JPH0742103B2 - Method for producing alkali metal fluoride - Google Patents

Description

Description: TECHNICAL FIELD OF THE INVENTION The present invention relates to a method for producing an alkali metal fluoride, and more particularly, in the synthesis of an ultra-high purity raw material for a fluoride optical fiber. The present invention relates to a manufacturing method.

[Prior Art of the Invention]

LiF and NaF are one of the constituent raw materials of the fluoride optical fiber. As a factor that inhibits the ultra-low loss of the fluoride optical fiber, transition metals such as chromium, iron, cobalt, nickel, and copper mixed in the optical fiber can be mentioned. Since these transition metals exist as impurities in the constituent raw materials, the production of transition metal-free LiF and NaF is indispensable for reducing the loss of fluoride optical fibers.

As conventional methods for producing high-purity lithium fluoride and sodium fluoride, there are the following items (1), (2), and (3).

(1) Lithium fluoride production by sulfide precipitation method [Chemical Society of Japan, new experimental chemistry course 8, synthesis of inorganic compounds (I
I), Maruzen (1979), p. 459].

LiCl or LiNO ₃ was used as the starting material, NH ₄ F was added to form an aqueous solution, and (NH ₄ ) ₂ S. Is added to remove iron and heavy metals as a sulfide precipitate, and then a lithium salt is obtained. LiF can be produced by using a lithium salt as an aqueous solution and adding an NH ₄ F solution. This manufacturing method is effective when a large amount of impurities are present in the starting material, but when a small amount of impurities are present, a small amount of precipitate is easily formed into a colloid, and even when this method is used, the precipitation recovery rate is close to 100%. It is difficult to get a rate.

(2) Sodium fluoride production by neutralization precipitation method [Chemical Society of Japan, New Experimental Chemistry Course 8, Synthesis of inorganic compounds (I
I), Maruzen (1979), p. 466].

Using NaHCO ₃ and NA ₂ CO ₃ as starting materials, these are added to hydrofluoric acid as they are in a solid state to be neutralized to form a precipitate, which is dehydrated and dehydrofluorinated and dried to produce NaF. This production method leaves impurities in the aqueous solution, but since transition metal impurities co-precipitate with sodium as fluoride precipitate, it is difficult to remove the transition metal impurities even by using this method.

(3) Lithium fluoride production by vacuum distillation method [AJSi
ngh, Journal of Applied Physics, 36 (1965), 136
Page 7].

Perform vacuum distillation of LiF under reduced pressure and use Na, Ca, M
It is described that it is effective for removing impurities such as g and Mn, and there is no description about other transition metals. But Li
Since the vapor pressure curves of F and Cr, Fe, Co, Ni, and Cu fluorides are close to each other, it is difficult to remove these transition metals.

As described above, it has been difficult to obtain ultrahigh-purity lithium fluoride and sodium fluoride by the methods of sulfide precipitation, neutralization precipitation, and distillation.

[Object of the Invention]

The object of the present invention is to solve the above-mentioned drawbacks by solvent extraction of chromium, iron, cobalt, nickel, copper contained in the water-soluble salts of starting materials lithium and sodium by the use of individual organic reagents, It is an object of the present invention to provide a method for producing alkali metal fluorides such as lithium fluoride and sodium fluoride of ultra-high purity by precipitation.

[Structure of Invention]

In order to solve the problems of the conventional sulfide precipitation method, neutralization precipitation method, and vacuum distillation method, the present invention uses a water-soluble salt of an alkali metal such as lithium and sodium to prepare an aqueous solution and then dissolve For each element of chromium, iron, cobalt, nickel, and copper present in, the organic reagent forming the most stable complex, the solvent, and the extraction pH range were respectively determined, and the transition metal was extracted and removed in the solvent and remained. The most important thing is to produce a fluoride precipitate by adding a fluoride precipitation agent to an aqueous solution, and dehydrate and dehydrofluoride dry this to produce ultra-high-purity alkali metal fluorides such as lithium fluoride and sodium fluoride. It is a characteristic.

Compared with the conventional sulfide precipitation method, in which heavy metal impurities including transition metals are converted into sulfide by a single precipitation operation, it is more suitable for individual elements such as chromium, iron, cobalt, nickel and copper. The difference is that the extraction organic reagents are individually selected and determined, and impurities are extracted and excluded. It differs from the neutralization precipitation method in that the impurities in the aqueous solution are extracted and eliminated from the aqueous phase into the organic phase, as compared with the impurities remaining in the aqueous solution. It differs from the vacuum distillation method, which utilizes the difference in vapor pressure of elements, in that it uses a liquid-liquid reaction in solution.

[Specific Description of the Invention]

 The present invention will be described in more detail.

According to the present invention, first, an aqueous alkaline water-soluble salt solution is prepared, and transition metals such as chromium, iron, cobalt, nickel, and copper contained as impurities in the aqueous alkaline water-soluble salt solution are extracted and removed with an organic reagent.

Examples of such an alkali water-soluble salt include a water-soluble salt of Li or Na. For example, LiCl,
One or more Li water-soluble salts such as LiNO ₃ , or Na ₂ CO ₃ , NaH
One or more of Na water-soluble salts such as CO ₃ , NaCl, NaNO ₃ , and NaOH may be mentioned.

Examples of the transition metal removed by extraction from the aqueous alkaline water-soluble salt solution include chromium, iron, cobalt, nickel, and copper, as described above.
Such transition metals can be extracted using suitable conditions and suitable organic reagents. In this extraction, for example, an organic reagent or conditions for forming a stable complex is used for each transition metal or transition metal group, and each transition metal or transition metal group is extracted and removed by a plurality of extraction steps. Is good.

For example, using the diazone-carbon tetrachloride extraction system, the pH
Under the conditions of 1 to 5, Cu and Cr are extracted and removed, and similarly, under the conditions of pH 1 to 5, Fe and Cu are extracted in the cuperon-chloroform extraction system. Furthermore, in a dimethylglyoxime-ethanol extraction system under the conditions of pH 9-10,
Ni and Co can be extracted. It is clear that the order of removing the transition metals in the above-described three-step extraction system is not limited and can be performed in any order.

After removing the transition metal from the aqueous solution of the alkali-soluble salt in this manner, the alkali metal contained in the aqueous solution of the water-soluble salt is fluorinated.

The fluorinating agent for fluorinating the alkali metal is not basically limited in the present invention. For example,
Hydrofluoric acid and hydrogen fluoride can be used.

When the alkali metal is fluorinated in this way, lithium or sodium precipitates as a hydrogen salt.

In the present invention, this precipitate is preferably left to stand for one day or more to be aged.

From the precipitate thus produced, dehydration, dehydrofluorination,
Drying is performed to obtain a high-purity alkali metal fluoride.

That is, after discarding the supernatant of the aqueous solution that produced the precipitate, the precipitate is preferably washed in a clean atmosphere at 400 to 800 ° C.
Then, it is dehydrated, dehydrofluorinated and dried. In this dehydration, dehydrofluorination, and drying process, if the temperature is less than 400 ° C, dehydration and dehydrofluorination may not proceed completely, while if it exceeds 800 ° C, lithium fluoride or sodium fluoride will melt. This is because it was revealed by differential thermal analysis.

Examples of the present invention will be described below.

Example 1 A method for producing LiF using LiCl as a starting material will be described below.

FIG. 1 is a diagram for explaining a first embodiment of the present invention,
After weighing 100 g of Licl in a beaker, make an aqueous solution and adjust pH to 1 to 5. Add to this 50 mg dithizone 2 ml of a solution of carbon tetrachloride in 100 ml of carbon tetrachloride
After adding together with 20 ml, the whole solution is transferred to a separating funnel and shaken for 5 minutes on a shaker. After shaking, let stand for 5 minutes and discard the organic phase 1. Again, add the same amount of dithizone and carbon tetrachloride as above, shake under the same conditions, and add organic phase 1
Throw away. Next, 0.42g cuperon 2 ml of 100 ml of distilled water dissolved in 20 ml of chloroform
Put in water phase 1 and shake for 5 minutes. After completion of shaking, leave still for 5 minutes and discard the organic phase 2. Once again, extraction with chloroform and chloroform was performed under the same conditions, and the organic phase 2
Throw away. High-purity ammonia water is added to aqueous phase 2 to adjust the pH to 9-
Set to 10. Add 0.16 g of dimethylglyoxime 2 ml of 100 ml of ethanol was added, 20 ml of chloroform was added, and the mixture was shaken for 5 minutes. After shaking, let stand for 5 minutes and discard the organic phase 3. The above-mentioned extraction with dimethylglyoxime and chloroform is performed again under the same conditions, and then the organic phase 3 is discarded. 200 ml of high-purity hydrofluoric acid (containing 49% hydrogen fluoride) is added to the aqueous phase 3 to form a precipitate. The precipitate is left to stand for one day or more and aged. After discarding the supernatant liquid in the container containing the precipitate, 400 to 500 in a clean atmosphere.
Lithium fluoride (LiF) is obtained by dehydration, dehydrofluorination and drying at ℃.

Lithium fluoride can also be obtained when lithium nitrate is used as a starting material and the same operation as above is performed.

Fluoride precipitation can also be obtained by introducing high-purity hydrogen fluoride gas into the aqueous phase 3 in FIG. Further, the extraction procedure is not limited to this embodiment.

Table 1 shows analytical values of neutron activation analysis of chromium, iron, cobalt, nickel and copper in lithium fluoride produced by the production method of the present invention. Cobalt 0.02ppb as analytical value,
Chromium 1.0ppb, Copper 1.0ppb, Nickel less than 1.0ppb, Iron 10pp
Values less than b were obtained. Ultrahigh-purity lithium fluoride with an impurity concentration of less than 1.0 ppb can be produced for each of the four elements except iron, which is more than an order of magnitude higher than the commercially available high-purity lithium fluoride produced by the conventional technique shown in Table 1. There was an improvement. As a detection limit for neutron activation analysis, cobalt 0.01
ppb, chromium and copper 0.1ppb, nickel 1ppb, iron 10ppb were obtained.

Example 2 A method for producing sodium fluoride (NaF) using sodium carbonate (Na ₂ CO ₃ ) as a starting material will be described. Weigh 100 g of sodium carbonate (Na ₂ CO ₃ ), make an aqueous solution, and add concentrated nitric acid.
After adjusting the pH to 1 to 5, a precipitate is formed according to the procedure shown in FIG. The precipitate is sodium hydrogen fluoride (NaHF ₂ ), which is heated at 400-500 ° C in an electric furnace with an inert gas inflow atmosphere.
Sodium fluoride (NaF) was obtained by dehydration and dehydrofluorination within the range. Table 2 shows chromium and iron in sodium fluoride produced by the production method of the present invention and the prior art, respectively.
The analytical values of cobalt, nickel and copper are shown. As is clear from the analysis values in Table 2, there is an improvement in purification of one digit or more as compared with the prior art, and the production of ultra-high-purity sodium fluoride can be carried out by the present invention. Sodium fluoride can also be obtained by using sodium hydrogen carbonate, sodium chloride, sodium nitrate, or sodium hydroxide as a starting material and performing the same operation as described above. Fluoride precipitation can also be obtained by introducing high-purity hydrogen fluoride gas into the aqueous phase 3 in FIG.

In addition, in the dehydration and dehydrofluorination drying steps of fluoride precipitation, dehydration and dehydrofluorination do not proceed completely at 400 ° C or lower, and lithium fluoride and sodium fluoride melt at 800 ° C or higher. Confirmed by thermal analysis. Therefore, in the dehydration and dehydrofluorination drying steps of the fluoride precipitate, the optimum temperature range is 400 to 800 ° C.

(Effects of the Invention) As described above, according to the production method of the present invention, transition metal impurities are extracted and removed according to each component and produced by precipitation from the aqueous phase. As shown in Table 2, there is an advantage that the transition metal concentration can be made extremely low. Furthermore, there is an advantage that an ultra-low loss optical fiber can be manufactured by using this as a starting material for a fluoride optical fiber.

[Brief description of drawings]

FIG. 1 shows a method for producing ultra-high purity alkali metal fluoride.

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Claims (5)

[Claims] 1. A step of extracting and removing a transition metal mixed in an aqueous solution of an alkali water-soluble salt with an organic reagent, a step of fluorinating and precipitating an alkali metal in the aqueous solution as a hydrogen salt, and a dehydration dehydrofluorination drying step. A method for producing an alkali metal fluoride, comprising: 2. The water-soluble salt of the starting material is one or more of LiCl and LiNO ₃ , or one or more of Na ₂ CO ₃ , NaHCO ₃ , NaCl, NaNO ₃ and NaOH. The method for producing an alkali metal fluoride according to item 1. 3. The extraction step comprises dithizone-carbon tetrachloride and cuperone-chloroform adjusted to pH = 1 to 5 and pH = 9.
The method for producing an alkali metal fluoride according to claim 1 or 2, which is a step in which a dimethylglyoxime-chloroform extraction system adjusted to 10 is combined. 4. A hydrofluoric acid or hydrogen fluoride gas is used as a precipitant for fluorinating an alkali metal to precipitate it as a hydrogen salt, and the precipitate is aged by standing for one day or more after the precipitation is formed. The method for producing an alkali metal fluoride according to any one of claims 1 to 3, wherein: 5. The dehydration dehydrofluorination drying step is performed at a temperature of 400 to 8
The method for producing an alkali metal fluoride according to any one of claims 1 to 4, which comprises drying in a clean and inert atmosphere at 00 ° C.