Method for preparing soluble aluminum oxide based on two-stage roasting

Abstract

The invention relates to the technical field of aluminum oxide production and preparation, in particular to a method for preparing soluble aluminum oxide based on two-stage roasting. The method comprises the following steps: performing primary roasting on aluminum hydroxide at a first preset heating speed to obtain a primary roasting product containing a boehmite component; wherein the temperature of primary roasting is less than or equal to 500 DEG C; the first-stage roasting time is less than or equal to 120 minutes; performing second-stage roasting on the first-stage roasting product containing the boehmite component at a second preset heating speed, so that the boehmite component is subjected to phase change and dehydrated, and the easily-soluble aluminum oxide is obtained; wherein the temperature T2 of the second-stage roasting and the temperature T1 of the first-stage roasting meet the relational expression that T2-T1 is larger than or equal to 250 DEG C, and the time of the second-stage roasting is smaller than or equal to 30 min. According to the method, through the synergistic effect of the two-stage roasting process, the roasting phase transformation process and the dehydration reaction speed are accurately regulated and controlled, and the dual purposes of reducing the production cost and improving the dissolving performance are achieved.

Description

Technical Field

[0001] This application relates to the technical field of alumina production and preparation, and particularly relates to a method for preparing easily soluble alumina based on secondary calcination. Background Art

[0002] After alumina with poor dissolution performance is added to the electrolyte melt, the dissolution rate of the electrolyte melt will be slow, and precipitation is likely to occur. These disadvantages will lead to unstable operation of the aluminum electrolysis cell and even trigger the anode effect of the aluminum electrolysis cell, thereby reducing the current efficiency of the aluminum electrolysis cell, increasing the power consumption and material consumption of the aluminum electrolysis cell, and even increasing the emission of greenhouse gases such as perfluorocarbons (PFCs). Therefore, using alumina with poor dissolution performance in the aluminum electrolysis cell will not only affect the production process of aluminum electrolysis but also pollute the environment.

[0003] In order to solve the problem of poor dissolution performance of alumina in current aluminum electrolysis production, at present, easily soluble alumina products can be prepared based on hydrothermal reactions. However, hydrothermal reactions require the construction of high-temperature hydrothermal production lines. Some alumina production enterprises are restricted by on-site basic conditions such as site area and energy supply, and it is difficult to build high-temperature hydrothermal production lines that meet the requirements, which makes the industrial promotion of easily soluble alumina production technology relatively difficult.

[0004] The specific process of the existing hydrothermal reaction is as follows: First, an aluminum hydroxide slurry is prepared using aluminum hydroxide and sodium aluminate as raw materials. After the aluminum hydroxide slurry undergoes a high-temperature hydrothermal reaction, the crystal form of aluminum hydroxide is reconstructed to obtain an alumina hydrate with a specific crystal form. Then, the alumina hydrate is subjected to low-temperature calcination treatment to obtain an easily soluble alumina product. Summary of the Invention

[0005] This application provides a method for preparing easily soluble alumina based on multi-stage calcination and an alumina product to solve the following technical problems: how to balance the production cost and dissolution performance of easily soluble alumina.

[0006] In a first aspect, an embodiment of this application provides a method for preparing easily soluble alumina based on secondary calcination, and the method includes:

[0007] Perform primary calcination on aluminum hydroxide at a first preset heating rate to obtain a primary calcination product containing a boehmite component; wherein, the temperature of the primary calcination ≤ 500°C; the time of the primary calcination ≤ 120 min;

[0008] The primary calcined product containing boehmite is subjected to secondary calcination at a second preset heating rate, causing the boehmite to undergo a phase change and dehydration to obtain readily soluble alumina; wherein, the temperature T2 of the secondary calcination and the temperature T1 of the primary calcination satisfy the relation: T2 - T1 ≥ 250°C, and the time of the secondary calcination ≤ 30 min.

[0009] Optionally, the primary calcination includes a first heating section, and the end temperature of the first heating section is 350°C to 500°C.

[0010] Optionally, the first preset heating rate of the first heating section is 20°C / min to 60°C / min.

[0011] Optionally, the primary calcination further includes a first heat preservation section, and the time of the first heat preservation section is 20 min to 120 min.

[0012] Optionally, the secondary calcination includes a second heating section, and the end temperature of the second heating section is 750°C to 950°C.

[0013] Optionally, the second preset heating rate of the second heating section is 15°C / min to 65°C / min.

[0014] Optionally, the secondary calcination includes a second heat preservation section, and the time of the second heat preservation section is 2 s to 1800 s.

[0015] Optionally, the primary calcined product includes a boehmite component, and the mass of the boehmite component is greater than or equal to 50% of the total mass of the primary calcined product.

[0016] In a second aspect, the present application provides a readily soluble alumina product, which is prepared by the method described in the first aspect. The specific surface area of the alumina product ≥ 100 m 2 / g, and the loss on ignition of the alumina product ≤ 1.10%.

[0017] Optionally, the mass percentage content of fine particle alumina with a particle size ≤ 20 μm in the readily soluble alumina product ≤ 3%.

[0018] The above technical solutions provided by the embodiments of the present application have the following advantages compared with the prior art:

[0019] A method for preparing easily soluble alumina based on secondary calcination provided by an embodiment of the present application. This method controls the temperature of the first-stage calcination below 500°C and the time of the first-stage calcination ≤ 120 min through two-stage calcination. The first-stage calcination with a longer calcination time and a lower calcination temperature can cause the primary phase transformation of aluminum hydroxide and the primary removal of seed moisture to form a boehmite component with a loose porous structure. This porous structure can endow the boehmite component with a sufficiently large specific surface area and a loose pore structure. The loose pore structure with a higher specific surface area can prevent the agglomeration of the first-stage calcination product in the second-stage calcination stage, thereby forming an easily soluble alumina product with a dispersed and high reaction activity site. Additionally, control the temperature difference between the second-stage calcination and the first-stage calcination above 250°C, and control the time of the second-stage calcination within 30 min. The second-stage calcination with a higher calcination temperature and a shorter calcination time can enable the boehmite component with a porous structure to fully undergo phase transformation and dehydration to fix the active crystal form formed by the phase transformation of the boehmite component, thereby enhancing the surface activity of the easily soluble alumina and improving the dissolution performance of the easily soluble alumina. Furthermore, the method of combining the first-stage calcination with a longer calcination time and a lower calcination temperature and the second-stage calcination with a higher calcination temperature and a shorter calcination time can effectively reduce the energy consumption of the overall calcination process. Therefore, this method can effectively balance the production cost and dissolution performance of alumina through two-stage calcination. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] The accompanying drawings herein are incorporated into the specification and form a part of the specification, showing embodiments consistent with the present application and used together with the specification to explain the principles of the present application.

[0021] 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 accompanying drawings required for the description of the embodiments or the prior art. Obviously, for those of ordinary skill in the art, other accompanying drawings can be obtained based on these accompanying drawings without creative efforts.

[0022] Figure 1 It is a schematic flow chart of a method for preparing easily soluble alumina based on multi-stage calcination provided by an embodiment of the present application. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0023] To make the objectives, technical solutions, and advantages of the embodiments of this application clearer, the technical solutions in the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings in the embodiments of this application. Obviously, the described embodiments are some, but not all, of the embodiments of this application. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of this application without creative efforts shall fall within the scope of protection of this application.

[0024] The various embodiments of this 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 this application; therefore, it should be considered that the described range description has specifically disclosed all possible sub-ranges and individual 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 individual numbers within that range, such as 1, 2, 3, 4, 5, and 6, regardless of the range; in addition, whenever a numerical range is indicated herein, it means including any cited number (fraction or integer) within the indicated range.

[0025] In this document, terms such as "including" mean "including but not limited to". Relative 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 actual relationship or order between these entities or operations. "And / or" describes the associated relationship of associated objects and indicates that three relationships may exist. For example, A and / or B may represent: A exists alone, A and B exist simultaneously, or B exists alone; where A and B may be singular or plural. "At least one" means one or more, and "multiple" 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 item (piece) 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. "Parts representation method" such as parts by weight, parts by mass, etc. represents the proportional relationship between each component. In the proportional relationships involved in this document, the parameters that need to be described by proportion should be understood as the antecedents of the proportional formula in the order of description, and the proportional numbers should be understood as the consequents of the proportional 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 proportional 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.

[0026] Unless otherwise specified, all kinds of raw materials, reagents, instruments, equipment, etc. used in this article can be obtained through market purchase or can be prepared by existing methods.

[0027] Figure 1 Exemplarily shown is a schematic flow chart of a method for preparing easily soluble alumina based on secondary calcination provided by an embodiment of the present application;

[0028] As Figure 1 shown, a method for preparing easily soluble alumina based on secondary calcination provided by an embodiment of the present application, the method includes:

[0029] S1. Calcining aluminum hydroxide at a first preset heating rate to obtain a first-stage calcination product containing boehmite components; wherein, the temperature of the first-stage calcination ≤ 500 °C; the time of the first-stage calcination ≤ 120 min;

[0030] S2. Calcining the first-stage calcination product containing boehmite components at a second preset heating rate to cause the phase change and dehydration of the boehmite components, and obtain easily soluble alumina; wherein, the temperature T2 of the second-stage calcination and the temperature T1 of the first-stage calcination satisfy the relationship: T2 - T1 ≥ 250 °C, and the time of the second-stage calcination ≤ 30 min.

[0031] The temperature of the first-stage calcination can be 350 °C, 360 °C, 370 °C, 380 °C, 390 °C, 400 °C, 450 °C or 500 °C.

[0032] The time of the first-stage calcination can be 40 min, 50 min, 60 min, 70 min, 80 min, 90 min, 100 min, 110 min or 120 min.

[0033] The temperature of the second-stage calcination can be 750 °C, 760 °C, 770 °C, 780 °C, 790 °C, 800 °C, 810 °C, 820 °C, 830 °C, 840 °C or 850 °C.

[0034] The time of the second-stage calcination can be 5 min, 10 min, 15 min, 20 min, 25 min or 30 min.

[0035] It should be noted that for a method for preparing easily soluble alumina based on secondary calcination provided by an embodiment of the present application, this method realizes the dual goals of reducing production costs and improving dissolution performance through the synergistic effect of a two-stage calcination process. Its technical principle and optimization path can be decomposed as follows:

[0036] 1. Process principle and key parameter design: (1) Primary calcination (low temperature and long time): Mechanism: Under the primary calcination conditions of T1≤500℃ and t1≤120min, aluminum hydroxide is initially dehydrated of seed water (adsorbed water and structural water) and forms a porous precursor of boehmite (AlOOH). This primary calcination stage can obtain a specific surface area of ​​≥200m by rapidly increasing the temperature. 2 / g loose pore structure.

[0037] (2) Structural advantages: The porous skeleton provides a diffusion channel for subsequent phase change, while inhibiting particle agglomeration during secondary calcination and improving the dispersion performance of raw materials for subsequent secondary calcination.

[0038] (3) Secondary calcination (high temperature and short time): 1) Phase change control: T2-T1 ≥ 250℃, t2 ≤ 30min, to promote the rapid dehydration of boehmite into the active γ-Al2O3 crystal form. 2) Performance enhancement: Short-term high temperature treatment can fix the number of surface dissolution active sites and avoid the formation of inert phases such as α-Al2O3.

[0039] 2. Production cost optimization path: (1) Energy consumption control: The first-stage roasting uses low temperature (≤500℃) to reduce the heat load, and combined with the suspension roasting technology to achieve the cascade utilization of waste heat, the energy consumption can be reduced by 20% to 30% compared with the traditional single-stage roasting. The second-stage roasting quickly heats up (≥15℃ / min) and shortens the residence time in the high-temperature section, which can reduce fuel consumption. (2) Raw material and equipment optimization: Eliminate the hydrothermal treatment process of the existing soluble alumina production process.

[0040] 3. Mechanism of improving solubility: Porous structure enhances mass transfer efficiency: The mesopores formed by the primary calcination and the micropores formed by the secondary calcination can form hierarchical pores, making the specific surface area of ​​soluble alumina ≥100m 2 / g, these characteristics can accelerate solvent penetration and reactant diffusion.

[0041] 4. Process parameter comparison table, as shown in Table 1.

[0042] Table 1 Comparison of characteristics of various levels of roasting

[0043]

[0044] As shown in Table 1, through the synergistic effect of the two-stage roasting, the dissolution rate of the final product can be increased by more than 15% compared with the traditional process, and the roasting energy consumption can be reduced by 25% to 30%.

[0045] In some optional embodiments, the primary calcination includes a first temperature rising section, and the terminal temperature of the first temperature rising section is 350°C to 500°C.

[0046] In these embodiments, the primary calcination may include a first heating section, and the end temperature of the first heating section may be 350°C to 500°C, such that the primary calcination is carried out under relatively low temperature conditions to preliminarily cause phase transformation of aluminum hydroxide and preliminarily remove the seed moisture, so as to form a boehmite component with a loose porous structure. This porous structure can enable the boehmite component to have a sufficiently large specific surface area and a loose pore structure, and can form a readily soluble alumina product with high dispersion and a high number of reactive sites.

[0047] The end temperature of this first heating section may be 350°C, 360°C, 370°C, 380°C, 390°C, 400°C, 450°C or 500°C.

[0048] In some alternative embodiments, the first preset heating rate of the first heating section is 20°C / min to 60°C / min.

[0049] In these embodiments, the first preset heating rate of the first heating section may be 20°C / min to 60°C / min, such that the first heating section of the primary calcination is at an appropriate level, and the primary calcination is in a state for a relatively long time, which can cause the phase transformation of aluminum hydroxide to occur preliminarily and the seed moisture to be removed preliminarily, so as to form a boehmite component with a loose porous structure. This porous structure can enable the boehmite component to have a sufficiently large specific surface area and a loose pore structure, thereby forming a readily soluble alumina product with high dispersion and a high number of reactive sites.

[0050] The first preset heating rate of this first heating section may be 20°C / min, 30°C / min, 40°C / min, 50°C / min or 60°C / min.

[0051] In some alternative embodiments, the primary calcination further includes a first heat preservation section, and the time of the first heat preservation section is 20 min to 120 min.

[0052] In these embodiments, the primary calcination may further include a first heat preservation section, and the time of the first heat preservation section may be 20 min to 120 min, such that the primary calcination is in a state for a relatively long time, which can cause the phase transformation of aluminum hydroxide to occur preliminarily and the seed moisture to be removed preliminarily, so as to form a boehmite component with a loose porous structure. This porous structure can enable the boehmite component to have a sufficiently large specific surface area and a loose pore structure, thereby forming a readily soluble alumina product with high dispersion and a high number of reactive sites.

[0053] The time of this first heat preservation section may be 20 min, 30 min, 40 min, 50 min, 60 min, 70 min, 80 min, 90 min, 100 min, 110 min or 120 min.

[0054] In some alternative embodiments, the secondary calcination includes a second heating section, and the end temperature of the second heating section is 750°C to 950°C.

[0055] In these embodiments, the secondary calcination may include a second heating section, and the end temperature of the second heating section may be 750°C to 950°C, such that the secondary calcination is under relatively high calcination temperature conditions. The secondary calcination at a relatively high calcination temperature enables the boehmite component with a porous structure to fully undergo phase transformation and dehydration to fix the active crystal form formed by the phase transformation of the boehmite component, thereby improving the dissolution performance of the readily soluble alumina.

[0056] The end temperature of the second heating section may be 750°C, 760°C, 770°C, 780°C, 790°C, 800°C, 810°C, 820°C, 830°C, 840°C, 850°C, 900°C or 950°C.

[0057] In some alternative embodiments, the second preset heating rate of the second heating section is 15°C / min to 65°C / min.

[0058] In these embodiments, the second preset heating rate of the second heating section may be 15°C / min to 65°C / min, such that after the primary calcination is completed, the temperature can be quickly raised to the calcination temperature of the secondary calcination to shorten the time of the secondary calcination. The secondary calcination with a shorter calcination time enables the boehmite component with a porous structure to fully undergo phase transformation and dehydration to fix the active crystal form formed by the phase transformation of the boehmite component, so as to improve the dissolution performance of the readily soluble alumina.

[0059] The second preset heating rate of the second heating section may be 15°C / min, 20°C / min, 25°C / min, 30°C / min, 35°C / min, 40°C / min, 45°C / min, 50°C / min, 55°C / min or 60°C / min.

[0060] In some alternative embodiments, the secondary calcination includes a second heat preservation section, and the time of the second heat preservation section is 2 s to 1800 s.

[0061] In these embodiments, the secondary calcination may include a second heat preservation section, and the time of the second heat preservation section may be 2 s to 1800 s, shortening the time required for the secondary calcination. The secondary calcination with a shorter calcination time enables the boehmite component with a porous structure to fully undergo phase transformation and dehydration to fix the active crystal form formed by the phase transformation of the boehmite component, improving the dissolution performance of the readily soluble alumina.

[0062] The time of the second heat preservation stage can be 2s, 3s, 4s, 5s, 6s, 7s, 8s, 9s, 10s, 50s, 100s, 150s, 200s, 250s, 300s, 400s, 500s, 1000s, 1500s or 1800s.

[0063] In some alternative embodiments, the primary calcined product comprises a boehmite component, and the mass of the boehmite component is greater than or equal to 50% of the total mass of the primary calcined product.

[0064] In these embodiments, the primary calcined product may comprise a boehmite component, and the mass of the boehmite component is greater than or equal to 50% of the total mass of the primary calcined product, such that there is an adequate amount of boehmite component with a porous structure within the primary calcined product. This porous structure can endow the boehmite component with a sufficiently large specific surface area and a porous structure, thereby enabling the formation of a readily soluble alumina product with a dispersed and highly reactive active site.

[0065] The mass of the boehmite component can be 50%, 55%, 60% or 65% of the total mass of the primary calcined product.

[0066] Based on a general inventive concept, embodiments of the present application provide an alumina product prepared by the method. The specific surface area of the alumina product is ≥ 100m 2 / g, and the loss on ignition of the alumina product is ≤ 1.10%.

[0067] This alumina product is realized based on the above method. The specific steps of the method can refer to the above embodiments. Since this alumina product adopts some or all of the technical solutions of the above embodiments, it at least has all the beneficial effects brought by the technical solutions of the above embodiments, which will not be elaborated herein one by one.

[0068] It should be noted that the specific surface area of the alumina product ≥ 100m 2 / g indicates that the alumina product has uniformly dispersed particles, enabling the alumina product to have a high dissolution rate.

[0069] It should be noted that the loss on ignition of this alumina product is ≤ 1.10%, which indicates that the loss of the alumina product during the preparation stage is small, thereby effectively reducing the consumption in the preparation of the alumina product and reducing the preparation cost of alumina.

[0070] In some alternative embodiments, the mass percentage content of alumina fine particles with a particle size of -20μm in the alumina product is ≤ 3%.

[0071] The present application will be further described below in conjunction with specific embodiments. For the experimental methods without specific conditions noted in the following embodiments, they are generally determined in accordance with national standards / industry standards; if there are no corresponding national standards / industry standards, they are carried out in accordance with general international standards, conventional conditions or the conditions recommended by the manufacturer.

[0072] Example 1

[0073] Using industrial aluminum hydroxide 1 as the raw material, the particle size D50 of industrial aluminum hydroxide 1 is 85 μm, the aluminum hydroxide with a particle size greater than or equal to 45 μm accounts for 87% of the total mass of industrial aluminum hydroxide, and the aluminum hydroxide with a particle size less than or equal to 20 μm accounts for 0.90% of the total mass of industrial aluminum hydroxide.

[0074] As Figure 1 shown, a method for preparing easily soluble alumina based on multi-stage roasting includes:

[0075] S1. Roast aluminum hydroxide at a first preset heating rate for the first-stage roasting to obtain a first-stage roasted product containing boehmite components;

[0076] S2. Roast the first-stage roasted product containing boehmite components at a second preset heating rate for the second-stage roasting to cause the phase change and dehydration of the boehmite components, and obtain easily soluble alumina.

[0077] The first-stage roasting includes a first heating section, and the end temperature of the first heating section is 350 °C.

[0078] The first preset heating rate in the first heating section is 20 °C / min.

[0079] The first-stage roasting further includes a first heat preservation section, and the time of the first heat preservation section is 120 min.

[0080] The second-stage roasting includes a second heating section, and the end temperature of the second heating section is 940 °C.

[0081] The second preset heating rate in the second heating section is 30 °C / min.

[0082] The second-stage roasting includes a second heat preservation section, and the time of the second heat preservation section is 2 s.

[0083] The first-stage roasted product includes boehmite components, and the mass of the boehmite components is 52% of the total mass of the first-stage roasted product.

[0084] Example 2

[0085] Compared with Example 1, the differences in this example are as follows, and the rest are the same:

[0086] The end temperature of the first heating section is 500 °C.

[0087] The first preset heating rate in the first heating stage is 60 °C / min.

[0088] The time of the first heat preservation stage is 20 min.

[0089] The end temperature of the second heating stage is 760 °C.

[0090] The second preset heating rate in the second heating stage is 15 °C / min.

[0091] The time of the second heat preservation stage is 1800 s.

[0092] The mass of the boehmite component is 56% of the total mass of the first-stage calcined product.

[0093] Example 3

[0094] Compared with Example 1, the differences in this example are as follows, and the rest are the same:

[0095] The first-stage calcination includes a first heating stage, and the end temperature of the first heating stage is 430 °C.

[0096] The first preset heating rate in the first heating stage is 60 °C / min.

[0097] The first-stage calcination also includes a first heat preservation stage, and the time of the first heat preservation stage is 20 min.

[0098] The second-stage calcination includes a second heating stage, and the end temperature of the second heating stage is 800 °C.

[0099] The second preset heating rate in the second heating stage is 40 °C / min.

[0100] The second-stage calcination includes a second heat preservation stage, and the time of the second heat preservation stage is 1200 s.

[0101] The mass of the boehmite component is 53% of the total mass of the first-stage calcined product.

[0102] Example 4

[0103] Compared with Example 1, the differences in this example are as follows, and the rest are the same:

[0104] The end temperature of the first heating stage is 400 °C.

[0105] The first preset heating rate in the first heating stage is 50 °C / min.

[0106] The time of the first heat preservation stage is 60 min.

[0107] The end temperature of the second heating stage is 930 °C.

[0108] The second preset heating rate in the second heating stage is 40 °C / min.

[0109] The time of the second heat preservation stage is 5 s.

[0110] The mass of the boehmite component is 65% of the total mass of the first-stage calcined product.

[0111] Example 5

[0112] Compared with Example 1, the differences in this example are as follows, and the rest are the same:

[0113] The particle size D50 of the industrial aluminum hydroxide 2 is 75 μm, the aluminum hydroxide with a particle size greater than or equal to 45 μm accounts for 85% of the total mass of the industrial aluminum hydroxide, and the aluminum hydroxide with a particle size less than or equal to 20 μm accounts for 0.80% of the total mass of the industrial aluminum hydroxide.

[0114] The end temperature of the first heating stage is 380 °C.

[0115] The first preset heating rate of the first heating stage is 25 °C / min.

[0116] The time of the first heat preservation stage is 90 min.

[0117] The end temperature of the second heating stage is 780 °C.

[0118] The second preset heating rate of the second heating stage is 30 °C / min.

[0119] The time of the second heat preservation stage is 1800 s.

[0120] The mass of the boehmite component is 67% of the total mass of the first-stage calcined product.

[0121] Example 6

[0122] Compared with Example 5, the differences in this example are as follows, and the rest are the same:

[0123] The end temperature of the first heating stage is 460 °C.

[0124] The first preset heating rate of the first heating stage is 20 °C / min.

[0125] The time of the first heat preservation stage is 30 min.

[0126] The end temperature of the second heating stage is 930 °C.

[0127] The second preset heating rate of the second heating stage is 40 °C / min.

[0128] The time of the second heat preservation stage is 5 s.

[0129] The mass of the boehmite component is 63% of the total mass of the first-stage calcined product.

[0130] Example 7

[0131] Compared with Example 5, the differences in this example are as follows, and the rest are the same:

[0132] The end temperature of the first heating section is 420 °C.

[0133] The first preset heating rate of the first heating section is 30 °C / min.

[0134] The time of the first heat preservation section is 30 min.

[0135] The end temperature of the second heating section is 930 °C.

[0136] The second preset heating rate of the second heating section is 40 °C / min.

[0137] The time of the second heat preservation section is 5 s.

[0138] The mass of the boehmite component is 72% of the total mass of the first-stage calcined product.

[0139] Example 8

[0140] Compared with Example 5, the differences in this example are as follows, and the rest are the same:

[0141] The end temperature of the first heating section is 400 °C.

[0142] The first preset heating rate of the first heating section is 60 °C / min.

[0143] The time of the first heat preservation section is 120 min.

[0144] The end temperature of the second heating section is 950 °C.

[0145] The second preset heating rate of the second heating section is 60 °C / min.

[0146] The time of the second heat preservation section is 2 s.

[0147] The mass of the boehmite component is 75% of the total mass of the first-stage calcined product.

[0148] Comparative Example 1

[0149] Compared with Example 1, the differences in this comparative example are as follows, and the rest are the same:

[0150] Calcining industrial aluminum hydroxide 1 using the traditional method, the calcining temperature is 1080 °C, the calcining time is 2 s, the D50 of the alumina product is 71 μm, and the mass of alumina with a particle size greater than 45 μm is 80% of the total mass of the alumina product, and the mass of alumina with a particle size less than 20 μm is 3.50% of the total mass of the alumina product. Specific surface area 85 m2 / g, loss on ignition 0.90%.

[0151] Comparative Example 2

[0152] Compared with Example 5, the differences of this comparative example are as follows, and the rest are the same:

[0153] Using the traditional method to calcine industrial aluminum hydroxide 2, the calcination temperature is 960 °C, the calcination time is 25 min, the D50 of the alumina product is 57 μm, the mass of alumina with a particle size greater than 45 μm is 65% of the total mass of the alumina product, and the mass of alumina with a particle size less than 20 μm is 4.50% of the total mass of the alumina product. Specific surface area 55m 2 / g, loss on ignition 0.82%.

[0154] Comparative Example 3

[0155] Compared with Example 5, the differences of this comparative example are as follows, and the rest are the same:

[0156] Using the traditional method to calcine industrial aluminum hydroxide 2, the calcination temperature is 1050 °C, the calcination time is 2 s, the D50 of the alumina product is 67 μm, and the mass of alumina with a particle size greater than 45 μm is 80% of the total mass of the alumina product, and the mass of alumina with a particle size less than 20 μm is 2.90% of the total mass of the alumina product. The specific surface area of this alumina product is 75m 2 / g, loss on ignition 0.95%.

[0157] Related experiments and effect data:

[0158] 1. Respectively count the characteristics of the easily soluble alumina in each example and comparative example, and the results are shown in Table 2.

[0159] Table 2 Distribution of the characterization of the alumina products in each example and comparative example

[0160]

[0161] 2. Test the dissolution performance of the easily soluble alumina in each example and comparative example. The specific process is as follows: First, add 200 g of a mixture of cryolite and aluminum fluoride into a platinum crucible, and control the molecular ratio of cryolite to aluminum fluoride to be 2.50; then place the crucible in a heating furnace with a set temperature increase and holding program and start heating to 940 °C. When the electrolyte in the crucible is completely dissolved and becomes a molten electrolyte, then add 2 g of the easily soluble alumina products of each example and comparative example respectively, and record the time when the easily soluble alumina product is completely dissolved. Then calculate the dissolution rate according to the complete dissolution time. The calculation formula is: Dissolution rate = 2 g / complete dissolution time, and the results are shown in Table 3.

[0162] Table 3 Test Results of Dissolution Performance of Alumina Products in Examples and Comparative Examples

[0163]

[0164] As can be seen from Table 2 and Table 3, a method for preparing easily soluble alumina based on secondary calcination provided by the embodiments of the present application can precisely control the calcination phase transition process and dehydration reaction rate of aluminum hydroxide through the synergistic effect of a two-stage calcination process, so as to improve the surface reaction activity of the easily soluble alumina product, thereby achieving the dual goals of reducing production costs and improving dissolution performance. In addition, although this method will cause an increase in the ignition loss of the easily soluble alumina, its ignition loss still remains at about 1%, which will not affect the performance of the alumina product. In addition, a method for preparing easily soluble alumina based on multi-stage calcination provided by the embodiments of the present application can reduce the overall energy consumption in the calcination stage through two-stage calcination, can reduce the cost of producing alumina from aluminum hydroxide, and also has the advantages of simple process, less equipment investment cost, and easy industrial application.

[0165] In addition, an easily soluble alumina product provided by the embodiments of the present application has a dissolution rate of more than 0.020 g / s. Compared with traditional industrial alumina products, its dissolution rate is increased by more than 15%. Therefore, it can be used as a metallurgical grade alumina product.

[0166] In addition, a method for preparing easily soluble alumina by secondary calcination provided by the embodiments of the present application can significantly reduce the particle size breakage during the alumina calcination process and improve the surface activity of the alumina product, thereby increasing the dissolution rate of alumina in the electrolyte melt and improving the operation effect of the dry purification of flue gas in aluminum electrolysis production.

[0167] 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. The general principles defined in the present application 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 in the present application, but will conform to the widest scope consistent with the principles and novel features claimed in the present application.

Claims

1. A method for preparing readily soluble alumina based on secondary calcination, the method comprising: Performing primary calcination on aluminum hydroxide at a first preset heating rate to obtain a primary calcination product containing boehmite component; wherein, the temperature of the primary calcination ≤ 500 °C; the time of the primary calcination ≤ 120 min; Performing secondary calcination on the primary calcination product containing boehmite component at a second preset heating rate to cause the phase change and dehydration of the boehmite component, thereby obtaining readily soluble alumina; wherein, the temperature T2 of the secondary calcination and the temperature T1 of the primary calcination satisfy the relation: T2 - T1 ≥ 250 °C, and the time of the secondary calcination ≤ 30 min.

2. The method according to claim 1, wherein the primary calcination comprises a first heating section, and the end temperature of the first heating section is 350 °C to 500 °C.

3. The method according to claim 2, wherein the first preset heating rate of the first heating section is 20 °C / min to 60 °C / min.

4. The method according to claim 1, wherein the primary calcination further comprises a first heat preservation section, and the time of the first heat preservation section is 20 min to 120 min.

5. The method according to claim 1, wherein the secondary calcination comprises a second heating section, and the end temperature of the second heating section is 750 °C to 950 °C.

6. The method according to claim 5, wherein the second preset heating rate of the second heating section is 15 °C / min to 65 °C / min.

7. The method according to claim 1, wherein the secondary calcination comprises a second heat preservation section, and the time of the second heat preservation section is 2 s to 1800 s.

8. The method according to claim 1, wherein the primary calcination product comprises boehmite component, and the mass percentage content of the boehmite component is greater than or equal to 50% of the total mass of the primary calcination product.

9. An alumina product, which is prepared by the method according to any one of claims 1 to 8, wherein the specific surface area of the alumina product is ≥ 100 m 2 / g, and the loss on ignition of the alumina product is ≤ 1.10%.

10. The alumina product according to claim 9, wherein the mass percentage content of fine particles with a particle size of ≤ 20 μm in the alumina product ≤ 3%.

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