Method for removing silicon in aluminum oxide

Abstract

The invention provides a method for removing silicon in aluminum oxide, and belongs to the field of aluminum oxide production. The method comprises the following steps: carrying out primary desiliconization on bauxite ore pulp, so that SiO2 in the bauxite ore pulp is converted from a supersaturated metastable state into sodium silicon slag precipitate, and obtaining primary desiliconized slurry; performing secondary desiliconization on first mixed slurry of the primary desiliconization slurry and the blending liquid, so that silicon minerals in the first mixed slurry form hydrated sodium aluminosilicate, and secondary desiliconization slurry is obtained; carrying out settling separation on the secondary desiliconized slurry with the set solid content to obtain second mixed slurry; adding an additive into the second mixed slurry to carry out tertiary desilicication so as to obtain tertiary desilicication slurry; carrying out solid-liquid separation on the tertiary desilicication slurry to obtain decomposed mother liquor; and performing low-temperature decomposition and high-temperature roasting on the decomposition mother liquor to obtain aluminum oxide. Therefore, high-quality aluminum oxide with the silicon content lower than 50 ppm is directly produced in the Bayer process production process, and the production requirement for producing high-purity aluminum raw materials is met.

Description

Technical Field

[0001] This application relates to the technical field of alumina production, and particularly to a method for removing silicon from alumina. Background Art

[0002] High-purity aluminum refers to aluminum with an aluminum content of 99.999%. High-purity aluminum has many excellent properties. It has better electrical conductivity, ductility, reflectivity, and corrosion resistance than primary aluminum, and has a wide range of uses in the fields of electronics industry and aerospace. The impurities contained in high-purity aluminum are mainly iron, silicon, and copper. These trace elements have an important impact on the specific capacitance, lifespan, etc. of electrolytic capacitors. As the silicon content increases, the reduction amplitude of the thermal conductivity of high-silicon aluminum alloy materials will increase, the coefficient of thermal expansion will decrease, the tensile strength will weaken, and the thermal conductivity will decrease. Excessive silicon content will affect the physical properties of aluminum alloys. Therefore, the silicon content in high-purity aluminum must be strictly controlled.

[0003] Alumina is one of the raw materials for producing high-purity aluminum. In order to control the silicon content in high-purity aluminum, it is necessary to control the silicon content in the special high-quality alumina for producing high-purity aluminum. In ordinary alumina, the silicon content is generally required to be less than 0.015%. Most alumina production enterprises use ordinary metallic aluminum as raw materials and obtain aluminum products with a silicon content of about 100 ppm through special impurity removal processes, which cannot meet the production requirements of high-purity aluminum. Summary of the Invention

[0004] This application provides a method for removing silicon from alumina to solve the following technical problem: how to reduce the silicon content in the special high-quality alumina for high-purity aluminum.

[0005] An embodiment of this application provides a method for removing silicon from alumina, and the method includes:

[0006] Under the conditions of the first set temperature and the first set time, performing primary desilication on the bauxite pulp so that SiO2 in the bauxite pulp changes from a supersaturated metastable state to sodium silicate slag precipitation, and obtaining a primary desilication slurry;

[0007] Under the conditions of the second set temperature and the second set time, performing secondary desilication on the first mixed slurry of the primary desilication slurry and the blending liquid so that the silicon minerals in the first mixed slurry form sodium aluminosilicate hydrate, and obtaining a secondary desilication slurry;

[0008] Diluting the secondary desilication slurry to a set solid content, and performing sedimentation separation on the secondary desilication slurry with the set solid content to obtain a second mixed slurry;

[0009] Adding an additive to the second mixed slurry to perform tertiary desilication to obtain a tertiary desilication slurry; the additive can combine with the silicon-containing compounds in the second mixed slurry to form a precipitate;

[0010] Perform solid-liquid separation on the said third desilication slurry to obtain the decomposition mother liquor; and

[0011] Perform low-temperature decomposition and high-temperature roasting on the said decomposition mother liquor to obtain alumina.

[0012] Optionally, the preparation method of the bauxite slurry includes:

[0013] Mix bauxite with a blending liquid and grind to obtain a slurry; by mass fraction, the bauxite consists of the following chemical components: SiO2: 5% - 8%, Al2O3: 47% - 50%, quartz silicon: 1% - 3%, diaspore 1% - 3%, gibbsite: 65% - 70%; the aluminum-silicon ratio of the bauxite is 7 - 10, and the grinding particle size of the ore in the slurry meets the following conditions: 35um% < 1%, 60um% < 12%, 100um% < 30%;

[0014] Perform hydrocyclone classification on the said slurry to obtain the bauxite slurry; the bauxite slurry meets the following conditions: solid content is 400g / L - 500g / L, ak is 1.8 - 2.0.

[0015] Optionally, the blending liquid meets the following conditions: NK is 190g / L - 220g / L, AO is 105g / L - 115g / L, NT is 210g / L - 230g / L, ak is 3.5 - 4.5, and the temperature is 80°C - 90°C.

[0016] Optionally, the first set temperature is 70°C - 80°C, and the first set time is 5h - 8h.

[0017] Optionally, the second set temperature is 130°C - 150°C, and the second set time is 100min - 120min.

[0018] Optionally, the second desilication slurry meets the following conditions: solid content is 70g / L - 90g / L, ak is 1.35 - 1.4, A / S is 160 - 180.

[0019] Optionally, the set solid content is 55g / L - 70g / L.

[0020] Optionally, the additive is lime milk slurry, and the lime milk slurry meets the following conditions: solid content is 200g / L - 300g / L, and the effective calcium is 180g / L - 200g / L.

[0021] Optionally, the decomposition mother liquor meets the following conditions: A / S is 180 - 200, ak is 1.38 - 1.45, NK is 140g / L - 150g / L, and the silicon content < 150ppm.

[0022] Optionally, the silicon content in the alumina is < 50 ppm.

[0023] The above technical solutions provided by the embodiments of the present application have the following advantages compared with the prior art:

[0024] The embodiments of the present application provide a method for removing silicon from alumina. First, SiO2 in the bauxite pulp is in a supersaturated metastable state. By primary desilication, the metastable state of silicon dioxide is destroyed, and the silicate ions in the bauxite replace the complex aluminate ions without seeds to transform into sodium silicate slag precipitation. Secondly, during secondary desilication, the silicon minerals in the bauxite form sodium aluminosilicate hydrate and enter the solid red mud during the digestion process. Finally, through tertiary desilication, the silicon-containing compounds in the sodium aluminate solution combine with the additives to form precipitation, thereby reducing the silicon content in the high-quality alumina dedicated to high-purity aluminum. Description of the Drawings

[0025] The drawings herein are incorporated into the specification and form a part of this specification, showing embodiments consistent with the present application, and are used together with the specification to explain the principles of the present application.

[0026] In order to more clearly illustrate the technical solutions in the embodiments of the present application or the prior art, the following will briefly introduce the drawings required for the description of the embodiments or the prior art. Obviously, for those of ordinary skill in the art, other drawings can also be obtained based on these drawings without creative efforts.

[0027] Figure 1 It is a first process schematic diagram of a method for removing silicon from alumina provided by an embodiment of the present application;

[0028] Figure 2 It is a second process schematic diagram of a method for removing silicon from alumina provided by an embodiment of the present application. Detailed Embodiments

[0029] To make the objectives, technical solutions, and advantages of the embodiments of the present application clearer, the following will clearly and completely describe the technical solutions in the embodiments of the present application with reference to the drawings in the embodiments of the present application. Obviously, the described embodiments are some, but not all, of the embodiments of the present application. Based on the embodiments of the present application, all other embodiments obtained by those of ordinary skill in the art without creative efforts fall within the scope of protection of the present application.

[0030] Various embodiments of the present application may exist in the form of a range; it should be understood that the description in the form of a range is only for convenience and brevity, and should not be construed as a rigid limitation on the scope of the present application; therefore, it should be considered that the range description has specifically disclosed all possible sub-ranges and single values within that range. For example, it should be considered that the range description from 1 to 6 has specifically disclosed sub-ranges such as from 1 to 3, from 1 to 4, from 1 to 5, from 2 to 4, from 2 to 6, from 3 to 6, etc., and single numbers within the range, such as 1, 2, 3, 4, 5, and 6, and this applies regardless of the range. Additionally, whenever a numerical range is indicated herein, it means including any cited number (fraction or integer) within the indicated range.

[0031] In addition, in the description of the specification of the present application, terms such as "comprising" and "including" mean "including but not limited to". In this text, relational terms such as "first" and "second" are only used to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any such actual relationship or order between these entities or operations. In this text, "and / or" describes the association relationship of associated objects, indicating that three relationships can exist. For example, A and / or B can represent: A exists alone, A and B exist simultaneously, and B exists alone. Where A and B can be singular or plural. In this text, "at least one" means one or more, and "a plurality" means two or more. "At least one kind", "at least one of the following items (pieces)" or similar expressions refer to any combination of these items, including any combination of single items (pieces) or plural items (pieces). For example, "at least one of a, b, or c", or, "at least one of a, b, and c" can both represent: a, b, c, a - b (i.e., a and b), a - c, b - c, or a - b - c, where a, b, and c can be single or multiple respectively. The "parts representation method" such as weight parts and mass parts represents the proportional relationship between each component. In the proportional relationships involved in this text, the parameters that need to be described by proportion should be understood as the antecedents of the proportion formula in the order of description, and the proportional numbers should be understood as the consequents of the proportion formula. For example, if the mass ratio of substance A, substance B, and substance C is 1:2:3, then substance A, substance B, and substance C should correspond one by one with the proportional numbers in the proportion formula in the order of description, that is, the mass of substance A: the mass of substance B: the mass of substance C = 1:2:3.

[0032] Unless otherwise specifically stated, various raw materials, reagents, instruments, and equipment used in the present application can be obtained through market purchase or can be prepared by existing methods.

[0033] Figure 1 It is the first process schematic diagram of a method for removing silicon from alumina provided for the embodiments of the present application;Figure 2 This is the second process schematic diagram of a method for removing silicon from alumina provided by an embodiment of the present application.

[0034] As Figure 1 and Figure 2 shown, an embodiment of the present application provides a method for removing silicon from alumina, and the method includes:

[0035] S1. Under the conditions of a first set temperature and a first set time, perform primary desilication on the bauxite pulp so that SiO2 in the bauxite pulp changes from a supersaturated metastable state to sodium silicate slag precipitation, and obtain a primary desilication slurry;

[0036] SiO2 in the bauxite pulp is in a supersaturated metastable state. By controlling measures such as the temperature, solid content, and enhanced stirring of the primary desilication, the metastable state of silicon dioxide is destroyed, and the silicate ions in the bauxite replace the complex aluminate ions without seed crystals to transform into sodium silicate slag precipitation.

[0037] In some embodiments, the preparation method of the bauxite pulp includes:

[0038] Mix the bauxite with a preparation liquid and grind it to obtain a pulp; in terms of mass fraction, the bauxite is composed of the following chemical components: SiO2: 5% - 8%, Al2O3: 47% - 50%, quartz silicon: 1% - 3%, boehmite 1% - 3%, gibbsite: 65% - 70%; the aluminum-silicon ratio of the bauxite is 7 - 10, and the particle size of the ore ground in the pulp satisfies the following conditions: 35um% < 1%, 60um% < 12%, 100um% < 30%;

[0039] Perform hydrocyclone classification on the pulp to obtain the bauxite pulp; the bauxite pulp satisfies the following conditions: the solid content is 400g / L - 500g / L, and ak is 1.8 - 2.0.

[0040] Limiting the particle size of the ore ground: 35um% < 1%; 60um% < 12%; 100um% < 30% affects the rate and efficiency of the digestion reaction. If the particle size is too large, the reaction will be incomplete, and if the particle size is too small, the energy consumption will increase.

[0041] In some embodiments, the preparation liquid satisfies the following conditions: NK is 190g / L - 220g / L, AO is 105g / L - 115g / L, NT is 210g / L - 230g / L, ak is 3.5 - 4.5, and the temperature is 80°C - 90°C.

[0042] It should be noted that NT represents the caustic soda content, AO represents the alumina content, NK represents the total alkali content, and ak represents the alkali concentration ratio.

[0043] Limiting NT to 210 g / L - 230 g / L can provide an alkaline environment, promote the dissolution of alumina in bauxite, and at the same time affect the progress of the desilication reaction. Limiting AO to 105 g / L - 115 g / L can act as one of the reactants, participate in the subsequent digestion process, and affect the alumina content in the final product. Limiting NK to 190 g / L - 220 g / L can control the total alkalinity of the solution, and affect the rate and efficiency of the desilication and digestion reactions. Limiting ak to 3.5 - 4.5 can reflect the ratio of caustic soda to alumina in the solution, and affect the reaction equilibrium and product quality. Limiting the temperature to 80°C - 90°C affects the chemical reaction rate, improves the reaction efficiency, and at the same time avoids equipment corrosion and increased energy consumption caused by too high a temperature. Exemplarily, the NK of the preparation liquid can be 190 g / L, 195 g / L, 200 g / L, 205 g / L, 210 g / L, 215 g / L, 220 g / L, etc., AO can be 105 g / L, 107 g / L, 109 g / L, 111 g / L, 113 g / L, 115 g / L, etc., NT can be 210 g / L, 215 g / L, 220 g / L, 225 g / L, 230 g / L, etc., ak can be 3.5, 3.7, 3.9, 4.1, 4.3, 4.5, etc., and the temperature can be 80°C, 82°C, 84°C, 86°C, 88°C, 90°C, etc.

[0044] In some embodiments, the first set temperature is 70°C - 80°C, and the first set time is 5 h - 8 h.

[0045] Limiting the temperature of the first-stage desilication to 70°C - 80°C and the time to 5 h - 8 h can control the desilication reaction rate, avoid side reactions caused by too high a temperature, and at the same time ensure the reaction efficiency. At the same time, ensure that the desilication reaction proceeds fully to improve the desilication efficiency. Exemplarily, the temperature of the first-stage desilication can be 70°C, 72°C, 74°C, 76°C, 78°C, 80°C, etc., and the time can be 5 h, 6 h, 7 h, 8 h, etc.

[0046] S2. Under the conditions of the second set temperature and the second set time, subject the first mixed slurry of the first-stage desilication slurry and the preparation liquid to second-stage desilication, so that the silicon minerals in the first mixed slurry form sodium aluminosilicate hydrate, and obtain a second-stage desilication slurry;

[0047] During the second-stage desilication process, the silicon minerals in the bauxite form sodium aluminosilicate hydrate (Na2O·Al2O3·1.7SiO2·xH2O) during the digestion process and enter the solid red mud.

[0048] In some embodiments, the second set temperature is 130°C - 150°C, and the second set time is 100 min - 120 min.

[0049] Secondary desilication is carried out by introducing high-pressure steam into the digester, using low-temperature Bayer process for digestion, passing through the first, second, and third stage self-evaporators, and adopting shell-and-tube indirect heating. The temperature of secondary desilication is limited to 130°C to 150°C, and the time is 100 min to 120 min, which can improve the digestion efficiency, promote the formation of sodium aluminosilicate hydrate from silicon minerals, and enter the solid red mud. Exemplarily, the temperature of secondary desilication can be 130°C, 135°C, 140°C, 145°C, 150°C, etc., and the time can be 100 min, 105 min, 110 min, 115 min, 120 min, etc.

[0050] In some embodiments, the secondary desilication slurry satisfies the following conditions: solid content is 70 g / L to 90 g / L, ak is 1.35 to 1.4, and A / S is 160 to 180.

[0051] S3. Dilute the secondary desilication slurry to a set solid content, and perform sedimentation separation on the secondary desilication slurry with the set solid content to obtain a second mixed slurry;

[0052] In some embodiments, the set solid content is 55 g / L to 70 g / L.

[0053] Limiting the set solid content to 55 g / L to 70 g / L can control the slurry concentration, facilitate sedimentation separation and subsequent processing. Exemplarily, the set solid content can be 55 g / L, 60 g / L, 65 g / L, 68 g / L, 70 g / L, etc.

[0054] In some embodiments, polyacrylamide and other polymer flocculants are used for the sedimentation separation.

[0055] S4. Add an additive to the second mixed slurry for tertiary desilication to obtain a tertiary desilication slurry; the additive can combine with the silicon-containing compounds in the second mixed slurry to form a precipitate;

[0056] Through tertiary desilication, the silicon-containing compounds in the sodium aluminate solution combine with the additive to form a precipitate, which is refined and filtered by a vertical leaf filter. By adjusting the concentration, addition amount, and feed amount, a pure decomposition mother liquor with aluminum-silicon separation is obtained.

[0057] In some embodiments, the additive is lime milk slurry, and the lime milk slurry satisfies the following conditions: solid content is 200 g / L to 300 g / L, and effective calcium is 180 g / L to 200 g / L.

[0058] S5. Perform solid-liquid separation on the tertiary desilication slurry to obtain a decomposition mother liquor; and

[0059] In some embodiments, the digestion mother liquor meets the following conditions: A / S is 180 - 200, ak is 1.38 - 1.45, NK is 140 g / L - 150 g / L, and the silicon content is < 150 ppm.

[0060] S6. Subject the digestion mother liquor to low-temperature decomposition and high-temperature calcination to obtain alumina.

[0061] In some embodiments, the silicon content in the alumina is < 50 ppm.

[0062] The embodiments of the present application provide a bauxite with an aluminum-silicon ratio of 7 - 10 and a quartz silicon percentage of 1 - 3. Through primary desilication of the ore pulp, secondary desilication during digestion, and tertiary desilication during crude liquid refining, the tertiary desilication process focuses on controlling parameters such as the desilication index, solid content, digestion temperature, reaction time, and the selection of additives in the ore pulp grinding process, digestion process, and crude liquid refining process. After the digestion mother liquor undergoes tertiary desilication, low-temperature decomposition, and high-temperature digestion, high-quality alumina products with a silicon content of less than 50 ppm can be obtained, meeting the raw material requirements for high-purity aluminum.

[0063] In summary, the method for removing silicon from alumina provided by the embodiments of the present application has the following remarkable advantages:

[0064] (1) High-efficiency desilication: Through the finely controlled ore pulp grinding process, primary desilication, secondary desilication, and tertiary desilication processes, the silicon content in the bauxite is effectively reduced to an extremely low level. Especially in the tertiary desilication process, by adding additives such as lime milk slurry, precipitates are formed by combining with silicon-containing compounds, further improving the desilication efficiency.

[0065] (2) Production of high-quality alumina: The silicon content in the alumina product finally obtained by this method is less than 50 ppm, meeting the raw material requirements for high-purity aluminum. High-quality alumina is an important basic raw material in the fields of producing high-performance aluminum materials, aerospace materials, etc.

[0066] (3) Precise parameter control: The present application precisely controls key parameters such as the particle size of the ore pulp grinding, desilication temperature, time, solid content, digestion temperature, reaction time, and the selection of additives. The precise control of these parameters ensures the smooth progress of the desilication reaction and the quality of the final product.

[0067] (4) Stable and reliable process: Through steps such as low-temperature decomposition and high-temperature calcination, this method realizes the stable and reliable production of high-quality alumina from bauxite. The entire process is easy to control and is conducive to large-scale industrial production.

[0068] (5) High resource utilization efficiency: This method makes full use of the effective components in the bauxite, reducing resource waste. At the same time, by precisely controlling the process parameters, energy consumption and production costs are reduced.

[0069] (6) Environmentally friendly: This method generates less waste during the production process and is easy to handle. At the same time, the production of high-quality alumina helps to reduce the dependence on traditional highly polluting energy sources, which is in line with the concept of sustainable development.

[0070] The following will further elaborate on this application in combination with specific embodiments. It should be understood that these embodiments are only used to illustrate this application and not to limit the scope of this application. For the experimental methods without specific conditions indicated in the following embodiments, they are usually determined according to industry standards. If there is no corresponding industry standard, they are carried out according to general international standards, conventional conditions, or the conditions recommended by the manufacturer.

[0071] Example 1

[0072] Bauxite is mixed with a formulation liquid and ground into a slurry. At this time, the particle size of the slurry grinding: 35um% < 1%; 60um% < 12%; 60um% < 30%. The ground slurry is sent to a pre-desilication tank for primary desilication, with a reaction time of 8 hours and a temperature of 70°C. A mixed slurry (solid content 450g / L, ak: 1.8 - 2.0) is obtained. The mixed slurry and the formulation liquid (NK: 206; ak: 3.6) are mixed (at this time the solid content is 220g / L) and sent to a digestion preheater to increase the temperature for digestion for secondary desilication. High-pressure steam is introduced into the digester, and low-temperature Bayer process digestion is used, with a digestion temperature of 142°C and a heat preservation time of 120 minutes. After passing through the first, second, and third self-evaporators, the digested slurry (solid content: 85g / L; ak: 1.357; A / S: 170) and the first-stage settling wash liquid enter a dilution tank. The diluted slurry (at this time the slurry concentration is NK: 146; ak: 1.395; solid content: 68g / L) is sent to a settling and separation tank. The overflow of the settling and separation tank is simultaneously added with a lime milk slurry (solid content 220g / L, effective calcium: 191g / L) for tertiary desilication. After passing through a vertical leaf filter for refined filtration, a decomposition mother liquor is obtained. After tertiary desilication, the obtained decomposition mother liquor has A / S: 196; ak: 1.405; NK: 142; SiO2: 0.85g / L. From this decomposition mother liquor, alumina with a silicon content of 44ppm is obtained through cooling decomposition and high-temperature roasting, meeting the raw material requirements for high-purity aluminum.

[0073] Example 2

[0074] Bauxite is mixed with a formulation solution and ground into a slurry. At this time, the particle size of the ground slurry is: 35um% < 1%; 60um% < 12%; 60um% < 30%. The ground slurry is sent to a pre-desilication tank for primary desilication. The reaction time is 7 hours and the temperature is 80°C. A mixed slurry (solid content: 430 g / L, ak: 1.90) is obtained. The mixed slurry and the formulation solution (NK: 210; ak: 3.6) are mixed (at this time, the solid content is 200 g / L) and sent to a digestion preheater to increase the temperature for digestion and secondary desilication. High-pressure steam is introduced into the digester, and digestion is carried out using the low-temperature Bayer process. The digestion temperature is 140°C and the heat preservation time is 100 minutes. After passing through the first, second, and third self-evaporators, the digested slurry (solid content: 90 g / L; ak: 1.1.4; A / S: 180) and the first washing liquid for sedimentation enter a dilution tank. The diluted slurry (at this time, the slurry concentration is NK: 150; ak: 1.45; solid content: 70 g / L) is sent to a sedimentation and separation tank. Lime milk slurry (solid content: 300 g / L, effective calcium: 200 g / L) is added to the overflow of the sedimentation and separation tank for tertiary desilication. Refined filtration is carried out through a vertical leaf filter to obtain the decomposition mother liquor. After tertiary desilication, the obtained decomposition mother liquor has A / S: 200; ak: 1.45; NK: 150; SiO2: 0.85 g / L. The alumina obtained from this decomposition mother liquor through cooling decomposition and high-temperature roasting has a silicon content of 41 ppm, meeting the raw material requirements for high-purity aluminum.

[0075] Example 3

[0076] Bauxite is mixed with a preparation solution and ground into a slurry. At this time, the particle size of the slurry grinding is: 35um% < 1%; 60um% < 12%; 60um% < 30%. The ground slurry is sent to a pre-desilication tank for primary desilication, with a reaction time of 6 hours and a temperature of 75°C. A mixed slurry (solid content: 440g / L, ak: 1.89) is obtained. The mixed slurry and the preparation solution (NK: 220; ak: 4.5) are mixed (at this time, the solid content is 200g / L) and sent to a digestion preheater to raise the temperature for digestion and secondary desilication. High-pressure steam is introduced into the digester, and low-temperature Bayer process digestion is used, with a digestion temperature of 130°C and a heat preservation time of 120 minutes. After passing through the first, second, and third stage self-evaporators, the digested slurry (solid content: 75g / L; ak: 1.384; A / S: 176) and the first-stage settling wash liquid enter a dilution tank. The diluted slurry (at this time, the slurry concentration is NK: 145; ak: 1.405; solid content: 70g / L) is sent to a settling and separation tank. Lime milk slurry (solid content: 280g / L, effective calcium: 200g / L) is added to the overflow of the settling and separation tank for tertiary desilication. Refined filtration is carried out through a vertical leaf filter to obtain the decomposition mother liquor. After tertiary desilication, the obtained decomposition mother liquor has A / S: 194; ak: 1.425; NK: 146; SiO2: 0.87g / L. The alumina with a silicon content of 45ppm is obtained by cooling decomposition and high-temperature roasting of this decomposition mother liquor, meeting the raw material requirements of high-purity aluminum.

[0077] Comparative Example 1

[0078] Bauxite is mixed with a preparation solution and ground into a slurry. At this time, the particle size of the slurry grinding is: 35um% < 1%; 60um% < 12%; 60um% < 30%. The ground mixed slurry (solid content 180 - 200g / L, ak: 1.8 - 2.0) directly enters the digestion preheater for temperature raising and digestion for primary desilication. High-pressure steam is introduced into the digester, and low-temperature Bayer process digestion is adopted. The digestion temperature is 143°C, and the heat preservation is 60 - 80 minutes. After passing through the first, second, and third self-evaporators, the digested slurry (solid content: 70 - 90g / L; ak: 1.35 - 1.4; A / S: 150 - 160) and the first-stage settling washing liquid enter the dilution tank. The diluted slurry (at this time, the slurry concentration is NK: 140 - 150; ak: 1.38 - 1.45; solid content: 55 - 70g / L) is sent to the sedimentation separation tank. The overflow after sedimentation separation is added with lime milk slurry (solid content 180g / L, effective calcium: 150g / L) for secondary desilication. At this time, the slurry concentration is NK: 140 - 150; ak: 1.38 - 1.45; solid content: 55 - 70g / L. After being refined and filtered by a leaf filter, the decomposition mother liquor is obtained. After desilication, the decomposition mother liquor is: (A / S: 160 - 170; ak: 1.38 - 1.45; NK: 140 - 150; SiO2: 0.9 - 1.1g / L). The high-quality alumina produced from this decomposition mother liquor through cooling decomposition and high-temperature roasting has a silicon content of 95ppm, which cannot meet the raw material requirements of high-purity aluminum.

[0079] In addition, one or more technical solutions in the embodiments of the present application at least further have the following technical effects or advantages:

[0080] In the embodiment of the present application, bauxite is digested by the low-temperature Bayer process, and the A / S of the decomposition mother liquor prepared after three-stage desilication is 180 - 200; the A / S ratio is increased by 20 compared with that before the implementation of this technology.

[0081] In the embodiment of the present application, the silicon in the decomposition mother liquor is controlled within 150ppm.

[0082] In the embodiment of the present application, the silicon content of the alumina produced from the decomposition mother liquor is ≤50ppm, meeting the raw material requirements of high-purity aluminum.

[0083] In the embodiment of the present application, the mother liquor generated by this process is recycled, and the production process is green and environmentally friendly.

[0084] The above are only specific embodiments of the present application, enabling those skilled in the art to understand or implement the present application. Various modifications to these embodiments will be obvious to those skilled in the art, and the general principles defined herein can be implemented in other embodiments without departing from the spirit or scope of the present application. Therefore, the present application will not be limited to these embodiments shown herein, but rather to the broadest scope consistent with the principles and novel features claimed herein.

Claims

1. A method for removing silicon from aluminum oxide, the method comprising: Under the conditions of a first set temperature and a first set time, the bauxite slurry is subjected to a primary desiliconization so that SiO2 in the bauxite slurry is transformed from a supersaturated metastable state to a sodium-silicon slag precipitation to obtain a primary desiliconized slurry; Under the conditions of a second set temperature and a second set time, the first mixed slurry of the primary desiliconization slurry and the formulation liquid is subjected to a secondary desiliconization so that the silicon minerals in the first mixed slurry form hydrated sodium aluminosilicate to obtain a secondary desiliconization slurry; diluting the secondary desiliconization slurry to a set solid content, and subjecting the secondary desiliconization slurry with the set solid content to sedimentation separation to obtain a second mixed slurry; Adding an additive to the second mixed slurry to perform a third desiliconization to obtain a third desiliconized slurry; the additive can combine with the silicon-containing compound in the second mixed slurry to form a precipitate; The tertiary desiliconization slurry is subjected to solid-liquid separation to obtain a decomposition mother liquor; as well as The decomposition mother liquid is subjected to low-temperature decomposition and high-temperature calcination to obtain aluminum oxide.

2. The method according to claim 1, characterized in that The method for preparing the bauxite slurry comprises: Adding bauxite to a preparation liquid and grinding the mixture to obtain a slurry; the bauxite is composed of the following chemical components by mass fraction: SiO2: 5% to 8%, Al2O3: 47% to 50%, quartz silicon: 1% to 3%, gibbsite 1% to 3%, and gibbsite: 65% to 70%; the aluminum-silicon ratio of the bauxite is 7 to 10, and the grinding particle size of the ore in the slurry meets the following conditions: 35um% <1%, 60um% <12%, and 100um% <30%; The slurry is subjected to cyclone classification to obtain the bauxite slurry; the bauxite slurry meets the following conditions: the solid content is 400g / L to 500g / L, and ak is 1.8 to 2.

0.

3. The method according to claim 1 or 2, characterized in that: The prepared liquid meets the following conditions: NK is 190g / L-220g / L, AO is 105g / L-115g / L, NT is 210g / L-230g / L, ak is 3.5-4.5, and the temperature is 80°C-90°C.

4. The method according to claim 1, characterized in that: The first set temperature is 70° C. to 80° C., and the first set time is 5 h to 8 h.

5. The method according to claim 1, characterized in that The second set temperature is 130° C. to 150° C., and the second set time is 100 min to 120 min.

6. The method according to claim 1, characterized in that The secondary desiliconization slurry meets the following conditions: solid content is 70g / L-90g / L, ak is 1.35-1.4, and A / S is 160-180.

7. The method according to claim 1, characterized in that The solid content is set to be 55 g / L to 70 g / L.

8. The method according to claim 1, characterized in that The additive is lime milk slurry, and the lime milk slurry meets the following conditions: solid content is 200g / L to 300g / L, and effective calcium is 180g / L to 200g / L.

9. The method according to claim 1, characterized in that: The decomposition mother liquor meets the following conditions: A / S is 180-200, ak is 1.38-1.45, NK is 140g / L-150g / L, and silicon content is less than 150ppm.

10. The method according to claim 1, characterized in that The silicon content in the alumina is less than 50 ppm.

Images