DE1052956B - Process for the separation and purification of insoluble or sparingly soluble oxalate-forming elements, especially rare earths - Google Patents

Description

Process for the separation and purification of insoluble or sparingly soluble Oxalate-forming elements, in particular rare earths, are the subject of the process is a new method for the separation and purification of insoluble or sparingly soluble Oxalate-forming elements, especially rare earths, via soluble complex salts with organic acids and fractional decomposition of the complex compounds.

To separate these elements, especially the rare earths, are various methods are known, of which the following should be emphasized: 1. Separation by fractional crystallization according to Auer v. Welsbach.

2. Tiennunig through fractional precipitation.

3. Separation by fractional extraction of salts, oxides, etc. with acids.

4. Separation by fractional sublimation of the rare chlorides Earth.

5. Separation by fractional adsorption.

6. Separation of rare earths in aqueous solution by ion migration in the electric field.

7. Separation in the magnetic field.

8. Separation with the help of base exchangers.

9. Separation with the help of selective solvents.

10. In addition, all those procedures that are based on the transfer of individual Rare earths are based in other degrees of freedom.

All known methods of rare earth separation except those mentioned under 10 have the disadvantage that they require multi-stage work, because only fractional enrichment takes place. So you get z. B. too pure Neodymium from a mixture of cerite earths only if one uses the fractional crystallization has repeated a few hundred times. Fractional extraction always leads, too only to concentrates, from which pure only after multiple repetitions of the operation Fractions are to be obtained. Many methods have the disadvantage of being pure or uniform To deliver fractions only with poor yields, and in many cases the technical one is available Application of the high cost point against that due to the high expenditure of reagents and working time is caused.

It has now been found that the separation and pure representation of rare Earth or the like. Difficult separable elements such. B. Thorium and Uranium, the insoluble or poorly soluble oxalates 7; u are able to form when certain soluble ones are used Complex salts can be carried out with a surprisingly high separation factor and thus the hitherto indispensable multiple repetition of the fractionation in its entirety or at least for the most part makes it superfluous. To achieve this goal are according to the invention with a di- or polybasic organic acid, such as B. Oxal acid, citric acid or tartaric acid or a chloru first or sulfurized carboxylic acid compounds, optionally with a metal compound as an additional complexing agent produced soluble complex salts of the to be separated Elements in the presence of substances containing oxalate groups under gradual Precipitation of insoluble oxalates of the elements to be separated decomposed.

The gradual precipitation is expediently particularly slow and in in this way ensures that the resulting change in the environmental conditions, these are in particular the concentration of the respective practitioners, the p-value and the temperature, from stage to stage only in very small, the optimal Separation conditions exactly corresponding sections is made.

The gradual decomposition of the complex compounds used is best carried out according to the invention so that one begins with the onset of nucleation the further addition of the precipitant used until it is completely separated and separation of the respective fraction interrupted. The onset of nucleation can be seen at the beginning of the turbidity (Tyndall effect), which is caused by the Failure of the fraction to be separated is caused.

The step-wise precipitation of the elements carried out according to the invention x in the form of oxalates can be achieved with advantage that one for the preparation of soluble oxalato complexes of the elements to be separated as additional complexing agents a metal compound, in particular an aluminum compound, preferably in the form their salts are used with. This is in the complex compounds thus obtained the solubility and stability are strong depending on the nature of the elements to be separated difference. i, rt and from the Q; dilution of the solutions, from the temperature and hydrogen ion concentration largely dependent on the effectiveness of the separation operation Good is coming.

In concentrated solution, these complex compounds are often very stable.

As additional complexing agents, instead of aluminum or nebeff: - this also other elements can be used with good success, such as z. B.

Beryllium, boron, scandium, yttrium, indium, gallium, zirconium, tin, Vanadium, nioh, tantalum, arsenic, antimony, chromium, molybdenum, tungsten, uranium, iron. These elements, expediently in the form of their salts or of complex-forming ions or compounds containing ionic groups can also be used capable of forming soluble oxalato complexes of differentiated stability, which an excellent one in the stepwise precipitation carried out according to the invention Have separation factor.

With certain elements; oi. B. with the cerite earths with organic Acids, especially with oxalic acid, form insoluble salts, aluminum should or Another of the above-mentioned additional elements for the purpose of forming the '- water-soluble Complex salts may be present. To this end .. be another feature of the According to the invention, the oxalates of the elements to be separated in aluminum salt solutions or in solutions containing the ions or ion groups of the other additional complexing agents contained, dissolved and then the gradual precipitation under the conditions of Subject to invention.

The production of this z. B. aluminum-containing complex salts can be done in several ways. It is very simple and practical, for example. if possible freshly precipitated oxalates with aluminum salt solutions, 'for example ammonine malum, Aluminum nitrate; Aluminum sulfate or aluminum chloride, to be stirred or digested, whereby the insoluble oxalates are smoothly dissolved with complex formation.

Another possibility is to use soluble salts, e.g. B.

Acetates or nitrates; of the elements to be separated with Mix in solutions of aluminimoxalic acid or a similar complex acid, clear solutions are produced in certain concentration ranges.

The gradual decomposition. the 'soluble oxalsato complexes can preferably by successively diluting, adding ammonoxalate, of Oxalic acid and finally of dilute mineral acids and keeping the pI value constant and carried out at constant temperature to transfer the to be separated However, elements in soluble complex compounds are not considered to be present bound by oxalate mixtures as starting materials. So can according to a further advantageous Embodiment of the invention, the production of soluble composite compounds for - later step precipitation using such organic acids. how Citric acid and tartaric acid, taken by themselves or in the form of their salts for fractionation these complex compounds are not or only less suitable; the step precipitation can then be brought about again via the oxalates. For example, if you want soluble Citric acid complex compounds of the elements to be separated, e.g. B. of rare Earth, produce, so this can be done directly using citric acid and by dilute ammonia happen, whereby one obtains soluble complex compounds, which is then gradually decomposed by adding oxalate ions will. This step-by-step decomposition can, as in the case of the soluble oxalato complexes, again by successive addition of ammonoxalate, oxalic acid and finally of mineral acids, keeping the pn value constant and at constant temperature, be made.

In contrast to the soluble oxalato complexes in which the Separation of insoluble oxalates in the first stage of precipitation just by bare Dilution can be effected, must in the case of the oxalate-free complex compounds Precipitation must be initiated with oxalate-containing precipitants.

The solubility and stability of the water-soluble ones used in the invention Complex compounds of rare earths or similar elements that are difficult to separate with di- or more-basic organic acids it can also be done by incorporating further mono- or polybasic, organic and inorganic acid amino groups, such as z. B. of acetate, citrate, nitrate, sulfate, C'hlolr.id-, fluoride or Pshospthations, still largely change.

Many of the present complex compounds are also in organic Solvents soluble, so that by appropriate combination of the options listed subtlest separation operations can be performed. The stability and the These compounds are complex in nature for the individual rare earths and others rare elements such as zirconium, hafnium, thorium, niobium, tantalum, gallium, indium, Thallium and the platinum metals are so different that these complex salts in a very effective way, in many cases even in a single operation to one quantitative separation of rare elements are to be used.

The achievable separation effects and the speed with which the separation takes place, have proven to be far superior to all previously known methods. The method is suitable for both preparative and technical presentation very many rare elements. In addition, it can also be used for analytical purposes find diverse application. It should be emphasized as a particular advantage that the Process with those generally customary in inorganic preparative work technology Methods can be carried out in a simple manner.

The wide range of possible variations in terms of the anions used, Cations and complexing agents, especially through their simultaneous use The formation of mixed complexes enables the production of a large number of previously unknown Complex compounds.

To give a few examples, it should be mentioned that the oxalates of the rare earths are readily soluble in solutions of most aluminum salts that the phosphates of zirconium, hafnium and thorium e.g. B. soluble with aluminum tartrate Complex compounds form that the oxides or hydroxides of niobium or tantalum very much easily complex oxalato compounds that form the sulfates of the alkaline earths with z. B. aluminum oxalic acid or aluminum citric acid lei chtlösli before Kompiexverb indungen and that the aluminum in many of these complex compounds is replaced by beryllium, Iron, chromium, molybdenum, tungsten, vanadium, indium, gallium, boron etc. can be replaced can and the simultaneous presence of two or more anions or cations in general, the solubility of the complex salts changed, in many cases greatly elevated.

An essential and new feature of the separation method according to the present The invention consists in incorporating ions or ion groups into the complexes mentioned or in the form of the precipitating agent -added with the to be separated Elements form poorly soluble or insoluble compounds.

A second important characteristic of this method of loyalty is that the precipitation medium is chosen so that the complex compounds in solution an element or a group of elements remain completely stable, while the complex of another element to be separated first becomes stepwise Brought dissociation and this element in the same degree by the likewise from the Ions or ion groups that dissociate complex or are added in excess, which act as precipitants for the element in question, as insoluble or sparingly soluble Connection is liked. The setting of these necessary environmental conditions for the fractional splitting of the complex compounds by dilution, by adding ammonoxalate, oxalic acid or other acids, bases or salts, the compounds that are insoluble or completely soluble with the elements to be separated form, achieved, at the same time the hydrogen ion concentration (pE value) and the temperature of the solution is chosen so that optimal separation effects are achieved will.

By using this trick, the separation also succeeds Elements, their complex compounds per se only minor differences in their stability have such. B. the separation of immediately adjacent in the periodic system Elements such as cerite earths, ytter earths or platinum metals, in fractions that contain the individual elements already contained in high purity, although only proportionally small unseparated intermediate fractions remain.

Example 1 A mixture of lanthanum, didymammon nitrate as described in the previously customary technical representation of the rare earths after separation of the Cers as a basic cerium salt and separation of the ytter earths by multiple fractionated Crystallization occurs and that, in addition to lanthanum, praseodymium and neodymium, is considerable Containing quantities of samarium and ytter earth is treated as follows: The rare Soils are precipitated as oxalates from the hot solution of nitrates with ammonoxalate, the fine-grained precipitate is filtered off and washed thoroughly with water. the Precipitated oxalates are still in the moist state in a 100% ammonium alum solution brought into solution with vigorous stirring and boiling heat, for which one per kilogram Oxalate mixture of the rare earths requires about 5 kg of crystallized NH4Al (SO4) 2 12H2 0. Fractional precipitation is carried out with the solution prepared in this way by at a temperature of 70 to 800 C slowly cold (20 to 300 C) saturated ones Ammonoxalate solution is added with intensive stirring, with additional heating for it is taken care of; that the - temperature does not fall below 650 C. The addition of the precipitant occurs gradually in small proportions until the appearance of a weak one Cloudiness. From this point onwards, no further addition of precipitant is required, however with intensive stirring and maintaining the precipitation temperature of 70 to 800 C. - causes the complete precipitation of the first fraction, whereby - the initially weak turbidity intensifies by itself and leads to the formation of precipitation.

The precipitate will then settle in the warmth for about an hour left, then decanted or filtered and the resulting filtrate of the other fractional precipitation as described above, subjected.

If no further precipitation can be achieved by adding ammonoxalate, 100% oxalic acid is used as the precipitating agent and the same is used for the precipitation Way done. The last fractions from the resulting filtrates are finally precipitated by acidification with dilute hydrochloric acid (1: 3).

The fractions obtained in the manner described give the rare earths in the following order: The first fraction contains the ytter earths with traces of Samariurn, the second fraction the entire Samarium - with little - Proportions of neodymium, the third fraction contains all of the neodymium small amounts of praseodymium, in the fourth fraction all of the praseodymium and some lanthanum, while the fifth fraction already consists of pure larithane. With such a precipitation series, up to 9010/0 of the earths can be considered highly concentrated Individual fractions are obtained. These can then be used in a second precipitation operation be cleaned, whereby the individual earths must already be isolated in a spectrally pure manner. This second precipitation is assumed in such a way that the - in the first separation. precipitated oxalates are dissolved again in 100% ammonium alum solution at boiling point and fractional precipitation in the same way, but depending on the composition the fraction with ammonium oxalate, oxalic acid or finally with hydrochloric acid will.

Example 2 A mixture of the ammonium double nitrates of neodymium and the Ytter earths, as is the case with fractional crystallization according to the anchor method v. Welsbach remains after separation of the cerium, lanthanum and praseodymium by precipitation with a dilute (e.g. 100%) ammonium hydroxide solution in the Heat (600 C) transferred into the hydroxides. The precipitate is filtered off, Washed nitrate-free and while still moist in a straight to dissolve still sufficient amount of concentrated citric acid solution dissolved and then up to concentrated to a honey-like consistency, whereby no precipitation may occur. this The concentrate is now taken up with dilute ammonium hydroxide, whereby a clear solution is produced, which is reduced to a p-value by the addition of ammonia is set from 8.5 to 9.0. After the solution was found to be favorable Precipitation temperature was brought from 70 to 800 C, the precipitation is gradual by adding oxalate ions, first of all with cold-saturated ones Ammonoxalate solution, then with 100% above oxalic acid solution and finally with dilute hydrochloric acid (1: 3) carried out with intensive stirring. This precipitation is carried out analogously to Example 1 by adding the respective precipitant only effected until the onset of turbidity. The temperature is increased by an appropriate supply of heat kept constant at 70 to 800 C. The pI value of the solution decreases during the precipitation from the original value depending on the composition of the rare earth mixture down to about 2.0. The precipitation of the individual fractions is strongly p-dependent. The following fractions are obtained in this fractional precipitation: Precipitant: cold saturated ammonium oxalate solution 1. At p, = 8.0 the first fraction with the Most of the neodymium and some samarium precipitated.

2. At pH = 7.6 the second fraction, which is the entire samarium and contains the rest of the neodymium.

3. If pure = 6.2, the third fraction with the main amount is erbium obtain. This fraction also includes europium, dysprosium and holmium.

4. Bleilpn- = 5.7 falls the fourth fraction, which is the rest of the erbium together with terbium.

Precipitant: 100% oxalic acid 5. At per = 4.6 a fifth falls Fraction which corresponds to the atomic weight after the gadolinium.

6. The precipitation of the yttrium begins at p = 2.9.

Precipitant: dilute hydrochloric acid 7. When pure = 1.8, the main amount falls Yttrium.

8. There is still yttrium and all of the -Scandium in the filtrate, which can be precipitated with strong hydrochloric acid.

All precipitates consist of oxalates, their individual fractions if desired, for further purification, again via their hydroxides into the citric acid complex overfilled and a repeated fractional precipitation in the same way can be subjected to the individual fractions of the first separation operation the rare earths already with 88 to 90 per cent yield in high concentration are to be won. As far as the earths are still small impurities from neighboring elements contained, a single further reprecipitation according to the above method is sufficient for complete Pure display.

Example 3 A middle fraction of the rare earth oxalate precipitation, wile it was obtained in Example 2 and that the erbium was enriched with about 55% contains, is used for the pure representation of the erbium in dilute nitric acid (1: 4) solved. The rare earths are made with dilute (about 100%) aqueous ammonia solution precipitated as hydroxides, washed and the still moist hydroxide precipitate Completely dissolved in concentrated citric acid solution at boiling point.

The solution, concentrated to a honey-like consistency, is 100 / above Ammonium hydroxide solution added and by adding an appropriate excess set to pT value 9. The precipitation is now carried out at a temperature of 70 to 800 C carried out with intensive stirring with cold saturated ammonoxalate solution.

If turbidity occurs before the pr value of 6.2 is reached, interrupt the ammonaxalate is added immediately, it is allowed to settle in the heat and remove it like that formed precipitate containing any neodymium, samarium, etc. that may still be present can.

After further adding the precipitant, when the pH 6.2 of the solution, the addition is again interrupted and adhered to the precipitation temperature of 700 C and intensive stirring, the end of the precipitation waited. After about one hour of settling of the precipitate in the heat filtered to obtain a fraction containing 800 / o of the erbium present contains in the highest purity. The filtrate is again with Ain'monoxalatlösung up to reach the p-value of 5.7, at which the precipitation of the remaining With the exception of ytterbium and its closest related earths Yttrium and scandium, which are then precipitated from the filtrate with hydrochloric acid (1: 3) - can.

The pure representation of all rare earths can be done in an analogous manner take place.

Example 4 The in the alkaline digestion of monazite sand according to The hydroxides that remain are filtered off and washed out converted into oxides by annealing in air. This oxidized precipitate will leached with a 103 / above aluminum salt solution at boiling point, the aluminum nitrate can be given preference over other aluminum salts.

All rare earths with the exception of thorium oxide, cerium oxide and uranium oxide go into solution as water-soluble aluminum complexes. From this solution, the Rare earths, as described in working examples 1 to 3, are precipitated in a fractionated manner and be represented in pure form.

Example 5 That after separation of the rare earths according to Example 4 remaining oxide mixture of ger, thorium and uranium oxide is known per se Way reduced with hydrogen, the resulting trivalent cerium with 100% Aluminum nitrate solution extracted and the remaining oxides of thorium and Uranium converted into sulphates. These are in ammonia-alkaline aluminum oxalic acid solution dissolved, with about 1500 cmS aluminum oxalic acid as 1.0 molar solution is applied. An excess of ammonia and oxalic acid does not harm.

Freshly precipitated was used to produce the complex aluminum oxalic acid and clay suspended in water with 100% oxalic acid solution on the water bath in a time reaction of 3 to 5 days until a honey-like mass is formed treated and the complex maturation continued for 2 days on the water bath until no more free oxalic acid was detectable. After diluting with water, one day Standing and filtering off the remaining alumina, the filtrate was concentrated and crystallized left to settle, leaving a white, cauliflower-like crystal mass, correspondingly a defined compound H6 [Al2 (C2 04) 6] 3 H2 O was obtained. the from a 1 molar solution of this complex acidic compound and the sulphate mixture The solution obtained in the manner described above is now more intense Stirring at 70 to 800 C with a mixture of 7 parts of cold saturated ammonoxalate solution and 3 parts of concentrated hydrochloric acid are added, with only the thorium as oxalate is precipitated. The addition of the precipitant is when it occurs the first turbidity interrupted immediately. This gradually intensifies to a finely crystalline one Precipitation containing all of the thorium in pure form. The uranium stays in Solution and can be precipitated as uranium with ammonia.

From the cerium-aluminum-nitrate extract, fractional precipitation with ammonoxalate according to Examples 1 to 3 any impurities still present be separated in a pre-precipitation, while the middle fractions of the cerium in pure Shape included.

PATENT CLAIM: 1. Process for the separation and purification of insoluble or sparingly soluble oxalate-forming elements, especially the rare ones Earth via soluble complex salts with organic acids, especially oxalic acid, and fractional decomposition of the complex compounds, thereby marked that the soluble, optionally with a metal compound as an additional Complexing agents produced complex compounds in the presence of oxalate groups Substances with gradual precipitation of insoluble oxalates to be separated Elements decomposed.

Claims (1)

2. The method according to claim 1, characterized in that the stepwise Decomposition of the complex compounds is carried out in such a way that one starts at the beginning Turbidity the further addition of the precipitant used until complete Separation and separation of the respective fraction interrupted. 3. The method according to claim 1 or 2, characterized in that for the production of soluble oxalato complexes of the elements to be separated as additional Complexing agents aluminum salts, preferably in the form of their solutions, can be used. 4. The method according to claim 3, characterized in that as an additional Complexing agents instead of or in addition to aluminum salts complexing dend ions resp. Compounds containing ion groups, such as beryllium, boron, scandium, yttrium, Indium, gallium, zirconium, zinc, vanadium, niobium, tantalum, arsenic, antimony, chromium, Molybdenum, tungsten, uranium or iron salts can be used. 5. The method according to claim 3 or 4, characterized in that the oxalates of the elements to be separated in aluminum salt solutions or salt solutions solves the elements mentioned in claim 4. 6. The method according to claims 1 to 5, characterized in that that the gradual decomposition of the soluble complex compounds by successive Dilute their solutions, add ammonoxalate, oxalic acid and dilute mineral acids while keeping the po value constant and at a constant temperature, preferably 70 up to 800 C. 7. The method according to claim 1 or 2, characterized in that soluble citric acid complex compounds using citric acid and dilute ammonia of the elements to be separated generated and containing oxalate ions by adding Solutions are gradually decomposed. 8. The method according to claim 7, characterized in that the stepwise Decomposition of the soluble complex compounds by successive addition of Ammonoxalate, oxalic acid and mineral acids while keeping the p-value constant and at constant temperature, preferably 70 to 800 C, is taken. 9. The method according to claims 1 to 8, characterized in that that an aluminum-oxalic acid complex compound was added as an additional complexing agent will. Considered publications: German Patent Specifications No. 621 309, 806 137, 905 134; Chem. Zentralblatt, 1950, vol. 2, p. 2102, ref. Of the work by Gordon, Vanselow and Will ard.