A method for preparing rare earth master alloy by pyrometallurgical recovery of rare earth smelting slag

Abstract

The present invention provides a method for preparing rare earth master alloy by pyrometallurgical recovery of rare earth smelting slag, belonging to the technical field of non-ferrous metal smelting. In the process of pyrometallurgical reduction and recovery of rare earth smelting slag, pulsed direct current is introduced, so that the reduction reaction in the high-temperature molten smelting slag proceeds efficiently near the cathode of the stratified liquid interface, thereby significantly improving the pyrometallurgical reduction efficiency; the reduced rare earth metal directly diffuses and mixes with the molten aluminum liquid to form rare earth-aluminum master alloy products in one step, greatly increasing the added value of the recovered products of rare earth smelting slag.

Description

Technical Field

[0001] The invention relates to the technical field of nonferrous metal smelting, and in particular to a method for preparing a rare earth master alloy by recycling rare earth smelting slag through pyrometallurgical method. Background Art

[0002] Rare earth metals such as gadolinium (Gd), terbium (Tb), dysprosium (Dy), holmium (Ho), erbium (Er), and lutetium (Lu) generally use metallic calcium as a reducing agent due to their high melting points, and are obtained by thermal reduction with rare earth fluoride powder in a vacuum melting furnace. However, due to the spherical shape of molten metallic calcium under the action of surface tension, the contact area with rare earth oxide / fluoride powder is relatively small, and only the contact part undergoes reduction reaction, resulting in low reduction reaction efficiency. Therefore, a large amount of unreacted rare earth fluoride or small-sized rare earth metal particles often remain in the residue after smelting, which are of great recycling value.

[0003] At present, the recycling of rare earth smelting slag is mainly limited to wet recycling, that is, the rare earth smelting slag reacts with strong acid, and the rare earth elements in the smelting slag are precipitated and separated through chemical treatment; small-sized rare earth metal particles are separated by filtering through a filter, effectively realizing the recycling of rare earth smelting slag. However, with the gradual increase in environmental protection requirements and recycling costs, the value of the products obtained by wet recycling of rare earth smelting slag is even lower than the recycling cost, resulting in the problem of difficulty in recycling rare earth smelting slag and large-scale accumulation.

[0004] In addition, researchers have developed a pyrometallurgical method for recovering rare earth smelting slag. However, this method requires the design of a sophisticated reduction system, and because the Gibbs free energy required for the thermal reduction of calcium fluoride requires a relatively high temperature to achieve the forward reaction, the research is difficult. Pyrometallurgical recovery also faces the problem of high costs, so it has been in a relatively blank stage. Summary of the invention

[0005] The purpose of the present invention is to provide a method for preparing rare earth master alloy by pyrometallurgical recovery of rare earth smelting slag, which can significantly improve the thermal reduction efficiency, form a rare earth-aluminum master alloy product in one step, and greatly increase the added value of the product recovered from the hot rare earth smelting slag.

[0006] In order to achieve the above-mentioned object of the invention, the present invention provides the following technical solutions:

[0007] The present invention provides a method for preparing a rare earth master alloy by recycling rare earth smelting slag through pyrometallurgical method, comprising the following steps:

[0008] Rare earth smelting slag, calcium element and aluminum element are mixed and vacuum smelted. During the vacuum smelting process, pulse direct current is introduced to perform a reduction reaction to obtain a rare earth-aluminum intermediate alloy.

[0009] Preferably, the rare earth smelting slag is yttrium smelting slag, gadolinium smelting slag, terbium smelting slag, dysprosium smelting slag, holmium smelting slag, erbium smelting slag or lutetium smelting slag.

[0010] Preferably, the particle size of the rare earth smelting slag ≥ 10 mesh, and the particle sizes of the calcium and aluminum elements are independently ≥ 10 mesh.

[0011] Preferably, the weight ratio of the rare earth smelting slag to the calcium element is (5 - 25):1; the weight ratio of the rare earth smelting slag to the aluminum element is (1 - 5):1.

[0012] Preferably, the vacuum melting is carried out in a crucible with an electrode; the crucible is a tungsten crucible, tantalum crucible, niobium crucible or platinum crucible.

[0013] Preferably, the electrode is a tungsten rod, tantalum rod, niobium rod, platinum rod or carbon rod.

[0014] Preferably, the electrode is connected to the anode, and the crucible is connected to the cathode.

[0015] Preferably, the temperature of the vacuum melting is 1000 - 1600 °C.

[0016] Preferably, before the vacuum melting, the vacuum is pumped to a pressure ≤ 10 Pa, and then argon is filled until the pressure in the vacuum melting furnace is 100 Pa - 10000 Pa.

[0017] Preferably, the frequency of the pulsed direct current is 50 - 100 HZ, the current waveform is a square wave, the voltage is 10 - 36 V, and the energization time is 10 - 30 min.

[0018] The present invention provides a method for fire recovery of rare earth smelting slag to prepare rare earth master alloy. During the thermal reduction recovery of rare earth smelting slag, pulsed direct current is introduced into the high-temperature molten mixed slag, so that the reduction reaction in the high-temperature molten smelting slag proceeds efficiently near the cathode of the stratified liquid interface, thereby significantly improving the thermal reduction efficiency; the reduced rare earth metal directly diffuses and mixes with the molten aluminum liquid to form a rare earth-aluminum master alloy product in one step, greatly increasing the added value of the rare earth smelting slag recovery product.

[0019] Under the high temperature of smelting, the mixed rare earth smelting slag (including calcium fluoride), metal calcium and metal aluminum are all melted into liquid. Due to the density difference of metal aluminum, metal calcium and calcium fluoride slag, the high temperature molten liquid is layered according to the density, which is not conducive to the calcium thermal reduction reaction to recover the residual rare earth fluoride in the rare earth smelting slag. The present invention promotes the enrichment of anions and cations on both sides of the solution interface after layering by passing pulse direct current, so as to reduce the free energy required for the reaction and promote the reduction reaction to occur near the cathode; the promotion effect is reflected in: first, the contact interface between calcium fluoride and metal calcium molten liquid is enriched with rare earth cations, thereby promoting the reduction reaction of metal calcium and rare earth cations to obtain rare earth metal elements, significantly improving the recovery efficiency of residual rare earth oxides / fluorides in smelting slag, and intermittent pulse current can accelerate ion movement and diffusion, further improving efficiency; second, based on the direction of current electron movement, the atomic movement in the molten metal liquid is promoted, especially the diffusion of molten rare earth metal atoms into metal aluminum, which is conducive to the formation of rare earth intermediate alloys, thereby significantly improving the added value of the recovered product. The method of the present invention provides a new idea for the recovery of rare earth smelting slag, and alleviates the problem of recovery of rare earth smelting slag to a certain extent. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 This is a physical photo of the rare earth-aluminum master alloy prepared in Example 1;

[0021] Figure 2 This is a scanning electron microscope (SEM) image of the crushed rare earth smelting yttrium slag used in Example 1;

[0022] Figure 3 This is an electron backscattering (BSE) image of the crushed rare earth smelting yttrium slag used in Example 1;

[0023] Figure 4 This is a SEM image of the internal precipitation phase of the rare earth-aluminum master alloy prepared in Example 1;

[0024] Figure 5 This is the BSE diagram of the internal precipitation phase of the rare earth-aluminum master alloy prepared in Example 1. DETAILED DESCRIPTION

[0025] The present invention provides a method for preparing a rare earth master alloy by recycling rare earth smelting slag through pyrometallurgical method, comprising the following steps:

[0026] Rare earth smelting slag, calcium element and aluminum element are mixed and vacuum smelted. During the vacuum smelting process, pulse direct current is introduced to perform a reduction reaction to obtain a rare earth-aluminum intermediate alloy.

[0027] In the present invention, unless otherwise specified, the required materials or reagents are commercially available products well known to those skilled in the art.

[0028] In the present invention, the rare earth smelting slag is preferably yttrium smelting slag, gadolinium smelting slag, terbium smelting slag, dysprosium smelting slag, holmium smelting slag, erbium smelting slag or lutetium smelting slag. The present invention has no special limitation on the source, composition and acquisition method of the rare earth smelting slag, and it can be obtained from the calcium thermal reduction smelting process in a manner well-known in the art.

[0029] In the present invention, the components of the rare earth smelting slag preferably include calcium fluoride (CaF2), residual rare earth fluorides and rare earth metal particles.

[0030] In the present invention, it is preferred to perform vacuum melting after crushing the rare earth smelting slag. The particle size of the rare earth smelting slag obtained after crushing is preferably ≥10 mesh, more preferably 50 - 100 mesh. The particle sizes of the calcium and aluminum elements are preferably independently ≥10 mesh, more preferably 50 - 100 mesh. The present invention has no special limitation on the process of obtaining the rare earth smelting slag, calcium element and aluminum element with the above particle size requirements, and it can be crushed according to the process well-known in the art.

[0031] In the present invention, the weight ratio of the rare earth smelting slag to the calcium element is preferably (5 - 25):1, more preferably 20:1; the weight ratio of the rare earth smelting slag to the aluminum element is preferably (1 - 5):1, more preferably 4:1.

[0032] The present invention has no special limitation on the process of mixing the rare earth smelting slag, calcium element and aluminum element, and it can be carried out according to the process well-known in the art.

[0033] In the present invention, the vacuum melting is preferably carried out in a crucible with an electrode; the crucible is preferably a tungsten crucible, tantalum crucible, niobium crucible or platinum crucible; the electrode is preferably a tungsten rod, tantalum rod, niobium rod, platinum rod or carbon rod.

[0034] In the present invention, it is preferred to place the mixed slag obtained by mixing the rare earth smelting slag, calcium element and aluminum element in a crucible with an electrode, insert the electrode into the mixed slag, connect the electrode to the anode, connect the crucible to the cathode, place the obtained system in a vacuum melting furnace, evacuate to a pressure ≤10 Pa (more preferably 5 Pa), then fill with argon until the pressure in the vacuum melting furnace is 10 Pa - 10000 Pa, more preferably 5000 - 9000 Pa, and then start heating to carry out vacuum melting. In the present invention, argon is filled as a protective gas to isolate oxygen, while reducing the vacuum degree (increasing the pressure in the furnace) to reduce the volatilization of metallic aluminum.

[0035] In the present invention, the temperature of the vacuum melting is preferably 1000 - 1600 °C, more preferably 1450 - 1550 °C, and further preferably 1500 °C; it is preferred to heat the mixed slag to 1000 - 1600 °C and pass a pulsed direct current.

[0036] In the present invention, the frequency of the pulsed direct current is preferably 50 - 100 HZ, the current waveform is preferably a square wave, the voltage is preferably 10 - 36 V, more preferably 24 V; the energization time is preferably 10 - 30 min, more preferably 20 min.

[0037] After completing the reduction reaction, the present invention preferably cuts off the power supply and heating. After the vacuum melting furnace is cooled to a temperature ≤ 100 °C, the surface calcium fluoride slag is removed to obtain a rare earth-aluminum master alloy. The present invention has no special limitation on the cooling and removal processes, and they can be carried out according to the processes well-known in the art.

[0038] Next, the technical solutions in the present invention will be clearly and completely described in conjunction with the embodiments in the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. Based on the embodiments in the present invention, all other embodiments obtained by those of ordinary skill in the art without making creative efforts belong to the scope of protection of the present invention.

[0039] Example 1

[0040] 20 kg of calcium thermal reduction smelting yttrium slag (particle size 10 - 50 mesh) is mixed with 1 kg of calcium element (particle size 10 - 50 mesh) and 5 kg of aluminum element (particle size 10 - 50 mesh). After mixing evenly, the obtained mixed slag is loaded into a tungsten crucible with tungsten rod electrodes. The electrodes are inserted into the mixed slag, the crucible is placed in a vacuum melting furnace and connected to the power supply line, then the vacuum is pumped to make the pressure in the furnace lower than 5 Pa, and then argon is filled into the furnace to make the pressure in the furnace rise to 10000 Pa; the temperature in the furnace is heated to 1500 °C; a pulsed direct current with a square wave waveform is passed into the crucible, the voltage is 36 V, the pulse frequency is 100 HZ, and the energization time is 10 min. Then the current and heating are cut off. When the furnace temperature is reduced to below 100 °C, the furnace is opened and taken out, and the surface calcium fluoride slag is removed to obtain a yttrium-aluminum master alloy.

[0041] Example 2

[0042] 20kg of calcium thermal reduction yttrium slag (with a particle size of 50-100 meshes) is mixed with 1kg of calcium element (with a particle size of 50-100 meshes) and 5kg of aluminum element (with a particle size of 50-100 meshes). After uniform mixing, the obtained mixed slag is loaded into a tantalum crucible with a tantalum rod electrode, the electrode is inserted into the mixed slag, the crucible is placed in a vacuum melting furnace and connected to a power line, and then vacuum is evacuated to make the pressure in the furnace lower than 5Pa, and then argon is filled into the furnace to increase the pressure in the furnace to 5000Pa; the temperature in the furnace is heated to 1550°C; a pulsed direct current with a square wave waveform is introduced into the crucible, the voltage is 36V, the pulse frequency is 100HZ, and the power-on time is 20min, and then the current and heating are cut off. When the furnace temperature is reduced to less than 100°C, the furnace is opened and taken out, and the calcium fluoride slag on the surface is scraped off to obtain a yttrium-aluminum intermediate alloy.

[0043] Example 3

[0044] 10kg of calcium thermal reduction smelting dysprosium slag (with a particle size of 100-200 meshes) is mixed with 0.5kg of calcium element (with a particle size of 100-200 meshes) and 2.5kg of aluminum element (with a particle size of 100-200 meshes). After uniform mixing, the obtained mixed slag is loaded into a platinum crucible with a platinum rod electrode, the electrode is inserted into the mixed slag, the crucible is placed in a vacuum melting furnace and connected to a power line, and then vacuum is evacuated to make the pressure in the furnace lower than 5Pa, and then argon is filled into the furnace to increase the pressure in the furnace to 9000Pa; the temperature in the furnace is heated to 1450°C; pulsed direct current with a square wave waveform is introduced into the crucible, the voltage is 24V, the pulse frequency is 50HZ, and the power-on time is 20min, and then the current and heating are cut off. When the furnace temperature is reduced to less than 100°C, the furnace is opened and taken out, and the calcium fluoride slag on the surface is scraped off to obtain a dysprosium-aluminum intermediate alloy.

[0045] Characterization and performance testing

[0046] 1) Figure 1 This is a photo of the yttrium-aluminum master alloy prepared in Example 1; it shows that the method of the present invention can effectively recover the rare earth element yttrium from the calcium thermal reduction yttrium slag and prepare the yttrium-aluminum master alloy, and the obtained yttrium-aluminum master alloy has good molding and good slag-gold separation.

[0047] 2) Figure 2 The SEM image of the crushed rare earth smelting yttrium slag used in Example 1 is shown in FIG. Figure 2 It can be seen that the particle size of the rare earth smelting yttrium slag after crushing is 500μm.

[0048] 3) Figure 3 This is an electron backscatter image (BSE) of the crushed rare earth smelting yttrium slag used in Example 1. The highlighted area in the BSE image is the residual rare earth metal yttrium included in the smelting slag. Figures 2 - 3It is noted that there are residual rare earth metals in rare earth smelting slag, which have good recycling value.

[0049] 4) Figure 4 SEM image of the internal precipitation phase of the yttrium-aluminum master alloy prepared in Example 1 Figure 5 BSE image of the internal precipitation phase of the yttrium-aluminum master alloy prepared in Example 1; from Figures 4 - 5 EDS analysis, it is found that there are a large number of yttrium-containing precipitation phases in the prepared yttrium-aluminum master alloy, which proves that the method described in the present invention can prepare high-quality yttrium-aluminum master alloy.

[0050] The above are only the preferred embodiments of the present invention. It should be noted that for those of ordinary skill in the art, without departing from the principle of the present invention, several improvements and modifications can be made, and these improvements and modifications should also be regarded as the protection scope of the present invention.

Claims

1. A method for preparing rare earth master alloy by pyrometallurgical recovery of rare earth smelting slag, comprising the following steps: Mix rare earth smelting slag, calcium element and aluminum element, and carry out vacuum melting. During the vacuum melting process, pulsed direct current is introduced to carry out a reduction reaction to obtain a rare earth-aluminum master alloy; The temperature of the vacuum melting is 1000-1600 °C; the vacuum melting is carried out in a crucible with an electrode; the crucible is connected to the cathode; The current waveform of the pulsed direct current is a square wave, the frequency of the pulsed direct current is 50-100 HZ, the voltage is 10-36 V, and the energization time is 10-30 min; The rare earth smelting slag is yttrium smelting slag, gadolinium smelting slag, terbium smelting slag, dysprosium smelting slag, holmium smelting slag, erbium smelting slag or lutetium smelting slag; The weight ratio of the rare earth smelting slag to the calcium element is (5-25):1; the weight ratio of the rare earth smelting slag to the aluminum element is (1-5):1; The electrode is a tungsten rod, tantalum rod, niobium rod, platinum rod or carbon rod.

2. The method according to claim 1, wherein The particle size of the rare earth smelting slag is ≥10 mesh, and the particle sizes of the calcium element and the aluminum element are independently ≥10 mesh.

3. The method according to claim 1, characterized in that, The crucible is a tungsten crucible, tantalum crucible, niobium crucible or platinum crucible.

4. The method according to claim 1, characterized in that The electrode is connected to the anode.

5. The method according to claim 1, wherein Before carrying out the vacuum melting, evacuate to a pressure ≤10 Pa, and then fill with argon until the pressure in the vacuum melting furnace is 100 Pa-10000 Pa.

Images