A method for separating rare earth elements and fluorine in fluorinated rare earth slag

Abstract

The present invention relates to a method for separating rare earth elements and fluorine in fluoride rare earth slag, comprising: mixing the fluoride rare earth slag with a zinc compound and then calcining it at normal pressure; then calcining it at reduced pressure, collecting zinc fluoride condensate, and obtaining calcined slag. The method according to the present invention can use cheap raw materials and simple equipment to achieve the separation of rare earth elements and fluorine in the fluoride rare earth slag, so it is efficient and low in cost.

Description

Technical Field

[0001] The invention belongs to the technical field of recycling rare earth fluoride slag resources, and in particular relates to a method for separating rare earth elements and fluorine in rare earth fluoride slag. Background Art

[0002] At present, the molten salt electrolysis of rare earth metals adopts a fluoride system. During the process of metal removal from the furnace, anode replacement, and periodic maintenance of the electrolytic cell, a large amount of fluorine-containing molten salt electrolytic slag (hereinafter referred to as fluoride rare earth slag) is produced. The rare earth content is 10%-80%, and the fluorine content is 8.28%-22.75%. It contains rare earth fluoride, rare earth oxide, magnesium oxide, aluminum oxide, iron oxide, calcium oxide, tungsten oxide and graphite. It is a rare earth secondary resource with complex composition, difficult to handle and difficult to recover.

[0003] For fluoridated rare earth slag, the methods that have been developed include sodium hydroxide roasting method, calcium hydroxide roasting method, sodium carbonate roasting method, sodium silicate roasting method, negative pressure heating alkali decomposition method, etc. These methods all obtain rare earth oxides and water-soluble sodium fluoride through mixed calcination, and separate the rare earth from fluorine by water washing. However, a large amount of fluoride-containing wastewater will be generated in the process, which will seriously pollute the environment and put great pressure on enterprises to protect the environment.

[0004] Therefore, it is urgent to develop new separation processes to achieve resource recycling of fluorinated rare earth slag. Summary of the invention

[0005] The present invention provides a method for separating rare earth elements and fluorine in fluoridated rare earth slag. The method can separate rare earth elements and fluorine in fluoridated rare earth slag by using cheap raw materials and simple equipment, thus achieving high efficiency and low cost.

[0006] In one aspect, the present invention provides a method for separating rare earth elements and fluorine in fluoridated rare earth slag, comprising the following steps:

[0007] S1 atmospheric pressure roasting: mixing the rare earth fluoride slag and the zinc compound and then roasting them at atmospheric pressure;

[0008] S2 Reduced-pressure roasting: Reduced-pressure roasting is performed to collect zinc fluoride condensate and obtain roasting slag at the same time.

[0009] Step S1

[0010] In step S1, the rare earth fluoride and the zinc compound in the reaction system can be converted into zinc fluoride and rare earth oxide by calcination at normal pressure.

[0011] The zinc compound may be selected from zinc carbonate, basic zinc carbonate, zinc oxide, zinc hydroxide or a combination thereof. The zinc compound may be any suitable zinc compound, including industrial grade, experimental pure, chemical pure, analytical pure, superior pure, etc., such as zinc carbonate or zinc oxide with a purity of more than 50%. In step S1, the specific reaction may be as follows: 2REF3+3ZnCO3=3ZnF2+RE2O3+3CO2↑, or 2REF3+3ZnO=3ZnF2+RE2O3, but the existence state of the substance may be more complicated, so the present invention is not limited thereto. For basic zinc carbonate and zinc hydroxide, they can first be dehydrated and converted into zinc carbonate or zinc oxide, and then the above reaction occurs. In addition, in the case of zinc carbonate, since one of the products of the above reaction is a gas, the reaction will proceed in a positive direction and the reaction will be more thorough, which is conducive to the transformation of rare earth fluoride to zinc fluoride.

[0012] In step S1, the fluoride rare earth slag is not particularly limited and may be any fluorine-containing molten salt electrolytic slag obtained by molten salt electrolysis of rare earth metals using a fluoride system, for example, may be a single or mixed fluoride rare earth molten salt electrolytic slag.

[0013] In step S1, the molar ratio F / Zn of F in the fluorided rare earth slag to Zn in the zinc compound is 3.0 or less, 2.5 or less, or 2.1 or less, for example, the molar ratio F / Zn can be 1-3:1, for example, 1.2:1, 1.5:1, 1.6:1, 1.7:1, 1.8:1, 1.9:1, 2.0:1, 2.1:1, 2.2:1, 2.3:1, 2.4:1, 2.5:1, etc., preferably 1.5-2.5:1, more preferably 1.8-2:1. Within the above range, it is beneficial to achieve the reaction of the zinc compound with F in the fluorided rare earth slag to generate low-boiling ZnF2. When the F / Zn molar ratio is too low, although the reaction of F and Zn can be more complete, it will cause waste of the additive zinc compound.

[0014] In step S1, the normal pressure calcination means that the calcination is performed directly in an air atmosphere without pressurizing or depressurizing the calcination equipment.

[0015] In step S1, the atmospheric pressure calcination temperature can be 800-1500°C, for example, 850, 900, 950, 1000, 1050, 1100, 1150, 1200, 1300, 1350, 1400, 1450°C, etc., preferably 850-1100°C, more preferably 900-1000°C.

[0016] In step S1, the normal pressure roasting time can vary according to the amount of raw materials, the roasting temperature, etc. Generally speaking, the more raw materials, the lower the temperature, the longer the roasting time, and the less raw materials, the higher the temperature, the shorter the roasting time. Considering the uniformity and sufficiency of the roasting effect, the roasting time of not less than 1 hour is preferably, for example, 1-8 hours, 1-5 hours, 1-4 hours, etc.

[0017] In some embodiments, step S1 may further include a pre-baking step, that is, the rare earth fluoride slag is mixed with the zinc compound and then pre-baked at normal pressure, and then baked at normal pressure. The pre-baking step is performed at a temperature lower than the above-mentioned normal pressure baking temperature. Pre-baking is beneficial to remove moisture from the raw materials and activate the rare earth fluoride, thereby improving the conversion efficiency of the rare earth fluoride to the rare earth oxide.

[0018] In some embodiments, the pre-calcination temperature may be 250 to less than 800°C, for example 300, 350, 400, 450, 500, 550, 600, 650, 700, 750°C, etc., preferably 250-500°C, more preferably 300-400°C.

[0019] The pre-calcination time may vary according to the amount of raw materials, the calcination temperature, etc., for example, it may be 10 min-5 h, 0.5-3 h, 1-2 h, etc., but is not limited thereto.

[0020] Step S2

[0021] In step S2, zinc fluoride can be discharged from the system as steam by roasting under reduced pressure, and zinc fluoride condensate is obtained by cooling, and roasting slag is obtained at the same time. Since rare earth fluoride and rare earth oxide have high boiling points, rare earth elements remain in the roasting slag, thereby achieving separation of rare earth elements and fluorine. In addition, since zinc fluoride is discharged from the system, the forward reaction of rare earth fluoride and zinc carbonate will be further promoted, making the reaction more thorough.

[0022] In step S2, the reduced pressure roasting refers to roasting in a roasting device under a pressure reduced compared to an air atmosphere.

[0023] In step S2, the temperature and vacuum degree of the reduced pressure roasting can be controlled in coordination. Generally speaking, the higher the temperature, the lower the required vacuum degree can be, and the lower the temperature, the higher the required vacuum degree will be.

[0024] In some embodiments, the reduced pressure calcination temperature can be 800-1500°C, for example 850, 900, 950, 1000, 1050, 1100, 1150, 1200, 1300, 1350, 1400, 1450°C, etc., preferably 850-1100°C, more preferably 900-1000°C.

[0025] In some embodiments, the relative vacuum degree (gauge pressure) of the reduced pressure roasting may be below -0.05 MPa, below -0.06 MPa, or below -0.07 MPa, for example, about -0.075, -0.080, -0.085, -0.090, -0.095, -0.10 MPa, etc. In some embodiments, the relative vacuum degree of the reduced pressure roasting may be about -0.10 to -0.07 MPa, preferably -0.10 to -0.075 MPa.

[0026] The reduced pressure roasting time can vary according to the amount of raw materials, roasting temperature, vacuum degree, etc. Generally speaking, the more raw materials, the lower the temperature, the lower the vacuum degree, the longer the roasting time, while the less raw materials, the higher the temperature, the higher the vacuum degree, the shorter the roasting time. The reduced pressure roasting time can be 1-8h, or 2-4h, but is not limited thereto, and the specific roasting time can be determined by conventional experiments.

[0027] By controlling the reduced pressure roasting conditions, it is beneficial to obtain high-purity zinc fluoride condensate and reduce the fluorine content in the roasting slag.

[0028] In some embodiments, the fluorine content in the calcined slag may be controlled to be ≤0.25 wt %.

[0029] In the method of the present invention, steps S1 and S2 can be performed separately or continuously, preferably continuously.

[0030] In the method of the present invention, steps S1 and S2 can be performed in the same device or in different devices, preferably in the same device. The device may be, for example, a high-temperature distillation furnace, a vacuum tube furnace, a rotary calcining furnace equipped with a condensation system, etc., but is not limited thereto.

[0031] In some embodiments, the method for separating rare earth elements and fluorine in fluoridated rare earth slag of the present invention comprises the following steps:

[0032] S1-1: mixing the fluoride rare earth slag and the zinc compound and calcining them at 250-500°C, preferably 300-400°C, under normal pressure for 0.5-3h, preferably 1-2h;

[0033] S1-2: heating to 800-1500°C, preferably 850-1100°C, more preferably 900-1000°C, and calcining at normal pressure for more than 1 hour, preferably 1-8 hours;

[0034] S2: calcining at 800-1500°C, preferably 850-1100°C, more preferably 900-1000°C for 1-8h, or 2-4h at a relative vacuum degree of less than -0.05 MPa, less than -0.06 MPa, or less than -0.07 MPa, collecting zinc fluoride condensate and obtaining calcined slag.

[0035] Another aspect of the present invention provides a method for recovering rare earth elements from fluorinated rare earth slag, comprising the following steps:

[0036] (1) using the method for separating rare earth elements and fluorine in fluorinated rare earth slag according to the present invention to obtain roasted slag;

[0037] (2) The roasted slag is acid-leached and then the solid-liquid separation is performed to obtain acid-leached slag and acid-leaching liquid containing acid-soluble rare earths.

[0038] The description of the method for separating rare earth elements and fluorine in fluoridized rare earth slag according to the present invention in step (1) is the same as that described above and will not be repeated here.

[0039] In step (2), acid leaching refers to the process of mixing the roasted slag with an acid to react so as to convert the rare earth elements therein into soluble salts, thereby recovering the rare earth elements into the acid leaching solution.

[0040] The acid leaching can be carried out by any suitable acid leaching process in rare earth element extraction without particular limitation. Those skilled in the art can select suitable acid leaching acid and its concentration and suitable reaction conditions (such as temperature, stirring speed, etc.) according to the substances to be separated (such as alkali metals, silicates, etc.) based on the existing technology or through conventional selection tests to carry out the acid leaching process, or can further process the acid leaching liquid to achieve further separation.

[0041] In some embodiments, the acid for acid leaching can be selected from hydrochloric acid, nitric acid, sulfuric acid or a combination thereof. The specific acid used can be selected according to the subsequent extraction process. For example, when the subsequent extraction process uses the P507 system, the preferred acid for acid leaching is hydrochloric acid. In some embodiments, during the acid leaching process, the H in the feed solution obtained by mixing the roasted slag with the acid is + The concentration is controlled between 0.05-2 mol / L, preferably between 0.2-0.8 mol / L.

[0042] The temperature and time for acid leaching are not particularly limited, as long as the rare earth is dissolved (preferably completely dissolved). Generally speaking, the higher the temperature of acid leaching, the shorter the time required. Other conditions that affect the acid leaching time include the ratio of roasted slag to acid, the concentration of acid, the size of roasted slag, etc. For example, acid leaching can be carried out at room temperature -100°C, preferably at a temperature of 70-90°C, and the time can be 2-48 h, 8-24 h, 12-20 h, etc., but is not limited thereto.

[0043] By controlling the acid leaching conditions, it is beneficial to recover rare earth elements as much as possible. In some embodiments, the rare earth content in the acid leaching residue is ≤0.5%.

[0044] The method for recovering rare earth elements from fluorinated rare earth slag of the present invention may further include a step of extracting the rare earth elements in the obtained acid leaching solution with a rare earth extraction system. The rare earth elements can be further purified by this step. The rare earth extraction system may be any suitable rare earth extraction system, such as a solid phase extraction system or a liquid phase extraction system, such as a P507 system, etc., but is not limited thereto.

[0045] Unless otherwise specified, the numerical ranges listed in the present invention include the endpoints and all point values ​​therein that are increased or decreased by the smallest unit of the endpoints and all sub-ranges composed of these point values.

[0046] Unless otherwise stated, the numerical values ​​in the present invention represent approximate measurements or limitations of the range of embodiments including slight deviations from given values ​​and having approximately the mentioned values ​​and having the mentioned exact values. Except for the last example described in detail, all numerical values ​​of parameters (e.g., quantities or conditions) in this application document (including the attached claims) should be understood as modified by the term "approximately" in all cases, regardless of whether "approximately" actually appears before the numerical value. "Approximately" means that the numerical value described allows for slight imprecision (some close to precision in the value; approximately or reasonably close to the value; approximately). If the imprecision provided by "approximately" is not understood in this ordinary sense in the art, the "approximately" used herein at least represents the changes that can be produced by ordinary methods of measuring and using these parameters. For example, "approximately" can include less than or equal to 15%, less than or equal to 10%, less than or equal to 5%, less than or equal to 4%, less than or equal to 3%, less than or equal to 2%, less than or equal to 1%, less than or equal to 0.5%, less than or equal to 0.1% of the change, and in some aspects, less than or equal to 0.01% of the change.

[0047] The present invention has been described in detail above, but the above embodiments are only illustrative in nature and are not intended to limit the present invention. In addition, this article is not limited by any theory described in the above prior art or invention content or the following examples.

[0048] Beneficial Effects

[0049] The present invention utilizes the characteristic that the vapor pressure of zinc fluoride is greater than that of rare earth fluoride, and rare earth fluoride slag is mixed with zinc compound and then subjected to normal pressure roasting and reduced pressure roasting to achieve separation of rare earth elements and fluorine. The method of the present invention recovers fluorine resources in the slag in the form of zinc fluoride. Compared with the method of recovering fluorine resources in the slag by reduced pressure distillation of rare earth fluoride which requires higher temperature, the method can be carried out at a lower temperature due to the low boiling point of zinc fluoride, thereby greatly reducing the energy consumption of the reduced pressure roasting process, and realizing the green separation and high-value utilization of rare earth and fluorine resources in rare earth fluoride slag.

[0050] The method of the present invention can process different types of single or mixed fluoride rare earth molten salt electrolytic slag, realizes efficient separation of rare earth and fluorine, the recovery rate of rare earth can reach more than 90%, and fluorine can be basically fully recycled, the process is simple and easy to operate. In addition, atmospheric pressure roasting and reduced pressure roasting can be operated in the same equipment, the equipment selection is simple and can greatly improve production efficiency. DETAILED DESCRIPTION

[0051] The present invention is further described below in conjunction with examples. It should be noted that the following examples are provided for illustrative purposes only and do not constitute a limitation on the scope of protection claimed for the present invention.

[0052] Example

[0053] Reagents and equipment

[0054] Unless otherwise specified, the raw materials, reagents, methods, etc. used in the examples are conventional raw materials, reagents, methods in the art.

[0055] The zinc carbonate is Adamas-50471H with a purity of ≥57% ZnO basis. The dosage is calculated based on 57% when used.

[0056] The fluoride rare earth slag produced by a rare earth plant is used as raw material. The fluorine mass percentage is about 12-15%, and it contains Mg, Al, Si, Ti, Ca, Fe, W, Cr, La, Pr, Nd, Gd, Ho, etc. The content of each component may fluctuate due to different sampling sites.

[0057] The composition of the roasted slag was analyzed by X-ray fluorescence spectroscopy.

[0058] The calcination is carried out in a vacuum tube furnace with a distillation collection device.

[0059] Examples 1-3

[0060] Take 10g of rare earth fluoride slag, add 5.67g of zinc carbonate (corresponding to F / Zn molar ratio of about 1.8) and mix evenly, first calcine at normal pressure: after calcining at 400℃ for 1h, then heat to 1400℃, 1200℃ and 1050℃ respectively, and keep warm for 1h.

[0061] Then, the temperature is maintained and the roasting system is decompressed to a relative vacuum degree of about -0.10 MPa. The roasting is continued for 3 hours, and the condensate is collected to obtain condensed zinc fluoride and roasting slag.

[0062] The composition and mass percentage of the roasted slag were tested, and the results are shown in Table 1.

[0063] Table 1 Composition and mass percentage of roasted slag

[0064]

[0065] In the above embodiment, the reduced pressure roasting temperature is 1050°C to 1400°C, and the removal rate of fluorine in the process can reach 100%. However, the higher the temperature, the more impurities with low boiling points will be vaporized into the condensate, which is not conducive to the subsequent separation and utilization of zinc fluoride. Therefore, in subsequent experiments, lower temperatures are tried, which can reduce energy consumption costs on the one hand, and help obtain purer zinc fluoride on the other hand.

[0066] Embodiment 4-8

[0067] Take 10g of rare earth fluoride slag, add 5.67g of zinc carbonate (corresponding to a F / Zn molar ratio of about 1.8), mix well, and first calcine at normal pressure: after calcining at 400℃ for 1h, heat to 950℃ and keep warm for 1h.

[0068] After that, the temperature was maintained and the roasting system was decompressed to a relative vacuum degree of about -0.10 MPa. The roasting was continued for 1 h, 1.5 h, 2 h, 3 h and 4 h respectively, and the condensate was collected to obtain condensed zinc fluoride and roasting slag.

[0069] The composition and mass percentage of the roasted slag were detected. The composition of the roasted slag is shown in Table 2.

[0070] Table 2 Composition and mass percentage of roasted slag

[0071]

[0072] In the above embodiment, the reduced pressure roasting temperature is reduced to 950°C, and the reduced pressure roasting time is within the range of 1-4 hours, and the fluorine removal rate of the process of the present invention can still reach 100%. The reduction of the reduced pressure roasting temperature is beneficial to equipment selection and energy consumption reduction, while reducing the volatilization loss of rare earth.

[0073] Example 9

[0074] Take 10g of rare earth fluoride slag, add 5.67g of zinc carbonate (corresponding to a F / Zn molar ratio of about 1.8), mix well, and first calcine at normal pressure: after calcining at 350°C for 1h, heat to 950°C and keep warm for 1h.

[0075] Then, the temperature was maintained and the roasting system was subjected to a decompression treatment with a relative vacuum degree of about -0.10 MPa. The reduced pressure roasting time was 1 hour to obtain condensed zinc fluoride and roasting slag. The composition of the roasting slag is shown in Table 3.

[0076] Table 3 Composition and mass percentage of roasted slag

[0077]

[0078] 100g of roasted slag was leached with hydrochloric acid at 80-90℃ for 16h. + The concentration was controlled at about 0.5 mol / L. Then, the solid was filtered, dried and weighed to obtain 10.13 g of acid leaching residue, from which the dissolution rate of the roasted residue was calculated to be 89.86%.

[0079] The composition of the acid leaching residue is shown in Table 4.

[0080] Table 4 Composition and mass percentage of acid leaching residue

[0081]

[0082] As can be seen from Table 4, the total mass of rare earth oxide before acid dissolution is 58.2%×100g, and after acid dissolution is 2.3%×10.13g. Therefore, the recovery rate of rare earth elements in the method of the present invention reaches 99.6%, achieving efficient recovery of rare earths.

[0083] The above embodiments are only preferred implementation modes of the present invention, but the protection scope of the present invention is not limited thereto. Any equivalent replacement or change made by any technician familiar with the field in the technical scheme and inventive concept of the present invention should be covered within the protection scope of the present invention.

Claims

1. A method for separating rare earth elements and fluorine in fluorinated rare earth slag, characterized in that: The method comprises the following steps: S1 normal pressure roasting: mixing the rare earth fluoride slag with a zinc compound and then roasting them at normal pressure; wherein the zinc compound is selected from zinc carbonate, basic zinc carbonate, zinc oxide, zinc hydroxide or a combination thereof; S2 Reduced-pressure roasting: Reduced-pressure roasting is performed to collect zinc fluoride condensate and obtain roasting slag at the same time.

2. The method according to claim 1, characterized in that The molar ratio F / Zn of F in the fluorided rare earth slag to Zn in the zinc compound is 3.0 or less.

3. The method according to claim 1, characterized in that The molar ratio F / Zn of F in the fluoridated rare earth slag to Zn in the zinc compound is 2.5 or less.

4. The method according to claim 1, characterized in that: In step S1, the normal pressure calcination temperature is 800-1500°C.

5. The method according to claim 4, characterized in that The calcination temperature at atmospheric pressure is 850-1100℃.

6. The method according to claim 4, characterized in that The calcination temperature at atmospheric pressure is 900-1000℃.

7. The method according to claim 1, characterized in that Step S1 also includes a pre-baking step, and the pre-baking temperature is lower than the normal pressure baking temperature.

8. The method according to claim 7, characterized in that The pre-calcination temperature is 250-500°C.

9. The method according to claim 1, characterized in that In step S2, the reduced pressure roasting temperature is 800-1500°C, and the relative vacuum degree of the reduced pressure roasting is below -0.05 MPa.

10. The method according to claim 9, characterized in that The reduced pressure roasting temperature is 850-1100°C, and the relative vacuum degree of the reduced pressure roasting is below -0.06 MPa.

11. The method according to claim 9, characterized in that The reduced pressure roasting temperature is 900-1000°C, and the relative vacuum degree of the reduced pressure roasting is below -0.07 MPa.

12. The method according to claim 1, characterized in that The method comprises the following steps: S1-1: Mix the rare earth fluoride slag and the zinc compound and calcine at 250-500°C under normal pressure for 0.5-3h; S1-2: heating to 800-1500℃ and calcining at normal pressure for more than 1h; S2: calcining at 800-1500°C for 1-8h at a temperature below -0.05 MPa, collecting zinc fluoride condensate and obtaining calcined slag.

13. The method according to claim 12, characterized in that In S1-1, calcining at 300-400°C under normal pressure for 1-2h; In S1-2, the temperature is raised to 850-1100°C and calcined at normal pressure for 1-8h; In S2, calcination is carried out at 850-1100°C for 2-4h at below -0.06 MPa.

14. A method for recovering rare earth elements from fluorinated rare earth slag, characterized in that: The method comprises the following steps: (1) obtaining roasted slag using the method according to any one of claims 1 to 13; (2) The roasted slag is acid-leached and then the solid-liquid separation is performed to obtain acid-leached slag and acid-leaching liquid containing acid-soluble rare earths.

15. The method according to claim 14, characterized in that The acid used for acid leaching is selected from hydrochloric acid, nitric acid, sulfuric acid or a combination thereof. The H + The concentration is controlled between 0.05-2mol / L.

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