Method for recovering fluorine, phosphorus and rare earth through hydrochloric acid leaching and two-step alkaline decomposition of mixed rare earth concentrate

Abstract

The invention belongs to the technical field of rare earth ore concentrate treatment, and particularly relates to a method for recycling fluorine, phosphorus and rare earth through mixed rare earth ore concentrate hydrochloric acid leaching and two-step alkaline decomposition. The method comprises the following steps: mixing hydrochloric acid and mixed rare earth concentrate, reacting and leaching to obtain acid leached mixed ore and an acidic rare earth chloride solution; uniformly stirring the acid-leached mixed ore and a sodium hydroxide solution A, heating for reaction, adding water for washing, filtering to obtain a first-step alkali cake and a first-step alkali liquor, and concentrating the first-step alkali liquor to obtain sodium fluoride; uniformly stirring the first-step alkali cake and a sodium hydroxide solution B, and treating to obtain a second-step alkali cake and a second-step alkali solution; treating the two-step alkali liquor to obtain trisodium phosphate dodecahydrate; and putting the two-step alkali cake into an acidic rare earth chloride solution, and treating to obtain rare earth chloride feed liquid. The method for recycling fluorine, phosphorus and rare earth through hydrochloric acid leaching and two-step alkaline decomposition of the mixed rare earth concentrate has the advantages of being low in production cost, small in three-waste generation amount, easy to operate and high in rare earth, fluorine and phosphorus recycling rate.

Description

Technical Field

[0001] The present invention belongs to the technical field of the treatment of rare earth concentrates, and particularly relates to a method for hydrochloric acid leaching of mixed rare earth concentrates and two-step alkali decomposition to recover fluorine, phosphorus and rare earths. Background Art

[0002] The Bayan Obo rare earth ore in Baotou is a mixed rare earth ore, and its rare earth elements are respectively hosted in bastnaesite and monazite ores. In the raw ores mined in different periods, the proportions of bastnaesite and monazite ores are not fixed.

[0003] At present, the large-scale treatment methods for the Bayan Obo rare earth ore in Baotou are mainly the concentrated sulfuric acid high-temperature roasting process; followed by the traditional caustic soda decomposition process. The advantages of the concentrated sulfuric acid high-temperature roasting process are simple and efficient, and the rare earth recovery rate is about 94% or more. In order to achieve a higher rare earth recovery rate, the addition amount of sulfuric acid is much larger than the theoretical amount. A large amount of sulfuric acid decomposes into SO2 and SO3 at high temperature, and the F element in the mineral also reacts with sulfuric acid at high temperature to generate HF. The treatment of a large amount of highly polluting tail gas is complex and costly; the phosphorus element in the mineral forms pyrophosphate after sulfuric acid roasting, resulting in a waste of phosphorus resources; at the same time, the amount of tailings generated during the production process is also very large, and the cost of solid waste disposal is high. The characteristics of the caustic soda decomposition process are mild reaction conditions, and no highly polluting tail gas will be generated during the production process, but a large amount of waste water and solid waste will be generated, and the overall treatment cost is relatively high.

[0004] Patent CN102251106A discloses a method for decomposing Baotou rare earth concentrates by an alkali method, which uses hydrochloric acid to remove calcium + alkali decomposition + acid dissolution to obtain a rare earth chloride solution. This method is simple, has a short process, and less pollution, and can recover resources such as F and P. However, the recovered fluorine and phosphorus are mixtures with a low market value; at the same time, the overall production consumption of flake caustic soda is relatively high.

[0005] Patent CN106978531A discloses a method for jointly decomposing mixed rare earth concentrates by acid and alkali. This method mixes mixed rare earth concentrates with REO≥50%, CaO≤12% and SiO2≤1.5% with concentrated sulfuric acid, roasts at 120~180°C, and the roasted product is leached with water to obtain a mixed water leaching residue of calcium sulfate and monazite ore. The calcium sulfate and monazite ore are separated by a gravity separation process and then the monazite ore is decomposed by an alkali solution. Although this method realizes the comprehensive recovery of fluorine and phosphorus resources and the recycling of washing alkali waste water, it is easy to cause the rotary kiln to form rings during the low-temperature roasting process. At the same time, due to the small amount of sulfuric acid, the decomposition control of bastnaesite ore becomes more difficult; a part of radioactive calcium sulfate waste residue is obtained by gravity separation, resulting in the loss of fine-grained rare earths and making them unable to be recovered.

[0006] Patent CN103103349A discloses a method for the combined acid-base low-temperature decomposition of Bayan Obo rare earth concentrate. The rare earth concentrate with a rare earth oxide content greater than 65% uses AlCl3 as a complexing agent and is leached by hydrochloric acid complexation. Na2SO4 is added to convert the rare earth in the leaching solution into RENa(SO4)2 precipitate. The rare earth sodium sulfate double salt and monazite slag are decomposed by the alkali method. Although there is no harmful waste gas produced, the composition of the alkali wastewater is complex, the recovery of valuable elements is difficult, and the production cost is relatively high.

[0007] Patent CN109536746A discloses a method for the cyclic slurry decomposition of low-calcium high-grade mixed rare earth concentrate. The mixed rare earth concentrate with REO≥62% and CaO≤3% is mixed with sulfuric acid solution in proportion and heated for slurry reaction to mainly decompose fluorine-containing minerals. The tail gas is absorbed to form a by-product of fluorosilicic mixed acid. After the reaction, the acid leaching residue is leached with water to dissolve calcium sulfate and rare earth sulfate in the water leaching solution. After neutralization and impurity removal of the water leaching solution, a phosphorus-iron-thorium slag is formed. The acid leaching solution is supplemented with sulfuric acid and then recycled to treat new ore. The water leaching residue and phosphorus-iron-thorium slag are decomposed with concentrated alkali solution. After the alkali wastewater is crystallized to recover sodium phosphate, it is recycled. Although this method effectively improves the separation efficiency of fluorine and phosphorus elements, during the sulfuric acid slurry process of this process, Si element escapes together with F in the form of SiF4 gas, resulting in a long process and high cost for the recovery and utilization of F element. In addition, the overall process steps for recovering rare earth from the concentrate are numerous, resulting in large investment in production equipment and floor area.

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

[0009] In patents CN103045851A and CN105132682A, the oxidation roasting and alkali decomposition processes are combined to treat the Baotou mixed rare earth concentrate. Utilizing the non-reducing property of sulfuric acid, all the rare earth in the roasting is leached out, and the tetravalent cerium in the leaching solution forms complexes with fluorine and phosphorus. Then, the complexes are separated to a limited extent by extraction method to produce a mixed product of cerium fluoride and cerium phosphate. Although this technology effectively reduces the alkali consumption during the alkali decomposition process, there are still problems such as the difficult treatment of mixed sodium salt wastewater and the difficult application and development of 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 existing in the prior art, and provide a method for hydrochloric acid leaching of mixed rare earth concentrates and two-step alkali decomposition to recover fluorine, phosphorus and rare earths, which has the advantages of low production cost, less generation of three wastes, simple operation, high rare earth recovery rate, and comprehensive utilization of valuable elements, realizes the efficient and green extraction of rare earths in Baotou mixed rare earth concentrates and the resource utilization of valuable elements such as fluorine and phosphorus, and prepares high-quality rare earth chlorides, trisodium phosphate dodecahydrate and sodium fluoride products.

[0011] The method for hydrochloric acid leaching of mixed rare earth concentrates and two-step alkali decomposition to recover fluorine, phosphorus and rare earths according to the present invention includes the following steps: (1) Mix hydrochloric acid with mixed rare earth concentrates, and carry out heating and pressurized leaching to obtain acid-leached mixed ore and acidic rare earth chloride solution; (2) Stir the acid-leached mixed ore evenly with sodium hydroxide solution A, heat and keep warm for reaction. After the reaction is completed, wash with water and filter to obtain the first-step alkali cake and the first-step alkali solution. The first-step alkali solution is concentrated to obtain sodium fluoride and the first-step alkali water; (3) Stir the first-step alkali cake evenly with sodium hydroxide solution B, heat and keep warm for reaction. 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 alkali solution is further concentrated to obtain the second-step alkali water, which is recycled to sodium hydroxide solution B in this step, and the concentrated condensate water is returned to the washing cycle of the second-step alkali cake for reuse. The second-step alkali cake is washed with water, and the washing water is returned for use as diluting the alkali decomposition slurry; (4) The second-step alkali cake is washed with water and then put into the acidic rare earth chloride solution in step (1), heated and kept warm for reaction. After the reaction is completed, filter, and the filtrate is purified to finally obtain the rare earth chloride feed liquid.

[0012] In the mixed rare earth concentrates described above, the REO content is 45% - 70%, the F content is 4% - 9%, and the P content is 3% - 7%.

[0013] The hydrochloric acid in step (1) is industrial hydrochloric acid, which is added according to the ratio of mixed rare earth concentrates (REO) to hydrochloric acid of 1:1.8 - 1:2.0 g / mL. The industrial hydrochloric acid is normal commercially available hydrochloric acid, and its mass content is about 30%.

[0014] The heating temperature in step (1) is 100°C - 150°C, the reaction pressure is 0.1 - 1.0 MPa, and the reaction time is 4 h - 6 h.

[0015] In step (2), the addition amount of sodium hydroxide solution A, calculated as sodium hydroxide, is 0.5 - 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% - 30%.

[0016] In step (2), the heating temperature is 105°C to 135°C, and the holding reaction is carried out for 3 h to 5 h.

[0017] In step (3), the addition amount of sodium hydroxide solution B, calculated as sodium hydroxide, is such that the mass of sodium hydroxide is 1.5 to 1.8 times the mass of REO in the one-step alkali cake, and the mass fraction of sodium hydroxide solution B is controlled to be 45% to 70%.

[0018] In step (3), the heating temperature is 130°C to 170°C, and the holding reaction is carried out for 5 h to 10 h.

[0019] In step (4), the heating temperature is 90 to 140°C, the reaction pressure is 0 to 1.0 MPa, and the reaction time is 1 h to 4 h.

[0020] When removing impurities from the filtrate after filtration in step (4), hydrogen peroxide, ammonium bicarbonate, and sodium sulfide are added in sequence for impurity removal. The amounts of hydrogen peroxide, ammonium bicarbonate, and sodium sulfide used for impurity removal only need to meet the requirement of the impurity concentration to be removed, and they are all conventional operations of those skilled in the art, so the specific added mass is not described in detail.

[0021] Specifically, the method for hydrochloric acid leaching of mixed rare earth concentrate and two-step alkali decomposition to recover fluorophosphorus and rare earths includes the following steps: (1) According to the ratio of mixed rare earth concentrate (REO) to hydrochloric acid of 1:1.8 to 1:2.0 g / mL, concentrated hydrochloric acid is added to the Baotou mixed rare earth concentrate; the mixed slurry is heated at 100°C to 150°C under a pressure of 0.1 to 1.0 MPa for 4 h to 6 h for leaching. The bastnaesite in the concentrate reacts with hydrochloric acid to generate rare earth fluoride, rare earth chloride, and CO2. Among them, rare earth chloride exists in the hydrochloric acid leaching solution, rare earth fluoride and unreacted rare earth phosphate enter the acid leaching mixed ore, and CO2 escapes in the form of gas. The reaction tail gas is recovered and utilized by condensation. The reaction equation during the reaction is as follows: 3REFCO3 + 6HCl = 2RECl3 + REF3↓ + 3CO2↑ + 3H2O.

[0022] (2) The acid-leached mixed ore obtained in step (1) is subjected to alkaline decomposition with sodium hydroxide solution A with a mass fraction of 15% - 30%. The addition amount of sodium hydroxide is 0.5 - 0.8 times the mass of REO in the acid-leached mixed ore. The heating temperature is 105°C - 135°C, and the heat preservation reaction is carried out for 3 - 5 hours. By utilizing the difference in the difficulty of the reaction between rare earth fluoride and rare earth phosphate with NaOH, the rare earth fluoride therein is decomposed to form rare earth hydroxide (RE(OH)3) and sodium fluoride (NaF), while the rare earth phosphate basically does not participate in the reaction at this time. After the reaction, water is added for washing and filtration to obtain a first-stage alkaline cake and a first-stage alkaline solution. The first-stage alkaline solution is concentrated to obtain sodium fluoride and first-stage alkaline water. The first-stage alkaline cake is a mixture of rare earth hydroxide and rare earth phosphate; the first-stage alkaline solution is a mixed solution of sodium fluoride and sodium hydroxide, and sodium fluoride products are obtained through concentrated crystallization and solid-liquid separation. The concentrated condensed water is returned to the washing of the first-stage alkaline cake for recycling, and the first-stage alkaline water is returned to the first-stage alkaline decomposition for recycling. The reaction equations during the reaction are as follows: REF3 + 3NaOH = RE(OH)3↓ + 3NaF.

[0023] (3) The first-stage alkaline cake obtained in step (2) is subjected to alkaline decomposition with sodium hydroxide solution B with a mass fraction of 45% - 70%. The addition amount of sodium hydroxide is 1.5 - 1.8 times the mass of REO in the first-stage alkaline cake. The heating temperature is 130°C - 170°C, and the heat preservation reaction is carried out for 5 - 10 hours, so that rare earth phosphate reacts with NaOH to form rare earth hydroxide (RE(OH)3) precipitate and trisodium phosphate dodecahydrate (Na3PO4). After the reaction, filtration is carried out to obtain a second-stage alkaline cake and a second-stage alkaline solution; the second-stage alkaline solution is subjected to impurity removal and cooling crystallization to obtain trisodium phosphate dodecahydrate, and the alkaline solution is further concentrated to obtain second-stage alkaline water, which is recycled to the sodium hydroxide solution B for the second-stage alkaline decomposition. The concentrated condensed water is returned to the washing of the second-stage alkaline cake for recycling. The second-stage alkaline cake is washed, and the washing water is returned for use in diluting the alkaline decomposition slurry. The main component of the second-stage alkaline cake is rare earth hydroxide. The reaction equations during the reaction are as follows: REPO4 + 3NaOH = RE(OH)3↓ + Na3PO4.

[0024] (4) The second-stage alkaline cake obtained in step (3) is added to the acidic rare earth chloride solution in step (1). The heating temperature is 90 - 140°C, the reaction pressure is 0 - 1.0 MPa, and the reaction time is 1 - 4 hours, so that rare earth hydroxide reacts with the remaining hydrochloric acid to obtain a mixed rare earth chloride feed liquid with a higher concentration. Then, through impurity removal and concentration processes, impurity ions such as iron, fluorine, phosphorus, aluminum, lead, and zinc are removed, and finally qualified mixed rare earth chloride products are obtained.

[0025] In the above step (1), the concentrated hydrochloric acid is used to decompose bastnasite in the Baotou mixed rare earth concentrate, so that about 2 / 3 of the rare earths in bastnasite are leached to form rare earth chlorides, and about 1 / 3 of the rare earths exist in the solid phase in the form of rare earth fluorides. In this step, if too little hydrochloric acid is added, the decomposition of bastnasite will be incomplete; but if the amount of hydrochloric acid added is too large, the remaining hydrochloric acid will ultimately not be completely neutralized by rare earth hydroxide, resulting in acid imbalance.

[0026] In the above step (1), the temperature is a key factor affecting the reaction effect and process. If the temperature is too low, such as below 100 °C, the reaction rate is too slow and the required reaction time is very long, which not only reduces the production efficiency of the equipment but also increases energy consumption; while if the reaction temperature is to be increased, such as 120 °C, a certain pressure needs to be maintained. Therefore, in this step, the reaction temperature is required to be between 100 °C and 150 °C, and the reaction pressure is between 0.1 and 1.0 MPa. The preferred reaction temperature is between 110 °C and 140 °C, the reaction pressure is between 0.4 and 0.6 MPa, and the reaction time is 4.5 h to 5.5 h.

[0027] In the above step (2), in the one-step alkali decomposition process of rare earth fluoride, the concentration of sodium hydroxide has a significant impact on the reaction effect, and the mass fraction of sodium hydroxide in the starting alkali solution is controlled between 15% and 30%. If the mass fraction of sodium hydroxide in the alkali solution is less than 15%, the reaction rate of rare earth fluoride is slow; if the mass fraction of sodium hydroxide in the alkali solution is greater than 30%, a part of rare earth phosphate will also be decomposed, resulting in the excessive content of trisodium phosphate in the sodium fluoride product. The reaction temperature also has a very important impact on the reaction effect. When the reaction temperature is less than 105 °C, the reaction rate is slow; when the reaction temperature is greater than 135 °C, a part of rare earth phosphate will be decomposed. Therefore, the reaction temperature is controlled between 105 °C and 135 °C. The preferred mass fraction of sodium hydroxide in the alkali solution is controlled between 20% and 25%, and the reaction temperature is controlled between 115 °C and 125 °C.

[0028] In the above step (2), the obtained one-step alkali solution is concentrated, crystallized and solid-liquid separated to produce sodium fluoride products. The concentrated condensate is returned to the washing of the one-step alkali cake for recycling, and the one-step mother liquor is returned to the one-step alkali decomposition for recycling.

[0029] In the above step (3), during the two-step alkali decomposition process of rare earth phosphate, the effects of sodium hydroxide concentration and reaction temperature on the reaction process are very important. The mass fraction of sodium hydroxide in the alkali solution is generally controlled between 45% and 70%, and the reaction temperature is generally controlled between 130°C and 170°C. If the sodium hydroxide concentration is too low or the reaction temperature is too low, the reaction rate is slow and the decomposition of rare earth phosphate is incomplete, resulting in a decrease in the recovery rates of rare earth and phosphorus elements. If the sodium hydroxide concentration and reaction temperature are too high, it is easy to cause the reaction slurry to be thick and the decomposition of rare earth phosphate to be incomplete. Preferably, the mass fraction of sodium hydroxide is controlled between 50% and 60%, and the reaction temperature is controlled between 140°C and 160°C.

[0030] In the above step (3), the two-step alkali decomposition slurry is subjected to 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 purified and then subjected to solid-liquid separation. The filtrate is slowly cooled and crystallized and centrifugally filtered to obtain a trisodium phosphate dodecahydrate product and a sodium hydroxide two-step mother liquor. The mother liquor is concentrated and then returned to the two-step alkali decomposition for recycling, and the concentrated condensed water is returned to the two-step alkali cake washing for recycling.

[0031] The present invention is applicable to the process of producing mixed rare earth chlorides from mixed rare earth concentrates. By hydrochloric acid leaching and two-step alkali decomposition, the rare earth, fluorine, and phosphorus resources in the rare earth concentrates are recovered, and the unit consumption of the main auxiliary materials such as sodium hydroxide and hydrochloric acid is significantly reduced. It avoids the problems of complex tail gas treatment and difficult recovery of fluorine and phosphorus resources existing in the process of treating mixed rare earth concentrates by the sulfuric acid method, and has the advantages of low production cost, less generation of three wastes, simple operation, high recovery rates of rare earth, fluorine, and phosphorus, and comprehensive utilization of valuable elements.

[0032] Compared with the prior art, the beneficial effects of the present invention are as follows: (1) In the method for hydrochloric acid leaching of mixed rare earth concentrates and two-step alkali decomposition to recover fluorine, phosphorus, and rare earth of the present invention, the bastnaesite minerals in the Baotou mixed rare earth concentrates are basically completely decomposed by concentrated hydrochloric acid, and more than 38% of the rare earth in the concentrates is converted into rare earth chlorides, reducing the sodium hydroxide consumption required for subsequent mineral alkali decomposition by more than 33%. At the same time, it avoids the influence of Na2CO3 generated during the alkali decomposition process on the fluorine and phosphorus recovery system.

[0033] (2) The method for hydrochloric acid leaching of mixed rare earth concentrate of the present invention and two-step alkali decomposition to recover fluorine, phosphorus and rare earths ensures the efficient decomposition of rare earth fluoride and improves the recovery rate of fluorine by precisely controlling the concentration of sodium hydroxide and the reaction temperature during the one-step alkali decomposition process. Meanwhile, the decomposition of rare earth phosphate is avoided as much as possible to ensure the purity of sodium fluoride products. During the two-step alkali decomposition process, a sodium hydroxide solution with a higher concentration is used at a higher temperature to achieve the rapid and efficient decomposition of rare earth phosphate, improving the recovery rates of trisodium phosphate dodecahydrate and rare earths and the production efficiency of the equipment. During the two-step alkali decomposition process, the alkaline water containing fluorine and phosphorus is evaporated and concentrated, and all the concentrated alkaline water is recycled to the alkali decomposition process, greatly reducing the unit consumption of alkali in the alkali decomposition process; all the concentrated condensed water is recycled to the washing process of the alkali cake, achieving zero discharge of alkaline wastewater in the alkali decomposition process.

[0034] (3) The method for hydrochloric acid leaching of mixed rare earth concentrate of the present invention and two-step alkali decomposition to recover fluorine, phosphorus and rare earths realizes the efficient recovery of rare earths, fluorine and phosphorus in the minerals of Baotou mixed rare earth concentrate, and prepares high-quality mixed rare earth chlorides, sodium fluoride and trisodium phosphate dodecahydrate products. Among them, the rare earth recovery rate for producing mixed rare earth chlorides 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%. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] Figure 1 It is the main process flow chart of the method for hydrochloric acid leaching of mixed rare earth concentrate of the present invention and two-step alkali decomposition to recover fluorine, phosphorus and rare earths. DETAILED DESCRIPTION OF THE INVENTION

[0036] The present invention will be further described below in conjunction with specific embodiments.

[0037] The raw materials and auxiliaries used in the following examples and comparative examples are all commercially available products. The hydrochloric acid used is commercially available industrial hydrochloric acid without dilution. The main process of the present invention is as Figure 1 shown.

[0038] Example 1 The raw material used in this example is Baotou mixed rare earth concentrate, and the main components are: the REO content is 61.2%, the F content is 5.8%, and the P content is 5.1%. The method for hydrochloric acid leaching of the mixed rare earth concentrate and two-step alkali decomposition to recover fluorine, phosphorus and rare earths includes the following steps: (1) Weigh according to the ratio of Baotou mixed rare earth concentrate (REO) to hydrochloric acid of 1:1.8 g / mL. Under stirring, add Baotou mixed rare earth concentrate into the industrial hydrochloric acid in the reaction kettle and stir evenly.

[0039] (2) Under sealed conditions, gradually heat the temperature inside the reaction kettle to 130 °C. At this time, the pressure inside the reaction kettle is 0.5 MPa. Stir and react for 5 h. After the reaction is completed, filter the slurry. Keep the leaching solution (acidic rare earth chloride solution) for use. Wash the acid-leached mixed ore with water until it is qualified. The mass of REO in the acid-leached mixed ore is calculated by adding the mass of the Baotou mixed rare earth concentrate and the mass of REO in the leaching solution.

[0040] (3) Calculate the dosage of NaOH 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 according to a mass fraction of 20% of NaOH. Put it into the alkali decomposition reaction kettle, start stirring, add the acid-leached mixed ore into the reaction kettle, start heating, and raise the temperature to 125 °C for heat preservation reaction for 4 h.

[0041] (4) After the reaction is completed, filter the slurry to obtain washing solution 1. Transfer the filter cake to a beaker, add water and stir to wash twice to wash out the sodium fluoride completely to obtain washing solution 2 and washing solution 3. The filter cake is the first-step alkali cake (a mixture of rare earth phosphate and rare earth hydroxide). After mixing the three washing solutions evenly, measure the volume and take a sample to detect the fluorine content, and calculate the sodium fluoride recovery rate based on this (because in this process, there is no other outlet for fluorine elements, so this is used as the basis for calculating the sodium fluoride recovery rate). Evaporate and concentrate the mixed washing solution, cool it down and crystallize, filter and quickly wash the crystals with water to obtain sodium fluoride, and take a sample to analyze the purity of sodium fluoride.

[0042] (5) Calculate the dosage of NaOH according to 1.7 times the mass of REO in the first-step alkali cake in step (4). Prepare sodium hydroxide solution B by adding water according to a mass fraction of 60% of NaOH. Put it into the alkali decomposition reaction kettle, start stirring, add the first-step alkali cake into the reaction kettle, start heating, and raise the temperature to 150 °C for heat preservation reaction for 8 h.

[0043] (6) After the reaction is completed, filter the slurry to obtain the second-step alkali cake and washing solution 1. Transfer the second-step alkali cake to a beaker, add water and stir to wash twice to wash out the trisodium phosphate dodecahydrate completely to obtain washing solution 2 and washing solution 3. The main component of the second-step alkali cake is rare earth hydroxide. After mixing the three washing solutions evenly, concentrate them, and then slowly cool down under stirring. Use a drum centrifuge for centrifugal filtration to obtain trisodium phosphate dodecahydrate, weigh it and take a sample to analyze the purity of trisodium phosphate dodecahydrate.

[0044] (7) Put the second-step alkali cake obtained in step (6) into the leaching solution obtained in step (2), keep the pressure at 0.5 MPa and the temperature at 120 °C, stir and react for 2.5 h and then filter. Add impurity removal agents such as hydrogen peroxide, ammonium bicarbonate, and sodium sulfide to the filtrate for reaction to remove impurity ions such as iron, fluorine, phosphorus, aluminum, lead, and zinc. Finally, obtain a mixed rare earth chloride solution with a concentration of 300 g / L.

[0045] In this example, the recovery rate of rare earth is 98.5%; the recovery rate of sodium fluoride is 96.3% and the purity is 96.6%; the recovery rate of trisodium phosphate dodecahydrate is 95.8% and the purity is 96.4%.

[0046] Example 2 The raw material used in this example is Baotou mixed rare earth concentrate, and the main components are: the REO content is 61.2%, the F content is 5.8%, and the P content is 5.1%. The method for hydrochloric acid leaching and two-step alkali decomposition of the mixed rare earth concentrate to recover fluorine, phosphorus and rare earth includes the following steps: (1) According to the ratio of mixed rare earth concentrate (REO) to hydrochloric acid of 1:2.0 g / mL, under stirring, add Baotou mixed rare earth concentrate into industrial hydrochloric acid in the reaction kettle and stir evenly.

[0047] (2) Under sealed conditions, gradually heat the temperature in the reaction kettle to 150 °C. At this time, the pressure in the reaction kettle is 0.4 MPa, and stir and react for 5.5 h. After the reaction is completed, filter the slurry, keep the leaching solution (acidic rare earth chloride solution) for use, and wash the acid-leached mixed ore with water until it is 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.

[0048] (3) Calculate the dosage of NaOH 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 according to the mass fraction of NaOH of 15%, put it into the alkali decomposition reaction kettle, start stirring, add the acid-leached mixed ore into the reaction kettle, start heating, and raise the temperature to 110 °C to start heat preservation reaction, and keep the heat preservation reaction for 4.5 h.

[0049] (4) After the reaction is completed, filter the slurry to obtain washing solution 1. Transfer the filter cake to a beaker, add water and stir and wash twice to wash out the sodium fluoride therein to obtain washing solution 2 and washing solution 3. The filter cake is the first-step alkali cake (a mixture of rare earth phosphate and rare earth hydroxide). After mixing the three washing solutions evenly, measure the volume and take samples to detect the fluorine content, and calculate the sodium fluoride recovery rate based on this (because in this process, there is no other outlet for fluorine element, so this is used as the basis for calculating the sodium fluoride recovery rate). Evaporate and concentrate the mixed washing solution, cool it down and crystallize, filter and quickly wash the crystals with water to obtain sodium fluoride, and take samples to analyze the purity of sodium fluoride.

[0050] (5) Calculate the dosage of NaOH according to 1.6 times the mass of REO in the first-step alkali cake in step (4), prepare sodium hydroxide solution B by adding water according to the mass fraction of NaOH of 50%, put it into the alkali decomposition reaction kettle, start stirring, add the first-step alkali cake into the reaction kettle, start heating, and raise the temperature to 160 °C to start heat preservation reaction, and keep the heat preservation reaction for 7 h.

[0051] After the reaction is completed, the slurry is filtered to obtain the second-stage alkali cake and washing solution 1. The second-stage alkali cake is transferred to a beaker and stirred and washed twice with water to thoroughly wash out the trisodium phosphate dodecahydrate therein, obtaining washing solutions 2 and 3. The main component of the second-stage alkali cake is rare earth hydroxide. After the three washing solutions are mixed evenly, they are concentrated, and then slowly cooled and cooled under stirring. A drum centrifuge is used for centrifugal filtration to obtain trisodium phosphate dodecahydrate, which is weighed and sampled to analyze the purity of trisodium phosphate dodecahydrate.

[0052] (7)The second-stage alkali cake obtained in step (6) is put into the leaching solution obtained in step (2), maintaining a pressure of 0.6 MPa and a temperature of 140 °C. After stirring and reacting for 1 h, it is filtered. The filtrate is respectively added with impurity removal agents such as hydrogen peroxide, ammonium bicarbonate, and sodium sulfide for reaction to remove impurity ions such as iron, fluorine, phosphorus, aluminum, lead, and zinc, and finally a mixed rare earth chloride solution with a concentration of 295 g / L is obtained.

[0053] In this example, the rare earth recovery rate is 98.2%; the sodium fluoride recovery rate is 95.6% and the purity is 96.3%; the trisodium phosphate dodecahydrate recovery rate is 95.3% and the purity is 95.2%.

[0054] Example 3 The raw material used in this example is Baotou mixed rare earth concentrate, and the main components are: the REO content is 61.2%, the F content is 5.8%, and the P content is 5.1%. The method for hydrochloric acid leaching and two-step alkali decomposition of the mixed rare earth concentrate to recover fluorine, phosphorus, and rare earths includes the following steps: (1)According to the ratio of mixed rare earth concentrate (REO) to hydrochloric acid of 1:2.0 g / mL, under stirring, the Baotou mixed rare earth concentrate is added to 10 mol / L hydrochloric acid in the reaction kettle and stirred evenly.

[0055] (2)Under sealed conditions, the temperature in the reaction kettle is gradually heated to 145 °C. At this time, the pressure in the reaction kettle is 0.6 MPa, and it is stirred and reacted for 4 h. After the reaction is completed, the slurry is filtered, and the leaching solution (acidic rare earth chloride solution) is reserved. The acid-leached mixed ore is washed with water until qualified. The mass of REO in the acid-leached mixed ore is calculated by the mass of REO in the added Baotou mixed rare earth concentrate and the leaching solution.

[0056] (3)According to 0.6 times the mass of REO in the acid-leached mixed ore in step (2), calculate the dosage of NaOH, prepare sodium hydroxide solution A by adding water according to a NaOH mass fraction of 25%, put it into the alkali decomposition reaction kettle, start stirring, add the acid-leached mixed ore into the reaction kettle, start heating, and raise the temperature to 135 °C for heat preservation reaction for 3 h.

[0057] After the reaction is completed, the slurry is filtered to obtain washing solution 1. The filter cake is transferred to a beaker, and water is added for stirring and washing twice to thoroughly wash out the sodium fluoride therein, obtaining washing solutions 2 and 3. The filter cake is the first-stage alkali cake (a mixture of rare earth phosphates and rare earth hydroxides). After the three washing solutions are mixed evenly, the volume is measured, and a sample is taken for detecting the fluorine content, and based on this, the sodium fluoride recovery rate is calculated (since there is no other outlet for fluorine elements in this process, this is used as the basis for calculating the sodium fluoride recovery rate). The mixed washing solutions are evaporated and concentrated, cooled and crystallized, filtered, and the crystals are quickly rinsed with water to obtain sodium fluoride, and a sample is taken to analyze the purity of sodium fluoride.

[0058] (5)Calculate the dosage of NaOH according to 1.5 times the mass of REO in the first-stage alkali cake in step (4). Prepare sodium hydroxide solution B by adding water according to a mass fraction of 70% of NaOH, put it into the alkali decomposition reaction kettle, start stirring, add the first-stage alkali cake into the reaction kettle, start heating, and raise the temperature to 130 °C for heat preservation reaction for 10 h.

[0059] (6)After the reaction is completed, the slurry is filtered to obtain the second-stage alkali cake and washing solution 1. The second-stage alkali cake is transferred to a beaker, and water is added for stirring and washing twice to thoroughly wash out the trisodium phosphate dodecahydrate therein, obtaining washing solutions 2 and 3. The main component of the second-stage alkali cake is rare earth hydroxide. After the three washing solutions are mixed evenly, they are concentrated, and then slowly cooled down under stirring, and centrifugally filtered with a drum centrifuge to obtain trisodium phosphate dodecahydrate, which is weighed and a sample is taken to analyze the purity of trisodium phosphate dodecahydrate.

[0060] (7)The second-stage alkali cake obtained in step (6) is put into the leaching solution obtained in step (2), keeping the pressure at 0 MPa and the temperature at 90 °C, stirring and reacting for 4 h and then filtering. The filtrate is respectively added with impurity removal agents such as hydrogen peroxide, ammonium bicarbonate, and sodium sulfide for reaction to remove impurity ions such as iron, fluorine, phosphorus, aluminum, lead, and zinc, and finally a mixed rare earth chloride solution with a concentration of 296 g / L is obtained.

[0061] In this example, the rare earth recovery rate is 98.3%; the sodium fluoride recovery rate is 95.9% and the purity is 96.8%; the trisodium phosphate dodecahydrate recovery rate is 96.1% and the purity is 95.5%.

[0062] Example 4 The raw materials used in this example are Baotou mixed rare earth concentrate, and the main components are: the REO content is 61.2%, the F content is 5.8%, and the P content is 5.1%. The method for hydrochloric acid leaching, two-stage alkali decomposition, and recovery of fluorine, phosphorus, and rare earths from the mixed rare earth concentrate includes the following steps: (1)According to the ratio of mixed rare earth concentrate (REO) to hydrochloric acid of 1:1.9 g / mL, under stirring, add the Baotou mixed rare earth concentrate into the industrial hydrochloric acid in the reaction kettle and stir evenly.

[0063] (2) Under sealed conditions, gradually heat the temperature inside the reaction kettle to 100 °C. At this time, the pressure inside the reaction kettle is 0.8 MPa, and stir and react for 4.5 h. After the reaction is completed, filter the slurry, retain the leaching solution (acidic rare earth chloride solution), and wash the acid-leached mixed ore with water until it is qualified. The mass of REO in the acid-leached mixed ore is calculated from the mass of the Baotou mixed rare earth concentrate added and the mass of REO in the leaching solution.

[0064] (3) Calculate the dosage of NaOH 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 according to a mass fraction of 18% of NaOH, put it into the alkali decomposition reaction kettle, start stirring, add the acid-leached mixed ore into the reaction kettle, start heating, and raise the temperature to 105 °C to start the holding reaction for 5 h.

[0065] (4) After the reaction is completed, filter the slurry to obtain washing solution 1. Transfer the filter cake into a beaker, add water and stir and wash it twice to wash out the sodium fluoride completely to obtain washing solutions 2 and 3. The filter cake is the first-step alkali cake (a mixture of rare earth phosphate and rare earth hydroxide). After mixing the three washing solutions evenly, measure the volume and take samples to detect the fluorine content, and calculate the sodium fluoride recovery rate based on this (because in this process, there is no other outlet for fluorine elements, so this is used as the basis for calculating the sodium fluoride recovery rate). Evaporate and concentrate the mixed washing solutions, cool down and crystallize, filter and quickly wash the crystals with water to obtain sodium fluoride, and take samples to analyze the purity of sodium fluoride.

[0066] (5) Calculate the dosage of NaOH according to 1.7 times the mass of REO in the first-step alkali cake in step (4). Prepare sodium hydroxide solution B by adding water according to a mass fraction of 55% of NaOH, put it into the alkali decomposition reaction kettle, start stirring, add the first-step alkali cake into the reaction kettle, start heating, and raise the temperature to 145 °C to start the holding reaction for 5 h.

[0067] (6) After the reaction is completed, filter the slurry to obtain the second-step alkali cake and washing solution 1. Transfer the second-step alkali cake into a beaker, add water and stir and wash it twice to wash out the trisodium phosphate dodecahydrate completely to obtain washing solutions 2 and 3. The main component of the second-step alkali cake is rare earth hydroxide. After mixing the three washing solutions evenly, concentrate them, and then slowly cool down under stirring, and perform centrifugal filtration with a drum centrifuge to obtain trisodium phosphate dodecahydrate, weigh it and take samples to analyze the purity of trisodium phosphate dodecahydrate.

[0068] (7) Put the second-step alkali cake obtained in step (6) into the leaching solution obtained in step (2), keep the pressure at 0.2 MPa and the temperature at 100 °C, stir and react for 3 h and then filter. Add impurity removal agents such as hydrogen peroxide, ammonium bicarbonate, and sodium sulfide to the filtrate for reaction to remove impurity ions such as iron, fluorine, phosphorus, aluminum, lead, and zinc, and finally obtain a mixed rare earth chloride solution with a concentration of 287 g / L.

[0069] In this example, the rare earth recovery rate is 98.5%; the sodium fluoride recovery rate is 95.2%, and the purity is 96.2%; the recovery rate of trisodium phosphate dodecahydrate is 95.4%, and the purity is 96.1%.

[0070] Example 5 The raw material used in this example is Baotou mixed rare earth concentrate, and its main components are: the REO content is 61.2%, the F content is 5.8%, and the P content is 5.1%. The method for hydrochloric acid leaching of the mixed rare earth concentrate and two-step alkali decomposition to recover fluorine, phosphorus and rare earths includes the following steps: (1) According to the ratio of mixed rare earth concentrate (REO) to hydrochloric acid of 1:2.0 g / mL, under stirring, add Baotou mixed rare earth concentrate into the industrial hydrochloric acid in the reaction kettle and stir evenly.

[0071] (2) Under sealed conditions, gradually heat the temperature in the reaction kettle to 110 °C. At this time, the pressure in the reaction kettle is 1.0 MPa, and stir and react for 4 h. After the reaction is completed, filter the slurry, keep the leaching solution (acidic rare earth chloride solution) for use, and wash the acid-leached mixed ore with water until it is qualified. The mass of REO in the acid-leached mixed ore is calculated by adding the mass of REO in the added Baotou mixed rare earth concentrate and the leaching solution.

[0072] (3) Calculate the dosage of NaOH 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 according to the mass fraction of NaOH of 20%, put it into the alkali decomposition reaction kettle, start stirring, add the acid-leached mixed ore into the reaction kettle, start heating, and raise the temperature to 130 °C to start heat preservation reaction, and keep the heat preservation reaction for 4 h.

[0073] (4) After the reaction is completed, filter the slurry to obtain washing solution 1. Transfer the filter cake to a beaker, add water and stir and wash twice to wash out the sodium fluoride therein to obtain washing solution 2 and washing solution 3. The filter cake is the one-step alkali cake (a mixture of rare earth phosphate and rare earth hydroxide). After mixing the three washing solutions evenly, measure the volume and take a sample to detect the fluorine content, and calculate the sodium fluoride recovery rate based on this (because in this process, there is no other outlet for fluorine element, so this is used as the basis for calculating the sodium fluoride recovery rate). Evaporate and concentrate the mixed washing solution, cool it down to crystallize, filter and quickly wash the crystals with water to obtain sodium fluoride, and take a sample to analyze the purity of sodium fluoride.

[0074] (5) Calculate the dosage of NaOH according to 1.8 times the mass of REO in the one-step alkali cake in step (4). Prepare sodium hydroxide solution B by adding water according to the mass fraction of NaOH of 50%, put it into the alkali decomposition reaction kettle, start stirring, add the one-step alkali cake into the reaction kettle, start heating, and raise the temperature to 170 °C to start heat preservation reaction, and keep the heat preservation reaction for 6 h.

[0075] After the reaction is completed, the slurry is filtered to obtain a secondary alkali cake and washing solution 1. The secondary alkali cake is transferred to a beaker, stirred and washed twice with water to fully wash out the trisodium phosphate dodecahydrate therein, obtaining washing solutions 2 and 3. The main component of the secondary alkali cake is rare earth hydroxide. After the three washing solutions are mixed evenly, they are concentrated, and then slowly cooled and cooled under stirring. A drum centrifuge is used for centrifugal filtration to obtain trisodium phosphate dodecahydrate, which is weighed and sampled to analyze the purity of trisodium phosphate dodecahydrate.

[0076] (7) The secondary alkali cake obtained in step (6) is put into the leaching solution obtained in step (2), maintaining a pressure of 1.0 MPa and a temperature of 135 °C. After stirring and reacting for 1.5 h, it is filtered. The filtrate is respectively added with impurities removing agents such as hydrogen peroxide, ammonium bicarbonate, and sodium sulfide for reaction 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.

[0077] In this example, the rare earth recovery rate is 98.6%; the sodium fluoride recovery rate is 96.1% with a purity of 97.0%; the trisodium phosphate dodecahydrate recovery rate is 95.7% with a purity of 95.6%.

[0078] Example 6 The raw material used in this example is Baotou mixed rare earth concentrate, and its main composition is: the REO content is 61.2%, the F content is 5.8%, and the P content is 5.1%. The method for hydrochloric acid leaching and two-step alkali decomposition of the mixed rare earth concentrate to recover fluorine, phosphorus, and rare earth includes the following steps: (1) According to the ratio of mixed rare earth concentrate (REO) to hydrochloric acid of 1:1.8 g / mL, under stirring, the Baotou mixed rare earth concentrate is added to the industrial hydrochloric acid in the reaction kettle and stirred evenly.

[0079] (2) Under sealed conditions, the temperature in the reaction kettle is gradually heated to 105 °C. At this time, the pressure in the reaction kettle is 0.1 MPa, and it is stirred and reacted for 6 h. After the reaction is completed, the slurry is filtered, and the leaching solution (acidic rare earth chloride solution) is reserved. The acid-leached mixed ore is washed with water until qualified. The mass of REO in the acid-leached mixed ore is calculated by the mass of REO in the added Baotou mixed rare earth concentrate and the leaching solution.

[0080] (3) Calculate the dosage of NaOH 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 according to a mass fraction of 30% of NaOH, put it into the alkali decomposition reaction kettle, start stirring, add the acid-leached mixed ore into the reaction kettle, start heating, and raise the temperature to 120 °C for heat preservation reaction for 4.5 h.

[0081] After the reaction is completed, filter the slurry to obtain washing solution 1. Transfer the filter cake into a beaker, add water and stir to wash twice to fully wash out the sodium fluoride therein, obtaining washing solution 2 and washing solution 3. The filter cake is the first-stage alkali cake (a mixture of rare earth phosphate and rare earth hydroxide). After the three washing solutions are mixed evenly, measure the volume and take samples to detect the fluorine content, and calculate the sodium fluoride recovery rate based on this (since there is no other outlet for fluorine element in this process, it is used as the basis for calculating the sodium fluoride recovery rate). Evaporate and concentrate the mixed washing solutions, then cool down to crystallize, filter and quickly wash the crystals with water to obtain sodium fluoride, and take samples to analyze the purity of sodium fluoride.

[0082] (5)Calculate the dosage of NaOH according to 1.6 times the REO mass of the first-stage alkali cake in step (4). Prepare sodium hydroxide solution B by adding water according to a mass fraction of 45% of NaOH, put it into the alkali decomposition reaction kettle, start stirring, add the first-stage alkali cake into the reaction kettle, start heating, and raise the temperature to 150 °C to start heat preservation reaction for 7 h.

[0083] (6)After the reaction is completed, filter the slurry to obtain the second-stage alkali cake and washing solution 1. Transfer the second-stage alkali cake into a beaker, add water and stir to wash twice to fully wash out the trisodium phosphate dodecahydrate therein, obtaining washing solution 2 and washing solution 3. The main component of the second-stage alkali cake is rare earth hydroxide. After the three washing solutions are mixed evenly, concentrate them, then slowly cool down under stirring, and perform centrifugal filtration with a drum centrifuge to obtain trisodium phosphate dodecahydrate, weigh it and take samples to analyze the purity of trisodium phosphate dodecahydrate.

[0084] (7)Put the washed second-stage alkali cake obtained in step (6) into the leaching solution obtained in step (2), keep the pressure at 0.5 MPa and the temperature at 125 °C, stir and react for 2 h and then filter. Add impurity removal agents such as hydrogen peroxide, ammonium bicarbonate, and sodium sulfide to the filtrate for reaction to remove impurity ions such as iron, fluorine, phosphorus, aluminum, lead, and zinc, and finally obtain a mixed rare earth chloride solution with a concentration of 291 g / L.

[0085] In this example, the rare earth recovery rate is 98.4%; the sodium fluoride recovery rate is 95.7% and the purity is 96.5%; the trisodium phosphate dodecahydrate recovery rate is 95.5% and the purity is 95.8%.

[0086] Comparative Example 1 Compared with Example 4, the difference in this comparative example is that in this comparative example, the temperature of the first-stage alkali hydrolysis is 70 °C, that is, after starting heating in step (3), the temperature is raised to 70 °C, and other conditions are the same as those in Example 4.

[0087] Due to the relatively low temperature in the one-step alkaline hydrolysis, the rare earth fluoride is not completely decomposed, resulting in a low recovery rate of sodium fluoride. The undecomposed rare earth fluoride enters the two-step alkaline hydrolysis process, and the purity of trisodium phosphate dodecahydrate is low. In this comparative example, the rare earth recovery rate is 96.2%; the sodium fluoride recovery rate is 72.4%, and the purity is 95.6%; the trisodium phosphate dodecahydrate recovery rate is 95.3%, and the purity is 76.5%.

[0088] Comparative Example 2 The difference between this comparative example and Example 5 is that in this comparative example, the temperature of the two-step alkaline hydrolysis is 115 °C, that is, after heating is started in step (5), the temperature is raised to 115 °C, and other conditions are the same as those in Example 5.

[0089] Due to the relatively low temperature in the two-step alkaline hydrolysis, the rare earth phosphate is not completely decomposed, and the undecomposed rare earth phosphate cannot be dissolved by hydrochloric acid, resulting in low recovery rates of rare earth and trisodium phosphate dodecahydrate. In this comparative example, the rare earth recovery rate is 85.3%; the sodium fluoride recovery rate is 96.1%, and the purity is 97.0%; the trisodium phosphate dodecahydrate recovery rate is 62.1%, and the purity is 95.3%.

[0090] Comparative Example 3 The difference between this comparative example and Example 4 is that in this comparative example, the mass fraction of the NaOH solution used in the one-step alkaline hydrolysis is 6%, and other conditions are the same as those in Example 4.

[0091] Due to the too low mass fraction of the NaOH solution in the one-step alkaline hydrolysis, the rare earth fluoride is not completely decomposed, and the undecomposed rare earth phosphate cannot be dissolved by hydrochloric acid, resulting in a low recovery rate of sodium fluoride. The undecomposed rare earth fluoride enters the two-step alkaline hydrolysis process, and the purity of trisodium phosphate dodecahydrate is low. In this comparative example, the rare earth recovery rate is 95.3%; the sodium fluoride recovery rate is 58.4%, and the purity is 96.2%; the trisodium phosphate dodecahydrate recovery rate is 94.2%, and the purity is 71.7%.

[0092] Comparative Example 4 The difference between this comparative example and Example 6 is that in this comparative example, the mass fraction of the NaOH solution used in the two-step alkaline hydrolysis is 35%, and other conditions are the same as those in Example 6.

[0093] Due to the relatively low mass fraction of the NaOH solution in the two-step alkaline hydrolysis, the rare earth phosphate is not completely decomposed, and the undecomposed rare earth phosphate cannot be dissolved by hydrochloric acid, resulting in low recovery rates of rare earth and trisodium phosphate dodecahydrate. In this comparative example, the rare earth recovery rate is 84.5%; the sodium fluoride recovery rate is 95.7%, and the purity is 96.5%; the trisodium phosphate dodecahydrate recovery rate is 64.3%, and the purity is 87.9%.

Claims

1. A method for hydrochloric acid leaching of mixed rare earth concentrates and two-step alkali decomposition to recover fluorine, phosphorus and rare earths, which is characterized in that: It includes the following steps: (1) Mix hydrochloric acid with the mixed rare earth concentrate, carry out heating and pressurization reaction, and leach to obtain acid-leached mixed ore and acidic rare earth chloride solution; (2) Stir the acid-leached mixed ore evenly with sodium hydroxide solution A, carry out heating and heat preservation reaction. After the reaction ends, wash with water and filter to obtain the first-stage alkali cake and the first-stage alkali solution. The first-stage alkali solution is concentrated to obtain sodium fluoride and the first-stage alkali water; (3) Stir the first-stage alkali cake evenly with sodium hydroxide solution B, carry out heating and heat preservation reaction. After the reaction ends, filter to obtain the second-stage alkali cake and the second-stage alkali solution; the second-stage alkali solution is purified, cooled and crystallized to obtain trisodium phosphate dodecahydrate. The remaining alkali solution is further concentrated to obtain the second-stage alkali water, which is recycled to sodium hydroxide solution B in this step. The concentrated condensate water is returned to the second-stage alkali cake water washing for recycling; the second-stage alkali cake is washed with water, and the washing water is returned for diluting the alkali decomposition slurry; (4) After the second-stage alkali cake is washed with water, put it into the acidic rare earth chloride solution in step (1), carry out heating and heat preservation reaction. After the reaction ends, filter, and purify the filtrate to obtain rare earth chloride liquor.

2. The method for hydrochloric acid leaching of mixed rare earth concentrate and two-step alkali decomposition to recover fluorine, phosphorus and rare earth according to claim 1, wherein: In the mixed rare earth concentrate in step (1), the REO content is 45% - 70%, the F content is 4% - 9%, and the P content is 3% - 7%.

3. The method for hydrochloric acid leaching of mixed rare earth concentrate and two-step alkali decomposition to recover fluorine, phosphorus and rare earth according to claim 2, characterized in that: The hydrochloric acid in step (1) is industrial hydrochloric acid, which is added according to the mass of REO in the mixed rare earth concentrate and the volume of HCl at 1:1.8 - 1:2.0 g / mL.

4. The method for hydrochloric acid leaching of mixed rare earth concentrate and two-step alkali decomposition to recover fluorine, phosphorus and rare earths according to claim 3, characterized in that: The heating temperature in step (1) is 100°C - 150°C, the reaction pressure is 0.1 - 1.0 MPa, and the reaction time is 4h - 6h.

5. The method for hydrochloric acid leaching of mixed rare earth concentrate and two-step alkali decomposition to recover fluorine, phosphorus and rare earth according to claim 1, characterized in that: In step (2), the addition amount of sodium hydroxide solution A, calculated by sodium hydroxide, the mass of sodium hydroxide is 0.5 - 0.8 times the mass of REO in the acid-leached mixed ore, and the mass fraction of sodium hydroxide solution A is controlled at 15% - 30%.

6. The method for hydrochloric acid leaching of mixed rare earth concentrate and two-step alkali decomposition to recover fluorine, phosphorus and rare earth according to claim 5, characterized in that: The heating temperature in step (2) is 105°C - 135°C, and the heat preservation reaction is carried out for 3h - 5h.

7. The method for hydrochloric acid leaching of mixed rare earth concentrate and two-step alkali decomposition to recover fluorine, phosphorus and rare earth according to claim 1, characterized in that: In step (3), the addition amount of sodium hydroxide solution B, calculated by sodium hydroxide, the mass of sodium hydroxide is 1.5 - 1.8 times the mass of REO in the first-stage alkali cake, and the mass fraction of sodium hydroxide solution B is controlled at 45% - 70%.

8. The method for hydrochloric acid leaching of mixed rare earth concentrate and two-step alkali decomposition to recover fluorine, phosphorus and rare earth according to claim 7, characterized in that: The heating temperature in step (3) is 130°C - 170°C, and the heat preservation reaction is carried out for 5h - 10h.

9. The method for hydrochloric acid leaching of mixed rare earth concentrate and two-step alkali decomposition to recover fluorine, phosphorus and rare earth according to claim 1, characterized in that: The heating temperature in step (4) is 90 - 140°C, the reaction pressure is 0 - 1.0 MPa, and the reaction time is 1h - 4h.

10. The method for hydrochloric acid leaching of mixed rare earth concentrate and two-step alkali decomposition to recover fluorine, phosphorus and rare earths according to claim 9, characterized in that: When purifying the filtrate after filtration in step (4), hydrogen peroxide, ammonium bicarbonate, and sodium sulfide are added in sequence for purification.

Images