JPS6256087B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for purifying strontium salts useful for electronic materials, and particularly to a method for effectively removing calcium salts contained as impurities.

Generally, strontium salts such as strontium carbonate are produced by reacting ores (mainly celestite ores) containing strontium sulfate as a main component with soda carbonate. By the way, this ore contains a large amount of the homologous element calcium, and since calcium has similar chemical properties to strontium, it is difficult to separate it, and it often remains as an impurity in strontium products. Strontium usually contains 0.5% or more of calcium carbonate as an impurity.

Since such products are unsuitable for use as precision electronic materials, a method has been proposed in which strontium salts are produced by blending the ore with a reducing agent such as reduced coal and performing reduction roasting at high temperatures to improve purity. The calcium carbonate content of products produced by this method is 0.25%
Even before and after, I am still not satisfied.

As a result of various studies on the purification method of the above-mentioned strontium salt, the present inventors have found that by reacting an alkali with an aqueous solution of strontium salt in which calcium salt coexists, fine calcium hydroxide is produced with a particle size of 0.05 to 10.
If mm of strontium hydroxide is crystallized and strontium hydroxide is separated from the crystal slurry, calcium hydroxide can be efficiently removed, and when this strontium hydroxide is dissolved to produce strontium carbonate, _the It has been found that a highly pure strontium salt with a calcium content of 0.1% or less can be obtained.

According to the present invention, a high-quality strontium salt can be industrially advantageously obtained in a short time without complicated operations such as concentration.

As the aqueous strontium salt solution coexisting with calcium used as a raw material in the present invention, an aqueous solution of mineral acid salts such as chlorides and nitrates or sulfides is used. That is, a solution obtained by reducing and roasting ore and leaching the ore with water and adding an acid to the leaching solution is used, but it also includes an aqueous solution of a strontium salt in which common calcium coexists.

Of course, there is no problem even if other water-soluble impurities are dissolved.

Further, as the alkali used in the present invention, caustic soda, caustic potash, strontium oxide, strontium hydroxide, etc. are all effective, and caustic soda is particularly preferably used.

The amount of these alkalis to be used is sufficient to convert both the calcium salt and the strontium salt into hydroxides. The reaction may be carried out at room temperature, but preferably at 70°C.
The particle size of calcium hydroxide, which is preferably carried out under heating at ~100°C to facilitate the subsequent separation of crystals, does not increase much even when heated, and the particle size is usually 0.03 mm or less. When strontium hydroxide is heated at 70 to 100°C, its crystals quickly grow to a size of 0.05 mm or more. Also,
By aging the reaction for 10 minutes or more, preferably 15 minutes or more, the particle size of strontium hydroxide is further coarsened, but calcium hydroxide is not coarsened.

Although the concentration of the strontium salt aqueous solution coexisting with the calcium salt used as a raw material in the present invention does not affect the particle size of the generated hydroxide, an extremely dilute or concentrated solution is not desirable from the viewpoint of economy and reaction operation. is 20gr/~500gr/. Fine calcium hydroxide and particle size 0.05~10 by reaction
This results in a mixed slurry of mm of strontium hydroxide, which may be transferred to the next separation step immediately, but is usually transferred to the separation step after cooling.

General mechanical separation means may be used to separate the mixed slurry of crystals in the method of the present invention, but it is preferably carried out using a filtration device having a predetermined mesh or by sedimentation separation. conduct. Other mechanical methods such as centrifugation may also be used.

If separation is performed by
It is necessary to use the one between meshes. By carrying out the filtration, strontium hydroxide crystals remain and fine calcium hydroxide passes along with the liquid. In some cases, in order to remove calcium hydroxide that adheres to the surface of the obtained strontium hydroxide crystals, the above calcium hydroxide is resuspended using the mother liquor from which calcium hydroxide has been removed and the washing process is carried out. You can also.

Another preferred example of the separation operation in the present invention is sedimentation separation. When a mixed slurry of crystals is left, fine calcium hydroxide will float in the upper layer of the liquid due to the difference in sedimentation speed of the crystals, and can be removed by being washed away. Further, calcium hydroxide can be separated more effectively by removing calcium hydroxide from the above liquid, mixing it again with the strontium hydroxide precipitate, and repeating the sedimentation separation.

The strontium hydroxide obtained by the separation of the present invention is dried to produce a product after other impurities are removed. It can also be used as a raw material for other strontium salts depending on the purpose.

Example 1 Aqueous solution 1 in which 322 g of SrCl ₂ and 1.7 g of CaCl ₂ were dissolved was heated to 90° C., 170 g of NaOH was added thereto, stirring was continued for 15 minutes, and then left to stand and cooled with water. The resulting Sr(OH) 2.8H ₂ O having an average particle size of 0.5 mm was passed through a 250 mesh filter while stirring, and further washed with 100 ml _of water. The obtained strontium hydroxide crystals were dissolved in water at 80°C and then CO ₂ gas was passed through the solution to obtain strontium salt as SrCO ₃ . The CaCO ₃ content of this product was analyzed and found to be 0.08%.

In addition, in the above method, if Na ₂ CO ₃ is directly added to the mixed solution to make SrCO ₃ without using NaOH,
The content of _CaCO3 was 0.5%.

Example 2 Aqueous solution 1 in which 158 g of SrCl ₂ and 42 g of CaCl ₂ were dissolved was heated to 80° C., 130 g of NaOH was added thereto, stirred for 15 minutes, and then allowed to cool.

The resulting slurry of Sr(OH) ₂ ·8H ₂ O with an average particle size of 4 mm and fine Ca(OH) ₂ was stirred a little, and then the suspended Ca(OH) ₂ was separated by a gradient method. Further, the Ca(OH) ₂ particles in the mother liquor were separated and removed, and the solution was returned to the slurry of Sr(OH) _{2.8H 2} O, stirred, and then Ca(OH) ₂ was separated again by the gradient method.

The same operation was repeated, and the obtained crystals were dissolved in pure water and CO ₂ gas was passed through to obtain a strontium salt as SrCO ₃ . The CaCO ₃ content of this product was analyzed and found to be 0.09%.

In addition, in the above method, if Na ₂ CO ₃ is added directly to the mixed solution to make SrCO ₃ without using NaOH,
The content of _CaCO3 was 20.5%.

Example 3 Add 200 g of 99% Sr(OH) 2.8H ₂ O to the stock solution of Example 1 _.
was added, and the mixture was reacted and aged at 80°C for 30 minutes, and then allowed to cool. While stirring the generated Sr(OH) ₂ slurry having an average particle size of 5 mm, the entire amount was passed through a 40-mesh sieve to separate Sr(OH) _{2.8H 2} O crystals. Furthermore, the Sr(OH) 2.8H ₂ O crystals were washed again using the supernatant obtained by settling the fine particles _of Ca(OH) ₂ in the mother liquor, and after dissolving them in water at 80°C, CO SrCO ₃ through ₂ gas
Strontium salt was obtained as of this
The CaCO ₃ content was analyzed and found to be 0.07%.

Claims (1)

[Claims] 1. Add an equivalent amount of alkali to each strontium salt aqueous solution in which calcium salt coexists, react at room temperature to 100°C, and age for 10 minutes or more to form fine calcium hydroxide and particle size 0.05. A method for purifying strontium salt, comprising crystallizing strontium hydroxide of ~10 mm and separating strontium hydroxide from the crystal slurry. 2. The method for purifying strontium salt according to claim 1, wherein the crystal slurry is passed through a filtration layer of 325 to 3.5 mesh in separating strontium hydroxide from the crystal slurry. 3. A method for purifying a strontium salt according to claim 1, wherein strontium hydroxide is separated from a crystal slurry by sedimentation separation of the crystal slurry. 4. In separating strontium hydroxide from the crystal slurry, the mother liquor from which calcium hydroxide has been removed from the filtrate from which strontium hydroxide has been separated is added again to the strontium hydroxide and the separation is repeated. A method for purifying a strontium salt according to any one of Items 1 to 3.