Method for recovering cerium, cerium-poor rare earth and fluorine and phosphorus from mixed rare earth concentrate

Abstract

The application discloses a method for recovering cerium, low-cerium rare earth, fluorine and phosphorus from mixed rare earth concentrate, which comprises the following steps: 1) reacting the mixed rare earth concentrate with a hydrochloric acid solution, and performing solid-liquid separation to obtain a chemical dressing mineral and a chemical dressing mother liquor; 2) performing oxidation roasting on the chemical dressing mineral to obtain a roasting ore, reacting the roasting ore with a first alkali solution, and performing solid-liquid separation to obtain a filtrate I and a solid I; washing the solid I to obtain an alkali cake I and a washing alkali solution I; recovering fluorides from the washing alkali solution I; reacting the alkali cake I with a hydrochloric acid solution, and performing solid-liquid separation to obtain an acid-soluble residue I and an acid solution I; 3) reacting the acid-soluble residue I with a second alkali solution, and performing solid-liquid separation to obtain a filtrate II and a solid II; washing the solid II to obtain an alkali cake II and a washing alkali solution II; and cooling and crystallizing the washing alkali solution II to obtain a phosphate; and 4) reacting the alkali cake II with a hydrochloric acid solution to obtain an acid solution II and a cerium dioxide enrichment. The method can recover cerium, low-cerium rare earth, fluorine and phosphorus separately.

Description

Technical Field

[0001] This invention relates to a method for recovering cerium, low-cerium rare earth elements, fluorine, and phosphorus from mixed rare earth concentrates. Background Technology

[0002] The mixed rare earth concentrate obtained through beneficiation mainly includes bastnaesite and monazite. Due to the complexity of its composition, it is recognized as a difficult-to-smelt mineral. The rare earth elements in the mixed rare earth concentrate are mainly light rare earth elements such as lanthanum, cerium, praseodymium, and neodymium. Cerium accounts for approximately 50 wt%, while praseodymium and neodymium together account for about 18–20 wt%. Cerium has a larger proportion.

[0003] Currently, the processing of mixed rare earth concentrates typically yields chloride or sulfate solutions of the mixed rare earth elements. However, in downstream applications, individual rare earth elements need to be extracted, which is costly. While praseodymium and neodymium are the primary elements used in downstream applications, cerium oxide is increasingly being used. Therefore, extracting cerium oxide separately during the processing of mixed rare earth concentrates could shorten the production process and reduce costs. Furthermore, since mixed rare earth concentrates also contain fluorine and phosphorus, their separate recovery must also be considered.

[0004] CN109161702A discloses a method for selectively extracting non-cerium rare earth elements from mixed rare earth concentrates. The mixed rare earth concentrate is oxidatively roasted to obtain roasted ore. The roasted ore is then mixed with concentrated sulfuric acid and roasted again, followed by water leaching to obtain a low-cerium sulfate rare earth solution and a cerium phosphate concentrate. This method yields a cerium phosphate concentrate, but does not produce cerium dioxide on its own. Furthermore, the separate recovery of fluorine is not considered.

[0005] CN116987914A discloses a method for sodium-based pelletizing, roasting, and decomposing mixed rare earth concentrates. The method involves oxidizing and roasting the mixed rare earth concentrates, followed by leaching with hydrochloric acid to obtain an acid leaching solution and acid leaching residue. The acid leaching residue is then washed with water to obtain a water-washed residue 1 and a water-washed solution 1. The water-washed residue 1 is dried, mixed with sodium carbonate and an organic binder, ground evenly, and then placed in a pelletizing machine to form pellets. Qualified pellets are screened out, and after roasting, washing, and leaching, a rare earth chloride solution is obtained. The water-washed residue 1 should be a mixture of rare earth fluorides and rare earth phosphates. The recovered sodium phosphate has low purity and failed to form cerium dioxide enrichment on its own.

[0006] CN112534072A discloses a combined process for processing rare earth concentrates. The rare earth concentrates are roasted to obtain roasted ore. The roasted ore is then leached with hydrochloric acid to obtain leaching residue and leachate. The leaching residue is further roasted with sulfuric acid to decompose the remaining undecomposed minerals and rare earth fluorides. This method uses weak oxidation roasting and sulfuric acid roasting to process rare earth concentrates. It does not recover fluorine and phosphorus elements, nor does it form cerium dioxide enrichment separately.

[0007] CN106978531A discloses a method for the combined acid-base decomposition of mixed rare earth concentrates. This method involves mixing the mixed rare earth concentrate with concentrated sulfuric acid (greater than 92% by mass) in a specific ratio, and then calcining the mixture at 120–180°C for 150–300 min. After neutralization, the water leaching solution yields phosphorus-iron-thorium slag and a rare earth sulfate solution. The leaching residue is separated by gravity separation to obtain calcium sulfate waste and phosphorus-containing minerals. The phosphorus-containing minerals and phosphorus-iron-thorium slag are then decomposed with a sodium hydroxide solution (45–70% by mass) at 130–180°C, and rare earth chloride is obtained by dissolution with hydrochloric acid. This method separates calcium sulfate and phosphorus-containing minerals by gravity separation. However, gravity separation, as a conventional beneficiation method, has poor mineral separation efficiency, resulting in a low rare earth yield and the inability to form cerium dioxide enrichment independently.

[0008] CN101824553A discloses a high-temperature alkaline roasting and decomposition process for mixed rare earth concentrate, comprising: mixing mixed rare earth concentrate with sodium hydroxide; roasting the mixed rare earth ore; washing the roasted ore with water until neutral; preferentially dissolving the alkaline cake after washing with hydrochloric acid to obtain a low-cerium rare earth chloride solution; and reducing and dissolving the residue after hydrochloric acid dissolution with nitric acid to obtain a cerium nitrate solution. This process yields cerium nitrate and a low-cerium rare earth chloride solution. It does not involve the separate recovery of fluorine and phosphorus.

[0009] CN102212674A discloses a comprehensive resource recovery process for alkaline roasting of mixed rare earth concentrate, comprising: mixing and roasting a mixed rare earth concentrate with sodium hydroxide; washing the roasted ore to neutrality, preferentially dissolving the alkali cake with hydrochloric acid to obtain a low-cerium rare earth chloride solution; subjecting the residue after hydrochloric acid preferential dissolution to hydrochloric acid reduction dissolution to obtain a cerium-rich rare earth chloride solution; neutralizing the cerium-rich rare earth chloride solution after extracting and recovering phosphorus from the cerium-rich rare earth chloride solution to obtain thorium concentrate; recovering fluorine and sodium hydroxide from the roasted ore washing liquid, and recovering calcium chloride after extraction and separation from the low-cerium rare earth chloride solution. In this process, after roasting with sodium hydroxide, the resulting roasted ore washing liquid is a mixed solution of sodium carbonate, sodium fluoride, and sodium phosphate, which is difficult to separate. Summary of the Invention

[0010] In view of this, the purpose of the present invention is to provide a method for recovering cerium, cerium rare earth, fluorine, and phosphorus from mixed rare earth concentrates, which can recover cerium dioxide, cerium rare earth, fluorine, and phosphorus resources respectively, and obtain cerium dioxide concentrate, cerium rare earth chloride solution, fluoride, and phosphate respectively.

[0011] The present invention achieves the above objectives through the following technical solutions.

[0012] This invention provides a method for recovering cerium, low-cerium rare earth elements, fluorine, and phosphorus from mixed rare earth concentrates, comprising the following steps:

[0013] 1) The mixed rare earth concentrate is reacted with hydrochloric acid solution, and the solid and liquid are separated to obtain chemically beneficiated minerals and chemically beneficiated mother liquor;

[0014] 2) The chemically beneficiated minerals are oxidized and roasted to obtain roasted ore; the roasted ore is reacted with the first alkaline solution, and solid-liquid separation is performed to obtain filtrate I and solid I; solid I is washed to obtain alkali cake I and washing alkali solution I; fluoride is recovered from washing alkali solution I; alkali cake I is reacted with hydrochloric acid solution, and solid-liquid separation is performed to obtain acid residue I and acid solution I; wherein, acid solution I is a cerium-containing rare earth chloride solution;

[0015] 3) React acid residue I with the second alkaline solution, separate the solid and liquid, and obtain filtrate II and solid II; wash solid II to obtain alkaline cake II and washing solution II; cool washing solution II to crystallize and obtain phosphate;

[0016] 4) React alkali cake II with hydrochloric acid solution to obtain acid solution II and cerium dioxide enrichment; wherein, acid solution II is a cerium-containing rare earth chloride solution.

[0017] This invention also provides a method for recovering cerium, low-cerium rare earth elements, fluorine, and phosphorus from mixed rare earth concentrates, comprising the following steps:

[0018] 1) The mixed rare earth concentrate is reacted with hydrochloric acid solution, and the solid and liquid are separated to obtain chemically beneficiated minerals and chemically beneficiated mother liquor;

[0019] 2) The chemically beneficiated minerals are oxidized and roasted to obtain roasted ore; the roasted ore is reacted with the first alkaline solution, and the solid and liquid are separated to obtain filtrate I and solid I; solid I is washed to obtain alkali cake I and washing alkali solution I; fluoride is recovered from washing alkali solution I;

[0020] 3) React alkali cake I with the second alkali solution, separate the solid and liquid, and obtain filtrate III and solid III; wash solid III to obtain alkali cake III and washing alkali solution III; cool and crystallize washing alkali solution III to obtain phosphate;

[0021] 4) React alkali cake III with hydrochloric acid solution to obtain acid solution III and cerium dioxide enrichment; wherein, acid solution III is a low-cerium rare earth chloride solution.

[0022] According to the method of the present invention, preferably, in step 1), the concentration of hydrochloric acid solution is 3-6 mol / L, the solid-liquid ratio of mixed rare earth concentrate to hydrochloric acid solution is 1 kg: 1-5 L, the reaction temperature is 80-100 °C, and the reaction time is 1-6 h.

[0023] According to the method of the present invention, preferably, in step 1), the tail gas is absorbed by spraying during the reaction of the mixed rare earth concentrate with hydrochloric acid solution to obtain a mixed acid containing hydrochloric acid and hydrofluoric acid; step 1) further includes: neutralizing the chemical beneficiation mother liquor to a pH value of 8-9 with calcium-containing inorganic substances to obtain calcium chloride solution and rare earth phosphate precipitate.

[0024] According to the method of the present invention, preferably, in step 2), the oxidative calcination is carried out in an oxygen-containing atmosphere, the calcination temperature is 400-600°C, and the calcination time is 1-5 hours.

[0025] According to the method of the present invention, preferably, in step 2), the first alkaline solution is selected from one or both of alkali metal hydroxide solution and alkali metal carbonate solution; the concentration of the first alkaline solution is 10-50 wt%.

[0026] According to the method of the present invention, preferably, in step 2), the solid-liquid ratio of roasted ore to the first alkaline solution is 1 kg: 1-3 L; the reaction temperature of roasted ore and the first alkaline solution is 100-130°C, the pressure is 0.1-1 MPa, and the time is 0.5-4 h.

[0027] According to the method of the present invention, preferably, in step 3), the second alkaline solution is an alkali metal hydroxide solution with a concentration of 20-65 wt%.

[0028] According to the method of the present invention, preferably, in step 3), the solid-liquid ratio of acid slag I to the second alkaline solution is 1 kg: 1-4 L; the reaction temperature of acid slag I and the second alkaline solution is 140-300 °C, the pressure is 0.6-10 MPa, and the time is 0.5-12 h.

[0029] According to the method of the present invention, preferably, in step 2), the concentration of the hydrochloric acid solution is 6-12 mol / L; in step 4), the concentration of the hydrochloric acid solution is 6-12 mol / L.

[0030] The method of this invention can recover cerium dioxide, cerium-rich rare earth elements, fluorine, and phosphorus resources from mixed rare earth concentrates, respectively, to obtain cerium dioxide concentrate, cerium-rich rare earth chloride solution, fluorides (e.g., sodium fluoride), and phosphates (e.g., trisodium phosphate). The cerium-rich rare earth chloride solution has a high rare earth leaching rate, and the obtained fluorides and phosphates have high purity. Detailed Implementation

[0031] The present invention will be further described below with reference to specific embodiments, but the scope of protection of the present invention is not limited thereto.

[0032] The method of this invention, through a combination of hydrochloric acid pretreatment, oxidative roasting, two-stage gradient alkaline hydrolysis, and selective acid leaching, can achieve the stepwise separation of mixed rare earth concentrates, yielding fluorides (e.g., sodium fluoride), phosphates (e.g., trisodium phosphate), cerium dioxide concentrate, and low-cerium rare earth chloride solution. This method is not a conventional approach.

[0033] In some embodiments, a method for recovering cerium, less cerium rare earth elements, fluorine, and phosphorus from a mixed rare earth concentrate according to the present invention includes the following steps: 1) reacting the mixed rare earth concentrate with hydrochloric acid solution; 2) oxidative roasting and reacting the roasted ore with a first alkaline solution; 3) reacting acid-soluble residue I with a second alkaline solution; and 4) reacting alkaline cake II with hydrochloric acid solution.

[0034] In other embodiments, a method for recovering cerium, less-cerium rare earth elements, fluorine, and phosphorus from a mixed rare earth concentrate according to the present invention includes the following steps: 1) reacting the mixed rare earth concentrate with hydrochloric acid solution; 2) oxidative roasting and reacting the roasted ore with a first alkaline solution; 3) reacting alkaline cake I with a second alkaline solution; and 4) reacting alkaline cake III with hydrochloric acid solution. Optionally, a purification step of the less-cerium rare earth chloride solution is also included. A detailed description follows.

[0035] <Reaction steps of mixed rare earth concentrate with hydrochloric acid solution>

[0036] The mixed rare earth concentrate is reacted with hydrochloric acid solution, followed by solid-liquid separation to obtain chemically beneficiated minerals and chemically beneficiated mother liquor. This process is beneficial for removing calcium-containing minerals and increasing the cerium dioxide content and the purity of cerium-poor rare earth elements.

[0037] In this invention, the mixed rare earth concentrate mainly consists of bastnaesite and monazite, and also contains apatite, fluorite, etc. In the mixed rare earth concentrate of this invention, the REO content is 45-65 wt%, the fluorine (F) content is 5-9 wt%, the P2O5 content is 8-14 wt%, and the CaO content is 3-15 wt%. The REO content is preferably 50-65 wt%, more preferably 54-62 wt%. The F content is preferably 5.5-8.6 wt%, more preferably 5.8-8.5 wt%. The P2O5 content is preferably 9-14 wt%, more preferably 10-12 wt%. The CaO content is preferably 5-14 wt%, more preferably 7-13 wt%.

[0038] In this step, the concentration of the hydrochloric acid solution can be 3–6 mol / L, preferably 4–6 mol / L, for example, 4 mol / L, 5 mol / L, or 6 mol / L. The mass ratio of the mixed rare earth concentrate to the volume of the hydrochloric acid solution (i.e., the solid-liquid ratio) is 1 kg: 1–5 L, preferably 1 kg: 2–5 L, and more preferably 1 kg: 3–5 L. The reaction temperature of the mixed rare earth concentrate with the hydrochloric acid solution can be 80–100°C, for example, 80°C, 90°C, or 100°C. The reaction time can be 1–6 h, preferably 2–6 h, for example, 2 h, 3 h, 4 h, 5 h, or 6 h. This facilitates the dissolution of calcium in the hydrochloric acid solution and reduces the dissolution of rare earth elements.

[0039] In the reaction process of mixed rare earth concentrate and hydrochloric acid solution, the tail gas can be absorbed by spraying to obtain a mixed acid containing hydrochloric acid and hydrofluoric acid, which can be used as a hydrochloric acid solution for subsequent reactions.

[0040] In this invention, the mother liquor from chemical separation is neutralized with a calcium-containing inorganic substance to obtain a calcium chloride solution and a rare earth phosphate precipitate. The calcium-containing inorganic substance is calcium oxide or calcium hydroxide, preferably calcium oxide. Neutralization is performed to a pH of 8-9, preferably 8-8.5.

[0041] <Steps of Oxidative Roasting and Reaction of Roasted Ore with First Alkali Solution>

[0042] In some embodiments, the chemically beneficiated minerals are oxidatively roasted to obtain roasted ore; the roasted ore is reacted with a first alkaline solution, and solid-liquid separation is performed to obtain filtrate I and solid I; solid I is washed to obtain alkaline cake I and washing alkaline solution I; fluoride is recovered from washing alkaline solution I; alkaline cake I is reacted with hydrochloric acid solution, and solid-liquid separation is performed to obtain acid residue I and acid solution I; wherein, acid solution I is a low-cerium rare earth chloride solution. In this scheme, alkaline cake I is reacted with hydrochloric acid solution. This is beneficial for obtaining cerium dioxide enriched products with a high cerium dioxide content.

[0043] In other embodiments, the chemically beneficiated minerals are oxidatively roasted to obtain roasted ore; the roasted ore is reacted with a first alkaline solution, and solid-liquid separation is performed to obtain filtrate I and solid I; solid I is washed to obtain alkali cake I and washing alkali solution I; fluoride is recovered from washing alkali solution I. In this embodiment, alkali cake I is not reacted with hydrochloric acid solution. This is beneficial for obtaining cerium dioxide enriched products with a high cerium dioxide content.

[0044] In this invention, oxidative roasting is performed under an oxygen-containing atmosphere. The roasting temperature can be 400–600°C, for example, 400°C, 500°C, or 600°C, and the roasting time can be 1–5 hours, for example, 1 hour, 2 hours, 3 hours, 4 hours, or 5 hours. This invention believes that the roasting pretreatment disrupts the rare earth mineral lattice, which is beneficial for constructing a step-by-step decomposition system of "first alkaline hydrolysis (100-130°C) + second alkaline hydrolysis (160-300°C)". The first alkaline hydrolysis extracts sodium fluoride, the second alkaline hydrolysis treats the recalcitrant mineral phase and recovers trisodium phosphate, and then selective acid leaching yields cerium dioxide enrichment and a low-cerium rare earth chloride solution.

[0045] In this invention, the first alkaline solution is selected from one or both of alkali metal hydroxide solutions and alkali metal carbonate solutions. The alkali metal hydroxide solution is a sodium hydroxide solution or a potassium hydroxide solution, preferably a sodium hydroxide solution. The alkali metal carbonate solution is a sodium carbonate solution or a potassium carbonate solution, preferably a sodium carbonate solution. The first alkaline solution is more preferably a sodium hydroxide solution. The concentration of the first alkaline solution can be 10–50 wt%, for example, 10 wt%, 20 wt%, 30 wt%, 40 wt%, or 50 wt%.

[0046] The solid-liquid ratio of the roasted ore to the first alkaline solution can be 1 kg: 1–3 L, for example, 1 kg: 1 L, 1 kg: 1.5 L, 1 kg: 2 L, 1 kg: 2.5 L, or 1 kg: 3 L. The reaction temperature between the roasted ore and the first alkaline solution can be 100–130 °C, for example, 100 °C, 115 °C, 120 °C, 125 °C, or 130 °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, or 1 MPa. The reaction time can be 0.5–4 h, preferably 0.5–3 h, for example, 0.5 h, 1 h, 1.5 h, 2 h, 2.5 h, or 3 h.

[0047] According to a specific embodiment of the present invention, the first alkaline solution is a sodium hydroxide solution, and sodium fluoride is recovered from the washing alkaline solution I.

[0048] In the reaction of alkali cake I with hydrochloric acid solution, the hydrochloric acid solution is selected from the mixed acid containing hydrochloric acid and hydrofluoric acid obtained above, or prepared hydrochloric acid, preferably prepared hydrochloric acid. The concentration of the hydrochloric acid solution can be 6–12 mol / L, for example, 6 mol / L, 7 mol / L, 8 mol / L, 9 mol / L, 10 mol / L, 11 mol / L, or 12 mol / L. The temperature of alkali cake I reacting with the hydrochloric acid solution can be 80–100℃, for example, 80℃, 90℃, or 100℃, and the reaction time can be 0.5–3 h, for example, 0.5 h, 1 h, 1.5 h, 2 h, 2.5 h, or 3 h. The acidity (i.e., the concentration of hydrogen ions) at the end of the reaction is 0.1–0.8 mol / L.

[0049] <Reaction steps of acid residue I with second alkaline solution>

[0050] In some embodiments, acid residue I is reacted with a second alkaline solution, followed by solid-liquid separation to obtain filtrate II and solid II; solid II is washed to obtain alkali cake II and washing alkali solution II; washing alkali solution II is cooled and crystallized to obtain phosphate. In other embodiments, acid residue I and rare earth phosphate precipitate are reacted with a second alkaline solution, followed by solid-liquid separation to obtain filtrate II and solid II; solid II is washed to obtain alkali cake II and washing alkali solution II; washing alkali solution II is cooled and crystallized to obtain phosphate. This is advantageous for obtaining inorganic phosphate salts (e.g., trisodium phosphate) and for the subsequent reaction to obtain a low-cerium rare earth chloride solution and cerium dioxide enrichment.

[0051] The second alkaline solution is an alkali metal hydroxide solution, which is either a sodium hydroxide solution or a potassium hydroxide solution, preferably a sodium hydroxide solution. The concentration of the second alkaline solution can be 20-65 wt%, for example, 20 wt%, 30 wt%, 40 wt%, 50 wt%, 60 wt%, or 65 wt%. The solid-liquid ratio of the acid-dissolving residue I to the second alkaline solution is 1 kg: 1-4 L, for example, 1 kg: 1 L, 1 kg: 2 L, 1 kg: 2.5 L, 1 kg: 3 L, or 1 kg: 4 L. According to a specific embodiment of the present invention, the solid-liquid ratio of the mixture of acid-dissolving residue I, rare earth phosphate precipitate, and the second alkaline solution is 1 kg: 1-4 L, for example, 1 kg: 1 L, 1 kg: 2 L, 1 kg: 2.5 L, 1 kg: 3 L, or 1 kg: 4 L. The reaction temperature between acid-dissolving residue I and the second alkaline solution can be 140–300°C, for example, 140°C, 150°C, 160°C, 170°C, 180°C, 190°C, 200°C, 220°C, 240°C, 250°C, 270°C, 280°C, or 300°C. The reaction pressure can be 0.6–10 MPa, for example, 0.6 MPa, 1 MPa, 2 MPa, 3 MPa, 4 MPa, 4.6 MPa, 5.5 MPa, 6 MPa, 7 MPa, 9.5 MPa, or 10 MPa. The reaction time can be 0.5–12 h, preferably 0.5–6 h, more 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.

[0052] In this invention, washing solution II is cooled and crystallized to obtain phosphate. According to a specific embodiment of the invention, the second alkali solution is a sodium hydroxide solution, and washing solution II is cooled and crystallized to obtain trisodium phosphate.

[0053] <Reaction steps of alkali cake II with hydrochloric acid solution>

[0054] The alkali cake II is reacted with hydrochloric acid solution to obtain acid solution II and cerium dioxide enrichment; wherein, acid solution II is a low-cerium rare earth chloride solution. This is beneficial for obtaining cerium dioxide enrichment and low-cerium rare earth chloride solution.

[0055] In this step, the concentration of the hydrochloric acid solution can be 6–12 mol / L, for example, 6 mol / L, 7 mol / L, 8 mol / L, 9 mol / L, 10 mol / L, 11 mol / L, or 12 mol / L. The temperature of the reaction between the alkali cake I and the hydrochloric acid solution can be 80–100℃, for example, 80℃, 90℃, or 100℃. The reaction time can be 0.5–3 h, for example, 0.5 h, 1 h, 1.5 h, 2 h, 2.5 h, or 3 h. The acidity (i.e., the concentration of hydrogen ions) at the end of the reaction is 0.1–0.8 mol / L, for example, 0.1 mol / L, 0.2 mol / L, 0.3 mol / L, 0.4 mol / L, 0.5 mol / L, 0.6 mol / L, 0.7 mol / L, or 0.8 mol / L. In this invention, because the cerium content in the actual grade of the mixed rare earth concentrate is different, the cerium dioxide content in the cerium dioxide enrichment also varies depending on the actual grade of the different mixed rare earth concentrates.

[0056] In this step, further acid solution II can be used to remove impurities, resulting in a purified cerium-containing rare earth chloride solution. The REO content of the purified cerium-containing rare earth chloride solution is less than or equal to 300 g / L.

[0057] <Reaction steps of alkali cake I and second alkali solution>

[0058] The alkali cake I is reacted with the second alkali solution, and the solid and liquid are separated to obtain filtrate III and solid III. Solid III is washed to obtain alkali cake III and washing alkali solution III. Washing alkali solution III is cooled and crystallized to obtain phosphate. This is beneficial for obtaining phosphate (e.g., trisodium phosphate) and for the next step of obtaining a low-cerium rare earth chloride solution and cerium dioxide enrichment.

[0059] In this step, the second alkaline solution is an alkali metal hydroxide solution, which is either a sodium hydroxide solution or a potassium hydroxide solution, preferably a sodium hydroxide solution. The concentration of the second alkaline solution can be 20–65 wt%, for example, 20 wt%, 30 wt%, 40 wt%, 50 wt%, 60 wt%, or 65 wt%. The solid-liquid ratio of the alkali cake I to the second alkaline solution is 1 kg: 1–4 L, for example, 1 kg: 1 L, 1 kg: 2 L, 1 kg: 2.5 L, 1 kg: 3 L, or 1 kg: 4 L. The reaction temperature between the alkali cake I and the second alkali solution can be 140–300°C, for example, 140°C, 150°C, 160°C, 170°C, 180°C, 190°C, 200°C, 220°C, 240°C, 250°C, 270°C, 280°C, or 300°C. The reaction pressure can be 0.6–10 MPa, for example, 0.6 MPa, 1 MPa, 2 MPa, 3 MPa, 4 MPa, 4.6 MPa, 5.5 MPa, 6 MPa, 7 MPa, 9.5 MPa, or 10 MPa. The reaction time can be 0.5–12 h, preferably 0.5–6 h, more 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.

[0060] According to a specific embodiment of the present invention, the second alkaline solution is a sodium hydroxide solution, and the washing alkaline solution III is cooled and crystallized to obtain trisodium phosphate.

[0061] <Reaction steps of alkali cake III with hydrochloric acid solution>

[0062] Alkali cake III is reacted with hydrochloric acid solution to obtain acid solution III and cerium dioxide enrichment; wherein acid solution III is a low-cerium rare earth chloride solution. In this way, cerium dioxide enrichment and low-cerium rare earth chloride solution are obtained separately by selective acid leaching.

[0063] In this step, the concentration of the hydrochloric acid solution can be 6–12 mol / L, for example, 6 mol / L, 7 mol / L, 8 mol / L, 9 mol / L, 10 mol / L, 11 mol / L, or 12 mol / L. The temperature of the reaction between the alkali cake I and the hydrochloric acid solution can be 80–100℃, for example, 80℃, 90℃, or 100℃. The reaction time can be 0.5–3 h, for example, 0.5 h, 1 h, 1.5 h, 2 h, 2.5 h, or 3 h. The acidity (i.e., the concentration of hydrogen ions) at the end of the reaction is 0.1–0.8 mol / L, for example, 0.1 mol / L, 0.2 mol / L, 0.3 mol / L, 0.4 mol / L, 0.5 mol / L, 0.6 mol / L, 0.7 mol / L, or 0.8 mol / L.

[0064] In this invention, acid solution III can be further purified to obtain a purified cerium-containing rare earth chloride solution. The REO content of the purified cerium-containing rare earth chloride solution is less than or equal to 300 g / L.

[0065] In this invention, solid-liquid separation can be achieved by centrifugation or filtration, with filtration being preferred.

[0066] <Analytical Methods>

[0067] REO content: analyzed by gravimetric method.

[0068] P2O5 content: analyzed by bismuth-phosphorus-molybdenum blue spectrophotometry.

[0069] F content: analyzed by distillation.

[0070] CaO content: analyzed by EDTA titration.

[0071] Purity of trisodium phosphate: determined using the industrial standard method for trisodium phosphate, HGT2517-2009.

[0072] The purity of sodium fluoride was determined using the method specified in YS / T 517-2024, the industry standard for sodium fluoride.

[0073] Example 1

[0074] In this embodiment, the mixed rare earth concentrate contains 60.46 wt% REO, 6.66 wt% F, 11.14 wt% P2O5, and 7.85 wt% CaO.

[0075] Mixed rare earth concentrate was mixed with 6 mol / L hydrochloric acid solution at a solid-liquid ratio of 1 kg: 4 L and reacted at 90 °C for 2 h. After filtration, the minerals were obtained by chemical beneficiation (REO content 71.26 wt%, CaO content 1.13 wt%) and chemical beneficiation mother liquor. The mother liquor was neutralized with calcium oxide to a pH of 8 to obtain calcium chloride solution and rare earth phosphate precipitate.

[0076] The minerals were oxidatively roasted at 500℃ for 2 hours in an oxygen-containing atmosphere to obtain roasted ore. The roasted ore was reacted with a 20wt% sodium hydroxide solution (i.e., the first alkali solution, with a solid-liquid ratio of 1 kg:1.5 L) at 0.6 MPa and 100℃ for 3 hours. The mixture was filtered to obtain filtrate I and solid I. Solid I was washed with water to obtain alkali cake I and washing alkali solution I. Sodium fluoride was recovered from washing alkali solution I, and residual alkali was obtained. The purity of sodium fluoride was 96.4%. The residual alkali and filtrate I were recycled by adding sodium hydroxide solid to prepare a 20wt% sodium hydroxide solution. Alkali cake I was slowly added to a 12 mol / L hydrochloric acid solution until the acidity reached 0.1 mol / L, then the reaction was stopped at 95℃ for 2 hours. The mixture was filtered to obtain acid residue I and acid solution I.

[0077] Acid-dissolved residue I, rare earth phosphate precipitate, and 20 wt% sodium hydroxide solution (i.e., the second alkali solution, solid-liquid ratio 1 kg: 4 L) were reacted at 9.5 MPa and 300 °C for 4 h. The mixture was filtered to obtain filtrate II and solid II. Solid II was washed to obtain alkali cake II and washing solution II. Washing solution II was cooled and crystallized to obtain trisodium phosphate with a purity of 96.7%.

[0078] Alkali cake II was slowly added to a 12 mol / L hydrochloric acid solution until the acidity reached 0.1 mol / L, then the reaction was stopped. The mixture was reacted at 95 °C for 2 h to obtain acid solution II and cerium dioxide enrichment. Acid solutions I and II were combined and purified to obtain a low-cerium rare earth chloride solution. The REO concentration was 273 g / L, and the leaching rate of low-cerium rare earth was 98.7%.

[0079] Example 2

[0080] In this embodiment, the mixed rare earth concentrate contains 60.46 wt% REO, 6.66 wt% F, 11.14 wt% P2O5, and 7.85 wt% CaO.

[0081] Mixed rare earth concentrate was mixed with 6 mol / L hydrochloric acid solution at a solid-liquid ratio of 1 kg: 4 L and reacted at 90 °C for 2 h. After filtration, the minerals were obtained by chemical beneficiation (REO content 71.26 wt%, CaO content 1.13 wt%) and chemical beneficiation mother liquor. The mother liquor was neutralized with calcium oxide to a pH of 8.5 to obtain calcium chloride solution and rare earth phosphate precipitate.

[0082] The minerals were oxidatively roasted at 600℃ for 1 hour in an oxygen-containing atmosphere to obtain roasted ore. The roasted ore was reacted with a 50wt% sodium hydroxide solution (i.e., the first alkali solution, with a solid-liquid ratio of 1 kg:1 L) at 0.2 MPa and 110℃ for 0.5 hours. The mixture was filtered to obtain filtrate I and solid I. Solid I was washed with water to obtain alkali cake I and washing alkali solution I. Sodium fluoride was recovered from washing alkali solution I, and residual alkali was obtained. The purity of sodium fluoride was 96.6%. The residual alkali and filtrate I were recycled by adding sodium hydroxide solid to prepare a 50wt% sodium hydroxide solution. Alkali cake I was slowly added to an 8 mol / L hydrochloric acid solution until the acidity reached 0.2 mol / L, and the reaction was stopped at 80℃ for 3 hours. The mixture was filtered to obtain acid residue I and acid solution I.

[0083] Acid-dissolved residue I, rare earth phosphate precipitate, and 40 wt% sodium hydroxide solution (i.e., the second alkali solution, solid-liquid ratio 1 kg: 2.5 L) were reacted at 4.6 MPa and 200 °C for 3 h. The mixture was filtered to obtain filtrate II and solid II. Solid II was washed to obtain alkali cake II and washing alkali solution II. Washing alkali solution II was cooled and crystallized to obtain trisodium phosphate with a purity of 97.1%.

[0084] Alkali cake II was slowly added to an 8 mol / L hydrochloric acid solution until the acidity reached 0.2 mol / L. The reaction was stopped at 80℃ for 3 hours, followed by filtration to obtain acid solution II and cerium dioxide enrichment. Acid solutions I and II were combined and purified to obtain a low-cerium rare earth chloride solution. The REO concentration was 295 g / L, and the leaching rate of low-cerium rare earth was 98.9%.

[0085] Example 3

[0086] In this embodiment, the mixed rare earth concentrate contains 54.22 wt% REO, 8.50 wt% F, 11.96 wt% P2O5, and 11.40 wt% CaO.

[0087] Mixed rare earth concentrate was mixed with 6 mol / L hydrochloric acid solution at a solid-liquid ratio of 1 kg: 5 L and reacted at 100 °C for 6 h. After filtration, the minerals were obtained by chemical beneficiation (REO content 69.63 wt%, CaO content 1.87 wt%) and the chemical beneficiation mother liquor. The mother liquor was neutralized with calcium oxide to a pH of 8.5 to obtain calcium chloride solution and rare earth phosphate precipitate.

[0088] The minerals were oxidatively roasted at 400℃ for 4 hours in an oxygen-containing atmosphere to obtain roasted ore. The roasted ore was reacted with a 10wt% sodium hydroxide solution (i.e., the first alkali solution, with a solid-liquid ratio of 1 kg:3 L) at 1 MPa and 115℃ for 1 hour. The mixture was filtered to obtain filtrate I and solid I. Solid I was washed with water to obtain alkali cake I and washing alkali solution I. Sodium fluoride was recovered from washing alkali solution I, and residual alkali was obtained. The purity of sodium fluoride was 97.1%. The residual alkali and filtrate I were recycled by adding sodium hydroxide solid to prepare a 10wt% sodium hydroxide solution. Alkali cake I was slowly added to a 6 mol / L hydrochloric acid solution until the acidity reached 0.5 mol / L, and the reaction was stopped at 90℃ for 2 hours. The mixture was filtered to obtain acid residue I and acid solution I.

[0089] Acid-dissolved residue I, rare earth phosphate precipitate, and 65 wt% sodium hydroxide solution (i.e., the second alkali solution, solid-liquid ratio 1 kg:1 L) were reacted at 1 MPa and 140 °C for 0.5 h. The mixture was filtered to obtain filtrate II and solid II. Solid II was washed to obtain alkali cake II and washing alkali solution II. Washing alkali solution II was cooled and crystallized to obtain trisodium phosphate with a purity of 98.1%.

[0090] Alkali cake II was slowly added to a 6 mol / L hydrochloric acid solution until the acidity reached 0.5 mol / L. The reaction was carried out at 90℃ for 2 hours, followed by filtration to obtain acid solution II and cerium dioxide enrichment. Acid solutions I and II were combined and purified to obtain a low-cerium rare earth chloride solution. The REO concentration was 279 g / L, and the leaching rate of low-cerium rare earth was 98.4%.

[0091] Example 4

[0092] In this embodiment, the mixed rare earth concentrate contains 54.22 wt% REO, 8.50 wt% F, 11.96 wt% P2O5, and 11.40 wt% CaO.

[0093] Mixed rare earth concentrate was reacted with 6 mol / L hydrochloric acid solution at a solid-liquid ratio of 1 kg: 5 L at 100 °C for 6 h. After filtration, the minerals were obtained by chemical beneficiation (REO content 69.63 wt%, CaO content 1.87 wt%) and the chemical beneficiation mother liquor. The mother liquor was neutralized with calcium oxide to a pH of 8.5 to obtain calcium chloride solution and rare earth phosphate precipitate.

[0094] The minerals were oxidatively roasted at 500℃ for 2 hours in an oxygen-containing atmosphere to obtain roasted ore. The roasted ore was reacted with a 40wt% sodium hydroxide solution (i.e., the first alkali solution, with a solid-liquid ratio of 1 kg:2 L) at 0.1 MPa and 100℃ for 3 hours. The mixture was filtered to obtain filtrate I and solid I. Solid I was washed with water to obtain alkali cake I and washing alkali solution I. Sodium fluoride was recovered from washing alkali solution I, and residual alkali was obtained. The purity of sodium fluoride was 96.8%. The residual alkali and filtrate I were recycled by adding sodium hydroxide solid to prepare a 40wt% sodium hydroxide solution. Alkali cake I was slowly added to a 6 mol / L hydrochloric acid solution until the acidity reached 0.6 mol / L, and the reaction was stopped at 100℃ for 0.5 hours. The mixture was filtered to obtain acid residue I and acid solution I.

[0095] Acid-dissolved residue I, rare earth phosphate precipitate, and 60 wt% sodium hydroxide solution (i.e., the second alkali solution, solid-liquid ratio 1 kg: 2 L) were reacted at 0.6 MPa and 170 °C for 1.5 h. The mixture was filtered to obtain filtrate II and solid II. Solid II was washed to obtain alkali cake II and washing alkali solution II. Washing alkali solution II was cooled and crystallized to obtain trisodium phosphate with a purity of 98.7%.

[0096] Alkali cake II was slowly added to a 6 mol / L hydrochloric acid solution until the acidity reached 0.6 mol / L. The reaction was stopped at 100℃ for 0.5 hours, and then filtered to obtain acid solution II and cerium dioxide enrichment. Acid solutions I and II were combined and purified to obtain a low-cerium rare earth chloride solution. The REO concentration was 287 g / L, and the leaching rate of low-cerium rare earth was 98.7%.

[0097] Example 5

[0098] In this embodiment, the mixed rare earth concentrate contains 58.31% wt% REO, 6.53 wt% F, 10.30 wt% P2O5, and 8.20 wt% CaO.

[0099] Mixed rare earth concentrate was mixed with 4 mol / L hydrochloric acid solution at a solid-liquid ratio of 1 kg: 3 L, and reacted at 95 °C for 1 h. After filtration, chemically beneficiated minerals (REO content 70.54 wt%, CaO content 1.64 wt%) and chemical beneficiation mother liquor were obtained. The chemical mother liquor was neutralized with calcium oxide to a pH of 8.5 to obtain calcium chloride solution and rare earth phosphate precipitate.

[0100] The chemically separated minerals were oxidatively roasted at 400℃ for 4 hours in an oxygen-containing atmosphere to obtain roasted ore. The roasted ore was reacted with a 30wt% sodium hydroxide solution (i.e., the first alkali solution, with a solid-liquid ratio of 1 kg:2.5 L) at 0.4 MPa and 110℃ for 3 hours. The mixture was filtered to obtain filtrate I and solid I. Solid I was washed with water to obtain alkali cake I and washing alkali solution I. Sodium fluoride was recovered from washing alkali solution I, and residual alkali was obtained. The purity of sodium fluoride was 96.4%. The residual alkali and filtrate I were recycled by adding sodium hydroxide solid to prepare a 30wt% sodium hydroxide solution.

[0101] Alkali cake I was reacted with 50 wt% sodium hydroxide solution (i.e., the second alkali solution, with a solid-liquid ratio of 1 kg: 2.5 L) at 0.6 MPa and 160 °C for 3 h. The mixture was filtered to obtain filtrate III and solid III. Solid III was washed to obtain alkali cake III and washing solution III. Washing solution III was cooled and crystallized to obtain trisodium phosphate with a purity of 97.3%.

[0102] Alkali cake III was slowly added to a 10 mol / L hydrochloric acid solution until the acidity reached 0.8 mol / L. The reaction was carried out at 95 °C for 1 h, followed by filtration to obtain acid solution III and cerium dioxide enrichment. Acid solution III was purified to obtain a low-cerium rare earth chloride solution. The REO concentration was 273 g / L, and the leaching rate of low-cerium rare earth was 98.3%.

[0103] Table 1

[0104] Example 1 96.4 96.7 98.7 Example 2 96.6 97.1 98.9 Example 3 97.1 98.1 98.4 Example 4 96.8 98.7 98.7 Example 5 96.4 97.3 98.3

[0105] Note: Leaching rate % of cerium-poor rare earth = Amount of REO in cerium-poor rare earth chloride solution / Amount of REO other than cerium in mixed rare earth concentrate × 100%.

[0106] This invention is not limited to the above-described embodiments. Any modifications, improvements, or substitutions that can be conceived by those skilled in the art without departing from the essential content of this invention fall within the scope of this invention.

Claims

1. A method for recovering cerium, less cerium rare earth elements, fluorine, and phosphorus from mixed rare earth concentrates, characterized in that, Includes the following steps: 1) The mixed rare earth concentrate is reacted with hydrochloric acid solution, and the solid and liquid are separated to obtain chemically beneficiated minerals and chemically beneficiated mother liquor; the mixed rare earth concentrate contains 45-65 wt% REO, 5-9 wt% F, 8-14 wt% P2O5, and 3-14 wt% CaO. The concentration of the hydrochloric acid solution is 3-6 mol / L, the solid-liquid ratio of the mixed rare earth concentrate to the hydrochloric acid solution is 1 kg: 1-5 L, the reaction temperature is 80-100℃, and the reaction time is 1-6 h. 2) The chemically beneficiated minerals are oxidized and roasted to obtain roasted ore; the roasted ore is reacted with the first alkaline solution at a pressure of 0.2–0.8 MPa and a temperature of 100–130 °C for 0.5–4 h, followed by solid-liquid separation to obtain filtrate. and solid ; to solid Washing yields sodium carbonate cake. and washing alkali solution ; wash alkaline solution Fluoride recovery; reacting alkali cake I with hydrochloric acid solution, followed by solid-liquid separation, yielding acid-soluble residue. and acid solution Among them, acid solution I is a cerium-containing rare earth chloride solution; The first alkaline solution is selected from one or two of alkali metal hydroxide solutions and alkali metal carbonate solutions; the concentration of the first alkaline solution is 10-50 wt%; the solid-liquid ratio of the roasted ore to the first alkaline solution is 1 kg: 1-3 L; and the concentration of the hydrochloric acid solution is 6-12 mol / L. 3) Dissolve the acid residue The solution is reacted with the second alkaline solution at a pressure of 2–10 MPa and a temperature of 200–300 °C for 2–4 hours, followed by solid-liquid separation to obtain the filtrate. and solid ; to solid Washing yields sodium carbonate cake. and washing alkali solution ; wash alkaline solution Cooling and crystallization yields phosphate; The second alkaline solution is an alkali metal hydroxide solution with a concentration of 20–65 wt%; the solid-liquid ratio of acid slag I to the second alkaline solution is 1 kg: 1–4 L. 4) Place the alkali cake It reacts with hydrochloric acid solution to give an acidic solution. and cerium dioxide enrichment; wherein, acid solution It is a cerium-containing rare earth chloride solution; The concentration of the hydrochloric acid solution is 6–12 mol / L.

2. The method according to claim 1, characterized in that, In step 1), the tail gas is absorbed by spraying during the reaction of the mixed rare earth concentrate with hydrochloric acid solution to obtain a mixed acid containing hydrochloric acid and hydrofluoric acid.

3. The method according to claim 1, characterized in that, Step 1) also includes: neutralizing the chemical separation mother liquor to a pH of 8-9 using calcium-containing inorganic substances to obtain calcium chloride solution and rare earth phosphate precipitate.

4. The method according to claim 1, characterized in that, In step 2), the oxidative calcination is carried out in an oxygen-containing atmosphere at a temperature of 400–600°C for 1–5 hours.