JPH05170432A - Alumina having low cao content and its production - Google Patents

Abstract

PURPOSE:To obtain alumina having low CaO and K2O contents and suitable for use as starting material for beta-alumina by washing alumina having a specified CaO content or below obtd. by the Bayer process with a mineral acid. CONSTITUTION:Alumina having <=120ppm CaO content obtd. by the Bayer process is washed with a mineral acid to obtain the objective alumina having such low CaO and K2O contents as <=30ppm CaO and <=10ppm K2O. Dil. hydrochloric acid or dil. nitric acid is used as the mineral acid but dil. hydrochloric acid is preferably used.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a low CaO-containing alumina obtained by the Bayer method, and particularly to a low CaO-containing alumina obtained by the Bayer method suitable as a raw material for beta-alumina and a method for producing the same.

[0002]

2. Description of the Related Art Conventionally, alumina containing few impurities has been used as beta-alumina which is a solid electrolyte for sodium-sulfur batteries. In particular, the presence of CaO or K ₂ O in beta-alumina shortens the life of the sodium-sulfur battery, so CaO is required to be at least 50 ppm or less, and K ₂ O is also required to be as small as possible. [For example, Osaka Industrial Technology Laboratory Quarterly Report Vol. 37, No. 3, 1986, pp. 255-270, development status of batteries for electric vehicles 6. Sodium-sulfur battery]

Therefore, for these uses, a method for hydrolyzing an organic aluminum salt such as aluminum alkoxide, a method for thermally decomposing purified aluminum alum, an inorganic aluminum salt such as ammonium aluminum carbonate, and aluminum chloride which is easily vaporized High-purity alumina obtained by a method such as a gas-phase oxidation method in which oxygen is oxidized with oxygen or steam is used, but since these aluminas are expensive as compared with Bayer method alumina, sodium-
The cost of the sulfur battery is high.

[0004]

On the other hand, commercially available buyers
Lumina is usually cheaper than the above alumina, but
CaO about 130 to about 500 ppm, K₂About 40 ~
Since it contains about 200 ppm, it was synthesized using this as a raw material.
Beta-alumina shortens the life of sodium-sulfur batteries
To get rid of Impurities that are causative substances as a solution to the problem
Is the above CaO, K ₂Because it is an alkaline substance of O
Na in the field₂Hydrochloric acid, which is already known as a method for reducing O,
The acid cleaning by
Alumina from about 130 to about 500 ppm has various acid concentrations.
50p even after repeated washing with acid or repeated washing with acid
The result obtained is that it can be removed only up to about pm.

[Means for Solving the Problems]

Under the circumstances, the inventors of the present invention have made earnest investigations for the purpose of providing an inexpensive Bayer alumina containing CaO and K ₂ O in the above-mentioned ranges. If the concentration of CaO in the alumina obtained by the Bayer method before is less than a specific value, CaO suitable as a raw material for beta-alumina by treatment with mineral acid,
The inventors have found that alumina having a K ₂ O concentration can be obtained, and completed the present invention.

That is, the present invention is CaO 30ppm or less,
Another object is to provide a low CaO-containing alumina obtained by the Bayer method, which comprises K ₂ O of 10 ppm or less. Another object of the present invention is to provide an alumina for beta-alumina obtained by the Bayer method, which contains CaO of 30 ppm or less and K ₂ O of 10 ppm or less, which gives a long life as a solid electrolyte material of a sodium-sulfur battery. Furthermore, the CaO content is 1
CaO 30 ppm or less characterized by washing alumina obtained by the Bayer method of 20 ppm or less with a mineral acid,
Another object of the present invention is to provide a method for producing low-low CaO-containing alumina obtained by the Bayer method, which comprises K ₂ O of 10 ppm or less.

The present invention will be described in more detail below. Alumina obtained by the Bayer method of the present invention is CaO30p
It is an alumina composed of pm or less and K ₂ O of 10 ppm or less. Alumina having such physical properties is recommended as a raw material for beta alumina.

The alumina having the above physical properties has a CaO content of about 120 ppm or less, preferably about 100 ppm or less, and a K ₂ O content of about 200 ppm or less, preferably about 150 ppm or less obtained by the Bayer method with a mineral acid. Obtained by washing. In the Bayer process alumina manufacturing process, in addition to Ca compounds and K compounds contained in raw materials such as bauxite and caustic soda as impurities, sodium carbonate generated in the oxidation of organic substances in bauxite and carbon dioxide gas in the air are included. It reacts with the circulating sodium aluminate solution and accumulates in the circulating sodium aluminate solution as sodium carbonate. In the buyer process, Ca compounds such as slaked lime are added and used for the purpose of decomposing the sodium carbonate accumulated in this liquid and recovering the alkali. Due to these various causes, CaO and K ₂ O contained in alumina are used. Is presumed to have a concentration of the above level.

The CaO content in alumina is about 120 pp
There is no particular limitation on the method of making the m or less, but the cost burden is the known method such as the method of removing the organic matter in the circulating sodium aluminate solution by adsorption removal using an adsorbent, wet oxidation removal, precipitation removal by concentration cooling, Is recommended because it is less. Upon removal, the organic matter concentration may be operated under the condition that the concentration in the precipitated aluminum hydroxide is about 0.02% by weight or less, preferably about 0.015% by weight or less in terms of carbon. It is not clear why increasing the removal degree of organic substances in the circulating sodium aluminate solution is effective in reducing the CaO content in the alumina obtained by the Bayer method, but the Ca compound added for the purpose of alkali recovery is not known. It reacts with the organic acid sodium in the circulating sodium aluminate solution to produce calcium organic acid having a high solubility, so it is speculated that the enhancement of the removal of organic substances has a great effect on the reduction of the CaO content. The removal of organic matter from the circulating sodium aluminate solution may be performed in any of the buyer steps.

In the practice of the present invention, the method of treating the alumina with a mineral acid is not particularly limited.
Alumina is added to the dilute nitric acid solution, stirred at room temperature, filtered, and washed. As the mineral acid used for pickling, hydrochloric acid is recommended because of its removal effect and its effect on the substance after treatment. The concentration of hydrochloric acid used for pickling is about 0.03N to about 12N, preferably about 0.1N to about 6N. The solution temperature and time for pickling are not particularly limited as long as the CaO content in the alumina after the washing treatment is 30 ppm or less and the K ₂ O content is 10 ppm or less, and are usually room temperature to 100.
℃ several minutes or more, usually room temperature to about 75 ℃ about 5 minutes to about 1
It should be carried out on time.

The form of alumina to be treated is not particularly limited, but in the case of beta sodium raw material alumina, one having an average primary particle diameter of about 1 μm or less is used. The larger the average secondary particle diameter, the easier the treatment such as filtration during the pickling treatment. In addition, even if the alumina has an average secondary particle size of about 20 to 60 μm, if the CaO content in the raw material alumina is about 120 ppm or less, the desired CaO content is obtained.
Since the concentration can be reduced, it may be subjected to treatment without crushing. As the alumina, alumina having a crystal form of either transition alumina or α-alumina can be used, but α-alumina is preferable for use in, for example, beta-alumina or the like which requires molding dimensional accuracy.

The mineral acid treatment of alumina may be carried out once or plural times. In this case, CaO, K
_There is almost no effect of reducing the concentration of ₂ O, and treatment of once, preferably twice is usually sufficient.

[0013]

As described in detail above, according to the present invention, the CaO concentration in the alumina obtained by the Bayer method is about 120 ppm.
With the extremely simple method of treating the following with mineral acid,
Inexpensive CaO content 30ppm or less, K ₂ O content 10
It is possible to supply alumina suitable for a raw material for beta-alumina of ppm or less, and its industrial value is enormous.

[0014]

EXAMPLES The present invention will be described in more detail with reference to examples below, but the present invention is not limited to the following examples. Incidentally, the analysis of CaO and K ₂ O was carried out by the emission spectroscopic analysis method.

Example 1 and Comparative Examples 1 to 3 200 g of Bayer alumina having the composition shown in Table 1 was dispersed in 200 ml of 0.1N hydrochloric acid at 75 ° C., stirred for 30 minutes, filtered with a No. 6 quantitative filter paper, and then 60. It was washed with warm water at ℃. After washing the alumina, warm water at 60 ° C 2
The mixture was dispersed in 00 ml and stirred for 10 minutes, then filtered through No6 quantitative filter paper and dried. CaO and K ₂ in the obtained alumina
The O content was measured. The results are shown in Table 2.

Example 2 A pickling treatment was carried out in the same manner as in Example 1 except that the hydrochloric acid concentration in Example 1 was changed from 0.1N to 1.0N. Table 2 shows the measurement results of CaO and K ₂ O contents in the treated alumina.

Example 3 A pickling treatment was carried out in the same manner as in Example 1 except that the hydrochloric acid concentration in Example 1 was changed from 0.1N to 6.0N. Table 2 shows the measurement results of CaO and K ₂ O contents in the treated alumina.

Example 4 Instead of hydrochloric acid in Example 1, nitric acid 20 having a concentration of 0.1 N was used.
The pickling treatment was performed in the same manner as in Example 1 except that 0 m was used. Table 2 shows the measurement results of CaO and K ₂ O contents in the treated alumina.

Comparative Example 4 Hydroxide hydroxide shown in Table 1 was used in place of alumina in Example 1.
Pickling treatment was carried out in the same manner as in Example 1 except that luminium was used.
It was CaO, K in aluminum hydroxide after treatment ₂Including O
Table 2 shows the measurement results of the abundant amounts.

Comparative Example 5 The alumina used in Comparative Example 3 was pickled and water washed in the same manner as in Example 1, and then the pickling and water washing were repeated twice in total. Table 2 shows the measurement results of the CaO and K ₂ O contents in the treated aluminum hydroxide.

Comparative Example 6 The same treatment as in Example 1 was carried out except that warm water was used instead of hydrochloric acid in Example 1. C in alumina after treatment
Table 2 shows the measurement results of the aO and K ₂ O contents.

[0022]

[Table 1]

[0023]

[Table 2]

Claims (3)

[Claims] 1. CaO 30 ppm or less, K ₂ O 10 pp
A low CaO-containing alumina obtained by the Bayer method having a particle size of m or less. _2. CaO 30 ppm or less, K ₂ O 10 pp
Alumina for beta-alumina obtained by the Bayer method containing m or less. 3. A low CaO-containing alumina obtained by the Bayer method comprising CaO of 30 ppm or less and K ₂ O of 10 ppm or less, characterized in that alumina obtained by the Bayer method of CaO content of 120 ppm or less is washed with a mineral acid. Production method.