A low-cost and efficient aluminum removal method for magnesium smelting by silicon thermal method based on CaO filter material

Abstract

The present invention relates to the technical field of raw magnesium smelting, and in particular to a low-cost and efficient aluminum removal method for silicon-thermal magnesium smelting based on CaO filter material. The aluminum removal method is to use CaO filter material to purify and remove aluminum-containing impurities in magnesium vapor, comprising the following steps: heating the raw materials for silicon-thermal magnesium smelting to react to generate magnesium vapor, allowing the magnesium vapor to pass through the CaO filter material to remove aluminum-containing impurities, and then condensing and crystallizing to obtain low-aluminum high-purity magnesium. The filter material and method provided by the present invention are low-cost and can be directly grafted with the silicon-thermal method, which is the main production method of existing metallic magnesium. The use of CaO filter material can significantly reduce the impurity aluminum content in crude magnesium, with a reduction ratio of up to 90%, and the preparation cost of CaO filter material is low, and can be widely used in the purification of magnesium vapor in silicon-thermal magnesium smelting to remove aluminum-containing impurities.

Description

Technical Field

[0001] The invention relates to the technical field of raw magnesium smelting, and in particular to a low-cost and high-efficiency aluminum removal method for silicon-thermal magnesium smelting based on CaO filter material. Background Art

[0002] Magnesium metal has great application prospects in the fields of lightweight rail transit, strategic metal reducing agent, and degradable implant materials due to its high specific strength, strong reducibility, and excellent biocompatibility. However, if the impurity content of upstream raw magnesium metal is high and fluctuates greatly, it will often significantly deteriorate the performance of downstream magnesium-based materials, making its application far less than expected. Taking impure aluminum as an example, in the application of degradable implant materials, aluminum is neurotoxic and may cause Alzheimer's disease; in terms of being a reducing agent for the preparation of electronic-grade high-purity titanium, the impurity aluminum in high-purity sponge titanium is mainly inherited to magnesium metal and is difficult to remove in subsequent processes.

[0003] At present, the main production method of commercially available raw magnesium is the silicon thermal reduction method, which mainly refers to mixing calcined ochre (CaO, MgO), ferrosilicon (Si(Fe)), fluorite (CaF2) and other materials into balls, reacting them under vacuum conditions of about 1200°C and 20Pa to generate magnesium vapor, which is then condensed into crystalline magnesium. However, the raw magnesium produced by this method faces the problem of high and fluctuating impurity aluminum content.

[0004] In the early stage, some scholars have proposed that the high content and large fluctuation of impurity aluminum are related to the addition of fluorite (CaF2) to form AlF, and have given measures to "prepare metallic raw magnesium with ultra-low aluminum impurity content by reducing or even abandoning fluorite powder". Although the above method is effective, fluorite is a commonly used catalyst for magnesium smelting by silicon thermal method, which can significantly improve the reaction efficiency and the output per unit production cycle, and the method of raw material control is not easy to operate. In addition, the method of purifying magnesium in the prior art also has a vapor deposition method using filter material to assist impurity removal (CN110724825B, CN110835694B, CN110835695B), but the filter material is generally metal or semi-metal, which is costly in large-scale production applications, and mainly removes aluminum impurities in the form of a single substance, while impurity aluminum in the silicon thermal method has other forms of existence.

[0005] In view of this, it is urgent to find a method for removing aluminum that does not affect the yield, is low-cost, simple and efficient. Summary of the invention

[0006] To achieve the above-mentioned purpose, the present invention provides a low-cost and efficient aluminum removal method for silicon thermal magnesium smelting based on CaO filter material. The aluminum removal method of the present invention can be directly connected with the silicon thermal magnesium smelting production process, and the magnesium vapor generated by silicon thermal reduction is filtered through the CaO filter material or the filter structure containing the CaO coating to purify and remove aluminum impurities in the magnesium vapor.

[0007] The purpose of the present invention is to provide a low-cost and high-efficiency aluminum removal method for magnesium smelting by silicon thermal method based on CaO filter material.

[0008] According to the purpose of the present invention, the low-cost and efficient aluminum removal method for silicothermic magnesium smelting of the present invention uses CaO filter material to purify and remove aluminum-containing impurities in magnesium vapor, including the following steps: heating the raw materials for silicothermic magnesium smelting to react to generate magnesium vapor, allowing the magnesium vapor to pass through the CaO filter material to remove aluminum-containing impurities, and then condensing and crystallizing to obtain high-purity magnesium.

[0009] In the present invention, the silicon thermal magnesium smelting raw material is a ball, which contains 28.53wt.% MgO, 40.12wt.% CaO, 0.62wt.% SiO2, 0.16wt.% Al2O3, 0.28wt.% Fe2O3, 0.05wt.% MnO, 0.0005wt.% PbO, 0.001wt.% ZnO, 21.94% Si, 6.14wt.% Fe, 0.51wt.% Al, 0.276wt.% Ca, 0.023wt.% Mn, 0.0006wt.% Zn, 0.0009wt.% Pb, 0.005wt.% P, 1.32wt.% CaF2, and 0.014wt.% CaCO3. Through thermodynamic calculation of the pellets with the above components, it can be known that when the silicon thermal reduction reaction occurs, the main products of the gas phase at 1250°C are Mg, SiO, Ca, AlF (aluminum monofluoride, CAS No. 13595-82-9), CaF2, Mn, Si, Fe, etc.; and the above gas phase substances are expected to form stable compounds or single substances, such as Ca-Si-O, Ca-Al-Si-O, Ca-AlFO, Fe, Mn, etc. in the process of gradual cooling and condensation.

[0010] As for aluminum impurities, the main aluminum impurities in the high-temperature magnesium vapor produced by silicon thermal reduction of magnesium are in the form of AlF(g). It can be seen that the use of substances containing Ca and O to induce AlF co-deposition can obtain a high-aluminum precipitation phase of Ca-AlFO and remove AlF(g) in magnesium vapor. The present invention selects CaO as the filter material and calculates the reactivity between CaO and AlF(g). It can be seen that within the range of 1250-1050℃, both CaO and AlF(g) are significantly reduced, and the reduction is the largest at 1050℃; the present invention also calculates the situation of CaO after adding the entire system of magnesium vapor containing impurities in silicon thermal magnesium smelting. It can be seen that CaO significantly consumes AlF(g) in the gas phase and forms a substance Ca 12 A l 14 F2O 32Although the use of CaO filter material generates a large amount of Ca vapor in the system, the Ca vapor can be deposited and removed during the subsequent vapor cooling process, and can also be removed in large quantities during the silicon thermal magnesium refining process, and will not bring impurity effects to the crystalline magnesium system.

[0011] In the above-mentioned low-cost and high-efficiency aluminum removal method for silicon thermal magnesium smelting based on CaO filter material, preferably, the aluminum-containing impurity is AlF.

[0012] In the above-mentioned low-cost and efficient aluminum removal method for silicon thermal magnesium smelting based on CaO filter material, preferably, the working temperature of the CaO filter material is 600-1250°C; further preferably, the working temperature of the CaO filter material is 1050-1250°C.

[0013] In the above-mentioned low-cost and high-efficiency aluminum removal method for silicothermic magnesium smelting based on CaO filter material, preferably, the heating temperature of the silicothermic magnesium smelting raw material is controlled to be 1250-1300°C.

[0014] The above-mentioned low-cost and efficient aluminum removal method for silicon thermal magnesium smelting based on CaO filter material, preferably, the CaO filter material is arranged on the movement path of the magnesium vapor by natural filling or compaction using CaO raw material, and the CaO raw material is any one of block, sphere, powder, and sheet; when the CaO raw material is block, the diameter is 8 to 20 mm; when the CaO raw material is spherical, the diameter is 0.3 to 8 mm; when the CaO raw material is powder, the particle size is 1 to 300 μm; when the CaO raw material is sheet, the thickness is 0.1 to 5 mm.

[0015] In the above-mentioned low-cost and high-efficiency aluminum removal method for silicon thermal magnesium smelting based on CaO filter material, preferably, the CaO filter material is a carrier containing CaO, and the carrier is arranged on the movement path of the magnesium vapor.

[0016] The above-mentioned low-cost and high-efficiency aluminum removal method for silicon thermal magnesium smelting based on CaO filter material, preferably, the CaO filter material is coated or impregnated with CaO on a carrier, comprises the following steps:

[0017] Immersing the support in a Ca(OH)2 suspension so that the support is coated or impregnated with a Ca(OH)2 coating;

[0018] The carrier coated with Ca(OH)2 is taken out, dried and thermally decomposed to obtain the product.

[0019] In the above-mentioned low-cost and high-efficiency aluminum removal method for silicon thermal magnesium smelting based on CaO filter material, preferably, the drying temperature is 190 to 1200° C. and the drying time is 0.5 to 2 hours.

[0020] In the above-mentioned low-cost and high-efficiency aluminum removal method for silicon thermal magnesium smelting based on CaO filter material, preferably, the mass percentage of the Ca(OH)2 suspension is 1 to 50wt.%.

[0021] Since the reaction between CaO solid and AlF(g) is a gas-solid reaction, the larger the specific surface area of ​​CaO solid, the larger the contact area between it and AlF(g), the greater the degree of reaction, and the higher the utilization rate of CaO. In order to increase the specific surface area of ​​CaO and improve its utilization rate, a CaO coating can be applied to the filter mechanism. The purpose is to place the CaO filter material on the path of magnesium vapor, thereby purifying and removing aluminum impurities in the magnesium vapor.

[0022] In the present invention, the Ca(OH)2 suspension can be prepared by dissolving CaO in water, or can be a Ca(OH)2 suspension having a mass percentage of 1 to 50 wt.% obtained by other methods.

[0023] The beneficial effects of the present invention are:

[0024] 1. The impurity aluminum in the silicon thermal magnesium smelting system of the present invention mainly exists in the form of Al and AlF (aluminum monofluoride) gas. The CaO filter material can remove Al and AlF gas specifically and form high-aluminum CaO. 12 Al 14 F2O 32 Sediments have significant aluminum removal effects; at the same time, the action temperature of the CaO filter material is significantly higher than the deposition temperature of magnesium vapor. When the CaO filter material is used to fully capture impurity aluminum, it will not cause the deposition of magnesium vapor, and can significantly increase the deposition distance of aluminum and magnesium to separate them; the CaO filter material does not react with magnesium vapor, and has good purification efficiency;

[0025] 2. In addition to high-efficiency aluminum removal, the CaO filter material of the present invention can also provide heterogeneous nuclear sites for impurity condensation and physically intercept dust particles, thereby further reducing impurities in magnesium vapor;

[0026] 3. The CaO filter material of the present invention is a mineral filter material and is a main component of the raw material for magnesium smelting by silicon thermal method. It is abundant, easy to obtain and low in cost.

[0027] 4. The method of the present invention utilizes a Ca(OH)2 suspension to soak the filter structure and then thermally decomposes it to prepare a CaO coating, which can further increase the specific surface area of ​​CaO as a filter material and improve its utilization rate, thereby saving CaO usage and further reducing costs. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0029] Figure 1 Schematic diagram of thermodynamic calculation reaction between AlF and excess CaO filter material in magnesium vapor at different temperatures of the present invention;

[0030] Figure 2 It is a schematic diagram of the changes in the composition of the gas phase and condensed substances calculated by thermodynamics before and after the addition of CaO filter material in the silicon thermal magnesium smelting gas phase system of the present invention;

[0031] Figure 3 Schematic diagram of the change of magnesium purity before and after adding CaO filter material in Comparative Example 1 and Example 1 of the present invention;

[0032] Figure 4 This is a schematic diagram of the macroscopic morphology change of the CaO filter material before and after use in Example 1 of the present invention;

[0033] Figure 5 Schematic diagram of scanning electron microscope (SEM) of CaO filter material before and after use in Example 1 of the present invention

[0034] Figure 6 Schematic diagram of energy dispersive X-ray spectra (EDS) of the CaO filter material before and after use in Example 1 of the present invention;

[0035] Figure 7 Schematic diagram of X-ray diffraction (XRD) of the CaO filter material before and after use in Example 1 of the present invention. DETAILED DESCRIPTION

[0036] To make the purpose, technical solution and advantages of the present invention clearer, the technical solution of the present invention will be described in detail below. Obviously, the described embodiments are only part of the embodiments of the present invention, rather than all the embodiments. Based on the embodiments of the present invention, all other implementation methods obtained by ordinary technicians in this field without creative work belong to the scope of protection of the present invention.

[0037] Example

[0038] Based on the attached Figure 1-7The present embodiment provides a low-cost and efficient aluminum removal method for silicon thermal magnesium smelting based on CaO filter material. Based on the silicon thermal magnesium smelting process, the CaO filter material is used to purify and remove aluminum impurities in magnesium vapor, comprising the following steps: heating the raw materials for silicon thermal magnesium smelting to react and generate magnesium vapor, allowing the magnesium vapor to pass through the CaO filter material to remove aluminum impurities, and then condensing and crystallizing to obtain low-aluminum high-purity magnesium.

[0039] In this embodiment, the silicon thermal method for magnesium smelting includes the following steps: placing the raw materials for magnesium smelting by silicon thermal method in a closed container, evacuating the closed container so that the vacuum degree of the closed container is 10Pa; heating the closed container so that the magnesium vapor passes through the CaO filter material arranged in the closed container to remove aluminum impurities, and then crystallizes to obtain low-aluminum high-purity magnesium.

[0040] In this embodiment, a reaction zone, a temperature transition zone and a crystallization zone are sequentially arranged in a closed container in the silicon thermal magnesium smelting process, and the reaction zone, the temperature transition zone and the crystallization zone form a channel for the movement of magnesium vapor. The movement path of magnesium vapor under vacuum is the reaction zone, the temperature transition zone and the crystallization zone in sequence;

[0041] The reaction zone is used to load the raw materials for magnesium smelting by silicon thermal process, and the raw materials for magnesium smelting by silicon thermal process loaded in the reaction zone are heated, so that the raw materials react at 1250-1300°C to generate magnesium vapor, and the magnesium vapor contains aluminum impurities, and the main existing form of aluminum is AlF;

[0042] A CaO filter material is arranged in the temperature transition zone, and the magnesium vapor generated by the reaction in the reaction zone moves to the temperature transition zone under the action of vacuum, and the magnesium vapor contacts the CaO filter material, thereby removing aluminum-containing impurities in the magnesium vapor, and obtaining purified magnesium vapor;

[0043] A crystallizer is arranged in the crystallization zone, and the purified magnesium vapor is condensed and crystallized in the crystallization zone, thereby obtaining high-purity magnesium solid.

[0044] In this embodiment, the temperature of the silicon thermal magnesium smelting process is controlled at 200-1300°C, and is controlled in three sections corresponding to the reaction zone, the temperature transition zone and the crystallization zone;

[0045] The first section corresponds to the reaction zone for heating, and the temperature of the first section is controlled to be 1250-1300°C. Since the raw materials in the reaction zone absorb heat during reaction, the temperature control in the first section is mainly to increase heat, that is, to provide heat energy to the reaction zone so that the raw materials react at 1250-1300°C to generate magnesium vapor;

[0046] The second section heats the temperature transition zone, and the temperature of the second section is controlled to be 600-1250°C; the temperature control of the second section is mainly based on heat increase and synergistic heat dissipation. Since the initial temperature of the magnesium vapor generated by the reaction is higher than 600-1250°C, the magnesium vapor needs to be properly dissipated and cooled in the temperature transition zone, and the temperature of the magnesium vapor is adjusted to the working temperature of the CaO filter material for purification; however, when the temperature heat dissipation of the magnesium vapor in the temperature transition zone is too strong, making the temperature of the magnesium vapor too low, there is a risk of crystallization of the magnesium vapor in the temperature transition zone, and the temperature transition zone needs to be heated; whether it is heating or heat dissipation, its purpose is to adjust the temperature of the temperature transition zone, especially to adjust the CaO filter material in the temperature transition zone to the optimal working temperature, purify and remove aluminum-containing impurities in the magnesium vapor, and obtain purified magnesium vapor.

[0047] The third section controls the temperature of the crystallization zone, and the temperature of the third section is controlled at 200-600°C; the temperature control of the third section is mainly based on heat dissipation, and a heat exchanger is set in the crystallization zone to promote the heat dissipation of magnesium vapor, so that the magnesium vapor condenses and crystallizes into a solid; to cooperate with the heat dissipation of the purified magnesium vapor, the heat exchanger can be optionally a water-cooled heat exchanger; in order to allow the magnesium vapor to pass through the temperature transition zone from the reaction zone and condense and crystallize in the crystallization zone, an optional method is to connect a vacuum on the side of the crystallization zone away from the temperature transition zone.

[0048] In some examples, the aluminum-containing impurities are AlF; the CaO filter material can not only remove the Al element, but also remove the AlF formed by the Al element and the F element during the purification and removal of magnesium vapor, thereby simultaneously reducing the Al element and the F element in the magnesium product.

[0049] In some examples, the working temperature of the above-mentioned CaO filter material for removing aluminum-containing impurities is 600-1250°C; in order to ensure that the CaO filter material is at an optimal working temperature, an optional method is to place the CaO filter material in a temperature transition zone to purify and remove aluminum-containing impurities in magnesium vapor.

[0050] In some examples, the working temperature of the above-mentioned CaO filter material for removing aluminum-containing impurities is 1050-1250°C; in order to ensure that the CaO filter material achieves purification at this optimal working temperature, an optional method is to place the CaO filter material in an area with a temperature of 1050-1250°C in the temperature transition zone based on the temperature distribution area in the temperature transition zone.

[0051] In some instances, the heating temperature is controlled at 1250-1300°C; an optional method is to heat the reaction zone so that the temperature of the reaction zone is controlled at 1250-1300°C and generate magnesium vapor of corresponding temperature, and appropriately and reasonably cool the magnesium vapor, so that the temperature transition zone can meet the working temperature requirements for removing aluminum impurities and the working temperature requirements for crystallization in the crystallization zone, without the need to heat the temperature transition zone and the crystallization zone.

[0052] In some examples, the CaO filter material is arranged on the movement path of the magnesium vapor by natural filling or compaction using a CaO raw material, and the CaO raw material is in any one of a block, a sphere, a powder, and a sheet. In an optional manner, the sealed container is placed horizontally, and a reaction zone, a temperature transition zone, and a crystallization zone are sequentially arranged in the sealed container in the horizontal direction. The CaO filter material is filled into the temperature transition zone, and the self-weight of the CaO filter material forms a shearing effect with the movement path of the magnesium vapor, so that the CaO filter material and the magnesium vapor are sheared. The gas is fully contacted to purify and remove aluminum impurities; in another optional way, the CaO raw material is compacted into a tangible structure and placed in the temperature transition zone of a closed container. The compaction can be compacted into a solid but microporous cylinder, a hollow ring cylinder, a hollow and porous ring cylinder, a hollow square cylinder, a hollow and porous square cylinder, a hollow round cake, a hollow and porous round cake, a hollow square cake, a hollow and porous square cake and other tangible structures, and they are stacked and placed in the temperature transition zone.

[0053] In some examples, when the CaO raw material is in block form, the diameter is 8 to 20 mm.

[0054] In some examples, when the CaO raw material is spherical, the diameter is 0.3-8 mm.

[0055] In some examples, when the CaO raw material is in powder form, the particle size is 1 to 300 μm.

[0056] In some examples, when the CaO raw material is in the form of flakes, the thickness is 0.1 to 5 mm.

[0057] In some examples, the CaO filter material is a CaO carrier containing CaO, and the CaO carrier is arranged on the movement path of the magnesium vapor; in order to facilitate the temperature control zone or remove other impurities in the magnesium vapor, filters, filter screens and other special structures can be arranged in the temperature transition zone, and these special structures can be used as carriers of CaO; one way is to fill the CaO raw material into the channel of the carrier that allows magnesium vapor to pass through, so as to contact with the magnesium vapor and remove aluminum-containing impurities; another way is to coat or impregnate the surface of the carrier with a CaO component, so that a CaO coating is formed on the surface of the carrier and used as a filter material for removing aluminum-containing impurities.

[0058] In some examples, the CaO carrier is prepared by coating or impregnating CaO on the carrier, and the step of coating or impregnating CaO on the carrier includes:

[0059] Immersing the support in a Ca(OH)2 suspension so that the support is coated or impregnated with a Ca(OH)2 coating;

[0060] The carrier coated with Ca(OH)2 inside is taken out, dried and thermally decomposed to obtain a carrier coated or impregnated with CaO.

[0061] In some examples, the drying temperature is 190-1200° C., and the drying time is 0.5-2 h.

[0062] In some instances, the above-mentioned drying is not limited to drying in an oven, but can also be dried in other temperature environments that meet the temperature range of 190 to 1200°C. If the working temperature of the above-mentioned temperature transition zone is within the drying temperature range, the carrier coated with Ca(OH)2 can be placed in the temperature transition zone. According to the production process requirements of silicothermic magnesium smelting, the temperature of the temperature transition zone is 600 to 1250°C, so that Ca(OH)2 can be dried and decomposed to obtain CaO; the carrier carrying CaO can be retained in the temperature transition zone, and after loading the silicothermic magnesium smelting raw material, silicothermic magnesium smelting can continue, and aluminum impurities in the magnesium vapor can be removed based on CaO purification.

[0063] In some examples, the mass percentage of the Ca(OH)2 suspension is 1 to 50 wt.%.

[0064] In some embodiments, the Ca(OH)2 suspension is prepared by mixing CaO and water.

[0065] In some examples, CaO formed on the carrier may also be formed by decomposing precursors such as CaCO3, Ca(HCO3)2, etc., and the precursor may be formed by reacting other raw materials.

[0066] In some instances, the above-mentioned compact or carrier is not limited to using only CaO material, and CaO can also be blended with other filter materials that are beneficial to the purification of magnesium vapor, such as the pure iron filter material disclosed in CN201911178561.X, the elemental silicon filter material disclosed in CN201911178325.8, the nickel-based filter material disclosed in CN201911178562.4, etc. Of course, the dosage ratio is adjusted according to the adaptability of the impurity removal effect on magnesium vapor.

[0067] In order to illustrate the role of CaO filter material in removing aluminum-containing impurities in magnesium vapor produced by silicon thermal magnesium smelting, the following experimental examples, comparative examples and test examples are provided:

[0068] Experimental Example 1

[0069] (1) Weigh 300 g of raw materials for magnesium smelting by silicon thermal reduction method and place them in the reaction zone of a sealed container; evacuate the inside of the sealed container to a vacuum degree of 10 Pa;

[0070] (2) The reaction zone of the container is heated to cause the conventional pellets to undergo a silicon thermal reduction reaction to generate magnesium vapor, and the magnesium vapor is purified by a CaO filter material and then condensed and crystallized to obtain high-purity magnesium; the heating is carried out in three stages, the first stage is to heat the reaction zone of the sealed container at a temperature of 1250°C; the second stage is to heat the temperature transition zone of the sealed container, a CaO filter material is provided in the temperature transition zone, and the working temperature of the second stage is 800-1250°C; the third stage is to heat the crystallization zone of the sealed container, a crystallizer for capturing condensed and crystallized magnesium is provided in the crystallization zone, and the working temperature of the third stage is 600°C.

[0071] The raw material for silicon thermal reduction magnesium smelting is a pellet, which contains 28.53wt.% MgO, 40.12wt.% CaO, 0.62wt.% SiO2, 0.16wt.% Al2O3, 0.28wt.% Fe2O3, 0.05wt.% MnO, 0.0005wt.% PbO, 0.001wt.% ZnO, 21.94% Si, 6.14wt.% Fe, 0.51wt.% Al, 0.276wt.% Ca, 0.023wt.% Mn, 0.0006wt.% Zn, 0.0009wt.% Pb, 0.005wt.% P, 1.32wt.% CaF2, and 0.014wt.% CaCO3. Through thermodynamic calculations of conventional pellets with the above components, it can be seen that when silicon thermal reduction reaction occurs, the main products of the gas phase at 1250°C are Mg, SiO, Ca, AlF (aluminum monofluoride, CAS No. 13595-82-9), CaF2, Mn, Si, Fe, etc.; and the above gas phase substances are expected to form stable compounds or single substances in the process of gradual cooling and condensation, such as Ca-Si-O, Ca-Al-Si-O, Ca-AlFO, Fe, Mn, etc. For impurity aluminum, the initial existence form of impurity aluminum in magnesium-containing vapor at high temperature is Al(g) and AlF(g), and the high aluminum deposition phase is Ca-AlFO. It can be seen that in order to deposit more Al(g) and AlF(g), it is necessary to have Ca and O-containing substances co-deposited.

[0072] The present invention selects CaO as the filter material and calculates the reactivity between CaO and AlF(g), as shown in FIG. Figure 1 shown.

[0073] according to Figure 1It can be seen that in the range of 1250-1050℃, CaO(s), Al(g) and AlF(g) all decrease significantly, and the reduction is the largest at 1050℃.

[0074] The present invention also calculates the situation of CaO after adding the whole system of silicon thermal magnesium smelting containing impurity magnesium vapor, such as Figure 2 shown.

[0075] according to Figure 2 It can be seen that CaO significantly consumes Al(g) and AlF(g) in the gas phase and forms Ca 12 Al 14 F2O 32 Although the use of CaO filter material generates a large amount of Ca vapor in the system, the Ca vapor can be deposited and removed during the subsequent vapor cooling process, and can also be removed in large quantities during the silicon thermal magnesium refining process, and will not bring impurity effects to the crystalline magnesium system.

[0076] In step (2) of this embodiment, the CaO filter material is in the form of a block with a diameter of 10 mm, and the CaO filter material is filled inside the filter mechanism.

[0077] In step (2) of this embodiment, the operating temperature of the CaO filter material in the temperature transition zone is 1185-1228°C.

[0078] According to the above method, after 120 min of silicon thermal reduction reaction, the crystalline magnesium in the crystallizer was collected and weighed to obtain 43.7 g of pure magnesium from which aluminum had been removed.

[0079] The content of each element in pure magnesium was analyzed. The purity of magnesium in the low-aluminum high-purity magnesium prepared in this embodiment reached 99.986%, and the content of impurity elements was shown in Table 1.

[0080] Table 1

[0081]

[0082] Experimental Example 2

[0083] The difference between this embodiment and embodiment 1 is that:

[0084] In this embodiment, the CaO filter material is placed in the temperature transition zone, and the working temperature of the CaO filter material is 1050-1139°C.

[0085] After 120 min of silicon thermal reduction reaction, the crystalline magnesium in the crystallizer was collected and weighed to obtain 43.4 g of pure magnesium from which aluminum had been removed.

[0086] The content of each element in pure magnesium was analyzed. The purity of magnesium in the low-aluminum high-purity magnesium prepared in this embodiment reached 99.988%, and the content of impurity elements was shown in Table 2.

[0087] Table 2

[0088]

[0089] Experimental Example 3

[0090] The difference between this embodiment and embodiment 1 is that:

[0091] In this embodiment, the CaO filter material used is in the form of a block with a diameter of 20 mm.

[0092] After 120 min of silicon thermal reduction reaction, the crystalline magnesium in the crystallizer was collected and weighed to obtain 42.6 g of pure magnesium from which aluminum had been removed.

[0093] The content of each element in pure magnesium was analyzed. The purity of magnesium in the low-aluminum high-purity magnesium prepared in this embodiment reached 99.986%, and the content of impurity elements was shown in Table 3.

[0094] Table 3

[0095]

[0096] Experimental Example 4

[0097] The difference between this embodiment and embodiment 1 is that:

[0098] In this embodiment, the CaO filter material used is a hollow and porous disc with an outer diameter of 45 mm and a thickness of 5 mm. A central hole with a pore diameter of 25 mm is arranged at the center of the porous disc; 10 circular holes are arranged on the filter structure around the circumference of the central hole, and the pore diameter of the circular holes is 6 mm.

[0099] Experimental Example 5

[0100] The difference between this embodiment and embodiment 1 is that:

[0101] In this embodiment, a carrier containing CaO is provided in the temperature transition zone. The carrier is a filter, and the preparation of coating CaO on the surface of the filter includes the following steps:

[0102] Prepare a Ca(OH)2 suspension with a mass percentage of 1 to 50 wt.%, place a filter in the Ca(OH)2 suspension, so that the Ca(OH)2 suspension submerges the filter and the surface of the filter is coated with Ca(OH)2;

[0103] The filter with the surface coated with Ca(OH)2 is taken out and placed at the mouth of the reduction tank of the silicon thermal reduction magnesium smelting system. The filter is heated by relying on the naturally formed temperature gradient of the reduction tank and controlled to be heated to 800-1250°C, so that the Ca(OH)2 dehydrates and reacts to generate CaO, thereby obtaining a filter with the surface coated with CaO coating.

[0104] Comparative Example

[0105] The difference between this comparative example and Example 1 is that in step (2), no CaO filter material is provided in the temperature transition section.

[0106] In this comparative example, the method of Example 1 was followed to collect the magnesium in the crystallizer and weigh it. The mass of the obtained crystalline magnesium was 43.2 g.

[0107] Test example

[0108] The crystalline magnesium samples obtained in Example 1 and Comparative Example 1 were tested for purity after remelting. Figure 3 As shown;

[0109] Figure 3 It can be seen that when no CaO filter material is added, the impurity aluminum content in the crystalline magnesium sample is 109.5ppm, and when CaO filter material is added, the impurity aluminum content in the crystalline magnesium is 6.3ppm. The aluminum content in Experimental Example 1 is much lower than that in the comparative example. It can be seen that the use of CaO filter material can effectively purify and remove Al and Al F in the magnesium vapor generated by silicon thermal smelting of magnesium.

[0110] The CaO filter material before and after filtration in Experimental Example 1 was subjected to macroscopic morphology observation, scanning electron microscope (SEM) observation, energy dispersive X-ray spectroscopy (EDS) analysis and X-ray diffraction (XRD) phase analysis. The results are as follows: Figure 4-7 shown.

[0111] Figure 4 It can be seen that the appearance size of the CaO filter material changes before and after the use of the CaO filter material, indicating that there is no lossy pollution to the magnesium vapor system during its use; there are obvious attachments on the surface of the CaO filter material after use, and the color changes, indicating that the CaO filter material is deposited and blocks the impurities in the magnesium vapor.

[0112] Figure 5 It can be seen that the CaO filter material before use is loose and porous, and the size of the particle unit is about 1-2um; after use, the pores of the CaO filter material are obviously closed, and the size of the particle unit increases to more than 20um.

[0113] Figure 6It can be seen that the elements F and Al are significantly increased in the CaO filter material after use compared with the CaO filter material before use, indicating that the CaO filter material can not only purify Al(g) in magnesium vapor, but also capture Al F.

[0114] Figure 7 It can be seen that the CaO filter material before use contains only CaO, but the CaO filter material after use contains CaO and CaO. 12 Al 14 F2O 32 The results show that CaO filter material can capture aluminum impurities in magnesium vapor produced by silicon thermal magnesium smelting mainly by adsorption filtration and the formation of compounds, and is especially capable of removing Al F.

[0115] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principle of the present invention should be included in the protection scope of the present invention.

Claims

1. A low-cost and efficient aluminum removal method for magnesium smelting by silicon thermal method based on CaO filter material, characterized in that: The CaO filter material is used to purify and remove aluminum impurities in magnesium vapor, comprising the following steps: heating a silicon thermal method magnesium smelting raw material to generate magnesium vapor, allowing the magnesium vapor to pass through the CaO filter material to remove aluminum impurities, and then condensing and crystallizing to obtain low-aluminum high-purity magnesium; The CaO filter material is made of CaO raw material and is naturally filled or compacted and arranged on the movement path of the magnesium vapor. The CaO raw material is in any one of block, spherical, powdery and sheet shapes. When the CaO raw material is in block shape, the diameter is 8 to 20 mm; when the CaO raw material is in spherical shape, the diameter is 0.3 to 8 mm; when the CaO raw material is in powdery shape, the particle size is 1 to 300 μm; when the CaO raw material is in sheet shape, the thickness is 0.1 to 5 mm.

2. The low-cost and high-efficiency aluminum removal method for magnesium smelting by silicon thermal method based on CaO filter material according to claim 1 is characterized in that: The aluminum-containing impurity is AlF.

3. The low-cost and high-efficiency aluminum removal method for magnesium smelting by silicon thermal method based on CaO filter material according to claim 1 is characterized in that: The working temperature of the CaO filter material for removing aluminum-containing impurities is 600-1250°C.

4. The low-cost and high-efficiency aluminum removal method for magnesium smelting by silicon thermal method based on CaO filter material according to claim 3 is characterized in that: The working temperature of the CaO filter material for removing aluminum-containing impurities is 1050-1250°C.

5. The low-cost and high-efficiency aluminum removal method for magnesium smelting by silicon thermal method based on CaO filter material according to any one of claims 1 to 4, characterized in that: The heating temperature of the silicon thermal method magnesium smelting raw material is controlled to be 1250-1300°C.

6. The low-cost and high-efficiency aluminum removal method for magnesium smelting by silicon thermal method based on CaO filter material according to any one of claims 1 to 4, characterized in that: The CaO filter material is a carrier containing CaO, and the carrier is arranged on the movement path of the magnesium vapor.

7. The low-cost and high-efficiency aluminum removal method for magnesium smelting by silicon thermal method based on CaO filter material according to claim 1 is characterized in that: The CaO filter material is a carrier coated with or impregnated with CaO, comprising the following steps: Immersing the support in a Ca(OH)2 suspension so that the support is coated or impregnated with a Ca(OH)2 coating; The carrier coated with Ca(OH)2 is taken out, dried and thermally decomposed to obtain the product.

8. The low-cost and high-efficiency aluminum removal method for magnesium smelting by silicon thermal method based on CaO filter material according to claim 7 is characterized in that: The drying temperature is 190-1200° C., and the drying time is 0.5-2 hours.

9. The low-cost and high-efficiency aluminum removal method for magnesium smelting by silicon thermal method based on CaO filter material according to claim 7, characterized in that , the mass percentage of the Ca(OH)2 suspension is 1 to 50wt.%.

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