A method for recovering rare earth elements

Abstract

The present invention provides a method for recovering rare earth elements, and belongs to the technical field of rare earth pyrometallurgy. The waste carbon material produced by molten salt electrolysis of rare earth metals or alloys is crushed and then magnetically separated to obtain a concentrate with high content of iron, lithium and rare earth elements and a tailing with low content of iron, lithium and rare earth elements. More than 70% of the rare earth elements are enriched in the 15-25% concentrate, which can be directly reused or recycled after further treatment, thereby avoiding the waste of rare earths in the waste carbon material. At the same time, the carbon content in the tailings is increased and the impurities in the tailings are reduced. The subsequent processing amount of the waste carbon material is reduced, and the process has the advantages of simple process, convenience and reliability, no pollution to the environment, and high recovery rate.

Description

Technical Field

[0001] The present invention relates to a method for recovering rare earth elements, and in particular to a method for recovering rare earth elements from waste carbon materials produced by preparing rare earth metals or rare earth alloys by molten salt electrolysis, belonging to the technical field of rare earth metallurgy. Background Art

[0002] In the process of producing rare earth metals or rare earth alloys by molten salt electrolysis, carbon materials are usually used to make anodes and electrolytic furnaces. These carbon materials are immersed in molten salts composed of rare earth fluorides, lithium fluorides, etc. for a long time. Molten salts and rare earth raw materials such as rare earth oxides dissolved in molten salts (hereinafter collectively referred to as molten salts) penetrate into the interior of the carbon materials (the penetration depth varies with the cracks and micropore depths on the surface of the waste carbon materials) and adhere to the surface of the carbon materials. When waste carbon materials are generated due to damage or scrapping of the electrolytic furnace and replacement of anode fragments, molten salts also adhere to the surface and interior of these waste carbon materials and become waste molten salts and are wasted.

[0003] The Chinese patent application with publication date of October 26, 2016 and publication number CN106044833A discloses "a method for recovering rare earth fluoride from recycled rare earth waste electrode materials and slag, taking recycled rare earth waste electrode materials and slag as raw materials, sieving the block raw materials, removing non-rare earth bulk impurities, sieving, ball milling, and magnetic separation; mixing the raw materials from which most of the iron is removed after magnetic separation with lithium fluoride; heating the mixture to melt it until a sufficient liquid level is reached; stirring the molten liquid and filtering the residue; electrolyzing the filtrate after filtering the residue to remove impurities, removing the residue after the anode effect appears in the electrolysis, and circulating the supernatant; testing the obtained supernatant, and weighing and packaging it after meeting the standard, which is the final recovered product." The technical scheme achieves the technical effect of "the present invention can conveniently and effectively purify rare earth fluoride from recycled rare earth waste electrode materials and slag, saving resources, reducing pollution, and having the characteristics of simple process and low cost".

[0004] A Chinese patent application with publication date of October 18, 2019 and publication number CN110344086A discloses a method for separating and recovering electrolyte components from fluoride salt system rare earth electrolysis molten salt slag, which adopts the technical scheme of "first crushing the rare earth electrolysis molten salt slag, and then vacuum distilling the crushed rare earth electrolysis molten salt slag, collecting the fluoride electrolyte after the vacuum distillation, and directly returning it to the rare earth electrolysis process", and has achieved the technical effect of "the present invention directly recovers the fluoride electrolyte by vacuum distillation, and the whole recovery process does not generate secondary pollution. The separated fluoride electrolyte is directly returned to the rare earth electrolysis process, further realizing the efficient comprehensive recovery and utilization of rare earth, lithium, fluorine and graphite resources in the difficult-to-treat rare earth electrolysis molten salt slag".

[0005] The Chinese patent application with publication date of August 14, 2020 and publication number CN111534701A discloses "a method for efficiently recovering valuable elements from rare earth molten salt electrolytic slag, wherein the rare earth molten salt electrolytic slag and a lithium source are uniformly mixed to obtain a mixture; the obtained mixture is successively subjected to a first stage of vacuum roasting and a second stage of vacuum distillation to obtain high-purity lithium fluoride. The present invention is based on the characteristics that the melting and boiling points of lithium fluoride are lower than those of rare earth fluoride and the vapor pressure of lithium fluoride is greater than that of rare earth fluoride. First, a vacuum roasting conversion is performed, The technical solution of converting the non-volatile rare earth fluoride in the slag into volatile lithium fluoride, and then recovering the fluorine resource in the form of lithium fluoride through a two-stage vacuum distillation process can effectively reduce the vacuum distillation temperature, distillation time and distillation energy consumption, and can achieve the clean separation of fluorine and rare earth in the slag, further improving the comprehensive recovery rate of fluorine and rare earth" has achieved the technical effect of "realizing the green and high-value comprehensive recovery of rare earth, lithium and fluorine resources in rare earth molten salt electrolysis slag, and the comprehensive recovery rate of rare earth and fluorine elements can reach more than 99%".

[0006] Although the above-mentioned existing technologies can recover valuable elements such as rare earths and lithium from rare earth molten salt electrolytic slag, they have defects such as complex recovery process, harsh working conditions, high energy consumption, low rare earth recovery rate and inability to recover rare earths from waste carbon materials. Summary of the invention

[0007] In view of the above-mentioned defects in the prior art, the present invention provides a method for recovering rare earth elements from waste carbon materials. The following technical scheme is adopted:

[0008] A method for recovering rare earth elements comprises the following steps:

[0009] Step 1: crushing the waste carbon material to obtain waste carbon material powder;

[0010] Step 2, magnetically separating the waste carbon material powder obtained in step 1 to obtain concentrate and tailings;

[0011] The waste carbon material is waste carbon material produced by molten salt electrolysis of rare earth metals or alloys.

[0012] The concentrate is a substance with high content of iron, lithium, rare earth elements, etc. after magnetic separation, and the tailings is a substance with low content of iron, lithium, rare earth elements, etc. after magnetic separation.

[0013] One of the preferred technical solutions of the present invention is to first strip off the rare earth molten salt on the surface of the waste carbon and then crush and recover them separately.

[0014] Another preferred technical solution of the present invention is to incinerate the concentrate obtained in step 2 in an oxidizing atmosphere to remove the carbonaceous material therein and obtain recovered molten salt.

[0015] Another preferred technical solution of the present invention is to return the recovered molten salt or concentrate to the electrolysis system for electrolytic production of rare earth metals or alloys.

[0016] According to another preferred technical solution of the present invention, the particle size of the waste graphite powder is -1 to -400 mesh.

[0017] Another preferred technical solution of the present invention is that the magnetic field strength of the magnetic separation is ≥0.2 Tesla.

[0018] In another preferred technical solution of the present invention, the magnetic field strength is ≥ 1 Tesla.

[0019] Another preferred technical solution of the present invention is that the pulsation frequency during magnetic separation is 10-200 times / minute

[0020] One of the preferred technical solutions of the present invention is that the purity of the graphite powder in the tailings is improved, and after drying, it can be sold as higher-grade graphite powder, or used for building rare earth metal or alloy electrolytic furnaces.

[0021] One of the preferred technical solutions of the present invention is to crush the waste carbon material into waste carbon material powder that all passes 400 mesh, and after the waste carbon material powder is pulped, it is subjected to multiple magnetic separations at a pulsation rate of 130-150 times / minute under a 0.2-0.8 Tesla magnetic field.

[0022] One of the preferred technical solutions of the present invention is to crush the waste carbon materials of molten salt electrolysis rare earth metals or alloys until all of them pass through a 150-mesh sieve to obtain waste graphite powder, and to perform dry magnetic separation several times in a 1.0 Tesla magnetic field without adding water to the waste graphite powder to obtain concentrate and tailings.

[0023] One of the preferred technical solutions of the present invention is to crush the waste graphite of molten salt electrolysis rare earth metal or alloy until it all passes through a 300-mesh sieve, and the obtained waste graphite powder is subjected to wet magnetic separation in a 1.0 Tesla magnetic field with a pulsation of 100 times / minute to obtain concentrate and tailings.

[0024] The present invention separates most of the carbon materials that are basically free of molten salt by magnetic separation, and enriches more than 70% of the rare earth elements in 15-25% concentrate, which can be directly reused or recycled after further treatment, thereby avoiding the waste of rare earths in the waste carbon materials. At the same time, the carbon content in the tailings is increased, and the impurities in the tailings are reduced. The subsequent processing amount of the waste carbon materials is reduced, and the process is simple, convenient and reliable, no pollution to the environment, and the recovery rate is high. DETAILED DESCRIPTION

[0025] Since rare earth raw materials such as rare earth oxides and rare earth fluorides contain trace amounts of iron impurities, and during the electrolysis process, a small amount of iron from parts and tools such as the conductive plates of the electrolytic furnace is gradually enriched in the molten salt in the electrolytic furnace, the waste molten salt containing rare earth raw materials such as rare earth oxides and rare earth fluorides and impurities such as iron has weak magnetism. However, the carbon material used in the electrolysis process has no magnetism or very weak magnetism. The present invention utilizes the weak magnetism generated by impurities such as iron in the waste molten salt to separate materials such as graphite that do not contain waste molten salt or contain very little waste molten salt from most of the waste molten salt in the waste carbon material through magnetic separation, so that the waste molten salt can be directly reused after enrichment or re-enriched or purified to recover rare earth elements in the next step, thereby reducing the processing volume.

[0026] Embodiment 1

[0027] 4007.7 g of waste graphite from molten salt electrolysis of rare earth metals or alloys (dry basis, the same below. The content of rare earth and iron elements is detailed in Table 1, and each element is calculated as oxide, the same below) was crushed and passed through a 100-mesh sieve to obtain waste graphite powder. The waste graphite powder was prepared into waste graphite slurry with water, and firstly separated by magnetic separation under a 0.8 Tesla magnetic field at a pulsation of 130 times / min to obtain concentrate 1 and tailings 1.

[0028] The tailings 1 were crushed again until all of them passed through a 200-mesh sieve, and then separated by scanning under a 1.0 Tesla magnetic field to obtain concentrate 2 and tailings 2.

[0029] The tailings 2 were crushed until all of them passed through a 300-mesh sieve, and separated under a 1.2 Tesla magnetic field to obtain concentrate 3, and 2912.0 grams of tailings 3 were obtained. Concentrate 1, concentrate 2 and concentrate 3 were combined to obtain 1095.7 grams of concentrate. The components of the concentrate and tailings 3 were determined separately. The components of the concentrate and tailings 3 are detailed in Table 1. Except for the units indicated in Table 1, all other data are in grams (dry basis).

[0030] 1000 g of the above concentrate is placed in air or oxygen-enriched air for roasting, and combustibles are removed therefrom to obtain 152.2 g of burning material, the main components of which are rare earth element compounds, lithium fluoride, and iron element compounds. The burning material is further subjected to chemical treatment to separate impurities such as iron and recover rare earth and other elements. The main components of the burning material are shown in Table 1.

[0031] Since rare earth molten salts of varying thicknesses adhere to the surface of waste carbon materials such as waste anode blocks, these rare earth molten salts adhering to the surface of the waste carbon materials can be peeled off and recovered by rubbing and scraping, and then the remaining waste carbon materials can be crushed and magnetically separated to recover rare earth elements.

[0032] The above concentrates or calcined materials can be directly added to the same type of electrolytic cells for electrolytic production of rare earth metals or alloys, or chemical methods can be used to transform and separate and recover the various elements therein. Tailings can be used to make electrolytic furnaces or sold as graphite powder.

[0033] Embodiment 2

[0034] 4007.7 g (dry) of waste graphite from molten salt electrolysis of rare earth metals or alloys was crushed and all passed through a 300-mesh sieve to obtain waste graphite powder, which was then subjected to water magnetic separation in a 1.0 Tesla magnetic field with a pulsation of 100 times / min to obtain 1195.9 g of concentrate enriched in valuable elements such as rare earths and lithium and 6450.5 g of tailings enriched in graphite, etc. The composition of the concentrate and tailings is detailed in Table 1.

[0035] Embodiment 3

[0036] 5006.6 g of waste graphite from molten salt electrolysis of rare earth metals or alloys was crushed until all of the waste graphite passed through a 400-mesh sieve to obtain waste graphite powder. The waste graphite powder was slurried with an aqueous solution and subjected to multiple magnetic separations at a 0.2-0.8 Tesla magnetic field at a pulsation rate of 130-150 times / minute to obtain 695.5 g of concentrate and 4311.1 g of tailings. The components of the concentrate and tailings are detailed in Table 1.

[0037] Embodiment 4

[0038] 3742.3 g of waste graphite from molten salt electrolysis of rare earth metals or alloys was crushed until all of it passed through a 150-mesh sieve to obtain waste graphite powder. The waste graphite powder was subjected to three dry magnetic separations in a 1.0 Tesla magnetic field without adding water, and 951.1 g of concentrate and 4311.1 g of tailings were obtained by combining them. The compositions of the concentrate and tailings are detailed in Table 1.

[0039] Embodiment 5

[0040] 8271.3 grams of waste graphite blocks from molten salt electrolysis of rare earth metals or alloys were crushed and passed through a 1-mesh standard sieve, and dry magnetic separation was performed with a magnetic field intensity of 0.1 Tesla and a pulsation frequency of 10 times / minute to obtain recovered molten salt that was essentially free of graphite and fell off the surface of the waste graphite blocks during the crushing process. The recovered molten salt can be directly returned to the electrolysis production for use. The remaining waste graphite was further crushed until it all passed through a 50-mesh sieve to obtain waste graphite powder. After the waste graphite powder aqueous solution was pulped, it was first magnetically separated at a magnetic field intensity of 0.5 Tesla and a pulsation frequency of 50 times / minute to obtain concentrate 1 and tailings 1; tailings 1 was crushed until it all passed through a 200-mesh sieve, and then magnetically separated at 1.0 Tesla and a pulsation frequency of 200 times / minute to obtain concentrate 2 and tailings 2; finally, tailings 1 was crushed until it all passed through a 350-mesh sieve, and magnetic separation was performed for multiple times at 1.2 Tesla and a pulsation frequency of 50 times / minute to obtain concentrate 3 and 6625.1 grams of tailings; the molten salt and concentrate 1, concentrate 2, and concentrate 3 were recovered together to obtain 1645.8 grams of concentrate. The components of the concentrate and tailings are detailed in Table 1.

[0041] Table 1 (Unit: g)

[0042]

[0043] As can be seen from Table 1, the recovery efficiency of wet magnetic separation is higher than that of dry magnetic separation; in wet magnetic separation, as the iron content in waste graphite increases, the enrichment efficiency of high-value elements such as rare earth elements increases. And within a certain range, the enrichment efficiency is inversely proportional to the particle size of waste graphite powder. This is because after proper grinding, the waste graphite is less adhered to the molten salt, and the magnetic field strength can be appropriately reduced during magnetic separation.

[0044] The above are only several preferred embodiments of the present invention. Those skilled in the art should understand that the embodiments of the present invention are not limited to the above embodiments, and any equivalent changes made on the basis of the present invention should fall within the scope of protection of the present invention.

Claims

1. A method for recovering rare earth elements, characterized in that: The following steps are involved: Recovering valuable elements from waste carbon materials produced by molten salt electrolysis to prepare rare earth metals or rare earth alloys, the valuable elements including rare earth elements and lithium; Waste carbon materials are mainly composed of rare earth fluorides, lithium fluoride and carbon; Step 1: crushing the waste carbon material to obtain waste carbon material powder; the waste carbon material is waste carbon material produced by molten salt electrolysis of rare earth metals or alloys; The molten salt and the rare earth raw materials dissolved in the molten salt penetrate into the interior of the carbon material and adhere to the surface of the carbon material. The waste molten salt containing the rare earth raw materials and iron impurities has weak magnetism. Step 2, magnetically separating the waste carbon material powder obtained in step 1 to obtain concentrate and tailings; The concentrate is a substance enriched with high-value elements in waste carbon materials, and the tailings is a substance enriched with low-value elements in waste carbon materials; The concentrate obtained in step 2 is incinerated in an oxidizing atmosphere to remove the carbon material therein and obtain recovered molten salt.

2. A method for recovering rare earth elements as claimed in claim 1, characterized in that: The concentrate obtained in step 2 is returned to the electrolysis system for electrolytic production of rare earth metals or alloys.

3. A method for recovering rare earth elements as claimed in claim 1, characterized in that: The recovered molten salt concentrate is chemically treated to obtain rare earth oxides or rare earth fluorides.

4. A method for recovering rare earth elements as claimed in claim 1, characterized in that: The particle size of the waste carbon powder is 100-300 meshes.

5. A method for recovering rare earth elements as claimed in claim 1, characterized in that: The magnetic field strength of the magnetic separation is ≥0.2 Tesla.

6. A method for recovering rare earth elements as claimed in claim 5, characterized in that: The magnetic field strength is ≥1.0 Tesla.

7. A method for recovering rare earth elements as claimed in claim 1, characterized in that: The magnetic separation is performed at least twice.

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