JP2655014B2 - Method for producing rare earth-ammonium composite oxalate and obtained composite oxalate - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a process for the preparation of rare earth-ammonium complex oxalates, their use for obtaining rare earth oxides and the products obtained. More particularly, the present invention relates to a method which makes it possible to obtain complex oxalates exhibiting a particular morphology and particle size.

[0002]

BACKGROUND OF THE INVENTION Rare earth oxides have many uses, particularly in the ceramic and electronics fields, but currently in this market,
It has been found that the demand for products with a controlled particle size is increasing.

[0003] One of the conventional methods for obtaining rare earth oxides, which is widely described in the literature, is described in particular by Paul Pascal in "Nouveau Traite de Chi
mieMinerale ", Volume VII (1959), 1007
What is described on the page is obtained by calcining a rare earth oxalate obtained by precipitating a rare earth salt in the form of an aqueous solution with oxalic acid in the range of 500 to 900 ° C. However, in such a production method, only a rare earth element oxide having a coarse particle size is obtained.

According to Japanese Patent Application Laid-Open No. 53-095911 (“Chemical Abstracts”, 90 , 40940w), fine rare earth element oxides, more specifically, fine yttrium oxide are obtained by calcining yttrium ammonium oxalate. It is also known to be prepared by the reaction of an yttrium salt, starting from an aqueous solution of the yttrium salt, in the form of its hydroxide prepared by the reaction of an aqueous solution of the yttrium salt with a basic aqueous solution such as aqueous ammonia. This yttrium is precipitated, then the resulting hydroxide slurry is treated with oxalic acid, and the finally obtained precipitate is separated,
It is washed and calcined at a temperature of 750 ° C.
According to JP-A-53-095911, fine yttrium oxide can be obtained by this method. Its particle size is 0.9-4.5 μm and the crystals are in the form of platelets with rounded edges. However, this particle size is still relatively large when compared to the dimensions required for certain applications such as luminescence. Furthermore, in this method, the conditions of implementation have a great influence on the particle size,
It is relatively difficult to control the particle size.

One object of the present invention is, inter alia, to provide a process for producing rare earth-ammonium complex oxalates having a narrow particle size distribution and having an average crystal size which can be smaller than 1 μm. Is to overcome. Rare earth element-ammonium composite oxalate shall mean a compound that contains one or more rare earth elements and makes it possible to produce a single or mixed oxide after firing.

[0006]

To this end, the present invention provides
A method for producing a rare earth element-ammonium complex oxalate, comprising: adding a second solution containing a rare earth element compound to a first solution containing oxalate ions and ammonium ions; Separating the obtained precipitate, and optionally drying the precipitate.

According to a feature of the present invention, the rare earth compound is advantageously a soluble compound such as a rare earth salt.
Among the salts suitable for the present invention, for example, scandium,
Yttrium, lanthanum, cerium, praseodymium, neodymium, samarium, europium, gadolinium, terbium, dysprosium, holmium, erbium,
Mention may be made of thulium, ytterbium and lutetium chlorides, nitrates, sulphates or acetates or mixtures thereof. In particular, an aqueous solution containing a rare earth element salt can be used, which solution will result directly or indirectly from the treatment of the rare earth ore.

Although the method of the present invention is fully satisfactorily applicable to cerium-based rare earth elements, it is more particularly suitable for yttrium-based rare earth elements. `` Cerium rare earth elements '' are lighter rare earth elements, starting from lanthanum according to atomic numbers and extending to neodymium, and `` yttrium rare earth elements '' are heavier rare earth elements according to atomic numbers, Starting from samarium and ending with lutetium, but containing yttrium.

[0009] The concentration of the rare earth compound is not critical. The second solution is an aqueous solution whose pH can be adjusted to a specific value or a specific range by adding a buffer or an acid as necessary. This second solution generally contains essentially one or more rare earth compounds. Inorganic acids such as nitric acid can be mentioned as acids.

The first solution contains ammonium ions and oxalate ions, which may be in the form of one or more salts containing these two ions, for example ammonium oxalate or ammonium hydrogen oxalate, or ammonium ions. Alternatively, it is introduced by a mixture of a plurality of compounds each providing one of two kinds of oxalate ions. Thus, examples which may be mentioned for the addition of ammonium ions are various ammonium salts such as nitrates, ammonium chloride or ammonia in gaseous or solution form. As regards the oxalate ions, mention may be made of various metal oxalates such as, for example, sodium oxalate, and preferably oxalic acid.

(C ₂ O ₄ ) ^2- and NH _{4 in} this solution
The concentration of ⁺ is not critical and can vary within wide limits.

According to a preferred embodiment, the concentrations of oxalate ion and ammonium ion and the concentration of the rare earth element in the second solution, and the amounts of the first and second solutions are:
When the addition of the second solution is complete, the molar ratio of oxalate ions to rare earth elements (C ₂ O ₄ ) ^2- / RE is greater than 2 and preferably greater than 2.5 and the molar ratio NH of ammonium to rare earth elements is NH ₄ ⁺ / RE is determined to be 2 or more, preferably greater than 2.5. 1 of the present invention
In one embodiment, the first solution is a solution of ammonium oxalate. According to another embodiment of the present invention, the first solution is a solution of ammonium oxalate and oxalic acid. Molar ratio (C
₂ O ₄ ) ^2- / NH ₄ ⁺ is advantageously greater than 2;
Between four. According to another embodiment of the present invention, the first solution is a solution of ammonium oxalate and ammonia, the molar ratio ^{_{(C 2 O 4) 2- /}} NH 4 + must be greater than 0, this case , Preferably between 0.4 and 2.

[0013] The first solution can also contain an inorganic acid (HA) such as, for example, nitric acid. This acid can also be added to the solution of ammonium oxalate,
It can also be liberated in situ by adding oxalic acid to a solution of an ammonium salt such as, for example, ammonium nitrate. When the inorganic acid HA is present in the first solution or the second solution, the amount of the acid HA used is determined so that the molar ratio of the anion A ^{− to} the total oxalate ion of the acid is less than 5. .

The operating conditions of this method are not critical for obtaining complex oxalates. However, by adjusting the rate of introduction of the second solution, the temperature and the stirring of the mixture, the form of the precipitated complex oxalate can be varied and controlled. In addition, the first solution and the second solution
Can be continuously carried out by continuously mixing the solutions of the present invention. In addition, the temperature affects the yield of the precipitate, as the solubility coefficient of the complex oxalate increases with increasing temperature.

The obtained precipitate is subjected to, for example, filtration, centrifugation,
It is separated from the supernatant by any solid-liquid separation method such as decantation. It can also be subjected to one or more washes, for example to remove soluble salts.

The rare earth element-ammonium composite oxalate is
For example, by heat treatment between 50 ° C. and 100 ° C. or by drying under reduced pressure, a drying operation to evaporate free (unbound) water can be performed.

The rare earth element-ammonium complex oxalate obtained by the method of the present invention is composed of particles, and the shape and size of the particles are determined by the type, pH of the solution, temperature conditions, stirring conditions, and introduction when mixing the solutions. Depends on speed. Thus, when the first solution is an ammonium oxalate solution, the resulting product is small in thickness (approximately 0.3 μm thick) and has an average dimension of 0.5 μm to 3 μm, preferably 0.5 μm to 3 μm. It consists of platelet-shaped particles in the range of 1 μm.
When the first solution is a solution of a mixture of oxalic acid and aqueous ammonia or other ammonium compounds other than ammonium oxalate, the average particle size varies between 1 μm and 5 μm. These particles are substantially cubic.

The process of the invention makes it possible to produce rare earth-ammonium complex oxalates having a uniform particle size. Thus, the crystal size distribution is very narrow. The crystal size distribution coefficient of the crystals is generally less than 0.7, preferably between 0.2 and 0.6. The dispersion coefficient is defined as the ratio (φ ₈₄ −φ ₁₆ ) / 2φ ₅₀ (where φ ₈₄ , φ ₁₆ and φ ₅₀ are the 84%, 16% and 50% accumulated from smaller particles. % Means the particle diameter).

One of the uses of these rare earth-ammonium complex oxalates is in the production of rare earth oxides obtained by their thermal decomposition. The morphology and particle size of the rare earth oxide obtained by decomposition of the composite oxalate are generally the same as those of the composite oxalate used as the precursor. However, depending on the conditions of the heat treatment of the composite oxalate, the particle size of the oxide may be slightly different from the particle size of the oxalate. The heat treatment or calcination is generally carried out at a temperature in the range from 600 to 1200C, preferably from 800C to 1000C. The firing time is successfully determined by examining the constant weight. As an index, the firing time is 30
It can vary between minutes and about 6 hours.

[0020]

EXAMPLES Hereinafter, the present invention will be described by way of examples.
These are only given as indices.

Example Series I To a solution of ammonium oxalate at a variable concentration of less than 0.9 M was added a solution of yttrium nitrate at a concentration of 170 g / l, expressed as Y ₂ O ₃ . The various tests performed are summarized in Table 1 below. The particle size and particle size distribution of the resulting product were measured with a Sedigraph 5000D instrument. It measures the sedimentation velocity of suspended particles and determines the particle size distribution as an accumulation as a function of sphere equivalent diameter. This measurement is based on Stokes law.

[0022]

[Table 1]

In the table, [Y] is the total concentration of yttrium in the reaction mixture represented by Y ₂ O ₃ , and D ₅₀ is the rare earth element oxidation obtained by calcining the composite oxalate (at 900 ° C. for 1 hour). average size der of things is, the particle size dispersion coefficient rare earth
This is for the oxides of the same kind . The particles were platelet-shaped with rather irregular contours.

Example Series II The examples in this series use the same second solution of yttrium nitrate as Series I, but with (NH ₄ ) ₂ C ₂ H ₄ and H ₂ C ₂ O
_This was performed using the first solution containing the mixture with ( ₄ ). The ratios and results of the various substances used are summarized in Table 2 below. The concentration of yttrium in the reaction mixture is 17 g / l as Y ₂ O ₃ .

[0025]

[Table 2]

The crystals of the obtained composite oxalate are approximately 0.3
It was in the form of platelets having a thickness of μm and average dimensions of 0.7 and 1 μm. The oxalate and calcined oxide forms are shown in FIGS. 1 and 2, respectively.

[0027]

[0028]

Example III Y ₂ O was added to a solution of 25 g / l ammonium oxalate.
A solution containing 150 g / l of yttrium nitrate and 0.8 mol / l of nitric acid, represented by ₃ , was added. The amount of solution used was determined such that the ratio of ammonium oxalate to the rare earth element salt was 10% greater than the stoichiometric ratio. Separating yttrium ammonium oxalate,
Dried, after firing, yttrium oxide was obtained having a particle size dispersion index of 2μm of D ₅₀ and 0.5 (F).

Example IV Example III was reproduced except that the yttrium nitrate solution contained no nitric acid, while the ammonium oxalate solution contained 0.2 mol / l nitric acid. Yttrium oxide obtained after calcining the oxalate yttrium ammonium had a particle size dispersion index of D ₅₀ and 0.45 of 2.3 .mu.m.

Example V A solution of a soluble rare earth salt at a concentration of 170 g / l as RE ₂ O ₃ containing 148 g / l (Y ₂ O ₃ ) of yttrium nitrate and 22 g / l (La ₂ O ₃ ) of lanthanum nitrate Example I was reproduced except that was used. The precipitated solution contained 25 g / l ammonium oxalate. The amount of the solution used was the molar ratio NH ₄
/ RE was determined to be 4. The resulting precipitate is an ammonium yttrium lanthanum oxalate complex salt. 9
After firing at 00 ° C., a composite lanthanum yttrium oxide containing 12.6% of La ₂ O ₃ was obtained. The properties are shown in the table below.

[0032]

[Table 3]

EXAMPLE VI An ammonium complex oxalate was prepared by continuously mixing a solution of yttrium nitrate at a concentration of 170 g / l, represented by Y ₂ O _3, with a solution of ammonium oxalate at a concentration of 25 g / l. The NH ₄ / Y ratio is 4.7
5, and the final Y ₂ O ₃ concentration was 16 g / l. The precipitate collected after separation and washing was 1.4 μm
And a particle size distribution coefficient F of 0.4.

[Brief description of the drawings]

FIG. 1 is a photograph of the particle structure of oxalate.

FIG. 2 is a photograph of a particle structure of a calcined oxide.

 ──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Bernard Pacote Nanterre, France, Boulevard Nacional, 66 (72) Inventor Michel Ries Vitri, France Sur Sur Seine, Alle des Noyers, 5 (56 References JP-A-4-187516 (JP, A) JP-A-4-187517 (JP, A) JP-A-2-258624 (JP, A) JP-B-61-43285 (JP, B2)

Claims (6)

(57) [Claims] 1. A method comprising: adding a second solution containing a rare earth element compound to a first solution which is an ammonium oxalate solution ; and separating the resulting precipitate; At least one of the solutions contains an inorganic acid (HA); and the amount of the inorganic acid (HA) in the first solution and / or the second solution is such that the ratio of the anion A ^{− to} the oxalate ion is mixed. Rare earth element in the form of platelets having an average size in the range of 0.5 μm to 3 μm and a particle size distribution coefficient of less than 0.7, characterized in the subsequent reaction mixture to be determined to be less than 5 -Method for producing ammonium complex oxalate. 2. The method according to claim 1, wherein the precipitate obtained after the separation step is dried. 3. The method according to claim 1, wherein the molar ratios C ₂ O ₄ ²⁻ / RE and NH ₄ ⁺ / RE when the addition of the second solution is completed are greater than 2. . 4. The molar ratio (C ₂ O ₄ ) ^{2- in} the first solution.
_4. The method according to claim 1, wherein / NH ₄ ⁺ is less than 4 and greater than 0. 5. A rare earth element-ammonium composite oxalate crystallized into platelets having an average size in the range of 0.5 μm to 3 μm and a particle size distribution coefficient smaller than 0.7. 6. When the particle size distribution coefficient is in the range of 0.2 to 0.6.
The rare earth element according to claim 5, wherein
Nummonium composite oxalate.