JPH0617207B2 - Method for producing high-purity metal fluoride - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a method for producing a high-purity metal fluoride useful as a raw material for a fluoride optical fiber, and more particularly to a metal fluoride containing extremely few transition metal impurities, oxygen and carbon. The present invention relates to a method for producing a compound.

[Prior Art] Iron, copper, nickel, which is mixed in the optical fiber, is a factor that inhibits the ultra-low loss of the fluoride optical fiber.
Transition metals such as cobalt and oxygen are mentioned. In order to obtain a metal fluoride containing less transition metal impurities than in the past, it is generally fluorinated after purification by a solvent extraction method or an ion exchange method, but in order to reduce the oxygen content, a metal fluoride is used. Is dehydrated and baked by introducing hydrogen fluoride gas in an atmosphere of an inert gas such as nitrogen or argon. These metal fluorides are mixed with organic substances derived from raw materials or reagents, solvents, ion exchange resins, etc. in the purification process, but in such an inert atmosphere, desorption of carbon does not sufficiently occur, and the calcined metal is Carbon will be contained in the fluoride. When fiber is formed using carbon-containing metal fluoride,
It is not preferable because it causes scattering.

[Means for Solving the Problems] As a result of intensive studies in view of the present situation, the present inventors have surprisingly found that extremely high-purity metal fluoride can be obtained by treatment in a system in which oxygen is present. The present invention has been reached. That is, the present invention is an alkali metal, an alkaline earth metal, a lanthanide metal, zirconium, hafnium, yttrium, indium, a fluoride of at least one metal selected from aluminum, while flowing a mixed gas of a fluorinating agent and oxygen 300 ~ The method for producing a high-purity metal fluoride is characterized by treating at 700 ° C.

The method for producing the metal fluoride as the raw material of the present invention is not particularly limited, but the present inventors have already proposed JP-A-64-45715.
No. method is preferred. That is, the pH of the aqueous solution of the soluble salt of the metal is maintained at 1.0 to 11, and the weight of the starting compound is 0.0
05% or more of diethyldithiocarbamate (DDTC),
Or ammonium pyrrolidine dithiocarbamate (A
PDC) is added, and the formed precipitate is filtered and removed. Here, as the metal soluble salt of the raw material, a sulfate, a hydroxide, a carbonate, a bicarbonate, a chloride, a nitrate, an acid chloride or the like is used. Al, Li, Na, K as alkaline metals, Ca, Ba, Mg, Be as alkaline earth metals, La, Nb, Gd, Tb, Yb as lanthanide metals, sodium salt as diethyldithiocarbamate. , Potassium salt, ammonium salt and the like are used respectively.

As a chelating agent, as an aqueous solution of the above metal to which DDTC or APDC is added, it is possible to use not only a soluble aqueous solution but also a solution in which an insoluble compound such as an oxide is dissolved with an acid to form a soluble salt and then the pH is adjusted. can do.

The pH range for adding the chelating agent is preferably maintained at 1.0 to 11. If the amount is out of this range, the precipitation of the transition metal will not be sufficiently generated and the purification will be insufficient. The high-purity solution thus obtained is used for fluorination. Examples of the fluorinating agent include hydrofluoric acid, hydrogen fluoride gas, ammonium fluoride, ammonium acid fluoride, fluorine gas, and fluorine halides. , Nitrogen trifluoride and the like.

The soluble salt of the metal in the present invention often forms a fluoride insoluble in water, but after the addition of the soluble fluorinating agent, the liquid is concentrated to precipitate the fluoride. However, it is also possible to add the fluorinating agent in the middle stage of the concentration and simultaneously carry out the reaction and the concentration. Further, once concentrated, a soluble salt is precipitated, separated, dried, and then reacted with a gaseous fluorinating agent to produce a fluoride. The metal fluoride thus obtained may be subjected to another purification method.

In the present invention, the metal fluoride produced in this manner is further processed to extremely reduce oxygen and carbon. First, after sufficiently drying, while flowing a mixed gas of a fluorinating agent and oxygen. Bake in the range of 300-700 ℃.

Examples of the fluorinating agent include hydrogen fluoride, fluorine, nitrogen trifluoride, halogenated fluorine gas and the like, and among these, hydrogen fluoride is most preferable from the viewpoint of easy handling and material. The concentration of the fluorinating agent is preferably in the range of 1 to 50% as the concentration in gas, and if it is less than this range, oxygen cannot be sufficiently removed. Moreover, if it exceeds this range, carbon cannot be sufficiently scattered. The concentration of oxygen is preferably in the range of 1 to 50%, and if it is less than this range, carbon cannot be sufficiently scattered, and if it exceeds this range, the oxygen content increases. The firing temperature is preferably in the range of 300 to 700 ° C. If it is less than this range, deoxidation is not sufficiently performed, and if it exceeds this range, the oxygen content becomes large.

The present invention will be specifically described below with reference to examples.

Example 1 Commercially available reagent 100 g of aluminum chloride hexahydrate was placed in a 2 beaker, 1 of ultrapure water was added to dissolve and adjust pH, 0.5 g of ammonium pyrrolidinedithiocarbamate was added, and the solution was transferred to a separating funnel and chloroform was added. Extracted.
Hydrofluoric acid was added to this purified solution, and the mixture was heated and concentrated to obtain aluminum fluoride trihydrate crystals. The crystals are filtered and dried in a tetrafluoroethylene resin drying oven, and the dried product is placed in a platinum dish and a platinum furnace tube is used to flow high-purity air and hydrogen fluoride gas at 0.5 / min each at 600 ° C. And baked for 2 hours to obtain high-purity aluminum fluoride. The results of this analysis are shown in Table 1.

Example 2 500 g of a commercially available reagent zirconium oxychloride was placed in a 5 beaker, and ultrapure water was added to dissolve it to make a total amount of 5. Filter this solution through a membrane filter (pore size 0.2 μm),
Insoluble impurities were removed. Next, inner diameter 26 mm, length 50
A 0 mm column was packed with a cation exchange resin to a height of 300 mm, and the filtration liquid was passed at 11 ml / cm / min. Aqueous ammonia was added to the ion-exchange purified liquid to form a hydroxide, which was filtered and then hydrofluoric acid was added to the solution and the mixture was heated and concentrated to obtain trihydrate crystals of zirconium fluoride. Place this crystal in a platinum dish and use a platinum core tube to obtain high-purity air 1 / min and hydrofluoric acid gas.
Firing was performed at 500 ° C. for 2 hours while flowing at 0.5 / min to obtain high-purity zirconium fluoride. This analysis result is the first
Shown in the table.

Comparative Examples 1 to 4 The same procedure as in Example 1 was carried out except that the hydrofluoric acid gas was not passed during firing (Comparative Example 1). The same procedure was performed as in Example 1 except that high-purity air was not passed during firing (Comparative Example 2). The same procedure was performed as in Example 2 except that the hydrofluoric acid gas was not passed during firing (Comparative Example 3). The same procedure was performed as in Example 2 except that high-purity air was not passed during firing (Comparative Example 4). The results of these analyzes are shown in Table 1.

[Effects of the Invention] According to the method of the present invention, it is possible to efficiently obtain a high-purity metal fluoride as a raw material for an optical fiber or the like, and particularly to obtain a metal fluoride containing very little oxygen and carbon. .

Claims (1)

[Claims] 1. An alkali metal, an alkaline earth metal, a lanthanide metal, zirconium, hafnium, yttrium,
A method for producing a high-purity metal fluoride, which comprises treating a fluoride of at least one metal selected from indium and aluminum at 300 to 700 ° C. while circulating a mixed gas of a fluorinating agent and oxygen.