A method for recovering rare earth elements and fluorine from fluorine-containing rare earth slag

Abstract

This invention relates to a method for recovering rare earth elements and fluorine from fluorine-containing rare earth slag. The method includes the following steps: (1) mixing the fluorine-containing rare earth slag and acid, followed by solid-liquid separation to obtain a first filter residue and a first filtrate containing rare earth elements; (2) mixing the first filter residue obtained in step (1) with molten aluminum chloride, followed by calcination, washing, and solid-liquid separation to obtain a second filtrate containing rare earth elements and a second filter residue containing fluorine. The method for recovering rare earth elements and fluorine from fluorine-containing rare earth slag provided by this invention can achieve efficient recovery of rare earth elements and fluorine, is simple to operate, low in cost, clean and environmentally friendly, and has a high resource utilization rate and comprehensive recovery value.

Description

Technical Field

[0001] This invention relates to the field of non-ferrous metal metallurgy and resource recycling technology, specifically to a method for recovering rare earth elements and fluorine elements from fluorine-containing rare earth slag. Background Technology

[0002] Molten salt electrolysis and calcothermal reduction are the main methods for preparing rare earth metals and alloys. Molten salt electrolysis is primarily used to produce pure metals such as lanthanum, cerium, praseodymium, and neodymium, as well as alloys such as lanthanum-nickel, gadolinium-iron, dysprosium-iron, holmium-iron, and samarium-cobalt. The electrolytes used are mainly rare earth fluorides and lithium fluoride. During the electrolysis process, a large amount of rare earth molten salt slag is inevitably generated due to operations such as feeding, tapping, electrode replacement, and electrolytic cell maintenance and replacement. Its main components are rare earth fluorides, lithium fluoride, graphite, calcium fluoride, alumina, iron oxide, and silicon dioxide, with the rare earth content (calculated as rare earth metals) ranging from 5% to 60%. Calcothermal reduction is the main method for producing medium and heavy rare earth pure metals such as scandium, yttrium, gadolinium, terbium, dysprosium, holmium, erbium, thulium, and lutetium. This method uses metallic calcium as a reducing agent and pure single rare earth fluorides as raw materials, carrying out a reduction reaction at 1400-1600℃ under vacuum or an inert atmosphere to obtain pure rare earth metals and reduction slag. Therefore, a large amount of reduction slag is inevitably generated during the production of rare earth metals. The main components are calcium fluoride, small amounts of rare earth fluorides, rare earth metals, metallic calcium, and rare earth oxides, with the rare earth content (calculated as rare earth metals) ranging from 2% to 15%. Due to the large variety of rare earth elements, the types and contents of rare earth elements in the waste slag produced from the production of different rare earth metals and alloys vary considerably. Furthermore, because rare earth fluorides and calcium fluoride have high stability, the treatment of fluorine-containing rare earth slag is difficult and costly.

[0003] Currently, the main methods for treating fluorine-containing rare earth slag are acid methods and alkaline methods. The acid method generally uses concentrated sulfuric acid roasting, which utilizes the principle that concentrated sulfuric acid reacts with fluorides to produce HF. This method has a long production process, generates a large amount of highly toxic HF gas, and requires sophisticated equipment.

[0004] CN104843761A discloses an environmentally friendly and low-cost method for recovering rare earths from rare earth fluoride molten salt electrolysis waste. The method uses rare earth fluoride molten salt electrolysis waste as raw material and obtains single or mixed rare earth oxides through processes such as crushing and grinding, stirring and mixing, roasting and alkali conversion, ball milling, washing, optimal leaching, extraction and separation, precipitation, washing, and calcination.

[0005] CN101956078A discloses a method for separating and recovering rare earth elements from rare earth molten salt electrolysis waste. The method uses rare earth metal molten salt electrolysis waste as raw material and proceeds through the following steps: raw material crushing, calcium hydroxide preparation, fluorine replacement, hydrochloric acid dissolution, extraction and separation using a P507 kerosene hydrochloric acid system, carbonic acid precipitation, and calcination to obtain a single rare earth oxide.

[0006] CN105369042A discloses a method for extracting rare earths from rare earth molten salt electrolytic slag in a fluoride system. The method involves mixing silicate with rare earth molten salt electrolytic slag in a fluoride system, followed by roasting, washing, filtering, and acid leaching to obtain a rare earth solution.

[0007] The above methods mainly utilize the reaction of alkaline substances with rare earth fluorides at high temperatures to transform rare earth elements into acid-soluble rare earth oxides, thereby enabling acid leaching extraction and recovery. Therefore, these methods require large quantities of acid and alkali solutions, demand high-level equipment and processing costs, and do not consider the recovery and utilization of fluorine.

[0008] CN111534701A discloses a method for efficiently recovering valuable elements from rare earth molten salt electrolytic slag. The method involves mixing rare earth molten salt electrolytic slag and a lithium source to obtain a uniform mixture. The resulting mixture is then subjected to a first-stage vacuum roasting and a second-stage vacuum distillation to obtain high-purity lithium fluoride.

[0009] CN111961872A discloses a method for extracting valuable elements from rare earth slag subjected to calcothermal vacuum reduction. The method employs vacuum displacement and vacuum distillation to directly replace fluorine in the calcothermal reduction rare earth slag with lithium salt to produce lithium fluoride. The distillation residue is then subjected to an acid leaching-extraction separation process to produce rare earth fluorides or oxides.

[0010] The above methods use lithium carbonate or lithium hydroxide to decompose rare earth molten salt slag and reduction slag, and recover rare earth elements, and recover fluorine elements in the form of lithium fluoride. However, lithium carbonate and lithium hydroxide are expensive, and the production cost is relatively high.

[0011] Therefore, it is of great significance to develop a method for the comprehensive recycling and utilization of fluorine-containing rare earth slag that is efficient, energy-saving, and environmentally friendly. Summary of the Invention

[0012] To address the above problems, the present invention aims to provide a method for recovering rare earth elements and fluorine elements from fluorine-containing rare earth slag. Compared with the prior art, the method of the present invention can efficiently recover rare earth elements and fluorine elements from fluorine-containing rare earth slag and convert fluorine elements into high-value-added aluminum fluoride, which has high application value.

[0013] To achieve this objective, the present invention employs the following technical solution:

[0014] This invention provides a method for recovering rare earth elements and fluorine elements from fluorine-containing rare earth slag, the method comprising the following steps:

[0015] (1) Mix fluorine-containing rare earth slag and acid solution, and then separate the solid and liquid to obtain the first filter residue and the first filtrate containing rare earth elements;

[0016] (2) The first filter residue obtained in step (1) and the aluminum chloride molten salt are mixed and then roasted, washed and separated in sequence to obtain the second filtrate containing rare earth elements and the second filter residue containing fluorine elements.

[0017] In this invention, fluorine-containing rare earth slag is first mixed with acid, followed by solid-liquid separation to obtain a first filtrate and a first filter residue. The first filtrate contains rare earth elements, meaning that step (1) can convert insoluble rare earth metals and rare earth oxides into soluble rare earth elements, thereby recovering some rare earth elements. Simultaneously, since metal fluorides are insoluble in acid, step (1) can also separate the metal fluorides in the fluorine-containing rare earth slag, retaining them in the first filter residue. Furthermore, acid can remove some oxide impurities from the fluorine-containing rare earth slag, such as calcium oxide, iron oxide, and magnesium oxide. Further, the first filter residue obtained in step (1) is mixed with aluminum chloride-containing molten salt and then calcined. The metal fluorides in the first filter residue react with aluminum chloride to form metal chlorides and aluminum fluoride, recovering another portion of rare earth elements and fluorine from metal fluorides (e.g., rare earth fluorides, calcium fluoride, and lithium fluoride). Aluminum fluoride has high added value and can be applied in industries such as aluminum electrolysis. The method provided by this invention can efficiently recover rare earth elements and fluorine, converting fluorine into high-value aluminum fluoride. Furthermore, the recovery process is clean and pollution-free. The reaction process of fluorides (taking rare earth fluorides, calcium fluoride, and lithium fluoride as examples) with aluminum chloride in this invention is as follows:

[0018] REF3 + AlCl3 = RECl3 + AlF3

[0019] 3CaF2 + 2AlCl3 = 3CaCl2 + 2AlF3

[0020] 3LiF + AlCl3 = 3LiCl + AlF3

[0021] In this context, RE represents rare earth atoms, such as any one of lanthanum, cerium, praseodymium, neodymium, promethium, samarium, europium, gadolinium, terbium, dysprosium, holmium, erbium, thulium, ytterbium, lutetium, scandium, or yttrium.

[0022] In this invention, the aluminum chloride-containing molten salt is obtained by mixing aluminum chloride and other metal chlorides in a molar ratio of 1:(0.5-4) and then melting them. The other metal chlorides include alkali metal chlorides or alkaline earth metal chlorides, such as sodium chloride, potassium chloride, or calcium chloride.

[0023] This invention utilizes molten aluminum chloride for roasting. Compared to existing technologies that use lithium carbonate or lithium hydroxide as additives for fluorine extraction, the cost of the molten aluminum chloride in this invention is significantly lower than that of lithium carbonate or lithium hydroxide, and it also achieves a higher fluorine recovery rate. Furthermore, by using molten aluminum chloride for roasting, this invention effectively prevents aluminum chloride volatilization, saves processing costs, and improves the recovery rate of rare earth elements and the purity of aluminum fluoride, compared to roasting with only aluminum chloride.

[0024] Preferably, the fluorine-containing rare earth slag includes rare earth reduction slag and / or rare earth molten salt slag.

[0025] The present invention does not specifically limit the rare earth reduction slag, which can be any rare earth reduction slag produced in the production of rare earth metals that is well known to those skilled in the art. Its main components include rare earth oxides, rare earth fluorides, other metal fluorides (e.g., calcium fluoride), rare earth metals, and other elemental metals (e.g., calcium).

[0026] The present invention does not specifically limit the rare earth molten salt slag, which can be any rare earth molten salt slag produced in the production of rare earth metals that is well known to those skilled in the art. Its main components include rare earth fluorides, other metal fluorides (such as lithium fluoride and calcium fluoride), metal oxides (such as aluminum oxide and iron oxide), and silicon dioxide.

[0027] In this invention, the first and second filtrates can be extracted to separate rare earth elements from other metal elements, resulting in a rare earth feed solution.

[0028] In this invention, there is no particular limitation on the method of solid-liquid separation; it can be any method of solid-liquid separation known to those skilled in the art, such as filtration or centrifugation.

[0029] Preferably, the fluorine-containing rare earth slag in step (1) is ground before mixing.

[0030] Preferably, the particle size of the ground fluorine-containing rare earth slag is 30-160 μm, for example, it can be 30 μm, 32 μm, 34 μm, 35 μm, 36 μm, 38.5 μm, 70 μm, 72 μm, 74 μm, 76 μm, 78 μm, 80 μm, 90 μm, 100 μm, 110 μm, 120 μm, 130 μm, 140 μm, 150 μm, 154 μm or 160 μm, but is not limited to the listed values, and other unlisted values ​​within the range are also applicable.

[0031] Preferably, the acid solution in step (1) includes hydrochloric acid.

[0032] Preferably, the molar ratio of rare earth elements to hydrochloric acid in the fluorinated rare earth slag is 1:(5.6-15), for example, it can be 1:5.6, 1:6, 1:7, 1:8, 1:9, 1:10, 1:11, 1:12, 1:13, 1:14 or 1:15, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0033] The present invention preferably controls the molar ratio of rare earth elements to hydrochloric acid in fluorine-containing rare earth slag within a specific range, which is beneficial to fully dissolve rare earth elements and improve the recovery rate of rare earth elements and the purity of AlF3.

[0034] In this invention, the main components of the first filtrate include rare earth chlorides and other metal chlorides (such as ferric chloride, magnesium chloride and calcium chloride).

[0035] In this invention, when the fluorine-containing rare earth slag is only a rare earth reduction slag, the main components of the first filter residue include rare earth fluorides and other metal fluorides (e.g., lithium fluoride and calcium fluoride); when the fluorine-containing rare earth slag contains rare earth molten salt slag, the main components of the first filter residue include rare earth fluorides, other metal fluorides (e.g., lithium fluoride and calcium fluoride), silicon dioxide, and aluminum silicate, etc.

[0036] Preferably, the concentration of the hydrochloric acid is 0.5-12 mol / L, for example, it can be 0.5 mol / L, 0.6 mol / L, 0.7 mol / L, 0.8 mol / L, 0.9 mol / L, 1 mol / L, 2 mol / L, 3 mol / L, 4 mol / L, 5 mol / L, 6 mol / L, 7 mol / L, 8 mol / L, 9 mol / L, 10 mol / L, 11 mol / L or 12 mol / L, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0037] The present invention preferably controls the concentration of hydrochloric acid within a specific range, which can effectively control acid consumption, reduce the concentration of fluoride ions in the first filtrate, and is more conducive to dissolving rare earth elements in the fluorine-containing rare earth slag that exist in the metal phase and oxide phase.

[0038] Preferably, the solid-liquid ratio of the fluorinated rare earth slag to the acid solution is 1:(1-5) kg / L, for example, it can be 1:1 kg / L, 1:1.2 kg / L, 1:1.5 kg / L, 1:1.8 kg / L, 1:2 kg / L, 1:2.2 kg / L, 1:2.5 kg / L, 1:2.8 kg / L, 1:3 kg / L, 1:3.2 kg / L, 1:3.5 kg / L, 1:3.8 kg / L, 1:4 kg / L, 1:4.2 kg / L, 1:4.5 kg / L, 1:4.8 kg / L or 1:5 kg / L, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable, preferably 1:(1-5) kg / L.

[0039] The present invention preferably controls the solid-liquid ratio of fluorine-containing rare earth slag and acid solution within a specific range to obtain a first filtrate with a higher rare earth concentration.

[0040] Preferably, the mixing time in step (1) is 10-120 min, for example, it can be 10 min, 20 min, 30 min, 40 min, 50 min, 60 min, 70 min, 80 min, 90 min, 100 min, 110 min or 120 min, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0041] Preferably, the mixing temperature in step (1) is 20-100℃, for example, it can be 20℃, 25℃, 30℃, 35℃, 40℃, 45℃, 50℃, 55℃, 60℃, 65℃, 70℃, 75℃, 80℃, 85℃, 90℃, 95℃ or 100℃, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0042] Preferably, in step (2), the mass ratio of the first filter residue to aluminum chloride in the aluminum chloride-containing molten salt is 1:(1-3), for example, it can be 1:1, 1:1.2, 1:1.4, 1:1.6, 1:1.8, 1:2, 1:2.2, 1:2.4, 1:2.6, 1:2.8 or 1:3, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable, preferably 1:(1.6-3).

[0043] The present invention preferably controls the mass ratio of the first filter residue to aluminum chloride in the aluminum chloride-containing molten salt within a specific range, which can effectively utilize the aluminum chloride molten salt and control the aluminum ion content in the second filtrate.

[0044] In this invention, the first filter residue is dried and then mixed with molten salt containing aluminum chloride.

[0045] Preferably, the aluminum chloride molten salt in step (2) includes any one or a combination of at least two of NaAlCl4, KAlCl4 or CaAlCl5, wherein typical but non-limiting combinations include a combination of NaAlCl4 and KAlCl4, a combination of KAlCl4 and CaAlCl5, or a combination of NaAlCl4, KAlCl4 and CaAlCl5.

[0046] Preferably, the roasting temperature in step (2) is 300-800℃, for example, it can be 300℃, 310℃, 320℃, 330℃, 340℃, 350℃, 400℃, 450℃, 500℃, 600℃, 650℃, 700℃, 750℃ or 800℃, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0047] Preferably, the roasting time in step (2) is 30-180 min, for example, it can be 30 min, 40 min, 50 min, 60 min, 70 min, 80 min, 90 min, 100 min, 110 min, 120 min, 130 min, 140 min, 150 min, 160 min, 170 min or 180 min, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0048] In this invention, the washing solution includes water.

[0049] Preferably, the second filter residue obtained in step (2) is subjected to vacuum distillation to obtain aluminum fluoride.

[0050] In this invention, the main components of the second filtrate include rare earth chlorides and other metal chlorides (such as sodium chloride, potassium chloride, calcium chloride, and lithium chloride).

[0051] In this invention, when the fluorinated rare earth slag is only a rare earth reduction slag, the main component of the second filter residue is aluminum fluoride, with a recovery rate exceeding 95%. Furthermore, when the fluorinated rare earth slag is only a rare earth reduction slag, the impurities in the second filter residue are Al2O3. Since Al2O3 does not affect the application of AlF3 in aluminum electrolysis, the second filter residue has high application value. When the fluorinated rare earth slag contains rare earth molten salt slag, the main components of the second filter residue include aluminum fluoride and impurities (such as silicon dioxide and aluminum silicate). In this invention, when the fluorinated rare earth slag contains rare earth molten salt slag, the resulting second filter residue is vacuum distilled to obtain high-purity aluminum fluoride (99%), which can be applied in the aluminum electrolysis industry and has high application value.

[0052] Preferably, the temperature of the vacuum distillation is 600-1400℃, for example, it can be 600℃, 650℃, 700℃, 750℃, 800℃, 850℃, 900℃, 950℃, 1000℃, 1050℃, 1100℃, 1150℃, 1200℃, 1250℃, 1300℃, 1350℃ or 1400℃, but is not limited to the listed values, and other unlisted values ​​within the range are also applicable.

[0053] Preferably, the vacuum distillation time is 30-120 min, for example, it can be 30 min, 40 min, 50 min, 60 min, 70 min, 80 min, 90 min, 100 min, 110 min or 120 min, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0054] Preferably, the vacuum degree of the vacuum distillation is 10-1000 Pa, for example, it can be 10 Pa, 20 Pa, 30 Pa, 40 Pa, 50 Pa, 100 Pa, 200 Pa, 300 Pa, 400 Pa, 500 Pa, 600 Pa, 700 Pa, 800 Pa, 900 Pa or 1000 Pa, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0055] As a preferred embodiment of the present invention, the method includes the following steps:

[0056] (1) Grind the rare earth fluoride slag to a particle size of 30-160μm, then mix the rare earth fluoride slag and hydrochloric acid at a solid-liquid ratio of 1:(1-5)kg / L, wherein the molar ratio of rare earth elements in the rare earth fluoride slag to hydrochloric acid is 1:(5.6-15), the concentration of hydrochloric acid is 0.5-12mol / L, the mixing time is 10-120min, the temperature is 20-100℃, and then the solid and liquid are separated to obtain the first filter residue and the first filtrate containing rare earth elements;

[0057] (2) The first filter residue obtained in step (1) and the aluminum chloride-containing molten salt are mixed. The mass ratio of aluminum chloride in the first filter residue to aluminum chloride-containing molten salt is 1:(1-3). The aluminum chloride-containing molten salt includes any one or at least two of NaAlCl4, KAlCl4 or CaAlCl5. Then, the mixture is calcined at 300-800℃ for 30-180 min. After washing and solid-liquid separation, a second filtrate containing rare earth elements and a second filter residue containing fluorine elements are obtained.

[0058] The second filter residue obtained in step (2) is vacuum distilled for 30-120 minutes at a temperature of 600-1400℃ and a vacuum degree of 10-1000Pa to obtain aluminum fluoride.

[0059] Compared with the prior art, the present invention has the following beneficial effects:

[0060] (1) The method for recovering rare earth elements and fluorine from fluorine-containing rare earth slag provided by this invention can achieve efficient recovery of rare earth elements and fluorine, with a recovery rate of over 84% for rare earth elements and over 90% for fluorine. Taking praseodymium-neodymium molten salt slag and yttrium reduction slag as examples, when the fluorine-containing rare earth slag is praseodymium-neodymium molten salt slag, the recovery rate of praseodymium reaches over 94%, the recovery rate of rubidium reaches over 93%, the recovery rate of fluorine reaches over 90%, and the purity of AlF3 reaches over 99%. Under optimal conditions, the recovery rate of praseodymium is also higher. The recovery rate reaches over 95%, the recovery rate of rubidium reaches over 97%, the recovery rate of fluorine reaches over 91%, and the purity of AlF3 reaches over 99%. When the fluorine-containing rare earth slag is yttrium reduction slag, the method provided by this invention achieves a recovery rate of over 84% for yttrium, a recovery rate of over 95% for fluorine, and a purity of over 56% for AlF3. Under optimal conditions, the recovery rate of yttrium can reach over 90%, the recovery rate of fluorine can reach over 95%, and the purity of AlF3 can reach over 88%.

[0061] (2) The method for recovering rare earth elements and fluorine elements from fluorine-containing rare earth slag provided by the present invention is simple to operate, low in cost, clean and environmentally friendly, and has a high resource utilization rate and comprehensive recycling value. Attached Figure Description

[0062] Figure 1 This is a process flow diagram of the method for recovering rare earth elements and fluorine elements from fluorine-containing rare earth slag according to a specific embodiment of the present invention. Detailed Implementation

[0063] The technical solution of the present invention will be further illustrated below through specific embodiments. Those skilled in the art should understand that the embodiments described are merely illustrative of the present invention and should not be construed as limiting the invention in any way.

[0064] Specifically, a method for recovering rare earth elements and fluorine elements from fluorine-containing rare earth slag is provided, such as... Figure 1 As shown, fluorine-containing rare earth slag and acid solution are mixed, and then solid-liquid separation is performed to obtain a first filter residue and a first filtrate containing rare earth elements. The obtained first filter residue is mixed with aluminum chloride molten salt, and then roasted, washed and solid-liquid separated in sequence to obtain a second filtrate containing rare earth elements and a second filter residue containing fluorine.

[0065] Example 1

[0066] This embodiment provides a method for recovering rare earth elements and fluorine elements from fluorine-containing rare earth slag, the method comprising the following steps:

[0067] (1) Grind the rare earth reduction residue to a particle size of 60-154μm, then mix the rare earth reduction residue and hydrochloric acid at a solid-liquid ratio of 1:5kg / L, the concentration of the hydrochloric acid is 2mol / L, the molar ratio of rare earth elements in the rare earth reduction residue to hydrochloric acid is 1:11, the mixing time is 120min, the temperature is 25℃, and then filter to obtain the first filter residue and the first filtrate containing rare earth elements.

[0068] (2) The first filter residue obtained in step (1) and NaAlCl4 molten salt are mixed. The mass ratio of aluminum chloride in the first filter residue to NaAlCl4 molten salt is 1:2.4, and the molar ratio of sodium chloride to aluminum chloride in the NaAlCl4 molten salt is 1:1. Then, the mixture is calcined at 600℃ for 120 min, washed with water, and then filtered to obtain a second filtrate containing rare earth elements and a second filter residue containing fluorine. The main component of the second filter residue is aluminum fluoride.

[0069] The rare earth reducing slag described in this embodiment is yttrium reducing slag, and the rare earth element is yttrium. Its main components are shown in Table 1.

[0070] Table 1

[0071] mass percentage content / % 39.77 0.01 52.4737 0.0139 0.4927 0.0073 7.2171

[0072] Example 2

[0073] This embodiment provides a method for recovering rare earth elements and fluorine elements from fluorine-containing rare earth slag, the method comprising the following steps:

[0074] (1) Grind the rare earth molten salt slag to a particle size of 60-120μm, and then mix the rare earth molten salt slag and hydrochloric acid at a solid-liquid ratio of 1:2.5kg / L. The concentration of the hydrochloric acid is 6mol / L, and the molar ratio of rare earth elements in the rare earth molten salt slag to hydrochloric acid is 1:6.3. The mixing time is 120min and the temperature is 80℃. Then filter to obtain the first filter residue and the first filtrate containing rare earth elements.

[0075] (2) The first filter residue obtained in step (1) and NaAlCl4 molten salt are mixed. The mass ratio of aluminum chloride in the first filter residue to NaAlCl4 molten salt is 1:1.5, and the molar ratio of sodium chloride to aluminum chloride in NaAlCl4 molten salt is 1:1. Then, the mixture is calcined at 400°C for 120 min, washed with water, and then filtered to obtain a second filtrate containing rare earth elements and a second filter residue containing fluorine.

[0076] The second filter residue obtained in step (2) was vacuum distilled for 60 minutes at a temperature of 1000℃ and a vacuum degree of 500Pa to obtain aluminum fluoride.

[0077] The rare earth molten salt slag described in this embodiment is praseodymium-neodymium molten salt slag, and the rare earth elements are praseodymium and neodymium, the main components of which are shown in Table 2.

[0078] Table 2

[0079] mass percentage content / % 1.01 0.9 8.57 30.42 2.93 5.98 9.3 12.97 14.14 10.95

[0080] In this embodiment, the recovery rate of praseodymium was 95.8%, the recovery rate of neodymium was 97.9%, the recovery rate of fluorine was 90%, and the purity of AlF3 was 99%.

[0081] Example 3

[0082] This embodiment provides a method for recovering rare earth elements and fluorine elements from fluorine-containing rare earth slag, the method comprising the following steps:

[0083] (1) Grind the rare earth molten salt slag to a particle size of 60-120μm, then mix the rare earth molten salt slag and hydrochloric acid at a solid-liquid ratio of 1:1.5kg / L, wherein the concentration of the hydrochloric acid is 12mol / L, the molar ratio of rare earth elements in the rare earth molten salt slag to hydrochloric acid is 1:7.6, the mixing time is 10min, the temperature is 100℃, and then filter to obtain the first filter residue and the first filtrate containing rare earth elements;

[0084] (2) The first filter residue obtained in step (1) and NaAlCl4 molten salt are mixed. The mass ratio of aluminum chloride in the first filter residue to NaAlCl4 molten salt is 1:1, and the molar ratio of sodium chloride to aluminum chloride in NaAlCl4 molten salt is 1:1. Then, the mixture is calcined at 500°C for 30 min, washed with water, and then filtered to obtain a second filtrate containing rare earth elements and a second filter residue containing fluorine.

[0085] The second filter residue obtained in step (2) was vacuum distilled for 120 minutes at a temperature of 800℃ and a vacuum degree of 1000Pa to obtain aluminum fluoride.

[0086] In this embodiment, the rare earth molten salt slag and rare earth elements are the same as in Example 2.

[0087] In this embodiment, the recovery rate of praseodymium was 94.2%, the recovery rate of neodymium was 98.3%, the recovery rate of fluorine was 91%, and the purity of AlF3 was 99%.

[0088] Example 4

[0089] This embodiment provides a method for recovering rare earth elements and fluorine elements from fluorine-containing rare earth slag, the method comprising the following steps:

[0090] (1) Grind the rare earth molten salt slag to a particle size of 60-120μm, then mix the rare earth molten salt slag and hydrochloric acid at a solid-liquid ratio of 1:10kg / L, wherein the concentration of the hydrochloric acid is 2mol / L, the molar ratio of rare earth elements in the rare earth molten salt slag to hydrochloric acid is 1:8.4, the mixing time is 80min, the temperature is 25℃, and then filter to obtain the first filter residue and the first filtrate containing rare earth elements;

[0091] (2) The first filter residue obtained in step (1) and CaAlCl5 molten salt are mixed. The mass ratio of aluminum chloride in the first filter residue to CaAlCl5 molten salt is 1:3, and the molar ratio of calcium chloride to aluminum chloride in the CaAlCl5 molten salt is 1:1. Then, the mixture is calcined at 600°C for 180 min, washed with water, and then filtered to obtain a second filtrate containing rare earth elements and a second filter residue containing fluorine.

[0092] The second filter residue obtained in step (2) was vacuum distilled for 30 minutes at a temperature of 1400℃ and a vacuum degree of 10Pa to obtain aluminum fluoride.

[0093] In this embodiment, the rare earth molten salt slag and rare earth elements are the same as in Example 2.

[0094] In this embodiment, the recovery rate of praseodymium was 96.1%, the recovery rate of neodymium was 93.4%, the recovery rate of fluorine was 93%, and the purity of AlF3 was 99%.

[0095] As can be seen from Examples 2-4, when the fluorine-containing rare earth slag is praseodymium-neodymium molten salt slag, the method provided by the present invention for recovering rare earth elements and fluorine elements from fluorine-containing rare earth slag achieves a praseodymium recovery rate of over 94%, a rubidium recovery rate of over 93%, a fluorine recovery rate of over 90%, and an AlF3 purity of over 99%. Under more favorable conditions, the praseodymium recovery rate reaches over 95%, the rubidium recovery rate reaches over 97%, the fluorine recovery rate reaches over 91%, and the AlF3 purity reaches over 99%.

[0096] Example 5

[0097] This embodiment provides a method for recovering rare earth elements and fluorine elements from fluorine-containing rare earth slag. The only difference from Example 1 is that the concentration of hydrochloric acid is 0.8 mol / L, and the molar ratio of rare earth elements to hydrochloric acid in the rare earth reduction slag is 1:4.4.

[0098] Example 6

[0099] This embodiment provides a method for recovering rare earth elements and fluorine elements from fluorine-containing rare earth slag. The only difference from Embodiment 1 is that the mass ratio of the first filter residue to aluminum chloride in the NaAlCl4 molten salt is 1:1.4.

[0100] Comparative Example 1

[0101] This comparative example provides a method for recovering rare earth elements and fluorine elements from fluorine-containing rare earth slag, the only difference from Example 1 is that step (1) is omitted.

[0102] Comparative Example 2

[0103] This comparative example provides a method for recovering rare earth elements and fluorine elements from fluorine-containing rare earth slag. The only difference from Example 1 is that the NaAlCl4 molten salt in step (2) is replaced with AlCl3, and the mass of AlCl3 is the same as the mass of AlCl3 contained in the NaAlCl4 molten salt.

[0104] Comparative Example 3

[0105] This comparative example provides a method for recovering rare earth elements and fluorine elements from fluorine-containing rare earth slag. The only difference from Example 1 is that the NaAlCl4 molten salt in step (2) is replaced with lithium carbonate.

[0106] In Comparative Example 3, lithium carbonate was used instead. Although fluorine can be recovered in the form of lithium fluoride, the price of lithium carbonate is much higher than that of NaAlCl4 molten salt. Therefore, the method described in this invention uses aluminum chloride-containing molten salt to recover fluorine, which is low-cost and has high economic and social benefits.

[0107] The recovery rate of a certain rare earth element (yttrium in Examples 1, 5-6 and Comparative Examples 1-2, and praseodymium and rubidium in Examples 2-4) contained in the fluorine-containing rare earth slags (yttrium reduction slag in Examples 1, 5-6 and Comparative Examples 1-2, and praseodymium and rubidium in Examples 2-4) was determined. The determination method was as follows: the fluorine-containing rare earth slag (mass m1) was dissolved to obtain a sample solution, and the mass fraction ω1 of the rare earth element in the sample solution was determined.

[0108] A mass of m1 containing fluorine-containing rare earth slag was treated according to the methods described in Examples 1-6 and Comparative Examples 1-2. The volume (V1) of the first filtrate and the concentration c1 of the rare earth element in the first filtrate were measured. The volume (V2) of the second filtrate and the concentration c2 of the rare earth element in the second filtrate were measured. The concentration of the rare earth element was determined by inductively coupled plasma atomic emission spectrometry (ICP). The method for calculating the recovery rate of the rare earth element is as follows, and the data of Examples 1, 5-6 and Comparative Examples 1-2 are shown in Table 3.

[0109]

[0110] The recovery rate of fluorine in the metal fluorides of the rare earth slag containing fluorine in Examples 1-6 and Comparative Examples 1-2 (yttrium reduction slag in Examples 1, 5-6 and Comparative Examples 1-2, and praseodymium-rubidium molten salt slag in Examples 2-4) was determined. The determination method was as follows: take the rare earth slag containing fluorine (mass m2) and determine the mass fraction ω2 of fluorine in the metal fluorides contained in the rare earth slag containing fluorine.

[0111] Fluorine-containing rare earth slag with a mass of m2 was treated according to the methods described in Examples 1-6 and Comparative Examples 1-2. The mass of the second filter residue m3 and the mass fraction of fluorine ω3 in the second filter residue were determined. The mass fraction of fluorine was determined according to the method in GB / T34500.1-2017. The method for calculating the fluorine recovery rate is as follows, and the data of Examples 1, Examples 5-6 and Comparative Examples 1-2 are shown in Table 3.

[0112]

[0113] The purity of aluminum fluoride in Examples 1-6 and Comparative Examples 1-2 was determined by dissolving the second filter residue according to the method specified in GB / T34500.1-2017, and then determining the mass content of Al ω4 in the second filter residue by ICP. The calculation method of aluminum fluoride purity is as follows, and the data of Examples 1, Examples 5-6 and Comparative Examples 1-2 are shown in Table 3.

[0114] Aluminum fluoride purity = 3.11ω4

[0115] The method for recovering rare earth elements and fluorine from fluorine-containing rare earth slag provided by this invention is applicable not only to yttrium reduction slag and praseodymium-rubidium rare earth slag, but also to other rare earth reduction slags and rare earth molten salt slags. The above examples and comparative examples are only for illustrating the recovery effect of the method of this invention on rare earth elements and fluorine, as well as the purity of the obtained AlF3.

[0116] Table 3

[0117]

[0118] The following points can be observed from Table 3:

[0119] (1) As can be seen from Examples 1 and 5-6, when the fluorine-containing rare earth slag is yttrium reduction slag, the method provided by the present invention for recovering rare earth elements and fluorine elements from fluorine-containing rare earth slag achieves a recovery rate of over 84% for yttrium, a recovery rate of over 95% for fluorine, and a purity of over 56% for AlF3. Under better conditions, the recovery rate of yttrium can reach over 90%, the recovery rate of fluorine can reach over 95%, and the purity of AlF3 can reach over 88%.

[0120] (2) A comprehensive comparison of Examples 1 and 5 shows that the molar ratio of rare earth elements to hydrochloric acid in the rare earth reduction residue of Example 1 is 1:11, which is higher than the molar ratio of rare earth elements to hydrochloric acid of 1:4.4 in the rare earth reduction residue of Example 5. This indicates that the present invention preferably controls the molar ratio of rare earth elements to hydrochloric acid in the rare earth reduction residue, which can help recover rare earth elements and improve the purity of AlF3.

[0121] (3) A comprehensive comparison of Examples 1 and 6 shows that in Example 1, the mass ratio of the first filter residue to aluminum chloride in the NaAlCl4 molten salt is 1:2.4. Compared with the mass ratio of the first filter residue to aluminum chloride in the NaAlCl4 molten salt of Example 6, which is 1:1.4, the recovery rate of rare earth elements and the purity of AlF3 in Example 1 are higher than those in Example 6. This indicates that the present invention preferably controls the mass ratio of the first filter residue to aluminum chloride in the aluminum chloride-containing molten salt, which is beneficial to the recovery of rare earth elements and the improvement of the purity of AlF3.

[0122] (4) A comprehensive comparison of Example 1 and Comparative Example 1 shows that the only difference between Comparative Example 1 and Example 1 is that step (1) is not performed. The recovery rate of rare earth elements and the purity of AlF3 in Example 1 are higher than those in Comparative Example 1. This indicates that the present invention, by mixing fluorine-containing rare earth slag with acid, and then performing a combination of operations such as mixing with aluminum chloride molten salt, roasting, washing and solid-liquid separation, is conducive to fully recovering rare earth elements and improving the purity of AlF3.

[0123] (5) A comprehensive comparison of Example 1 and Comparative Example 2 shows that the only difference between Comparative Example 2 and Example 1 is that the NaAlCl4 molten salt in step (2) is replaced with AlCl3. The recovery rate of rare earth elements and the purity of AlF3 in Example 1 are higher than those in Comparative Example 2. This indicates that by using aluminum chloride molten salt mixed with the first filter residue, the present invention can prevent aluminum chloride from volatilizing, which is conducive to the full recovery of rare earth elements and improves the purity of AlF3.

[0124] In summary, the method for recovering rare earth elements and fluorine from fluorine-containing rare earth slag provided by this invention can achieve highly efficient recovery of rare earth elements and fluorine, with a recovery rate of over 84% for rare earth elements and over 90% for fluorine. When the fluorine-containing rare earth slag is praseodymium-neodymium molten salt slag, the recovery rate of praseodymium reaches over 94%, the recovery rate of rubidium reaches over 93%, the recovery rate of fluorine reaches over 90%, and the purity of AlF3 reaches over 99%. Under optimal conditions, the recovery rate of praseodymium reaches over 95%, and the recovery rate of rubidium reaches over 90%. The recovery rate of rare earth elements and fluorine is over 97%, the recovery rate of fluorine is over 91%, and the purity of AlF3 is over 99%. When the fluorine-containing rare earth slag is yttrium reduction slag, the method for recovering rare earth elements and fluorine from fluorine-containing rare earth slag provided by this invention achieves a yttrium recovery rate of over 84%, a fluorine recovery rate of over 95%, and an AlF3 purity of over 56%. Under optimal conditions, the yttrium recovery rate can reach over 90%, the fluorine recovery rate can reach over 95%, and the AlF3 purity can reach over 88%.

[0125] The applicant declares that the above description is only a specific embodiment of the present invention, but the protection scope of the present invention is not limited thereto. Those skilled in the art should understand that any changes or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in the present invention fall within the protection and disclosure scope of the present invention.

Claims

1. A method for recovering rare earth elements and fluorine elements from fluorine-containing rare earth slag, characterized in that, The method includes the following steps: (1) Mix the fluorine-containing rare earth slag and acid solution, and then separate the solid and liquid to obtain the first filter residue and the first filtrate containing rare earth elements; (2) The first filter residue obtained in step (1) and the aluminum chloride molten salt are mixed and then roasted, washed and separated in sequence to obtain the second filtrate containing rare earth elements and the second filter residue containing fluorine elements. In step (2), the mass ratio of the first filter residue to aluminum chloride in the aluminum chloride-containing molten salt is 1:(1.6-3); The aluminum chloride-containing molten salt in step (2) includes any one or a combination of at least two of NaAlCl4, KAlCl4, or CaAlCl5.

2. The method according to claim 1, characterized in that, The fluorine-containing rare earth slag in step (1) is ground before mixing.

3. The method according to claim 2, characterized in that, The particle size of the ground fluorine-containing rare earth slag is 30-160 μm.

4. The method according to claim 1, characterized in that, The fluorine-containing rare earth slag includes rare earth reduction slag and / or rare earth molten salt slag.

5. The method according to claim 1, characterized in that, The acid solution in step (1) includes hydrochloric acid.

6. The method according to claim 5, characterized in that, The molar ratio of rare earth elements to hydrochloric acid in the fluorine-containing rare earth slag is 1:(5.6-15).

7. The method according to claim 5, characterized in that, The concentration of the hydrochloric acid is 0.5-12 mol / L.

8. The method according to claim 1, characterized in that, The solid-liquid ratio of the fluorine-containing rare earth slag to the acid solution is 1:(1-10)kg / L.

9. The method according to claim 8, characterized in that, The solid-liquid ratio of the fluorine-containing rare earth slag to the acid solution is 1:(1-5)kg / L.

10. The method according to claim 1, characterized in that, The mixing time in step (1) is 10-120 min.

11. The method according to claim 1, characterized in that, The mixing temperature in step (1) is 20-100℃.

12. The method according to claim 1, characterized in that, The roasting temperature in step (2) is 300-800℃.

13. The method according to claim 1, characterized in that, The roasting time in step (2) is 30-180 min.

14. The method according to claim 1, characterized in that, The second filter residue obtained in step (2) is subjected to vacuum distillation to obtain aluminum fluoride.

15. The method according to claim 14, characterized in that, The temperature of the vacuum distillation is 600-1400℃.

16. The method according to claim 14, characterized in that, The vacuum distillation time is 30-120 minutes.

17. The method according to claim 14, characterized in that, The vacuum degree of the vacuum distillation is 10-1000 Pa.

18. The method according to claim 1, characterized in that, The method includes the following steps: (1) Grind the rare earth fluoride slag to a particle size of 30-160 μm, then mix the rare earth fluoride slag and hydrochloric acid at a solid-liquid ratio of 1:(1-5) kg / L, wherein the molar ratio of rare earth elements to hydrochloric acid in the rare earth fluoride slag is 1:(5.6-15), the concentration of hydrochloric acid is 0.5-12 mol / L, the mixing time is 10-120 min, the temperature is 20-100℃, and then the solid and liquid are separated to obtain the first filter residue and the first filtrate containing rare earth elements; (2) The first filter residue obtained in step (1) and the aluminum chloride-containing molten salt are mixed. The mass ratio of aluminum chloride in the first filter residue to that in the aluminum chloride-containing molten salt is 1:(1.6-3). The aluminum chloride-containing molten salt includes any one or at least two of NaAlCl4, KAlCl4 or CaAlCl5. Then, the mixture is calcined at 300-800℃ for 30-180 min. After washing and solid-liquid separation, a second filtrate containing rare earth elements and a second filter residue containing fluorine elements are obtained. The second filter residue obtained in step (2) is vacuum distilled for 30-120 minutes at a temperature of 600-1400℃ and a vacuum degree of 10-1000Pa to obtain aluminum fluoride.

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