JPS632893B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for producing rare earth compounds. More specifically, the present invention relates to a method for producing a rare earth compound with an extremely low content of lead compounds.

Rare earth elements are increasingly being used in electronics and other fields, but in the case of electronics materials, they are particularly required to be free of impurities.

Separation and purification of rare earth compounds is usually carried out by methods such as liquid-liquid extraction and ion exchange extraction. For example, in the separation of yttrium using a thiocyanate quaternary ammonium salt extraction solvent, lead is The extraction behavior is similar to that of
It is difficult to obtain rare earth compounds with low lead content because separation is difficult, and lead compounds contained in acids such as nitric acid, hydrochloric acid, and sulfuric acid used during extraction operations may be mixed in. It was difficult.

A known method for removing lead compounds from an aqueous solution is to use hydrogen sulfide, sodium sulfide, etc. to generate lead sulfide from the lead in the aqueous solution. Lead cannot be reduced to less than about 1 ppm.

Even if this method is applied to an aqueous solution of a rare earth compound, the rare earth compound is usually treated as an aqueous solution with a concentration of about 0.1 to 1.0 mol/kg, and even if the amount of lead in the aqueous solution is 1 ppm, Lead is concentrated in the rare earth elements obtained.
The content is about 9 ppm or more, which is not satisfactory as a rare earth element for the above-mentioned purpose.

The inventors of the present invention have conducted extensive research to produce rare earth compounds with a low lead content. As a result, the inventors have found that by subjecting an aqueous solution of a rare earth compound to a specific treatment in the presence of sulfide, lead can be reduced. The present invention was completed based on the knowledge that the compound can be almost completely removed.

That is, the purpose of the present invention is to industrially advantageously produce a rare earth compound with a small content of lead compounds, and this purpose is to add a rare earth compound containing a lead compound as an impurity to an aqueous solution of a rare earth compound containing a lead compound as an impurity. In the presence of hydrogen sulfide, ammonium sulfide, or metal sulfide, at pH 2 to 7, oxalic acid or its ammonium salt is added to precipitate a portion of the rare earth compound as the oxalate of the rare earth element, and the generated precipitate is separated. This is achieved by removing.

The present invention will be explained in detail below.

The rare earth compound referred to in the present invention has an atomic number of 57.
It refers to compounds of a group of elements including ~71 elements, yttrium, and scandium.

The aqueous solution of a rare earth compound containing a lead compound as an impurity targeted by the present invention (hereinafter referred to as a lead-containing rare earth aqueous solution) is an aqueous solution of an acid salt such as a nitrate, chloride, or sulfate of a rare earth element, It contains lead compounds as impurities. The concentration of the rare earth compound is preferably selected from about 0.01 to 1.5 mol, preferably from 0.1 to 1.0 mol.

Hydrogen sulfide, ammonium sulfide, or metal sulfides (hereinafter simply referred to as sulfides) include hydrogen sulfide, ammonium sulfide, alkali metal sulfides such as sodium sulfide, potassium sulfide, yttrium sulfide, samarium sulfide, and cerium sulfide. Examples include sulfides of rare earth elements, such as sulfides of various metals other than lead, but if it is inconvenient that different metals are mixed into rare earth compounds, hydrogen sulfide, ammonium sulfide, and sulfides of alkali metals are used. Alternatively, it is better to use sulfides of rare earth elements.

After the treatment of the present invention, the alkali metal can be separated from the rare earth element, for example, by employing a method of obtaining the rare earth element as an oxalate from the rare earth compound. Furthermore, when using a sulfide of a rare earth element, mixing of different metals can be avoided by using the same type of element as the rare earth element in the lead-containing rare earth aqueous solution.

In order to make the above sulfides exist, it is sufficient to simply mix the lead-containing rare earth aqueous solution and the sulfide, but in the case of a lead-containing rare earth aqueous solution with a high lead content, it is necessary to mix excess sulfide and solidify it. It is also possible to use a product in which lead sulfide is generated and separated and removed.

The amount of sulfide to be present is preferably about 5 to 200 times, preferably about 30 to 150 times, the amount of lead in the lead-containing rare earth aqueous solution. If the amount is too small, the effects of the present invention cannot be expected. On the other hand, there is no particular problem in using too much, but no particular effect can be expected from using too much.

The pH of the lead-containing rare earth aqueous solution used in the treatment of the present invention must be between 2 and 7, preferably between about 5 and 6.5. If the pH is lower than 2, the effect of the present invention will be small and will be impractical. On the other hand, if the pH is higher than 7,
This is not preferable because the rare earth compound becomes a hydroxide and precipitates, resulting in a large loss of the rare earth compound.

To adjust the pH of the lead-containing rare earth aqueous solution, ammonia, sodium hydroxide, potassium hydroxide, etc. can be used.

In the present invention, some rare earth compounds in the lead-containing rare earth aqueous solution are precipitated as oxalates by adding oxalic acid or its ammonium salt to the lead-containing rare earth aqueous solution at pH 2 to 7 in the presence of sulfide. let When this is done, the lead compounds in the lead-containing rare earth aqueous solution are also precipitated.

Oxalic acid or its ammonium salt may be added as a solid or as an aqueous solution. The ammonium salt of oxalic acid may be either ammonium oxalate or ammonium hydrogen oxalate.

The amount of oxalic acid or its ammonium salt to be used is based on the rare earth compound in the lead-containing rare earth aqueous solution.
It is preferable to use 0.05 to 0.7 times the mole, preferably 0.1 to 0.3 times the mole. If it is too small, it will be difficult to obtain the effects of the present invention. On the contrary, although it is preferable to remove lead compounds, it is not a good idea to increase the amount of rare earth elements, which become oxalate and precipitate together with the lead compounds.

Although a temperature other than room temperature can be adopted as the temperature for producing the above-mentioned precipitate, a temperature around room temperature is usually sufficient.

After the precipitate is formed, an aqueous solution of a rare earth compound with an extremely low content of lead compounds can be obtained by separating the precipitate by filtration or other means. A rare earth compound with a lead content of about 2 ppm or less can be obtained by adding an acid to precipitate the rare earth element as an oxalate, or adding ammonia to precipitate the rare earth element as a hydroxide. .

The present invention can be applied at any stage of purification of crude rare earth compounds, but considering the contamination of lead compounds from acids used during operations such as extraction, the present invention can be applied to the final stage of purification. That is, it is preferable to apply it immediately before obtaining the rare earth compound product from the aqueous solution of the rare earth compound.

Further, the rare earth element oxalate containing precipitated lead may be used in applications where the lead content is not a problem, and may also be used as a raw material in the present invention.

The method of the present invention has great industrial value because rare earth compounds with extremely low lead compound content can be produced with easy operations.

EXAMPLES The present invention will be specifically explained below with reference to examples, but the present invention is not limited to the following examples unless it exceeds the gist thereof.

In addition, the content of lead in the examples is a value analyzed by atomic absorption spectrometry.

Example 1 To 155 ml of a 0.4 mol/aqueous solution of yttrium nitrate [Y(NO ₃ ) ₃ ] containing 33 ppm lead per Y ₂ O ₃ ,
2 ml of 0.5% sodium sulfide aqueous solution was added, and the pH was adjusted to 6.5 using aqueous ammonia. No solid precipitation was observed at this stage.

Add 2.36 g of solid oxalic acid to this solution and
After stirring for a period of time to form a precipitate, the precipitate was separated using 5C paper (manufactured by Toyo Paper Co., Ltd.). Add nitric acid to the obtained yttrium nitrate aqueous solution to adjust the pH.
After adjusting the concentration to 0.4, 170 ml of a 7% aqueous oxalic acid solution was added to precipitate yttrium as an oxalate salt.

The amount of yttrium oxide obtained by calcining this yttrium oxalate was 5.95 g (yield: 85.2%), and the lead content was 2.7 ppm.

The amount of yttrium oxide obtained by calcining the precipitate was 1.03 g (loss 14.8%), and the lead content was
It was 200ppm.

Example 2 Weight percent of oxides: yttrium 25.3%, erbium 6.6%, holmium 1.5%, dysprosium
18.7%, gadolinium 20.3%, samarium 27.6%
A mixed rare earth having the composition and containing 35 ppm of Pb per rare earth oxide was dissolved in nitric acid to prepare a 0.4 mol/aqueous rare earth nitrate solution.

Using 155 ml of this aqueous solution, the same operation as in the example was carried out under the same conditions as in the example, and as a result, 8.68 g of mixed rare earth oxide having a Pb content of 2.3 ppm per oxide was obtained (yield: 88.6%).

The precipitate was calcined to obtain 1.12 g of mixed rare earth oxide having a Pb content of 220 ppm. (Loss 11.4%)

Claims (1)

[Claims] 1. Oxalic acid or its ammonium salt is added to an aqueous solution of a rare earth compound containing a lead compound as an impurity in the presence of hydrogen sulfide, ammonium sulfide, or metal sulfide at a pH of 2 to 7 to convert a portion of the rare earth compound into a rare earth compound. A method for purifying a rare earth compound, which comprises precipitating the element as an oxalate and separating and removing the generated precipitate.