KR101010524B1 - Purification of aluminum hydroxide - Google Patents

Abstract

The present invention relates to a method for producing high purity aluminum hydroxide (Al (OH) ₃ ). Specifically, dissolving aluminum hydroxide in an aqueous citric acid solution and then filtering the residual material, adding ammonium thiocyanate to the aluminum hydroxide solution, precipitation of aluminum hydroxide by adjusting the pH with ammonia water, precipitated aluminum hydroxide It relates to a method for producing high purity aluminum hydroxide comprising the step of filtration and washing repeatedly with pure distilled water.

According to the present invention, compared to the conventional method using hydrochloric acid or sulfuric acid does not cause environmental pollution problems, there is a feature that does not have to go through a separate complicated purification process. In particular, there is an advantage that the iron component can be removed very effectively by adding a thiocyanate ion. In addition, compared to the conventional method using a very expensive high-purity aluminum metal powder as a raw material, it is characterized by the production of high-purity aluminum hydroxide with a purity of 99.99% or more at a fairly low cost by using low-purity aluminum hydroxide as a raw material.

Aluminum hydroxide, citric acid, ammonium thiocyanate, precipitation, wet treatment

Description

Purification method of aluminum hydroxide {PURIFICATION OF ALUMINUM HYDROXIDE}

The present invention relates to a method for producing high value added high purity aluminum hydroxide from aluminum hydroxide (Al (OH) ₃ ) having a relatively low purity using a wet treatment method.

Aluminum hydroxide is a basic inorganic chemical raw material with excellent basic properties such as heat resistance, flame retardancy, and transparency, and is widely used as an additive for water treatment and ceramic raw materials for industrial use. In particular, aluminum hydroxide is used in various industries such as refractory materials, fillers, ceramic raw materials, catalysts and electronics. It is a basic raw material of alumina, a ceramic material widely used in parts and the like. Alumina white crystalline powder obtained by calcination of aluminum hydroxide, but various forms of alumina according to the firing temperature goes increasing the firing temperature γ - and finally through the various intermediate alumina such as alumina is α - there is an alumina, α - alumina Among the alumina forms, it is the most chemically stable, has a high melting point and high mechanical strength. Recently, the use of high purity alumina in the electronics industry of 99.99% or more has soared, and the demand for high purity alumina products for blue LEDs, surface acoustic wave device substrates, and semiconductor substrate applications has increased significantly.

Aluminum hydroxide, which is a raw material of alumina, is generally manufactured by treating minerals such as bauxite by a Bayer process, and it is generally known that the purity of aluminum hydroxide produced by Bayer process is about 99.6%. In particular, due to the characteristics of the Bayer method, a large amount of sodium (Na) component is contained as an impurity, and other elements such as silicon (Si), iron (Fe), calcium (Ca) and the like are contained. Therefore, in order to obtain high value-added high purity (more than 99.99%) alumina, it is necessary to remove the impurities contained in aluminum hydroxide, but there is a problem such as economical efficiency because various purification methods must be used in combination. Domestically produced and sold industrial purity (99.6 to 99.8%) of aluminum hydroxide manufactured by Bayer method, high purity products of more than 99.99% depend on the total import.

Commercially available high-purity aluminum hydroxide can be classified into two types according to the raw materials. The first method uses high-purity (more than 99.99%) aluminum metal as a raw material, which is in the form of powder or thin plate. use. In the case of using such aluminum metal as a raw material, a method of preparing aluminum hydroxide by oxidizing or electrolytically oxidizing an organic compound in an aqueous solution, a method of preparing aluminum hydroxide by oxidizing in a high temperature and high pressure reactor, and hydrolyzing alkoxide There is a method of manufacturing aluminum hydroxide, but there is a problem that the economical efficiency is lowered because the high-purity aluminum metal material is very expensive. The second method is to use aluminum hydroxide produced by Bayer method as a raw material. First, aluminum hydroxide is dissolved using hydrochloric acid or sulfuric acid, and then impurities in the solution are removed by a conventional wet purification method. To manufacture. However, the method of using aluminum hydroxide as a raw material is not commercially used because of the complex and difficult disadvantages of the purification method for removing impurities while causing environmental pollution and device corrosion problems by hydrochloric acid or sulfuric acid.

Data published to date relating to the production of high purity aluminum hydroxide or alumina from various aluminum sources include U.S. Pat.Nos. 7,067,106, 6,162,413, 4,615,875, 4,486,402 and Japanese Laid-Open Patent Publication 2008. -150238, 2005-281063, 2003-95730, 1997-221319, and the like.

The above-mentioned methods of manufacturing high purity aluminum hydroxide or alumina have a problem of environmental pollution because hydrochloric acid should be used, and there is a problem of explosion or fire when aluminum metal powder is used as a raw material. In addition, when aluminum hydroxide is used as a raw material, there are limitations in that aluminum hydroxide should be substantially free of impurities such as silicon, iron, calcium, and the like, and it is cumbersome in the method of repeating high temperature baking and water washing several times.

The present invention has been made to solve the conventional problems,

An object of the present invention is to provide a method for producing high purity aluminum hydroxide at a low cost by using aluminum hydroxide having a relatively low purity as a raw material compared to the conventional method using an expensive aluminum metal powder as a raw material.

It is also an object of the present invention to provide a method for producing high purity aluminum hydroxide that does not require a separate purification process.

It is also an object of the present invention to provide a method for producing environmentally friendly high purity aluminum hydroxide.

The above objects can be achieved by the following configuration of the present invention.

The manufacturing method which can produce high purity aluminum hydroxide by using wet treatment method using industrial low purity aluminum hydroxide as a raw material,

(1) dissolving aluminum hydroxide in an aqueous citric acid solution and then filtering out the residual material,

(2) adding ammonium thiocyanate to the aluminum hydroxide solution;

(3) precipitating aluminum hydroxide by adjusting the pH with ammonia water,

(4) filtering the precipitated aluminum hydroxide, washing with distilled water and drying

It is made, including.

In the case of purifying industrial low purity aluminum hydroxide using the method of the present invention, the process does not cause environmental pollution problems compared to the conventional method using hydrochloric acid or nitric acid, and since most impurities are removed in the process of precipitating aluminum hydroxide, This is very simple and economical. In particular, there is an advantage that the iron component can be removed very effectively by adding a thiocyanate ion. In addition, high purity aluminum hydroxide with a purity of 99.99% or more can be produced at a relatively low cost by using industrial low purity aluminum hydroxide as a raw material, compared to a conventional high purity aluminum hydroxide manufacturing method using a very expensive high purity aluminum metal powder as a raw material.

The method of the present invention is described in more detail.

In the step (1), 99.6 to 99.8% of industrial low purity aluminum hydroxide powder as a raw material is added to an aqueous citric acid solution and dissolved while stirring and heating.

In the dissolution step of the aluminum hydroxide, the citric acid concentration in the aqueous solution is adjusted to 0.5 to 2.5 mol / liter, more preferably 1 to 1.5 mol / liter, and the aluminum hydroxide solid concentration in the aqueous solution is 20 to 300 g / liter, The furnace is preferably dissolved at 50 to 150 g / liter. If the citric acid concentration is lower than the above range, the aluminum hydroxide dissolution rate is lowered, the recovery rate of aluminum hydroxide is reduced, if higher than the above range there is a problem that the drug cost is excessively required. In addition, when the aluminum hydroxide solid concentration is lower than the above range, the throughput decreases, resulting in an increase in the production cost, and when higher than the above range, the aluminum hydroxide dissolution rate is lowered.

In step (1), for 16 to 20 hours while maintaining the temperature 70 to 95 ℃ Stir to disperse the aluminum hydroxide sufficiently in the reaction vessel. If the temperature is lower than the dissolution temperature or the reaction time is insufficient, the dissolution rate of aluminum hydroxide is reduced. After the dissolution process is completed, undissolved residual material is filtered off to obtain an aluminum hydroxide solution.

In the case of dissolving aluminum hydroxide, there is also a method of dissolving using inorganic acid such as hydrochloric acid and nitric acid, but in this case, strong acid must be used, which may cause problems of environmental pollution and device corrosion, especially in the final product. The nitric acid (NO ₃ ) component is likely to be contained as an impurity. Therefore, the present invention is characterized by dissolving aluminum hydroxide using citric acid, which is an organic acid, instead of these inorganic acids having such problems.

In step (2), ammonium thiocyanate is added to the aluminum hydroxide solution obtained in step (1). The reason for adding ammonium thiocyanate to the solution of aluminum hydroxide is to suppress precipitation of the iron component as an impurity in the precipitation step of aluminum hydroxide, which is the next step. Among impurities contained in low-purity aluminum hydroxide, which is a raw material, sodium, calcium, and silicon remain as ions in aqueous solution during aluminum hydroxide precipitation, but iron can be removed, but iron is precipitated like aluminum (Al). Therefore, in order to obtain high purity aluminum hydroxide, the precipitation of iron should be suppressed. The test was repeated several times, and it was confirmed that thiocyanate (SCN ⁻ ) ion has a function of inhibiting iron precipitation in citric acid aqueous solution. The reason why the thiocyanate ions suppress the precipitation of iron in the citric acid aqueous solution is that the iron ions and the thiocyanate ions form very stable complex ions in the aqueous solution. Thus, when the iron ions are fixed to the stable complex ions, the solution Even if the pH is increased, it is possible to obtain an effect of suppressing precipitation of iron. In addition, the compound having a thiocyanate ion may be various, such as sodium thiocyanate (NaSCN) and potassium thiocyanate (KSCN), but in the present invention, in order to suppress the incorporation of impurities such as Na and K as much as possible, Ammonium ansulfate (NH ₄ SCN) was selected.

The amount of ammonium thiocyanate added is preferably adjusted to 5 to 10 times, more preferably 7 to 8 times in molar ratio with respect to the iron content in the aluminum hydroxide solution. When the amount of the ammonium thiocyanate added is less than the above range, it is difficult to effectively suppress the precipitation of iron, and when the amount exceeds the above range, an unnecessarily excessive drug requirement occurs.

In step (3), ammonia water is added little by little while stirring the aluminum hydroxide solution to adjust the pH of the solution. Increasing the pH of the solution by adding ammonia water gradually precipitates aluminum hydroxide, resulting in a cloudy suspension. At this time, the pH of the solution is adjusted to 7 to 10, more preferably to 8 to 9, the reaction time is 1 to 2 hours at room temperature. If it is lower than the pH, the aluminum hydroxide is not sufficiently precipitated, so that the recovery rate is lowered. If the pH is higher than the pH, the ammonia water is unnecessarily added. In precipitation of aluminum hydroxide, an important point is that aluminum hydroxide of high purity can be obtained because it is not mixed with aluminum hydroxide in which ions such as sodium, calcium, silicon, and iron which are present as impurities in the aluminum hydroxide solution are precipitated. That is, the low-purity aluminum hydroxide, which is an initial raw material, contains impurities such as sodium, calcium, silicon, and iron, so that the aqueous solution of aluminum hydroxide obtained in step (1) is also included to contain these ions, but step (2) When thiocyanate ions are added at, the precipitation of iron is suppressed in step (3), and the remaining impurities such as sodium, calcium, and silicon are not precipitated even when the pH is increased. Purification of aluminum hydroxide enables the production of very high purity aluminum hydroxide.

In the step (4), the precipitated aluminum hydroxide is filtered and then washed with distilled water to wash off the adhered impurities and dried in an oven.

Purification of industrial low purity aluminum hydroxide using the method of the present invention enables the production of high purity aluminum hydroxide with a purity of 99.99% or more.

As a raw material of the present invention, a low purity aluminum hydroxide for general industrial use may be used, and the present invention is not limited to aluminum hydroxide produced through a specific manufacturing method.

Hereinafter, specific process conditions and features of the present invention will be described in detail through the following examples.

Example 1

300 g of industrial low-purity aluminum hydroxide powder containing 0.12% Na, 0.012% Fe, 0.02% Si, and 0.016% Ca was charged to a reaction vessel equipped with a stirrer and a heater, and filled with a 2.5 mol / liter aqueous citric acid solution. . The stirrer was operated to sufficiently disperse the aluminum hydroxide in the aqueous solution, and the heater was operated to dissolve the aluminum hydroxide in the aqueous citric acid solution at 70 ° C. for 20 hours. After the dissolution process was completed, undissolved residues were filtered off. Ammonium thiocyanate was added 10 times in molar ratio to the iron content in the aluminum hydroxide solution, and then ammonia water was added slowly while stirring to adjust the pH of the aqueous solution to 7. As the aluminum hydroxide precipitate formed in the process, the solution was changed into a cloudy suspension. Aluminum hydroxide was precipitated for 1 hour and then filtered to separate aluminum hydroxide, washed three times with pure distilled water, and dried in an oven. As a result of analyzing the components of the aluminum hydroxide prepared according to the present Example, it was found that the purity was high purity aluminum hydroxide of 99.99% or more.

Analysis of high purity aluminum hydroxide component prepared by the method of Example 1 element Al (OH) ₃ Na Fe Si Ca content
(weight%) > 99.99 0.0011 0.0005 0.0016 0.0008

Example 2

20 g of the same industrial low-purity aluminum hydroxide powder as in Example 1 was placed in a reaction vessel equipped with a stirrer and a heater, and filled with 1 liter of an aqueous 0.5 mol / liter citric acid concentration. In the same manner as in Example 1, aluminum hydroxide was dissolved in an aqueous citric acid solution at 95 ° C. for 16 hours. After the dissolution process was completed, the remaining undissolved substances were filtered out in the same manner as in Example 1, and ammonium thiocyanate was added to the aluminum hydroxide solution in a molar ratio of 5 times the iron content in the aluminum hydroxide solution, followed by stirring. As in Example 1, ammonia water was added to adjust the pH to 10. As the aluminum hydroxide precipitate formed in the process, the solution was changed into a cloudy suspension. For 2 hours Aluminum hydroxide was precipitated and then filtered in the same manner as in Example 1 to separate the aluminum hydroxide, washed three times with pure distilled water and dried in an oven. As a result of analyzing the components of the aluminum hydroxide prepared according to the present Example, it was found that the purity is high purity aluminum hydroxide of 99.99% or more.

High purity aluminum hydroxide component analysis prepared by the method of Example 2 element Al (OH) ₃ Na Fe Si Ca content
(weight%) > 99.99 0.0014 0.0008 0.0015 0.0009

Claims (6)

(1) dissolving low purity aluminum hydroxide having a purity of 99.6 to 99.8% in an aqueous citric acid solution and then filtering the remaining material, (2) adding ammonium thiocyanate to the aluminum hydroxide solution, (3) adjusting the pH with ammonia water to precipitate aluminum hydroxide, (4) filtering precipitated aluminum hydroxide, followed by washing with distilled water and drying. Method for producing a high purity aluminum hydroxide of 99.99% or more purity from low purity aluminum hydroxide of 99.6 to 99.8% purity comprising a. The method of claim 1, wherein the aluminum hydroxide solid concentration in the aqueous citric acid solution of step (1) is 20 to 300 g / liter. The method of claim 1, wherein the concentration of the citric acid aqueous solution of step (1) is 0.5 to 2.5 mol / liter. The method of claim 1, wherein in step (1), aluminum hydroxide is dissolved at 70 to 95 ° C. for 16 to 20 hours. The method for producing high purity aluminum hydroxide according to claim 1, wherein the amount of ammonium thiocyanate in step (2) is 5 to 10 times in molar ratio relative to the iron content in the aluminum hydroxide solution.  The method of claim 1, wherein in step (3), the pH of the aluminum hydroxide solution is adjusted to 7 to 10 using ammonia water.