阅读说明：本技术 高纯氧化铝的生产方法及生产的高纯氧化铝 (Production method of high-purity alumina and high-purity alumina produced by same ) 是由 魏际伦 魏存弟 徐少南 于 2019-04-10 设计创作，主要内容包括：本发明公开了一种高纯氧化铝的生产方法,包括：a.取金属铝,与金属催化剂进行熔炼,所得合金铝与水反应,制取氢气；b.铝水反应后对料浆进行分离,将分离得到的悬浮料浆进行干燥,获得拟薄水铝石；c.将拟薄水铝石粉体进行焙烧,得到氧化铝粉体；d.将所述氧化铝粉体进行蒸馏,以脱除夹杂的金属催化剂成分而得到高纯α-氧化铝粉体；本发明还公开了制得的高纯氧化铝产品；本发明工艺简单,流程短、制备高纯氧化铝同时获得氢气副产品,经济效益显著；作为原料的合金中镓、铟用量少,成本低且容易回收重复使用；本发明制得的高纯氧化铝杂质含量低、附加值高、制备过程无污染、无设备腐蚀,易于推广应用。(The invention discloses a production method of high-purity alumina, which comprises the following steps: a. taking metal aluminum, smelting the metal aluminum and a metal catalyst, and reacting the obtained alloy aluminum with water to prepare hydrogen; b. separating slurry after the reaction of aluminum water, and drying the separated suspension slurry to obtain pseudo-boehmite; c. roasting the pseudo-boehmite powder to obtain alumina powder; d. distilling the alumina powder to remove the mixed metal catalyst component to obtain high-purity alpha-alumina powder; the invention also discloses a prepared high-purity alumina product; the method has the advantages of simple process, short flow, preparation of high-purity alumina and acquisition of hydrogen byproduct, and remarkable economic benefit; the alloy used as the raw material has the advantages of small consumption of gallium and indium, low cost and easy recovery and reuse; the high-purity aluminum oxide prepared by the method has the advantages of low impurity content, high additional value, no pollution in the preparation process, no equipment corrosion and easy popularization and application.)

1. A method for producing high purity alumina, comprising the steps of:

a. smelting metal aluminum and a metal catalyst, wherein the metal catalyst is a metal mixture containing metal gallium and metal indium, the sum of the contents of the metal gallium and the metal indium in the metal mixture is not less than 85 wt%, and performing hydrolysis reaction on the alloy aluminum obtained after smelting the mixed gallium indium catalyst and water to prepare hydrogen; wherein the purity of the metallic aluminum is not less than 99.9 wt%;

b. separating the slurry after the hydrolysis reaction to separate residual metal to obtain suspended slurry, and drying the suspended slurry to obtain pseudo-boehmite powder; optionally, treating the separated metal for recycling;

c. roasting the pseudo-boehmite powder to obtain alumina powder;

d. and distilling the alumina powder to remove the included metal catalyst component to obtain the high-purity alpha-alumina powder.

2. The production method according to claim 1, wherein the metal Ga to In mass ratio In the metal catalyst is 74-84: 16-26, preferably 76-82: 18-24, and the sum of the contents of metal gallium and metal indium In the metal catalyst is preferably not less than 90 wt%, preferably not less than 95 wt%;

preferably, when the alloy aluminum is prepared by smelting, the sum of the dosage of the gallium and the indium is 1.5 to 0.01 weight percent of the dosage of the aluminum.

3. The production method according to claim 1 or 2, wherein in the step c, the pseudo-boehmite powder is roasted in a rotary kiln with an air extractor, and nitrogen is introduced for protection to obtain gamma-alumina powder; preferably, the calcination temperature is 300-.

4. A production method according to any one of claims 1 to 3, wherein the temperature of water at the time of hydrolysis reaction is not lower than 85 ℃, preferably not lower than 90 ℃, further preferably not lower than 95 ℃;

preferably, the hydrolysis reaction is carried out under pressure.

5. The production method according to any one of claims 1 to 4, wherein in the step b, residual metals in the slurry after the reaction are separated by means of cyclone separation to obtain suspended slurry.

6. The production method according to any one of claims 1 to 5, wherein in the step b, the separated suspension slurry is dried by means of spray drying to obtain pseudo-boehmite powder; preferably, the spray drying temperature is 170 ℃ to 240 ℃.

7. The production method according to any one of claims 1 to 6, wherein in the step b, the solid content of the suspension slurry obtained after separation is adjusted to 20 to 30 wt%.

8. The production method according to any one of claims 1 to 7, wherein in the step a, before the hydrolysis reaction, the alloy aluminum obtained by smelting is divided to obtain refined alloy aluminum fragments so as to carry out the hydrolysis reaction.

9. The production method according to any one of claims 1 to 8, wherein in step d, the distillation is performed under negative pressure, and the distillation temperature is 1100-1800 ℃, preferably 1250-1350 ℃; the vacuum degree during distillation is 10.0-9.0 x 10^-5Pa, preferably 1.0 to 9.0X 10^-3Pa。

10. A high purity alumina product produced by the production method according to any one of claims 1 to 9.

Technical Field

The invention belongs to the technical field of alumina preparation, and particularly relates to a method for preparing high-purity alumina powder by reacting high-purity metal aluminum with pure water to obtain an aluminum hydrolysate and further processing the aluminum hydrolysate, and the prepared high-purity alumina.

Background

The high-purity alumina is Al₂O₃The alumina powder with the content of more than or equal to 99.99 percent not only has the excellent characteristics of high temperature resistance, chemical corrosion resistance, shock cooling and heat resistance, difficult burst cracking and the like, but also can be widely applied to the fields of LED artificial sapphire crystals, PDP fluorescent powder, high-pressure sodium lamps, luminescent materials, special ceramics, functional coatings, tricolor, catalyst carriers, biological materials and the like, and is one of high-end products with large yield, high output value and wide application in the field of new materials in future.

Aiming at the preparation of high-purity aluminum oxide, the preparation of the high-purity aluminum oxide starts from the beginning of the century, and mainly comprises an inorganic aluminum salt thermal decomposition method, a high-purity aluminum hydrolysis method, an organic alkoxide hydrolysis method, a modified Bayer method and the like. For example, Renyeirong and Zhu Zikang (1991) utilize the thermal decomposition method of aluminum ammonium sulfate to prepare high-purity aluminum oxide, industrial-grade ammonium sulfate reacts with aluminum sulfate to generate aluminum ammonium sulfate, high-purity aluminum ammonium sulfate is obtained through extraction, and then high-purity aluminum oxide is obtained through thermal decomposition. The method has low cost of raw materials and mature process, but the purification process has complex process and low yield, and can prevent a large amount of harmful gases.

Likewise, similar problems exist with ammonium aluminum carbonate pyrolysis processes. In addition, a metal aluminum hydrolysis method, such as Zheng Fu Qian (2000 years), adopts a quenching atomization device to spray molten and overheated aluminum liquid at 200-300 ℃ to prepare superfine aluminum powder with the average particle size of 5-10 mu m, then the superfine aluminum powder reacts with pure water to obtain a high-purity aluminum hydrolysate, and the obtained product is calcined at high temperature to form high-purity aluminum oxide. The process needs to spray molten aluminum liquid under the protection of inert gas to prepare powder, and the prepared aluminum powder needs to be stored in the inert gas in an air-isolated manner, so that the process conditions are harsh, and the production cost is high.

The organic aluminium alkoxide hydrolysis method is one of the more common methods at present. If the product is at a peak, the method uses aluminum sheets (the aluminum content is more than or equal to 99.9 percent) with the purity of more than 3N to react with isopropanol with higher purity to prepare aluminum isopropoxide firstly, and then the aluminum isopropoxide is purified, hydrolyzed, aged, dried and calcined by rectification and the like to prepare high-purity superfine Al₂O₃The method has complex preparation process and high production cost. In recent years it has become possible to use,with the technical progress and the increasing demand of high-purity alumina, new reports on the preparation method of the high-purity alumina are continuously made. For example, cn201711258212.x describes a method for preparing high-purity ultrafine alumina powder, which utilizes the feature that alumina is an amphoteric oxide, obtains aluminum chloride by acid-dissolving high-purity aluminum, and then performs purification, crystallization, microwave pyrolysis, high-temperature pyrolysis and other processes on the aluminum chloride to prepare the high-purity ultrafine alumina powder. CN201711340661.9 introduces a preparation method of high-purity alumina ceramic powder, which comprises the steps of dissolving aluminum alkoxide in deionized water, adding a water-soluble magnesium salt to obtain an aluminum-magnesium alkoxide mixed solution, then adding the aluminum-magnesium alkoxide mixed solution into the deionized water with the temperature of 50-70 ℃ to form milky white slurry, adding acid to fully mix, standing the mixed solution to form clear sol, converting the sol into gel through spray drying, drying to obtain ultra-fine alumina raw powder, and finally calcining the raw powder to obtain the high-purity alumina ceramic powder. CN201810781272.8 introduces a clean production process of nano-sphere high-purity alumina, which comprises the specific steps of processing an aluminum ingot into an aluminum sheet, fully cleaning, immersing the aluminum sheet into pure water, ablating the surface of the aluminum sheet by laser to obtain alumina slurry, filtering the alumina slurry again to obtain an alumina filter cake, and drying and calcining the alumina filter cake to obtain an alumina finished product. The preparation methods of the new high-purity alumina are endless, but most of the high-purity alumina have the defects of complex process, serious corrosion to equipment or high cost, and difficult industrialization.

Disclosure of Invention

The invention aims to provide a simpler, lower-cost and high-purity alumina production method and a method for producing high-purity alumina and hydrogen in parallel.

In order to achieve one aspect of the above purpose, the invention adopts the following technical scheme:

a method for producing high purity alumina, said method comprising the steps of:

a. smelting metal aluminum and a metal catalyst, wherein the metal catalyst is a metal mixture containing metal gallium and metal indium, the sum of the contents of the metal gallium and the metal indium in the metal mixture is not less than 85 wt%, and performing hydrolysis reaction on alloy aluminum obtained after smelting the mixed gallium indium catalyst and water to prepare hydrogen; wherein the purity of the metallic aluminum is not less than 99.9 wt%;

b. separating the slurry after the hydrolysis reaction to separate residual metal to obtain suspended slurry, and drying the suspended slurry to obtain pseudo-boehmite powder; optionally, treating the separated metal for recycling;

c. roasting and roasting the pseudo-boehmite powder to obtain alumina powder;

d. and distilling the alumina powder to remove the included metal catalyst component to obtain the high-purity alpha-alumina powder.

In step a of the present invention, the metallic aluminum is high-purity metallic aluminum (such as 3N, 4N or 5N aluminum), for example, purity of not less than 99.9 wt%, or 99.99 wt%, or 99.999 wt%; the metal catalyst has a metal ratio of Ga to In of 74-84: 16-26, for example 76-82: 18-24 or 78-80: 20-22, for example, gallium to indium is 78.9: 21.1.

When the alloy aluminum is prepared by smelting, the aluminum ingot can be prepared by mixing the metallic aluminum and the metallic catalyst (the catalyst can be added as a whole or the components can be added separately) under the condition of fully stirring by adopting the vacuum smelting or inert gas protection smelting technology of the metal, and the technology is well known in the art and is not described again. The gallium and indium content of the obtained alloy aluminum (or aluminum ingot) is 1.5-0.01 wt%, such as 1.0 wt%, 0.5 wt%, 0.2 wt% or 0.1 wt% of the aluminum content. Although those skilled in the art will appreciate that higher purity of the starting material is more beneficial to the high purity of the subsequent product, those skilled in the art will appreciate that the starting material purity may not be as critical as the maximum amount of aluminum metal used because the overall amount of metal catalyst used in the present invention is lower.

In the present invention, the sum of the contents of metal gallium and metal indium in the metal catalyst is preferably not less than 90 wt%, not less than 95 wt%, not less than 99 wt%, or the metal catalyst is an alloy catalyst composed of gallium and indium.

Cutting an aluminum ingot obtained by smelting, and then carrying out hydrolysis reaction with water, for example, cutting particles with the particle size of below 1cm, such as 0.2-1cm, preparing hydrogen, and collecting, wherein the water can be deionized water, which is beneficial to improving the purity of the subsequently obtained pseudo-boehmite; the temperature of water in the hydrolysis reaction may be not less than 85 ℃ and not less than 90 ℃, for example, 92 ℃, 95 ℃, 97 ℃ or 99 ℃, 100 ℃ and the water may be nearly boiling or boiling in the reaction, or the pressure of the reaction system may be appropriately increased to increase the reaction temperature. Because the hydrolysis temperature is higher, close to or at the boiling point, the hydrogen generated by the reaction is mixed with the water vapor and coexists, and then the water can be recovered by a condensation separation mode and recycled, so that the pure hydrogen is obtained.

In one embodiment, the hydrolysis reaction is carried out under pressure, for example, at a pressure of not less than 0.2MPa, 0.5MPa, 1MPa, 2MPa or higher, since the hydrolysis reaction can be carried out at a higher temperature, for example, not less than 100 ℃, 120 ℃, 150 ℃, 200 ℃ or 250 ℃ or higher, the speed of the hydrolysis reaction is increased, which is not only beneficial to obtaining high-quality steam for recovering heat, but also beneficial to reducing the amount of metal catalyst and improving the purity of the product.

In the step b of the present invention, in the reaction system obtained after the reaction of the aluminum water is completed, the aluminum hydroxide generated by the hydrolysis reaction of the present invention has low density and fine particles in a suspension state, and the residual metal (a small amount of residual metal aluminum and unreacted gallium-indium alloy catalyst) is easily gathered at the bottom of the reaction system because of significantly large relative specific gravity, so that the separation of the aluminum hydroxide and the residual metal can be smoothly realized, and the temperature of the system can be properly reduced to be lower than 70 ℃ after the reaction is completed, for example, or the system is directly sent to the separation step without arranging a special temperature reduction step. The specific separation method may be to directly extract the reaction system suspended slurry to facilitate the separation of the metal (residue) at the bottom or to separate the suspended slurry at the middle upper part by using the overflow principle to make the metal at the bottom remain in the reaction system, or preferably may be cyclone separation, for example, cyclone separation under stirring condition to separate the residual metal with high specific gravity, which will not be described in detail herein.

Drying the separated pseudo-boehmite slurry, for example, spray drying to obtain pseudo-boehmite powder, for example, spray drying at 170 ℃ to 240 ℃ under normal pressure, such as 180 ℃, 200 ℃, 210 or 220 ℃, or spray drying at a reduced temperature under reduced pressure, can obtain substantially pure pseudo-boehmite powder, although one skilled in the art can also appreciate that the higher the purity of the raw material aluminum, the higher the purity of the aluminum hydrolysate obtained.

In one embodiment, after separation and before spray drying, the suspended slurry is adjusted to have a solid content of 20-30 wt%, such as 22 wt%, 24 wt%, 26 wt% or 28 wt%, for example, the obtained suspended slurry can be filtered to obtain a filter cake, and then the filter cake is added with water for pulping, so that not only can the solid content be adjusted and controlled to better perform spray drying to obtain pseudo-boehmite powder, but also the filtering is beneficial to filtering out part of possible impurities, such as soluble impurities, and improving the purity of the pseudo-boehmite powder.

In the step b of the invention, optionally, gallium indium alloy and residual aluminum which do not participate in the hydrolysis reaction can be recovered and reused, a small amount of aluminum hydrolysate coated on the surface is washed and separated by ultrasonic and other modes, and residual aluminum metal and gallium indium alloy are recovered, tested for content and reused.

In the step c, the pseudo-boehmite powder is roasted to obtain alumina powder; preferably, the alumina powder is obtained by roasting under the inert gas protection atmosphere, such as nitrogen atmosphere; the calcination temperature is a temperature at which the pseudo-boehmite powder can be better decomposed into alumina (such as gamma-alumina), such as 300-700 ℃, for example 400 ℃, 450 ℃, 500 ℃ or 600 ℃. In a preferred embodiment, the pseudo-boehmite powder is roasted in a rotary kiln with an air extractor, and nitrogen is introduced for protection to obtain the gamma-alumina powder. Research shows that the powder may still contain small amount of metallic gallium and indium impurities.

Step d of the invention is to distill the alumina powder to remove the mixed metal catalyst component and obtain high-purity alpha-alumina powder; it is composed ofIn the above-mentioned method, the distillation temperature is a temperature at which the metallic gallium and indium in the alumina powder can volatilize, and in order to facilitate the volatilization and removal of impurities, the distillation is preferably performed under a negative pressure which can be as high as possible to some extent (i.e., as low as possible in absolute pressure); in one embodiment, the distillation temperature is 1100-1800 ℃, preferably 1250-1350 ℃; the vacuum degree during distillation is 10.0-9.0 x 10^-5Pa, preferably 1.0 to 9.0X 10^-3And (3) carrying out vacuum distillation under the condition of Pa to remove metal gallium and indium contained in the alpha-alumina to obtain the high-purity alpha-alumina.

In order to achieve another aspect of the above objects, the present invention further provides high purity α -alumina prepared according to the above method.

The invention adopts high-purity aluminum (such as 3N, 4N or 5N aluminum or higher) as a raw material, is matched with low-consumption gallium-indium low-melting-point alloy as a catalyst, and reacts with boiling water to produce hydrogen and produce the high-purity alumina precursor pseudo-boehmite at the same time. The pseudo-boehmite generates gamma-alumina under the protection of low-temperature inert gas; the gamma-alumina is further vacuum distilled at high temperature, and a small amount of metal gallium and indium contained in the gamma-alumina are evaporated to obtain the high-purity alpha-alumina.

Research finds that the limiting factor of hydrogen production through the aluminum water reaction is the reaction inhibition of an aluminum oxide film, the aluminum alloy containing low-melting-point metal has the low-melting-point metal in the grain interior or in the grain boundary, when the aluminum alloy reaches the molten-state temperature of the low-melting-point metal or above, the molten-state metal has strong permeability, particularly the gallium has small surface tension, can be spread on the surface of the aluminum metal and melted and permeated in the grain boundary, and interferes with the formation of aluminum oxide, cracks or cavities are easy to occur even if the aluminum oxide film is generated, and compared with a structure without the low-melting-point metal, the aluminum water reaction hydrogen production method has obvious local embrittlement and atomic arrangement disordered regions, and provides favorable conditions for the aluminum water reaction. On the other hand, because water is polar molecules, the water exists in an aggregation state of weak intermolecular force combination at normal temperature, the binding force is weakened along with the increase of the water temperature, the kinetic energy of small molecular water is increased, particularly when the water reaches a boiling point, the mass transfer capacity is enhanced, the reaction induction period of the aluminum water can be obviously shortened, the hydrogen generated on the surface of metal aluminum is promoted to be rapidly diffused, and the reaction rate is greatly improved. In fact, the low-melting-point alloy formed by gallium and indium can be molten at a low temperature at and near the eutectic composition, the viscosity of the melt is reduced and the surface tension is reduced along with the increase of the temperature, and the low-melting-point alloy is also more favorable for wetting the aluminum crystal boundary and surface and preventing the aluminum from being oxidized due to element migration. Therefore, the invention uses a small amount of low melting point gallium-indium alloy as the catalyst, and realizes the rapid and continuous aluminum-water reaction by increasing the reaction temperature (reaching the boiling point of water), thereby greatly reducing the cost of raw materials and the difficulty of recovery. The reaction product of aluminum and boiling water except hydrogen is hydrolyzed to produce pseudoboehmite phase. Previous studies have confirmed that aluminum reacts with water at temperatures below 60 ℃ in the form of a mixed crystal of bayer and pseudoboehmite, with the pseudoboehmite phase being predominant at temperatures above 60 ℃. The reaction conditions of the invention just meet the formation of the pseudo-boehmite structure of the aluminum hydrolysis product.

In conclusion, the invention adopts the metal aluminum hydrolysis method to prepare the high-purity aluminum oxide, and the dosage of the low-melting-point alloy element added in the raw material aluminum in the aluminum water reaction process is obviously reduced compared with the reported (the minimum dosage is 3wt percent), and is only 1.5wt percent to 0.01wt percent, so that the cost of the method is greatly reduced. The process for preparing the aluminum oxide by the method omits the aluminum alkylation or alcoholization step which is mostly adopted at present, so that the process is simpler, more environment-friendly, safer and easier to realize. The alumina obtained by the method has high purity, can meet the technical standard requirement of high-purity alumina, and simultaneously obtains a high-purity hydrogen byproduct, thereby having remarkable economic benefit.

Drawings

FIG. 1 is an XRD pattern of alpha-alumina for various examples;

fig. 2 and 3 are SEM images of the α -alumina of example 1.

Detailed Description

The present invention will be described in detail with reference to examples, but the present invention is not limited thereto.

The following examples are given below for the determination of the parameters/conditions, all according to the methods customary in the art, unless otherwise specified:

XRD: using a DX-2700 x-ray diffractometer; wavelength:

target material: Cu-Kalpha radiation; tube voltage: 40 kV; pipe flow: 30mA