1:2.0 g / mL of mixed rare earth concentrate (REO) to hydrochloric acid. The industrial hydrochloric acid mentioned is commercially available hydrochloric acid with a mass content of about 30%.

[0018] The heating temperature in step (1) is 100℃~150℃, the reaction pressure is 0.1~1.0MPa, and the reaction time is 4h~6h.

[0019] In step (2), the amount of sodium hydroxide solution A added is calculated as sodium hydroxide. The mass of sodium hydroxide is 0.5 to 0.8 times the mass of REO in the acid-leached mixed ore, and the mass fraction of sodium hydroxide solution A is controlled to be 15% to 30%.

[0020] Step (2) The heating temperature is 105℃~135℃, and the reaction is kept at this temperature for 3h~5h.

[0021] In step (3), the amount of sodium hydroxide solution B added is calculated as sodium hydroxide. The mass of sodium hydroxide is 1.5 to 1.8 times the mass of REO in the alkali cake in step one, and the mass fraction of sodium hydroxide solution B is controlled to be 45% to 70%.

[0022] Step (3) The heating temperature is 130℃~170℃, and the reaction is kept at this temperature for 5h~10h.

[0023] Step (4) The heating temperature is 90~140℃, the reaction pressure is 0~1.0MPa, and the reaction time is 1h~4h.

[0024] In step (4), hydrogen peroxide, ammonium bicarbonate, and sodium sulfide are added sequentially to remove impurities from the filtrate after filtration. The amounts of hydrogen peroxide, ammonium bicarbonate, and sodium sulfide used for impurity removal are all sufficient to achieve the required concentration of impurities. These are routine operations for those skilled in the art, and their specific addition amounts will not be elaborated further.

[0025] Specifically, the method for recovering fluorine, phosphorus, and rare earth elements by hydrochloric acid leaching and two-step alkaline decomposition of mixed rare earth concentrate includes the following steps:

[0026] (1) Concentrated hydrochloric acid was added to the Baotou mixed rare earth concentrate according to the ratio of mixed rare earth concentrate (REO) to hydrochloric acid of 1:1.8~1:2.0 g / mL; the mixed slurry was heated at 100℃~150℃ and pressurized at 0.1~1.0MPa for 4h~6h for leaching. The fluorocarbon cerium ore in the concentrate reacted with hydrochloric acid to generate rare earth fluoride, rare earth chloride, and CO2. Rare earth chloride was present in the hydrochloric acid leaching solution, rare earth fluoride and unreacted rare earth phosphate entered the acid leaching mixed ore, and CO2 escaped in gaseous form. The reaction tail gas was condensed and recovered for reuse. The reaction equations in the reaction process are as follows:

[0027] 3REFCO3+6HCl=2RECl3+REF3↓+3CO2↑+3H2O.

[0028] (2) The acid-leached mixed ore obtained in step (1) is subjected to alkaline decomposition using a 15%~30% mass fraction sodium hydroxide solution A. The amount of sodium hydroxide added is 0.5 to 0.8 times the mass of REO in the acid-leached mixed ore. The heating temperature is 105℃~135℃, and the reaction is maintained for 3h~5h. Taking advantage of the difference in the difficulty of the reaction between rare earth fluoride and rare earth phosphate and NaOH, the rare earth fluoride in it is decomposed to generate rare earth hydroxide (RE(OH)3) and sodium fluoride (NaF). At this time, rare earth phosphate basically does not participate in the reaction. After the reaction is completed, water is added for washing and filtration to obtain a one-step alkaline cake and a one-step alkaline solution. The one-step alkaline solution is concentrated to obtain sodium fluoride and one-step alkaline water. The one-step alkaline cake is a mixture of rare earth hydroxide and rare earth phosphate; the one-step alkaline solution is a mixed solution of sodium fluoride and sodium hydroxide. After concentration, crystallization, and solid-liquid separation, sodium fluoride product is obtained. The concentrated condensate is returned to the one-step alkaline cake for water washing and recycling, and the one-step alkaline water is returned to the one-step alkaline decomposition and recycling. The reaction equations in the reaction process are as follows:

[0029] REF3 + 3NaOH = RE(OH)3↓ + 3NaF.

[0030] (3) The first-step alkali cake obtained in step (2) is decomposed with a 45%~70% mass fraction sodium hydroxide solution B. The amount of sodium hydroxide added is 1.5 to 1.8 times the mass of REO in the first-step alkali cake. The heating temperature is 130℃~170℃, and the reaction is kept at this temperature for 5h~10h to allow rare earth phosphate to react with NaOH, generating rare earth hydroxide (RE(OH)3) precipitate and trisodium phosphate dodecahydrate (Na3PO4). After the reaction, the second-step alkali cake and the second-step alkali solution are obtained by filtration. The second-step alkali solution is purified by cooling and crystallization to obtain trisodium phosphate dodecahydrate. The alkali solution is further concentrated to obtain second-step alkali water, which is reused in the sodium hydroxide solution B obtained from the second-step alkali decomposition. The concentrated condensate is returned to the second-step alkali cake for water washing and recycling. The second-step alkali cake is washed with water, and the washing water is returned to dilute the alkali decomposition slurry. The main component of the second-step alkali cake is rare earth hydroxide. The reaction equations in the reaction process are as follows:

[0031] REPO4+3NaOH=RE(OH)3↓+Na3PO4.

[0032] (4) Add the two-step alkali cake obtained in step (3) to the acidic rare earth chloride solution in step (1), heat the temperature to 90~140℃, the reaction pressure to 0~1.0MPa, and the reaction time to 1h~4h, so that the rare earth hydroxide reacts with the remaining hydrochloric acid to obtain a mixed rare earth chloride solution with a high concentration. Then, through the impurity removal and concentration process, remove iron, fluorine, phosphorus, aluminum, lead and zinc impurity ions to finally obtain a qualified mixed rare earth chloride product.

[0033] In step (1) above, the concentrated hydrochloric acid is used to decompose the bastnaesite in the Baotou mixed rare earth concentrate, causing about 2 / 3 of the rare earth elements in the bastnaesite to be leached out to form rare earth chlorides, while the remaining 1 / 3 of the rare earth elements exist in the solid phase as rare earth fluorides. In this step, if too little hydrochloric acid is added, the bastnaesite will not decompose completely; however, if too much hydrochloric acid is added, the remaining hydrochloric acid will not be completely neutralized by rare earth hydroxides, resulting in an acid imbalance.

[0034] In step (1) above, temperature is a key factor affecting the reaction effect and progress. If the temperature is too low, such as below 100℃, the reaction rate will be too slow, requiring a long reaction time, which will not only reduce the production efficiency of the equipment but also increase energy consumption. If the reaction temperature is to be increased, such as to 120℃, a certain pressure needs to be maintained. Therefore, this step requires a reaction temperature between 100℃ and 150℃ and a reaction pressure between 0.1 and 1.0 MPa. The preferred reaction temperature is 110℃ to 140℃, the reaction pressure is 0.4 to 0.6 MPa, and the reaction time is 4.5 h to 5.5 h.

[0035] In step (2) above, the sodium hydroxide concentration has a significant impact on the reaction effect during the one-step alkaline decomposition of rare earth fluoride. The mass fraction of sodium hydroxide in the initial alkaline solution is controlled between 15% and 30%. If the mass fraction of sodium hydroxide in the alkaline solution is less than 15%, the reaction rate of rare earth fluoride is slow; if the mass fraction of sodium hydroxide in the alkaline solution is greater than 30%, some rare earth phosphate will also be decomposed, resulting in excessive trisodium phosphate in the sodium fluoride product. The reaction temperature also has a very important effect on the reaction effect. When the reaction temperature is less than 105℃, the reaction rate is slow; when the reaction temperature is greater than 135℃, some rare earth phosphate will be decomposed. Therefore, the reaction temperature is controlled between 105℃ and 135℃. Preferably, the mass fraction of sodium hydroxide in the alkaline solution is controlled between 20% and 25%, and the reaction temperature is controlled between 115℃ and 125℃.

[0036] In step (2) above, the obtained alkaline solution is concentrated, crystallized and separated into solid and liquid components to produce sodium fluoride. The concentrated condensate is returned to the alkaline cake washing and recycled, and the mother liquor is returned to the alkaline decomposition and recycled.

[0037] In step (3) above, during the two-step alkaline decomposition of rare earth phosphate, the concentration of sodium hydroxide and the reaction temperature have a significant impact on the reaction process. The mass fraction of sodium hydroxide in the alkaline solution is generally controlled between 45% and 70%, and the reaction temperature is generally controlled between 130℃ and 170℃. If the sodium hydroxide concentration is too low or the reaction temperature is too low, the reaction rate will be slow, the rare earth phosphate will not decompose completely, and the yield of rare earth and phosphorus elements will decrease. If the sodium hydroxide concentration and reaction temperature are too high, the reaction slurry will easily become thick, and the rare earth phosphate will not decompose completely. Preferably, the mass fraction of sodium hydroxide is controlled between 50% and 60%, and the reaction temperature is controlled between 140℃ and 160℃.

[0038] In step (3) above, the two-step alkali decomposition slurry undergoes solid-liquid separation to obtain a two-step alkali cake and a two-step alkali solution containing trisodium phosphate dodecahydrate and sodium hydroxide. The two-step alkali solution is then purified and subjected to solid-liquid separation. The filtrate is slowly cooled and crystallized, and then centrifuged and filtered to obtain the trisodium phosphate dodecahydrate product and the sodium hydroxide two-step mother liquor. This mother liquor is concentrated and returned to the two-step alkali decomposition for recycling, while the concentrated condensate is returned to the two-step alkali cake washing for recycling.

[0039] This invention is applicable to the process of producing mixed rare earth chlorides from mixed rare earth concentrates. It recovers rare earth, fluorine, and phosphorus resources from rare earth concentrates through hydrochloric acid leaching and two-step alkaline decomposition, and significantly reduces the consumption of sodium hydroxide and hydrochloric acid as the main auxiliary materials. It avoids the problems of complex tail gas treatment and difficult recovery of fluorine and phosphorus resources in the sulfuric acid process for processing mixed rare earth concentrates. It has the advantages of low production cost, low waste generation, simple operation, high recovery rate of rare earth, fluorine and phosphorus, and comprehensive utilization of valuable elements.

[0040] Compared with the prior art, the beneficial effects of the present invention are:

[0041] (1) The method of hydrochloric acid leaching and two-step alkaline decomposition of mixed rare earth concentrate to recover fluorine, phosphorus and rare earth in the present invention uses concentrated hydrochloric acid to basically completely decompose the fluorine carbon cerium minerals in the Baotou mixed rare earth concentrate. More than 38% of the rare earth in the concentrate is converted into rare earth chloride, which reduces the amount of sodium hydroxide required for subsequent mineral alkaline decomposition by more than 33%, and at the same time avoids the impact of Na2CO3 generated during alkaline decomposition on the fluorine and phosphorus recovery system.

[0042] (2) The method for recovering fluoride, phosphorus, and rare earth elements by hydrochloric acid leaching and two-step alkaline decomposition of mixed rare earth concentrates of the present invention ensures efficient decomposition of rare earth fluorides and improves the recovery rate of fluoride by precisely controlling the concentration of sodium hydroxide and the reaction temperature during the first-step alkaline decomposition process, while minimizing the decomposition of rare earth phosphates and ensuring the purity of sodium fluoride products. During the second-step alkaline decomposition process, a higher concentration of sodium hydroxide solution is used at a higher temperature to achieve rapid and efficient decomposition of rare earth phosphates, improving the recovery rate of trisodium dodecahydrate and rare earth elements and the production efficiency of the equipment. During the two-step alkaline decomposition process, the alkaline water containing fluoride and phosphorus is evaporated and concentrated, and all the concentrated alkaline water is recycled back to the alkaline decomposition process, greatly reducing the alkaline consumption per unit of the alkaline decomposition process; all the concentrated condensate is recycled back to the washing process of the alkaline cake, achieving zero discharge of alkaline wastewater from the alkaline decomposition process.

[0043] (3) The method of hydrochloric acid leaching and two-step alkaline decomposition for the recovery of fluorine, phosphorus and rare earth from mixed rare earth concentrate of the present invention achieves efficient recovery of rare earth, fluorine and phosphorus from Baotou mixed rare earth concentrate, and produces high-quality mixed rare earth chloride, sodium fluoride and trisodium phosphate dodecahydrate products. Among them, the rare earth recovery rate of mixed rare earth chloride production from Baotou mixed rare earth concentrate reaches >98%; the sodium fluoride recovery rate reaches >95% and the purity of sodium fluoride reaches >96%; the trisodium phosphate dodecahydrate recovery rate reaches >95% and the purity of trisodium phosphate dodecahydrate reaches >95%. Attached Figure Description

[0044] Figure 1 This is a flowchart of the main process flow of the method for recovering fluorine, phosphorus and rare earths by hydrochloric acid leaching and two-step alkaline decomposition of mixed rare earth concentrates according to the present invention. Detailed Implementation

[0045] The present invention will be further described below with reference to specific embodiments.

[0046] The raw materials and additives used in the following examples and comparative examples are all commercially available products. The hydrochloric acid used is commercially available industrial hydrochloric acid, undiluted. The main process of this invention is as follows: Figure 1 As shown.

[0047] Example 1

[0048] The raw material used in this embodiment is Baotou mixed rare earth concentrate, with the main components being: REO content of 61.2%, F content of 5.8%, and P content of 5.1%. The method for recovering fluorine, phosphorus, and rare earth elements from the mixed rare earth concentrate by hydrochloric acid leaching and two-step alkaline decomposition includes the following steps:

[0049] (1) Weigh the Baotou mixed rare earth concentrate (REO) and hydrochloric acid at a ratio of 1:1.8 g / mL. Add the Baotou mixed rare earth concentrate to the industrial hydrochloric acid in the reactor while stirring, and stir until uniform.

[0050] (2) Under sealed conditions, the temperature inside the reactor is gradually heated to 130°C. At this time, the pressure inside the reactor is 0.5 MPa. The reaction is stirred for 5 hours. After the reaction is completed, the slurry is filtered, the leaching solution (acidic rare earth chloride solution) is retained, and the acid-leached mixed ore is rinsed with water until qualified. The mass of REO in the acid-leached mixed ore is calculated by adding the mass of Baotou mixed rare earth concentrate and the mass of REO in the leaching solution.

[0051] (3) Calculate the amount of NaOH to be used according to 0.65 times the mass of REO in the acid-leached mixed ore in step (2). Prepare sodium hydroxide solution A by adding water with a mass fraction of 20% NaOH and put it into the alkaline decomposition reactor. Turn on the stirring, add the acid-leached mixed ore into the reactor, turn on the heating, raise the temperature to 125℃ and keep it at the temperature for 4 hours.

[0052] (4) After the reaction is completed, the slurry is filtered to obtain washing liquid 1. The filter cake is transferred to a beaker and washed twice with water and stirring to fully wash out the sodium fluoride, resulting in washing liquid 2 and washing liquid 3. The filter cake is a one-step alkali cake (a mixture of rare earth phosphate and rare earth hydroxide). The volume of the three washing liquids is measured after they are mixed evenly, and the fluorine content is tested. The yield of sodium fluoride is calculated based on this (since there is no other outlet for fluorine in this process, this is used as the basis for calculating the yield of sodium fluoride). The mixed washing liquid is evaporated, concentrated, cooled and crystallized. It is filtered and quickly washed with water to obtain sodium fluoride. The purity of sodium fluoride is analyzed by sampling.

[0053] (5) Calculate the amount of NaOH to be used according to 1.7 times the mass of the alkali cake REO in step (4). Prepare sodium hydroxide solution B by adding water with a mass fraction of 60% NaOH and put it into the alkali decomposition reactor. Start stirring, add the alkali cake from step one into the reactor, start heating, raise the temperature to 150℃ and keep it at that temperature for 8 hours.

[0054] (6) After the reaction is completed, the slurry is filtered to obtain two-step alkali cake and washing solution 1. The two-step alkali cake is transferred to a beaker, water is added and stirred and washed twice to fully wash out the trisodium dodecahydrate, and washing solution 2 and washing solution 3 are obtained. The main component of the two-step alkali cake is rare earth hydroxide. After the three washing solutions are mixed evenly, they are concentrated and then slowly cooled under stirring. The mixture is centrifuged and filtered using a rotary drum centrifuge to obtain trisodium dodecahydrate. The purity of trisodium dodecahydrate is weighed and sampled for analysis.

[0055] (7) The two-step alkali cake obtained in step (6) is put into the immersion solution obtained in step (2), and the pressure is maintained at 0.5 MPa and the temperature at 120℃. After stirring and reacting for 2.5 h, the mixture is filtered. Hydrogen peroxide, ammonium bicarbonate, sodium sulfide and other impurity removal agents are added to the filtrate to remove impurity ions such as iron, fluorine, phosphorus, aluminum, lead and zinc. Finally, a mixed rare earth chloride solution with a concentration of 300 g / L is obtained.

[0056] In this embodiment, the rare earth recovery rate was 98.5%; the sodium fluoride recovery rate was 96.3% and the purity was 96.6%; and the trisodium dodecahydrate recovery rate was 95.8% and the purity was 96.4%.

[0057] Example 2

[0058] The raw material used in this embodiment is Baotou mixed rare earth concentrate, with the main components being: REO content of 61.2%, F content of 5.8%, and P content of 5.1%. The method for recovering fluorine, phosphorus, and rare earth elements from the mixed rare earth concentrate by hydrochloric acid leaching and two-step alkaline decomposition includes the following steps:

[0059] (1) According to the ratio of mixed rare earth concentrate (REO) to hydrochloric acid 1:2.0 g / mL, under stirring, Baotou mixed rare earth concentrate is added to industrial hydrochloric acid in the reactor and stirred evenly.

[0060] (2) Under sealed conditions, the temperature inside the reactor was gradually heated to 150℃, at which point the pressure inside the reactor was 0.4MPa, and the reaction was stirred for 5.5 hours. After the reaction was completed, the slurry was filtered, the leaching solution (acidic rare earth chloride solution) was retained, and the acid-leached mixed ore was rinsed with water until it met the requirements. The mass of REO in the acid-leached mixed ore was calculated by the mass of the added Baotou mixed rare earth concentrate and the mass of REO in the leaching solution.

[0061] (3) Calculate the amount of NaOH to be used according to 0.8 times the mass of REO in the acid-leached mixed ore in step (2). Prepare sodium hydroxide solution A by adding water with a mass fraction of 15% NaOH and put it into the alkaline decomposition reactor. Turn on the stirring, add the acid-leached mixed ore into the reactor, turn on the heating, raise the temperature to 110℃ and start the heat preservation reaction for 4.5h.

[0062] (4) After the reaction is completed, the slurry is filtered to obtain washing liquid 1. The filter cake is transferred to a beaker and washed twice with water and stirring to fully wash out the sodium fluoride, resulting in washing liquid 2 and washing liquid 3. The filter cake is a one-step alkali cake (a mixture of rare earth phosphate and rare earth hydroxide). The volume of the three washing liquids is measured after they are mixed evenly, and the fluorine content is tested. The yield of sodium fluoride is calculated based on this (since there is no other outlet for fluorine in this process, this is used as the basis for calculating the yield of sodium fluoride). The mixed washing liquid is evaporated, concentrated, cooled and crystallized. It is filtered and quickly washed with water to obtain sodium fluoride. The purity of sodium fluoride is analyzed by sampling.

[0063] (5) Calculate the amount of NaOH to be used according to 1.6 times the mass of the alkali cake REO in step (4). Prepare sodium hydroxide solution B by adding water with a mass fraction of 50% NaOH and put it into the alkali decomposition reactor. Start stirring, add the alkali cake from step one into the reactor, start heating, raise the temperature to 160℃ and start the heat preservation reaction, and keep the reaction at the heat preservation temperature for 7 hours.

[0064] (6) After the reaction is completed, the slurry is filtered to obtain two-step alkali cake and washing solution 1. The two-step alkali cake is transferred to a beaker, water is added and stirred and washed twice to fully wash out the trisodium dodecahydrate, and washing solution 2 and washing solution 3 are obtained. The main component of the two-step alkali cake is rare earth hydroxide. After the three washing solutions are mixed evenly, they are concentrated and then slowly cooled under stirring. The mixture is centrifuged and filtered using a rotary drum centrifuge to obtain trisodium dodecahydrate. The purity of trisodium dodecahydrate is weighed and sampled for analysis.

[0065] (7) The two-step alkali cake obtained in step (6) is put into the immersion solution obtained in step (2), and the pressure is maintained at 0.6 MPa and the temperature at 140℃. After stirring and reacting for 1 hour, the mixture is filtered. Hydrogen peroxide, ammonium carbonate, sodium sulfide and other impurity removal agents are added to the filtrate to remove impurity ions such as iron, fluorine, phosphorus, aluminum, lead and zinc. Finally, a mixed rare earth chloride solution with a concentration of 295 g / L is obtained.

[0066] In this embodiment, the rare earth recovery rate was 98.2%; the sodium fluoride recovery rate was 95.6% and the purity was 96.3%; and the trisodium dodecahydrate recovery rate was 95.3% and the purity was 95.2%.

[0067] Example 3

[0068] The raw material used in this embodiment is Baotou mixed rare earth concentrate, with the main components being: REO content of 61.2%, F content of 5.8%, and P content of 5.1%. The method for recovering fluorine, phosphorus, and rare earth elements from the mixed rare earth concentrate by hydrochloric acid leaching and two-step alkaline decomposition includes the following steps:

[0069] (1) According to the ratio of mixed rare earth concentrate (REO) to hydrochloric acid 1:2.0 g / mL, under stirring, Baotou mixed rare earth concentrate is added to 10 mol / L hydrochloric acid in the reactor and stirred evenly.

[0070] (2) Under sealed conditions, the temperature inside the reactor was gradually heated to 145℃, at which point the pressure inside the reactor was 0.6MPa, and the reaction was stirred for 4 hours. After the reaction was completed, the slurry was filtered, the leaching solution (acidic rare earth chloride solution) was retained, and the acid-leached mixed ore was rinsed with water until it met the requirements. The mass of REO in the acid-leached mixed ore was calculated by the mass of the added Baotou mixed rare earth concentrate and the mass of REO in the leaching solution.

[0071] (3) Calculate the amount of NaOH to be used according to 0.6 times the mass of REO in the acid-leached mixed ore in step (2). Prepare sodium hydroxide solution A by adding water with a mass fraction of 25% NaOH and put it into the alkaline decomposition reactor. Start stirring, add the acid-leached mixed ore into the reactor, start heating, raise the temperature to 135℃ and start the heat preservation reaction for 3 hours.

[0072] (4) After the reaction is completed, the slurry is filtered to obtain washing liquid 1. The filter cake is transferred to a beaker and washed twice with water and stirring to fully wash out the sodium fluoride, resulting in washing liquid 2 and washing liquid 3. The filter cake is a one-step alkali cake (a mixture of rare earth phosphate and rare earth hydroxide). The volume of the three washing liquids is measured after they are mixed evenly, and the fluorine content is tested. The yield of sodium fluoride is calculated based on this (since there is no other outlet for fluorine in this process, this is used as the basis for calculating the yield of sodium fluoride). The mixed washing liquid is evaporated, concentrated, cooled and crystallized. It is filtered and quickly washed with water to obtain sodium fluoride. The purity of sodium fluoride is analyzed by sampling.

[0073] (5) Calculate the amount of NaOH to be used according to 1.5 times the mass of the alkali cake REO in step (4). Prepare sodium hydroxide solution B by adding water with a mass fraction of 70% NaOH and put it into the alkali decomposition reactor. Start stirring, add the alkali cake from step one into the reactor, start heating, raise the temperature to 130℃ and start the heat preservation reaction, and keep the reaction at the heat preservation temperature for 10h.

[0074] (6) After the reaction is completed, the slurry is filtered to obtain two-step alkali cake and washing solution 1. The two-step alkali cake is transferred to a beaker, water is added and stirred and washed twice to fully wash out the trisodium dodecahydrate, and washing solution 2 and washing solution 3 are obtained. The main component of the two-step alkali cake is rare earth hydroxide. After the three washing solutions are mixed evenly, they are concentrated and then slowly cooled under stirring. The mixture is centrifuged and filtered using a rotary drum centrifuge to obtain trisodium dodecahydrate. The purity of trisodium dodecahydrate is weighed and sampled for analysis.

[0075] (7) The two-step alkali cake obtained in step (6) is put into the immersion solution obtained in step (2), and the pressure is kept at 0 MPa and the temperature at 90℃. After stirring and reacting for 4 hours, the mixture is filtered. Hydrogen peroxide, ammonium carbonate, sodium sulfide and other impurity removal agents are added to the filtrate to remove impurity ions such as iron, fluorine, phosphorus, aluminum, lead and zinc. Finally, a mixed rare earth chloride solution with a concentration of 296 g / L is obtained.

[0076] In this embodiment, the rare earth recovery rate was 98.3%; the sodium fluoride recovery rate was 95.9% and the purity was 96.8%; and the trisodium dodecahydrate recovery rate was 96.1% and the purity was 95.5%.

[0077] Example 4

[0078] The raw material used in this embodiment is Baotou mixed rare earth concentrate, with the main components being: REO content of 61.2%, F content of 5.8%, and P content of 5.1%. The method for recovering fluorine, phosphorus, and rare earth elements from the mixed rare earth concentrate by hydrochloric acid leaching and two-step alkaline decomposition includes the following steps:

[0079] (1) According to the ratio of mixed rare earth concentrate (REO) to hydrochloric acid 1:1.9 g / mL, under stirring, Baotou mixed rare earth concentrate is added to industrial hydrochloric acid in the reactor and stirred evenly.

[0080] (2) Under sealed conditions, the temperature inside the reactor was gradually heated to 100℃, at which point the pressure inside the reactor was 0.8MPa, and the reaction was stirred for 4.5h. After the reaction was completed, the slurry was filtered, the leaching solution (acidic rare earth chloride solution) was retained, and the acid-leached mixed ore was rinsed with water until it met the requirements. The mass of REO in the acid-leached mixed ore was calculated by the mass of the added Baotou mixed rare earth concentrate and the mass of REO in the leaching solution.

[0081] (3) Calculate the amount of NaOH to be used according to 0.75 times the mass of REO in the acid-leached mixed ore in step (2). Prepare sodium hydroxide solution A by adding water with a mass fraction of 18% NaOH and put it into the alkaline decomposition reactor. Start stirring, add the acid-leached mixed ore into the reactor, start heating, raise the temperature to 105℃ and start the heat preservation reaction for 5 hours.

[0082] (4) After the reaction is completed, the slurry is filtered to obtain washing liquid 1. The filter cake is transferred to a beaker and washed twice with water and stirring to fully wash out the sodium fluoride, resulting in washing liquid 2 and washing liquid 3. The filter cake is a one-step alkali cake (a mixture of rare earth phosphate and rare earth hydroxide). The volume of the three washing liquids is measured after they are mixed evenly, and the fluorine content is tested. The yield of sodium fluoride is calculated based on this (since there is no other outlet for fluorine in this process, this is used as the basis for calculating the yield of sodium fluoride). The mixed washing liquid is evaporated, concentrated, cooled and crystallized. It is filtered and quickly washed with water to obtain sodium fluoride. The purity of sodium fluoride is analyzed by sampling.

[0083] (5) Calculate the amount of NaOH to be used according to 1.7 times the mass of the alkali cake REO in step (4). Prepare sodium hydroxide solution B by adding water with a mass fraction of 55% NaOH and put it into the alkali decomposition reactor. Start stirring, add the alkali cake from step one into the reactor, start heating, raise the temperature to 145℃ and start the heat preservation reaction, and keep the reaction at the heat preservation temperature for 5 hours.

[0084] (6) After the reaction is completed, the slurry is filtered to obtain two-step alkali cake and washing solution 1. The two-step alkali cake is transferred to a beaker, water is added and stirred and washed twice to fully wash out the trisodium dodecahydrate, and washing solution 2 and washing solution 3 are obtained. The main component of the two-step alkali cake is rare earth hydroxide. After the three washing solutions are mixed evenly, they are concentrated and then slowly cooled under stirring. The mixture is centrifuged and filtered using a rotary drum centrifuge to obtain trisodium dodecahydrate. The purity of trisodium dodecahydrate is weighed and sampled for analysis.

[0085] (7) The two-step alkali cake obtained in step (6) is put into the immersion solution obtained in step (2), and the pressure is maintained at 0.2 MPa and the temperature at 100℃. After stirring and reacting for 3 hours, the mixture is filtered. Hydrogen peroxide, ammonium carbonate, sodium sulfide and other impurity removal agents are added to the filtrate to remove impurity ions such as iron, fluorine, phosphorus, aluminum, lead and zinc. Finally, a mixed rare earth chloride solution with a concentration of 287 g / L is obtained.

[0086] In this embodiment, the rare earth recovery rate was 98.5%; the sodium fluoride recovery rate was 95.2% and the purity was 96.2%; and the trisodium dodecahydrate recovery rate was 95.4% and the purity was 96.1%.

[0087] Example 5

[0088] The raw material used in this embodiment is Baotou mixed rare earth concentrate, with the main components being: REO content of 61.2%, F content of 5.8%, and P content of 5.1%. The method for recovering fluorine, phosphorus, and rare earth elements from the mixed rare earth concentrate by hydrochloric acid leaching and two-step alkaline decomposition includes the following steps:

[0089] (1) According to the ratio of mixed rare earth concentrate (REO) to hydrochloric acid 1:2.0 g / mL, under stirring, Baotou mixed rare earth concentrate is added to industrial hydrochloric acid in the reactor and stirred evenly.

[0090] (2) Under sealed conditions, the temperature inside the reactor was gradually heated to 110℃, at which point the pressure inside the reactor was 1.0 MPa, and the reaction was stirred for 4 hours. After the reaction was completed, the slurry was filtered, the leaching solution (acidic rare earth chloride solution) was retained, and the acid-leached mixed ore was rinsed with water until it met the requirements. The mass of REO in the acid-leached mixed ore was calculated by the mass of the added Baotou mixed rare earth concentrate and the mass of REO in the leaching solution.

[0091] (3) Calculate the amount of NaOH to be used according to 0.5 times the mass of REO in the acid-leached mixed ore in step (2). Prepare sodium hydroxide solution A by adding water with a mass fraction of 20% NaOH and put it into the alkaline decomposition reactor. Start stirring, add the acid-leached mixed ore into the reactor, start heating, raise the temperature to 130℃ and start the heat preservation reaction for 4 hours.

[0092] (4) After the reaction is completed, the slurry is filtered to obtain washing liquid 1. The filter cake is transferred to a beaker and washed twice with water and stirring to fully wash out the sodium fluoride, resulting in washing liquid 2 and washing liquid 3. The filter cake is a one-step alkali cake (a mixture of rare earth phosphate and rare earth hydroxide). The volume of the three washing liquids is measured after they are mixed evenly, and the fluorine content is tested. The yield of sodium fluoride is calculated based on this (since there is no other outlet for fluorine in this process, this is used as the basis for calculating the yield of sodium fluoride). The mixed washing liquid is evaporated, concentrated, cooled and crystallized. It is filtered and quickly washed with water to obtain sodium fluoride. The purity of sodium fluoride is analyzed by sampling.

[0093] (5) Calculate the amount of NaOH to be used according to 1.8 times the mass of the alkali cake REO in step (4). Prepare sodium hydroxide solution B by adding water with a mass fraction of 50% NaOH and put it into the alkali decomposition reactor. Start stirring, add the alkali cake from step (4) into the reactor, start heating, raise the temperature to 170℃ and start the heat preservation reaction, and keep the reaction at the heat preservation temperature for 6 hours.

[0094] (6) After the reaction is completed, the slurry is filtered to obtain two-step alkali cake and washing solution 1. The two-step alkali cake is transferred to a beaker, water is added and stirred and washed twice to fully wash out the trisodium dodecahydrate, and washing solution 2 and washing solution 3 are obtained. The main component of the two-step alkali cake is rare earth hydroxide. After the three washing solutions are mixed evenly, they are concentrated and then slowly cooled under stirring. The mixture is centrifuged and filtered using a rotary drum centrifuge to obtain trisodium dodecahydrate. The purity of trisodium dodecahydrate is weighed and sampled for analysis.

[0095] (7) The two-step alkali cake obtained in step (6) is put into the immersion solution obtained in step (2), and the pressure is maintained at 1.0 MPa and the temperature at 135℃. After stirring and reacting for 1.5 h, the mixture is filtered. Hydrogen peroxide, ammonium carbonate, sodium sulfide and other impurity removal agents are added to the filtrate to remove impurity ions such as iron, fluorine, phosphorus, aluminum, lead and zinc. Finally, a mixed rare earth chloride solution with a concentration of 302 g / L is obtained.

[0096] In this embodiment, the rare earth recovery rate was 98.6%; the sodium fluoride recovery rate was 96.1% and the purity was 97.0%; and the trisodium dodecahydrate recovery rate was 95.7% and the purity was 95.6%.

[0097] Example 6

[0098] The raw material used in this embodiment is Baotou mixed rare earth concentrate, with the main components being: REO content of 61.2%, F content of 5.8%, and P content of 5.1%. The method for recovering fluorine, phosphorus, and rare earth elements from the mixed rare earth concentrate by hydrochloric acid leaching and two-step alkaline decomposition includes the following steps:

[0099] (1) According to the ratio of mixed rare earth concentrate (REO) to hydrochloric acid 1:1.8 g / mL, Baotou mixed rare earth concentrate is added to industrial hydrochloric acid in the reactor under stirring and stirred evenly.

[0100] (2) Under sealed conditions, the temperature inside the reactor was gradually heated to 105℃, at which point the pressure inside the reactor was 0.1MPa, and the reaction was stirred for 6 hours. After the reaction was completed, the slurry was filtered, the leaching solution (acidic rare earth chloride solution) was retained, and the acid-leached mixed ore was rinsed with water until it met the requirements. The mass of REO in the acid-leached mixed ore was calculated by the mass of the added Baotou mixed rare earth concentrate and the mass of REO in the leaching solution.

[0101] (3) Calculate the amount of NaOH to be used according to 0.6 times the mass of REO in the acid-leached mixed ore in step (2). Prepare sodium hydroxide solution A by adding water with a mass fraction of 30% NaOH and put it into the alkaline decomposition reactor. Start stirring, add the acid-leached mixed ore into the reactor, start heating, raise the temperature to 120℃ and start the heat preservation reaction for 4.5h.

[0102] (4) After the reaction is completed, the slurry is filtered to obtain washing liquid 1. The filter cake is transferred to a beaker and washed twice with water and stirring to fully wash out the sodium fluoride, resulting in washing liquid 2 and washing liquid 3. The filter cake is a one-step alkali cake (a mixture of rare earth phosphate and rare earth hydroxide). The volume of the three washing liquids is measured after they are mixed evenly, and the fluorine content is tested. The yield of sodium fluoride is calculated based on this (since there is no other outlet for fluorine in this process, this is used as the basis for calculating the yield of sodium fluoride). The mixed washing liquid is evaporated, concentrated, cooled and crystallized. It is filtered and quickly washed with water to obtain sodium fluoride. The purity of sodium fluoride is analyzed by sampling.

[0103] (5) Calculate the amount of NaOH to be used according to 1.6 times the mass of the alkali cake REO in step (4). Prepare sodium hydroxide solution B by adding water with a mass fraction of 45% NaOH and put it into the alkali decomposition reactor. Start stirring, add the alkali cake from step (4) into the reactor, start heating, raise the temperature to 150℃ and start the heat preservation reaction, and keep the reaction at the heat preservation temperature for 7 hours.

[0104] (6) After the reaction is completed, the slurry is filtered to obtain two-step alkali cake and washing solution 1. The two-step alkali cake is transferred to a beaker, water is added and stirred and washed twice to fully wash out the trisodium dodecahydrate, and washing solution 2 and washing solution 3 are obtained. The main component of the two-step alkali cake is rare earth hydroxide. After the three washing solutions are mixed evenly, they are concentrated and then slowly cooled under stirring. The mixture is centrifuged and filtered using a rotary drum centrifuge to obtain trisodium dodecahydrate. The purity of trisodium dodecahydrate is weighed and sampled for analysis.

[0105] (7) The two-step alkali cake obtained in step (6) after washing is put into the immersion solution obtained in step (2), and the pressure is maintained at 0.5 MPa and the temperature at 125℃. After stirring and reacting for 2 hours, the mixture is filtered. Hydrogen peroxide, ammonium carbonate, sodium sulfide and other impurity removal agents are added to the filtrate to remove impurity ions such as iron, fluorine, phosphorus, aluminum, lead and zinc. Finally, a mixed rare earth chloride solution with a concentration of 291 g / L is obtained.

[0106] In this embodiment, the rare earth recovery rate was 98.4%; the sodium fluoride recovery rate was 95.7% and the purity was 96.5%; and the trisodium dodecahydrate recovery rate was 95.5% and the purity was 95.8%.

[0107] Comparative Example 1

[0108] The difference between this comparative example and Example 4 is that the temperature of the one-step alkaline hydrolysis in this comparative example is 70°C, that is, after turning on the heating in step (3), the temperature is raised to 70°C, and the other conditions are the same as those in Example 4.

[0109] Because the first-step alkaline hydrolysis temperature was low, the rare earth fluorides were not completely decomposed, resulting in a low sodium fluoride recovery rate. This undecomposed rare earth fluorides entered the second-step alkaline hydrolysis process, leading to a low purity of trisodium dodecahydrate. In this comparative example, the rare earth recovery rate was 96.2%; the sodium fluoride recovery rate was 72.4% with a purity of 95.6%; and the trisodium dodecahydrate recovery rate was 95.3% with a purity of 76.5%.

[0110] Comparative Example 2

[0111] The difference between this comparative example and Example 5 is that the temperature of the two-step alkaline hydrolysis in this comparative example is 115°C, that is, after the heating is turned on in step (5), the temperature is raised to 115°C. Other conditions are the same as in Example 5.

[0112] Because the two-step alkaline hydrolysis temperature is relatively low, the rare earth phosphate is not completely decomposed. The undecomposed rare earth phosphate cannot be dissolved by hydrochloric acid, resulting in low recovery rates of rare earth elements and trisodium phosphate dodecahydrate. In this comparative example, the rare earth recovery rate was 85.3%; the sodium fluoride recovery rate was 96.1% with a purity of 97.0%; and the trisodium phosphate dodecahydrate recovery rate was 62.1% with a purity of 95.3%.

[0113] Comparative Example 3

[0114] The difference between this comparative example and Example 4 is that the mass fraction of the NaOH solution used in the one-step alkaline hydrolysis in this comparative example is 6%, while the other conditions are the same as in Example 4.

[0115] Because the mass fraction of the NaOH solution in the first-step alkaline hydrolysis was too low, the rare earth fluorides were not completely decomposed. The undecomposed rare earth phosphates could not be dissolved by hydrochloric acid, resulting in a low sodium fluoride recovery rate. This undecomposed rare earth fluorides entered the second-step alkaline hydrolysis process, leading to low purity of trisodium phosphate dodecahydrate. In this comparative example, the rare earth recovery rate was 95.3%; the sodium fluoride recovery rate was 58.4% with a purity of 96.2%; and the trisodium phosphate dodecahydrate recovery rate was 94.2% with a purity of 71.7%.

[0116] Comparative Example 4

[0117] The difference between this comparative example and Example 6 is that the mass fraction of the NaOH solution used in the two-step alkaline hydrolysis in this comparative example is 35%, while the other conditions are the same as in Example 6.

[0118] Because the NaOH solution had a low mass fraction in the two-step alkaline hydrolysis, the rare earth phosphate was not completely decomposed. The undecomposed rare earth phosphate could not be dissolved by hydrochloric acid, resulting in low recovery rates of rare earth elements and trisodium phosphate dodecahydrate. In this comparative example, the rare earth recovery rate was 84.5%; the sodium fluoride recovery rate was 95.7% with a purity of 96.5%; and the trisodium phosphate dodecahydrate recovery rate was 64.3% with a purity of 87.9%.

Claims

1. A method for recovering fluorine, phosphorus, and rare earth elements from mixed rare earth concentrate by hydrochloric acid leaching and two-step alkaline decomposition, characterized in that: Includes the following steps: (1) Hydrochloric acid is mixed with mixed rare earth concentrate, and the mixture is heated and pressurized to leach, resulting in acid-leached mixed ore and acidic rare earth chloride solution; The mixed rare earth concentrate contains 45% to 70% REO, 4% to 9% F, and 3% to 7% P. The hydrochloric acid is industrial hydrochloric acid, added at a ratio of REO mass to HCl volume of 1:1.8~1:2.0 g / mL in the mixed rare earth concentrate; (2) Stir the acid-leached mixed ore with sodium hydroxide solution A evenly, heat and keep warm to react. After the reaction is completed, add water to wash and filter to obtain one-step alkali cake and one-step alkali solution. The one-step alkali solution is concentrated to obtain sodium fluoride and one-step alkali water. The mass fraction of sodium hydroxide solution A is controlled at 15%~30%, and the mass of sodium hydroxide is 0.5 to 0.8 times the mass of REO in the acid-leached mixed ore. (3) Stir the first-step alkali cake and sodium hydroxide solution B evenly, heat and keep warm to react. After the reaction is completed, filter to obtain the second-step alkali cake and the second-step alkali solution. The second-step alkali solution is purified, cooled and crystallized to obtain trisodium phosphate dodecahydrate. The remaining alkali solution is further concentrated to obtain the second-step alkali water, which is reused in the sodium hydroxide solution B of this step. The concentrated condensate is returned to the second-step alkali cake water washing and recycled. The second-step alkali cake water washing, the washing water is returned to be used to dilute the alkali decomposition slurry. The mass fraction of sodium hydroxide solution B is controlled at 45%~70%, and the mass of sodium hydroxide is 1.5 to 1.8 times the mass of REO in the first-step alkali cake. (4) After the two-step alkali cake is washed with water, it is put into the acidic rare earth chloride solution in step (1), heated and kept warm for reaction. After the reaction is completed, it is filtered, and the filtrate is purified to obtain rare earth chloride solution.

2. The method for recovering fluorine, phosphorus, and rare earth elements by hydrochloric acid leaching and two-step alkaline decomposition of mixed rare earth concentrate according to claim 1, characterized in that: The heating temperature in step (1) is 100℃~150℃, the reaction pressure is 0.1~1.0MPa, and the reaction time is 4h~6h.

3. The method for recovering fluorine, phosphorus, and rare earth elements by hydrochloric acid leaching and two-step alkaline decomposition of mixed rare earth concentrate according to claim 1, characterized in that: Step (2) The heating temperature is 105℃~135℃, and the reaction is kept at this temperature for 3h~5h.

4. The method for recovering fluorine, phosphorus, and rare earth elements by hydrochloric acid leaching and two-step alkaline decomposition of mixed rare earth concentrate according to claim 1, characterized in that: Step (3) The heating temperature is 130℃~170℃, and the reaction is kept at this temperature for 5h~10h.

5. The method for recovering fluorine, phosphorus, and rare earth elements by hydrochloric acid leaching and two-step alkaline decomposition of mixed rare earth concentrate according to claim 1, characterized in that: Step (4) The heating temperature is 90~140℃, the reaction pressure is 0~1.0MPa, and the reaction time is 1h~4h.

6. The method for recovering fluoride, phosphorus, and rare earth elements from mixed rare earth concentrate by hydrochloric acid leaching and two-step alkaline decomposition according to claim 5, characterized in that: In step (4), hydrogen peroxide, ammonium bicarbonate, and sodium sulfide are added sequentially to remove impurities from the filtrate after filtration.

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