Process for the treatment of mischmetal concentrates

Abstract

The application discloses a treatment method of mixed rare earth concentrate. The treatment method comprises the following steps: reacting the mixed rare earth concentrate with first hydrochloric acid to obtain a roasting ore and a roasting liquid; roasting the roasting ore to obtain a roasted ore; performing a first alkali dissolution reaction on the roasted ore and a first alkali solution to obtain a first alkali dissolution product; washing the first alkali dissolution solid product with water to obtain an alkali cake I and a washing alkali liquid I; precipitating sodium fluoride in the washing alkali liquid I to obtain sodium fluoride and residual alkali I; performing a second alkali dissolution reaction on raw materials comprising phosphorus-containing materials and a second alkali solution to obtain a second alkali dissolution product; washing the second alkali dissolution solid product with water to obtain an alkali cake II and a washing alkali liquid II; precipitating trisodium phosphate in the washing alkali liquid II to obtain trisodium phosphate and residual alkali II. The method can recover the fluorine element and the phosphorus element in the mixed rare earth concentrate respectively, and the obtained sodium fluoride and trisodium phosphate have high purity.

Description

Technical Field

[0001] This invention relates to a method for processing mixed rare earth concentrates. Background Technology

[0002] The Bayan Obo rare earth concentrate in Baotou, as the world's largest proven and mined rare earth deposit, contains abundant rare earth resources. Currently, the main mineable mineral-type rare earth ores include bastnaesite, monazite, and mixed rare earth ores. Mixed rare earth concentrate is composed of bastnaesite and monazite, with a ratio generally between 9:1 and 3:2. Due to its complex composition, mixed rare earth concentrate is widely recognized as a difficult-to-smelt mineral.

[0003] Currently, the main industrialized technologies for decomposing mixed rare earth concentrates include high-temperature roasting with concentrated sulfuric acid and atmospheric pressure decomposition with concentrated alkali. The high-temperature roasting process involves mixing rare earth concentrate with concentrated sulfuric acid and roasting at 400–1000℃. During the reaction, the concentrate and concentrated sulfuric acid rapidly transform from a solid-liquid mixture into a pure solid phase. When the mineral particles are too large, incomplete internal reactions can occur, affecting the rare earth decomposition rate. Furthermore, this process produces large amounts of high-temperature mixed acidic gases, making the conversion of sulfate wastewater and radioactive waste residue difficult to treat, resulting in a large and costly environmental treatment system. The concentrated alkali decomposition process treats mixed rare earth concentrates with a REO grade of approximately 60%. It decomposes rare earth minerals using sodium hydroxide, generating large amounts of mixed alkaline wastewater. Resource recovery is difficult, leading to excessive waste of sodium hydroxide. The wastewater can only be neutralized to meet discharge standards and cannot recover resources such as fluorine and phosphorus.

[0004] CN102277484A discloses a method for separating and recovering sodium phosphate and sodium fluoride in an alkaline smelting process for mixed rare earth concentrates. The mixed rare earth concentrate is roasted at 450–600℃ for 30–120 minutes; the roasted ore is leached with hydrochloric acid to obtain acid leaching residue and acid leaching solution; sodium hydroxide solution is added to the acid leaching residue for alkaline decomposition; the alkaline-decomposed minerals are washed with water, the washed residue is used for rare earth recovery, and the washed solution is used to separate and recover sodium phosphate and sodium fluoride. The washing is done using a countercurrent washing method with 4–6 stages; the first stage of the countercurrent washing solution is heated and evaporated to obtain crystalline sodium fluoride; the filtrate after evaporation and crystallization is cooled to allow crystallization, and the crystalline substance is recovered as sodium phosphate; the condensed and crystallized liquid is further heated and concentrated to obtain a sodium hydroxide solution, which is used as a diluent for sodium hydroxide during alkaline decomposition of the minerals, or further evaporated to prepare solid hydroxide. The sodium fluoride and sodium phosphate recovered by this method have low purity.

[0005] CN109536746A discloses a method for the cyclic pulping and decomposition of low-calcium, high-grade mixed rare earth concentrate. The method involves mixing the low-calcium, high-grade mixed rare earth concentrate with sulfuric acid solution in a certain proportion and carrying out a pulping reaction under heating. The reaction decomposes fluorine-containing minerals, and the tail gas is absorbed to form a fluorosilicone mixed acid byproduct. After the reaction is completed, solid-liquid separation yields acid leaching solution and acid leaching residue. The acid leaching residue is further treated with water to obtain water-leached residue and water-leached solution. After neutralization, the water-leached solution forms phosphorus-iron-thorium slag and rare earth sulfate solution, in which the generated calcium sulfate dissolves into the water-leached solution. The acid leaching solution is replenished with sulfuric acid to continue processing new mixed rare earth concentrates. The water-leached residue and phosphorus-iron-thorium slag are mixed with a sodium hydroxide solution (45-70% by mass) at a mass ratio of 1:0.1-0.8 for low-calcium, high-grade mixed rare earth concentrate to sodium hydroxide, and then subjected to pulping decomposition at 130-180℃. After washing, the alkali-dissolved ore is dissolved and neutralized with hydrochloric acid to remove impurities, forming acid-dissolved residue, radioactive iron-thorium slag, and rare earth chloride solution. The alkali-washing wastewater is concentrated and crystallized to produce trisodium phosphate as a byproduct. The concentrated solution is replenished with sodium hydroxide to continue decomposing phosphorus-containing minerals and phosphorus-iron-thorium slag. This method requires a high grade of mixed rare earth concentrate. Summary of the Invention

[0006] In view of this, the object of the present invention is to provide a method for processing mixed rare earth concentrates. This method can recover fluorine and phosphorus elements from the mixed rare earth concentrates separately, and the obtained sodium fluoride and trisodium phosphate have high purity. Furthermore, the method of the present invention has a high recovery rate of fluorine and phosphorus elements. Even further, the method of the present invention has a high rare earth leaching rate.

[0007] The present invention achieves the above objectives through the following technical solutions.

[0008] This invention provides a method for processing mixed rare earth concentrate, comprising the following steps:

[0009] (1) The mixed rare earth concentrate is reacted with first hydrochloric acid to obtain chemical beneficiation and chemical beneficiation solution;

[0010] (2) Roast the chemically beneficiated ore to obtain roasted ore;

[0011] (3) The roasted ore is subjected to a first alkaline reaction with the first alkaline solution at 100-135℃ to obtain the first alkaline reaction product; the first alkaline reaction product is separated into solid and liquid to obtain the first alkaline reaction solid product and the first alkaline reaction liquid product; the first alkaline reaction solid product is washed with water to obtain alkaline cake I and washing alkaline solution I; sodium fluoride is precipitated from washing alkaline solution I to obtain sodium fluoride and residual alkali I;

[0012] The alkaline substance in the first alkaline solution is selected from one or more of sodium hydroxide and sodium carbonate.

[0013] (4) The raw materials, including phosphorus-containing materials and a second alkaline solution, are subjected to a second alkaline hydrolysis reaction at 140-180°C to obtain a second alkaline hydrolysis product; the second alkaline hydrolysis product is separated into solid and liquid phases to obtain a second alkaline hydrolysis solid product and a second alkaline hydrolysis liquid product; the second alkaline hydrolysis solid product is washed with water to obtain alkaline cake II and washing alkaline solution II; trisodium phosphate is precipitated from washing alkaline solution II to obtain trisodium phosphate and residual alkali II;

[0014] The alkaline substance in the second alkaline solution is selected from one or more of sodium hydroxide and sodium carbonate, and the phosphorus-containing material is alkali cake I or acid-soluble residue obtained by acid hydrolysis of alkali cake I.

[0015] According to the processing method of the present invention, preferably, it further includes the following steps:

[0016] During the reaction of mixed rare earth concentrate with first hydrochloric acid, the tail gas is absorbed by spraying to obtain a mixed acid of hydrochloric acid and hydrofluoric acid.

[0017] The pH of the chemical separation solution was adjusted to 7-9 using calcium oxide to obtain calcium chloride solution and rare earth phosphate precipitate;

[0018] The raw materials in step (4) also include rare earth phosphate precipitate.

[0019] According to the processing method of the present invention, preferably, the phosphorus-containing material is an acid-soluble residue obtained by acid hydrolysis of alkali cake I;

[0020] It also includes the following steps: reacting alkali cake I with a first solution containing hydrogen chloride to obtain acid solution I and acid residue.

[0021] According to the processing method of the present invention, preferably, the calcination is carried out in an oxygen-free atmosphere or an oxygen-containing atmosphere, the calcination temperature is 400-600°C, and the calcination time is 1-5 hours.

[0022] According to the processing method of the present invention, preferably, 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, the first alkaline hydrolysis is carried out at a pressure of 0.1-1 MPa, and the reaction time of the first alkaline hydrolysis is 0.5-4 h.

[0023] According to the processing method of the present invention, preferably, the concentration of the second alkaline solution is 40-65 wt%;

[0024] In the raw materials of step (4), the solid-liquid ratio of the solid material to the second alkaline solution is 1 kg: (1-2.5) L;

[0025] The secondary alkaline hydrolysis is carried out at a pressure of 0.1–1 MPa, and the reaction time for the secondary alkaline hydrolysis is 0.5–4 h.

[0026] According to the processing method of the present invention, preferably, sodium fluoride in washing alkali solution I is precipitated by concentration crystallization or salting out;

[0027] The trisodium phosphate in washing solution II was precipitated by cooling crystallization.

[0028] According to the processing method of the present invention, preferably, it further includes the following steps:

[0029] Soda cake II is dissolved in a second solution containing hydrogen chloride to obtain acid solution II and leaching residue.

[0030] According to the processing method of the present invention, preferably, in the chemical beneficiation, the content of REO is ≥65wt% and the content of CaO is ≤2.5wt%.

[0031] According to the processing method of the present invention, preferably, the purity of the sodium fluoride precipitated in step (3) is ≥96wt%, and the purity of the trisodium phosphate obtained in step (4) is ≥95.5wt%.

[0032] The method of this invention can recover fluorine and phosphorus elements from mixed rare earth concentrates, and the obtained sodium fluoride and trisodium phosphate have high purity. Furthermore, the method of this invention has a high recovery rate of fluorine and phosphorus elements. Even further, the method of this invention has a high rare earth leaching rate. Attached Figure Description

[0033] Figure 1 This is a flowchart of a method for processing mixed rare earth concentrate according to the present invention. Detailed Implementation

[0034] 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.

[0035] The method for processing mixed rare earth concentrates according to the present invention includes the following steps: (1) hydrochloric acid beneficiation; (2) roasting; (3) primary alkaline hydrolysis; and (4) secondary alkaline hydrolysis. In some embodiments, an acid dissolution step is also included. Each step is described in detail below.

[0036] Steps of hydrochloric acid selection

[0037] The mixed rare earth concentrate is reacted with hydrochloric acid to obtain chemical beneficiation and chemical beneficiation solution.

[0038] In the mixed rare earth concentrate, the REO content can be 45 wt% or more; preferably 50 wt% or more; more preferably 55 wt% or more. The REO content can be 60 wt% or less. In some embodiments, the REO content is 56 wt% or less.

[0039] In the mixed rare earth concentrate, the CaO content can be less than 15 wt%; preferably less than 12 wt%; more preferably less than 10 wt%. The CaO content can be more than 5 wt%; preferably, the CaO content is more than 9 wt%.

[0040] The concentration of hydrochloric acid can be 2–6 mol / L; preferably 3–5 mol / L; more preferably 4–5 mol / L.

[0041] The solid-liquid ratio of the mixed rare earth concentrate to hydrochloric acid can be 1:(1-8); preferably 1:(2-6); more preferably 1:(3-4).

[0042] The reaction time of the mixed rare earth concentrate with hydrochloric acid can be 30-200 min; preferably 60-180 min; more preferably 100-150 min.

[0043] The reaction temperature of the mixed rare earth concentrate with hydrochloric acid can be 80-150℃; preferably 85-100℃; more preferably 90-95℃.

[0044] This is beneficial for improving the grade of mixed rare earth concentrate and for the recovery of fluorine, phosphorus and rare earth elements.

[0045] During the reaction of mixed rare earth concentrate with hydrochloric acid, a mixed acid of hydrochloric acid and hydrofluoric acid can be obtained by spraying and absorbing the tail gas.

[0046] In the chemical beneficiation process, the REO content can be greater than or equal to 65 wt%; preferably, the REO content is 68–75 wt%. In some embodiments, the REO content is 69–72 wt%.

[0047] In the chemical beneficiation process, the CaO content can be less than or equal to 2.5 wt%; preferably, the CaO content is 1 to 2 wt%. In some embodiments, the CaO content is 1.5 to 1.9 wt%.

[0048] In some embodiments, the method further includes the following step: adjusting the pH of the chemical separation solution to 7-9 using calcium oxide to obtain a calcium chloride solution and a rare earth phosphate precipitate. Preferably, the pH of the chemical separation solution is adjusted to 8-8.5 using calcium oxide to obtain a calcium chloride solution and a rare earth phosphate precipitate. This helps to improve the recovery rate of phosphorus and rare earth elements.

[0049] roasting steps

[0050] The ore is roasted after chemical beneficiation to obtain roasted ore.

[0051] Calcination can be carried out in an oxygen-containing atmosphere or an oxygen-free atmosphere. An oxygen-containing atmosphere can be an air atmosphere. An oxygen-free atmosphere can be an inert gas atmosphere, such as a nitrogen atmosphere, an argon atmosphere, or a helium atmosphere.

[0052] The calcination temperature can be 400–600°C. In some embodiments, the calcination temperature is 400–430°C. In other embodiments, the calcination temperature is 500–520°C.

[0053] The roasting time can be 1 to 5 hours. In some embodiments, the roasting time is 2 to 3 hours. In other embodiments, the roasting time is 3.5 to 4 hours.

[0054] This facilitates the decomposition of ore by roasting, and the resulting roasted ore is easier to decompose with alkali.

[0055] One-step alkaline hydrolysis

[0056] The roasted ore is subjected to a first alkaline hydrolysis reaction with a first alkaline solution at 100–135 °C to obtain a first alkaline hydrolysis product. The first alkaline hydrolysis product is separated into solid and liquid phases to obtain a first alkaline hydrolysis solid product and a first alkaline hydrolysis liquid product. The first alkaline hydrolysis solid product is washed with water to obtain alkaline cake I and washing alkaline solution I. Sodium fluoride is precipitated from washing alkaline solution I to obtain sodium fluoride and residual alkali I.

[0057] The primary alkaline hydrolysis temperature is 100–135°C. In some embodiments, the primary alkaline hydrolysis temperature is 100–110°C. In other embodiments, the primary alkaline hydrolysis temperature is 110–120°C. In still other embodiments, the primary alkaline hydrolysis temperature is 120–135°C.

[0058] The first alkaline solution is a solution formed by an alkaline substance and water. The alkaline substance in the first alkaline solution is selected from one or more of sodium hydroxide and sodium carbonate. Preferably, the alkaline substance in the first alkaline solution is sodium hydroxide.

[0059] The concentration of the first alkali solution can be 10–50 wt%. In some embodiments, the concentration of the first alkali solution is 20–30 wt%. In other embodiments, the concentration of the first alkali solution is 37–40 wt%.

[0060] The solid-liquid ratio of the roasted ore to the first alkaline solution can be 1 kg:(1-3) L. In some embodiments, the solid-liquid ratio of the roasted ore to the first alkaline solution is 1 kg:(1.5-2.5) L. In other embodiments, the solid-liquid ratio of the roasted ore to the first alkaline solution is 1 kg:(2-2.3) L.

[0061] The primary alkaline hydrolysis can be carried out at a pressure of 0.1–1 MPa. In some embodiments, the primary alkaline hydrolysis is carried out at a pressure of 0.2–0.6 MPa. In other embodiments, the primary alkaline hydrolysis is carried out at a pressure of 0.4–0.5 MPa.

[0062] The reaction time for a single alkaline hydrolysis can be 0.5 to 4 hours; preferably 1 to 3 hours. In some embodiments, the reaction time for a single alkaline hydrolysis is 2 to 3 hours.

[0063] This helps to fully recover fluorine from the roasted ore and improve the purity of sodium fluoride.

[0064] The solid and liquid products of the first alkaline hydrolysis were separated to obtain the solid product and the liquid product of the first alkaline hydrolysis.

[0065] Sodium fluoride can be precipitated from washing alkali solution I by concentration and crystallization or salting out. The liquid product from the first alkaline hydrolysis and the remaining alkali I can be used to prepare the first alkali solution.

[0066] The purity of sodium fluoride can be greater than or equal to 96 wt%; preferably, the purity of sodium fluoride is greater than or equal to 96.5 wt%; more preferably, the purity of sodium fluoride is greater than or equal to 97 wt%.

[0067] The recovery rate of fluorine can be greater than or equal to 94 wt%; preferably, the recovery rate of fluorine is greater than or equal to 95 wt%; more preferably, the recovery rate of fluorine is greater than or equal to 96 wt%.

[0068] The steps of secondary alkaline hydrolysis

[0069] The raw materials, including phosphorus-containing materials and a second alkaline solution, are subjected to a secondary alkaline hydrolysis reaction at 140–180°C to obtain a secondary alkaline hydrolysis product. The secondary alkaline hydrolysis product is then separated into a solid product and a liquid product. The solid product is washed with water to obtain an alkaline cake II and a washing solution II. The trisodium phosphate in the washing solution II is precipitated to obtain trisodium phosphate and residual alkali II.

[0070] The phosphorus-containing material can be alkali cake I or acid-soluble residue obtained by acid hydrolysis of alkali cake I. In some embodiments, the phosphorus-containing material is alkali cake I. In other embodiments, the phosphorus-containing material is acid-soluble residue obtained by acid hydrolysis of alkali cake I.

[0071] In some embodiments, the method further includes the following step: reacting the alkali cake I with a first solution containing hydrogen chloride to obtain acid solution I and acid residue.

[0072] The first hydrogen chloride-containing solution can be selected from hydrochloric acid, acid solution I, acid solution II, or a mixed acid of hydrochloric acid and hydrofluoric acid obtained by spraying and absorbing tail gas.

[0073] In the first solution containing hydrogen chloride, the concentration of hydrogen chloride can be 6 to 12 mol / L; preferably 8 to 12 mol / L; more preferably 10 to 12 mol / L.

[0074] The solid-liquid ratio of the alkali cake I to the first hydrogen chloride-containing solution can be 1:(1-6) kg / L; preferably 1:(2-5) kg / L; more preferably 1:(3-4) kg / L.

[0075] The reaction temperature of the alkali cake I with the first hydrogen chloride-containing solution can be 80–115°C; preferably 85–105°C; more preferably 90–95°C.

[0076] The reaction time between the alkali cake I and the first solution containing hydrogen chloride can be 0.5 to 5 hours; preferably 1 to 4 hours; more preferably 2 to 3 hours.

[0077] The reaction temperature for the secondary alkaline hydrolysis reaction is 140–180°C. In some embodiments, the reaction temperature is 140–150°C. In other embodiments, the reaction temperature is 160–170°C.

[0078] The second alkaline solution is a solution formed by an alkaline substance and water. The alkaline substance in the second alkaline solution is selected from one or more of sodium hydroxide and sodium carbonate. Preferably, the alkaline substance in the first alkaline solution is sodium hydroxide.

[0079] The concentration of the second alkali solution can be 40–65 wt%. In some embodiments, the concentration of the second alkali solution is 50–65 wt%. In other embodiments, the concentration of the second alkali solution is 60–63 wt%.

[0080] In the raw materials, the solid-liquid ratio of the solid material to the second alkaline solution can be 1 kg:(1-2.5) L. In some embodiments, the solid-liquid ratio of the solid material to the second alkaline solution is 1 kg:(1.5-2.5) L. In other embodiments, the solid-liquid ratio of the solid material to the second alkaline solution is 1 kg:(2-2.3) L. In some embodiments, the solid material can be acid slag. In other embodiments, the solid material is acid slag and rare earth phosphate precipitate. In still other embodiments, the solid material is alkaline cake I. In yet another embodiment, the solid material is alkaline cake I and rare earth phosphate precipitate.

[0081] The secondary alkaline hydrolysis can be carried out at a pressure of 0.1–1 MPa. In some embodiments, the secondary alkaline hydrolysis is carried out at a pressure of 0.2–0.6 MPa. In other embodiments, the secondary alkaline hydrolysis is carried out at a pressure of 0.8–0.9 MPa.

[0082] The reaction time for the secondary alkaline hydrolysis can be 0.5–4 h; preferably 0.5–2 h. In some embodiments, the reaction time for the secondary alkaline hydrolysis is 0.5–1.5 h.

[0083] This helps to fully recover phosphorus from sodium alkali cake I, thereby improving the purity of trisodium phosphate.

[0084] The trisodium phosphate in washing solution II can be precipitated by concentration crystallization or salting out.

[0085] The liquid product from the secondary alkaline hydrolysis and the residual alkali II can be used to prepare a second alkaline solution.

[0086] The purity of trisodium phosphate can be greater than or equal to 95.5 wt%; preferably, the purity of trisodium phosphate is greater than or equal to 97 wt%; more preferably, the purity of trisodium phosphate is greater than or equal to 98 wt%.

[0087] The phosphorus recovery rate is greater than or equal to 97 wt%; preferably, the phosphorus recovery rate is greater than or equal to 98 wt%; more preferably, the phosphorus recovery rate is greater than or equal to 98.5 wt%.

[0088] Acid dissolution steps

[0089] The alkali cake II is dissolved in a second solution containing hydrogen chloride to obtain acid solution II and leaching residue. In some embodiments, the step of mixing acid solution I and acid solution II is also included.

[0090] The second hydrogen chloride-containing solution can be selected from hydrochloric acid, acid solution I, acid solution II, or a mixed acid of hydrochloric acid and hydrofluoric acid obtained by spray absorption of tail gas. According to one embodiment of the present invention, the second hydrogen chloride-containing solution is hydrochloric acid.

[0091] The concentration of hydrogen chloride in the second hydrogen chloride solution can be 6–12 mol / L; preferably 8–12 mol / L; more preferably 9–12 mol / L.

[0092] The solid-liquid ratio of alkali cake II to the second hydrogen chloride-containing solution can be 1:(1-6) kg / L; preferably 1:(2-5) kg / L; more preferably 1:(3-4) kg / L.

[0093] The reaction temperature of the alkali cake II with the second hydrogen chloride-containing solution can be 80–115°C; preferably 85–105°C; more preferably 90–95°C.

[0094] The reaction time between the alkali cake II and the second solution containing hydrogen chloride can be 0.5 to 3 hours; preferably 1 to 2.5 hours; more preferably 1.5 to 2 hours.

[0095] The leaching rate of rare earth elements can be greater than or equal to 97 wt%; preferably, greater than or equal to 98 wt%; more preferably, greater than or equal to 98.5 wt%.

[0096] The testing method is described below:

[0097] The purity of sodium fluoride was tested using the method specified in YS / T 517-2024.

[0098] Purity of trisodium phosphate: tested according to the method specified in HG / T2517-2009.

[0099] Fluorine recovery rate: (mass of fluorine in the obtained sodium fluoride / mass of fluorine in the chemical beneficiation) × 100%.

[0100] Phosphorus recovery rate: (mass of phosphorus in the obtained trisodium phosphate / mass of phosphorus in the chemical beneficiation) × 100%.

[0101] Rare earth leaching rate: (mass of rare earth elements in rare earth chloride solution / mass of rare earth elements in mixed rare earth concentrate) × 100%.

[0102] The raw materials are described below:

[0103] The mixed rare earth concentrate comes from the Baiyun Obo mining area in Baotou City, Inner Mongolia Autonomous Region.

[0104] Examples 1 to 5

[0105] (1) The mixed rare earth concentrate is reacted with hydrochloric acid to obtain chemical beneficiation and chemical beneficiation solution. During the reaction, the tail gas is absorbed by spray water to obtain a mixed acid of hydrochloric acid and hydrofluoric acid. Calcium oxide is added to the chemical beneficiation solution to neutralize it to pH value A (representing a certain value), resulting in calcium chloride solution and rare earth phosphate precipitate.

[0106] (2) Roast the chemically beneficiated ore to obtain roasted ore.

[0107] (3) The roasted ore is subjected to a primary alkaline hydrolysis reaction with a first sodium hydroxide solution to obtain a primary alkaline hydrolysis product. The primary alkaline hydrolysis product is separated into a solid product and a liquid product. The primary alkaline hydrolysis solid product is washed with water to obtain alkali cake I and washing alkali solution I. Washing alkali solution I is concentrated and crystallized to obtain sodium fluoride and residual alkali I. The primary alkaline hydrolysis liquid product and residual alkali I are used to prepare a sodium hydroxide solution.

[0108] (4) The alkali cake I is reacted with the second hydrochloric acid to obtain acid solution I and acid residue. The acid residue and rare earth phosphate precipitate are subjected to a second alkaline hydrolysis reaction with the second sodium hydroxide solution to obtain the second alkaline hydrolysis product. The second alkaline hydrolysis product is separated into solid and liquid phases to obtain the second alkaline hydrolysis solid product and the second alkaline hydrolysis liquid product. The second alkaline hydrolysis solid product is washed with water to obtain alkali cake II and washing alkali solution II. The washing alkali solution II is cooled and crystallized to obtain trisodium phosphate and residual alkali II. The second alkaline hydrolysis liquid product and residual alkali II are used to prepare sodium hydroxide solution.

[0109] Soda cake II is dissolved in hydrochloric acid to obtain acid solution II and leaching residue. Acid solution I and acid solution II are combined to obtain rare earth chloride solution.

[0110] The raw materials and parameters for each step in Examples 1 to 5 are shown in Table 1. The purity of sodium fluoride, the recovery rate of fluorine, the purity of trisodium phosphate, the recovery rate of phosphorus, and the leaching rate of rare earth elements are shown in Table 1.

[0111] Table 1

[0112]

[0113]

[0114] Note: First hydrochloric acid, second hydrochloric acid, and third hydrochloric acid all refer to hydrochloric acid; "first," "second," and "third" are used only to distinguish them. First sodium hydroxide solution and second sodium hydroxide solution both refer to sodium hydroxide solution; "first" and "second" are used only to distinguish them.

[0115] As shown in Table 1, the method of this invention can recover fluorine, phosphorus, and rare earth elements from mixed rare earth concentrates. By controlling the above process parameters, the purity of sodium fluoride and trisodium phosphate can be improved, as can the recovery rates of fluorine and phosphorus, and the leaching rate of rare earth elements.

[0116] 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 of processing mixed rare earth concentrates, characterized by, The method comprises the following steps: (1) reacting mixed rare earth concentrate with first hydrochloric acid to obtain a chlorination concentrate and a chlorination solution; adjusting the pH of the chlorination solution to 7-9 by using calcium oxide to obtain a calcium chloride solution and a rare earth phosphate precipitate; (2) roasting the chlorination concentrate to obtain a roasted concentrate; (3) performing a first alkaline decomposition reaction on the roasted concentrate and a first alkali solution at 100-135 DEG C to obtain a first alkaline decomposition product; performing solid-liquid separation on the first alkaline decomposition product to obtain a first alkaline decomposition solid product and a first alkaline decomposition liquid product; washing the first alkaline decomposition solid product with water to obtain an alkali cake I and a washing alkali solution I; precipitating sodium fluoride in the washing alkali solution I to obtain sodium fluoride and residual alkali I; wherein the alkaline substance in the first alkali solution is selected from one or more of sodium hydroxide and sodium carbonate; wherein the concentration of the first alkali solution is 10-50 wt%, the solid-liquid ratio of the roasted concentrate to the first alkali solution is 1 kg:(1-3) L, the first alkaline decomposition is performed under a pressure of 0.1-1 MPa, and the reaction time of the first alkaline decomposition is 0.5-4 h; (4) reacting the alkali cake I with a first hydrogen chloride-containing solution to obtain an acid solution I and an acid residue; performing a second alkaline decomposition reaction on raw materials comprising the acid residue, the rare earth phosphate precipitate and a second alkali solution at 140-180 DEG C to obtain a second alkaline decomposition product; performing solid-liquid separation on the second alkaline decomposition product to obtain a second alkaline decomposition solid product and a second alkaline decomposition liquid product; washing the second alkaline decomposition solid product with water to obtain an alkali cake II and a washing alkali solution II; precipitating trisodium phosphate in the washing alkali solution II to obtain trisodium phosphate and residual alkali II; wherein the alkaline substance in the second alkali solution is selected from one or more of sodium hydroxide and sodium carbonate; wherein the concentration of hydrogen chloride in the first hydrogen chloride-containing solution is 6-12 mol / L, the solid-liquid ratio of the alkali cake I to the first hydrogen chloride-containing solution is 1:(1-4) kg / L, the reaction temperature of the alkali cake I to the first hydrogen chloride-containing solution is 80-95 DEG C, and the reaction time of the alkali cake I to the first hydrogen chloride-containing solution is 0.5-3 h; wherein the concentration of the second alkali solution is 40-65 wt%, the solid-liquid ratio of the solid material in the raw materials to the second alkali solution is 1 kg:(1-2.5) L, the second alkaline decomposition is performed under a pressure of 0.1-1 MPa, and the reaction time of the second alkaline decomposition is 0.5-4 h.

2. The treatment method according to claim 1, characterized in that, The method further comprises the following steps: In the process of reacting the mixed rare earth concentrate with the first hydrochloric acid, a mixed acid of hydrochloric acid and hydrofluoric acid is obtained by spraying and absorbing tail gas.

3. The treatment method of claim 1, wherein The roasting is performed in an oxygen-free atmosphere or an oxygen-containing atmosphere, the roasting temperature is 400-600 DEG C, and the roasting time is 1-5 h.

4. The treatment method of claim 1, wherein The sodium fluoride in the washing alkali solution I is precipitated by using a method of concentration crystallization or salting-out; The trisodium phosphate in the washing alkali solution II is precipitated by using a method of cooling crystallization.

5. The treatment method of claim 1, wherein The method further comprises the following steps: The alkali cake II is dissolved with a second hydrogen chloride-containing solution to obtain an acid solution II and a leaching residue.

6. The treatment method of claim 1, wherein In the chlorination concentrate, the content of REO is ≥65 wt%, and the content of CaO is ≤2.5 wt%.

7. The treatment method according to any one of claims 1 to 6, characterized in that, The purity of the precipitated sodium fluoride in step (3) is ≥96 wt%, and the purity of the trisodium phosphate obtained in step (4) is ≥95.5 wt%.

Images