One-step salt-free dry reduction process of rare earth metal oxide powder

Abstract

The invention discloses a one-step salt-free dry reduction process of rare earth metal oxide powder, which comprises the following steps: S1, polishing and cleaning a crucible and the inner wall of a furnace chamber to ensure that the crucible and the furnace chamber are clean; s2, rare earth oxide powder is put into the crucible in the step S1, and a layer of same metal blocks, metal plates or dissimilar metal with saturated vapor pressure is put on the surface of the crucible; s3, the lowermost end of the plasma gun is adjusted to be right above the crucible, and a furnace door is locked; s4, starting a mechanical pump to vacuumize a furnace chamber, and slowly filling high-purity argon when the pressure reaches 0.5-1Pa; in the smelting reduction process, only hydrogen and argon are used as working gases, other polluting gases or media are not used, the economic cost of reduction of the rare earth metal oxide can be well reduced, and generated trace hydrocarbon, sulfur hydrogen compounds and nitrogen hydrogen compounds can be removed through a tail gas filter; the pollution to the environment is greatly reduced, and the method is a green metallurgy method.

Description

Technical Field

[0001] The present invention belongs to the field of rare earth metal oxide powder reduction technology, and is used for rapid reduction of small batches of rare earth metal oxide powder and removal of non-metallic impurities to obtain rare earth metal elements in one step. Specifically, it relates to a one-step reduction and purification method for rapid reduction of rare earth metal oxide powder and removal of non-metallic impurities. Background Art

[0002] Rare earth elements, known as "industrial vitamins" for their unique optoelectronic and electromagnetic properties, play a core role in numerous high-tech fields thanks to their irreplaceable physical and chemical properties, and are of vital importance to economic, technological development, and national security. For example, cerium metal plays a crucial role in high-purity cerium sputtering targets, strongly correlated electronics, and nuclear energy. Because cerium and plutonium exhibit similar bulk structures, phase transitions, and physical and chemical properties, using cerium metal as a nuclear material analog is feasible. Neodymium metal exhibits paramagnetism and rapidly darkens in air, forming oxides. It is an essential component of permanent magnets and plays a vital role in various high-performance engines, medical applications, and other fields. Praseodymium has stronger corrosion resistance in air than lanthanum, cerium, and neodymium, but forms a brittle green oxide layer when exposed to air. Praseodymium is commonly used in electronic materials, permanent magnets, and laser materials. Lanthanum metal has a gray luster and a soft texture. It quickly loses its metallic luster when exposed to air, forming a blue oxide film, which, however, does not protect the metal and subsequently forms a white powder. Lanthanum is commonly used in piezoelectric materials, electrothermal materials, and hydrogen storage materials.

[0003] Due to their unique electronic structure, rare earth metals are extremely active and susceptible to oxidation corrosion and deterioration due to the influence of the ambient atmosphere, which seriously affects their subsequent functional applications. Rare earth metals are widely used in various industrial fields. Rapid reduction and purification of rare earth metal oxide powders to convert them into metals has significant industrial value. For actinides, the ability to quickly convert their oxides into metals in a one-step process also has great national defense significance.

[0004] Existing methods for reducing metal oxides mostly include vacuum thermal reduction, molten salt thermal reduction, and electrolysis. Examples include patents such as "CN111057850B: A method for preparing high-purity metallic lithium by vacuum thermal reduction," "CN112391653B: A method for reducing rare earth oxides to elemental rare earth metals in a chloride molten salt system," "CN85100812A: Reduction of rare earth oxides by calcium thermal reduction," and "CN1004427B: Metallothermic reduction of rare earth oxides." However, most of these methods require the introduction of molten salts or other metals, or have long reduction times and produce significant amounts of waste residue. There are also a few reports on the reduction of iron and copper oxides using hydrogen plasma, as well as on the removal of trace oxygen from rare earth gadolinium by hydrogen plasma smelting. However, to date, no technology has been reported for directly reducing rare earth oxide powders to elemental rare earth metals using hydrogen plasma smelting or arc smelting. Summary of the Invention

[0005] The purpose of the present invention is to provide a one-step salt-free dry reduction process for rare earth metal oxide powder to solve the problems of cumbersome steps, long reduction time, large amount of waste residue generated, and poor economic efficiency in the small-batch rare earth metal oxide reduction process proposed in the above-mentioned background technology, and is aimed at the reduction of metal oxide powder within 500g.

[0006] To achieve the above object, the present invention provides the following technical solution: a process for rapidly purifying and reducing rare earth metal oxide powder to prepare rare earth metals, comprising the following steps:

[0007] S1: First, polish and clean the crucible and the inner wall of the furnace chamber to ensure that the crucible and the furnace chamber are clean;

[0008] S2: placing rare earth oxide powder into the crucible described in step S1, and placing a layer of the same metal block, metal plate or dissimilar metal with saturated vapor pressure on the crucible;

[0009] S3: After step S2 is completed, adjust the lower end of the plasma gun to be directly above the crucible and lock the furnace door;

[0010] S4: After step S3 is completed, the mechanical pump is turned on to evacuate the furnace chamber. When the pressure reaches 0.5Pa-1Pa, high-purity argon gas with a purity of more than 99.99% is slowly filled in. When the pressure in the furnace chamber reaches 1500Pa-1700Pa, the argon filling is stopped;

[0011] S5: The furnace chamber after step S4 is evacuated again, and the pressure is pumped to 0.5Pa~1Pa and high vacuum is started. The high vacuum degree is 1×10 -4 When Pa, turn off the molecular pump and inflate the furnace chamber again;

[0012] S6: The furnace chamber after step S5 is vacuumed again. When the pressure is 0.5Pa-1Pa, the pre-evacuation valve is closed and high-purity argon is filled in. When the pressure is 15000Pa-17000Pa, the melting power is turned on.

[0013] S7: After completing the process of step S6, arc is started at a current of 110A, and then the current is controlled at 350A to 450A, and then a hydrogen-argon mixed gas is introduced;

[0014] S8: After completing S7, adjust the furnace chamber pressure and the ratio of hydrogen-argon mixed gas to control the furnace chamber pressure within 10,000 to 50,000 Pa and the hydrogen ratio within 10% to 25%. Under this atmosphere, according to different types of rare earth materials, control the current within 250A to 500A, smelt for 6 to 10 minutes, reduce the current to 0A, and then turn off the hydrogen-argon mixed gas. Cool the sample in a water-cooled copper crucible until it is completely cooled.

[0015] S9: After completing S8, raise the plasma gun, use the mechanical gripper to turn the metal ingot over, start vacuuming, and when the pressure reaches 0.5Pa~1Pa, slowly fill it with argon gas, and then repeat steps S7, S8, and S9;

[0016] S10: The rare earth metal sample after step S9 is subjected to multiple smelting reductions to obtain a purified reduced metal ingot, and after replacing the atmosphere in the furnace chamber, smelting is performed in a high-purity argon atmosphere to remove hydrogen in the rare earth metal;

[0017] S11: After completing step S10, the sample is subjected to low-current melting in a high-purity argon atmosphere after replacing the atmosphere in the furnace chamber to modify the surface of the rare earth metal and densify the metal surface. After the sample is cooled, a rare earth metal ingot is obtained.

[0018] Preferably, a conductive medium is added to the rare earth oxide powder of S2, and the conductive medium is one of the same metal block, metal plate, and dissimilar metals with saturated vapor pressure.

[0019] Preferably, the lowermost end of the plasma gun in S3 is located 1.5 cm to 3 cm above the crucible.

[0020] Compared with the prior art, the present invention has the following beneficial effects:

[0021] 1. The present invention uses only hydrogen and argon as working gases during the smelting reduction process, and does not utilize other polluting gases or media. This can significantly reduce the economic cost of reducing rare earth metal oxides. The extremely small amounts of hydrocarbons, sulfur hydrogen compounds, and nitrogen hydrogen compounds produced can be removed by tail gas filters, greatly reducing environmental pollution and making this a green metallurgical method.

[0022] 2. In the past, the reduction of rare earth metal oxides usually had disadvantages such as the introduction of other metals or molten salts, a long time, and a cumbersome process. This method does not introduce other impurities such as metals and non-metallic impurities, and the time required is shorter;

[0023] 3. Hydrogen plasma arc melting can achieve one-step reduction of metal oxides and effectively remove non-metallic impurities in rare earth metals. It can reduce rare earth metal oxides while purifying the metals, and has great application prospects for the reduction of transuranium metals.

[0024] 4. For the traditional reduction method, the rare earth metals obtained are directly exposed to the air to generate gray oxides on the surface. The surface oxides cannot slow down the oxidation of the rare earth metals. However, the surface of the rare earth metal ingots obtained by plasma melting can be densified due to the arc melting effect, which effectively delays the oxidation of the rare earth metals. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 It is a schematic diagram of the process flow of the present invention. DETAILED DESCRIPTION

[0026] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of the present invention.

[0027] See also Figure 1 The present invention provides a one-step salt-free dry reduction process for rare earth metal oxide powder, comprising the following steps:

[0028] S1: First, polish and clean the crucible and the inner wall of the furnace chamber to ensure that the crucible and the furnace chamber are clean;

[0029] S2: placing rare earth oxide powder into the crucible described in step S1, and placing a layer of the same metal block, metal plate or dissimilar metal with saturated vapor pressure on the crucible;

[0030] S3: After step S2 is completed, adjust the lower end of the plasma gun to be directly above the crucible and lock the furnace door;

[0031] S4: After step S3 is completed, the mechanical pump is turned on to evacuate the furnace chamber. When the pressure reaches 0.5Pa-1Pa, high-purity argon gas with a purity of more than 99.99% is slowly filled in. When the pressure in the furnace chamber reaches 1500Pa-1700Pa, the argon filling is stopped;

[0032] S5: The furnace chamber after step S4 is evacuated again, and the pressure is pumped to 0.5Pa~1Pa and high vacuum is started. The high vacuum degree is 1×10 -4 When Pa, turn off the molecular pump and inflate the furnace chamber again;

[0033] S6: The furnace chamber after step S5 is vacuumed again. When the pressure is 0.5Pa-1Pa, the pre-evacuation valve is closed and high-purity argon is filled in. When the pressure is 15000Pa-17000Pa, the melting power is turned on.

[0034] S7: After completing the process of step S6, arc is started at a current of 110A, and then the current is controlled at 350A to 450A, and then a hydrogen-argon mixed gas is introduced;

[0035] S8: After completing S7, adjust the furnace chamber pressure and the ratio of hydrogen-argon mixed gas to control the furnace chamber pressure within 10,000 to 50,000 Pa, preferably between 20,000 and 30,000 Pa, and control the hydrogen ratio to 10% to 25%. Under this atmosphere, according to different types of rare earth materials, control the current to 250A to 500A, smelt for 6 to 10 minutes, reduce the current to 0A, and then turn off the hydrogen-argon mixed gas. Cool the sample in a water-cooled copper crucible until it is completely cooled.

[0036] S9: After completing S8, raise the plasma gun, use the mechanical gripper to turn the metal ingot over, start vacuuming, and when the pressure reaches 0.5Pa~1Pa, slowly fill it with argon gas, and then repeat steps S7, S8, and S9;

[0037] S10: The rare earth metal sample after step S9 is subjected to multiple smelting reductions to obtain a purified reduced metal ingot, and after replacing the atmosphere in the furnace chamber, smelting is performed in a high-purity argon atmosphere to remove hydrogen in the rare earth metal;

[0038] S11: After completing step S10, replace the atmosphere in the furnace chamber and perform low current melting in a high-purity argon atmosphere to modify the surface of the rare earth metal and densify the metal surface. After the sample is cooled, a rare earth metal ingot is obtained.

[0039] Furthermore, the rare earth oxide powder in S2 is added with a conductive medium, and the conductive medium is one of the same metal block, metal plate, and dissimilar metals with extremely different saturated vapor pressures.

[0040] Furthermore, the lowest end of the plasma gun in S3 is located 1.5 cm to 3 cm above the crucible.

[0041] Example 1: Preparation of cerium from rare earth cerium oxide plate

[0042] A plasma arc melting furnace was used to reduce 150g of cerium metal oxide plate. The furnace chamber was purged twice with high-purity argon gas and vacuumed to 1×10 -4 Pa, filled with high-purity argon, the working hydrogen ratio was 10%, the smelting current was 350A, flipped multiple times, smelted for twenty-five minutes, and finally the surface was densified with low current; the sample lost 3.7g in weight, and the test results showed that there were a small amount of dark red granular metal particles in the obtained metal ingot, and a small amount of incomplete oxides in the metal ingot appeared dark red. The XRD analysis results showed that the composition of the obtained metal ingot was mainly cerium metal element, but contained a small amount of cerium oxide; the content of non-metallic impurities in cerium metal except oxygen was reduced from 808ppm to 216ppm. The metal ingot and the cerium metal without surface treatment were stored in an air environment for 30 days. The metal ingot still maintained a metallic luster, while the cerium metal without surface treatment had been oxidized.

[0043] Example 2: Preparation of cerium from rare earth cerium oxide plate

[0044] A plasma arc melting furnace was used to reduce 150g of cerium metal oxide plate. The furnace chamber was purged twice with high-purity argon gas and vacuumed to 1×10 -4 Pa, filled with high-purity argon, the working hydrogen ratio is 15%, the melting current is 350A, flipped multiple times, melted for 35 minutes, and finally the surface was densified with low current; after melting for 35 minutes, the sample lost 5.5g in weight, and the test results showed that the interior of the obtained metal ingot was completely silver-gray metallic luster metal. The XRD analysis results showed that the composition of the obtained metal ingot was cerium metal element, and the content of non-metallic impurities in cerium metal except oxygen dropped from 808ppm to 183ppm, and there was a dense film on its surface. The metal ingot and the cerium metal without surface treatment were stored in an air environment for 30 days. The metal ingot still maintained its metallic luster, while the metal without surface treatment had been oxidized.

[0045] Example 3: Preparation of cerium from rare earth cerium oxide powder

[0046] In a plasma arc melting furnace, 60g of cerium metal oxide powder and 85g of cerium metal oxide plate were reduced, and the furnace chamber was purged twice with high-purity argon gas and evacuated to a high vacuum of 1×10 -4Pa, filled with high-purity argon, the working hydrogen ratio was 20%, the melting current was 350A, it was turned over many times, and the melting was forty-five minutes, and finally the surface was densified with low current; the sample lost 10.9g in weight, and the test results showed that the interior of the obtained metal ingot was completely silver-gray metallic luster metal. The XRD analysis results showed that the composition of the obtained metal ingot was cerium metal element, and the content of non-metallic impurities other than oxygen dropped from 1170ppm to 268ppm, and there was a dense film on its surface. The metal ingot and the cerium metal without surface treatment were stored in an air environment for 30 days. The metal ingot still maintained its metallic luster, while the metal without surface treatment had undergone severe oxidation.

[0047] Example 4: Preparation of cerium from rare earth cerium oxide powder

[0048] In a plasma arc melting furnace, 110 g of cerium metal oxide powder and 99 g of cerium metal oxide plate were reduced, and the furnace chamber was purged twice with high-purity argon gas and evacuated to a high vacuum of 1 × 10 -4 Pa, filled with high-purity argon, the working hydrogen ratio was 25%, the melting current was 350A, it was turned over many times, and the melting was for sixty minutes, and finally the surface was densified with low current; the sample lost 18.8g in weight, and the test results showed that the interior of the obtained metal ingot was completely silver-gray metallic luster metal. The XRD analysis results showed that the composition of the obtained metal ingot was cerium metal element, and the content of non-metallic impurities other than oxygen dropped from 1170ppm to 159ppm; there was a dense film on its surface. The metal ingot and the cerium metal without surface treatment were stored in an air environment for 30 days. The metal ingot still maintained its metallic luster, while the metal without surface treatment had been oxidized.

[0049] Example 5: Preparation of Neodymium from Rare Earth Neodymium Oxide Metal Plate

[0050] A plasma arc melting furnace was used to reduce 150 g of neodymium metal oxide blocks. The furnace chamber was purged twice with high-purity argon gas and vacuumed to 1×10 -4 Pa, filled with high-purity argon, the working hydrogen ratio was 10%, the melting current was 400A, flipped multiple times, melted for thirty minutes, and finally the surface was densified with low current; the sample lost 5.5g in weight, and the test results showed that the interior of the obtained metal ingot was completely silver-gray metallic luster metal; XRD analysis results showed that the composition of the obtained metal ingot was neodymium metal element; the content of non-metallic impurities other than oxygen dropped from 910ppm to 269ppm; there was a dense film on its surface. The metal ingot and the cerium metal without surface treatment were stored in an air environment for 30 days. The metal ingot still maintained its metallic luster, while the metal without surface treatment had been oxidized.

[0051] Example 6: Preparation of Neodymium from Rare Earth Neodymium Metal Oxide Powder

[0052] In a plasma arc melting furnace, 40g of neodymium metal oxide powder and 130g of neodymium metal oxide block were reduced. The furnace chamber was purged twice with high-purity argon gas and high vacuum was drawn to 1×10 -4 Pa, filled with high-purity argon, the working hydrogen ratio was 15%, the melting current was 400A, it was turned over many times, and the melting was forty-five minutes, and finally the surface was densified with low current; the sample lost 8.7g in weight, and the test results showed that the interior of the obtained metal ingot was completely silver-gray metallic luster metal; XRD analysis results showed that the composition of the obtained metal ingot was neodymium metal element; the content of non-metallic impurities other than oxygen dropped from 1270ppm to 246ppm; there was a dense film on its surface. The metal ingot and the cerium metal without surface treatment were stored in an air environment for 30 days. The metal ingot still maintained its metallic luster, while the metal without surface treatment had been oxidized.

[0053] Example 7: Preparation of Neodymium from Rare Earth Neodymium Metal Oxide Powder

[0054] In a plasma arc melting furnace, 56.87g of neodymium metal oxide powder and 122.76g of neodymium metal oxide blocks were reduced. The furnace chamber was purged twice with high-purity argon gas and the vacuum was evacuated to 1×10 -4 Pa, filled with high-purity argon, the working hydrogen ratio was 20%, the melting current was 450A, flipped multiple times, melted for sixty minutes, and finally the surface was densified with low current; the sample lost 11.6g in weight, and the test results showed that the interior of the obtained metal ingot was completely silver-gray metallic luster metal; XRD analysis results showed that the composition of the obtained metal ingot was neodymium metal element; the carbon impurity content in the neodymium metal dropped from 1320ppm to 204ppm; there was a dense film on its surface. The metal ingot was stored in an air environment with untreated cerium metal for 30 days. The metal ingot still maintained its metallic luster, while the untreated metal had been oxidized.

[0055] Example 8: Preparation of Neodymium from Rare Earth Neodymium Metal Oxide Powder

[0056] A plasma arc melting furnace was used to reduce 93.5 g of neodymium metal oxide powder and 85.8 g of neodymium metal oxide blocks. The furnace chamber was purged twice with high-purity argon gas and vacuumed to 1 × 10 -4Pa, filled with high-purity argon, the working hydrogen ratio was 25%, the melting current was 450A, it was turned over many times, and the melting was done for seventy-five minutes, and finally the surface was densified with a low current; the sample lost 18.9g in weight, and the test results showed that the interior of the obtained metal ingot was completely silver-grey metallic luster metal; the XRD analysis results showed that the composition of the obtained metal ingot was neodymium metal element; the content of non-metallic impurities other than oxygen dropped from 1500ppm to 145ppm; there was a dense film on its surface. The metal ingot was stored in an air environment with cerium metal without surface treatment for 30 days. The metal ingot still maintained its metallic luster, while the metal without surface treatment had been oxidized.

[0057] In combination with the above embodiments, it can be seen that increasing the hydrogen content of the mixed gas and the smelting time have better effects on metal reduction and purification. However, since increasing the hydrogen ratio will cause the metal liquid in the crucible to splash, it has certain safety hazards. The hydrogen content of the mixed gas should not be continuously increased. As the rare earth metal is smelted, evaporation will occur, and the evaporated metal will adhere to the inner wall of the furnace chamber and the peep window glass. If the smelting time is too long, the metal evaporation will affect the operation and operation of the equipment.

[0058] The present invention proposes that during the generation and maintenance of an electric arc or a plasma arc, the ultra-high temperature generated will further ionize the hydrogen in the furnace chamber atmosphere into hydrogen plasma. The hydrogen plasma has extremely high reactivity and reducing properties, and can quickly reduce oxides to metals without adding a solid or liquid reducing agent. The total non-metallic elements in the oxide react with the hydrogen plasma to generate corresponding hydrides or hydride groups, which enter the furnace chamber. At the same time, due to the high surface temperature of the melt, the evaporation and removal of metal impurities with high saturated vapor pressure can be promoted. The entire treatment process has a high rate and no additional waste gas is generated except for the generated hydrides. The method can be applied to the rapid reduction of small batches of rare earth metal oxide powders within 500g to prepare metal elements. The process equipment is simple and the treatment process is green, convenient and fast.

[0059] Finally, it should be noted that the above content is only used to illustrate the technical solution of the present invention, rather than to limit the scope of protection of the present invention. Simple modifications or equivalent substitutions of the technical solution of the present invention by ordinary technicians in this field do not deviate from the essence and scope of the technical solution of the present invention.

Claims

1. A one-step salt-free dry reduction process for rare earth metal oxide powder, characterized in that: The steps include: S1: First, polish and clean the crucible and the inner wall of the furnace chamber to ensure that the crucible and the furnace chamber are clean; S2: placing rare earth oxide powder into the crucible described in step S1, and placing a layer of the same metal block, metal plate or dissimilar metal with saturated vapor pressure on the crucible; S3: After step S2 is completed, adjust the lower end of the plasma gun to be directly above the crucible and lock the furnace door; S4: After step S3 is completed, the mechanical pump is turned on to evacuate the furnace chamber. When the pressure reaches 0.5Pa-1Pa, high-purity argon gas with a purity of more than 99.99% is slowly filled in. When the pressure in the furnace chamber reaches 1500Pa-1700Pa, the argon filling is stopped; S5: The furnace chamber after step S4 is evacuated again, and the pressure is pumped to 0.5Pa~1Pa and high vacuum is started. The high vacuum degree is 1×10 -4 When Pa, turn off the molecular pump and inflate the furnace chamber again; S6: The furnace chamber after step S5 is vacuumed again. When the pressure is 0.5Pa-1Pa, the pre-evacuation valve is closed and high-purity argon is filled in. When the pressure is 15000Pa-17000Pa, the melting power is turned on. S7: After completing the process of step S6, arc is started at a current of 110A, and then the current is controlled at 350A to 450A, and then a hydrogen-argon mixed gas is introduced; S8: After completing S7, adjust the furnace chamber pressure and the ratio of hydrogen-argon mixed gas to control the furnace chamber pressure within 10,000 to 50,000 Pa and the hydrogen ratio within 10% to 25%. Under this atmosphere, according to different types of rare earth materials, control the current within 250A to 500A, smelt for 6 to 10 minutes, reduce the current to 0A, and then turn off the hydrogen-argon mixed gas. Cool the sample in a water-cooled copper crucible until it is completely cooled. S9: After completing S8, raise the plasma gun, use the mechanical gripper to turn the metal ingot over, start vacuuming, and when the pressure reaches 0.5Pa~1Pa, slowly fill it with argon gas, and then repeat steps S7, S8, and S9; S10: The rare earth metal sample after step S9 is subjected to multiple smelting reductions to obtain a purified reduced metal ingot, and after replacing the atmosphere in the furnace chamber, smelting is performed in a high-purity argon atmosphere to remove hydrogen in the rare earth metal; S11: After completing step S10, the sample is subjected to low-current melting in a high-purity argon atmosphere after replacing the atmosphere in the furnace chamber to modify the surface of the rare earth metal and densify the metal surface. After the sample is cooled, a rare earth metal ingot is obtained.

2. The one-step salt-free dry reduction process for rare earth metal oxide powder according to claim 1, characterized in that: The rare earth oxide powder in S2 is added with a conductive medium, and the conductive medium is one of the same metal block, metal plate, and dissimilar metals with saturated vapor pressure.

3. The one-step salt-free dry reduction process for rare earth metal oxide powder according to claim 1, characterized in that: The lowest end of the plasma gun in S3 is located 1.5 cm to 3 cm above the crucible.

Images