Method for preparing aluminum by low-temperature catalytic vacuum desilication of bauxite

Abstract

This invention discloses a method for vacuum desilication and low-temperature catalytic aluminum production from bauxite, belonging to the field of vacuum metallurgy technology. The method specifically involves: mixing and grinding bauxite, carbon powder, and a catalyst to obtain a mixture; adding pregelatinized starch paste to the mixture to form a blank; placing the blank in a vacuum system, introducing a protective gas, and performing vacuum carbothermic deoxidation and desilication at 1000-1200℃ to obtain a mixture; and performing vacuum separation of the mixture at 1400-1600℃, collecting metallic aluminum in the condensation zone. This invention lowers the reaction temperature and inhibits the volatilization of low-valence aluminum oxides through the synergistic effect of an iron-silicon catalyst, achieving deep deoxidation and reducing aluminum loss while allowing most silicon to volatilize in a low-valence state. Vacuum separation of the desilication-deoxidized mixture achieves efficient separation of aluminum from impurities such as iron and silicon carbide. This invention can directly obtain aluminum products from bauxite or high-silicon bauxite, without the generation of red mud, making it environmentally friendly, significantly shortening the smelting process, and reducing energy consumption.

Description

Technical Field

[0001] This invention relates to the field of vacuum metallurgy technology, specifically to a method for vacuum desilication and low-temperature catalytic aluminum production from bauxite. Background Technology

[0002] Aluminum is the most abundant metallic element in the Earth's crust (about 8%). It has many advantages, including being lightweight, conductive, corrosion resistant (thanks to its oxide film), and recyclable. It is widely used in high-precision fields such as aerospace, photovoltaic power generation, national defense and military industry, and new energy vehicles.

[0003] Current aluminum production typically involves preparing alumina from bauxite, and industrially using the Hall-Héroult process to electrolyze molten alumina in cryolite to produce metallic aluminum. While this method can efficiently produce high-purity aluminum ingots, it demands a huge amount of electricity, significantly increasing energy consumption. Furthermore, the process inevitably generates red mud as a byproduct. Red mud is highly corrosive and extremely environmentally hazardous. If not properly treated, it can lead to soil alkalization, groundwater pollution, and toxic effects on plants and animals. The fluoride salts contained in cryolite used in the electrolysis process also contribute to environmental pollution.

[0004] Patent application 201910288603.9 discloses a method for preparing metallic aluminum by vacuum distillation of bauxite. The method first involves a first carbothermic reduction of bauxite compacts under vacuum, at 1200-1400°C, to volatilize all Si and some Fe in the compacts, yielding a first carbothermic reduction product. This product is an aluminum-rich material with all silicon removed and only a small amount of iron remaining. Then, the aluminum-rich material is heated to a higher temperature (1500-1700°C) for a second carbothermic nitridation reduction, yielding a second carbothermic reduction product consisting of a mixture of FeN and AlN. Subsequently, the obtained product is subjected to magnetic separation to remove magnetic iron nitride, followed by decarburization to remove residual carbon powder, thus obtaining aluminum nitride. Finally, the aluminum nitride product is subjected to vacuum thermal decomposition at 1500-1700°C, causing aluminum to volatilize as vapor. After condensation and collection, metallic aluminum is obtained. This method completely volatilizes the silicon in bauxite at high temperatures, and the first carbothermal reduction temperature and vacuum thermal decomposition temperature are high. It also requires additional magnetic separation and decarburization treatment, resulting in a long process and increased energy consumption.

[0005] In addition, patent application 201910288599.6 discloses a method for preparing metallic aluminum and silicon carbide from bauxite. The method first mixes bauxite and carbon powder, ball mills and wet-presses them into a blank; then, it is carbothermic reduction nitrided at 1400~1650℃ under a nitrogen atmosphere to obtain a mixed product containing aluminum nitride (AlN), silicon carbide (SiC), iron nitride and excess carbon; then, the iron nitride is removed by magnetic separation, and the residue is decarburized in air at 600~800℃ to obtain a mixture of AlN and SiC; finally, the mixture is vacuum decomposed at 1550~1700℃, AlN decomposes to generate aluminum vapor and is condensed and collected, while SiC remains at the bottom of the crucible, thus obtaining metallic aluminum and SiC respectively. Although this method achieves the goal of directly preparing metallic aluminum from bauxite, it still has the following shortcomings: (1) The temperatures of carbothermic reduction nitridation and vacuum decomposition are both high, not lower than 1400℃ and 1550℃ respectively, which increases energy consumption; (2) The process flow is relatively complicated, requiring intermediate steps such as magnetic separation and decarburization to be carried out in sequence; (3) Since there is no desiliconization step, all silicon elements in bauxite are converted into silicon carbide, which limits the adaptability to processing high-silicon bauxite.

[0006] Therefore, developing a method for producing metallic aluminum from bauxite that avoids red mud and fluoride pollution, is simple in process, and has low energy consumption is of great significance for aluminum production. Summary of the Invention

[0007] To further address the problems existing in related technologies, this invention provides a method for vacuum desilication and low-temperature catalytic aluminum production from bauxite, specifically including the following steps:

[0008] (1) Mix and grind bauxite, carbon powder and catalyst to obtain a mixture, and then add pregelatinized starch paste to the mixture to make a blank.

[0009] (2) Place the billet in a vacuum system and introduce nitrogen or argon as a protective gas to perform vacuum carbothermic deoxidation and desiliconization at a temperature of 1000-1200℃ to obtain a mixture.

[0010] (3) The mixture obtained in step (2) is further separated under vacuum at a temperature of 1400-1600℃, and finally metallic aluminum is obtained in the condensation zone.

[0011] Preferably, in step (1) of the present invention, the molar ratio of SiO2 in bauxite to carbon powder is 1:3.1-4.1.

[0012] Preferably, the mass ratio of the mixed materials and the pregelatinized starch paste in step (1) of the present invention is 0.6-1:1.

[0013] Preferably, the pressure at which the blank is formed in step (1) of the present invention is 1-3 MPa.

[0014] Preferably, the catalyst in step (1) of the present invention is one or two of MgO, CaO, BaO, and NiO, and the amount of catalyst added is 0.5%-1% of the mass of bauxite.

[0015] Preferably, the conditions for vacuum carbothermal deoxidation and desiliconization in step (2) of the present invention are: the heat preservation time is 1.5-3h.

[0016] Preferably, in step (2) of the present invention, the vacuum degree is adjusted to 100-700 Pa after introducing a protective gas such as nitrogen or argon.

[0017] Preferably, the vacuum separation conditions in step (3) of the present invention are: vacuum degree of 4-100 Pa and heat preservation time of 2-3.5 h.

[0018] The mechanism of this invention is as follows: First, the iron and silicon components inherent in bauxite, along with an added catalyst (such as MgO, CaO, etc.), form a multi-component eutectic liquid phase, generating a synergistic catalytic effect to lower the reaction temperature. Simultaneously, the synergistic effect of the silicon-containing components and the catalyst in the system suppresses the volatilization of low-valence aluminum oxide gases. This achieves deep deoxidation and allows most of the silicon to volatilize in a low-valence state (such as SiO), while reducing aluminum loss and promoting the formation of a low-oxygen silicon-aluminum mixture at 1000-1200℃. Finally, at 1400-1600℃, the thermodynamic differences between silicon carbide and aluminum in the low-oxygen silicon-aluminum mixture are utilized to perform vacuum separation of the mixture, achieving efficient separation of aluminum from impurities such as iron and silicon carbide.

[0019] This invention provides a method for vacuum desilication and low-temperature catalytic aluminum production from bauxite, which has the following beneficial effects:

[0020] (1) By making reasonable use of the Fe and Si components in bauxite and the synergistic effect of the catalyst, the present invention effectively reduces the reaction temperature required during vacuum deoxidation and vacuum separation, and significantly reduces energy consumption in the production process.

[0021] (2) The present invention suppresses the volatilization of low-valence alumina gas through the synergistic effect of silicon-containing components and catalysts in the system, thereby reducing aluminum loss while achieving deep deoxidation and allowing most of the silicon to volatilize in a low-valence state.

[0022] (3) This invention does not produce red mud or use fluoride salts in the production of aluminum metal, thus eliminating the pollution problems of red mud and fluoride salts from the source and significantly reducing the risk of environmental pollution.

[0023] (4) The method of the present invention enables the direct production of aluminum products from bauxite (including high-silica bauxite) without the need for multiple intermediate steps in traditional smelting, which greatly simplifies the production process and reduces production costs. Attached Figure Description

[0024] Figure 1 This is a schematic diagram of the method flow of the present invention.

[0025] Figure 2 This is the XRD pattern of bauxite raw material in Example 1 of the present invention.

[0026] Figure 3 This is the XRD pattern of vacuum carbothermal deoxidation in Embodiment 1 of the present invention.

[0027] Figure 4 This is the XRD pattern of silicon removal collected at the top of the crucible at 1000°C in Embodiment 1 of the present invention.

[0028] Figure 5 This is the XRD pattern of the vacuum carbothermal deoxidation product of Comparative Example 1 of the present invention at 1000°C without the addition of a catalyst.

[0029] Figure 6 This is the XRD pattern of aluminum prepared in Example 1 of the present invention. Detailed Implementation

[0030] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0031] The method for preparing pregelatinized starch paste used in the embodiments and comparative examples of the present invention is as follows: pregelatinized starch and water are mixed to form a starch milk with a mass percentage concentration of 10%, and the mixture is continuously stirred and heated to 80-85°C and kept warm for 3 minutes until gelatinization is achieved, thereby obtaining pregelatinized starch paste.

[0032] Example 1

[0033] A method for vacuum desilication and low-temperature catalytic aluminum production from bauxite, the process flow diagram of which is shown below. Figure 1 As shown, the specific steps include:

[0034] (1) Mix and grind bauxite, carbon powder and catalyst to obtain a mixture, wherein the molar ratio of SiO2 in bauxite to carbon powder is 1:3.1, and the catalyst added is MgO and CaO (the total mass of MgO and CaO is 0.5% of the mass of the aluminum-rich material, and the mass ratio of MgO and CaO is 2:3). Add pregelatinized starch paste to the mixture (the mass ratio of the mixture and the pregelatinized starch paste is 0.6:1), and form a green body at 1 MPa.

[0035] (2) The billet is placed in a vacuum furnace, nitrogen gas is introduced and the vacuum degree is controlled at 100 Pa, and it is kept at 1000℃ for 1.5 h to obtain a mixture of aluminum nitride and a small amount of silicon carbide.

[0036] (3) The mixture in step (2) is kept at 1400℃ for 2 hours and then vacuum separated (vacuum degree is 4Pa). Aluminum evaporates to the condensation zone, while silicon carbide remains at the bottom of the crucible, and finally metallic aluminum is obtained.

[0037] The bauxite raw material and the products of vacuum carbothermic deoxidation and desilication at 1000℃ in this embodiment were characterized by XRD. The XRD patterns are shown below. Figure 2-4 As shown, the XRD pattern of bauxite is as follows: Figure 2 As shown, the main bauxite mineral phase is Al2(Si2O5)(OH)4; the XRD pattern of the product at the bottom of the crucible after vacuum carbothermic deoxidation and desilication treatment is shown in the figure. Figure 3 As shown, the silicon content is significantly reduced, most of the aluminum phase of bauxite is nitrided into aluminum nitride, and a small portion is converted into silicon carbide; Figure 4 The XRD pattern of the removed silicon collected at the top of the crucible.

[0038] The aluminum metal prepared in this embodiment has a purity of 97.5% and a yield of 97%. The XRD pattern of this aluminum metal is shown below. Figure 6 As shown, the product has a single phase, no obvious impurity phase residue, and good crystallization.

[0039] Example 2

[0040] A method for vacuum desilication and low-temperature catalytic aluminum production from bauxite, specifically including the following steps:

[0041] (1) Mix and grind bauxite, carbon powder and catalyst to obtain a mixture, wherein the molar ratio of SiO2 in bauxite to carbon powder is 1:4.1, and the catalyst added is MgO and CaO (the total mass of MgO and CaO is 1% of the mass of the aluminum-rich material, and the mass ratio of MgO and CaO is 3:4). Add pregelatinized starch paste to the mixture (the mass ratio of the mixture and the pregelatinized starch paste is 1:1), and form a green body at 3MPa.

[0042] (2) Place the billet into a vacuum furnace, introduce nitrogen gas and control the vacuum degree at 300 Pa, and keep it at 1200℃ for 3 hours to obtain a mixture of aluminum nitride and a small amount of silicon carbide.

[0043] (3) The mixture in step (2) is kept at 1600℃ for 3 hours and then vacuum separated (vacuum degree is 100Pa). Aluminum evaporates to the condensation zone, while silicon carbide remains at the bottom of the crucible, and finally metallic aluminum is obtained.

[0044] The aluminum metal prepared in this embodiment has a purity of 98.5% and a yield of 98%.

[0045] Example 3

[0046] A method for vacuum desilication and low-temperature catalytic aluminum production from bauxite, specifically including the following steps:

[0047] (1) A mixture of bauxite, carbon powder and catalyst is prepared by mixing and grinding to obtain a mixture, wherein the molar ratio of SiO2 in bauxite to carbon powder is 1:3.6, and the catalysts added are MgO and CaO (the total mass of MgO and CaO is 0.8% of the mass of the aluminum-rich material, and the mass ratio of MgO and CaO is 3:5). Pregelatinized starch paste is added to the mixture (the mass ratio of the mixture to the pregelatinized starch paste is 0.8:1), and a green body is prepared at 2 MPa.

[0048] (2) The billet is placed in a vacuum furnace, nitrogen gas is introduced and the vacuum degree is controlled at 700 Pa, and it is kept at 1100℃ for 2 hours to obtain a mixture of aluminum nitride and a small amount of silicon carbide.

[0049] (3) The mixture in step (2) is kept at 1500℃ for 2.5h and then vacuum separated (vacuum degree is 60Pa). Aluminum evaporates to the condensation zone, while silicon carbide remains at the bottom of the crucible, and finally metallic aluminum is obtained.

[0050] The aluminum metal prepared in this embodiment has a purity of 98% and a yield of 98%.

[0051] Example 4

[0052] A method for vacuum desilication and low-temperature catalytic aluminum production from bauxite, specifically including the following steps:

[0053] (1) Mix and grind bauxite, carbon powder and catalyst to obtain a mixture, wherein the molar ratio of SiO2 in bauxite to carbon powder is 1:3.9, the catalyst added is CaO (the total mass of CaO is 1% of the mass of the aluminum-rich material), pregelatinized starch paste is added to the mixture (the mass ratio of the mixture to the pregelatinized starch paste is 0.9:1), and a green body is formed at 2.5 MPa.

[0054] (2) The billet is placed in a vacuum furnace, nitrogen gas is introduced and the vacuum degree is controlled at 500 Pa, and it is kept at 1150℃ for 2.5 h to obtain a mixture of aluminum nitride and a small amount of silicon carbide.

[0055] (3) The mixture in step (2) is kept at 1550℃ for 3.5h and then vacuum separated (vacuum degree is 80Pa). Aluminum evaporates to the condensation zone, while silicon carbide remains at the bottom of the crucible, and finally metallic aluminum is obtained.

[0056] The aluminum metal prepared in this embodiment has a purity of 96% and a yield of 96%.

[0057] Comparative Example 1

[0058] This comparative example uses the same method as Example 1 to prepare metallic aluminum, except that no catalyst is added during the preparation process.

[0059] The product of vacuum carbothermic deoxidation of the mixture in this comparative example was characterized by XRD. The XRD pattern is shown below. Figure 5 As shown, the diffraction peak of Al2O3 in the product is quite obvious; since no catalyst was added in this comparative example, the bauxite could not be fully reduced and deoxidized, and there was still a relatively obvious Al2O3 diffraction peak, which ultimately led to a significant reduction in product purity, making it unable to meet the requirements for qualified applications.

[0060] When the comparative reaction continued until no more metallic aluminum was produced, the aluminum purity was found to be only 52.5%.

[0061] Comparative Example 2

[0062] This comparative example uses the same method as Example 2 to prepare metallic aluminum, except that no catalyst is added during the preparation process.

[0063] When the reaction in this comparative example continued until no more metallic aluminum was produced, the aluminum purity was only 50.5%. This comparative example contained a large amount of residual alumina and aluminum nitride. Because no catalyst was added to this comparative example, the bauxite could not be fully reduced and deoxidized, which ultimately led to a significant reduction in product purity, making it unable to meet the requirements for qualified applications.

[0064] Comparative Example 3

[0065] This comparative example uses the same method as Example 4 to prepare metallic aluminum, except that no catalyst is added during the preparation process.

[0066] When the reaction in this comparative example continued until no more metallic aluminum was produced, the aluminum purity was only 51.5%. This comparative example contained a large amount of residual alumina and aluminum nitride. Because no catalyst was added to this comparative example, the bauxite could not be fully reduced and deoxidized, resulting in a significant decrease in product purity, which could not meet the requirements for qualified applications.

[0067] In summary, without a catalyst, bauxite cannot fully undergo the vacuum carbothermal deoxidation process, making it difficult to efficiently convert alumina into the target product. This results in a large amount of unreacted phase remaining in the product, ultimately affecting the yield and purity of metallic aluminum. This invention, by introducing a catalyst, significantly promotes vacuum carbothermal deoxidation and vacuum separation, effectively reducing the reaction temperature and improving process efficiency.

[0068] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A method for vacuum desilication and low-temperature catalytic aluminum production from bauxite, characterized in that, Specifically, the following steps are included: (1) Mix and grind bauxite, carbon powder and catalyst to obtain a mixture, and then add pregelatinized starch paste to the mixture to make a blank; (2) The billet is placed in a vacuum system, and nitrogen or argon is introduced as a protective gas to perform vacuum carbothermic deoxidation and desiliconization at a temperature of 1000-1200℃ to obtain a mixture; (3) The mixture in step (2) is separated under vacuum at a temperature of 1400-1600℃, and finally metallic aluminum is obtained in the condensation zone.

2. The method for vacuum desilication and low-temperature catalytic aluminum production from bauxite according to claim 1, characterized in that, In step (1), the molar ratio of SiO2 in bauxite to carbon powder is 1:3.1-4.

1.

3. The method for vacuum desilication and low-temperature catalytic aluminum production from bauxite according to claim 1, characterized in that, The mass percentage concentration of the pregelatinized starch paste in step (1) is 10%; the mass ratio of the mixture to the pregelatinized starch paste is 0.6-1:1; and the pressure of the blank is 1-3 MPa.

4. The method for vacuum desilication and low-temperature catalytic aluminum production from bauxite according to claim 1, characterized in that, The catalyst mentioned in step (1) is one or two of MgO, CaO, BaO, and NiO, and the amount of catalyst added is 0.5%-1% of the mass of bauxite.

5. The method for vacuum desilication and low-temperature catalytic aluminum production from bauxite according to claim 1, characterized in that, The conditions for vacuum carbon thermal deoxidation and desiliconization in step (2) are: the holding time is 1.5-3h.

6. The method for vacuum desilication and low-temperature catalytic aluminum production from bauxite according to claim 1, characterized in that, Step (2) After introducing nitrogen or argon protective gas, adjust the vacuum degree to 100-700 Pa.

7. The method for vacuum desilication and low-temperature catalytic aluminum production from bauxite according to claim 1, characterized in that, The conditions for vacuum separation in step (3) are: vacuum degree of 4-100 Pa and heat preservation time of 2-3.5 h.

Images