CS252287B1 - A method for preparing rare earth carbonates - Google Patents

Abstract

The purpose of the solution was to find a method for preparing rare earth carbonates that would guarantee a homogeneous product. This goal is achieved by introducing gaseous ammonia into an aqueous solution of rare earth salts until a pH of 3.5 to 8.5 is reached. After this pH adjustment, in addition to gaseous ammonia, a stoichiometric or superstoichiometric amount of carbon dioxide is also introduced into the reaction mixture. The completion of the precipitation reaction can be recognized, for example, by a sharp increase in pH. Rare earth carbonates serve as an intermediate in the production of catalysts or polishing powders.

Description

The invention relates to a process for the preparation of rare earth carbonates

Rare earth carbonates are an important intermediate in the preparation of other rare earth compounds, especially oxides · Oxides are widely used in various industries · pure oxides are mainly used in electrical engineering, nuclear power and as catalysts in the chemical industry · Oxide mixtures of these elements Cerium dioxide over 50% by weight · Used as polishing powders in the optical and glass industries ·

Rare earth carbonates are prepared on a laboratory scale by precipitation with an alkali metal carbonate solution, by treatment with carbon dioxide on rare earth oxides or hydroxides, or by homogeneous hydrolysis of trichloroacetates or chlorides in the presence of urea.

The disadvantage of the latter two methods is the relatively complicated execution of the process. · The conversion of hydroxides or oxides to carbonates is quite slow.

252,287 hours, but it is usually stated that more than 8 days are required for complete conversion · The process of homogeneous hydrolysis of trichloroacetates or chlorides proceeds at a sufficient rate only at a higher temperature · A disadvantage is also the use of relatively expensive chemicals. For these reasons, these processes have no chance of industrial use.

Precipitation of rare earth carbonates with sodium carbonate solution has been used on an industrial scale in the production of polishing powders · The disadvantage of this process is that the final product may be contaminated with sodium salts, which significantly deteriorates the quality of polishing powders in addition, there is a risk of local supersaturation associated with an increase in pH when precipitating the carbonates of the soil-containing elements with a solution of any carbonate. In doing so, low-soluble rare earth hydroxides may precipitate, resulting in a deterioration in the quality and homogeneity of the products.

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The process for preparing the rare earth carbonates of the present invention appears to be more advantageous in that the pH of the aqueous rare earth salt solution is adjusted as necessary by introducing ammonia gas, preferably mixed with air, to a pH of 3 to 5 to 8.5. »Stoichiometric or above-stoichiometric amount of carbon dioxide is then introduced into the reaction mixture in addition to the ammonia gas, up to the end of the precipitation reaction, as indicated, for example, by a rapid increase in pH ·

The process of the invention avoids contamination of the product with other elements, ensures physical homogeneity of the product and places it

252 287 Minimum requirements for the chemicals and equipment used · When a nitrate solution is used for precipitation, the ammonium nitrate solution, which can be used, for example, for the production of fertilizers, is omitted in the practice of the invention. The process according to the invention can be classified as waste-free technology.

Since all the rare-earth elements have very similar properties, the process according to the invention is applicable to the precipitation of any of them and to the precipitation of their mixtures. · The elements must be present in solution in oxidation stage III. forms stable compounds in oxidation stages III and IV, need to be reduced, eg with hydrogen peroxide in acidic environment · Other rare earth elements in solution occur exclusively in oxidation stage III · The precipitation process can be expressed, for example, for a nitrate solution by a stoichiometric summary *

Ln (NO0) ₃ ♦ 5 C0 ₂ Φ 6 NHj ♦ 5 HgO - ^ Ln ^ CO ^ + 6

In this case, Ln denotes elements with atomic number 27 (Ia) together with yttrium and scandium.

The rare earth element solution is prepared by any of the known methods, ie · dissolving salts in water, decomposing oxides or hydroxides by acids, etc. · adjust the pH of the solution to 2 * 5 to 8.5, if necessary, with ammonia gas. · The upper limit is given by the beginning of the area where rare earth hydroxides start to precipitate and this value depends mainly on the type of precipitated cation, concentration and temperature

252 287 solution * Gaseous carbon dioxide begins to be introduced with ammonia when the required pH value is reached · The actual precipitation reaction can also be carried out at normal temperature, but lowering the temperature results in more efficient carbon dioxide absorption · Ammonia absorption is quantitative carbon dioxide does not · Except for temperature, it depends on the pH of the reaction mixture · Therefore it is necessary to choose a higher rate of carbon dioxide introduction than Stoichiometry · It was found that at a sufficiently large flow of carbon dioxide the precipitation rate is given by ammonia introduction rate · mixtures practically unchanged during precipitation · The end of precipitation results in a sharp increase in pH. At a constant gas introduction rate, the time course of the pH deflection is close to the shape of the precipitation titration curve *

Appropriate choice of precipitation conditions, ie · temperature, pH, precipitation rate, clot aging time, concentrations can be prepared by carbonates in various forms * Precipitation conditions can also be adjusted by diluting the feed gases with air ·

The process according to the invention guarantees the preparation of a perfectly homogeneous product, which favorably influences the reproducibility of the process and the physical properties of the product. The process can be used in the preparation of polishing powders or catalysts based on IdigOj or CeOg

Example 1

X ..

A solution prepared by decomposing the rare earth hydroxide hydroxide concentrate with nitric acid in the presence of hydrogen peroxide was used for precipitation.

252 287 rare earths in solution were 0.3 mol / l, the proportion of individual lanthanides calculated on the sum of oxides was CeOg 83.4 LagOj 7.6%, NdgOj%, ^ 6θ11%, other Ln ^ O ^ 1.5? Β ·

^{Ν Ν07} content was 15.28 g / 1, pH of the solution was 0.1.

At 24 ° C, ammonia gas was introduced into one liter of this solution with stirring at a rate of 12.4 g BH 2 / h · Ammonia was diluted with air - air flow was 40 L / h · After reaching pH 4, the reaction mixture was introduced · Carbon dioxide gas at a rate of 142 l / h · A constant flow of all gases has been maintained since the introduction of carbon dioxide · After 10 minutes the pH of the reaction mixture has stabilized at -5 · 60 minutes after the start of CO 2 introduction. pH reached 5.95 precipitation ended · The precipitate was filtered off and dried at 100 ° C · Yield 65.55 8 rare earth carbonates · No rare earth elements were found in the filtrate ·

Example 2

A solution of the same composition as in Example 1 was diluted in half, ie · to a concentration of 0.15 mol Ln / 1 * pH of the solution was 0.5 · 2 liters of this solution were used for precipitation. * CO ₂ 355 g, NH 3 19.5 g. Carbonate yield was 66.38 g. Rare earth elements were not found in the filtrate · Nitrogen balance was carried out in the filtrate including washing water · Content was 15.79 g, content was 15.01 g, which are values in good agreement with input · ^

Example 3

1.83 L of a 0.15 mol Xn / L solution was used, i.e. a solution of the same composition as in Example 2. The reaction xeplo252 287 was maintained between 2 and 8 ° C. The rate of introduction of ammonia was 25 g NH 3 / h. When the pH of the reaction mixture reached 5.5, the air flow was stopped and CO 2 was started to flow at 142 L / h. 5 minutes after the start of CO 2 introduction, the pH of the reaction mixture dropped to 5.2 and remained constant at this value · After 50 minutes the pH rose sharply to 6 and the experiment was terminated · Rare earth carbonate precipitate was allowed to stand for 20 hours before filtering · Drying at 100 ° C revealed a carbonate yield of 56.89 S Rare earth elements were not found in the filtrate.

Claims (1)

SUBJECT OF THE INVENTION A process for the preparation of rare earth carbonates characterized in that the pH of the aqueous rare earth salt solution is adjusted as necessary _{from the} introduction of ammonia gas, preferably mixed with air, to a pH of 5.5 to 8.5, whereupon the reaction mixture begins gaseous ammonia gas can be used to introduce a stoichiometric or above-stoichiometric amount of carbon dioxide in relation to the supplied ammonia until the end of the precipitation reaction, which is indicated, for example, by a sharp increase in pH · Printed by Moravian Printing Works,