METHOD FOR LEACHING SEPARATION OF MIXED RARE EARTH CONCENTRATE

Description

CROSS REFERENCE TO RELATED APPLICATION

The present application claims priority to Chinese Patent Application No. 202411210144.X filed on Aug. 30, 2024. The entire contents of the above-listed application are hereby incorporated by reference for all purposes.

TECHNICAL FIELD

The present disclosure belongs to the technical field of rare earth beneficiation, and particularly relates to a method for leaching separation of a mixed rare earth concentrate.

BACKGROUND

On account of unique magnetic, optical and electrical performances, rare earth elements have become the core component of modern functional material systems such as permanent magnets, hydrogen storage, and catalysis. They are widely used in key fields such as machinery manufacturing, medical technology, and national defense, and are strategic resources to support technological innovation and industrial upgrading. However, since rare earth minerals have diverse occurrence forms and complex composition, different types of rare earth minerals require different smelting process systems. The mixed rare earth concentrate has complex mineral composition (paragenesis of various rare earth minerals such as bastnaesite and monazite in most cases) and has associated calcium-containing gangue minerals. As a result, a significant challenge is posed in selective and efficient extraction and separation of the rare earth elements.

At present, the industrial processes for smelting the mixed rare earth concentrate include concentrated sulfuric acid roasting and caustic soda decomposition. The concentrated sulfuric acid roasting process is the dominant method. With the process, mixed rare earth concentrates and concentrated sulfuric acid are mixed in a rotary kiln for being roasted at the high temperature, then the mixed solution of the rare earth is obtained through water leaching, and rare earth products are obtained through a series of neutralization, precipitation, and impurity removal. The process is simple and continuous, and has low production cost. However, the concentrated sulfuric acid is likely to decompose and waste in the high-temperature roasting stage, and produce sulfur-containing and fluorine-containing tail gas. In addition, ammonia-nitrogen wastewater is produced in the neutralization, precipitation, and impurity removal stages, and phosphorus and thorium exist in leaching residues in the form of insoluble salt. As a result, the problems such as resource waste and radioactive contamination are caused, restricting the green and healthy development of the rare earth industry. The main process of the caustic soda decomposition is liquid caustic soda decomposition under normal pressure. With such process, the mixed rare earth concentrate and sodium hydroxide are stirred and leached at the high temperature in a reaction vessel. Although no sulfur-containing and fluorine-containing tail gas is produced, the process has high requirements for the grade of the rare earth mixed concentrate and requires the pre-impurity removal process. As a result, the issues such as discontinuity of the process, and inadaptability to large-scale production are caused, which limits industrial application of the process.

To sum up, the main processes in the field restricts the green and sustainable development of the rare earth industry due to the factors such as three wastes pollution or inadaptability to the large-scale production. Hence, it is of great significance to explore a green, healthy, and sustainable process for smelting and separation of the mixed rare earth ore.

SUMMARY

In order to solve the shortcomings in the prior art, the present disclosure provides a method for leaching separation of a mixed rare earth concentrate.

In order to solve the technical problem described above, the present disclosure adopts the following technical solution:

A method for leaching separation of a mixed rare earth concentrate provided by the present disclosure comprises:

• • performing a surface modification on the mixed rare earth concentrate under the action of a plasma gas flow to obtain a surface-modified mixed rare earth concentrate;
  • performing a mineral phase transformation on the surface-modified mixed rare earth concentrate to transform a bastnaesite phase in the mixed rare earth concentrate into a cerium oxyfluoride and obtain a mineral phase transformation product containing the cerium oxyfluoride;
  • acid leaching the mineral phase transformation product to obtain an acid leachate and an acid leaching residue, where the acid leachate comprises a rare earth ion and a fluoride ion, and the acid leaching residue comprises monazite;
  • performing a surface modification on the acid leachate under the action of a plasma gas flow to obtain a surface-modified acid leaching residue; and
  • alkaline leaching the surface-modified acid leaching residue to obtain an alkaline leachate and an alkaline leaching residue, where the alkaline leachate comprises a phosphorus element, and the alkaline leaching residue includes a rare earth element.

Optionally, the step of performing a surface modification on the mixed rare earth concentrate under the action of a plasma gas flow to obtain a surface-modified mixed rare earth concentrate comprises:

• • processing the mixed rare earth concentrate in a plasma cleaner that has an atmosphere of a first preset atmosphere and a power of 100 W-300 W for 10 min-60 min to obtain the mixed rare earth concentrate whose surface oxidation performance is changed, where the first preset atmosphere is a gas mixture of hydrogen and inert gas.

Optionally, the step of performing a mineral phase transformation on the surface-modified mixed rare earth concentrate to transform a bastnaesite phase in the mixed rare earth concentrate into a cerium oxyfluoride and to obtain a mineral phase transformation product containing the cerium oxyfluoride comprises:

• • fluidized roasting the surface-modified mixed rare earth concentrate in an inert atmosphere to transform the bastnaesite phase in the mixed rare earth concentrate into the cerium oxyfluoride and obtain a roasted product containing the cerium oxyfluoride, and taking the roasted product as the mineral phase transformation product.

Optionally, the step of fluidized roasting the surface-modified mixed rare earth concentrate in an inert atmosphere to transform the bastnaesite phase in the mixed rare earth concentrate into the cerium oxyfluoride and obtain a roasted product containing the cerium oxyfluoride comprises:

• • putting the surface-modified mixed rare earth concentrate in a roasting furnace, then continuously introducing inert gas into the bottom of the roasting furnace, and keeping the mixed rare earth concentrate in a fluidized state in the inert atmosphere by using the inert gas as fluidizing gas; and
  • adjusting a heating temperature of the roasting furnace to heat the mixed rare earth concentrate in the fluidized state at a temperature of 450° C.-750° C. for 20 min-120 min, and completing a reaction of transforming the bastnaesite of the mixed rare earth concentrate into the cerium oxyfluoride to obtain the roasted product.

Optionally, a gas flow rate of the inert gas continuously introduced into the bottom of the roasting furnace is 300 mL/min-1000 mL/min.

Optionally, the step of acid leaching the mineral phase transformation product to obtain an acid leachate and an acid leaching residue comprises:

• • adding the mineral phase transformation product to a hydrochloric acid leachate, performing stirring at a temperature of 60° C.-100° C., an ultrasonic power of 300 W-600 W, and a stirring speed of 200 r/min-600 r/min for 20 min-120 min to obtain the acid leachate and the acid leaching residue.

Optionally, a liquid-solid ratio between the hydrochloric acid leachate and the mineral phase transformation product is 4-20:1, the hydrochloric acid leachate includes a hydrochloric acid solution with a concentration of 1 mol/L-10 mol/L and a leaching aid with a concentration of 0.1 mol/L-0.5 mol/L, and the leaching aid is aluminum chloride or boric acid.

Optionally, the step of performing a surface modification on the acid leaching residue under the action of a plasma gas flow to obtain a surface-modified acid leaching residue comprises:

• • processing the acid leaching residue in a plasma cleaner that has an atmosphere of a second preset atmosphere and a power of 100 W-300 W for 10 min-60 min, to obtain the acid leaching residue whose surface oxidation performance is changed, where the second preset atmosphere includes a gas mixture of hydrogen and inert gas.

Optionally, the step of performing alkaline leaching the surface-modified acid leaching residue to obtain an alkaline leachate and an alkaline leaching residue comprises:

• • adding the surface-modified acid leaching residue to a sodium hydroxide solution, performing a reaction at a temperature of 120° C.-200° C., a pressure of 0.1 MPa-5 MPa, and a stirring speed of 200 r/min-600 r/min for 60 min-360 min, to obtain the alkaline leachate and the alkaline leaching residue, where an alkali-mineral ratio between the sodium hydroxide solution and the acid leaching residue is 1-7:1, and a liquid-solid ratio is 1-10:1.

Optionally, the method further includes:

• • adding a hydrochloric acid solution with a concentration of 1 mol/L-10 mol/L to the alkaline leaching residue, to dissolve the alkaline leaching residue, and obtain an acid solution comprising the rare earth element.

The present disclosure provides the method for leaching separation of a mixed rare earth concentrate provided, the surface modification is performed on the mixed rare earth concentrate under the action of the plasma gas flow. In this way, CeO₂ generated during the mineral phase transformation of the surface-modified mixed rare earth concentrate is reduced, the bastnaesite in the mixed rare earth concentrate can be directionally transformed into the cerium oxyfluoride, and further the mineral phase transformation product has a higher rare earth leaching rate. Then, for the acid leaching residue obtained through the acid leaching on the mineral phase transformation product, the surface modification is performed on the acid leaching residue under the action of the plasma gas flow. In this way, oxidation reactions can be reduced during the alkaline leaching of the surface-modified acid leaching residue, and the obtained alkaline leaching residue does not contain or contains a small amount of tetravalent cerium ions. Finally, the alkaline leaching is performed on the surface-modified acid leaching residue, and then the alkaline leachate comprising the phosphorus element and the alkaline leaching residue comprising the rare earth element can be obtained. Thus, according to the present disclosure, the rare earth element, the phosphorus element, and a fluorine element can be effectively separated from the mixed rare earth concentrate, resources such as fluorite and apatite associated with the mixed rare earth concentrate are comprehensively recovered, and a comprehensive resource utilization rate of the mixed rare earth concentrate is increased.

Other features and advantages of the present disclosure will be set forth in the following description, and will partially become apparent in the description, or be learned by implementing the present disclosure. The objective and other advantages of the present disclosure can be achieved and obtained through structures particularly indicated in the description and the accompanying drawings.

Technical solutions of the present disclosure will be further described below in detail with reference to accompanying drawings and in conjunction with examples.

BRIEF DESCRIPTION OF DRAWINGS

The FIGURE is a flowchart of a method for leaching separation of a mixed rare earth concentrate according to an illustrative example of the present disclosure.

DETAILED DESCRIPTION OF THE EMBODIMENTS

In order to make objectives, technical solutions and advantages of the present disclosure clearer, the technical solutions of the present disclosure will be clearly and completely described with reference to the embodiments of the present disclosure. Apparently, the described embodiments are merely some rather than all of the embodiments of the present disclosure. Based on the embodiments of the present disclosure, all other embodiments derived by the skilled in the art without creative efforts are to fall within the protection scope of the present disclosure.

A method for leaching separation of a mixed rare earth concentrate according to the present disclosure includes:

Step 100: a surface modification is performed on the mixed rare earth concentrate under the action of a plasma gas flow to obtain a surface-modified mixed rare earth concentrate.

Step 200: a mineral phase transformation is performed on the surface-modified mixed rare earth concentrate, a bastnaesite phase in the mixed rare earth concentrate is transformed into a cerium oxyfluoride to obtain a mineral phase transformation product containing the cerium oxyfluoride.

Step 300: acid leach the mineral phase transformation product to obtain an acid leachate and an acid leaching residue, where the acid leachate includes a rare earth ion and a fluoride ion, and the acid leaching residue includes monazite.

Step 400: a surface modification is performed on the acid leaching residue under the action of a plasma gas flow to obtain a surface-modified acid leaching residue.

Step 500: alkaline leach the surface-modified acid leaching residue to obtain an alkaline leachate and an alkaline leaching residue, where the alkaline leachate includes a phosphorus element, and the alkaline leaching residue includes a rare earth element.

It should be noted that the mixed rare earth concentrate may be a mixed rare earth ore of the bastnasite and the monazite, a rare earth oxide (REO) grade of the mixed rare earth concentrate is 50%-67%, and main rare earth minerals included are the bastnasite and the monazite. An F grade of the mixed rare earth concentrate is 4%-10%, and main fluorine-containing minerals included are the bastnaesite, fluorite, and apatite. A P grade of the mixed rare earth concentrate is 4%-10%, and main phosphate-containing minerals included are the monazite and the apatite.

Herein, in step 100, under the action of the plasma gas flow, the plasma gas flow collides with a surface of the mixed rare earth concentrate, molecular chemical bonds of the surface of the mixed rare earth concentrate are caused to break and recombine, a new chemical structure is generated, and an oxidation performance of the surface of the mixed rare earth concentrate is changed. Thus, the surface-modified mixed rare earth concentrate is oxidized as little as possible during the mineral phase transformation in step 200, and further the bastnaesite phase in the mixed rare earth concentrate can be transformed into be the cerium oxyfluoride that is more easily acid leached.

In step 200, the mineral phase transformation is performed on the surface-modified mixed rare earth concentrate. In this way, the bastnaesite phase in the mixed rare earth concentrate is transformed into the rare earth oxyfluoride that more easily reacts in the acid leaching. Further, the acid leachate that contains the rare earth ion and the fluoride ion and is generated by the mineral phase transformation product containing the cerium oxyfluoride after the acid leaching in step 300 is completed contains a cerium rare earth element.

The acid leaching residue obtained in step 300 includes a trivalent cerium ion, and the trivalent cerium ion is easily oxidized during the alkaline leaching. Thus, before the alkaline leaching on the acid leaching residue, the surface modification is performed on the acid leaching residue by using the plasma gas flow through step 400. In this way, the surface-modified acid leaching residue is oxidized as little as possible during the alkaline leaching, and the alkaline leaching residue in step 500 does not contain or contains a small amount of tetravalent cerium ions.

In this example, the surface modification is performed on the mixed rare earth concentrate under the action of the plasma gas flow. In this way, CeO₂ generated during the mineral phase transformation of the surface-modified mixed rare earth concentrate is reduced, the bastnaesite in the mixed rare earth concentrate can be directionally transformed into the cerium oxyfluoride, and further the mineral phase transformation product has a higher rare earth leaching rate. Then, for the acid leaching residue obtained through the acid leaching on the mineral phase transformation product, the surface modification is completed on the acid leaching residue under the action of the plasma gas flow. In this way, oxidation reactions can be reduced during the alkaline leaching of the surface-modified acid leaching residue, and the obtained alkaline leaching residue does not contain or contains a small amount of the tetravalent cerium ions. Finally, the alkaline leaching is performed on the surface-modified acid leaching residue, and then the alkaline leachate comprising the phosphorus element and the alkaline leaching residue comprising the rare earth element can be obtained. Thus, according to the present disclosure, the rare earth element, the phosphorus element, and a fluorine element can be effectively separated from the mixed rare earth concentrate, resources such as fluorite and apatite associated with the mixed rare earth concentrate are comprehensively recovered, and a comprehensive resource utilization rate of the mixed rare earth concentrate is increased.

In some implementable examples, the steps that a surface modification is performed on the mixed rare earth concentrate under the action of a plasma gas flow to obtain a surface-modified mixed rare earth concentrate may include: the mixed rare earth concentrate is processed in a plasma cleaner that has an atmosphere of a first preset atmosphere and a power of 100 W-300 W for 10 min-60 min, and the mixed rare earth concentrate whose surface oxidation performance is changed is obtained. The first preset atmosphere is a gas mixture of hydrogen and inert gas.

Herein, the inert gas in the first preset atmosphere may be one or more of nitrogen, helium, and argon. The plasma cleaner may make the first preset atmosphere generate a hydrogen plasma flow.

In this example, by taking the gas mixture of the hydrogen and the inert gas as the first preset atmosphere, the plasma cleaner can generate the hydrogen plasma flow. In this way, the molecular chemical bonds of the surface of the mixed rare earth concentrate are broken and recombined, and generate the new chemical structure under the action of the hydrogen plasma flow, and the oxidation performance of the surface of the mixed rare earth concentrate is changed. Thus, the surface-modified mixed rare earth concentrate is oxidized as little as possible during the mineral phase transformation in step 200.

In some implementable examples, the steps that a mineral phase transformation is performed on the surface-modified mixed rare earth concentrate, a bastnaesite phase in the mixed rare earth concentrate is transformed into a cerium oxyfluoride to obtain a mineral phase transformation product containing the cerium oxyfluoride may include: fluidized roasting is performed on the surface-modified mixed rare earth concentrate in an inert atmosphere, the bastnaesite phase in the mixed rare earth concentrate is transformed into the cerium oxyfluoride to obtain a roasted product containing the cerium oxyfluoride, and the roasted product is taken as the mineral phase transformation product.

In this example, by performing the fluidized roasting on the surface-modified mixed rare earth concentrate in the inert gas atmosphere, the bastnaesite in the mixed rare earth concentrate can be prevented from generating CeO₂ with oxygen in air, and then the bastnaesite (REFCO₃) in the mixed rare earth concentrate is directionally transformed into the cerium oxyfluoride (REOF) that is more easily acid leached. Thus, the acid leachate in step 300 includes more cerium ions.

In some implementable examples, the steps that fluidized roasting is performed on the surface-modified mixed rare earth concentrate in an inert atmosphere, the bastnaesite phase in the mixed rare earth concentrate is transformed into the cerium oxyfluoride to obtain a roasted product containing the cerium oxyfluoride may include:

Step 201: the surface-modified mixed rare earth concentrate is put in a roasting furnace, then inert gas is continuously introduced into the bottom of the roasting furnace, and the mixed rare earth concentrate is kept in a fluidized state in the inert atmosphere by using the inert gas as fluidizing gas.

Step 202: heating temperature of the roasting furnace is adjusted, the mixed rare earth concentrate in the fluidized state is heated at a temperature of 450° C.-750° C. for 20 min-120 min, a reaction of transforming the bastnaesite in the mixed rare earth concentrate into the cerium oxyfluoride is performed to obtain the roasted product.

Herein, the roasting furnace may be a vertical tubular roasting furnace.

In step 201, by continuously introducing the inert gas into the bottom of the roasting furnace, the mixed rare earth concentrate can be guaranteed in the desirable fluidized state in the inert atmosphere by using the inert gas as the fluidizing gas.

In this example, by continuously introducing the inert gas as the fluidizing gas into the bottom of the roasting furnace, the oxygen in the air can be prevented from coming into contact with the mixed rare earth concentrate, and the bastnaesite in the mixed rare earth concentrate is further prevented from being oxidized. Moreover, since the fluidizing gas of the inert gas can keep the mixed rare earth concentrate in the fluidized state, the mixed rare earth concentrate in step 202 can be roasted in the fluidized state. Thus, reaction efficiency of transformation of the bastnaesite in the mixed rare earth concentrate into the rare earth oxyfluoride is improved, and an ore transformation rate of the bastnaesite can be further increased.

In some implementable examples, a gas flow rate of the inert gas continuously introduced into the bottom of the roasting furnace is 300 mL/min-1000 mL/min.

Herein, the gas flow rate of the inert gas may be, but not limited to, 300 mL/min, 350 mL/min, 400 mL/min, 450 mL/min, 500 mL/min, 550 mL/min, 600 mL/min, 650 mL/min, 700 mL/min, 750 mL/min, 800 mL/min, 850 mL/min, 900 mL/min, 950 mL/min, and 1000 mL/min.

In some implementable examples, the steps that acid leach the mineral phase transformation product to obtain an acid leachate and an acid leaching residue may include: the mineral phase transformation product is added to a hydrochloric acid leachate, stirring is performed at a temperature of 60° C.-100° C., an ultrasonic power of 300 W-600 W, and a stirring speed of 200 r/min-600 r/min for 20 min-120 min to obtain the acid leachate and the acid leaching residue.

Herein, by applying an external ultrasonic field, that is, an ultrasonic power of 300 W-600 W, during the acid leaching on the mineral phase transformation product, a cavitation effect of an ultrasonic wave can be utilized to break through a shackle of some conventional reactions. In addition, a passive film on a surface of the mineral phase transformation product can be removed by using shear force provided by the ultrasonic wave, so as to achieve an effect of enhanced leaching of the mineral phase transformation product.

In this example, when the mineral phase transformation product is added to the hydrochloric acid leachate for being acid leached, the ultrasonic power of 300 W-600 W is applied. In this way, the acid leaching reaction of the mineral phase transformation product is more thorough, and rare earth elements in the mineral phase transformation product are fully recovered.

In some implementable examples, a liquid-solid ratio between the hydrochloric acid leachate and the mineral phase transformation product is 4-20:1, the hydrochloric acid leachate includes a hydrochloric acid solution with a concentration of 1 mol/L-10 mol/L and a leaching aid with a concentration of 0.1 mol/L-0.5 mol/L, and the leaching aid is aluminum chloride or boric acid.

Herein, when the acid leaching is performed on the mineral phase transformation product, a mixed solution of the hydrochloric acid solution and the leaching aid is selected as the hydrochloric acid leachate. In this way, the leaching aid complexes fluoride ions, generation of CeF₃ precipitates is reduced, and a rare earth leaching rate of the mixed rare earth concentrate is increased.

In some implementable examples, the steps that a surface modification is performed on the acid leaching residue under the action of a plasma gas flow to obtain a surface-modified acid leaching residue may include: the acid leaching residue is processed in a plasma cleaner that has an atmosphere of a second preset atmosphere and a power of 100 W-300 W for 10 min-60 min to obtain the acid leaching residue whose surface oxidation performance is changed. The second preset atmosphere includes a gas mixture of hydrogen and inert gas.

Herein, the inert gas in the second preset atmosphere may be one or more of nitrogen, helium, and argon. The plasma cleaner may make the second preset atmosphere generate a hydrogen plasma flow.

In this example, by taking the gas mixture of the hydrogen and the inert gas as the second preset atmosphere, the plasma cleaner can generate the hydrogen plasma flow. In this way, the molecular chemical bonds of the surface of the acid leaching residue are broken and recombined, and generate the new chemical structure under the action of the hydrogen plasma flow, and the oxidation performance of the surface of the acid leaching residue is changed. Thus, the surface-modified acid leaching residue is oxidized as little as possible during the alkaline leaching in step 400.

In some implementable examples, the steps that alkaline leach the surface-modified acid leaching residue to obtain and an alkaline leachate and an alkaline leaching residue may include: the surface-modified acid leaching residue is added to a sodium hydroxide solution, a reaction is performed at a temperature of 120° C.-200° C., a pressure of 0.1 MPa-5 MPa, and a stirring speed of 200 r/min-600 r/min for 60 min-360 min to obtain the alkaline leachate and the alkaline leaching residue. An alkali-mineral ratio between the sodium hydroxide solution and the acid leaching residue is 1-7:1, and a liquid-solid ratio is 1-10:1.

It should be noted that when the alkaline leaching is performed on the surface-modified acid leaching residue, a reactor is filled with the inert gas. In this way, the acid leaching residue is leached in an environment under the protection of the inert gas.

Herein, in order to avoid oxidation of the trivalent cerium ions included in the surface-modified acid leaching residue during the alkaline leaching, the inert gas is adopted for pressure leaching during the alkaline leaching. In this way, the surface-modified acid leaching residue can be more easily alkaline leached, and the trivalent cerium ions can be further protected from being oxidized.

In this example, when the alkaline leaching is performed on the surface-modified acid leaching residue, the reaction is performed at a pressure of 0.1 MPa-5 MPa. In this way, the alkaline leaching reaction of the acid leaching residue can be performed more thoroughly, and reaction efficiency of the alkaline leaching on the acid leaching residue can be improved.

In some implementable examples, the method for leaching separation of a mixed rare earth concentrate further includes: a hydrochloric acid solution with a concentration of 1 mol/L-10 mol/L is added to the alkaline leaching residue to dissolve the alkaline leaching residue and obtain an acid solution comprising the rare earth element.

In this example, the hydrochloric acid solution having a temperature of 50° C.-70° C. is added to the alkaline leaching residue, and the hydrochloric acid solution dissolves the alkaline leaching residue. In this way, the rare earth element in the leaching residue is dissolved in the hydrochloric acid solution, the acid solution that comprises the rare earth element and is conducive to recovery of the rare earth element is obtained, and waste of resources and discharge of wastewater during the recovery of the rare earth element are reduced.

The method for leaching separation of a mixed rare earth concentrate according to the present disclosure will be described in detail below in conjunction with the examples. It should be noted that methods, reagents, and materials described in the following examples are available from commercial channels unless otherwise specified. The test methods are all conventional methods unless otherwise specified.

Example 1

A method for leaching separation of a mixed rare earth concentrate according to this example included:

(1) The mixed rare earth concentrate having an REO grade of 58.22%, an F grade of 6.11%, and a P grade of 5.30% was processed in a plasma cleaner that has a hydrogen-argon atmosphere and a power of 240 W for 20 min, and a mixed rare earth concentrate whose surface oxidation performance was changed was obtained.

(2) The surface-modified mixed rare earth concentrate was put into a roasting furnace, then nitrogen of 400 mL/min was continuously introduced into the bottom of the roasting furnace, and the mixed rare earth concentrate was kept in a fluidized state in a nitrogen atmosphere. Fluidized roasting was performed on the mixed rare earth concentrate in the roasting furnace for 60 min at a temperature of 650° C., and a mineral phase transformation product containing a cerium oxyfluoride was obtained.

(3) A hydrochloric acid leachate was added to the mineral phase transformation product per a liquid-solid ratio of 10:1 between the hydrochloric acid leachate and the mineral phase transformation product. Stirring was performed by setting a stirring speed as 600 r/min and an ultrasonic power as 300 W for 20 min at a temperature of 75° C. A hydrochloric acid leach mixture that included an acid leachate comprising a rare earth element and a fluorine element and a leaching residue comprising monazite was obtained. The hydrochloric acid leachate included a hydrochloric acid solution with a concentration of 4 mol/L and AlCl₃ solution with a concentration of 0.3 mol/L.

(4) The acid leaching residue was processed in a plasma cleaner that has a hydrogen-argon atmosphere and a power of 240 W for 20 min, and a surface-modified acid leaching residue was obtained.

(5) A sodium hydroxide solution was added to the surface-modified acid leaching residue per an alkali-mineral ratio of 5:1 and a liquid-solid ratio of 5:1 between an alkaline leachate and a secondary activation product. Stirring was performed at a temperature of 160° C., a pressure of 0.5 MPa, and a stirring speed of 600 r/min for 120 min. An alkaline leachate comprising a phosphorus element and an alkaline leaching residue comprising a rare earth element were obtained. The alkaline leachiate comprising the phosphorus element may be processed to recover an alkali solution.

(6) A hydrochloric acid solution with a concentration of 2 mol/L was added to the alkaline leaching residue, the alkaline leaching residue was stirred until the alkaline leaching residue was dissolved, and an acid solution comprising the rare earth element was obtained.

A total leaching rate of the leachate comprising the rare earth element (the leachate comprising the rare earth included the acid leachate comprising the rare earth element and the fluorine element in step (3) and the acid solution comprising the rare earth element in step (6)) finally obtained in this example was 98.01%. A leaching rate of the fluorine element in the acid leachate comprising the rare earth element and the fluorine element in step (3) was 97.82%, and a leaching rate of the phosphorus element in the alkaline leachate comprising the phosphorus element in step (5) was 98.58%.

Example 2

A method for leaching separation of a mixed rare earth concentrate according to this example included:

(1) The mixed rare earth concentrate having an REO grade of 58.22%, an F grade of 6.11%, and a P grade of 5.30% was processed in a plasma cleaner that has a hydrogen-argon atmosphere and a power of 240 W for 20 min, and a mixed rare earth concentrate whose surface oxidation performance was changed was obtained.

(2) The surface-modified mixed rare earth concentrate was put into a roasting furnace, then nitrogen of 400 mL/min was continuously introduced into the bottom of the roasting furnace, and the mixed rare earth concentrate was kept in a fluidized state in a nitrogen atmosphere. Fluidized roasting was performed on the mixed rare earth concentrate in the roasting furnace for 60 min at a temperature of 550° C., and a mineral phase transformation product containing a cerium oxyfluoride was obtained.

(3) A hydrochloric acid leachate was added to the mineral phase transformation product per a liquid-solid ratio of 10:1 between the hydrochloric acid leachate and the mineral phase transformation product. Stirring was performed by setting a stirring speed as 600 r/min and an ultrasonic power as 300 W for 20 min at a temperature of 75° C. A hydrochloric acid leach mixture that included an acid leachate comprising a rare earth element and a fluorine element and a leaching residue comprising monazite was obtained. The hydrochloric acid leachate included a hydrochloric acid solution with a concentration of 4 mol/L and AlCl₃ solution with a concentration of 0.3 mol/L.

(4) The acid leaching residue was processed in a plasma cleaner that has a hydrogen-argon atmosphere and a power of 240 W for 20 min, and a surface-modified acid leaching residue was obtained.

(5) A sodium hydroxide solution was added to the surface-modified acid leaching residue per an alkali-mineral ratio of 5:1 and a liquid-solid ratio of 5:1 between an alkaline leachate and a secondary activation product. Stirring was performed at a temperature of 160° C., a pressure of 0.5 MPa, and a stirring speed of 600 r/min for 120 min. An alkaline leachate comprising a phosphorus element and an alkaline leaching residue including a rare earth element were obtained. The alkaline leachate comprising the phosphorus element may be processed to recover an alkali solution.

(6) A hydrochloric acid solution with a concentration of 2 mol/L was added to the alkaline leaching residue, the alkaline leaching residue was stirred until the alkaline leaching residue was dissolved, and an acid solution comprising the rare earth element was obtained.

A total leaching rate of the leachate comprising the rare earth element (the leachate comprising the rare earth included the acid leachate comprising the rare earth element and the fluorine element in step (3) and the acid solution comprising the rare earth element in step (6)) finally obtained in this example was 95.32%. A leaching rate of the fluorine element in the acid leachate comprising the rare earth element and the fluorine element in step (3) was 93.82%, and a leaching rate of the phosphorus element in the alkaline leachate comprising the phosphorus element in step (5) was 97.58%.

Example 3

A method for leaching separation of a mixed rare earth concentrate according to this example included:

(1) The mixed rare earth concentrate having an REO grade of 58.22%, an F grade of 6.11%, and a P grade of 5.30% was processed in a plasma cleaner that has a hydrogen-argon atmosphere and a power of 240 W for 20 min, and a mixed rare earth concentrate whose surface oxidation performance was changed was obtained.

(2) The surface-modified mixed rare earth concentrate was put into a roasting furnace, then nitrogen of 400 mL/min was continuously introduced into the bottom of the roasting furnace, and the mixed rare earth concentrate was kept in a fluidized state in a nitrogen atmosphere. Fluidized roasting was performed on the mixed rare earth concentrate in the roasting furnace for 60 min at a temperature of 650° C., and a mineral phase transformation product containing a cerium oxyfluoride was obtained.

(3) A hydrochloric acid leachate was added to the mineral phase transformation product per a liquid-solid ratio of 10:1 between the hydrochloric acid leachate and the mineral phase transformation product. Stirring was performed by setting a stirring speed as 600 r/min and an ultrasonic power as 300 W for 20 min at a temperature of 90° C. A hydrochloric acid leach mixture that included an acid leachate comprising a rare earth element and a fluorine element and a leaching residue comprising monazite was obtained. The hydrochloric acid leachate included a hydrochloric acid solution with a concentration of 4 mol/L and AlCl₃ solution with a concentration of 0.3 mol/L.

(4) The acid leaching residue was processed in a plasma cleaner that has a hydrogen-argon atmosphere and a power of 240 W for 20 min, and a surface-modified acid leaching residue was obtained.

(5) A sodium hydroxide solution was added to the surface-modified acid leaching residue per an alkali-mineral ratio of 5:1 and a liquid-solid ratio of 5:1 between an alkaline leachate and a secondary activation product. Stirring was performed at a temperature of 160° C., a pressure of 0.5 MPa, and a stirring speed of 600 r/min for 120 min. An alkaline leachate comprising a phosphorus element and an alkaline leaching residue comprising a rare earth element were obtained. The alkaline leachate comprising the phosphorus element may be processed to recover an alkali solution.

(6) A hydrochloric acid solution with a concentration of 2 mol/L was added to the alkaline leaching residue, the alkaline leaching residue was stirred until the alkaline leaching residue was dissolved, and an acid solution comprising the rare earth element was obtained.

A total leaching rate of the leachate including the rare earth element (the leachate comprising the rare earth included the acid leachate comprising the rare earth element and the fluorine element in step (3) and the acid solution comprising the rare earth element in step (6)) finally obtained in this example was 96.28%. A leaching rate of the fluorine element in the acid leachate including the rare earth element and the fluorine element in step (3) was 94.36%, and a leaching rate of the phosphorus element in the alkaline leachate comprising the phosphorus element in step (5) was 99.19%.

Example 4

A method for leaching separation of a mixed rare earth concentrate according to this example included:

(1) The mixed rare earth concentrate having an REO grade of 58.22%, an F grade of 6.11%, and a P grade of 5.30% was processed in a plasma cleaner that has a hydrogen-argon atmosphere and a power of 240 W for 20 min, and a mixed rare earth concentrate whose surface oxidation performance was changed was obtained.

(2) The surface-modified mixed rare earth concentrate was put into a roasting furnace, then nitrogen of 400 mL/min was continuously introduced into the bottom of the roasting furnace, and the mixed rare earth concentrate was kept in a fluidized state in a nitrogen atmosphere. Fluidized roasting was performed on the mixed rare earth concentrate in the roasting furnace for 60 min at a temperature of 650° C., and a mineral phase transformation product containing a cerium oxyfluoride was obtained.

(3) A hydrochloric acid leachate was added to the mineral phase transformation product per a liquid-solid ratio of 10:1 between the hydrochloric acid leachate and the mineral phase transformation product. Stirring was performed by setting a stirring speed as 600 r/min and an ultrasonic power as 300 W for 20 min at a temperature of 75° C. A hydrochloric acid leach mixture that included an acid leachate comprising a rare earth element and a fluorine element and a leaching residue including monazite was obtained. The hydrochloric acid leachate included a hydrochloric acid solution with a concentration of 4 mol/L and AlCl₃ solution with a concentration of 0.3 mol/L.

(4) The acid leaching residue was processed in a plasma cleaner that has a hydrogen-argon atmosphere and a power of 240 W for 20 min, and a surface-modified acid leaching residue was obtained.

(5) A sodium hydroxide solution was added to the surface-modified acid leaching residue per an alkali-mineral ratio of 5:1 and a liquid-solid ratio of 5:1 between an alkaline leachate and a secondary activation product. Stirring was performed at a temperature of 180° C., a pressure of 1 MPa, and a stirring speed of 600 r/min for 120 min. An alkaline leachate comprising a phosphorus element and an alkaline leaching residue comprising a rare earth element were obtained. The alkaline leachate comprising the phosphorus element may be processed to recover an alkali solution.

(6) A hydrochloric acid solution with a concentration of 2 mol/L was added to the alkaline leaching residue, the alkaline leaching residue was stirred until the alkaline leaching residue was dissolved, and an acid solution comprising the rare earth element was obtained.

A total leaching rate of the leachate comprising the rare earth element (the leachate comprising the rare earth included the acid leachate comprising the rare earth element and the fluorine element in step (3) and the acid solution comprising the rare earth element in step (6)) finally obtained in this example was 98.68%. A leaching rate of the fluorine element in the acid leachate comprising the rare earth element and the fluorine element in step (3) was 98.82%, and a leaching rate of the phosphorus element in the alkaline leachate compring the phosphorus element in step (5) was 99.37%.

Comparative Example 1

A method for leaching separation of a mixed rare earth concentrate according to this comparative example included:

(1) The mixed rare earth concentrate was put into a roasting furnace, then nitrogen of 400 mL/min was continuously introduced into a bottom of the roasting furnace, and the mixed rare earth concentrate was kept in a fluidized state in a nitrogen atmosphere. Fluidized roasting was performed on the mixed rare earth concentrate in the roasting furnace for 60 min at a temperature of 650° C., and a mineral phase transformation product containing a cerium oxyfluoride was obtained.

(2) A hydrochloric acid leachate was added to the mineral phase transformation product per a liquid-solid ratio of 10:1 between the hydrochloric acid leachate and the mineral phase transformation product. Stirring was performed by setting a stirring speed as 600 r/min and an ultrasonic power as 300 W for 20 min at a temperature of 75° C. A hydrochloric acid leach mixture that included an acid leachate comprising a rare earth element and a fluorine element and a leaching residue comprising monazite was obtained. The hydrochloric acid leachate included a hydrochloric acid solution with a concentration of 4 mol/L and AlCl₃ solution with a concentration of 0.3 mol/L.

(3) A sodium hydroxide solution was added to the acid leaching residue per an alkali-mineral ratio of 5:1 and a liquid-solid ratio of 5:1 between an alkaline leachate and a secondary activation product. Stirring was performed at a temperature of 160° C., a pressure of 0.5 MPa, and a stirring speed of 600 r/min for 120 min. An alkaline leachate comprising a phosphorus element and an alkaline leaching residue comprising a rare earth element were obtained. The alkaline leachate comprising the phosphorus element may be processed to recover an alkali solution.

(4) A hydrochloric acid solution with a concentration of 2 mol/L was added to the alkaline leaching residue, the alkaline leaching residue was stirred until the alkaline leaching residue was dissolved, and an acid solution comprising the rare earth element was obtained.

A total leaching rate of the leachate comprising the rare earth element (the leachate comprising the rare earth included the acid leachate comprising the rare earth element and the fluorine element in step (2) and the acid solution comprising the rare earth element in step (4)) finally obtained in this comparative example was 94.55%. A leaching rate of the fluorine element in the acid leachate comprising the rare earth element and the fluorine element in step (2) was 92.49%, and a leaching rate of the phosphorus element in the alkaline leachate comprising the phosphorus element in step (3) was 97.63%.

Comparative Example 2

A method for leaching separation of a mixed rare earth concentrate included:

(1) The mixed rare earth concentrate having an REO grade of 58.22%, an F grade of 6.11%, and a P grade of 5.30% was processed in a plasma cleaner that has a hydrogen-argon atmosphere and a power of 240 W for 20 min, and a mixed rare earth concentrate whose surface oxidation performance was changed was obtained.

(2) The surface-modified mixed rare earth concentrate was put into a roasting furnace, then nitrogen of 400 mL/min was continuously introduced into the bottom of the roasting furnace, and the mixed rare earth concentrate was kept in a fluidized state in a nitrogen atmosphere. Fluidized roasting was performed on the mixed rare earth concentrate in the roasting furnace for 60 min at a temperature of 650° C., and a mineral phase transformation product containing a cerium oxyfluoride was obtained.

(3) A hydrochloric acid leachate was added to the mineral phase transformation product per a liquid-solid ratio of 10:1 between the hydrochloric acid leachate and the mineral phase transformation product. Stirring was performed by setting a stirring speed as 600 r/min for 20 min at a temperature of 75° C. A hydrochloric acid leaching mixture that included an acid leachate comprising a rare earth element and a fluorine element and a leaching residue comprising monazite was obtained. The hydrochloric acid leachate was a hydrochloric acid solution with a concentration of 4 mol/L.

(4) The acid leaching residue was processed in a plasma cleaner that has a hydrogen-argon atmosphere and a power of 240 W for 20 min, and a surface-modified acid leaching residue was obtained.

(5) A sodium hydroxide solution was added to the surface-modified acid leaching residue per an alkali-mineral ratio of 5:1 and a liquid-solid ratio of 5:1 between an alkaline leachate and a secondary activation product. Stirring was performed at a temperature of 160° C., a pressure of 0.5 MPa, and a stirring speed of 600 r/min for 120 min. An alkaline leachate comprising a phosphorus element and an alkaline leaching residue comprising a rare earth element were obtained. The alkaline leachate comprising the phosphorus element may be processed to recover an alkali solution.

(6) A hydrochloric acid solution with a concentration of 2 mol/L was added to the alkaline leaching residue, the alkaline leaching residue was stirred until the alkaline leaching residue was dissolved, and an acid solution comprising the rare earth element was obtained.

A total leaching rate of the leachate comprising the rare earth element (the leachate comprising the rare earth included the acid leachate comprising the rare earth element and the fluorine element in step (3) and the acid solution comprising the rare earth element in step (6)) finally obtained in this comparative example was 95.38%. A leaching rate of the fluorine element in the acid leachate comprising the rare earth element and the fluorine element in step (3) was 51.42%, and a leaching rate of the phosphorus element in the alkaline leachate comprising the phosphorus element in step (5) was 96.37%.

It can be seen from results of the examples and the comparative examples that as adopted by the present disclosure, the surface modification is performed on the mixed rare earth concentrate under the action of the plasma gas flow. In this way, CeO₂ generated during the mineral phase transformation of the surface-modified mixed rare earth concentrate is reduced, the bastnaesite in the mixed rare earth concentrate can be directionally transformed into the cerium oxyfluoride, and further the mineral phase transformation product obtained through roasting has a higher rare earth leaching rate. In addition, for the acid leaching residue obtained through the acid leaching on the mineral phase transformation product, the surface modification is performed on the acid leaching residue under the action of the plasma gas flow. In this way, oxidation reactions are reduced during the alkaline leaching of the surface-modified acid leaching residue, and the obtained alkaline leaching residue does not contain or contains a small amount of the tetravalent cerium ions. The rare earth element, the phosphorus element, and the fluorine element are effectively separated from the mixed rare earth concentrate, and the leaching rates of the rare earth element, the phosphorus element, and the fluorine element of the mixed rare earth concentrate can be further increased. In addition, by adding the leaching aid during the acid leaching to complex the fluoride ion, generation of CeF₃ can be reduced, and the leaching rate of the rare earth and a recovery rate of the fluorine element can be increased. In addition, by applying the external ultrasonic field during the acid leaching, the reaction is performed more thoroughly, and a recovery rate of the rare earth element is further increased.

Finally, it should be noted that the examples described above are merely used to describe the technical solution of the present disclosure rather than limit the same. Although the present disclosure has been described in detail with reference to the foregoing examples, those skilled in the art should understand that the technical solution described in the foregoing example can still be modified, or some of the technical features therein can be equivalently replaced. However, these modifications or substitutions do not make the essence of the corresponding technical solutions deviate from the spirit and scope of the technical solutions of the examples of the present disclosure.