JP3034854B2 - Strontium nitrate and method for producing the same - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to strontium nitrate and a method for producing the same, and more particularly to an object of the invention is to provide strontium nitrate having a low impurity content suitable for gas generation (oxidizing agent) of an automobile airbag. I do.

[0002]

2. Description of the Related Art The largest use of strontium nitrate is that it emits red light when burned, and is therefore used as a material for smoke canisters. It is also used as an ignition material for briquettes, albeit to a lesser extent, and as an intermediate material for semiconductors, phosphors and the like.

[0003] More recently, it has been used as an oxidizing agent for gas generation in airbags of automobiles because of its low deliquescence, low hygroscopicity and relatively stable against heat. Conventionally, metal oxidizers have been used as oxidizers for this gas generator for airbags, but deliquescence, hygroscopicity, heat stability, etc. are not always sufficient,
As described above, replacement with strontium nitrate has advanced. The method for producing strontium nitrate includes the following method.

[0004] First, strontium carbonate is produced as a starting material, and then strontium nitrate is produced.
A method of producing strontium carbonate by a reduction roasting method using O ₄ ) as a raw material; a method of producing strontium carbonate by SrSO ₄ + 2C → SrS + 2CO ₂ SrS + CO ₂ + H ₂ O → SrCO ₃ + H ₂ S or a soda method SrSO ₄ + Na ₂ CO ₃ → SrCO ₃ + Na ₂ SO _4. Strontium carbonate (SrCO ₃ ) obtained by these methods is dissolved in dilute nitric acid. After removing impurities in the generated strontium nitrate solution, until the crystal film is formed. Upon concentration, cooling and crystallization, strontium nitrate tetrahydrate (Sr (NO ₃ ) ₂ .4H ₂ O) is obtained.

Usually, it is known that the strontium nitrate solution from which impurities have been removed is concentrated in an evaporator to precipitate crystals under heating, centrifuged under heating, and dried at 100 ° C. or higher to obtain an anhydrous salt. SrCO ₃ + 2HNO ₃ → Sr (NO ₃ ) ₂ + CO ₂ +
H ₂ O (Chemical Handbook Applied Chemistry Edition, 1986)

Japanese Patent Application Laid-Open No. 57-209820 discloses that
After mixing and heating and reacting celestite, a natural ore whose main component is strontium sulfate, with calcium nitrate containing water of crystallization, the reaction mixture is brought into contact with water to extract the reaction product, strontium nitrate, and unreacted calcium nitrate with water. The extract was heated to evaporate water to precipitate strontium nitrate crystals, which were separated from the mother liquor, washed with water and dried to obtain 0.89% by weight of Ca, Ba
0.44% by weight, Mg 6.6 ppm, SiO ₂ 3
A method for obtaining strontium nitrate of 7 ppm, 0.43 ppm of Na, 5 ppm of Al, and 0.1 ppm or less of Fe is disclosed.

As a method for removing impurities of the obtained strontium nitrate, for example, Japanese Patent Publication No. 58-359
No. 35, calcium hydroxide was added to a crude strontium nitrate solution containing heavy metals and magnesium to adjust the pH to 7-8.
A method for precipitating and separating and removing heavy metals and magnesium as hydroxides by adjusting the pH is disclosed.

In Japanese Patent Publication No. 58-35935, celestite (S), which is a strontium sulfate produced naturally, is disclosed.
Using rSO ₄ ) as a raw material, strontium carbonate precipitated by the metathesis method SrSO ₄ + Na ₂ CO ₃ → Na ₂ SO ₄ + SrCO ₃ of the following formula was separated from the reaction mixture, washed to remove the attached sodium sulfate solution, I have a strontium cake.

The composition of the crude strontium carbonate in a dry amount is, for example, 86% of SrCO ₃ and CaCO ₃
8%, MgCO ₃ 2%, Na ₂ SO ₄ 2%, inert substance 1.5%, BaCO ₃ 1%, BaSO ₄ 0.5
%, Na ₂ CO ₃ 0.1%, and then the crude strontium carbonate cake is adjusted to a slurry having a solids content (dry basis) of about 0.5-6%, and nitric acid at a concentration of, for example, 69%. After reacting with nitric acid at about 40-90 ° C. and adding nitric acid until the generation of carbon dioxide is completed, the excess acidity is reduced by adding a small amount of a wet cake of strontium carbonate and adjusting the pH to about 3 to Adjust to 4.

Next, calcium hydroxide is added to adjust the pH.
To about 7 to 8 to precipitate the heavy metal and magnesium hydroxide present in the nitrate solution. This precipitate is
A crude strontium nitrate solution is obtained by filtration at 0 ° C. The composition of the resulting crude strontium nitrate solution is, as a typical example, Sr (NO ₃ ) ₂ 39%, Ca (NO ₃ )
_{2 6%, NaNO 3 1%} , Mg (NO 3) 2 1
%, Ba (NO ₃ ) ₂ 0.4%, and the remaining water.

The crude strontium nitrate solution is mixed with 60 to 9
Evaporative crystallization at 0 ° C. gives solid strontium nitrate. This is separated and washed, the adhered mother liquor is removed and dried. The composition of the anhydrous strontium nitrate crystal thus obtained is, as a typical example, Sr (NO ₃ ) ₂
98%, Ba (NO ₃ ) ₂ 1.0%, Ca (N
O ₃ ) ₂ 0.35%, NaNO ₃ 350 ppm, M
g (NO ₃ ) ₂ 550 ppm.

Another method for removing impurities is as follows.
For example, JP-A-9-77516 discloses that Na, K, Fe, Ni, U, Th, and Ni are added by adding nitric acid to a raw material strontium nitrate-containing aqueous solution to precipitate strontium nitrate, and separating the deposited strontium nitrate by solid-liquid separation. A method for obtaining strontium nitrate having a low Ca impurity content is disclosed as an intermediate operation in a method for producing high-purity strontium carbonate.

The impurities in this raw material strontium nitrate are Ca 270 ppm, Na 95 ppm, K 12
ppm, Fe 1 ppm, Ni 1 ppm, U 0.1
ppb and Th 0.1 ppb. Nitric acid corresponding to an acid concentration of 5.3 N is added to the aqueous solution, heated to 80 ° C., cooled to room temperature, and strontium nitrate crystallized is subjected to solid-liquid separation. The impurities in this recrystallized strontium nitrate were Ca 4 ppm, Na 3 ppm, K <1 ppm,
Fe <0.1 ppm, Ni <0.1 ppm, U <0.0
3 ppb, Th <0.03 ppb.

Further, as a method for purifying strontium nitrate, for example, in US Pat. No. 3,065,052, an aqueous solution of strontium nitrate containing barium impurities is prepared.
Bring this solution to at least the neutral region with nitric acid,
Further, the mixture was mixed with a chromic acid solution to form a strongly acidic solution. While stirring the solution containing the nitrate and the acid, a strontium hydroxide solution was gradually added thereto to adjust the pH to 11.
After precipitating barium impurities as barium chromate by maintaining for a few minutes, the solution was filtered to remove barium chromate, and then nitric acid was added thereto while boiling the filtrate to bring the pH to about 1, Further, by evaporating the filtrate to precipitate strontium nitrate crystals, the composition averaged 99.85% of Sr (NO ₃ ) ₂ and Ba (N
O ₃ ) ₂ 0.05%, Ca (NO ₃ ) ₂ not detected, N
A method for obtaining strontium nitrate such as 0.004% aNO ₃ is disclosed.

The quality of anhydrous strontium nitrate as a reagent specified in JIS is 0.0005% by weight or less for heavy metals (as Pb),
0.0005% by weight or less, Ca 0.02% by weight or less,
It is stipulated that a material having a K of 0.01% by weight or less and a Na of 0.02% by weight or less is used.

[0016]

The above-mentioned conventional strontium nitrate contains a large amount of Ba, Ca and Na.
For this reason, even if conventional strontium nitrate is used as an oxidizing agent for an airbag, the deliquescence and the hygroscopicity have not been sufficient yet. For this reason, in an airbag that has been stored for a long time under poor conditions and has absorbed moisture, the explosion characteristics of gas generation of the airbag were unstable. B in strontium nitrate
If a is included, barium as an oxide may remain after gas generation from the airbag.

In the case of impurities such as Cr, there is a concern that they may diffuse into the environment after the generation of airbag gas.
The conventional production method using chromic acid treatment has a problem that Cr remains as an impurity in strontium nitrate.

Furthermore, in the method of removing barium as a chromate, chromium is mixed into strontium nitrate and wastewater treatment of chromic acid used under strict regulations is inevitable.

In addition, the raw material often contains NH ₃ , and the final product also contains a small amount of NH ₃ (for example, 1).
(About 0 ppm by weight), the particle size was not sufficiently controlled, and the mother liquor was not sufficiently removed during the purification, so that the pH when dissolved in water varied. The water content was also high.

Therefore, NH _{3 is} contained in strontium nitrate.
Is present even in trace amounts, when the average particle size of the powder is too small, when there are many fine particles, or when the pH when dissolved in water is too low or too high, deliquescent In addition, there are problems such as increased hygroscopicity or increased reactivity, resulting in instability, making it difficult to manufacture airbags, inflators, etc., or having insufficient properties such as thermal stability as products. Was. When the water content was high, the explosion characteristics were not sufficient.

Therefore, barium, sodium, calcium, chromium and ammonia impurities which are less likely to have the above problems and are suitable for use as an oxidizing agent for airbags of automobiles are suppressed, and the particle diameter and pH are controlled. There has been a strong demand for the development of a highly pure strontium nitrate having a reduced water content and a method for producing strontium nitrate which does not require treatment with a chromic acid waste liquid.

[0022]

[0023]

[0024]

[0025]

Means for Solving the Problems As means for solving the above-mentioned problems, the first invention is characterized in that the Ba content is 0.05% by weight or less, the Na content is 0.005% by weight or less, and the Ca content is Is a granular strontium nitrate having a content of 0.01% by weight or less and a Cr content of less than 0.001% by weight, wherein the content of the average particle size is 200 μm or more and the particle size is 44 μm or less is less than 1% by weight. Strontium nitrate characterized by having a content exceeding 840 μm of less than 1% by weight.

According to a second aspect, in the strontium nitrate according to the first aspect, the content of NH ₃ is 0.0001.
It is strontium nitrate characterized by being less than weight%.

According to a third aspect of the present invention, there is provided the strontium nitrate according to the first or second aspect, wherein an aqueous solution obtained by dissolving 5 g of the strontium nitrate in 100 g of water has a pH of 5 to 9. is there.

A fourth aspect of the present invention is the strontium nitrate according to any one of the first to third aspects, wherein the strontium nitrate has a water content of 0.1% by weight or less.

According to a fifth aspect of the present invention, there is provided the strontium nitrate according to any one of the first to fourth aspects, wherein the purity is 9%.
Strontium nitrate characterized by being at least 9.5% by weight.

The sixth invention comprises a first step of adding at least one selected from the group consisting of nitric acid, sulfuric acid and sulfate to an aqueous solution containing strontium nitrate as a raw material to crystallize a substance containing an impurity compound, A second step of separating and removing a substance containing impurities crystallized in the first step from the solution to obtain a separated liquid; and crystallizing a substance containing strontium nitrate from the separated liquid obtained in the second step. A strontium nitrate production method, comprising: a third step of causing the strontium nitrate-containing substance crystallized in the third step to be separated and recovered from the solution, followed by drying.
In the third step, the temperature of the separated solution obtained in the second step is set to 30 ° C. or higher, and the evaporating water amount with respect to the amount of the strontium nitrate saturated aqueous solution is concentrated at an evaporation rate of 3% by volume / min or less. A method for producing strontium nitrate, wherein precipitated particles having a particle size of 200 μm or more are obtained.

According to a seventh aspect, in the method for producing strontium nitrate according to the sixth aspect, in the first step, the pH of the aqueous solution containing strontium nitrate is adjusted to 7 or more and the solution is heated to reduce NH ₃ . A method for producing strontium nitrate, comprising a process of evaporating.

According to an eighth invention, in the method for producing strontium nitrate according to the seventh invention, the pH adjustment is performed by
A method for producing strontium nitrate, characterized by comprising a step of adding at least one selected from the group consisting of strontium hydroxide and potassium hydroxide to a solution containing strontium nitrate to adjust pH.

According to a ninth aspect, in the method for producing strontium nitrate according to any one of the sixth to eighth aspects, the third step is to adjust the pH of the separated solution obtained in the second step to 7 or more. A method for producing strontium nitrate, characterized by including a process of adjusting and heating to evaporate NH ₃ .

According to a tenth aspect, in the method for producing strontium nitrate according to the ninth aspect, the pH is adjusted by adding a strontium hydroxide and a potassium hydroxide to the separated solution obtained in the second step. A process for producing strontium nitrate, comprising a treatment for adjusting pH by adding at least one selected from the group consisting of:

According to an eleventh aspect, in the method for producing strontium nitrate according to any one of the sixth to tenth aspects, the third step comprises adjusting the pH of the separated solution obtained in the second step to 4 to 10; A method for producing strontium nitrate, characterized by including a treatment for adjusting strontium nitrate.

According to a twelfth aspect, in the method for producing strontium nitrate according to the eleventh aspect, the pH is adjusted by adding strontium carbonate, strontium hydroxide, and potassium hydroxide to the separated solution obtained in the second step. A method for producing strontium nitrate, comprising a treatment for adjusting pH by adding at least one selected from the group consisting of:

According to a thirteenth aspect, in the method for producing strontium nitrate according to any one of the sixth to twelfth aspects, the substance recovered in the fourth step is washed with an organic solvent or a saturated aqueous solution of strontium nitrate. This is a method for producing strontium nitrate, which is a feature.

According to a fourteenth aspect, in the method for producing strontium nitrate according to any one of the sixth to thirteenth aspects, the fourth step includes the step of removing the substance containing strontium nitrate crystallized in the third step by using a solution thereof. Strontium nitrate, comprising a step of drying after separating and recovering the strontium from the strontium to a water content of 0.1% by weight or less.

A fifteenth invention is directed to the method for producing strontium nitrate according to any one of the sixth to fourteenth inventions, wherein the nitric acid is free nitric acid of 0.1 to 5 mol / dm.
^{3. A} method for producing strontium nitrate, which is added so as to be ³ .

According to a sixteenth aspect, in the method for producing strontium nitrate according to any one of the sixth to fifteenth aspects, the addition of the sulfuric acid or the sulfate is performed by setting the temperature of the aqueous solution to 80 ° C. or less, and Ba contained in the aqueous solution
A method for producing strontium nitrate, wherein the amount is 0.5 to 5.0 mol per 1 mol.

[0041]

In the above invention, the Ba content is 0.0
1% by weight or less, Na content 0.005% by weight or less, C
a content 0.01% by weight or less, Cr content 0.00
Strontium nitrate characterized by being less than 1% by weight can be used as an oxidizing agent having low deliquescence and low hygroscopicity and excellent in gas explosion characteristics of airbags and long-term storage properties. Strontium nitrate with less than 0.001% by weight of Cr can be used as an environmentally clean oxidizing agent.

Even when the content of Ba exceeds 0.01% by weight, when obtained as granular strontium nitrate of 0.05% by weight or less, the average particle size is 200 μm.
m or more, preferably 600 μm or less, more preferably 400 μm or less, if the content with a particle size of 44 μm or less is less than 1% by weight, and if the content with a particle size of more than 840 μm is less than 1% by weight, sufficient explosion characteristics will be obtained. It has low deliquescence and low hygroscopicity, is excellent in the explosive characteristics of gas generation of airbags and long-term storage, and can be used as an environmentally clean oxidizing agent. Further, the NH ₃ content is less than 0.0001% by weight, or the pH of an aqueous solution obtained by dissolving 5 g of the strontium nitrate in 100 g of distilled water obtained by removing CO ₂ by boiling (= 5% by weight water) (Dissolution pH) of 5 to 9, it is possible to make the deliquescence, hygroscopicity, reactivity, explosion characteristics, heat stability, and long-term storage more excellent.

Further, when the water content is 0.1% by weight or less, or the purity is 99.5% by weight or more, more preferably 99.8% by weight, deliquescent, hygroscopicity, reactivity , Explosion characteristics, thermal stability, and long-term storage characteristics are extremely excellent.

The purity at this time is measured by the following sulfuric acid method.
A predetermined amount of strontium nitrate is dissolved in water, and a larger amount of sulfuric acid than all strontium nitrate generated as strontium sulfate is added to precipitate a precipitate. The purity at this time is defined as the ratio of the weight of strontium nitrate calculated from the weight of the precipitate to the weight of strontium nitrate initially dissolved, expressed as a percentage, with all precipitated precipitates being strontium sulfate.

The strontium nitrate according to the first to fifth aspects of the present invention is characterized in that a strontium nitrate as a raw material is prepared by adding at least one of nitric acid, sulfuric acid and sulfate to an aqueous solution containing strontium nitrate as a raw material to crystallize a substance containing impurity compounds. A second step of separating and removing a substance containing impurities crystallized in the first step from the solution to obtain a separated liquid; and a substance containing strontium nitrate from the separated liquid obtained in the second step. A third step of crystallizing the strontium nitrate crystallized in the third step is separated and recovered from the solution,
And drying the strontium nitrate.

Here, the addition of nitric acid in the first step is as follows:
Free nitric acid 0.1 to 5 mol / dm ^3, but more preferably to a 0.8~3.5mol / dm ^3, to that this range is less than 0.1 mol / dm ³ the This is because sufficient strontium nitrate crystals containing barium cannot be obtained in the crystallization of No. 1 and barium will be transferred to the next step. Conversely, if it exceeds 5 mol / dm ³ , strontium nitrate of the first crystallization will not be obtained. This is because the yield is greatly reduced.

When sulfuric acid or sulfate is added, it depends on the quality of the raw material, but is preferably 0.5 to 5.0 mol, more preferably 1.5 to 4 mol, per mol of Ba. 0.5
If it is less than 0.5 mol, the remaining 0.5 mol will remain in the aqueous solution as barium nitrate, so that the concentration of Ba as an impurity cannot be made lower than required. On the other hand, when the amount exceeds 5.0 mol, strontium becomes strontium sulfate, which causes a decrease in the yield of strontium nitrate.

For the addition of sulfuric acid or sulfate, potassium sulfate, sodium sulfate, ammonium sulfate and the like can be added. Of these, sulfuric acid and potassium sulfate are preferred because they are difficult to be taken in as impurities in the subsequent steps. Sulfuric acid is preferred.

The temperature of the strontium nitrate solution at the time of the addition is preferably 80 ° C. or lower, more preferably 30 ° C. or lower. Although the solubility of strontium nitrate has little dependence on temperature, the solubility of barium sulfate increases as the temperature increases, so the lower the temperature, the better.

The sulfuric acid or sulfate is preferably added at a rate of 5 mol / min or less per 1 mol of Ba in the aqueous solution. If the addition is faster than this, sulfuric acid and sulfate are not sufficiently diffused into the solution, and the Ba removal rate decreases.

In the third step, the temperature of the separated liquid obtained in the second step is set to 30 ° C. or more, and the amount of evaporating water with respect to the amount of the saturated aqueous strontium nitrate solution is 3 v
By concentrating at an evaporation rate of ol% / min or less, it is possible to obtain a good strontium nitrate having an average particle diameter of 200 μm or more and having suppressed reactivity.

Further, in the first step, the pH of the aqueous solution containing strontium nitrate is adjusted to 7 or more, preferably 8 or more.
By adjusting and heating as described above, NH ₃ is evaporated to obtain strontium nitrate having a small NH ₃ content.

For pH adjustment, any one which can be used as a neutralizing agent can be used. However, strontium hydroxide and potassium hydroxide are preferable because they are hardly taken up as impurities which affect properties in a later step. Strontium oxide is preferred.

The NH ₃ can be evaporated and removed before and after crystallization of the substance containing the impurity compound.
From the viewpoint of the consumption of the regulator, the cost is preferably before crystallization. The heating temperature is preferably 50 ° C.
The above is preferable. In particular, 90 ° C. or higher is preferable.

Similarly, in the third step, the pH of the aqueous solution containing strontium nitrate is adjusted to 7 or more, preferably 8 or more.
By adjusting and heating as described above, NH ₃ is evaporated to obtain strontium nitrate having a small NH ₃ content.

For pH adjustment, strontium hydroxide and potassium hydroxide are preferred because they are less likely to be incorporated as impurities affecting the properties in the subsequent steps, and strontium hydroxide is particularly preferred.

The evaporation and removal of NH ₃ is preferably performed before crystallization of the substance containing strontium nitrate from the viewpoint of removal efficiency.

In the third step, the pH of the separated solution obtained in the second step is adjusted to 4 to 10 so that the pH when strontium nitrate is dissolved in water is adjusted to 5 to 5.
Since the strontium nitrate can be reduced to 9, the deliquescence and hygroscopicity of strontium nitrate can be reduced, and the handling at the time of producing an airbag gas generating agent can be facilitated.

For pH adjustment, strontium carbonate, strontium hydroxide, and potassium hydroxide are preferable because they are hardly taken up as impurities that affect the properties in the subsequent steps, and strontium carbonate and strontium hydroxide are particularly preferable.

The substance (strontium nitrate crystal) obtained in the fourth step is washed with an organic solvent or a saturated aqueous solution of strontium nitrate. The impurities of the strontium nitrate obtained thereby are suppressed and the pH of the strontium nitrate crystal itself is reduced. By adjusting to around the neutral region, it is possible to reduce the hygroscopicity and facilitate handling during manufacture.

As the organic solvent, various organic solvents can be used, but alcoholic solvents such as ethanol and methanol are preferable, and ethanol is particularly preferable.

Further, in the fourth step, the substance containing strontium nitrate crystallized in the third step is separated and recovered from the solution, and the water content is preferably reduced to 3% by weight or less, and the dehydrated strontium nitrate is removed. If the water content of the strontium is dried to 0.1% by weight or less, strontium nitrate which can be used as a clean oxidizing agent having more excellent explosive properties, lower deliquescence and hygroscopicity and excellent long-term storage properties can be obtained. It becomes possible.

[0064]

BEST MODE FOR CARRYING OUT THE INVENTION The present inventors have conducted intensive studies on the following cases, and as a result, have been able to produce strontium nitrate with little impurities of Ba, Na, Ca and Cr, and have found the present invention.

That is, Sr (NO ₃ ) ₂ , Ba (NO
_{3) 2, NaNO 3, Ca} (NO 3) results of examining the solubility ₂ water, the mass / g of anhydrous compound contained in saturated solution 100g converted to the mass / g of anhydrous compound soluble in water 100g At 80 ° C., Sr (NO ₃ ) ₂
97.6 g, Ba (NO ₃ ) ₂ 27.2 g, NaN
148.1 g of O ₃ , Ca (NO ₃ ) ₂ 344.2
g at 25 ° C., 78.9 g of Sr (NO ₃ ) ₂ , Ba
(NO ₃ ) ₂ 10.2 g, NaNO ₃ 91.9 g,
138.0 g of Ca (NO ₃ ) ₂ (Chemical Handbook)
Basic edition, published in 1984).

For example, the impurity of the raw anhydrous strontium nitrate (Sr (NO ₃ ) ₂ ) used in the present invention is Ba
Since it is 0.2% by weight, 0.1% by weight of Na and 0.1% by weight of Ca, when these are converted into nitrates, Ba (N
0.38% by weight of O ₃ ) ₂ , 0.37% by weight of NaNO _{3 and} 0.41% by weight of Ca (NO ₃ ) ₂ , and the remaining 98.8% by weight is Sr (NO ₃ ) _2. .
It is easily presumed that a saturated solution of strontium nitrate can be obtained by adding 100 g of this crude anhydrous strontium nitrate to 100 g of water and heating it to a temperature slightly above 80 ° C. Each impurity contained therein was 0.38 g of Ba (NO ₃ ) ₂ and NaNO
₃ 0.37g, Ca (NO ₃₎ a ₂ 0.41 g, these solubility 80 ° C., which are also estimated that would be dissolved in water.

The saturated solution of strontium nitrate was added to 2
When cooled to 5 ° C, Sr (NO ₃ )
₂ should have deposited 19.9 g. This means that about 20% of the raw material strontium nitrate was deposited.

It is presumed that impurities do not precipitate because the amount of impurities in the solution is lower than the solubility at 25 ° C.

If the contained water is reduced by evaporation, 2
Since it is possible to precipitate strontium nitrate without cooling to 5 ° C., in any case, the precipitated impurities are not included in the precipitation up to about 20% of the raw material strontium nitrate. Pure strontium nitrate should be obtained.

However, when the present inventors conducted a test, the results were completely unexpected. Surprisingly, barium nitrate, which has a lower solubility than strontium nitrate, was present in the deposited strontium nitrate.

Thus, the present inventors have conducted further intensive studies on the possibility of depositing more barium nitrate in the first precipitate, and as a result, have found the present invention.

That is, it has been found that nitrates of Sr and Ba are anhydrous, and the latter can be precipitated by adding fuming nitric acid to a cold aqueous solution (Cotton Wilkinson, Basic Inorganic Chemistry, 1979, p.231). The present invention was found by conducting a quantitative test in combination with the above results.

The present invention is to remove impurities by adjusting the pH to a very low value with nitric acid and separating the first precipitate, which normally would not contain impurities, from the viewpoint of impurity removal in conventional strontium nitrate production. It is a very good method that cannot be predicted at all.

Further, unlike the conventional method, there is no mixing of chromium into strontium nitrate, and there is no need to treat the used chromic acid as a waste liquid.

The raw materials used in the present invention include, but are not particularly limited to, water-soluble strontium compounds such as strontium nitrate and strontium carbonate.

The above water-soluble strontium compound as a raw material is dissolved in water or an acid to prepare a strontium nitrate-containing aqueous solution as a raw material. In consideration of a process for removing impurities, strontium nitrate and strontium carbonate are used as raw materials. Is preferred.

When strontium nitrate is used as the strontium compound, it may be an anhydrate, a tetrahydrate or a mixture thereof.

In this case, the purity of the raw material strontium nitrate is determined assuming that impurities are in Sr (NO ₃ ) ₂ , and that Ba is 0.1 to 1% by weight Na 0.1 to 1% by weight Ca 0.1 to 1% by weight Cr Commercially available products containing about 0.01 to 0.005% by weight are sufficient. But,
Strontium nitrate with Ba, Na, Ca, and Cr contents higher than these, although somewhat less efficient, is not unusable. This is the same for the purity of other strontium compounds.

The acid used for dissolution is sulfuric acid, hydrochloric acid,
Although nitric acid and the like can be used, nitric acid is used as an acid to be added for the purification operation after dissolution, so that the same nitric acid is preferably used for dissolution.

The concentration of strontium nitrate in preparing the aqueous solution containing strontium nitrate is usually 400 to 900 g / dm ³ as Sr (NO ₃ ) ₂ , more preferably 60 g / dm ^3.
0 to 800 g / dm ³ . The above range is 4
If the amount is less than 00 g / dm ³ , the amount of dissolution is small and the production efficiency is poor, which is not preferable. On the other hand, if the amount exceeds 900 g / dm ³ , crystals are deposited on pipes and the like, which hinders operation.

The concentration of free nitric acid in the strontium nitrate-containing aqueous solution after the addition of nitric acid is 0.1 to 5 mol as an excess nitric acid concentration of nitric acid such as strontium.
1 / dm ³ is preferable. In this case, 0.1m
ol / dm ³ , Sr containing Ba in the first step
Ba cannot be removed because no (NO ₃ ) ₂ crystals can be obtained. Conversely, if it exceeds 5 mol / dm ³ , the yield of strontium nitrate decreases, which is not preferable.

The temperature of the solution when preparing the aqueous solution containing strontium nitrate is preferably 30 ° C. or higher. In this case, 30
If the temperature is lower than ℃, the solubility of strontium decreases, and the crystallization of strontium decreases.

Prior to the heating (or reduced pressure) concentration, or by adding nitric acid during the concentration to partially crystallize the precipitate, or immediately after heating (or reduced pressure) to evaporate water and evaporate the crystals. Nitric acid is added for crystallization. Nitric acid may be added at any stage, but the temperature of the solution at the time of cooling after heating is preferably 20 to 60 ° C. Below 20 ° C, the yield of strontium nitrate is reduced,
If it exceeds 300, crystals of strontium nitrate cannot be obtained sufficiently.

The strontium nitrate to be partially deposited is preferably 5 to 50 parts by weight based on 100 parts by weight of strontium nitrate initially contained. The reason is that if the amount is less than 5 parts by weight, Ba cannot be sufficiently removed, which is not preferable. On the contrary, if the amount exceeds 50 parts by weight, the yield decreases.

The addition of sulfuric acid or sulfate is carried out according to the above eleventh,
This is performed under the same conditions as described in the description of the twelfth invention.

In the second step, the precipitation of barium-containing strontium nitrate containing barium thus partially or the precipitation of barium sulfate with strontium sulfate is carried out as follows:
Solid-liquid separation is performed to obtain a filtrate in which strontium nitrate is dissolved.

The solid-liquid separation is performed by filtration separation, gravity filtration, pressure filtration such as a filter press, or a centrifugal separator, but is not limited thereto.

In the third step, the filtrate in which strontium nitrate has been dissolved after solid-liquid separation is heated or decompressed, and concentrated by evaporating water to further crystallize strontium nitrate. In this case, the temperature during the heat concentration is 30 ° C.
The above is preferable, but if the temperature is lower than 30 ° C., tetrahydrate is generated, which is not preferable.

Further, the precipitation of strontium nitrate to be precipitated is preferably 40 to 90 parts by weight based on 100 parts by weight of strontium in the strontium compound initially dissolved. The reason for this is that if it is less than 40 parts by weight,
On the contrary, if the yield exceeds 90 parts by weight, Ca, Na and the like as impurities are undesirably contained. In the third step, the crystallization is carried out slowly over a long period of time, so that the average
Crystals of 0 μm or more, preferably 600 μm or less, more preferably 400 μm or less are deposited. Preferably, the concentration is performed at an evaporation rate of 3 vol% / min or less with respect to the amount of the saturated aqueous strontium nitrate solution. Concentration under reduced pressure may be appropriately performed. The temperature at this time is set to 30 ° C. or higher, preferably 50 to 70 ° C., since a hydrate of strontium nitrate is generated at a temperature lower than 30 ° C. In the following fourth step, the obtained crystals are subjected to solid-liquid separation, dehydration, and drying and then classification (such as JIS200 #, 250 #) if any fine powder is present. This is because if the average particle size is less than 200 μm or the particle size is often 44 μm or less, the hygroscopicity increases and the reactivity increases, which adversely affects the handling properties and explosion characteristics during gas generating agent production. This is not preferred.

In the fourth step, the strontium nitrate thus further precipitated is subjected to solid-liquid separation to obtain strontium nitrate crystals. In this case, the solid-liquid separation is performed by filtration separation, gravity filtration, pressure filtration such as a filter press, centrifugal filtration, or the like, but is not limited thereto. In this case, the time for dehydration by a filter press, a centrifuge or the like is preferably 30 minutes or more, and the mother liquor is sufficiently cut off.
It is preferable to control the water content at that time to be 3% by weight or less.

This is because the mother liquor (filtrate) attached to the surface of strontium nitrate increases the content of impurities,
This is to prevent H from becoming low or high. It is also to prevent the efficiency in the drying step and the aggregation of crystals during the drying.

After the solid-liquid separation, it is preferable to wash with a saturated strontium nitrate solution or an organic solvent such as ethanol in order to sufficiently remove the filtrate adhering to the surface of the strontium nitrate crystal.

The strontium nitrate after dehydration is dried until the water content becomes 0.1% by weight or less. Drying is preferably performed at a drying temperature of 100 ° C. or more, and particularly preferably under reduced pressure. If the obtained strontium nitrate particles have fine particles or coarse particles (large particles), they are removed by classification using a sieve or the like.

[0094] In order to avoid contamination, a material such as Teflon or quartz glass, or a material coated with these materials is used as a material of equipment or a container used in a wet purification step such as dissolution, filtration, or crystallization or a distillation step. It is preferable to select a suitable material.

The purity of the strontium nitrate obtained in this manner is such that the content of impurities is less than 0.0001% by weight of Ba (lower than the detection limit) to 0.01% by weight, and less than 0.0001% by weight of Na (lower than the detection limit). ) To 0.005% by weight, Ca less than 0.0001% by weight (lower than detection limit) to 0.01% by weight, and Cr less than 0.001% by weight (lower than detection limit).

The Ba content obtained in the present invention is 0.01%.
% By weight, Na content is 0.005% by weight or less, Ca
Strontium nitrate having a content of 0.01% by weight or less,
When the mixture was mixed with the main agent of a gas generating agent for an air bag and the burning rate as an explosion characteristic was measured, good explosion characteristics were obtained and stable explosion characteristics were obtained even after an accelerated test of long-term storage.

Further, strontium nitrate having a Ba content of 0.01% by weight or less was suitable as a gas generating agent for airbags which generates little barium oxide.
Similarly, strontium nitrate having a Cr content of less than 0.001% by weight was environmentally good as a gas generating agent for airbags.

The presence of NH ₃ increases the hygroscopicity and becomes unstable, which has an adverse effect on the explosion characteristics and the production of the gas generating agent. To remove NH ₃ , strontium hydroxide (Sr (OH) ₂ ) or potassium hydroxide (aqueous solution containing strontium nitrate in the first step, or the separated solution obtained in the second step in the third step) KOH)
Is added, and the mixture is heated to a pH of 7 to 10, preferably 8 to 9, preferably 50 ° C. or more, particularly preferably 90 ° C. or more, and is preferably maintained for 2 hours or more. As a result, NH ₃ is evaporated and removed.

Even when the content of Ba exceeds 0.01% by weight, the content of NH ₃ is less than 0.0001% by weight, the average particle size is 200 μm or more, and the particle size is 44 μm or less is less than 1% by weight. By satisfying all the conditions that the content exceeding 840 μm in diameter is less than 1% by weight, even when the Ba content is increased to 0.05% by weight, the hygroscopicity is suppressed sufficiently, the stability is enhanced, and the explosion characteristics are sufficiently improved. Can be secured well. In this case, if there are many particles having a particle diameter of 44 μm or less, the explosion characteristics become unstable and the hygroscopicity increases. Conversely, particle size 8
The same result is obtained even when there are many particles that are too coarse exceeding 40 μm.

Hereinafter, a method for producing strontium nitrate according to an embodiment of the present invention will be described with reference to examples. (Example 1) As raw materials, the content of impurities is Ba 0.2% by weight, Na 0.1% by weight, Ca 0.1% by weight, Cr
Strontium nitrate (Sr (N
O3) 2) 5.0 g and 4.5 kg of water were placed in a 15 dm ³ Teflon tank and dissolved and stirred. Then, 2.0 kg of 60% by weight of industrial nitric acid was added, and the mixture was stirred while cooling to 25 ° C. Strontium nitrate containing a large amount of Ba was crystallized as an impurity (first step).

The obtained crystal of strontium nitrate was subjected to solid-liquid separation with a filter press to obtain 0.90 kg of Ba-containing strontium nitrate.
Was separated. Analysis of this crystal revealed that the Ba concentration in the crystal was as high as 1.1% by weight (second step).

Then, the obtained filtrate is boiled at atmospheric pressure,
The solution was concentrated at an evaporation rate of 4 vol% / min, and strontium nitrate was crystallized again (third step). The obtained crystal was solid-liquid separated by a filter press. In this case, washing is performed using ethanol, and the obtained crystals are not re-dissolved, and after washing, dehydrated to a water content of 5.8% by weight, and after dehydration, dried to a water content of 0.2% by weight. Then, 3.0 kg of strontium nitrate crystals were recovered (fourth step).

Chemical analysis of the recovered strontium nitrate showed that Ba was 0.003% by weight and Na was 0.001% by weight.
% By weight, Ca is 0.002% by weight, Cr is less than 0.001% by weight (lower than the detection limit), the average particle size is 170 μm, the particle size is 44 μm or less 5% by weight, and the particle size exceeding 840 μm is 1.5% by weight. %, Purity by the sulfuric acid method was 99.8% by weight. This strontium nitrate was mixed with the main component of a gas generating agent for an air bag as an oxidizing agent for a gas generating agent for an air bag, and when the burning rate as an explosive characteristic was measured, a good explosive characteristic was obtained, It has low hygroscopicity, good thermal stability, and stable explosion characteristics even after an accelerated test of long-term storage.

(Example 2) As a raw material, the content of impurities was B
a 3.5 kg of strontium nitrate (Sr (NO ₃ ) ₂ ) containing 0.5 wt% of Na, 0.1 wt% of Na, 0.2 wt% of Ca, and 0.005 wt% of Cr, and 5.0 kg of water
After dissolving and stirring in a Teflon tank of 5 dm ³ ,
2.2 kg of industrial nitric acid in an amount of 0.2% by weight was added and stirred while cooling to 25 ° C. to crystallize strontium nitrate containing a large amount of Ba as an impurity (first step).

The obtained crystal of strontium nitrate was subjected to solid-liquid separation with a filter press to obtain 0.80 kg of Ba-containing strontium nitrate.
Was separated. Analysis of this crystal revealed that the Ba concentration in the crystal was as high as 2.16% by weight (second step).

Next, the obtained filtrate was boiled at atmospheric pressure, concentrated at an evaporation rate of 4.5 vol% / min, and strontium nitrate was crystallized again (third step). The obtained crystal was solid-liquid separated by a filter press. In this case, washing is performed using a saturated solution of strontium nitrate, and the obtained crystals are not re-dissolved. After washing, dehydration is performed to a water content of 5.9% by weight.
After drying to 2% by weight, crystals of strotium nitrate
kg was recovered (fourth step).

Chemical analysis of the recovered strontium nitrate showed that Ba was 0.009% by weight and Na was 0.001% by weight.
% By weight, Ca is 0.003% by weight, Cr is less than 0.001% by weight (lower than the detection limit), the average particle diameter is 150 μm, the particle diameter is 44 μm or less, 6% by weight, and the particle diameter exceeds 840 μm is 1.5% by weight. %, Purity by the sulfuric acid method was 99.8% by weight. The explosion characteristics of this strontium nitrate were measured in the same manner as in Example 1.
While obtaining good explosive characteristics, deliquescent and moisture absorption are low,
The thermal stability was good, and stable explosion characteristics were obtained even after a long-term storage accelerated test.

Example 3 In the first step, strontium carbonate (0.5% by weight of Ba as an impurity, Na
0.1% by weight, Ca 0.1% by weight, Cr 0.00
5 wt%, NH ₃ 0.01 wt% including) 3.0 kg, water 5.0 kg, dissolved putting 60 wt% nitric acid 4.3kg Teflon vessel of 15dm ^3, further 2 60 wt% nitric acid.
Add 0 kg and stir while cooling to 25 ° C.

In the second step, crystals of strontium nitrate were subjected to solid-liquid separation by a filter press to obtain 1.0 kg of crystals containing Ba. The Ba content was 1.4% by weight.

In the third step, strontium hydroxide was added to the separated solution obtained in the second step, the pH was raised to 5, the temperature was lowered as compared with Example 2, and 0.5 vol.
Concentration is performed at an evaporation rate of% / min to crystallize strontium nitrate.

In the fourth step, the strontium nitrate precipitated in the third step was filtered and dewatered by a centrifuge for 30 minutes to obtain strontium nitrate having a water content of 1.4% by weight. In this case, the washing was performed using a strontium nitrate saturated solution. This was vacuum-dried at 120 ° C. for 10 hours to obtain 2.8 kg of strontium nitrate having a water content of 0.1% by weight. The impurities were as follows. Ba 0.036 wt% Na 0.0003 wt% Ca less than 0.003 wt% Cr 0.001% by weight (below detection limit) NH ₃ 0.001 wt% average particle diameter 240μm particle size 44μm~840μm between (= 99.5% by weight of particles (particle size exceeding 44 μm and particle size of 840 μm or less) 5% by weight in water pH 4.8 Purity by sulfuric acid method 99.9% by weight Good as in Example 1.2 With explosive properties,
Low deliquescent, low moisture absorption, good thermal stability, and stable explosion characteristics even after long-term storage accelerated test. Furthermore, the handling during the production of the gas generating agent was also good.

(Example 4) Strontium nitrate (as impurities 0.4% by weight of Ba, 0.1% by weight of Na,
0.2% by weight, Cr 0.005% by weight, NH ₃ 0.
15 kg of 4.0 kg of water and 4.5 kg of water
After dissolving in a Teflon tank of m ³ , 1.8 kg of 60% by weight nitric acid is further added, and the mixture is stirred and cooled to 25 ° C. for crystallization (first step).

In the second step, strontium nitrate crystals (0.70 kg of Ba-containing crystals, 2.14% by weight of Ba) are removed by solid-liquid separation using a filter press.

Next, strontium carbonate was added to the obtained separated solution, the pH was raised to 5, and the pressure was reduced at 55 ° C. to 0.5 V under reduced pressure.
The strontium nitrate is crystallized by concentrating at an evaporation rate of ol% / min (third step).

In the fourth step, the strontium nitrate precipitated in the third step was filtered and dewatered by a centrifugal dehydrator for 30 minutes to obtain strontium nitrate having a water content of 1.2% by weight. In this case, the washing was performed using a strontium nitrate saturated solution. This was vacuum dried as in Example 3,
2.6k strontium nitrate having a water content of 0.1% by weight
g was obtained. The impurities were as follows. Ba 0.038 wt% Na 0.0005 wt% Ca less than 0.004 wt% Cr 0.001% (below the detection limit) NH ₃ 0.0005 wt% average particle diameter 260μm particle size 99 during 44Myuemu～840myuemu. 8% by weight of particles present 5% by weight of water-soluble pH 4.9 Purity by sulfuric acid method 99.8% by weight Similar to Example 3, good explosion characteristics are obtained, deliquescent and hygroscopicity are low, The stability was good, and stable explosion characteristics were obtained even after a long-term storage accelerated test. Furthermore, the handling during the production of the gas generating agent was also good.

(Example 5) Strontium nitrate (as impurities 0.3% by weight of Ba, 0.1% by weight of Na,
0.2% by weight, Cr 0.005% by weight, NH ₃ 0.
4.0 kg of water and 5.0 kg of water for 15 dm
After dissolving in a Teflon tank of No. ³ and cooling to 25 ° C., 75 g of 25% by weight sulfuric acid was stirred for 30 minutes using a pump.
Add over minutes.

Due to the above reaction, since nitric acid is produced, it is neutralized with potassium hydroxide, the pH is raised to 9.0, the temperature is raised to 90 ° C., and the temperature is maintained for 1 hour (first step). Then, it is filtered by a filter press (second step). Next, the temperature is lowered and the pressure is reduced at 50 ° C. at 0.5 vol% / min.
(The third step). The crystals obtained by concentration are filtered and dehydrated by a centrifugal dehydrator. Dehydration time 3
The strontium nitrate having a water content of 0.9% by weight was obtained for 0 minute or more. In this case, the washing was performed using a strontium nitrate saturated solution. This was vacuum-dried in the same manner as in Example 3 to obtain 3.0 kg of strontium nitrate having a water content of 0.05% by weight (fourth step). The impurities were as follows. Ba 0.035% by weight Na 0.0002% by weight Ca 0.001% by weight Less than 0.001% NH ₃ (below detection limit) Average particle size 280 μm Particles of 100% by weight exist between particle sizes 44 μm to 840 μm 5 Wt.% Water-soluble pH 6.9 Purity by sulfuric acid method 99.8 wt.% In addition to obtaining better explosion characteristics as compared with Examples 1-4, deliquescent and hygroscopicity are low, and thermal stability is better. And stable explosion characteristics were obtained even after a long-term storage accelerated test.
Further, the handling during the production of the gas generating agent was also very good.

Example 6 Strontium carbonate (0.4 wt% Ba, 0.1 wt% Na, Ca
0.3% by weight, including 0.01% by weight of NH ₃ ) 3.
0 kg, 5.0 kg of water, 4.3 kg of 60% by weight nitric acid
Dissolve in 5dm ³ Teflon tank, cool to 25 ° C,
While stirring, 100 g of 25% sulfuric acid was added using a pump.
Add over 5 minutes (first step).

Next, the mixture is neutralized with potassium hydroxide, the pH is raised to 9.5, the temperature is raised to 90 ° C., and the temperature is maintained for 2 hours (first step). Then, it is filtered by a filter press (second step). Then, the temperature is lowered, and the mixture is concentrated under reduced pressure at 60 ° C. at an evaporation rate of 0.5 vol% / min (third step). The obtained crystals are filtered and dehydrated by a centrifuge. Dehydration was performed for 50 minutes to obtain strontium nitrate having a water content of 0.5% by weight. In this case, the washing was performed using a strontium nitrate saturated solution. This was vacuum-dried in the same manner as in Example 3 to obtain 3.0 kg of strontium nitrate crystals having a water content of 0.04% by weight (fourth step). The impurities were as follows. Ba 0.031 wt%, Na 0.0002 wt% Ca 0.005 wt%, Cr of less than 0.001% (below the detection limit) NH ₃ less than 0.0001% by weight (below detection limit) average particle size, 99.9% by weight particles present between 240 μm 44 and 840 μm 5% by weight dissolved in water pH 7.3 Purity by sulfuric acid method 99.8% by weight More explosive properties are obtained compared to Examples 1-5 At the same time, deliquescence, low hygroscopicity, good thermal stability,
Very stable explosion characteristics were obtained even after the long-term storage accelerated test. Furthermore, the handling during the production of the gas generating agent was also good.

In the above embodiment, Ba, C
For measuring the contents of a and Cr, ICP-AEF was used.
For the measurement of Na, the atomic absorption method was used. For the measurement of NH ₃ ,
Distillation was performed by adding NaOH, and distilled water was measured with an ion electrode. Further, as a method for measuring the particle diameter, both the microtrack dry method and the sieve method were used. Further, the measurement of the pH in water dissolution was performed by dissolving 5 g of strontium nitrate in 100 g of distilled water from which carbon dioxide had been removed by boiling.
H was measured. The water content was measured by an infrared moisture meter.

(Comparative Example 1) As a raw material, the content of impurities was B
a To 15 dm ^{3 of} 5.0 kg of strontium nitrate (Sr (NO ₃ ) ₂ ) containing 0.2% by weight of Na, 0.1% by weight of Na, 0.1% by weight of Ca, and 0.005% by weight of Cr and 7.0 kg of water. After dissolving in a Teflon tank and stirring, 6
60 g of industrial nitric acid of 0% by weight was added and stirred while cooling to 25 ° C. to crystallize strontium nitrate containing Ba as an impurity.

The obtained crystal of strontium nitrate was subjected to solid-liquid separation with a filter press, and 20 g of a precipitate containing Ba was separated. When the crystal was analyzed, the Ba concentration in the crystal was as low as 0.4% by weight.

Next, the obtained filtrate was concentrated to crystallize strontium nitrate again, and the obtained crystal was separated into solid and liquid by a filter press. In this case, washing was partially performed using ethanol, and 3.5 kg of crystals of 5% by weight of strontium nitrate having a water dissolution pH of 4 was recovered so as not to redissolve the obtained crystals. When the explosion characteristics of this strontium nitrate were measured in the same manner as in Example 1, it was inferior to Example 1 and no sufficient characteristics were obtained.

Chemical analysis of the recovered strontium nitrate revealed that the content of Ba was 0.19% by weight, which was unsuitable as a raw material of an oxidizing agent for a gas generating agent for an air bag.

(Comparative Example 2) As a raw material, the content of impurities was B
a 5.0 kg of strontium nitrate (Sr (NO ₃ ) ₂ ) containing 0.2% by weight of Na, 0.1% by weight of Na, 0.1% by weight of Ca, and 0.005% by weight of Cr and 7.0 kg of water
After dissolving and stirring at 80 ° C. in a Teflon tank of 5 dm ³ , stirring was performed while cooling to 25 ° C. at a pH of 6 without adding 60 wt% of industrial nitric acid, and B was added as an impurity.
The strontium nitrate containing a was crystallized.

The obtained crystal of strontium nitrate was subjected to solid-liquid separation with a filter press to obtain 0.50 kg of Ba-containing strontium nitrate.
Was separated. When the crystal was analyzed, the Ba concentration in the crystal was as low as 0.4% by weight.

Next, the obtained filtrate was concentrated, strontium nitrate was crystallized again, and the obtained crystal was separated into solid and liquid by a filter press. In this case, the washing was partially performed using ethanol, and 2.7 kg of strotium nitrate crystals were recovered without re-dissolving the obtained crystals. When the explosion characteristics of this strontium nitrate were measured in the same manner as in Example 1, it was inferior to Example 1 and no sufficient characteristics were obtained.

Chemical analysis of the recovered strontium nitrate revealed that the content of Ba was 0.15% by weight, and was not suitable as an oxidizing agent for a gas generating agent for an air bag.

[0129]

As described above, according to the present invention, the contents of Ba, Na, Ca, Cr, NH ₃ , water and the like, which are contained as impurities in industrially produced strontium nitrate, are reduced to a predetermined value or less. In addition, by controlling the particle size to a predetermined range, strontium nitrate which is particularly suitable as an oxidizing agent for a gas generating agent for an airbag or the like is obtained. In addition, an aqueous solution containing strontium nitrate as a raw material,
The crystallization reaction is performed in the presence of free nitric acid in a specific concentration range, and strontium nitrate containing barium nitrate is precipitated, or a precipitate containing barium sulfate is precipitated by adding sulfuric acid or a sulfate in a specific range. The resulting precipitate is subjected to solid-liquid separation and removal, so that the contents of Ba, Na, Ca, and Cr as impurities, NH ₃ and water contents are low, the purity is high, and the particle size is controlled. This makes it possible to produce strontium nitrate suitable as an oxidizing agent for a gas generating agent such as an airbag.

──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Kazunari Suzuki 1-8-2 Marunouchi, Chiyoda-ku, Tokyo Dowa Mining Co., Ltd. Mining Co., Ltd. (56) References JP-A-9-77516 (JP, A) JP-A-2-233520 (JP, A) Patent 171320 (JP, C1) Riedel-de haen catalogue: Laboratory Chemicals (1997) p1063 ZH. PRIKL. KHIM 59 (12) (1986) P2679-2683 (58) Fields investigated (Int. Cl. ⁷ , DB name) C01F 11/36 B60R 21/26 C06B 31/02 C06D 5/00 C09K 3/00 109 CA ( STN)

Claims (16)

(57) [Claims] 1. The method according to claim 1, wherein the Ba content is 0.05% by weight or less,
The content is 0.005% by weight or less, and the Ca content is 0.01
% Strontium nitrate having an average particle diameter of 200 μm or more and a particle diameter of 44 μm or less less than 1% by weight and a particle diameter exceeding 840 μm. Strontium nitrate in an amount of less than 1% by weight. 2. The strontium nitrate according to claim 1, wherein the content of NH ₃ is less than 0.0001% by weight. 3. The strontium nitrate according to claim 1, wherein the pH of an aqueous solution obtained by dissolving 5 g of the strontium nitrate in 100 g of water is 5 to 9. 4. The strontium nitrate according to claim 1, wherein the water content is 0.1% by weight.
Strontium nitrate characterized by the following. 5. The strontium nitrate according to claim 1, wherein the strontium nitrate has a purity of 99.5% by weight or more. 6. A first step of adding at least one selected from the group consisting of nitric acid, sulfuric acid, and sulfate to an aqueous solution containing strontium nitrate as a raw material to crystallize a substance containing an impurity compound, and the first step. A second step of separating and removing a substance containing impurities crystallized in the solution from the solution to obtain a separated liquid; and a third step of crystallizing a substance containing strontium nitrate from the separated liquid obtained in the second step. A fourth step of separating and collecting the substance containing strontium nitrate crystallized in the third step from the solution and collecting and drying the strontium nitrate, wherein the third step includes the second step. The temperature of the separated liquid obtained in the step is set to 30 ° C. or more, and the amount of evaporating water with respect to the amount of the saturated aqueous solution of strontium nitrate is concentrated at an evaporating rate of 3% by volume / min or less, so that the average particle size is reduced. Method for producing strontium nitrate, characterized in that 00μm or more precipitated particles was obtained. 7. The method for producing strontium nitrate according to claim 6, wherein the first step is a step of preparing an aqueous solution containing strontium nitrate.
A method for producing strontium nitrate, comprising a process of adjusting H to 7 or more and heating to evaporate NH ₃ . 8. The method for producing strontium nitrate according to claim 7, wherein the pH is adjusted by adding at least one selected from the group consisting of strontium hydroxide and potassium hydroxide to a solution containing the strontium nitrate. And producing a strontium nitrate. 9. The method for producing strontium nitrate according to any one of claims 6 to 8, wherein the third step comprises adjusting a pH of the separated liquid obtained in the second step.
The method for producing strontium nitrate includes a process of evaporating NH ₃ by adjusting the temperature of the strontium to 7 or more and heating the mixture. 10. The method for producing strontium nitrate according to claim 9, wherein the adjusting of the pH is performed on the separated solution obtained in the second step.
A method for producing strontium nitrate, comprising adding at least one selected from the group consisting of strontium hydroxide and potassium hydroxide to adjust the pH. 11. The method for producing strontium nitrate according to any one of claims 6 to 10, wherein the third step comprises adjusting a pH of the separated liquid obtained in the second step.
A process for adjusting strontium nitrate to 4 to 10. 12. The method for producing strontium nitrate according to claim 11, wherein the pH is adjusted by selecting the separation solution obtained in the second step from a group consisting of strontium carbonate, strontium hydroxide, and potassium hydroxide. A method for producing strontium nitrate, comprising a treatment for adjusting pH by adding at least one kind of strontium nitrate. 13. The method for producing strontium nitrate according to claim 6, wherein the substance recovered in the fourth step is washed with an organic solvent or a saturated aqueous solution of strontium nitrate. Manufacturing method. 14. The method for producing strontium nitrate according to claim 6, wherein in the fourth step, the substance containing strontium nitrate crystallized in the third step is separated and recovered from the solution. After doing
A method for producing strontium nitrate, comprising a treatment of drying the water content to 0.1% by weight or less. 15. The method for producing strontium nitrate according to claim 6, wherein the nitric acid is added such that free nitric acid is 0.1 to 5 mol / dm ^3. For producing strontium nitrate. 16. The method for producing strontium nitrate according to claim 6, wherein the addition of the sulfuric acid or the sulfate reduces the temperature of the aqueous solution to 80.
A method for producing strontium nitrate, characterized in that the temperature is not more than ℃ and the amount of addition is 0.5 to 5.0 mol per 1 mol of Ba contained in the aqueous solution.