CS242846B1 - A method for separating cerium from other lanthanides and yttrium - Google Patents

Abstract

The solution concerns a method of separating cerium from other lanthanides and yttrium in suspension after cerium oxidation, the essence of which is that fractional dissolution is carried out at pH 2.4 to 2.6 at a temperature of 70 °C to the boiling point of the suspension and after separation of the liquid phase, the solid phase is dissolved again at pH 1.7 to 1.5 at the above-mentioned temperature and the filtrate is returned to the suspension intended for cerium oxidation.

Description

( ⁵⁴ ) Method for separating cerium from other lanthanides and yttrium

The solution concerns a method of separating cerium from other lanthanides and yttrium in suspension after cerium oxidation, the essence of which is that fractional dissolution is carried out at pH 2.4 to 2.6 at a temperature of 70 °C to the boiling point of the suspension and after separation of the liquid phase, the solid phase is dissolved again at pH 1.7 to 1.5 at the above-mentioned temperature and the filtrate is returned to the suspension intended for cerium oxidation.

242,846

- 1,242,846

The invention relates to the separation of cerium from other lanthanides and yttrium or a mixture of rare earths of various origins.

The known embodiments of the separation of cerium from other lanthanides are based on the oxidation of cerium from the trivalent to the tetravalent state and further precipitation of cerium compounds or extraction of cerium compounds into the organic phase. Although the cerium content in the sum of rare earths of all provenances is high /about 50%/, the costs of extraction equipment and extraction agents are extremely high and extraction of cerium is an uneconomical method. The precipitation of tetravalent cerium as CeO^xHgO or bwsic salt has so far always been carried out from an aqueous medium and is a method that is not demanding in terms of technical equipment. However, the precipitates are often semi-colloidal, for example during the hydrolysis of an oxidized 'concentrated solution of rare earth nitrates in dilute sulfuric acid, or during the precipitation of cerium phosphate from a nitrate or sulfate solution after electrolytic oxidation, which makes filtration difficult and additionally contaminates the products by occlusion of other lanthanides and other reactants. Cerium hydroxide or basic salts of tetravalent cerium precipitate at pH up to 4.5, hydroxides of other lanthanides begin to precipitate already at pH 6 to 7, therefore selectivity is often unsatisfactory. From a theoretical point of view, precipitation is an unsuitable method, since the ratio of cerium to other rare earths deteriorates with gradual precipitation.

The method of separating cerium, which is the subject of this invention, is based on the method of oxidizing cerium in an alkaline suspension. The perfection of oxidation and the fineness of the particles in the suspension are one of the prerequisites for the effectiveness of this method of separating cerium. Furthermore, it is based only on fractional dissolution, in which the ratio of cerium to other rare earths is constantly improving as the critical separation region approaches. However, the main moment of the method is the cyclical process of two-stage fractional

- 2,242,846 dissolutions. The suspension, which comes from the air oxidation process, is subjected to fractional dissolution at pH 2.5 and a temperature of 70 °C up to the boiling point for about 2 hours. In this case, all cerium remains undissolved, while about 95% of the other lanthanides go into solution. After filtration or decantation, when the overall separation effect is worse, but the practical implementation is more convenient, the raw cerium is subjected to a second stage of dissolution at pH 1.7 to 1.5 and a temperature of 70 °C up to the boiling point for about 2 hours. The filtrate from the second stage of dissolution, which contains about 5% of the total cerium /mostly as Ce ⁴⁺ ions, but partly as back-reduced Ce^ ⁴ ions / is transferred back to the oxidation together with another batch of mixed hydroxide concentrate. This enters the second cycle of the process, which is repeated in a two-stage dissolution at pH 2.5 and pH 1.7 to 1.5, etc. /see diagram/. Cyclization ultimately ensures quantitative yields of all components.

Scheme of the cyclic process of separating cerium by fractional dissolution of an oxidized suspension of rare earth hydroxides:

sum of rare earths in suspension · air fractional oxidation of solution

—^at pH 2.5 í

fractional

Filtrate II—dissolved.

rare cerium-free cerium product Filtrate I mines at pH 1.5 to 1.7

The invention is documented by the following application examples.

Example 1 ^f 1,000 ml of a solution containing 0.35 N Ln^ ⁺ in a molar composition of La 30%, Ce 50% and Nd 20% was, after adjusting the pH to 12.5 by adding NaOI-I, oxidized in air at 90 °C for 2 hours. This was followed by fractional dissolution of the suspension at 2.5 p.p. and a temperature of 70 °C for 2 hours. After filtration, the filter cake was subjected to further

- 5 242 846 fractional dissolution at pH 1.7 and temperature 70 °C for 2 hours. Further filtration gave the cerium product and filtrate II was returned to the beginning of a new cycle and combined with a new 1-liter batch of fresh concentrate solution. After oxidation, the suspension was subjected to a 2nd dissolution cycle, which was again carried out in two stages at pH 2.5 and 1.7, etc. It was found that the quality of the products quickly stabilizes after 5 cycles during cyclization. The purity of the cerium product increases from 96.8% after the 1st dissolution stage to 99.8% after the 2nd dissolution stage. No cerium was found in filtrate I.

Scheme and results, /data in grams/:

Oxidation in susp. solvent Filtrate I

cycle 1ΐ 2. 5. ..... 4· at pH “Cycle 1. 2. 5. 4. La 17.10 17.50 17.52 17.55 2 ,5 La 16.45 16.95 16.94 16.91 Ce 50.12 51.57 51.64 51.65 Ce 0 0 0 0 Sun 11.78 12.21 12.27 12.27 ( Sun 11.15 11.60 11.61. 11.60

transient cerium product

cycle 1. 2. 5. 4. La 0.48 0.49 0.49 0.48 Ce 50.10 51.55 51.55 51.55 Sun 0.55 0.55 0.54 0.52 cleanliness 96.7% 96.8% 96.8% 96.9%

and

Filtrate II dissolved at ¹ ........ ¹ ——————— ———————-

cycle 1. •ez.- 2. 5. 4t ⁺ PH 1.7 La 0.40 0.42 0.45 0.42 Ce 1.45 1.52 1.51 1.51 Sun 0.45 0.49 0.49 0.49 final J ( er's product cycle 1. 2o 5 o 4· La 0 ,2 0.2 0.2 0.2

Ce 28.61 29.90 29.91 29.95

Nd 0.05 0.05 0.05 0.05 purity 99.82%99.85> 99.85) 99.85% note:

⁺ : start of cyclic attempt ⁺⁺ : end of cyclic attempt

- 4 Example 2

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000 ml of solution containing 0.41 N Ln^* in molar composition La 22.25 Ce 54.2%, Př 5.9%, Nd 14.5% and other lanthanides 5.15%, was adjusted to pH 12.5 by adding NaOH and oxidized with air at 90 °C for 2 hours. This was followed by fractional dissolution of the suspension at pH 2.5 and temperature 70 °C for 2 hours. After filtration, the filter cake was subjected to another fractional dissolution at pH 1.5 and temperature 70 °C for also 2 hours. Further filtration yielded the cerium product, while filtrate II was returned to the beginning of a new cycle and combined with a new 1-liter batch of Fresh concentrate solution. After oxidation, the suspension was subjected to a 2nd dissolution cycle, which was carried out in two stages at pH 2.5 and 1.5, etc. It was found that the quality of the products stabilized rapidly after 5 or 4 cycles during cyclization. The purity of the cerium product increased from about 91% after the 1st dissolution stage to 98.7% after the 2nd dissolution stage. No cerium was found in the filtrate I.

Claims (1)

SUBJECT OF THE INVENTION 242 846 Process for separating cerium from other lanthanides and yttrium in a cerium oxidation slurry, characterized in that fractional dissolution is carried out at a pH of 2.4 to 2.6 at 70 ° C to the boiling point of the suspension and after separation of the liquid phase, the solid phase is recovered. it dissolves at a pH of 1.7 to 1.5 at the above temperature and the filtrate returns to the cerium oxidation slurry.