RU2693176C1 - Method of producing carbonates of rare-earth elements - Google Patents

Abstract

FIELD: chemistry.

SUBSTANCE: invention can be used in production of catalysts, individual rare-earth oxides and polishing powders. Method of producing carbonates of rare-earth elements (REE) involves feeding a solution of a lanthanum or cerium salt and a solution of a salt of carbonic acid, stirring at temperature of 20–45 °C to obtain a pulp of carbonates, filtration, washing and drying the lanthanum or cerium carbonate precipitate. Solution supply is controlled by pH change in process steps. At the first stage, the pH of the rare-earth carbonates pulp is fed in range of 4.1–5.5 by feeding the solution of the carbonic acid salt. At the second stage, the pH of the lanthanum or cerium salt solution is set in range of 3.7–4.5. At the third stage, the pH of the pulp is fed in range of 6.5–7.0 by feeding the solution of the carbonic acid salt. After reaching the preset value of pH, the pulp is agitated under mixer for 20–25 minutes at the first stage and for 20–30 minutes at the second and third stages. After that, mixer is switched off and pulp is left for 20–30 minutes to mature precipitate of carbonates. Then the pulp is filtered on a vacuum filter. Mixing is performed at agitator rotation speed 800–900 rpm.

EFFECT: invention allows to enhance the product quality and efficiency of the process due to the possibility of obtaining homogeneous crystals of a regular plate-like or acicular shape of controlled size.

2 cl, 5 dwg, 3 tbl, 3 ex

Description

The invention relates to the field of hydrometallurgy of rare-earth elements, in particular to the technology of producing carbonates of individual rare-earth elements (REE) with adjustable shape and particle size, and can be used in the production of catalysts, individual rare-earth oxides, polishing powders, etc.

Information on the composition of carbonates synthesized by various methods is rather contradictory (Komissarova LN, Shatsky VM, Pushkin G.Ya., etc. Compounds of rare-earth elements. Carbonates, oxalates, nitrates, titanates, M .: Nauka, 1984 - 235 p. (Chemistry of rare elements)). Special studies on the elucidation of the influence of various synthesis factors on the composition of the carbonates obtained made it possible to establish that the determining factor is the synthesis temperature. Compounds of the composition Ln ₂ (CO ₃ ) ₃ · 8H ₂ O with a structure of the type of lanthanum form light REE (La, Ce, Pr) in the temperature range of 20-80 ° C. Carbonates with a low hydration number of Ln ₂ (CO ₃ ) ₃ nН ₂ O (n = 2-4), having a tangerite-type structure, were obtained at temperatures of 40-70 ° С (Nd), 30-60 ° С (Sm) and 40-120 ° C (Gd, Dy, Er, Y). It can be said that this type of carbonates is characteristic of heavy REE, except Yb. Low temperatures favor the precipitation of double carbonates. The most common way to obtain medium rare-earth carbonates is the precipitation of solutions of their salts with solutions of alkali metal or ammonium carbonates during the interaction. In this case, voluminous X-ray amorphous precipitates are precipitated, which upon crystallization gradually crystallize and decrease in volume. Full precipitation of REE carbonates is achieved at a molar ratio of 1: 1.5. In the presence of large amounts of aluminum and iron, the degree of precipitation of REE carbonates can vary from 90-99% with an increase in pH from 5 to 6. When precipitating REE carbonates, an excess of precipitator and conditions that promote hydrolysis of carbonates, to which yttrium subgroup elements are especially affected, should be avoided. In the case of n> 2, the solubility of precipitation increases due to the formation of double carbonates. The tendency to hydrolyze carbonates increases with increasing temperature, duration of the process and decreasing the radius of the REE cation and increases over the series: La <Ce <Pr <Nd <Sm <Eu <Gd <Tb <Dy <Y <Tm <Yb. To prevent hydrolysis, the precipitation of REE carbonates is recommended to be performed from a cold solution using a solution of NH ₄ HCO ₃ saturated with CO ₂ as a precipitant. Using sodium carbonate or sodium bicarbonate as a precipitant gives similar results, but in the case of bicarbonate, usually crystallized precipitates are usually formed. By this method, the carbonates La, Ce (III), Gd, Dy, Er and Y can be obtained in crystalline form, while the carbonates Yb and Sc are amorphous.

There is a method of periodically obtaining highly dispersed cerium carbonates with lamellar particles, including the rapid addition of ammonium carbonate solution to an intensively mixed cerium nitrate solution to form a cerium carbonate suspension, stirring the suspension for 5 minutes at room temperature and the rotation speed of the stirrer 400 rpm, followed by unloading suspension of carbonate, its filtration, washing and drying (Protsenko, TP. Preparation of high specific surface area of cerium (IV) oxide: Author, dis. cand. tech. c. - M., 2000. - 16 p.).

The disadvantage of this method is to obtain cerium carbonates in the form of highly dispersed heterogeneous in shape and size of the plates, with low productivity thickening and filtering, as well as the frequency of the process for their production.

The authors (Ivanov, EN, Mikhailichenko, AI, Karmannikov, VP, Physico-chemical principles and technology for producing rare-earth polishing powders. // Non-ferrous metals. - 1991. - No. 11. - p. 49-51) describe the method of continuous production of highly dispersed rare earth carbonates with lamellar and needle-shaped particles, including continuous mixing of rare earth chloride solution with sodium carbonate solution to form a suspension of rare earth carbonates, mixing the suspension with simultaneous feeding of the initial solutions for at least 60 minutes, unloading suspensions AI, filtration, washing and drying of REE carbonates, needle-shaped carbonates being obtained at 20 ° С, lamellar at 60 ° С, submicron needle-shaped at 90 ° С. The speed and duration of mixing the suspension in each case is not specified.

The disadvantages of this method include the narrow temperature range for producing carbonates of a given shape, the heterogeneity of plate-shaped carbonates, the impossibility of obtaining carbonates of the dendritic form.

Closest to the claimed method is a method of obtaining carbonate REE plate or dendritic form, allowing you to extend the temperature range for producing carbonates of one form or another, as well as improve the particle size uniformity of the product. To do this, in a method that includes the continuous supply and mixing of a solution of REE salt and a solution of a salt of carbonic acid to obtain a suspension of REE carbonates, mixing the suspension while simultaneously feeding initial solutions, unloading, filtering, washing and drying the precipitate of REE carbonates, the process of mixing the suspension is carried out at 20 to 75 ° C and the speed of movement of the suspension from 0.5 to 20 m / s. To obtain plate-shaped carbonates, mixing is carried out for a time corresponding to a ratio of 1.5 * T ^0.5 ≤τ≤30, and to obtain dendritic form carbonates, mixing is carried out for a time corresponding to a ratio of 10 ⁶ * T ^2.5 ≤τ≤ 600, where τ is the numerical values of the mixing time, expressed in minutes; T is the numerical values of the temperature of the reaction medium, expressed in degrees Celsius (RF Patent No. 2245845, April 21, 2003).

The disadvantage of this method is the lack of control and regulation of the composition of the pulp at the stage of deposition, primarily on the content of H ⁺ and OH ^- ions (pulp pH), which is important at the stage of obtaining carbonates of individual REE.

The technical result of the invention is to improve the quality of products and the performance of the process as a whole due to the possibility of obtaining homogeneous crystals of the correct plate or needle shape of an adjustable size.

This technical result is achieved due to the fact that the method of obtaining rare-earth carbonates involves feeding a solution of a REE salt and a solution of carbonic acid salt, mixing at a temperature of 20-45 ° C to produce a slurry of REE carbonates, filtering, washing and drying the precipitate of REE carbonates. As a solution of salts of REE use a solution of salt of lanthanum or cerium. The supply of solutions is regulated by changing the pH of the process stages: in the first stage, the pH of the REE carbonate pulp is adjusted to 4.1.1.5.5 in the first stage by feeding the carbonate salt solution; the pulp pH is set to 3.7 in the second stage by feeding the lanthanum or cerium salt solution -4.5; in the third stage, the pulp is adjusted to a pH of 6.5-7.0 using a solution of a salt of carbonic acid. After reaching the specified pH value, the pulp agitates under the mixer for 20-25 minutes in the first stage and for 20-30 minutes in the second and third stages, then turn off the mixer and leave the pulp for 20-30 minutes to ripen the carbonate precipitate, and then the pulp is filtered on a vacuum filter. Stirring is carried out at a stirrer rotation speed of 800-900 rpm.

The implementation of the process of deposition of carbonates of cerium, lanthanum and other REE by the present method allows to obtain homogeneous crystals of carbonates of the correct lamellar or needle-shaped shape of an adjustable size of 15-20 microns. or 20-30 microns., which are well condensed, filtered, washed with water, which allows to improve the quality of products and productivity of the whole.

Example No. 1 (precipitation according to the method prototype).

The precipitation of cerium carbonates was carried out by pouring out a solution of soda with a concentration of 95 g / l and a solution containing 100 g / l of cerium, with a slow flow of precipitant (0.008 l / min) in a beaker at a molar ratio of cerium to precipitator 1: 0.8. The pulp was mixed using a propeller stirrer with a speed of 1200 per minute. The temperature of the reaction medium was 20 ° C.

When the solutions were mixed, a suspension of carbonates was formed, which was agitated under the stirrer for 20 minutes, the pH was measured and left under the mother liquor to mature for 23 hours. Determined the filtration performance of the pulp on a vacuum filter through a polypropylene fabric art. 931540.

The results of the experiments are shown in table 1.

The following are examples 2 and 3 illustrating the precipitation of cerium and lanthanum carbonates, respectively, where a solution of an ammonium salt was used as a precipitant (carbonic acid solution). The cerium reextract or lanthanum raffinate was taken as the initial solution, respectively, and the initial solution diluted with demineralized water was used as the working solution.

Example No. 2 (deposition by the present method).

The precipitation of cerium carbonates was carried out in a stirred reactor with a speed of 800-900 per minute from a solution (reextractor of cerium) containing 120 g / l of cerium and 80 g / l of nitric acid at a temperature of 20-45 ° C. Previously, the solution was diluted with demineralized water at a 1: 0.8 ratio of the initial solution to water. At the first stage of precipitation, the pH of the pulp was adjusted to 4.5-6.0 in the range of 4.5-6.0 by setting the solution of ammonium salt (180-200 g / l), after which the pulp was agitated under a stirrer for 20-25 minutes. In the second stage of the process, the pulp pH was adjusted to 3.0 to 5.0 by feeding the initial solution, after which the pulp was agitated under the mixer for 20-30 minutes; at the third stage, the pulp pH was adjusted in the range of 6.2-7.5 by feeding the ammonium salt solution, after which the pulp was agitated for 20-30 minutes. Then the mixer was turned off, the pulp was kept for 20-30 minutes and filtered on a vacuum drum filter through a polypropylene cloth art. 931540. Determined filtration performance and sediment morphology. The results of the experiments are shown in table 2 and figures 1-2.

Thus, the optimum pH ranges of precipitation of cerium carbonates, in which as a result of experiments homogeneous crystals of the correct lamellar form, well filtered, having a humidity of about 38-40%, are:

- at the first stage - pH 4.1-5.5;

- in the second stage - pH 3.7-4.5;

- at the third stage - pH 6.5-7.0.

Filtration performance of the obtained carbonate pulp at the same time on a vacuum filter reaches 1050-1200 l / m ² hour, and the product humidity - 38-39%.

Example No. 3 (deposition by the present method).

The precipitation of lanthanum carbonates was carried out from solutions (lanthanum raffinate) with a lanthanum concentration of 110-120 g / l, nitric acid 20 g / l at a temperature of 20-45 ° С Beforehand, demineralized water of 0.8 V was poured into the reactor to the initial solution, then when the agitator was turned on at 800-900 revolutions per minute, a solution of ammonium salt was fed in portions to the reactor until the pH of the pulp was in the range of 4.5-6.0. The pulp was agitated under the mixer for 20–25 minutes, after which the initial solution (lanthanum raffinate) was added in portions until a pH of 3.0–5.0 was achieved and the pulp was agitated for 20–30 minutes under the mixer. Next, by slowly feeding the solution of ammonium salt, the pH of the pulp was adjusted to 6.2-7.5, after which the agitation was continued for another 20-30 minutes. Then the mixer was turned off, the pulp was kept for 20-30 minutes and filtered on a vacuum drum filter through a polypropylene cloth art. 931540. Determined filtration performance and sediment morphology. The results of the experiments are shown in table 3 and figures 3-5.

Thus, the optimum pH ranges of precipitation of lanthanum carbonates, in which as a result of experiments homogeneous crystals of the correct needle shape were obtained, well filtered, having a humidity of about 37-39%, are:

- at the first stage - pH 4.1-5.5;

- in the second stage - pH 3.7-4.5;

- at the third stage - pH 6.5-7.0.

Filtration performance of the obtained carbonate pulp at the same time on a vacuum filter reaches 1200-1450 l / m ² hour, and the product humidity is 37.2-38.5%.

Claims (2)

1. A method of producing rare-earth carbonates, including feeding a solution of a REE salt and a solution of a salt of carbonic acid, mixing at a temperature of 20-45 ° C to obtain a slurry of REE carbonates, filtering, washing and drying the precipitate of REE carbonates, REE use a solution of salt of lanthanum or cerium, and the flow of solutions is regulated by changing the pH in the process stages: in the first stage, the pH of the pulp in the REE carbonate is adjusted to 4.1-5.5, in the second stage whose solution of salt of lanthanum or cerium pulp pH is set in the range of 3.7-4.5; in the third stage, by supplying a solution of carbonate salt, the pH of the pulp is set in the range of 6.5-7.0, while after reaching the set pH value, the pulp agitates under the mixer for 20-25 minutes in the first stage and for 20-30 minutes in the second and the third stage, after which the mixer is turned off and the carbonate pulp is left for maturation for 20-30 minutes, and then the pulp is filtered on a vacuum filter. 2. The method according to p. 1, characterized in that the mixing is carried out at a speed of rotation of the stirrer 800-900 rpm

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