JPH07330330A - Production of rare earth salt of ammonium oxalate and rare earth oxide - Google Patents

Abstract

PURPOSE:To obtain fine particles of a rare earth salt of ammonium oxalate and easily disintegrable fine particles of a rare earth oxide containing less aggregates, excellent in filtering and washing properties by suppressing a change in shape of the particles during drying and baking processes. CONSTITUTION:This method for producing a rare earth salt of ammonium oxalate is to wash the salt with an aqueous alkaline solution of >=pH 8 or replace the mother liquor therewith. Furthermore, this method for producing a rare earth oxide is to bake the above salt.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to the production of rare earth ammonium oxalate salts and rare earth oxides useful as raw materials for ceramics, phosphors, pigments and the like.

[0002]

2. Description of the Related Art As a method for producing a rare earth ammonium oxalate salt, a method of reacting an ammonium oxalate solution with a solution containing a rare earth element, a method of reacting an oxalate ion, an ammonium ion, a rare earth element salt, a rare earth hydroxide and ammonia , A method of reacting with oxalate ion is known. The precipitate obtained by these methods is filtered, washed with pure water,
After drying, a rare earth oxalic acid ammonium salt is obtained. Moreover, an oxide is obtained by baking this rare earth ammonium oxalate salt. The rare earth ammonium oxalate salt thus obtained is fine and scale-like particles of submicron to several micrometers in the state of precipitation, but the morphology is changed by a heating process such as drying and firing, and a plate of several micrometers is used. Shape or horny independence,
Alternatively, some particles are aggregated.

[0003]

When such particles are used as a sintering aid for ceramics such as silicon nitride and aluminum nitride, the individual particles are solid, and the particles are crushed by a ball mill together with a base material and a binder. Hard to be crushed when mixed. Therefore, there is a demand for rare earth salts and oxides which are excellent in filterability and washability during the production of the rare earth ammonium oxalate salt, and have little particle growth and sintering during drying and firing. The present invention solves such a problem, is excellent in filterability and washability, suppresses the morphological change of particles in the drying step and the firing step, and rare earth ammonium oxalate fine particles and rare earth oxide with less aggregation that is easily crushed. It is intended to provide fine particles.

[0004]

In order to solve the above problems, the present inventor has made extensive studies on the growth mechanism of precipitation, etc.,
The present invention has been completed by discovering a method for producing a new rare earth ammonium oxalate salt and a rare earth oxide and establishing various conditions, and the gist of the invention is to wash the rare earth ammonium oxalate salt with an alkaline aqueous solution or replace the mother liquor with the rare earth ammonium oxalate salt. It is a method for producing a salt, and a method for producing a rare earth oxide by baking a rare earth ammonium oxalate salt washed with an alkaline aqueous solution or replaced with a mother liquor. More specifically, the alkaline aqueous solution has a pH of 8 or more.

The present invention will be described in detail below. In the present invention, the method for producing a rare earth ammonium oxalate salt precipitation is a known method, for example, a method of reacting an ammonium oxalate solution with a solution containing a rare earth element, or a method of reacting a rare earth hydroxide with an oxalate ion (Japanese Patent Publication No. 57- (See No. 35853)
Either method may be used. The rare earth element used may be one kind or a combination of two or more kinds. The precipitate of the rare earth ammonium oxalate salt produced by either method is separated from the mother liquor by a usual method such as filtration, centrifugation, or filter pressing, and then washed or dispersed with an aqueous alkaline solution having a cake volume of 1 to 10 times. . Here, the alkaline aqueous solution is an aqueous solution of an alkali metal hydroxide such as sodium hydroxide or potassium hydroxide, an aqueous solution of organic amines and ammonia, and the pH is preferably 8 or more, and the upper limit is not particularly specified. Ammonia water is preferably used when the use of a rare earth oxalate ammonium salt or a rare earth oxide, which is a product, does not favor alkali metals. The use of an acidic aqueous solution as this cleaning solution is not preferable because the growth of precipitates and keratinization are promoted during cleaning. Further, when an alkaline aqueous solution having a pH of less than 8 or pure water is used, the particle morphology is changed to monodispersed or aggregated angular particles in the drying step and the firing step, which is not preferable. Here, in order to improve the cleaning effect, in addition to removing the crystallization reaction by-product and impurities in the mother liquor, the mother liquor of the filter cake is replaced. That is, there is no problem even if the cleaning is first performed with pure water and finally the mother liquor is replaced with an alkaline aqueous solution.

The rare earth ammonium oxalate salt thus obtained does not undergo a morphological change even after a drying step, and the same fine particles as when crystallized can be obtained. The rare earth ammonium oxalate salt obtained here is used for various purposes as it is, but most of it is used as an oxide. When it is used as an oxide, firing is performed, but in this case, the drying step may be omitted and firing may be performed directly. The firing temperature varies slightly depending on the rare earth element, but it is better to raise the temperature above the temperature at which the rare earth ammonium oxalate salt decomposes to form an oxide, generally from 600 ℃.
It is 1300 ° C, preferably 700 ° C to 1000 ° C. The firing time depends on the amount of rare earth ammonium oxalate salt,
30 minutes to 4 hours is sufficient. The rare earth oxide thus obtained is an agglomerate of amorphous fine particles in which keratinization is suppressed. As described above, according to the present invention, it is possible to obtain a fine particle rare earth ammonium oxalate salt or a fine particle rare earth oxide which is easily disintegrated, while suppressing the morphological change of the particles in the drying and firing steps. In the present invention, the rare earth refers to a lanthanoid element having an atomic number of 57 to 71 and yttrium, and may be one element selected from these elements or a mixed element of two or more elements.

[0007]

EXAMPLES The embodiments of the present invention will be specifically described below with reference to examples, but the present invention is not limited thereto. (Example 1) 68 g of oxalic acid dihydrate was added to a 3 L beaker of pure water 1
It was dissolved in L, and 60 ml of concentrated aqueous ammonia (28%) was added thereto to make an ammonium oxalate aqueous solution. While stirring this solution, add 1 solution of yttrium nitrate aqueous solution ([Y ³⁺ ] = 0.2 mol / L).
L was added to form a precipitate of ammonium oxalate-yttrium double salt. The obtained precipitate was filtered and washed with 500 ml of 0.1 mol / L ammonia water (pH 13). The obtained cake was dried at 80 ° C. for 5 hours with a drier to obtain ammonium oxalate / yttrium double salt. The obtained double salt was observed with an electron microscope and found to be scaly fine particles having the same shape as before drying.

Example 2 A cake obtained in the same manner as in Example 1 was filled in an alumina crucible and baked at 900 ° C. for 1 hour to obtain an oxide. When observed with an electron microscope (see FIG. 1), an aggregate of submicron amorphous fine particles was obtained.

Comparative Example 1 Ammonium oxalate-yttrium double salt was produced in the same manner as in Example 1, the precipitate was filtered, and then washed with 500 ml of pure water. 80 cakes obtained
It was dried in a drier at ℃ for 5 hours to obtain ammonium oxalate-yttrium double salt. Observed with an electron microscope, the particles were horny.

(Comparative Example 2) In the same manner as in Example 1, ammonium oxalate-yttrium double salt was produced, and the precipitate was filtered and washed with 500 ml of pure water. The obtained cake was filled in an alumina crucible and baked at 900 ° C. for 1 hour to give an oxide. Observation with an electron microscope (see FIG. 2) revealed that the particles were angular monodisperse or aggregates of several particles.

[0011]

EFFECTS OF THE INVENTION According to the present invention, it is possible to suppress the morphological change of particles during the drying and firing steps, to obtain a fine-grained rare earth ammonium oxalate salt and a finely divided fine-grained rare earth oxide. Is extremely high.

[Brief description of drawings]

FIG. 1 is an electron micrograph showing the particle morphology of yttrium oxide obtained in Example 2 of the present invention.

2 is an electron micrograph showing the particle morphology of yttrium oxide obtained in Comparative Example 2. FIG.

Claims (3)

[Claims] 1. A process for producing a rare earth ammonium oxalate salt, which comprises washing the rare earth ammonium oxalate salt with an alkaline aqueous solution or replacing the mother liquor with the alkaline solution. 2. The method for producing a rare earth oxalic acid ammonium salt according to claim 1, wherein the pH of the alkaline aqueous solution is 8 or more. 3. A method for producing a rare earth oxide, which comprises baking the rare earth ammonium oxalate salt washed or replaced with the mother liquor with the alkaline aqueous solution according to claim 1 or 2.