A method and apparatus for purifying excess magnesium metal from the reduction reaction of Zr metal.

Abstract

This invention discloses a method and apparatus for purifying excess magnesium metal from a Zr reduction reaction, belonging to the field of magnesium molten metal purification technology. The invention uses excess magnesium metal or magnesium alloy from the production of zirconium metal via a magnesothermic reduction reaction as raw material. Under a protective atmosphere, the mixture is heated to 700℃~720℃ and smelted to obtain a magnesium melt. Sodium fluorotitanate is added to the magnesium melt under stirring, resulting in a redox reaction to obtain elemental titanium. Simultaneously, the elemental titanium reacts with iron impurities in the magnesium melt to form iron-containing compounds TiFe and TiFe2 precipitates, yielding an iron-removed melt. The iron-removed melt is then filtered through a multi-media filter layer to obtain pure magnesium molten metal.

Description

Technical Field

[0001] This invention relates to the field of magnesium metal melt purification technology, specifically to a method and apparatus for purifying excess magnesium metal from a Zr reduction reaction. Background Technology

[0002] Zirconium metal possesses excellent nuclear properties, making it an indispensable material in the nuclear industry. Its unique characteristic lies in its very low thermal neutron absorption cross section, only 0.18 × 10⁻⁶. -28 m 2 Zirconium sponge does not absorb or waste thermal neutrons during nuclear reactions and is widely used in nuclear fuel cladding materials and reactor structural materials. Currently, the production of metallic zirconium mainly includes three methods: magnesothermic reduction, molten salt electrolysis, and zirconium iodide thermal dissociation. Among these, magnesothermic reduction remains the most important method for producing sponge zirconium, and no other process has yet been able to replace it.

[0003] The main raw materials for producing nuclear-grade sponge zirconium using the magnesothermic reduction method (Kroll process) are zirconium tetrachloride (ZrCl4), metallic magnesium, and high-purity argon. To ensure the quality of the sponge zirconium product, strict requirements are placed on the raw material zirconium tetrachloride, with particular emphasis on controlling the permissible impurity content. The purity of magnesium is generally required to be ≥99.5%. Since zirconium is a typical transition metal with multiple valence states, the reduction of its compounds usually occurs stepwise, first from a higher valence compound to a lower valence compound, and then reduced to the metal. To ensure complete reaction of zirconium tetrachloride, an excess of metallic magnesium is usually added. Therefore, in the magnesothermic reduction reaction, approximately 30% more magnesium than the required amount is generally used.

[0004] The products of the magnesothermic reduction reaction are a mixture of zirconium, magnesium chloride, and residual magnesium. Typically, the zirconium produced by reduction contains approximately 30% MgCl2 and approximately 8% Mg. Because a large amount of chloride solidifies with the metal during the reduction reaction, vacuum distillation is required. This method utilizes the vapor pressure difference between zirconium and magnesium chloride / magnesium under high temperature and vacuum conditions to separate zirconium from magnesium chloride and metallic magnesium. The metallic magnesium obtained after distillation often contains residual magnesium chloride and other impurities, such as Fe.

[0005] Traditional processes for removing magnesium chloride inclusions mostly employ refining agents, relying on fluxes primarily composed of chloride salts to adsorb and capture solid inclusions. However, the removal efficiency depends on the degree of mixing and contact between the flux and the molten magnesium. Because their physical properties are vastly different, achieving truly thorough mixing is difficult, thus failing to achieve satisfactory removal results. Furthermore, during flux refining, the chloride salts in the flux release toxic and harmful gases such as Cl2 and HCl at high temperatures, causing severe pollution, residue buildup, secondary contamination of the melt, and the formation of solvent inclusions.

[0006] In addition, during the magnesium reduction process for zirconium production, the main sources of iron impurities are twofold: firstly, iron impurities introduced by zirconium tetrachloride and the reducing agent metallic magnesium; and secondly, the reaction of gaseous zirconium tetrachloride with liquid magnesium to form sponge zirconium occurs at approximately 900°C. Furthermore, the solubility of Fe in liquid magnesium reaches 0.2% to 0.23% within the 900°C to 950°C temperature range. Therefore, prolonged contact between liquid magnesium and the stainless steel crucible leads to Fe dissolution and its entry into the liquid magnesium. Currently, commonly used iron removal methods employ elemental or compound forms of Mn, Ti, Zr, Be, and B as iron-removing agents to reduce Fe content. However, using these agents introduces new inclusions during iron removal, and iron removal typically requires high temperatures, which increases magnesium loss and raises smelting production costs. Summary of the Invention

[0007] This invention provides a method and apparatus for purifying excess magnesium metal from the reduction reaction of Zr metal. It effectively solves the technical problems that existing purification methods cannot effectively remove impurity iron, that existing iron removal agents will introduce new impurities, and that the use of refining agents to remove magnesium chloride inclusions will produce harmful gases. At the same time, it provides a method and apparatus for purifying excess magnesium metal from the reduction reaction of Zr metal that has high impurity removal efficiency, low cost and simple process.

[0008] The first objective of this invention is to provide a method for purifying excess magnesium metal from a Zr reduction reaction, comprising the following steps: Excess magnesium or magnesium alloy produced from the magnesium thermal reduction reaction of zirconium is used as raw material. Under a protective atmosphere, the mixture is heated to 700℃~720℃ and smelted to obtain magnesium liquid. Sodium fluorotitanate is added to the magnesium liquid under stirring to induce a redox reaction and obtain elemental titanium. At the same time, the elemental titanium reacts with iron impurities in the magnesium liquid to form iron-containing compounds TiFe and TiFe2 precipitates, resulting in an iron-free melt.

[0009] The iron-removing melt is filtered through a multi-media filter layer to remove magnesium chloride, resulting in purified metallic magnesium melt.

[0010] In a preferred embodiment, the amount of sodium fluorotitanate used is 0.1% to 1% based on the mass of the magnesium liquid.

[0011] In a preferred embodiment, the protective atmosphere is a CO2 / SF6 mixed atmosphere or an Ar / SF6 mixed atmosphere, which is used to protect the molten magnesium from oxidation.

[0012] In a preferred embodiment, the flow rate of the protective atmosphere is 10 mL / min to 20 mL / min, the volume ratio of CO2 to SF6 is 100:1, and the volume ratio of Ar to SF6 is 100:1.

[0013] As a preferred embodiment, before smelting, the excess metallic magnesium or magnesium alloy produced by the magnesium thermal reduction reaction to produce metallic zirconium is preheated with sodium fluorotitanate to 150°C~200°C.

[0014] In a preferred embodiment, the heating rate is 20℃ / min to 25℃ / min, and the redox reaction time is 30min to 90min.

[0015] A second objective of this invention is to provide a purification device for excess magnesium metal from a Zr reduction reaction, used to implement the purification method for excess magnesium metal from a Zr reduction reaction as described in any of the preceding claims, comprising: A melting furnace, wherein a sodium fluorotitanate dosing device and a gas supply device are connected and installed inside the melting furnace.

[0016] A negative pressure filtration and purification furnace includes a storage chamber, a multi-media filter layer, and a stationary chamber; a melt transfer device is provided between the storage chamber and the melting furnace, the inlet of the melt transfer device is connected to the melting furnace, and the outlet of the melt transfer device is connected to the storage chamber; the multi-media filter layer is located below the storage chamber, and the stationary chamber is located below the multi-media filter layer.

[0017] Excess magnesium is smelted into molten magnesium in the melting furnace. The gas supply device provides a protective atmosphere and sodium fluorotitanate is added through the sodium fluorotitanate dosing device to precipitate impurity iron. The melt transfer device is used to transfer the iron-removed melt to the storage chamber. The multi-media filter layer filters the iron-removed melt into the stationary chamber to obtain purified magnesium molten metal.

[0018] In a preferred embodiment, the multi-media filter layer comprises, from top to bottom, a first filter screen, a zirconium sponge layer, a third filter screen, and graphite paper. The graphite paper is used to seal the connection points of the device at high temperatures.

[0019] In a preferred embodiment, the first filter screen is a 50-100 mesh screen, the sponge zirconium layer has a porous structure with a porosity of 30%-50%, and the third filter screen is a 100-300 mesh screen. The first filter screen has low filtration resistance and high flow efficiency of the magnesium melt, which is conducive to the smooth passage of the magnesium melt. At the same time, it can filter out inclusions such as MgCl2 and MgO with a size of 150μm-300μm. The sponge zirconium layer adsorbs and removes inclusions such as MgCl2 and MgO smaller than 150μm, and can also adsorb and remove residual fine iron-containing particles such as TiFe or TiFe2, further reducing the amount of impurity iron in the magnesium melt. The third filter screen filters out even finer inclusions such as MgCl2 and MgO with a size of less than 40μm-150μm, further reducing the amount of MgCl2 and MgO inclusions in the magnesium melt.

[0020] In a preferred embodiment, the melt transfer device is a siphon tube, which is covered with an insulation layer.

[0021] Compared with the prior art, the beneficial effects of the present invention are as follows: This invention provides a method for purifying excess magnesium metal from the Zr reduction reaction. Using excess magnesium metal or magnesium alloy from the production of zirconium metal via magnesothermal reduction as raw material, the mixture is smelted at 700℃~720℃ under a protective atmosphere to obtain a magnesium melt. Sodium fluorotitanate is added to the magnesium melt under stirring, resulting in a redox reaction to obtain elemental titanium. Simultaneously, the elemental titanium reacts with iron impurities in the magnesium melt to form iron-containing compounds TiFe and TiFe2 precipitates, yielding an iron-removed melt. The iron-removed melt is then filtered through a multi-media filter to obtain a pure magnesium melt. This invention adds sodium fluorotitanate (Na2TiF6) to the molten magnesium melt. Na2TiF6 has a low melting point (approximately 700℃) and decomposes more quickly in the magnesium melt. Na2TiF6 can react with magnesium metal to form Ti, and Ti forms a solid deposit with Fe to achieve iron removal. It can also refine the magnesium metal, solving the technical problems of existing purification methods failing to effectively remove iron impurities, the introduction of new impurities with existing iron removal agents, and the generation of harmful gases when using refining agents to remove magnesium chloride inclusions.

[0022] This invention also provides a purification device for excess magnesium metal from the reduction reaction of Zr metal, including a melting furnace with a sodium fluorotitanate dosing device and a gas supply device connected within it; it also includes a negative pressure filtration purification furnace, which includes a storage chamber, a multi-media filter layer, and a settling chamber; a melt transfer device is provided between the storage chamber and the melting furnace, with its inlet connected to the melting furnace and its outlet connected to the storage chamber. In the melting furnace, excess magnesium metal is melted into molten magnesium. The gas supply device provides a protective atmosphere, and sodium fluorotitanate is added through the sodium fluorotitanate dosing device to precipitate impurity iron. The melt transfer device is used to transfer the iron-removed melt to the storage chamber, and the multi-media filter layer filters the iron-removed melt into the settling chamber to obtain pure magnesium metal melt. This invention integrates iron removal purification smelting, a gas supply device (mainly used for charging protective gas), multi-media filtration, negative pressure filtration purification, and melt collection and settling processes into one integrated process. This invention adjusts the filtration speed by regulating the negative pressure according to the inclusions in the original magnesium metal or the viscosity of the magnesium alloy, ensuring that the molten magnesium can smoothly pass through the multi-media filter layer and enter the static chamber. The multi-media filter layer effectively removes non-metallic inclusions and particles larger than 2μm and reduces the content of the impurity element iron.

[0023] Compared with existing purification technologies, this invention features a shorter process control, simpler operation, improved purification quality of magnesium molten metal, increased production efficiency, and reduced production costs. This invention has a wide range of applications, applicable to various grades of commercial magnesium alloys, such as AZ, ZM, ZK, and AM series, as well as rare-earth-containing magnesium alloys. Attached Figure Description

[0024] Figure 1 This is a schematic diagram of the purification device for excess magnesium metal in the Zr reduction reaction provided by the present invention. In the diagram, 1 is a gas supply device, 2 is a melting furnace, 3 is a sodium fluorotitanate dosing device, 4 is a melt transfer device, 5 is a storage chamber, 6 is a multi-media filter layer, 61 is a first filter screen, 62 is a sponge zirconium layer, 63 is a third filter screen, 64 is graphite paper, 7 is a static chamber, 8 is a vacuum buffer, 9 is a control valve, and 10 is a vacuum pump.

[0025] Figure 2 This is a comparison chart of the purity of magnesium metal before and after filtration through a multi-media filter layer in the purification device for excess magnesium metal from the Zr reduction reaction of the present invention.

[0026] Figure 3 The figure shows the effect of using a second filter with different pore sizes on the size and volume fraction of inclusions in AZ91 alloy in Example 4 of the present invention. (a) The figure shows the average volume fraction of inclusions when using a second filter with different pore sizes, and (b) The figure shows the percentage of inclusions of different sizes.

[0027] Figure 4 This illustrates the effect of the size of inclusions in the AZ91 alloy on the properties of the AZ91 alloy in Example 4 of the present invention. Detailed Implementation

[0028] To enable those skilled in the art to better understand and implement the technical solutions of this invention, the invention is further described below with reference to specific embodiments. However, the embodiments are not intended to limit the invention. Unless otherwise specified, the following test methods and detection methods are conventional methods; unless otherwise specified, the reagents and raw materials are commercially available.

[0029] The purification method for residual magnesium from the reduction reaction of Zr metal comprises the following four parts. The first step is vacuum distillation recovery. Utilizing the low boiling point of magnesium (approximately 1090℃), the mixture of sponge zirconium and residual magnesium after the reduction reaction is placed in a vacuum distillation furnace and heated to 1100℃~1200℃ under vacuum (pressure <10Pa) to vaporize the residual pure magnesium. The magnesium vapor is then cooled into liquid or solid magnesium using a condensation system (such as a water-cooled condenser), achieving separation from the sponge zirconium. The second step is secondary treatment of the magnesium residue after distillation. A small amount of magnesium (usually <5%) remains after vacuum distillation, adhering to the surface of the sponge zirconium or forming residue in the form of compounds such as MgCl2 and MgO. If the MgCl2 content in the residue is high, it can be removed by water washing or acid washing, yielding pure sponge zirconium. The filtrate is then evaporated and crystallized to recover MgCl2. The third step is environmental treatment and tail gas recovery. During vacuum distillation, a small amount of magnesium vapor may leak or MgCl2 may volatilize, forming magnesium-containing tail gas. An adsorption filtration device (such as an activated carbon adsorption bed or ceramic filter element) is installed at the distillation tail gas outlet to capture magnesium vapor and MgCl2 particles in the tail gas. The adsorbed magnesium compounds can be returned to the secondary treatment process for further magnesium recovery. The fourth step is to test the quality of the recovered magnesium and evaluate its reuse according to standards. For pure magnesium recovered by vacuum distillation, its purity (content of impurity elements such as Fe, Si, and Cl) and moisture content need to be tested to ensure that it meets the quality requirements of magnesium as a reducing agent in the sponge zirconium reduction process (usually requiring Mg purity ≥ 99.8% and impurities ≤ 0.2%). Qualified recovered magnesium can be directly fed into the ZrCl4 reduction reactor, while unqualified magnesium needs to be purified by refining (such as adding refining agents to remove impurities) before reuse to avoid impurities affecting the quality of sponge zirconium products.

[0030] To address the aforementioned problems with existing purification methods, firstly, magnesium metal often retains magnesium chloride and other impurity elements (such as Fe) that were not completely removed during distillation, and the purification process cannot effectively remove impurity iron. Secondly, using refining agents to remove magnesium chloride inclusions cannot achieve satisfactory impurity removal, and these refining agents release toxic and harmful gases such as Cl2 and HCl at high temperatures, causing severe pollution, residues, secondary contamination of the melt, and solvent inclusions. Thirdly, existing iron removal agents introduce new inclusions during iron removal, and iron removal usually requires high temperatures, which increases magnesium loss and raises smelting production costs. To address these technical problems, this invention provides a method and apparatus for purifying excess magnesium metal from the Zr reduction reaction.

[0031] The technical solution of the present invention will be described in detail below.

[0032] This invention first provides a method for purifying excess magnesium metal from the reduction reaction of Zr metal, comprising the following steps: S1, through a forced-air drying oven, preheat metallic magnesium or magnesium alloy, Na2TiF6 (added at 0.1%~1% of the magnesium liquid mass), stirring components, and sodium fluorotitanate dosing device 3 to 150℃~200℃ to completely remove moisture, to obtain preheated metallic magnesium or magnesium alloy and dried Na2TiF6.

[0033] S2. Place preheated metallic magnesium or magnesium alloy into a stainless steel crucible in melting furnace 2. Introduce a CO2 / SF6 mixed gas (Ar / SF6 mixed gas) with a flow rate of 10 mL / min to 20 mL / min and a volume ratio of 100:1. Simultaneously, raise the temperature to 700℃ to 720℃ at a rate of 20℃ / min to 25℃ / min and hold for 10 min to completely melt the metallic magnesium or magnesium alloy. Obtain magnesium liquid. Evenly sprinkle dried Na2TiF6 onto the surface of the magnesium liquid while stirring for 1 min to 3 min to ensure that the added Na2TiF6 is evenly dispersed in the magnesium liquid. Hold for 30 min to 90 min to allow the iron-containing compounds TiFe and TiFe2 generated by the reaction to fully settle to the bottom of melting furnace 2, thus completing the removal of impurity iron. Then clean the slag off the surface of the magnesium liquid to obtain iron-removed melt.

[0034] S3, turn on the vacuum control system connected to the negative pressure filtration and purification furnace, so that a negative pressure of 0.1~0.5 atmospheres (0.01MPa~0.05MPa) is generated in the vacuum buffer 8, and close the valve 9 connecting the vacuum buffer 8 and the vacuum pump 10. Then, the iron-removed melt in the melting furnace 2 is transported to the storage chamber 5 of the negative pressure filtration and purification furnace through the siphon pipe 4. The temperature of the storage chamber 5 is 700℃~720℃. Open the valve at the connection between the vacuum buffer 8 and the negative pressure filtration and purification furnace, and the iron-removed melt in the storage chamber 5 enters the static chamber 7 through the multi-media filter layer 6 to obtain purified metallic magnesium or magnesium alloy melt.

[0035] like Figure 1 The present invention also provides a purification device for excess magnesium metal in the Zr reduction reaction, comprising: a sodium fluorotitanate dosing device 3, a gas supply device 1, a melting furnace 2, a stirring component, a melt transfer device 4, a negative pressure filtration purification furnace, and a vacuum control system.

[0036] The melting furnace 2 is internally connected to a sodium fluorotitanate dosing device 3 and a gas supply device 1. The melting furnace 2 includes a melting furnace body with a semi-enclosed inner cavity, a stainless steel crucible and a stirring element disposed in the inner cavity of the melting furnace body, and a first protective gas inlet.

[0037] The negative pressure filtration and purification furnace includes a storage chamber 5, a multi-media filter layer 6, and a static chamber 7. The melt transfer device 4 is a siphon tube covered with an insulation layer. The inlet of the siphon tube is connected to the melting furnace 2, and the outlet is connected to the storage chamber 5. The melt transfer device 4 is used to transfer the melt in the melting furnace 2 to the storage chamber 5 of the negative pressure filtration and purification furnace. The negative pressure filtration and purification furnace includes a storage chamber 5 with a closed inner cavity. The storage chamber 5 is surrounded by a heating and insulation sleeve. The top of the storage chamber is provided with a second protective gas inlet and an inlet for the melt transfer device 4. Below the storage chamber 5 is a multi-media filter layer 61. The upper layer of the multi-media filter layer 61 is a first filter screen made of stainless steel with a mesh size of 50 to 100 mesh. The middle layer is a sponge zirconium layer 62 (industrial-grade sponge zirconium, with a high melting point and a sponge-like porous structure with a porosity of 30% to 50%). The lower layer is a second filter screen 63 with a mesh size of 100 to 300 mesh. The stationary chamber 7 is located below the multi-media filter layer 61. Both the storage chamber furnace body and the stationary chamber body that collects pure metallic magnesium melt have flanges with a graphite paper layer in the middle. The upper and lower flanges are connected by bolts.

[0038] The first and second filter screens are stainless steel wire mesh, pure titanium filter wire mesh, or titanium-plated stainless steel wire mesh.

[0039] The negative pressure filtration and purification furnace also includes a vacuum control system, which comprises a vacuum buffer 8, a valve 9, and a vacuum pump 10. The vacuum pump 10 is connected to the vacuum buffer 8, which is connected to a stationary chamber 7. A stainless steel wire mesh is installed at the front end of the pipe connected to the vacuum buffer 8 inside the stationary chamber 7 to prevent molten magnesium from accidentally entering the vacuum control system. The vacuum control system provides a negative pressure environment, which is an absolute pressure based on absolute vacuum. The specific negative pressure value can be adjusted according to the melt mass. 1 kg to 2 kg of melt can be processed smoothly and stably within the range of 0.1 to 0.5 atmospheres (0.01 MPa to 0.05 MPa).

[0040] The technical effects of the present invention will be described below through specific embodiments.

[0041] Example 1 A method for purifying excess magnesium metal from a Zr reduction reaction includes the following steps: S1, using a forced-air drying oven, preheat the remaining metallic magnesium, Na2TiF6 (added at 0.2% wt of magnesium liquid mass), agitator, and sodium fluorotitanate dosing device 3 in the reduction of 2000g of sponge zirconium to 150℃ to completely remove moisture, and obtain preheated metallic magnesium and dried Na2TiF6.

[0042] S2. Preheated metallic magnesium is placed in a stainless steel crucible inside melting furnace 2. A CO2 / SF6 mixed gas (Ar / SF6 mixed gas) with a flow rate of 20 mL / min and a volume ratio of 100:1 is introduced. At the same time, the temperature is raised to 700℃ at a rate of 20℃ / min and held at this temperature until all the metallic magnesium is melted. After holding at this temperature for 10 min, magnesium liquid is obtained. Dry Na2TiF6 is evenly sprinkled onto the surface of the magnesium liquid while stirring for 1 min to 3 min to ensure that the added Na2TiF6 is evenly dispersed in the magnesium liquid. The mixture is then held at this temperature and allowed to stand for 60 min to allow the iron-containing compounds TiFe and TiFe2 generated in the reaction to fully settle to the bottom of melting furnace 2, thus completing the removal of impurity iron. Finally, the slag on the surface of the magnesium liquid is cleaned to obtain the iron-removed melt.

[0043] S3, turn on the vacuum control system connected to the negative pressure filtration and purification furnace to generate a negative pressure of 0.01MPa in the vacuum buffer 8, and close the valve 9 connecting the vacuum buffer 8 and the vacuum pump 10. Then, the iron-removed melt in the melting furnace 2 is transported to the storage chamber 5 of the negative pressure filtration and purification furnace through the siphon pipe 4. The storage chamber 5 is kept at 700℃. Open the valve at the connection between the vacuum buffer 8 and the negative pressure filtration and purification furnace. The iron-removed melt in the storage chamber 5 passes through the multi-media filter layer 6 (a 50-mesh first filter screen, i.e., the upper stainless steel filter screen, a middle layer of sponge zirconium blocks with an average diameter of 5mm, and a 100-mesh third filter screen, i.e., the lower stainless steel filter screen) and enters the stationary chamber 7 to obtain purified metallic magnesium melt.

[0044] Example 2 A method for purifying excess magnesium metal from a Zr reduction reaction includes the following steps: S1, using a forced-air drying oven, preheat the remaining metallic magnesium, Na2TiF6 (added at 0.25%wt of the magnesium liquid mass), agitator, and sodium fluorotitanate dosing device 3 in the reduction of 2000g of sponge zirconium to 170℃ to completely remove moisture, and obtain preheated metallic magnesium and dried Na2TiF6.

[0045] S2. Preheated metallic magnesium is placed in a stainless steel crucible inside melting furnace 2. A CO2 / SF6 mixed gas (Ar / SF6 mixed gas) with a flow rate of 15 mL / min and a volume ratio of 100:1 is introduced. At the same time, the temperature is raised to 700℃ at a rate of 22℃ / min and held at this temperature until all the metallic magnesium is melted. After holding at this temperature for 10 min, magnesium liquid is obtained. Dry Na2TiF6 is evenly sprinkled onto the surface of the magnesium liquid while stirring for 1 min to 3 min to ensure that the added Na2TiF6 is evenly dispersed in the magnesium liquid. The mixture is then kept at this temperature and allowed to stand for 60 min to allow the iron-containing compounds TiFe and TiFe2 generated in the reaction to fully settle to the bottom of melting furnace 2, thus completing the removal of impurity iron. Finally, the slag on the surface of the magnesium liquid is cleaned to obtain the iron-removed melt.

[0046] S3, turn on the vacuum control system connected to the negative pressure filtration and purification furnace to generate a negative pressure of 0.03MPa in the vacuum buffer 8, and close the valve 9 connecting the vacuum buffer 8 and the vacuum pump 10. Then, the iron-removed melt in the melting furnace 2 is transported to the storage chamber 5 of the negative pressure filtration and purification furnace through the siphon pipe 4. The storage chamber 5 is kept at 710℃. Open the valve at the connection between the vacuum buffer 8 and the negative pressure filtration and purification furnace. The iron-removed melt in the storage chamber 5 passes through the multi-media filter layer 6 (a 60-mesh first filter screen, i.e., the upper stainless steel filter screen, a middle layer of sponge zirconium blocks with an average diameter of 5mm, and a 200-mesh third filter screen, i.e., the lower stainless steel filter screen) and enters the stationary chamber 7 to obtain purified metallic magnesium melt.

[0047] Example 3 A method for purifying excess magnesium metal from a Zr reduction reaction includes the following steps: S1, using a forced-air drying oven, preheat the remaining metallic magnesium, Na2TiF6 (added at 0.4% wt of magnesium liquid mass), agitator, and sodium fluorotitanate dosing device 3 from the reduction of 2000g of sponge zirconium to 200℃ to completely remove moisture, and obtain preheated metallic magnesium and dried Na2TiF6.

[0048] S2. Preheated metallic magnesium is placed in a stainless steel crucible inside melting furnace 2. A CO2 / SF6 mixed gas (Ar / SF6 mixed gas) with a flow rate of 20 mL / min and a volume ratio of 100:1 is introduced. At the same time, the temperature is raised to 700℃ at a rate of 25℃ / min and held at this temperature until all the metallic magnesium is melted. After holding at this temperature for 10 min, magnesium liquid is obtained. Dry Na2TiF6 is evenly sprinkled onto the surface of the magnesium liquid while stirring for 1 min to 3 min to ensure that the added Na2TiF6 is evenly dispersed in the magnesium liquid. The mixture is then kept at this temperature and allowed to stand for 60 min to allow the iron-containing compounds TiFe and TiFe2 generated in the reaction to fully settle to the bottom of melting furnace 2, thus completing the removal of iron impurities. Finally, the slag on the surface of the magnesium liquid is cleaned to obtain the iron-removed melt.

[0049] S3, turn on the vacuum control system connected to the negative pressure filtration and purification furnace to generate a negative pressure of 0.05MPa in the vacuum buffer 8, and close the valve 9 connecting the vacuum buffer 8 and the vacuum pump 10. Then, the iron-removed melt in the melting furnace 2 is transported to the storage chamber 5 of the negative pressure filtration and purification furnace through the siphon pipe 4. The storage chamber 5 is kept at 720℃. Open the valve at the connection between the vacuum buffer 8 and the negative pressure filtration and purification furnace. The iron-removed melt in the storage chamber 5 passes through the multi-media filter layer 6 (a 100-mesh first filter screen, i.e., the upper stainless steel filter screen, a middle layer of sponge zirconium blocks with an average diameter of 5mm, and a 300-mesh third filter screen, i.e., the lower stainless steel filter screen) and enters the stationary chamber 7 to obtain purified metallic magnesium melt.

[0050] Example 4 A method for purifying excess magnesium metal from a Zr reduction reaction includes the following steps: S1, using a forced-air drying oven, 2000g of commercial AZ91D magnesium alloy, Na2TiF6 (added at 0.2%wt of the magnesium liquid mass), agitator, and sodium fluorotitanate dosing device 3 are preheated to 150℃ to completely remove moisture, resulting in preheated metallic magnesium and dried Na2TiF6.

[0051] S2. Preheated metallic magnesium is placed in a stainless steel crucible inside melting furnace 2. A CO2 / SF6 mixed gas (Ar / SF6 mixed gas) with a flow rate of 20 mL / min and a volume ratio of 100:1 is introduced. At the same time, the temperature is raised to 700℃ at a rate of 20℃ / min and held at this temperature until all the metallic magnesium is melted. The temperature is held for 10 min to obtain magnesium liquid. Dry Na2TiF6 is evenly sprinkled onto the surface of the magnesium liquid while stirring. The stirring is carried out for 1 min to ensure that the added Na2TiF6 is evenly dispersed in the magnesium liquid. The temperature is maintained and the mixture is allowed to stand for 60 min to allow the iron-containing compounds TiFe and TiFe2 generated in the reaction to fully settle to the bottom of melting furnace 2, thus completing the removal of impurity iron. Then, the slag on the surface of the magnesium liquid is cleaned to obtain iron-removed melt.

[0052] S3, turn on the vacuum control system connected to the negative pressure filtration and purification furnace, so that a negative pressure of 0.05MPa is generated in the vacuum buffer 8, and close the valve 9 connected to the vacuum pump 10. Then, the iron-removed melt in the melting furnace 2 is transported to the storage chamber 5 of the negative pressure filtration and purification furnace through the siphon pipe 4. The storage chamber 5 is kept at a temperature of 700℃. The valve at the connection between the vacuum buffer 8 and the negative pressure filtration and purification furnace is opened. The iron-removed melt in the storage chamber 5 passes through the multi-media filter layer 6 (a 50-mesh first filter screen, i.e., the upper stainless steel filter screen, a middle layer of sponge zirconium blocks with an average diameter of 5mm, and a third filter screen, i.e., the lower stainless steel filter screen, using 100 mesh, 150 mesh, 250 mesh and 300 mesh in four experiments respectively. The filter screen apertures of 100 mesh, 150 mesh, 250 mesh and 300 mesh stainless steel filter screens are 150μm, 100μm, 60μm and 40μm respectively) and enters the static chamber 7 to obtain the purified magnesium alloy melt.

[0053] The technical effectiveness of the purification method for excess magnesium metal in the Zr reduction reaction provided in the embodiments of the present invention was tested, and the results are as follows.

[0054] 1. The method for detecting the degree of non-metallic inclusions is as follows: The fully solidified magnesium metal is removed, and the degree of inclusions is observed and detected from the longitudinal axis. The specific method for metallographic image analysis of inclusions is as follows: The ingot is divided into three layers at equal intervals along the axial direction. The longitudinal axis of each layer is prepared using standard metallographic methods, polished with magnesium-specific gold velvet polishing cloth, and washed with water; then cleaned with alcohol for 5 seconds and dried with a hair dryer; after drying, photography is performed, and 30 fields of view (×200x) are selected from each layer. Calculations and analyses are performed on 90 randomly selected statistical fields of view to obtain the volume fraction of inclusions, the distribution of inclusions in different size ranges, and the average size and total number of inclusions in each field of view. This invention uses SISC-IAS metallographic analysis software for quantitative metallographic analysis of inclusions. Based on quantitative metallography, EDS and XRD methods are combined to detect the content of magnesium chloride or magnesium oxide inclusions.

[0055] 2. The method for detecting element Fe is: Inductively coupled plasma atomic emission spectrometry (ICP-AES) to analyze the chemical composition of metallic magnesium or magnesium alloys.

[0056] For Example 1, the magnesium chloride inclusion content was found to be 0.03% after solidification of metallic magnesium using a combination of quantitative gold EDS and XRD.

[0057] Inductively coupled plasma atomic emission spectrometry (ICP-AES) analysis showed that the Fe content of the magnesium ingot prepared in Example 1 was 0.006%, which is lower than that of magnesium without negative pressure purification treatment (Fe content was 0.008%). Using the purification method provided in Example 1 of this invention, the chemical composition of magnesium ingots before and after purification was compared, as shown in Table 1. As can be seen from Table 1, the purification method provided in Example 1 of this invention can effectively reduce the Fe content in magnesium melt. Figure 2 The results show that the multi-media filter layer can effectively intercept non-metallic inclusions and effectively remove magnesium chloride inclusions.

[0058] Table 1. Chemical composition (wt.%) of residual magnesium metal before and after purification following the reduction reaction. For Example 2, the magnesium chloride inclusion content was found to be 0.02% after solidification of metallic magnesium using a combination of quantitative gold EDS and XRD.

[0059] Inductively coupled plasma atomic emission spectrometry (ICP-AES) analysis showed that the Fe content of the obtained magnesium ingot was 0.005%, which is lower than that of magnesium without negative pressure purification treatment (Fe content was 0.008%). Using the purification method provided in Example 2 of this invention, the chemical composition of magnesium ingots before and after purification was compared, as shown in Table 2. As can be seen from Table 2, the purification method provided in Example 2 of this invention can effectively reduce the Fe content in magnesium melt.

[0060] Table 2 Chemical composition (wt.%) of residual magnesium metal before and after purification in the reduction reaction For Example 3, the magnesium chloride inclusion content was found to be 0.01% after solidification of metallic magnesium using a combination of quantitative gold EDS and XRD.

[0061] Inductively coupled plasma atomic emission spectrometry (ICP-AES) analysis showed that the Fe content of the obtained magnesium ingot was 0.004%, which is lower than that of magnesium without negative pressure purification treatment (Fe content was 0.008%). Using the purification method provided in Example 3 of this invention, the chemical composition of magnesium ingots before and after purification was compared, as shown in Table 3. As can be seen from Table 3, the purification method provided in Example 3 of this invention can effectively reduce the Fe content in magnesium melt.

[0062] Table 3 Chemical composition (wt.%) of residual magnesium metal before and after purification in the reduction reaction For Example 4, the magnesium chloride inclusion content was determined by quantitative gold analysis combined with EDS and XRD after solidification of metallic magnesium. Figure 3 .

[0063] Figure 3 This is a comparison of statistical results before and after purification treatment of commercial AZ91 alloy. After four purification treatments using stainless steel filter screens of 100 mesh, 150 mesh, 250 mesh, and 300 mesh in the lower layer of a multi-media filtration system, the average size of inclusions in the alloy decreased from 10.8 μm to 2.0 μm, and the volume fraction of inclusions decreased from 0.32% to 0.02%. After purification treatment, the size distribution range of inclusions in the alloy decreased; when the pore size of the filter media decreased to 60 μm, the size distribution range of inclusions in the alloy was 0 μm to 50 μm, while when the pore size of the media decreased to 40 μm, the size distribution range of inclusions in the alloy shrank to 0 μm to 5 μm. Through filtration and purification, the purity of the alloy was improved, and the internal quality of the alloy was enhanced.

[0064] Inductively coupled plasma atomic emission spectrometry (ICP-AES) analysis, as shown in Table 4, revealed that the Fe content of the obtained magnesium ingot was 0.003%, which is lower than that of magnesium without negative pressure purification treatment (Fe content was 0.005%). Using the purification method provided in Example 4 of this invention, the chemical composition of magnesium ingots before and after purification was compared, as shown in Table 4. The method of this invention can effectively reduce the Fe content in magnesium melt.

[0065] Table 4 Chemical composition (wt.%) of commercial AZ91D magnesium alloy before and after purification Commercial AZ91 magnesium alloy was tested for room temperature tensile properties after being purified under negative pressure; the tensile rate was 10. -3 s -1 .

[0066] Figure 4 The effect of inclusion size on the properties of AZ91 alloy is shown. As the average size and volume fraction of inclusions in AZ91 alloy decrease, the tensile strength, yield strength, and elongation increase from 187.4 MPa, 101.7 MPa, and 4.4% to 225.5 MPa, 117.0 MPa, and 8.0%, respectively, representing increases of 20.3%, 15.0%, and 81.8%.

[0067] Based on the four embodiments described above, as shown in Tables 1, 2, and 3, metallic magnesium without iron and impurity removal treatment has high Fe and magnesium chloride content. Using Na2TiF6 salt for iron removal assisted by a multi-media layer negative pressure purification process can significantly reduce the Fe and magnesium chloride content. Increasing the filter mesh size (i.e., decreasing the filter pore size) and increasing the negative pressure both significantly improve purification efficiency and iron and impurity removal effects. This purification result allows the metallic magnesium to meet the purity requirements of magnesium, a key raw material for industrial sponge zirconium, and is also close to the magnesium purity requirements of key raw materials for nuclear-grade sponge zirconium. (See Table 4...) Figure 3 and Figure 4 It can be seen that this invention can not only effectively remove iron and impurities from metallic magnesium, but also achieve a good effect on removing iron and impurities from commercial magnesium alloys, meeting the requirements for the use of corrosion-resistant magnesium alloys.

[0068] Obviously, those skilled in the art can make various modifications and variations to this invention without departing from its spirit and scope. Therefore, if these modifications and variations fall within the scope of the claims of this invention and their equivalents, this invention also intends to include these modifications and variations.

Claims

1. A method for purifying excess metallic magnesium from a Zr reduction reaction, characterized in that, Includes the following steps: Excess magnesium or magnesium alloy produced from the magnesium thermal reduction reaction of zirconium is used as raw material. Under a protective atmosphere, the temperature is raised to 700℃~720℃ and smelted to obtain magnesium liquid. Sodium fluorotitanate is added to the magnesium liquid under stirring to undergo a redox reaction to obtain elemental titanium. At the same time, the elemental titanium reacts with iron impurities in the magnesium liquid to form iron-containing compounds TiFe and TiFe2 precipitates, thus obtaining an iron-free melt. The iron-removing melt is filtered through a multi-media filter layer to remove magnesium chloride, resulting in purified metallic magnesium melt. The amount of sodium fluorotitanate used is 0.1% to 1% based on the mass of the magnesium solution; A purification apparatus for purifying excess magnesium metal in a Zr reduction reaction includes: A melting furnace (2) is provided with a sodium fluorotitanate dosing device (3) and a gas supply device (1) connected inside the melting furnace (2). The negative pressure filtration and purification furnace includes a storage chamber (5), a multi-media filter layer (6), and a stationary chamber (7); a melt transfer device (4) is provided between the storage chamber (5) and the melting furnace (2), the inlet of the melt transfer device (4) is connected to the melting furnace (2), and the outlet of the melt transfer device (4) is connected to the storage chamber (5); the multi-media filter layer (6) is located below the storage chamber (5), and the stationary chamber (7) is located below the multi-media filter layer (6); In the melting furnace (2), excess metallic magnesium is smelted into magnesium liquid. The gas supply device (1) provides a protective atmosphere and sodium fluorotitanate is added through the sodium fluorotitanate addition device (3) to precipitate impurity iron. The melt transfer device (4) is used to transfer the iron-removed melt to the storage chamber (5). The multi-media filter layer (6) filters the iron-removed melt to the stationary chamber (7) to obtain pure metallic magnesium melt. The multi-media filter layer (6) includes, from top to bottom, a first filter screen (61), a sponge zirconium layer (62), a third filter screen (63), and graphite paper (64). The first filter screen (61) is a 50-100 mesh filter screen; the sponge zirconium layer (62) has a porous structure with a porosity of 30%-50%; the third filter screen (63) is a 100-300 mesh filter screen.

2. The method for purifying excess magnesium metal from the Zr reduction reaction according to claim 1, characterized in that, The protective atmosphere is a CO2 / SF6 mixture or an Ar / SF6 mixture.

3. The method for purifying excess magnesium metal from the Zr reduction reaction according to claim 2, characterized in that, The flow rate of the protective atmosphere is 10 mL / min to 20 mL / min, the volume ratio of CO2 to SF6 is 100:1, and the volume ratio of Ar to SF6 is 100:

1.

4. The method for purifying excess magnesium metal from the reduction reaction of metallic Zr according to claim 1, characterized in that, Before smelting, excess metallic magnesium or magnesium alloy produced from the magnesium thermal reduction reaction to metallic zirconium is preheated with sodium fluorotitanate to 150°C~200°C.

5. The method for purifying excess magnesium metal from the reduction reaction of metallic Zr according to claim 1, characterized in that, The heating rate is 20℃ / min to 25℃ / min, and the redox reaction time is 30min to 90min.

6. The method for purifying excess magnesium metal from the reduction reaction of metallic Zr according to claim 1, characterized in that, The melt transfer device (4) is a siphon tube, and the siphon tube is covered with an insulation layer.

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