Low-calcium boehmite and preparation method thereof

Abstract

The invention relates to the technical field of boehmite materials, in particular to low-calcium boehmite and a preparation method thereof.The preparation method comprises the steps that aluminum hydroxide prepared through a Bayer method is put into a muffle furnace, and light-burned aluminum hydroxide is obtained; mixing the light-burned aluminum hydroxide with deionized water, and pulping to obtain primary reaction pulp; adding organic acid into the primary reaction slurry to obtain a filter cake; mixing and pulping the filter cake and deionized water to obtain secondary reaction pulp; putting the secondary reaction slurry into a high-pressure reaction kettle, and adding organic acid to obtain powder; and putting the powder into a muffle furnace, and calcining to obtain the low-calcium boehmite. According to the invention, through low-temperature light burning pretreatment, calcium ions adsorbed on the surface and calcium ions between structures form migration activation sites on the premise of not destroying the lattice integrity of aluminum hydroxide; a reaction system is regulated and controlled by stages through organic acid, surface complexing removal of calcium ions is achieved in a normal-pressure environment, then the calcium ions doped in crystal lattices are deeply dissociated under the high-pressure hydrothermal condition, and the calcium content of the obtained product is lower than 22 ppm.

Description

Technical Field

[0001] The present invention relates to the technical field of boehmite materials, and in particular to low-calcium boehmite and a preparation method thereof. Background Art

[0002] In the field of new energy materials and advanced ceramics, boehmite (γ-AlOOH) is a high-performance aluminum source precursor. Its calcium impurity content has a significant impact on the crystal structure and ion conductivity of the downstream solid electrolyte β″-Al2O3. Due to the characteristics of the Bayer process, the calcium impurity content of aluminum hydroxide raw materials prepared by traditional industry is generally higher than 0.05wt%, resulting in the following technical bottlenecks in the subsequent synthesized β″-Al2O3 in sodium-sulfur battery applications: 1) Calcium ions occupy Al3+ lattice sites, destroying the β″ phase layered structure. Calcium ions occupy sodium ion sites in the conductive layer or block sodium ion migration channels, increasing grain boundary impedance and raising migration barriers, resulting in a decrease in electrical conductivity; 2) During high-temperature sintering, calcium and alumina form a low-melting-point phase of CaAl2O4, which induces local melting above 1150°C, resulting in an increase in grain boundary defect density and a reduction in the mechanical strength and thermal stability of the material.

[0003] In the existing technology, the introduction of calcium impurities is controlled through raw material purification and process optimization, but both methods have significant limitations. Regarding raw material purification: the preparation cost of high-purity aluminum source is high, and it is impossible to completely eliminate the calcium ions introduced in the Bayer process; the mechanical washing method can only remove surface-adsorbed calcium, and the removal rate of lattice-doped calcium is low; although the chemical precipitation method can deeply remove calcium, the cost is high. Especially for β″-Al2O3 used in sodium-sulfur batteries, its preparation temperature window (1150-1600℃) highly overlaps with the activation temperature of calcium impurities. The existing calcium removal technology is difficult to maintain the high-temperature stability of the material while ensuring the purity of the β″ phase. Regarding process optimization: Although deep calcium removal processes such as the sol-gel method can reduce the calcium content to below 0.01wt%, they require the use of expensive organic chelating agents, and the process flow is long and the production cost is high, which seriously restricts industrial application. Summary of the Invention

[0004] In response to the problem of high calcium content in boehmite in the above-mentioned prior art, the present invention provides a low-calcium boehmite and a preparation method thereof.

[0005] To achieve the above object, the technical solution of the present invention is as follows:

[0006] A method for preparing low-calcium boehmite comprises the following steps:

[0007] S1. Place aluminum hydroxide prepared by the Bayer process into a muffle furnace and calcine at 180-300° C. for 20-50 min to obtain light-burned aluminum hydroxide;

[0008] S2. Mixing light-burned aluminum hydroxide and deionized water to obtain a primary reaction slurry;

[0009] S3. Add organic acid to the primary reaction slurry, react at 50-80°C for 30-40 minutes, and filter to obtain a filter cake;

[0010] S4, mixing the filter cake with deionized water to obtain a secondary reaction slurry;

[0011] S5. Place the secondary reaction slurry into a high-pressure reactor, add an organic acid, react at 150-200° C. for 2-24 hours, cool, filter, wash, and dry to obtain a powder;

[0012] S6. Place the powder into a muffle furnace and calcine at 500-900° C. for 0.5-5 h to obtain low-calcium boehmite.

[0013] Furthermore, the solid content in the primary reaction slurry and the secondary reaction slurry is 200-400 g / L.

[0014] Furthermore, in S3 and S5, the organic acid includes one or more of acetic acid, lactic acid and gluconic acid.

[0015] Furthermore, in S3 and S5, the amount of organic acid added is such that the molar ratio of the acid radical ions in the organic acid to the calcium ions in the reaction slurry is ≥1.2.

[0016] The present invention also includes the following technical solutions:

[0017] A low-calcium boehmite prepared by the above-mentioned method for preparing low-calcium boehmite.

[0018] Furthermore, the calcium content is lower than 22 ppm.

[0019] In the present invention, the acid radical ions in the organic acid react with the calcium ions to form soluble calcium salts, which are discharged with the washing liquid during the washing process, thereby reducing the calcium content in the boehmite.

[0020] Compared with the prior art, the present invention has the following beneficial effects:

[0021] The present invention provides a low-calcium boehmite and a preparation method thereof. First, a low-temperature light calcination pretreatment is performed to form activation sites capable of migration between calcium ions adsorbed on the surface and calcium ions between the structures without destroying the integrity of the aluminum hydroxide lattice. Subsequently, an organic acid is used to regulate the reaction system in stages, achieving surface complexation and removal of calcium ions in a normal pressure environment of 50-80°C. Then, the calcium ions doped in the lattice are deeply dissociated under high-pressure hydrothermal conditions of 150-200°C. The synergistic effect of the two-step organic acid improves the efficiency of calcium ion removal. By controlling the amount of organic acid added, it is ensured that the calcium ions can be completely complexed, while aluminum dissolution caused by excessive acid etching is avoided. Finally, the boehmite crystal structure is reconstructed by calcination. The calcium content of the obtained product is less than 22ppm, providing a high-quality precursor with both purity and activity for the subsequent synthesis of β″-Al2O3 solid electrolyte. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] The embodiments of the present invention are further described below with reference to the accompanying drawings, in which:

[0023] Figure 1 Shown is a process flow chart of the present invention. DETAILED DESCRIPTION

[0024] In order to make the purpose, technical solutions and advantages of the present invention more clearly understood, the present invention is further described in detail below through specific embodiments in conjunction with the accompanying drawings. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not intended to limit the present invention.

[0025] The process of the present invention is shown in the attached Figure 1 shown.

[0026] Example 1

[0027] A method for preparing low-calcium boehmite comprises the following steps:

[0028] S1. Place aluminum hydroxide prepared by the Bayer process into a muffle furnace and calcine at 180° C. for 50 min to obtain light-burned aluminum hydroxide;

[0029] S2. Mixing light-burned aluminum hydroxide and deionized water to obtain a primary reaction slurry with a solid content of 200 g / L;

[0030] S3, adding lactic acid to the primary reaction slurry, with the molar ratio of the acid radical ions in the added lactic acid to the calcium ions in the primary reaction slurry being 1.2, reacting at 50° C. for 40 min, and filtering to obtain a filter cake;

[0031] S4, mixing the filter cake with deionized water to obtain a secondary reaction slurry with a solid content of 400 g / L;

[0032] S5. Place the secondary reaction slurry into a high-pressure reactor, add lactic acid, and react at 150° C. for 24 h. After cooling, filter, wash, and dry to obtain a powder.

[0033] S6. Place the powder into a muffle furnace and calcine at 900° C. for 0.5 h to obtain low-calcium boehmite.

[0034] The low-calcium boehmite obtained in this example was dissolved in hydrochloric acid and analyzed using an inductively coupled plasma emission spectrometer. The calcium content of the low-calcium boehmite obtained in this example was 17.5 ppm.

[0035] Example 2

[0036] A method for preparing low-calcium boehmite comprises the following steps:

[0037] S1. Place aluminum hydroxide prepared by the Bayer process into a muffle furnace and calcine at 300° C. for 20 min to obtain light-burned aluminum hydroxide;

[0038] S2. Mixing light-calcined aluminum hydroxide and deionized water to obtain a primary reaction slurry with a solid content of 400 g / L;

[0039] S3, adding a mixed solution of acetic acid and gluconic acid to the primary reaction slurry, wherein the molar ratio of the acid radical ions in the added mixed solution to the calcium ions in the primary reaction slurry is 1.4, reacting at 80° C. for 30 min, and filtering to obtain a filter cake;

[0040] S4, mixing the filter cake with deionized water to obtain a secondary reaction slurry with a solid content of 200 g / L;

[0041] S5. Place the secondary reaction slurry into a high-pressure reactor, add a mixed solution of acetic acid and gluconic acid, wherein the molar ratio of the acid radical ions in the added mixed solution to the calcium ions in the secondary reaction slurry is 1.2, react at 200° C. for 2 h, cool, filter, wash, and dry to obtain a powder;

[0042] S6. Place the powder into a muffle furnace and calcine at 500° C. for 5 h to obtain low-calcium boehmite.

[0043] The low-calcium boehmite obtained in this example was dissolved in hydrochloric acid and analyzed using an inductively coupled plasma emission spectrometer. The calcium content of the low-calcium boehmite obtained in this example was 15 ppm.

[0044] Example 3

[0045] A method for preparing low-calcium boehmite comprises the following steps:

[0046] S1. Place aluminum hydroxide prepared by the Bayer process into a muffle furnace and calcine at 240° C. for 35 min to obtain light-burned aluminum hydroxide;

[0047] S2. Mixing light-burned aluminum hydroxide and deionized water to obtain a primary reaction slurry with a solid content of 300 g / L;

[0048] S3, adding acetic acid to the primary reaction slurry, with the molar ratio of acid ions in the added acetic acid to calcium ions in the primary reaction slurry being 2.0, reacting at 65° C. for 35 minutes, and filtering to obtain a filter cake;

[0049] S4, mixing the filter cake with deionized water and beating the mixture to obtain a secondary reaction slurry with a solid content of 350 g / L;

[0050] S5. Place the secondary reaction slurry into a high-pressure reactor, add acetic acid, and react at 180° C. for 10 h. After cooling, filter, wash, and dry to obtain a powder.

[0051] S6. Place the powder into a muffle furnace and calcine at 700° C. for 3 h to obtain low-calcium boehmite.

[0052] The low-calcium boehmite obtained in this example was dissolved in hydrochloric acid and analyzed using an inductively coupled plasma emission spectrometer. The calcium content of the low-calcium boehmite obtained in this example was 21.3 ppm.

[0053] The present invention provides a low-calcium boehmite and a preparation method thereof. First, a low-temperature light calcination pretreatment is performed to form activation sites capable of migration between calcium ions adsorbed on the surface and calcium ions between the structures without destroying the integrity of the aluminum hydroxide lattice. Subsequently, an organic acid is used to regulate the reaction system in stages, achieving surface complexation and removal of calcium ions in a normal pressure environment of 50-80°C. Then, the calcium ions doped in the lattice are deeply dissociated under high-pressure hydrothermal conditions of 150-200°C. The synergistic effect of the two-step organic acid improves the efficiency of calcium ion removal. By controlling the amount of organic acid added, it is ensured that the calcium ions can be completely complexed, while aluminum dissolution caused by excessive acid etching is avoided. Finally, the boehmite crystal structure is reconstructed by calcination. The calcium content of the obtained product is less than 22ppm, providing a high-quality precursor with both purity and activity for the subsequent synthesis of β″-Al2O3 solid electrolyte.

[0054] Some exemplary embodiments of the present invention are described above. It will be understood that the above embodiments are only used to explain the present invention and do not constitute a limitation on the scope of protection of the present invention. The features in these embodiments can be recombined in an appropriate manner, and the solutions obtained thereby are still within the scope of protection claimed by the present invention. Based on the above embodiments, all other embodiments obtained by those skilled in the art without making creative work, that is, all modifications, equivalent substitutions and improvements made within the spirit and principles of this application, fall within the scope of protection claimed by the present invention.

Claims

1. A method for preparing low-calcium boehmite, characterized in that: The following steps are involved: S1. Place aluminum hydroxide prepared by the Bayer process into a muffle furnace and calcine at 180-300° C. for 20-50 min to obtain light-burned aluminum hydroxide; S2. Mixing light-burned aluminum hydroxide and deionized water to obtain a primary reaction slurry; S3. Add organic acid to the primary reaction slurry, react at 50-80°C for 30-40 minutes, and filter to obtain a filter cake; S4, mixing the filter cake with deionized water to obtain a secondary reaction slurry; S5. Place the secondary reaction slurry into a high-pressure reactor, add an organic acid, react at 150-200° C. for 2-24 hours, cool, filter, wash, and dry to obtain a powder; S6. Place the powder into a muffle furnace and calcine at 500-900° C. for 0.5-5 h to obtain low-calcium boehmite.

2. The method for preparing low-calcium boehmite according to claim 1, wherein: The solid content in the primary reaction slurry and the secondary reaction slurry is 200-400 g / L.

3. The method for preparing low-calcium boehmite according to claim 1, wherein: In S3 and S5, the organic acid includes one or more of acetic acid, lactic acid and gluconic acid.

4. The method for preparing low-calcium boehmite according to claim 1, wherein: In S3 and S5, the amount of organic acid added is such that the molar ratio of the acid radical ions in the organic acid to the calcium ions in the reaction slurry is 1.2-2.

0.

5. Low-calcium boehmite prepared by the method for preparing low-calcium boehmite according to any one of claims 1 to 5.

6. The low-calcium boehmite according to claim 6, characterized in that: The calcium content is less than 22ppm.

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