Method for producing aluminum hydroxide

Abstract

To provide a method for producing high-purity aluminum hydroxide by a simple method without requiring a seed crystal.SOLUTION: In the method for producing aluminum hydroxide according to the present disclosure, an aluminum alloy is dissolved in an alkali solution to prepare an alkali aluminate solution, aluminum hydroxide is precipitated from the alkali aluminate solution, the particle size distribution of the aluminum hydroxide is measured, the aluminum hydroxide is subjected to particle size separation based on the particle size distribution, and aluminum hydroxide having a small particle size is recovered. As a result, it is possible to provide a method for producing aluminum hydroxide that does not require a seed crystal and can be performed by a simple method.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present disclosure relates to a method for producing aluminum hydroxide. [Background technology]

[0002] Patent Document 1 discloses a method for producing aluminum hydroxide for obtaining high-purity aluminum hydroxide from aluminum hydroxide containing large amounts of impurities such as organic substances and iron compounds.

[0003] The method for producing aluminum hydroxide disclosed in Patent Document 1 is specifically as follows.

[0004] First, aluminum hydroxide containing a large amount of impurities obtained by the Bayer process or the like is dissolved, and an oxidizing agent is applied to the resulting crude aqueous sodium aluminate solution to decompose the organic matter. Next, aluminum hydroxide seed crystals are added to this aqueous solution to precipitate aluminum hydroxide, and impurities are attached to the precipitated aluminum hydroxide, which are then separated and removed. Finally, a chelating agent for removing impurities is added to the aqueous sodium aluminate solution from which the impurities have been removed, and carbon dioxide gas is blown in to obtain high-purity aluminum hydroxide. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Patent No. 5179095 Summary of the Invention [Problem to be solved by the invention]

[0006] The method for producing aluminum hydroxide disclosed in Patent Document 1 has the following problems.

[0007] First, high-purity seed crystals are used to remove impurities. Seed crystals are generally used to obtain only the same material as the seed crystal in high purity, and using a large amount of seed crystals to remove impurities is disadvantageous in terms of efficiency and cost.

[0008] Second, precipitation using seed crystals requires a long time because it is based on the hydrolysis reaction of sodium aluminate, which has a slow reaction rate. Therefore, the size of the apparatus is increased to ensure the residence time, and the amount of seed crystals used is also increased, which affects efficiency and cost.

[0009] Furthermore, in order to promote precipitation, i.e., to promote the hydrolysis reaction of sodium aluminate, which has a slow reaction rate, it is necessary to make the crude sodium aluminate aqueous solution extremely concentrated. Sodium aluminate is strongly alkaline, so it must be handled with care.

[0010] Furthermore, because the process is so diverse, there is also the issue of increased workload.

[0011] The present disclosure has been made to solve these problems, and an object of the present disclosure is to provide a method for producing high-purity aluminum hydroxide that does not require seed crystals and can be carried out in a simple manner. [Means for solving the problem]

[0012] The method for producing aluminum hydroxide according to the present disclosure includes dissolving an aluminum alloy in an alkaline solution to prepare an alkali aluminate solution, precipitating aluminum hydroxide from the alkali aluminate solution, measuring the particle size distribution of the aluminum hydroxide, separating the aluminum hydroxide by particle size based on the particle size distribution, and recovering aluminum hydroxide with small particle sizes. This makes it possible to provide a method for producing high-purity aluminum hydroxide that does not require seed crystals and can be carried out simply.

[0013] The precipitation of aluminum hydroxide may be carried out by adding an acidic substance to the alkali aluminate solution, thereby enabling efficient precipitation of aluminum hydroxide.

[0014] The particle size distribution may have two peaks, and the aluminum hydroxide having a small particle size may have the smaller particle size of the two peaks, thereby making it possible to obtain a precipitate of aluminum hydroxide with high purity.

[0015] Alternatively, the particle size separation may be carried out by filtering using a filter paper having a mesh size between the two peaks, thereby enabling the accurate production of a precipitate of high-purity aluminum hydroxide. [Effects of the Invention]

[0016] The present disclosure makes it possible to provide a method for producing aluminum hydroxide that does not require seed crystals and can be carried out in a simple manner. [Brief explanation of the drawings]

[0017] [Figure 1] 1 is a flowchart of a method for producing aluminum hydroxide according to the present disclosure. [Figure 2] 1 is a graph showing the particle size distribution of impurity precipitates before particle size separation of an aqueous aluminum hydroxide solution according to the present disclosure. [Figure 3] 1 is a graph showing the particle size distribution of impurity precipitates after particle size separation of an aqueous aluminum hydroxide solution according to the present disclosure. [Figure 4] 1 is a graph showing the ratio of elements contained in the precipitate of impurities in an aluminum hydroxide aqueous solution according to the present disclosure. DETAILED DESCRIPTION OF THE INVENTION

[0018] Hereinafter, embodiments of the present disclosure will be described with reference to the drawings, in which: Figure 1 is a flowchart of a method for producing aluminum hydroxide according to the present disclosure.

[0019] First, aluminum material is prepared as a raw material (S101). The aluminum material used here may be an aluminum alloy contained in waste materials.

[0020] Next, an aqueous sodium hydroxide solution (NaOHaq.) is prepared, and the aluminum material is added to the aqueous sodium hydroxide solution (S102). This step is preferably carried out using a dissolving device or the like. As a result, the aluminum material becomes sodium aluminate as shown in the following formula (1), and dissolves in the aqueous solution. The hydrogen generated at this time may be recovered and used in other steps. Al+NaOH+3H2O→Na[Al(OH)4]+3 / 2H2(1)

[0021] In the manufacturing method according to the present disclosure, the aluminum material is dissolved using an alkaline aqueous solution of sodium hydroxide, so that the concentration can be easily adjusted and handling is also easy.

[0022] Note that, as long as an alkaline solution exhibiting an appropriate pH can be prepared, other compounds may be used instead of sodium hydroxide, such as organic compounds such as amines, diamines, triamines, and tetraamines.

[0023] Although the above description cites an example of an aqueous solution in which the solvent is water, the present invention is not limited thereto, and subsequent steps may be carried out using an alkaline aluminate solution in which an alkaline compound is dissolved in an organic solvent. The use of an organic solvent can improve the drying properties of the solution. Furthermore, organic compounds such as the above-mentioned amines, diamines, triamines, and tetraamines are particularly preferred because of their high solubility in polar organic solvents.

[0024] Aluminum materials contain a large amount of impurities that are insoluble in aqueous sodium hydroxide solution, and the impurities precipitate as undissolved residue in the aqueous sodium hydroxide solution. Therefore, solid-liquid separation is performed to separate the undissolved residue from the aqueous solution (S103). This process can be performed using, for example, filter paper, a filter, or a centrifuge. The separated undissolved residue contains concentrated impurity elements, so it can be reused as a source of the detected impurity elements (S203).

[0025] Next, an acidic substance, such as CO2 (carbon dioxide gas), is added to the aqueous solution from which the undissolved residue has been removed (S104). This step may be performed by blowing carbon dioxide gas into the aqueous solution, or by adding carbonated water to the aqueous solution.

[0026] By adding carbon dioxide gas as an acidic substance to the aqueous solution from which undissolved residue has been removed, sodium aluminate turns into a precipitate of aluminum hydroxide as shown in the following formula (2). 2Na[Al(OH)4]+CO2→Na2CO3+2Al(OH)3+3 / 2H2(2)

[0027] In the production method according to the present disclosure, aluminum hydroxide is obtained by a neutralization reaction using CO2, rather than by crystallization through a hydrolysis reaction using seed crystals, and therefore the reaction rate is sufficiently fast, enabling improved efficiency.

[0028] The acidic substance is not limited to carbon dioxide gas, and may be hydrochloric acid, hydrogen chloride, sulfuric acid, sulfur oxide gas, nitric acid, nitrogen oxide gas, phosphoric acid, various organic acids, etc. Furthermore, other acidic substances may be used as long as the solubility of the resulting impurity metal salt in the solvent can be made smaller than the solubility of aluminum hydroxide in the solvent.

[0029] Here, the particle size distribution of the aluminum hydroxide precipitate is measured (S105). This step is preferably performed using a particle size distribution measuring device, but there are no particular limitations on the device or method as long as it is capable of measuring the target particle size range.

[0030] The measured particle size distribution is shown in Figure 2. The inventors discovered that the particle size distribution had two peaks in a series of reactions. The inventors consider this phenomenon as follows.

[0031] First, adding CO2 to an aqueous solution of sodium hydroxide forms impurity carbonates in the solution. These carbonates have lower solubility in water than the aluminum hydroxide formed in the reaction of formula (2), so the impurity carbonates precipitate before the aluminum hydroxide. The aluminum hydroxide precipitated by the reaction of formula (2) becomes large in particle size, using the impurity carbonates as crystal nuclei. After the impurity carbonates have sufficiently precipitated and the impurities have decreased, the crystal nuclei also decrease, making it difficult for aluminum hydroxide to precipitate, resulting in the formation of small-particle aluminum hydroxide. This results in two peaks in the particle size distribution. Therefore, high-purity aluminum hydroxide can be obtained by collecting only the small-particle aluminum hydroxide.

[0032] Therefore, the aluminum hydroxide precipitate is separated by particle size into small and large particle sizes (S106). This step is preferably carried out by filtering the aqueous solution containing the aluminum hydroxide precipitate using filter paper with mesh openings between the sizes of the two peaks mentioned above. The separated large particle size precipitate may be discarded, but since it contains a large amount of aluminum hydroxide despite containing impurities, it is preferable to re-dissolve it in an alkaline solution and reuse it as a raw material (S206).

[0033] The particle size distribution shown in Figure 2 shows peaks near 10 μm and 50 μm. Therefore, if an aqueous solution is filtered using filter paper with a mesh opening of 20 μm, small precipitates with an average particle size of about 10 μm will pass through the filter paper and remain in the aqueous solution, while large precipitates with an average particle size of about 50 μm will be separated as impurities.

[0034] 2, the particle size distribution has peaks near 10 μm and near 50 μm, but the peak positions vary depending on reaction conditions such as temperature and solution concentration. Therefore, it is important to measure the particle size distribution of the aluminum hydroxide precipitate in S105, and it is preferable to perform particle size separation based on the particle size distribution.

[0035] Figures 3(a) and (b) show the particle size distributions of small and large precipitates, respectively, after size separation, i.e., after filtration. It can be seen that the small precipitates that passed through the filter paper with a 20 μm mesh were accurately separated from the large precipitates that remained on the filter paper.

[0036] Figure 4 shows the proportions of impurity elements contained in the large-particle precipitates before and after particle size separation, and the small-particle precipitates after particle size separation. In this embodiment, the proportions of Mg, S, Cl, Sn, Ca, Cr, Mn, Fe, Ni, Cu, and Zn were investigated as impurity elements. The small-particle precipitates after filtration showed low proportions of all elements, indicating that the impurity elements were efficiently removed.

[0037] Thereafter, the aqueous solution is subjected to solid-liquid separation (S107) to remove small precipitates remaining in the aqueous solution. This step may be performed, for example, by filtration using filter paper with a mesh size even smaller than that described above, or by using a centrifuge.

[0038] The filtrate from which the small particle size precipitates have been removed is an aqueous sodium carbonate solution (Na2CO3aq), which may be discarded, or recovered and used in another process since it is an alkaline aqueous solution (S207).Furthermore, it may be evaporated to dryness and recovered as solid sodium carbonate for other uses.

[0039] Finally, the resulting small particle size precipitate is dried to obtain high-purity aluminum hydroxide (S108). As described above, the production method according to the present disclosure can obtain high-purity aluminum hydroxide by performing a neutralization reaction step using an acidic substance, such as CO (carbon dioxide), multiple solid-liquid separation steps, and a particle size separation step, thereby greatly simplifying the process.

[0040] In this way, it is possible to provide a method for producing high-purity aluminum hydroxide that does not require seed crystals and can be carried out in a simple manner.

[0041] The present disclosure is not limited to the above-described embodiment, and can be modified as appropriate within the scope of the present disclosure.

Claims

1. An aluminum alloy is dissolved in an alkaline solution to prepare an alkaline aluminate solution; Precipitating aluminum hydroxide from the alkali aluminate solution; measuring the particle size distribution of the aluminum hydroxide; The aluminum hydroxide is subjected to particle size separation based on the particle size distribution, and aluminum hydroxide with a small particle size is recovered. A method for producing aluminum hydroxide.

2. The precipitation of the aluminum hydroxide is carried out by adding an acidic substance to the alkali aluminate solution. The method for producing aluminum hydroxide according to claim 1.

3. The particle size distribution has two peaks, The aluminum hydroxide having a small particle size has a particle size that is smaller than the two peaks. The method for producing aluminum hydroxide according to claim 1 or 2.

4. The particle size separation is carried out by filtering using a filter paper having a mesh size between the two peaks. The method for producing aluminum hydroxide according to claim 3.

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