Method for decomposing mixed rare earth concentrate and comprehensively utilizing associated resources

Abstract

The invention discloses a method for decomposing mixed rare earth concentrate and comprehensively utilizing associated resources, which comprises the following steps: 1) reacting the mixed rare earth concentrate with a hydrochloric acid solution A to obtain roughed minerals and mother liquor; (2) the roughed minerals react with a hydrochloric acid solution B, and re-decomposed minerals and a first acid solution containing chlorinated rare earth are obtained; (3) reacting the re-decomposed minerals with alkali liquor C, and carrying out solid-liquid separation to obtain a first filter cake and first filtrate; washing the first filter cake to obtain a first alkali cake and first washing alkali liquor; reacting the first alkali cake with a solution containing hydrochloric acid to obtain first acid dissolving slag and a second acid solution containing rare earth chloride; (4) reacting the first acid soluble slag with alkali liquor D, and carrying out solid-liquid separation to obtain a second filter cake and second filtrate; washing the second filter cake to obtain a second alkali cake and second washing alkali liquor; and reacting the second alkali cake with a solution containing hydrochloric acid to obtain second acid slag and a third acid solution containing rare earth chloride. The method provided by the invention can be used for independently recovering rare earth, fluorine, phosphorus and calcium.

Description

Technical Field

[0001] The invention relates to a method for decomposing mixed rare earth concentrate and comprehensively utilizing associated resources. Background Art

[0002] The mixed rare earth concentrate obtained through mineral processing mainly includes fluorocarbon cerium ore and monazite. Due to the complexity of the concentrate composition, it is recognized as a difficult-to-smelt mineral.

[0003] Currently, the main industrialized technologies for decomposing mixed rare earth concentrates are concentrated sulfuric acid high-temperature roasting and decomposition, and concentrated alkali decomposition at atmospheric pressure. The concentrated sulfuric acid high-temperature roasting process involves mixing rare earth concentrate with concentrated sulfuric acid and roasting it at 500-800°C. During the reaction, if the mineral particles are too large, the internal reaction will be incomplete, affecting the rare earth decomposition rate. This process also produces a large amount of high-temperature mixed acidic tail gas (SO2, SO3, H2SO4, HF, SiF4), which is difficult to treat as sulfate wastewater and radioactive waste residue, resulting in a large and costly environmental treatment system. The concentrated alkali decomposition process treats mixed rare earth concentrates with an REO grade of approximately 60%. Using sodium hydroxide to decompose the rare earth minerals, it produces a large amount of mixed alkaline wastewater (NaOH, Na3PO4, NaF, Na2CO3, Na2SO4, and NaCl). This makes resource recovery difficult and results in excessive sodium hydroxide waste. This waste can only be simply neutralized and discharged to meet standards, without recovering resources such as fluorine and phosphorus.

[0004] CN106591607A discloses a liquid alkali decomposition method for high-grade mixed rare earth concentrate, comprising: mixing a high-grade mixed rare earth concentrate containing more than 60 wt% REO with a sodium hydroxide solution having a concentration greater than 60 wt%, wherein the weight ratio of the mixed rare earth concentrate to the sodium hydroxide is 1:3.5-7.5; reacting the mixed slurry at 150-160°C for 0.2-1 hour; after the reaction is completed, hot filtration is performed at a temperature greater than 60°C, and the filtered alkali cake is washed with water to a neutral state; and the neutralized alkali cake is dissolved with 6-10 mol / L hydrochloric acid, and the pH is controlled at 4-5 to obtain a pure rare earth chloride solution.

[0005] CN106978531A discloses a method for the combined acid-base decomposition of a mixed rare earth concentrate. The method comprises mixing the mixed rare earth concentrate with concentrated sulfuric acid having a mass percentage of greater than 92 wt%, calcining the mixture at 120-180°C for 150-300 min, neutralizing the aqueous extract to form a phosphorus-iron-thorium slag and a rare earth sulfate solution, and separating the aqueous extract by gravity separation to obtain calcium sulfate waste residue and phosphorus-containing minerals. The phosphorus-containing minerals and phosphorus-iron-thorium slag are then decomposed with a sodium hydroxide solution having a mass percentage of 45-70 wt% at a weight ratio of 1:0.1-0.2 at 130-180°C, and dissolved in hydrochloric acid to obtain rare earth chloride. This method separates calcium sulfate and phosphorus-containing minerals by gravity separation, but gravity separation, as a conventional mineral separation method, has poor mineral separation efficiency, resulting in a low rare earth yield.

[0006] CN112534072A discloses a combined method for treating rare earth concentrates by smelting and separating, wherein the rare earth concentrate containing fluorocarbon cerium ore is treated by atmosphere roasting-hydrochloric acid leaching-sulfuric acid roasting, and low-concentration hydrochloric acid step-by-step acid leaching is used during the hydrochloric acid leaching process to obtain a high-concentration rare earth solution, so that the Ce leaching rate reaches more than 60%, and the F content of the leachate is reduced by aging. - The leached residue is then roasted with sulfuric acid and then leached in water to further recover rare earths, with a total rare earth recovery rate exceeding 95%. This process cannot recover calcium and phosphorus separately. The total rare earth recovery rate still needs to be further improved.

[0007] CN114959319A discloses a method for treating solids obtained from the alkaline decomposition of mixed rare earth concentrates. The method comprises the following steps: 1) subjecting the mixed rare earth concentrate to caustic soda decomposition, alkali cake washing, and hydrochloric acid dissolution to obtain a rare earth chloride solution and a well-dissolved solid; neutralizing the rare earth chloride solution with an alkaline reagent to remove impurities, thereby obtaining a neutralized rare earth chloride solution and a neutralized solid; repeating the caustic soda decomposition, alkali cake washing, and hydrochloric acid dissolution steps twice or more with the mixture of the neutralized solid and the well-dissolved solid to obtain a solid to be treated; 2) washing the solid to be treated with hydrochloric acid solution N times, where N is a natural number between 3 and 9; the hydrochloric acid solution has an HCl concentration of 2.5 to 4.0 mol / L and a washing temperature of 50 to 70°C; and 3) washing with water to obtain discharged solids. This process cannot recover fluorine, phosphorus, and calcium individually. Summary of the Invention

[0008] In view of this, the object of the present invention is to provide a method for decomposing mixed rare earth concentrate and comprehensively utilizing associated resources, which can respectively recover rare earth, fluorine, phosphorus and calcium resources to obtain rare earth chloride solution, sodium fluoride, trisodium phosphate and calcium chloride solution respectively.

[0009] The present invention achieves the above-mentioned purpose through the following technical solutions.

[0010] The present invention provides a method for decomposing a mixed rare earth concentrate and comprehensively utilizing associated resources, comprising the following steps:

[0011] 1) reacting the mixed rare earth concentrate with hydrochloric acid solution A to obtain rough ore and mother liquor;

[0012] 2) reacting the coarsely selected ore with hydrochloric acid solution B to obtain a first acid solution containing re-decomposed ore and rare earth chloride; wherein the concentration of hydrochloric acid solution B is greater than that of hydrochloric acid solution A;

[0013] 3) reacting the re-decomposed mineral with alkali liquor C, separating the solid and the liquid to obtain a first filter cake and a first filtrate; washing the first filter cake to obtain a first alkali cake and a first alkali washing liquor; recovering fluoride salt from the first alkali washing liquor; reacting the first alkali cake with a solution containing hydrochloric acid to obtain a first acid slag and a second acid solution containing rare earth chloride; wherein the alkali liquor C is selected from at least one of an alkali metal carbonate solution and an alkali metal hydroxide solution;

[0014] 4) reacting the first acid slag with alkali liquor D to separate the solid and liquid to obtain a second filter cake and a second filtrate; washing the second filter cake to obtain a second alkali cake and a second alkali washing liquor; recovering phosphate from the second alkali washing liquor; and reacting the second alkali cake with a solution containing hydrochloric acid to obtain a second acid slag and a third acid solution containing rare earth chloride; wherein the alkali liquor D is an alkali metal hydroxide solution; and the alkalinity of the alkali liquor D is greater than the alkalinity of the alkali liquor C.

[0015] The present invention also provides a method for decomposing a mixed rare earth concentrate and comprehensively utilizing associated resources, comprising the following steps:

[0016] 1) reacting the mixed rare earth concentrate with hydrochloric acid solution A to obtain rough ore and mother liquor;

[0017] 2) reacting the coarsely selected ore with hydrochloric acid solution B to obtain a first acid solution containing re-decomposed ore and rare earth chloride; wherein the concentration of hydrochloric acid solution B is greater than that of hydrochloric acid solution A;

[0018] 3) reacting the re-decomposed mineral with alkali liquor C, separating the solid and the liquid to obtain a first filter cake and a first filtrate; washing the first filter cake to obtain a first alkali cake and a first alkali washing liquor; and recovering fluoride salt from the first alkali washing liquor; wherein the alkali liquor C is selected from at least one of an alkali metal carbonate solution and an alkali metal hydroxide solution;

[0019] 4) reacting the first alkali cake with alkali liquor D to separate the solid and liquid to obtain a third filter cake and a third filtrate; washing the third filter cake to obtain a third alkali cake and a third alkali washing liquor; recovering phosphate from the third alkali washing liquor; and reacting the third alkali cake with a solution containing hydrochloric acid to obtain a third acid slag and a fourth acid solution containing rare earth chloride; wherein the alkali liquor D is an alkali metal hydroxide solution; and the alkalinity of the alkali liquor D is greater than the alkalinity of the alkali liquor C.

[0020] According to the method of the present invention, preferably, in step 1), the concentration of hydrochloric acid solution A is 2 to 4 mol / L; the ratio of the mass of the mixed rare earth concentrate to the volume of hydrochloric acid solution A is 1 kg:0.8 to 4 L; the reaction temperature is 65 to 95° C., and the reaction time is 0.5 to 6.5 h.

[0021] According to the method of the present invention, preferably, step 1) further includes the following steps: neutralizing the mother liquor with a calcium-containing inorganic substance to a pH value of 6.5 to 7 to obtain a calcium chloride solution and a rare earth phosphate solid; wherein the calcium-containing inorganic substance is calcium oxide or calcium hydroxide.

[0022] According to the method of the present invention, preferably, in step 2), the concentration of hydrochloric acid solution B is 7-12 mol / L; the ratio of the mass of the rough ore to the volume of hydrochloric acid solution B is 1 kg:1-3 L; the reaction temperature is 80-110° C., and the reaction time is 0.5-4 h.

[0023] According to the method of the present invention, preferably, in step 1), during the reaction of the mixed rare earth concentrate and the hydrochloric acid solution A, the tail gas is sprayed and absorbed to obtain a mixed acid of hydrochloric acid and hydrofluoric acid; in step 2), during the reaction of the roughing ore and the hydrochloric acid solution B, the tail gas is sprayed and absorbed to obtain a mixed acid of hydrochloric acid and hydrofluoric acid;

[0024] In step 3), the solution containing hydrochloric acid is selected from at least one of directly prepared hydrochloric acid, the first acid solution containing rare earth chloride obtained in step 2), and a mixed acid of hydrochloric acid and hydrofluoric acid; in step 4), the solution containing hydrochloric acid is selected from at least one of directly prepared hydrochloric acid, the first acid solution containing rare earth chloride obtained in step 2), the second acid solution containing rare earth chloride obtained in step 3), and a mixed acid of hydrochloric acid and hydrofluoric acid.

[0025] According to the method of the present invention, preferably, in step 3), the concentration of the alkali solution C is 10 to 50 wt%; the ratio of the mass of the re-decomposed mineral to the volume of the alkali solution C is 1 kg:1 to 3 L; the reaction temperature is 100 to 135° C., the reaction pressure is 0.1 to 1 MPa, and the reaction time is 0.5 to 5 h.

[0026] According to the method of the present invention, preferably, in step 1), during the reaction of the mixed rare earth concentrate and the hydrochloric acid solution A, the tail gas is sprayed and absorbed to obtain a mixed acid of hydrochloric acid and hydrofluoric acid; in step 2), during the reaction of the roughing ore and the hydrochloric acid solution B, the tail gas is sprayed and absorbed to obtain a mixed acid of hydrochloric acid and hydrofluoric acid;

[0027] In step 4), the hydrochloric acid-containing solution is selected from at least one of directly prepared hydrochloric acid, the first acid solution containing rare earth chloride obtained in step 2), the second acid solution containing rare earth chloride obtained in step 3), and a mixed acid of hydrochloric acid and hydrofluoric acid.

[0028] According to the method of the present invention, preferably, step 4) includes the following specific steps: reacting the first acid slag, rare earth phosphate solid and alkali solution D; wherein the ratio of the sum of the mass of the first acid slag and the rare earth phosphate solid to the volume of the alkali solution D is 1 kg:1~2.5 L.

[0029] According to the method of the present invention, preferably, step 4) includes the following specific steps: reacting the first alkali cake, rare earth phosphate solid and alkali solution D; wherein the ratio of the sum of the mass of the first alkali cake and the rare earth phosphate solid to the volume of the alkali solution D is 1 kg:1~2.5 L.

[0030] According to the method of the present invention, preferably, in step 4), the concentration of the alkali solution D is 40-65 wt%; the reaction temperature is 140-180° C., the reaction pressure is 0.1-1 MPa, and the reaction time is 0.5-4.5 h.

[0031] The method of the present invention utilizes a low-concentration hydrochloric acid solution A, a high-concentration hydrochloric acid solution B, a low-concentration alkali solution C, and a high-concentration alkali solution D to perform step-by-step, directionally decomposing of a mixed rare earth concentrate. This allows for the separate recovery of rare earth, fluorine, phosphorus, and calcium, yielding rare earth chloride solution, sodium fluoride, trisodium phosphate, and calcium chloride solution, respectively. This method has mild process conditions, making it suitable for industrial application. Furthermore, the method produces virtually no wastewater, making it environmentally friendly. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] Figure 1 This is a schematic diagram of the process of Example 1, Example 2, and Example 3 of the present invention. DETAILED DESCRIPTION

[0033] The present invention will be further described below with reference to specific embodiments, but the protection scope of the present invention is not limited thereto.

[0034] In the prior art, although some literature reports that mixed rare earth concentrates are treated with low-concentration hydrochloric acid first, directly using alkaline decomposition after treatment cannot achieve the technical effects of the present invention. The method of decomposing mixed rare earth concentrates and comprehensively utilizing associated resources in the present invention is not a conventional option.

[0035] The present invention provides a method for decomposing a mixed rare earth concentrate and comprehensively utilizing associated resources, comprising the following steps: (1) reacting with hydrochloric acid solution A; (2) reacting with hydrochloric acid solution B; (3) reacting with alkaline solution C; and (4) reacting with alkaline solution D. Optionally, the method further comprises a purification step of the acid solution containing rare earth chloride. This is described in detail below.

[0036] <Reaction with Hydrochloric Acid Solution A>

[0037] The mixed rare earth concentrate is reacted with hydrochloric acid solution A to obtain roughing ore and mother liquor. This is conducive to preferentially decomposing calcium-containing minerals and substantially not decomposing other minerals.

[0038] In the present invention, the mixed rare earth concentrate is primarily composed of bastnaesite and monazite, and also contains apatite, fluorite, and the like. The mass ratio of bastnaesite to monazite is greater than or equal to 2:1. The mixed rare earth concentrate of the present invention has a REO content greater than or equal to 40 wt%, a fluorine (F) content of 4 to 10 wt%, a phosphorus (P) content of 3 to 7 wt%, and a CaO content of less than or equal to 15 wt%.

[0039] According to one embodiment of the present invention, in the mixed rare earth concentrate, the REO content is 42.3-51.4 wt%, the fluorine (F) content is 4.6-8.2 wt%, the phosphorus (P) content is 3.8-4.3 wt%, and the CaO content is 9.7-13.6 wt%.

[0040] According to another embodiment of the present invention, in the mixed rare earth concentrate, the REO content is 55-65wt% (for example, 55wt%, 58wt%, 60.8wt%, 65wt%), the fluorine (F) content is 8.5-9.5wt%, the phosphorus (P) content is 4.5-6.2wt%, and the CaO content is less than or equal to 5wt% (for example, 4.3wt%).

[0041] In the present invention, the mass ratio of the mixed rare earth concentrate to the volume of hydrochloric acid solution A is 1 kg:0.8 to 4 L, for example, 1 kg:0.8 L, 1 kg:1 L, 1 kg:1.5 L, 1 kg:2 L, 1 kg:2.5 L, 1 kg:3 L, 1 kg:3.5 L, or 1 kg:4 L. The concentration of hydrochloric acid solution A can be 2 to 4 mol / L, preferably 2.5 to 3.5 mol / L, for example, 2.5 mol / L, 3 mol / L, or 3.5 mol / L. The reaction temperature of the mixed rare earth concentrate and hydrochloric acid solution A can be 65 to 95°C, for example, 65°C, 70°C, 75°C, 80°C, 85°C, 90°C, or 95°C. The reaction time can be 0.5 to 6.5 hours, for example, 0.5 hours, 1 hour, 1.5 hours, 2 hours, 2.5 hours, 3 hours, 3.5 hours, 4 hours, 4.5 hours, 5 hours, 5.5 hours, 6 hours, or 6.5 hours. This is beneficial for dissolving the calcium element and reducing the dissolution of rare earth elements, thereby obtaining a calcium chloride solution with a higher calcium chloride content.

[0042] During the reaction of the mixed rare earth concentrate with the hydrochloric acid solution A, tail gas can be absorbed by spraying to obtain a mixed acid of hydrochloric acid and hydrofluoric acid. This mixed acid can be used to react with the first alkali cake or the second alkali cake obtained in the subsequent step.

[0043] In the present invention, the mother liquor is neutralized with a calcium-containing inorganic substance to obtain a calcium chloride solution and a rare earth phosphate solid. Specifically, the mother liquor is neutralized with the calcium-containing inorganic substance to a pH of 6.5 to 7, preferably to a pH of 7. The calcium-containing inorganic substance is calcium oxide or calcium hydroxide, preferably calcium oxide. The concentration of the resulting calcium chloride solution is greater than or equal to 55 g / L, preferably greater than or equal to 58 g / L, and more preferably greater than or equal to 60 g / L. The rare earth phosphate solid is a rare earth substance primarily bound to phosphate and can be used to react with the alkaline solution D to achieve decomposition.

[0044] In the present invention, the roughing minerals are the minerals obtained after removing the calcium-containing minerals, including rare earth minerals combined with carbonate, rare earth minerals combined with fluoride, rare earth minerals combined with phosphate, etc.

[0045] According to one embodiment of the present invention, a mixed rare earth concentrate is reacted with hydrochloric acid solution A, followed by solid-liquid separation to obtain a roughing ore and a mother liquor. The mother liquor is neutralized with a calcium-containing inorganic substance, followed by solid-liquid separation to obtain a calcium chloride solution and a rare earth phosphate solid. In the present invention, the solid-liquid separation can be performed by filtration or centrifugation, preferably filtration.

[0046] <Reaction with Hydrochloric Acid Solution B>

[0047] The rough ore obtained above is reacted with hydrochloric acid solution B to obtain re-decomposed ore and a first acid solution containing rare earth chloride. The concentration of hydrochloric acid solution B is greater than that of hydrochloric acid solution A. This is conducive to decomposing the rare earth ore bound to carbonate ions and obtaining the first acid solution containing rare earth chloride.

[0048] In the present invention, the ratio of the mass of the roughing ore to the volume of hydrochloric acid solution B can be 1 kg:1-3 L, for example, 1 kg:1 L, 1 kg:2 L, or 1 kg:3 L. The concentration of hydrochloric acid solution B can be 7-12 mol / L, preferably 8-12 mol / L, for example, 8 mol / L, 9 mol / L, 10 mol / L, 11 mol / L, or 12 mol / L. The reaction temperature of the roughing ore and hydrochloric acid solution B can be 80-110°C, preferably 80-100°C, for example, 80°C, 90°C, or 100°C. The reaction time can be 0.5-4 hours, for example, 0.5 h, 1 h, 1.5 h, 2 h, 2.5 h, 3 h, 3.5 h, or 4 h. In this step, the mass of the roughing ore refers to the dry weight of the roughing ore. This is beneficial for controlling the decomposition of rare earth minerals bound to carbonate in the roughing ore, while not decomposing rare earth minerals bound to fluoride ions and rare earth minerals bound to phosphate.

[0049] During the reaction of the roughing ore with the hydrochloric acid solution B, the tail gas is absorbed by spraying to obtain a mixed acid of hydrochloric acid and hydrofluoric acid. This mixed acid can be used to react with the first alkali cake or the second alkali cake obtained in the subsequent steps.

[0050] According to one embodiment of the present invention, the rough ore obtained above is reacted with hydrochloric acid solution B, and solid-liquid separation is performed to obtain re-decomposed ore and a first acid solution containing rare earth chloride. In the present invention, solid-liquid separation can be performed by filtration or centrifugation, preferably filtration.

[0051] <Reaction with Alkali Solution C>

[0052] In certain embodiments, the re-decomposed mineral is reacted with an alkaline solution C, and the solid and liquid are separated to obtain a first filter cake and a first filtrate; the first filter cake is washed to obtain a first alkaline cake and a first alkaline washing solution; the first alkaline washing solution is used to recover fluoride salts; the first alkaline cake is reacted with a solution containing hydrochloric acid to obtain a first acid slag and a second acid solution containing rare earth chloride; wherein the alkaline solution C is selected from at least one of an alkali metal carbonate solution and an alkali metal hydroxide solution.

[0053] In other embodiments, the re-decomposed mineral is reacted with alkaline solution C, followed by solid-liquid separation to obtain a first filter cake and a first filtrate; the first filter cake is washed to obtain a first alkaline cake and a first alkaline washing solution; the first alkaline washing solution is used to recover fluoride salts; and the first alkaline cake is not reacted with a solution containing hydrochloric acid (but is directly used to react with alkaline solution D, as described below). The alkaline solution C is selected from at least one of an alkali metal carbonate solution and an alkali metal hydroxide solution. This facilitates the decomposition of rare earth ores primarily bound to fluoride ions while sparing the decomposition of rare earth ores bound to phosphate ions.

[0054] In the present invention, the ratio of the mass of the re-decomposed mineral to the volume of the alkali solution C can be 1 kg:1-3 L, for example, 1 kg:1 L, 1 kg:2 L, or 1 kg:3 L. In this step, the mass of the re-decomposed mineral refers to the dry weight of the re-decomposed mineral. The concentration of the alkali solution C can be 10-50 wt%. The alkali solution C is selected from at least one of an alkali metal carbonate solution and an alkali metal hydroxide solution. The alkali metal is selected from one of sodium and potassium, preferably sodium. In certain embodiments, the alkali solution C is an alkali metal carbonate solution having a concentration of 30-50 wt%. In other embodiments, the alkali solution C is a sodium hydroxide solution having a concentration of 10-30 wt%. In still other embodiments, the alkali solution C is a mixed solution containing sodium carbonate and sodium hydroxide, wherein the concentration of sodium carbonate is 30-40 wt% and the concentration of sodium hydroxide is 5-20 wt%, with the concentration of sodium hydroxide being, for example, 5 wt%, 10 wt%, 15 wt%, or 20 wt%. The reaction temperature of the re-decomposed mineral and alkali solution C can be 100-135°C, for example, 100°C, 110°C, 115°C, 120°C, 125°C, 130°C, or 135°C. The reaction pressure can be 0.1-1 MPa, for example, 0.1 MPa, 0.2 MPa, 0.3 MPa, 0.4 MPa, 0.5 MPa, 0.6 MPa, 0.7 MPa, 0.8 MPa, 0.9 MPa, or 1 MPa. The reaction time can be 0.5-5 hours, preferably 0.5-4 hours, for example, 0.5 hours, 1 hour, 1.5 hours, 2 hours, 2.5 hours, 3 hours, 3.5 hours, or 4 hours. This is conducive to the complete decomposition of the rare earth mineral bound to the fluoride ions.

[0055] In the present invention, the first alkali wash solution can be concentrated and crystallized to recover fluoride salt and the first residual alkali. According to one embodiment of the present invention, the alkali solution C is selected from at least one of a sodium carbonate solution and a sodium hydroxide solution; the first alkali wash solution can be concentrated and crystallized to recover sodium fluoride and the first residual alkali. The purity of the sodium fluoride is ≥94 wt%, and can reach 94.6 wt%. The first residual alkali and the first filtrate are mixed and then supplemented with sodium hydroxide to prepare the alkali solution C required for the reaction in this step.

[0056] In the present invention, the first alkali cake is reacted with a solution containing hydrochloric acid, and solid-liquid separation is performed to obtain a first acid slag and a second acid solution containing rare earth chloride. The hydrochloric acid solution is selected from at least one of directly prepared hydrochloric acid, the first acid solution containing rare earth chloride obtained as described above, and a mixed acid of hydrochloric acid and hydrofluoric acid obtained as described above. The solid-liquid separation can be performed by centrifugation or filtration, preferably filtration.

[0057] In certain embodiments, the first alkali cake is reacted with a first acid solution containing rare earth chloride, filtered and washed to obtain a first acid slag and a second acid solution containing rare earth chloride.

[0058] In other embodiments, the first alkali cake is reacted with the mixed acid of hydrochloric acid and hydrofluoric acid obtained above, filtered and washed to obtain a first acid slag and a second acid solution containing rare earth chloride.

[0059] In still other embodiments, the first alkali cake is dissolved with freshly prepared hydrochloric acid, filtered and washed to obtain a first acid slag and a second acid solution containing rare earth chloride.

[0060] <Reaction with alkali solution D>

[0061] Reaction of the first acid slag with alkali solution D and reaction of the first acid slag, rare earth phosphate solid and alkali solution D

[0062] In certain embodiments, the first acid slag is reacted with alkaline solution D to separate the solid and liquid to obtain a second filter cake and a second filtrate; the second filter cake is washed to obtain a second alkaline cake and a second alkaline washing solution; the second alkaline washing solution is used to recover phosphate; the second alkaline cake is reacted with a solution containing hydrochloric acid to obtain a second acid slag and a third acid solution containing rare earth chloride; wherein the alkaline solution D is an alkali metal hydroxide solution; and the alkalinity of the alkaline solution D is greater than that of the alkaline solution C. This facilitates the decomposition of rare earth minerals bound to phosphate (i.e., the decomposition of monazite minerals) and the production of trisodium phosphate of higher purity.

[0063] According to one embodiment of the present invention, the first acid slag, the rare earth phosphate solid obtained as above, and alkali liquor D are reacted, and the solid-liquid separation is performed to obtain a second filter cake and a second filtrate; the second filter cake is washed to obtain a second alkali cake and a second alkali washing liquor; the phosphate is recovered from the second alkali washing liquor; the second alkali cake is reacted with a solution containing hydrochloric acid to obtain a second acid slag and a third acid solution containing rare earth chloride; wherein the alkali liquor D is an alkali metal hydroxide solution; and the alkalinity of the alkali liquor D is greater than the alkalinity of the alkali liquor C.

[0064] The ratio of the sum of the mass of the first acid slag and the rare earth phosphate solid to the volume of the alkali liquor D can be 1 kg:1-2.5 L, for example, 1 kg:1 L, 1 kg:1.5 L, 1 kg:1.8 L, 1 kg:2 L, or 1 kg:2.5 L. The concentration of the alkali liquor D can be 40-65 wt%, for example, 40 wt%, 45 wt%, 50 wt%, 55 wt%, 60 wt%, or 65 wt%. The alkali liquor D is an alkali metal hydroxide solution, specifically a sodium hydroxide solution or a potassium hydroxide solution, preferably a sodium hydroxide solution. The reaction temperature of the first acid slag and the alkali liquor D can be 140-180 ° C, for example, 140 ° C, 145 ° C, 150 ° C, 155 ° C, 160 ° C, 165 ° C, 170 ° C, 175 ° C, or 180 ° C. The reaction pressure can be 0.1-1 MPa, for example, 0.1 MPa, 0.2 MPa, 0.3 MPa, 0.4 MPa, 0.5 MPa, 0.6 MPa, 0.7 MPa, 0.8 MPa, 0.9 MPa, or 1 MPa. The reaction time can be 0.5-4.5 h, preferably 0.5-4 h, for example, 0.5 h, 1 h, 1.5 h, 2 h, 2.5 h, 3 h, 3.5 h, or 4 h. This can not only decompose the rare earth minerals bound to phosphate groups, but also facilitate the production of trisodium phosphate of higher purity.

[0065] According to one embodiment of the present invention, the alkali liquor D used is a sodium hydroxide solution, and the second alkali liquor is cooled and crystallized to recover trisodium phosphate, thereby obtaining a second surplus alkali. The trisodium phosphate is trisodium phosphate dodecahydrate, and its purity is ≥98 wt%, and can reach 98.7 wt%.

[0066] In the present invention, the second filtrate and the second residual alkali can be mixed and then alkali metal hydroxide can be added to form 40-65 wt% alkali solution D for the reaction in this step.

[0067] In the present invention, the hydrochloric acid-containing solution is selected from at least one of directly prepared hydrochloric acid, the first acid solution containing rare earth chloride obtained as described above, the second acid solution containing rare earth chloride obtained as described above, and a mixed acid of hydrochloric acid and hydrofluoric acid obtained as described above. The present invention further includes removing impurities from at least the third acid solution containing rare earth chloride to obtain a purified rare earth chloride solution.

[0068] In certain specific embodiments, the second alkaline cake is reacted with the obtained second acid solution containing rare earth chloride, followed by solid-liquid separation to obtain a second acid slag and a third acid solution containing rare earth chloride. The resulting third acid solution containing rare earth chloride is then neutralized and impurities removed to obtain a purified rare earth chloride solution. In the present invention, the concentration of the third acid solution containing rare earth chloride can be adjusted to a desired range by adding water.

[0069] In other specific embodiments, the second alkali cake is reacted with the first acid solution containing rare earth chloride, and the solid and liquid are separated to obtain a second acid slag and a third acid solution containing rare earth chloride; the second acid solution containing rare earth chloride and the third acid solution containing rare earth chloride are mixed, and the solution concentration is adjusted and then neutralized and impurities are removed to obtain a purified rare earth chloride solution.

[0070] In some further specific embodiments, the second alkali cake is reacted with directly prepared hydrochloric acid, and the solid and liquid are separated to obtain a second acid slag and a third acid solution containing rare earth chloride; the first acid solution containing rare earth chloride, the second acid solution containing rare earth chloride, and the third acid solution containing rare earth chloride are mixed, and the solution concentrations are adjusted and then neutralized and impurities are removed to obtain a purified rare earth chloride solution.

[0071] Compared with the process of directly decomposing mixed rare earth concentrate by alkali method, the method of the present invention does not produce complicated alkali wastewater, and the produced second filtrate and second residual alkali can be recycled, and the first filtrate and first residual alkali can be recycled.

[0072] Reaction of the first alkali cake with alkali solution D and reaction of the first alkali cake, rare earth phosphate solid and alkali solution D

[0073] In other embodiments, the first alkali cake is reacted with alkali liquor D, and the solid and liquid are separated to obtain a third filter cake and a third filtrate; the third filter cake is washed to obtain a third alkali cake and a third alkali washing liquor; the third alkali washing liquor is used to recover phosphate; the third alkali cake is reacted with a solution containing hydrochloric acid to obtain a third acid slag and a fourth acid solution containing rare earth chloride; wherein the alkali liquor D is an alkali metal hydroxide solution; and the alkalinity of the alkali liquor D is greater than the alkalinity of the alkali liquor C.

[0074] According to one embodiment of the present invention, a first alkali cake, a rare earth phosphate solid and an alkali liquor D are reacted, and the solid and liquid are separated to obtain a third filter cake and a third filtrate; the third filter cake is washed to obtain a third alkali cake and a third alkali washing liquor; the phosphate is recovered from the third alkali washing liquor; the third alkali cake is reacted with a solution containing hydrochloric acid to obtain a third acid slag and a fourth acid solution containing rare earth chloride; wherein the alkali liquor D is an alkali metal hydroxide solution; and the alkalinity of the alkali liquor D is greater than the alkalinity of the alkali liquor C.

[0075] In the present invention, the ratio of the sum of the mass of the first alkali cake and the rare earth phosphate solid to the volume of the alkali liquor D can be 1 kg:1 to 2.5 L, for example, 1 kg:1 L, 1 kg:1.5 L, 1 kg:1.8 L, 1 kg:2 L, or 1 kg:2.5 L. The concentration of the alkali liquor D can be 40 to 65 wt%, for example, 40 wt%, 45 wt%, 50 wt%, 55 wt%, 60 wt%, or 65 wt%. The alkali liquor D is an alkali metal hydroxide solution, specifically sodium hydroxide solution or potassium hydroxide solution, preferably sodium hydroxide solution. The reaction temperature of the first alkali cake, rare earth phosphate solid, and alkali liquor D can be 140 to 180° C., for example, 140° C., 145° C., 150° C., 155° C., 160° C., 165° C., 170° C., 175° C., or 180° C. The reaction pressure can be 0.1-1 MPa, for example, 0.1 MPa, 0.2 MPa, 0.3 MPa, 0.4 MPa, 0.5 MPa, 0.6 MPa, 0.7 MPa, 0.8 MPa, 0.9 MPa, or 1 MPa. The reaction time can be 0.5-4.5 h, preferably 0.5-4 h, for example, 0.5 h, 1 h, 1.5 h, 2 h, 2.5 h, 3 h, 3.5 h, or 4 h. This facilitates better decomposition of the first alkali cake and rare earth phosphate solids.

[0076] When the alkali liquor D is a sodium hydroxide solution, trisodium phosphate is recovered from the third washing alkali liquor, and its purity is ≥98wt%, and can reach 98.6wt%. The solution containing hydrochloric acid is selected from at least one of directly prepared hydrochloric acid, the first acid solution containing rare earth chloride obtained as described above, and a mixed acid of hydrochloric acid and hydrofluoric acid.

[0077] <Analysis Method>

[0078] REO content: analyzed by weight method.

[0079] P content: analyzed by phospho-bismuth molybdenum blue spectrophotometry.

[0080] F content: analyzed by distillation method.

[0081] CaO content: analyzed by EDTA titration method.

[0082] Purity of trisodium phosphate: Determined using the method of HGT2517-2009 industrial trisodium phosphate standard.

[0083] Concentration of calcium chloride solution: Use the weight method to determine the calcium content in the solution and calculate the calcium chloride concentration.

[0084] Purity of sodium fluoride: Determined using the method of YS / T 517-2024 sodium fluoride standard.

[0085] The following flow diagrams of Examples 1, 2, and 3 are shown in FIG. Figure 1 shown.

[0086] Example 1

[0087] In the mixed rare earth concentrate of this embodiment, the REO content is 42.3 wt%, the fluorine content is 4.6 wt%, the phosphorus content is 3.8 wt%, and the CaO content is 13.6 wt%.

[0088] 1) Mix the mixed rare earth concentrate with 2.5 mol / L hydrochloric acid solution A (the mass of the mixed rare earth concentrate to the volume of hydrochloric acid solution A is 1 kg:4 L) and react at 70°C for 4 hours. During the reaction, exhaust gas is absorbed by spraying to produce a mixed acid of hydrochloric acid and hydrofluoric acid. After the reaction is completed, the mixture is filtered to obtain a crude ore and a mother liquor. The mother liquor is neutralized with calcium oxide to a pH of 7 and filtered to obtain a calcium chloride solution and rare earth phosphate solids.

[0089] 2) The crude ore obtained above is mixed with 8 mol / L hydrochloric acid solution B (the ratio of the mass of the crude ore to the volume of hydrochloric acid solution B is 1 kg:3 L) and reacted at 100°C for 0.5 h. During the reaction, the tail gas is absorbed by spraying to produce a mixed acid of hydrochloric acid and hydrofluoric acid. After the reaction is completed, the solution is filtered to obtain a first acid solution containing the re-decomposed ore and rare earth chloride.

[0090] 3) The re-decomposed mineral obtained as above is mixed with a sodium hydroxide solution with a concentration of 10wt% (i.e., alkali solution C, the ratio of the mass of the re-decomposed mineral to the volume of alkali solution C is 1kg:3L), and the reaction is carried out at a temperature of 100°C and a pressure of 0.1MPa for 4h. After the reaction is completed, it is filtered to obtain a first filter cake and a first filtrate. The first filter cake is washed with water to obtain a first alkali cake and a first alkali washing solution. The first alkali washing solution is concentrated and crystallized to recover sodium fluoride and the first residual alkali. After the first residual alkali and the first filtrate are mixed, sodium hydroxide can be added to prepare the alkali solution C required for the reaction of this step. The first alkali cake is dissolved in a first acid solution containing rare earth chloride, filtered and washed to obtain a first acid slag and a second acid solution containing rare earth chloride.

[0091] 4) The first acid slag and rare earth phosphate solids obtained above are mixed with a 40 wt% sodium hydroxide solution (i.e., lye D, with the ratio of the sum of the mass of the first acid slag and rare earth phosphate solids to the volume of lye D being 1 kg:2.5 L) and reacted at a temperature of 140° C. and a pressure of 0.1 MPa for 4 hours. After the reaction is completed, the mixture is filtered to obtain a second filter cake and a second filtrate. The second filter cake is washed with water to obtain a second alkali cake and a second alkali wash solution. The second alkali wash solution is cooled and crystallized to recover trisodium phosphate and a second residual alkali. The second residual alkali and the second filtrate are mixed and supplemented with sodium hydroxide to prepare the alkali solution D required for the reaction in this step. The second alkali cake is dissolved in a second acid solution containing rare earth chloride, filtered, and washed to obtain a second acid slag and a third acid solution containing rare earth chloride. The third acid solution containing rare earth chloride is adjusted in concentration by adding water and neutralized to remove impurities to obtain a purified rare earth chloride solution.

[0092] Example 2

[0093] In the mixed rare earth concentrate of this embodiment, the REO content is 51.4 wt%, the fluorine content is 8.2 wt%, the phosphorus content is 4.3 wt%, and the CaO content is 9.7 wt%.

[0094] 1) Mix the mixed rare earth concentrate with 3 mol / L hydrochloric acid solution A (the mass of the mixed rare earth concentrate to the volume of hydrochloric acid solution A is 1 kg:1.5 L) and react at 90°C for 2 hours. During the reaction, exhaust gas is absorbed by spraying to produce a mixed acid of hydrochloric acid and hydrofluoric acid. After the reaction is completed, the mixture is filtered to obtain a crude ore and a mother liquor. The mother liquor is neutralized with calcium oxide to a pH of 7 to obtain a calcium chloride solution and rare earth phosphate solids.

[0095] 2) The crude ore obtained above is mixed with 10 mol / L hydrochloric acid solution B (the ratio of the mass of the crude ore to the volume of hydrochloric acid solution B is 1 kg:2 L) and reacted at 90°C for 2 hours. During the reaction, the tail gas is absorbed by spraying to produce a mixed acid of hydrochloric acid and hydrofluoric acid. After the reaction is completed, the solution is filtered to obtain a first acid solution containing the re-decomposed ore and rare earth chloride.

[0096] 3) The re-decomposed mineral obtained as above is mixed with a sodium carbonate solution with a concentration of 30wt% (i.e., alkali solution C, the ratio of the mass of the re-decomposed mineral to the volume of alkali solution C is 1kg:2L), and the reaction is carried out at a temperature of 110°C and a pressure of 0.3MPa for 2h. After the reaction is completed, the mixture is filtered to obtain a first filter cake and a first filtrate. The first filter cake is washed with water to obtain a first alkali cake and a first alkali washing solution. The first alkali washing solution is concentrated and crystallized to recover sodium fluoride and a first residual alkali. The first residual alkali and the first filtrate are mixed and supplemented with sodium carbonate to prepare the alkali solution C required for the reaction of this step. The first alkali cake is dissolved with a mixed acid of hydrochloric acid and hydrofluoric acid obtained in steps 1) and 2), filtered and washed to obtain a first acid slag and a second acid solution containing rare earth chloride.

[0097] 4) The first acid slag and rare earth phosphate solids obtained above are mixed with a 50 wt% sodium hydroxide solution (i.e., lye D, the ratio of the sum of the mass of the first acid slag and the rare earth phosphate solid to the volume of lye D is 1 kg:1.8 L) and reacted at a temperature of 160° C. and a pressure of 0.5 MPa for 3 hours. After the reaction is completed, the mixture is filtered to obtain a second filter cake and a second filtrate. The second filter cake is washed with water to obtain a second alkali cake and a second alkali wash solution. The second alkali wash solution is cooled and crystallized to recover trisodium phosphate and a second residual alkali. The second residual alkali and the second filtrate can be supplemented with sodium hydroxide to prepare the alkali solution D required for the reaction in this step. The second alkali cake is dissolved in the first acid solution containing rare earth chloride, filtered and washed to obtain a second acid slag and a third acid solution containing rare earth chloride. The second acid solution containing rare earth chloride and the third acid solution containing rare earth chloride are mixed, and the solution concentration is adjusted by adding water, neutralized and impurities removed to obtain a purified rare earth chloride solution.

[0098] Example 3

[0099] In the mixed rare earth concentrate of this embodiment, the REO content is 60.8 wt %, the fluorine content is 9.5 wt %, the phosphorus content is 6.2 wt %, and the CaO content is 4.3 wt %.

[0100] 1) Mix the mixed rare earth concentrate with 3.5 mol / L hydrochloric acid solution A (the mass of the mixed rare earth concentrate to the volume of hydrochloric acid solution A is 1 kg:0.8 L) and react at 95°C for 0.5 h. During the reaction, exhaust gas is absorbed by spraying to produce a mixed acid of hydrochloric acid and hydrofluoric acid. After the reaction is completed, the mixture is filtered to obtain a crude ore and a mother liquor. The mother liquor is neutralized with calcium oxide to a pH of 7 and filtered to obtain a calcium chloride solution and rare earth phosphate solids.

[0101] 2) The crude ore obtained above is mixed with 12 mol / L hydrochloric acid solution B (the ratio of the mass of the crude ore to the volume of hydrochloric acid solution B is 1 kg:1 L) and reacted at 80°C for 4 hours. During the reaction, the tail gas is absorbed by spraying to produce a mixed acid of hydrochloric acid and hydrofluoric acid. After the reaction is completed, the solution is filtered to obtain a first acid solution containing the re-decomposed ore and rare earth chloride.

[0102] 3) The re-decomposed mineral obtained above is mixed with a mixed solution containing sodium carbonate and sodium hydroxide (the mixed solution is referred to as alkali liquor C, wherein the concentration of sodium carbonate is 30 wt % and the concentration of sodium hydroxide is 20 wt %; the ratio of the mass of the re-decomposed mineral to the volume of the mixed solution is 1 kg:1 L), and the mixture is reacted at a temperature of 115° C. and a pressure of 1 MPa for 0.5 h. After the reaction is completed, the mixture is filtered to obtain a first filter cake and a first filtrate. The first filter cake is washed with water to obtain a first alkali cake and a first alkali wash solution. The first alkali wash solution is concentrated and crystallized to recover sodium fluoride and a first residual alkali. The first residual alkali and the first filtrate are mixed and supplemented with sodium carbonate and sodium hydroxide to prepare the alkali liquor C required for the reaction in this step. The first alkali cake is dissolved in freshly prepared hydrochloric acid, filtered, and washed to obtain a first acid slag and a second acid solution containing rare earth chloride.

[0103] 4) The first acid slag and rare earth phosphate solids obtained above are mixed with a 65 wt% sodium hydroxide solution (i.e., lye D, where the ratio of the combined mass of the first acid slag and rare earth phosphate solids to the volume of lye D is 1 kg:1 L) and reacted at 180° C. and 1 MPa for 0.5 h. After completion of the reaction, the mixture is filtered to obtain a second filter cake and a second filtrate. The second filter cake is washed with water to obtain a second alkali cake and a second alkali wash solution. The second alkali wash solution is cooled and crystallized to recover trisodium phosphate and a second residual alkali. The second residual alkali and the filtrate are supplemented with sodium hydroxide to prepare the alkali solution D required for this step. The second alkali cake is dissolved in freshly prepared hydrochloric acid, filtered, and washed to obtain a second acid slag and a third acid solution containing rare earth chloride. The first acid solution containing rare earth chloride, the second acid solution containing rare earth chloride, and the third acid solution containing rare earth chloride are mixed, the solution concentration is adjusted by adding water, and impurities are neutralized to obtain a purified rare earth chloride solution.

[0104] Example 4

[0105] In the mixed rare earth concentrate of this embodiment, the REO content is 51.4 wt%, the fluorine content is 8.2 wt%, the phosphorus content is 4.3 wt%, and the CaO content is 9.7 wt%.

[0106] 1) Mix the mixed rare earth concentrate with 3 mol / L hydrochloric acid solution A (the mass of the mixed rare earth concentrate to the volume of hydrochloric acid solution A is 1 kg:1 L) and react at 95°C for 1 hour. During the reaction, exhaust gas is absorbed by spraying to produce a mixed acid of hydrochloric acid and hydrofluoric acid. After the reaction is completed, the mixture is filtered to obtain a crude ore and a mother liquor. The mother liquor is neutralized with calcium oxide to a pH of 7 to obtain a calcium chloride solution and rare earth phosphate solids.

[0107] 2) The crude ore obtained above is mixed with 10 mol / L hydrochloric acid solution B (the ratio of the mass of the crude ore to the volume of hydrochloric acid solution B is 1 kg:1.5 L) and reacted at 95°C for 1 hour. During the reaction, the tail gas is absorbed by spraying to produce a mixed acid of hydrochloric acid and hydrofluoric acid. After the reaction is completed, the solution is filtered to obtain a first acid solution containing the re-decomposed ore and rare earth chloride.

[0108] 3) The re-decomposed mineral obtained as above is mixed with a mixed solution containing sodium carbonate and sodium hydroxide (the mixed solution is alkali liquor C, wherein the concentration of sodium carbonate is 25wt%, the concentration of sodium hydroxide is 25wt%; the ratio of the mass of the re-decomposed mineral to the volume of the mixed solution is 1kg:1.5L), and the reaction is carried out at a temperature of 135°C and a pressure of 0.8MPa for 1.5h. After the reaction is completed, the first filter cake and the first filtrate are obtained by filtration. The first filter cake is washed with water to obtain a first alkali cake and a first alkali washing solution. The first alkali washing solution is recovered by concentrated crystallization to recover sodium fluoride and the first residual alkali. The first residual alkali and the first filtrate are mixed and then supplemented with sodium carbonate to prepare the alkali liquor C required for the reaction of this step.

[0109] 4) The first alkali cake and rare earth phosphate solid obtained above are mixed with a 50 wt% sodium hydroxide solution (i.e., alkali solution D, where the ratio of the sum of the mass of the first alkali cake and rare earth phosphate solid to the volume of alkali solution D is 1 kg:1.8 L) and reacted at a temperature of 160° C. and a pressure of 0.5 MPa for 3 hours. After the reaction is completed, the mixture is filtered to obtain a third filter cake and a third filtrate. The third filter cake is washed with water to obtain a third alkali cake and a third alkali washing solution. The third alkali washing solution is cooled and crystallized to recover trisodium phosphate and a third residual alkali. The third residual alkali and the third filtrate can be supplemented with sodium hydroxide to prepare the alkali solution D required for the reaction in this step. The second alkali cake is dissolved in the first acid solution containing rare earth chloride, filtered, and washed to obtain a third acid residue and a fourth acid solution containing rare earth chloride. The fourth acid solution containing rare earth chloride is adjusted in concentration by adding water, neutralized, and impurities removed to obtain a purified rare earth chloride solution.

[0110] Table 1

[0111]

[0112] Note: In the table, M1 refers to the ratio of the mass of mixed rare earth concentrate to the volume of hydrochloric acid solution A; M2 refers to the ratio of the mass of roughing ore to the volume of hydrochloric acid solution B; M3 refers to the ratio of the mass of re-decomposed ore to the volume of alkali solution C; M4 refers to the ratio of the sum of the mass of the first acid slag and rare earth phosphate solid to the volume of alkali solution D.

[0113] Table 2

[0114]

[0115] Note: The calculation formula for the total rare earth yield is:

[0116] Total rare earth yield (%) = weight of rare earth in the purified rare earth chloride solution / weight of rare earth in the mixed rare earth concentrate × 100%.

[0117] The present invention is not limited to the above-mentioned embodiments. Any modification, improvement, or substitution that can be conceived by those skilled in the art without departing from the essential content of the present invention shall fall within the scope of the present invention.

Claims

1. A method for decomposing mixed rare earth concentrate and comprehensively utilizing associated resources, characterized in that: The following steps are involved: 1) reacting the mixed rare earth concentrate with hydrochloric acid solution A to obtain rough ore and mother liquor; 2) reacting the coarsely selected ore with hydrochloric acid solution B to obtain a first acid solution containing re-decomposed ore and rare earth chloride; wherein the concentration of hydrochloric acid solution B is greater than that of hydrochloric acid solution A; 3) reacting the re-decomposed mineral with alkali liquor C, separating the solid and the liquid to obtain a first filter cake and a first filtrate; washing the first filter cake to obtain a first alkali cake and a first alkali washing liquor; recovering fluoride salt from the first alkali washing liquor; reacting the first alkali cake with a solution containing hydrochloric acid to obtain a first acid slag and a second acid solution containing rare earth chloride; wherein the alkali liquor C is selected from at least one of an alkali metal carbonate solution and an alkali metal hydroxide solution; 4) reacting the first acid slag with alkali liquor D to separate the solid and liquid to obtain a second filter cake and a second filtrate; washing the second filter cake to obtain a second alkali cake and a second alkali washing liquor; recovering phosphate from the second alkali washing liquor; and reacting the second alkali cake with a solution containing hydrochloric acid to obtain a second acid slag and a third acid solution containing rare earth chloride; wherein the alkali liquor D is an alkali metal hydroxide solution; and the alkalinity of the alkali liquor D is greater than the alkalinity of the alkali liquor C.

2. A method for decomposing mixed rare earth concentrate and comprehensively utilizing associated resources, characterized in that: The following steps are involved: 1) reacting the mixed rare earth concentrate with hydrochloric acid solution A to obtain rough ore and mother liquor; 2) reacting the coarsely selected ore with hydrochloric acid solution B to obtain a first acid solution containing re-decomposed ore and rare earth chloride; wherein the concentration of hydrochloric acid solution B is greater than that of hydrochloric acid solution A; 3) reacting the re-decomposed mineral with alkali liquor C, separating the solid and the liquid to obtain a first filter cake and a first filtrate; washing the first filter cake to obtain a first alkali cake and a first alkali washing liquor; and recovering fluoride salt from the first alkali washing liquor; wherein the alkali liquor C is selected from at least one of an alkali metal carbonate solution and an alkali metal hydroxide solution; 4) reacting the first alkali cake with alkali liquor D to separate the solid and liquid to obtain a third filter cake and a third filtrate; washing the third filter cake to obtain a third alkali cake and a third alkali washing liquor; recovering phosphate from the third alkali washing liquor; and reacting the third alkali cake with a solution containing hydrochloric acid to obtain a third acid slag and a fourth acid solution containing rare earth chloride; wherein the alkali liquor D is an alkali metal hydroxide solution; and the alkalinity of the alkali liquor D is greater than the alkalinity of the alkali liquor C.

3. The method according to claim 1 or 2, characterized in that: In step 1), the concentration of hydrochloric acid solution A is 2 to 4 mol / L; the ratio of the mass of the mixed rare earth concentrate to the volume of hydrochloric acid solution A is 1 kg:0.8 to 4 L; the reaction temperature is 65 to 95° C., and the reaction time is 0.5 to 6.5 h; Step 1) further comprises the following steps: neutralizing the mother liquor with a calcium-containing inorganic substance to a pH value of 6.5 to 7 to obtain a calcium chloride solution and a rare earth phosphate solid; wherein the calcium-containing inorganic substance is calcium oxide or calcium hydroxide.

4. The method according to claim 1 or 2, characterized in that In step 2), the concentration of hydrochloric acid solution B is 7-12 mol / L; the ratio of the mass of the crude ore to the volume of hydrochloric acid solution B is 1 kg:1-3 L; the reaction temperature is 80-110° C., and the reaction time is 0.5-4 h.

5. The method according to claim 1, wherein: In step 1), during the reaction of the mixed rare earth concentrate and hydrochloric acid solution A, the tail gas is absorbed by spraying to obtain a mixed acid of hydrochloric acid and hydrofluoric acid; in step 2), during the reaction of the roughing ore and hydrochloric acid solution B, the tail gas is absorbed by spraying to obtain a mixed acid of hydrochloric acid and hydrofluoric acid; In step 3), the solution containing hydrochloric acid is selected from at least one of directly prepared hydrochloric acid, the first acid solution containing rare earth chloride obtained in step 2), and a mixed acid of hydrochloric acid and hydrofluoric acid; in step 4), the solution containing hydrochloric acid is selected from at least one of directly prepared hydrochloric acid, the first acid solution containing rare earth chloride obtained in step 2), the second acid solution containing rare earth chloride obtained in step 3), and a mixed acid of hydrochloric acid and hydrofluoric acid.

6. The method according to claim 1 or 2, characterized in that In step 3), the concentration of the alkali solution C is 10 to 50 wt%; the ratio of the mass of the re-decomposed mineral to the volume of the alkali solution C is 1 kg:1 to 3 L; the reaction temperature is 100 to 135° C., the reaction pressure is 0.1 to 1 MPa, and the reaction time is 0.5 to 5 h.

7. The method according to claim 2, wherein: In step 1), during the reaction of the mixed rare earth concentrate and hydrochloric acid solution A, the tail gas is absorbed by spraying to obtain a mixed acid of hydrochloric acid and hydrofluoric acid; in step 2), during the reaction of the roughing ore and hydrochloric acid solution B, the tail gas is absorbed by spraying to obtain a mixed acid of hydrochloric acid and hydrofluoric acid; In step 4), the solution containing hydrochloric acid is selected from at least one of directly prepared hydrochloric acid, the first acid solution containing rare earth chloride obtained in step 2), and a mixed acid of hydrochloric acid and hydrofluoric acid.

8. The method according to claim 3, characterized in that Step 4) includes the following specific steps: reacting the first acid slag, rare earth phosphate solid and alkali solution D; wherein the ratio of the sum of the mass of the first acid slag and the rare earth phosphate solid to the volume of the alkali solution D is 1 kg:1-2.5 L.

9. The method according to claim 3, characterized in that Step 4) comprises the following specific steps: reacting the first alkali cake, rare earth phosphate solid and alkali solution D; wherein the ratio of the sum of the mass of the first alkali cake and the rare earth phosphate solid to the volume of the alkali solution D is 1 kg:1-2.5 L.

10. The method according to claim 1 or 2, characterized in that In step 4), the concentration of the alkali solution D is 40-65 wt%; the reaction temperature is 140-180° C., the reaction pressure is 0.1-1 MPa, and the reaction time is 0.5-4.5 h.

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