KR100552136B1 - Process for preparation of activated alumina from Al dross - Google Patents

Abstract

The present invention relates to a method for producing activated alumina using aluminum dross, and more particularly, to adsorbents and chromatography using aluminum dross, which is an oxide layer formed on the surface of a molten metal when dissolving aluminum metal or scrap. It is to provide a method for producing high purity activated alumina that can be used as alumina for the purpose.

In the method for preparing activated alumina of the present invention, a small amount of aluminum hydroxide seed (Seed) is added to a filtrate (NaAlO ₂ ) in which aluminum is eluted with a sodium hydroxide (NaOH) solution to precipitate and recover aluminum hydroxide, followed by dilute acid. After treatment, the solid component obtained by neutralization with dilute base and filtration was washed with deionized water at 70 to 100 ° C., followed by drying and calcining. Thus, sodium oxide (Na ₂₎ , which is a major impurity, lowers the purity of alumina. O) can significantly reduce the content, such as has the effect of producing a good quality activated alumina that can be used for adsorbents and chromatography.

Activated alumina, alumina hydroxide, aluminum dross,

Description

Process for preparation of activated alumina from Al dross}             

1 is a flowchart of a method for preparing activated alumina of the present invention.

2 is a graph showing the results of X-ray diffraction analysis (XRD) of the activated alumina prepared according to Example 1.

The present invention relates to a method for producing activated alumina using aluminum dross, and more particularly, to adsorbents and chromatography using aluminum dross, which is an oxide layer formed on the surface of a molten metal when dissolving aluminum metal or scrap. It is to provide a method for producing high purity activated alumina that can be used as alumina for alumina, and a small amount of aluminum hydroxide in a filtrate (NaAlO ₂ ) in which aluminum dross is dissolved in a sodium hydroxide (NaOH) solution to elute aluminum. Seeds were added to precipitate aluminum hydroxide, recovered, treated with dilute acid, neutralized with dilute base, filtered, and washed with deionized water at 70-100 ° C., followed by drying and calcining. Nat oxide, which is a major impurity that lowers the purity of alumina Is possible to drastically reduce the content of such (Na ₂ O) there is an effect that it is possible to manufacture the active alumina of good quality which can be used as such for the adsorbent and chromatography.

Since aluminum is a well-oxidized metal, aluminum dross is always generated when aluminum is dissolved. The aluminum dross is removed from the melting furnace when casting after melting, and part of the aluminum dross remains in the melting furnace or crucible when the aluminum molten metal is poured into a mold, and is generated in a molten runner during the casting of the molten metal. Most of the spent dross produced is aluminum oxide, and 10-30% metallic aluminum, salts within 10%, and impurities such as Mg, Si, Fe, etc. originally present in Al scraps are often mixed. .

In the domestic method of treating the waste dross as described above, in Korea, aluminum melters are heated and melted first or second to reduce aluminum metal in the dross and reduce the amount of dross to be discarded. At this time, the generated waste dross is buried by itself or by consignment treatment.

When the aluminum dross is treated according to the above method, the cost of securing landfill or waste dross processing costs to be entrusted to a waste disposal company is required, and the landfilled aluminum dross wastes the surrounding soil and damages the natural environment. Several problems have been raised, such as making it difficult.

On the other hand, the main components of aluminum dross are aluminum oxide (alumina) or metal aluminum. Aluminum oxide exists in the form of alpha alumina (α-alumina), beta alumina (β-alumina), gamma alumina (γ-alumina), etc., depending on the temperature and growth process of the crystal. Many exist in the form of alpha alumina (α-alumina). The ultimately stable form of alumina is α-alumina. Products include fired alumina, sintered alumina, and fused alumina.

Activated alumina to be prepared in the present invention is a χ-, η-, γ- type transition alumina having excellent properties such as large specific surface area and fine pore diameter, so that high value-added industries such as catalysts, adsorbents, catalyst supports and chromatography It has the characteristics that can be applied to.

Kaolin is used as a raw material in the conventional method of manufacturing alumina, and the kaolin is decomposed into a sodium hydroxide (NaOH) solution at high temperature and high pressure to leach aluminum oxide in the ore into the solution, and the leaching solution is hydrolyzed to obtain aluminum hydroxide Making is a common method, and the basic process of this method is called Bayer method.

However, the alumina prepared by the Bayer method contains a considerable amount of impurities such as Na ₂ O, Fe ₂ O _3, and the raw material cost is required to use imported kaolin, to maintain high temperature and high pressure during ore decomposition In order to use the autoclave (autoclave) has a disadvantage in that the equipment cost is required, there are a lot of difficulties in the use as activated alumina.

As another method for producing alumina, the method of dissolving ammonium alum [NH ₄ Al (SO ₄ ) ₂ .12H ₂ O] in water, reprecipitating it and recrystallizing it several times, purifying and thermally decomposing the alumina There is an ammonium alum pyrolysis method (Scheme 1) and an aluminum hydrolysis method (Scheme 2) to obtain alumina gel (Gel) by hydrolyzing alkylaluminum or aluminum alkoxide, and calcining it. The cost of raw materials and refining is high, and there are fatal shortcomings such as the generation of by-products.

NH ⁴⁺ Al ³⁺ (SO ₄ ) ₂ ^2- · 12H ₂ O → Al ₂ O ₃ + NH ₃ (g) + SO ₃ (g) + H ₂ O (g)

Al (R) ₃ + H ₂ O → Al (OH) ₃ + ROH + H ₂ → Al ₂ O ₃ + H ₂ O

_{Al (OR) 3 + H 2} O → Al (OH) 3 + ROH → Al 2 O 3 + H 2 O

In addition, after leaching with sodium hydroxide solution using aluminum dross as a raw material in Korea recently, the residue was prepared as an alumina castable refractory material and used as a heat-resistant material [Korean Patent No. 278,777], and hydroxide in filtered NaAlO ₂ aqueous solution. Aluminum hydroxide has been prepared by adding aluminum seeds (Korean Patent No. 202,731).

However, the alumina castable refractories using the above residues cannot be applied to activated alumina in the form of α-alumina. In addition, if aluminum hydroxide is leached into sodium hydroxide solution and aluminum hydroxide is added thereto to precipitate aluminum hydroxide, it may be suitable for general use, but the reaction may be performed in a high concentration of sodium hydroxide solution. since the prepared alumina is always make it contains significant amounts of sodium as an impurity as well as a poor purity of the final product, alumina deterioration characteristics as the solid acid catalyst or adsorbent of the quality that the content of Na ₂ O should be less than 0.3% It is difficult to prepare an activated alumina precursor.

That is, when manufacturing aluminum hydroxide by the conventional Bayer method, excessive raw material costs due to the use of imported kaolin, and equipment cost due to the use of an autoclave to maintain high temperature and high pressure during ore decomposition In the case of using the seed method after dissolving with a sodium hydroxide solution, there is a need for an improved manufacturing method for solving various problems such as difficulty in producing a high quality activated alumina precursor due to excessive impurities.

Accordingly, the inventors of the present invention have solved the above problems and researched to find a method that can minimize the content of co-precipitated sodium oxide (Na ₂ O) during the precipitation of aluminum hydroxide from aluminum dross. Leaching aluminum hydroxide with sodium hydroxide, recovering a large amount of aluminum hydroxide by the seed method, adding a dilute acid to adjust the pH to 0.5-3, and then adding a diluted base again neutralizing the pH to 7-9 and washing the solid component obtained by filtration with deionized water of 70-100 ° C., followed by drying and calcining, in the final activated alumina prepared. It has been found that the sodium content can be lowered to complete the present invention.

Accordingly, an object of the present invention is to provide a method for producing high purity and high quality activated alumina which can be used for adsorbents, catalyst supports, chromatography, etc. using aluminum dross as a raw material.

The present invention provides a method for producing activated alumina (aluminum) from aluminum dross, a step of leaching aluminum dross with aqueous sodium hydroxide solution, by adding aluminum hydroxide seed (Seed) to the leached solution Two steps of recovering the precipitated aluminum hydroxide, adding acid to the recovered aluminum hydroxide to adjust the pH to 0.5 to 3, and then neutralizing and filtering to a pH of 7 to 9 by adding a base, and the solid obtained by the filtration. Characterized by a method for producing activated alumina using aluminum dross to produce a high purity activated alumina with a Na ₂ O content of 0.3% by weight or less, comprising four steps of washing the components with deionized water at 70 to 100 ° C., followed by drying and calcining. It is done.

The present invention will be described in detail as follows.

The present invention provides a method for producing high purity activated alumina that can be used as an adsorbent and chromatography alumina, using aluminum dross, which is an oxide layer formed on the surface of molten metal when dissolving aluminum metal or scrap. To do this, aluminum dross is added to a filtrate (NaAlO ₂ ) in which aluminum is eluted with a sodium hydroxide (NaOH) solution, and a small amount of aluminum hydroxide seed (Seed) is added to precipitate and recover aluminum hydroxide, followed by dilute acid. After treatment, the solid component obtained by neutralization with dilute base and filtration was washed with deionized water at 70 to 100 ° C., followed by drying and calcining. The activated alumina production method of the present invention configured as described above is shown in the accompanying drawings as a flowchart thereof.

While aluminum metal itself is an amphoteric element, it is well soluble in acids and alkalis, whereas aluminum oxide is less soluble than aluminum, and alpha alumina is more difficult to dissolve than gamma alumina.

As shown in Figure 1, leaching of aluminum dross using an NaOH solution, which is an alkaline solution, causes the aluminum metal component in the dross to leach into an aqueous solution, and most of the aluminum oxide remains in the leach residue. The chemical reaction in the solution when leaching aluminum dross with NaOH during the manufacturing process shown in FIG. 1 is shown in Scheme 3 below, and the chemical reaction of the conventional method of leaching kaolin ore with NaOH is shown in Scheme 4 below.

Al + NaOH + H ₂ O → NaAlO ₂ + 3 / 2H ₂ ↑

Al ₂ O ₃ + 2NaOH → 2NaAlO ₂ + H ₂ O

As shown in Scheme 3, a small amount of seed (Seed) is added for the purpose of quickly leaching the aluminum dross with NaOH solution and then precipitated with Al (OH) ₃ , and stirring the solution, NaAlO ₂ is hydrolyzed in the solution. To form an Al (OH) ₃ precipitate. The chemical reaction during precipitation is shown in Scheme 5 below.

NaAlO ₂ + 2H ₂ O → Al (OH) ₃ ↓ + NaOH

Al (OH) by washing with water and drying after precipitation the ₃ Al (OH) if the number of times the _3, according to the manufacturing Al (OH) ₃ containing a large amount of Na ₂ O impurities as a poor purity of the final product, alumina However, it is difficult to produce a high quality activated alumina precursor by deteriorating the properties for the adsorbent and the chromatography.

The aluminum hydroxide precipitated above contains Na ₂ O as an impurity in the crystal structure, so it is very difficult to remove it by the usual washing method. In order to facilitate Na ₂ O in the precipitate, the slurry solution was subjected to acid treatment to lower the pH, thereby weakening the alumina hydroxide structure, eluting impurities in the structure, neutralizing it, and heating the solid component obtained by filtration to a specific range. It is a technical feature of the present invention to add a process to wash using one deionized water.

That is, in order to remove impurities such as Na ₂ O, a pH is adjusted to 0.5 to 3 by adding a dilute acid, followed by stirring, followed by addition of a diluted base to neutralize the pH to 7-9. The acid may be selected from nitric acid, sulfuric acid, hydrochloric acid, acetic acid, and the like. If the pH range adjusted during acid treatment is out of the range, impurities may not be efficiently removed. In addition, the pH adjusted during the neutralization treatment is more preferably maintained in the above range, and an aqueous ammonia solution is used as the base.

As described above, after dissolving the impurities by adjusting the pH, the filtered and filtered solid components are washed with deionized water heated to a specific temperature, so that the temperature ranges from 70 to 100 ° C. At this time, if the temperature range is less than 70 ℃ there is a problem that the impurities are not easily washed, it is preferable to maintain the above range.

As described above, the washing using the deionized water heated and adjusted to pH is sufficiently performed to prepare activated alumina by drying and calcining, more preferably so that the temperature during firing is in the range of 400 to 800 ° C.

Activated alumina prepared as described above can be utilized for the catalyst support, adsorbent and chromatography by minimizing impurities such as Na ₂ O.

Hereinafter, the present invention will be described in detail with reference to the following examples, but the present invention is not limited by the following examples.

Example 1

The aluminum dross sample used in the present invention was generated by a domestic aluminum recycling now manufacturer, and in the present invention, mainly used dross generated after recovering aluminum metal by primarily dissolving aluminum dross in a recycling company.

First, 45 g of aluminum dross A (Al content ≒ 30%) was reacted with a 10% aqueous sodium hydroxide solution to which 20 g of sodium hydroxide (NaOH) was added, followed by filtration, and then seeding in an aqueous sodium aluminate (NaAlO ₂ ) solution. As (Seed) 0.8 g of aluminum hydroxide (Al (OH) ₃ ) was added, hydrolyzed and filtered to precipitate aluminum hydroxide. Based on 1 mol of aluminum hydroxide precipitated, the pH was adjusted to 1.5 by adding 0.038 mol of dilute nitric acid (HNO ₃ ) as shown in FIG. 1 and stirred for 1 hour, followed by addition of 0.071 mol of dilute aqueous ammonia (NH ₄ OH). Was neutralized to be 8. Again washed several times with deionized water of about 95 ℃ and filtered. The prepared aluminum hydroxide was dried overnight at 110 ° C and then calcined at 600 ° C for 6 hours. The final activated alumina had a recovery of 85% at 11.5 g. The product of Example 1 was analyzed and the results are shown in Table 1 below, and the results of X-ray diffraction analysis are shown in the accompanying drawings.

Example 2

Aluminum hydroxide was prepared in the same manner as in Example 1, but aluminum dross B (Al content ≒ 10%) was used as a raw material. The final activated alumina obtained at this time also showed a recovery of 80% at 3.5 g. The product analysis results of Example 2 are shown in Table 1 below.

Comparative Example 1

Prepare aluminum hydroxide in the same manner as in Example 1, but after omission of pH adjustment using dilute acid and base, washed with deionized water at room temperature several times and filtered. The results of the product analysis of Comparative Example 1 are shown in Table 1 below.

Comparative Example 2

Aluminum hydroxide was prepared in the same manner as in Example 1, but washed several times with deionized water at room temperature when washing after adjusting the pH. Product analysis results of Comparative Example 2 are shown in Table 1 below.

Comparative Example 3

Aluminum hydroxide was prepared in the same manner as in Example 1, but the pH adjustment using dilute acid and base was omitted, followed by washing several times with deionized water at about 95 ° C. The results of the product analysis of Comparative Example 3 are shown in Table 1 below.

division Na ₂ O content Average pore diameter Specific surface area (m ² / g) Pore Volume (cc / g)  XRD Example 1 0.13 57.47 201.37 0.29 Mixed form of γ-, χ-alumina Example 2 0.15 58.02 201.55 0.30 Same as above Comparative Example 1 0.79 56.76 205.57 0.29 Same as above Comparative Example 2 0.38 58.74 203.01 0.29 Same as above Comparative Example 3 0.47 64.03 207.41 0.32 Same as above

Table 1 summarizes the BET nitrogen adsorption method, ICP-AES and XRD measurement results of the activated alumina prepared in Examples 1 and 2 and Comparative Examples 1 to 3, and the Na ₂ O content is ICP-AES. The value measured by the instrument is converted.

As shown in Table 1, the results of XRD analysis of all samples up to Examples 1 and 2 and Comparative Examples 1 to 3, it can be seen that it appears as a mixed form of γ-alumina and χ-alumina. As a representative example, the XRD pattern of the activated alumina prepared in Example 1 is shown in FIG. 2. As can be seen in FIG. 2, typical peaks of γ-alumina are 2θ = 38 °, 2θ = 45 °, 2θ = 67 ° Although the peak appears at, 2θ = 33 ° The peak at is not the peak of γ-alumina but the peak of χ-alumina, and 2θ = 38 ° With 2θ = 45 ° It can be seen that the intensity ratio of the peaks shown in FIG. 2 differs from γ-alumina, which also proves that the prepared activated alumina contains χ-alumina.

As a result of BET nitrogen adsorption analysis, it was confirmed that Examples 1 and 2 and Comparative Examples 1 to 3 showed similar values. However, the content of Na ₂ O by ICP-AES analysis shows a big difference for each sample prepared. In Comparative Example 1 without a specific washing process of Na ions, the samples prepared in Examples 1 and 2 had a low Na ₂ O impurity content between 0.1 and 0.2, compared to the Na ₂ O content of 0.79. there was.

That is, it was confirmed that the Na ₂ O impurity content of the final product can be minimized through the process of washing the pH several times with 70 ~ 100 deionized water after adjusting the pH using dilute acid and base. .

As described above, in the present invention, by manufacturing the aluminum hydroxide by leaching the metal aluminum contained in the aluminum dross with NaOH solution, it is possible to reduce the raw material cost compared to the conventional method of manufacturing aluminum hydroxide using imported kaolin. In addition, there is an advantage that the cost of equipment can be reduced because there is no need to use autoclave, and it significantly reduces the amount of aluminum waste dross to be disposed of by landfilling, thereby reducing the processing cost and fundamentally preventing environmental pollution and It is possible to reduce the manufacturing cost of the product by enabling the alternative application as a manufacturing raw material.

In addition, by significantly reducing the content of impurities such as Na ₂ O to enable the production of high-purity activated alumina that can be used for adsorbents and chromatography, the application range of the related industry is significantly expanded to utilize high-quality activated alumina at low cost. Will create an effect.

Claims (5)

In the method for producing activated alumina (alumina) from aluminum dross, 1 step of leaching aluminum dross with aqueous sodium hydroxide solution, 2 steps to recover the precipitated aluminum hydroxide by adding aluminum hydroxide (Seed) to the leached solution, Adding acid to the recovered aluminum hydroxide to adjust the pH to 0.5 to 3, and then adding a base to neutralize and filter to pH 7 to 9, and Four steps of washing the solid component obtained by filtration with deionized water of 70 ~ 100 ℃ after drying and baking Method for producing activated alumina using aluminum dross to produce a high-purity activated alumina having a Na ₂ O content of 0.3 wt% or less. delete The method of claim 1, wherein the acid of the three steps is selected from nitric acid, sulfuric acid, hydrochloric acid and acetic acid is added to the method of producing activated alumina using aluminum dross. The method of claim 1, wherein in step 3, the base is ammonia (NH ₄ OH) aqueous solution, characterized in that using alumina dross manufacturing method. The method of claim 1, wherein the firing temperature in the fourth step is a method for producing activated alumina using aluminum dross, characterized in that the range.

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