DE1171876B - Process for the separation of difficult to separate compounds - Google Patents

Description

FEDERAL REPUBLIC OF GERMANY

GERMAN

PATENT OFFICE

EDITORIAL

Boarding school Kl .: BOIj

German class: 12 g -1/01

Number: 1 171 876

File number: P 17528 IV a / 12 g

Filing date: December 6, 1956

Opening day: June 11, 1964

The invention relates to a method for separation, in particular for quantitative separation and Pure representation, of difficult to separate connections and aims to improve the time-consuming separation processes that were previously indispensable for chemically similar elements.

Various elements are used to separate or purify chemically closely related elements Methods known. It can e.g. B. can be used:

1. Fractional precipitation of insoluble compounds from salt solutions or complex compounds,

2. fractional crystallization,

3. fractional solution in water, acids, alkalis or organic solvents,

4. fractional decomposition of soluble compounds,

5. fractional thermal decomposition,

6. fractional separation by ion exchange,

7. fractional adsorption and desorption,

8. fractional distillation of metals or volatile compounds.

All known methods have the disadvantage that they require multi-stage work because only one fractional enrichment takes place. In some cases, e.g. B. in the processing of cerite to pure Neodymium, the fractional crystallization must be repeated a few hundred times. With many methods the yields are so poor that the separation can be carried out on an industrial scale economic reasons is not acceptable.

It has now been found that it is surprisingly possible to quantitatively or at least approximately quantitatively separate elements which are difficult to separate and which are adjacent in the periodic system or have very similar properties with a single operation by fractional precipitation or fractional crystallization. The method according to the invention is based on a treatment in the "ideal homogeneous medium", the feature of which is that the changes in the environmental conditions that serve to separate fractions, namely the concentration of the components involved and / or hydrogen ion concentration and / or temperature, in very small amounts and in temporally and spatially in a steady, ie not abrupt manner and that these changes are interrupted when the optimal threshold value of the respective separation stage is reached until the separation of the separated fraction is completed, after which the back-process for separation of difficult to separate
links

Applicant:

Dipl.-Ing. Dr. phil. Dr. techn. Kurt Peters, Vienna

Representative:

Dr. F. Zumstein

and Dipl.-Chem. Dr. rer. nat. E. Assmann,

Patent Attorneys, Munich 2, Bräuhausstr. 4th

Named as inventor:

Dipl.-Ing. Dr. phil. Dr. techn. Kurt Peters, Vienna

Claimed priority:

Austria from April 27, 1956 (A 2546/56)

Remaining medium (solution or melt) for the alias due recovery of further fractions in an analogous manner Way until the optimal threshold value of the next separation stage is reached will. Below the optimal or characteristic threshold value of a separation stage, that stage is experimental understandable point at which the first still invisible crystal nuclei form. This threshold value becomes the first immediately before the visible start of the first Nucleation achieved. If this value were to be exceeded significantly, this would have been the case despite the continuation the separation operation in a particularly slow and steady manner already the deposition of the the next parliamentary group, or, in other words, from this point onwards it would be continued the change in the milieu to the separation of a fraction with a significantly worse separation factor than to Lead the beginning of the deposition.

An analogous proposal, which does not yet belong to the state of the art, is already made by the inventor for the Separation of niobium and tantalum has been made via their oxalic acid complexes, which are fractionated by Precipitation is carried out particularly slowly and with intensive mixing, the precipitation process is interrupted at the time of the first nucleation. This special separation process does not fall under the present invention.

409 599 / 30P

It is already known to avoid a concentration gradient which influences the quantity of precipitates, to precipitate chemically related elements from homogeneous solution in a fractionated manner, whereby the precipitant is formed by hydrolysis from the solution itself. A strict constant all for the quantitative separation of a single fraction is decisive environmental conditions, however, how practice has taught, is not possible in this way.

It should be noted here that the "ideal homogeneous medium" according to the invention differs significantly from the known "homogeneous field" in that the term "homogeneous" in the present case refers to both a spatial and a temporal homogeneity homogeneous field in the usual sense only includes a local homogeneity. If, for example, oxalic acid is split off by hydrolysis of oxalic acid esters or if ammonia is obtained from amines or from urea by hydrolysis, or phosphoric acid from dimethyl phosphate or sulfuric acid from dimethyl sulfate, then the hydrolysis achieves the same local concentrations at all points in the medium Oxalic acid, sulfuric acid, phosphoric acid, etc. occur. But the concentrations of these acids or the p _H values are in the whole medium at the same time quickly running changes. The precipitations caused by this therefore take place "homogeneously" throughout the medium, but suddenly at the same time.

Since temporal and spatial homogeneity is crucial in the method according to the invention, precipitation must be avoided suddenly in the entire medium, because such a medium is spatially homogeneous, but not temporally. Rather, the change in the milieu must also take place over time in such a way that sudden precipitation, crystallization and the like do not occur and thereby irreversible mixed precipitations, mixed crystal formations and the like are prevented. This temporal and spatial homogeneity must also be preserved in the boundary layers. If this does not happen, then in the microdimensions, e.g. As the usual dropping of the precipitant in the reaction medium, spatial and temporal inhomogeneities (high concentration differences, p _H -Differenzen or temperature differences), occur because, despite homogeneity in all, in the small inhomogeneity exists detrimental to all, irreversible consequences.

The conditions of the "ideal homogeneous medium" can then be met, as in accordance with the invention was recognized when the speed of the reaction (precipitation, crystallization) at any time and is nowhere greater than the diffusion rate. The realization of this realization, namely the retention of the diffusion rate as the rate-determining reaction is then can be met if the environmental conditions, yes, for the precipitation or crystallization of fractions need to be changed, changed only to such a small extent that changes are abrupt be excluded at any time and in any place of the medium, i.e. the medium in relation to it remains practically homogeneous to the milieu parameters already mentioned. According to the second stage of the The method according to the invention must then the changes in the environment immediately before the occurrence of the first nucleation of the fraction to be separated, i.e. at the optimal threshold value of the respective Separation stage, be interrupted immediately. As was found, those are up to the interruption Changes to the milieu parameters carried out continuously, but in the smallest amounts sufficient to cover the entry of the first

ίο Nucleation initiated reaction (precipitation, Crystallization) despite the fact that the environmental parameters are now kept constant and to resolve with the separation of a fraction of sufficient size and highest purity.

It has proven to be particularly favorable for the practical implementation of the method according to the invention proven when the critical environmental conditions for fractional precipitation or crystallization (temperature, Hydrogen ion concentration, concentration of the components involved), especially the optimal one Threshold value for the respective separation stage, i.e. the still invisible beginning of the first crystal nucleation, the rate of formation of the solids to be separated, the amounts of any additional components (complexing agents, solvents, etc.) by means of preliminary tests the actual separation operation precisely determined with the usual aids of the person skilled in the art will.

If solutions or melts are worked up by fractional crystallization, this can be done according to the invention by extremely slow temperature change or correspondingly slow Withdrawal of the solvent until the optimal threshold value is reached. In the event of the fractional precipitation from salt solutions, the separation operation can be carried out by ion reactions known per se can be achieved, the precipitating agent either being added in a correspondingly slowed manner or by hydrolysis in the solution itself. Fractional precipitation can also take place Solutions are caused by such complex or addition compounds, which with constant Changing the environmental conditions are able to either connect the elements to be separated to be split off directly or compounds acting as precipitants for the elements to be separated off split off and thereby fail the elements.

According to a particularly advantageous embodiment of the invention, the elements to be separated can initially in complex compounds with complex formation constants that are as different as possible be converted so that the differences in these compounds in stability, complexity and solubility in the case of two elements with inherently similar properties are as large as possible subjects these complexes to gradual decomposition by fractional precipitation. This decomposition is according to the invention in the ideal homogeneous medium in very small, the deposition conditions of the individual elements or their connections made exactly corresponding separation stages. This The procedure is based on the knowledge that when using complex compounds to separating elements in combination with the treatment in the ideal homogeneous medium the individual

Deposition of the chemically closely related elements succeeds in a way that is in stark contradiction to it all experiences gained so far. It is thus possible, for example, when working according to the invention to achieve an improvement in the separation effects, even with the known particularly difficult to separate rare earths result in a separation factor of 100% or almost 100%.

In the new separation process, the complex compounds used have the property of the separation operations gradually and automatically to set the optimal precipitation conditions. The prerequisite for the effectiveness of this procedure is, however, that the measures are taken to cease of the ideal homogeneous medium and its purposeful change in the course of the individual separation phases must be undertaken with particular caution. Environment conditions can be set for the step-by-step separation, realize the generally small differences that are known per se Great separation effects in the physical and chemical properties of elements can be achieved. In many cases it is possible to create environmental conditions in which z. B. a Complex salt of one element already quantitatively with the deposition of an insoluble precipitate decays while the other element still remains in solution quantitatively as a complex salt. That Successful separation operations, however, depends on compliance with the very special precautionary measures mentioned which avoids blurring the often extremely small separation steps.

For a better understanding of the method according to the invention and the advantages associated therewith, below the previous methodology compared with the new way of working and an interpretation for the occurring problems given:

The fractional crystallization is generally carried out so that, as for example in the rare earths according to Auer v. Welsbach, complex ammonium double nitrates dissolved in the heat and that this solution is cooled by allowing it to stand in the course of a few hours, wherein Crystallization occurs. Fractional precipitation is brought about from salts by adding precipitants, which contain ions which form insoluble precipitates with the soluble metal ions or by the fact that complex salts by relatively rapid change in temperature, des pH value, the concentration or decomposed by the addition of foreign ions. The precipitation takes place in the generally in such a way that you have a calculated and sufficient amount of the precipitant adds, so that only a part of the dissolved substances precipitates, whereby one in the first fractions one Enrichment of the more difficultly soluble and increasingly more easily soluble components in the precipitation.

The surprising finding according to the invention now says that the type of precipitation of Precipitation by precipitants or by the addition of complex salts or the way in which the fractional crystallization is carried out, has a decisive influence on the effect of the separations is. You can improve the separation factors quite significantly if you have the precipitates as slowly as possible in the case of fractional crystallization or fractional precipitation of precipitates undertakes, and in many cases the separation is not only better if you instead of a momentary one Precipitation the precipitation is carried out gradually, for example in 10 minutes, but when you Spends 1 hour for the operation, but the separation effects are also improved if one for the change in the environmental conditions that cause crystallization or precipitation, not 1 hour, but several hours, possibly also

ίο Spends days or weeks.

A close study of the causes of this surprising and technically very important phenomenon has shown that it is boundary layer problems that give good separation factors in the case of rapid precipitation impede. There are essentially two kinetic processes that have to be taken into account are:

On the one hand, there are diffusion processes in the solid-liquid boundary layer for which there is enough time must be made in order to achieve good separation effects. Namely, with a fractional Crystallization or, in the case of a fractional precipitation, a crystal nucleus is formed, it surrounds itself as if from from fluid mechanics and from adsorption technology, with a static liquid film. In This so-called Prandelian boundary layer can only be exchanged by diffusion is known to be extraordinarily slow. A complete balance of concentration between the surrounding liquid and the liquid from which the boundary layer is formed, requires about one Time of at least several minutes. The initially emerging crystal nuclei are very strong on the poorly soluble component enriched, which inevitably results that the boundary layer in the Measures of crystal growth in this component must be impoverished. If you let this crystal go quickly continue to grow, it draws its substance from the boundary layer, which is depleted of the material that one to enrich crystal growth. So the crystal grows, especially if that is the case less soluble compound of the element to be separated is isomorphic with it, below Separation of more easily soluble substances.

However, the crystal growth can take place in a much longer time and accordingly the boundary layer in complete mass transfer occur with the surrounding solution, the crystal becomes uniform continue to grow and significantly improve enrichment.

As a second factor, it should be noted that at the interface between the precipitant and the solution, due to the existing concentration gradient, all elements that are present in the diffusion layer precipitate, ie the so-called »grape effect« counteracts the achievement of good separation factors. To avoid this adverse effect, it is necessary to ensure that in each separation stage between the solution and the precipitating agent concentration as small as possible, p _H - are present and temperature differentials, that the precipitating agent in a very fine distribution, z. B. sprayed or as an aerosol, and not added in large quantities or large drops, that the precipitation or solvent is added extremely slowly and that care is taken for the most intensive and rapid mixing between solution and precipitant.

A third, very important phenomenon should be considered in the case of precipitations: If a precipitation is carried out by slowly changing the environmental conditions, e.g. B. by acidifying, making alkaline, adding a precipitant or hydrolysis of complexes and if you want to pay attention to the above, then it is necessary to proceed extremely gently and slowly from the time at which the crystal nucleation begins. It is not sufficient, as in analytical and preparative chemistry, to regard the appearance of a visible cloudiness as the beginning of the precipitation. At this moment the particles are already about 10 ~ ⁵ cm in diameter and already consist of several thousand layers of molecules. When the particles grow to this size, all decisive errors may have occurred which, according to what has been said above, must be avoided if one wants to achieve good separation effects.

For the separation technique it follows that the point in time for the termination of the addition of the precipitant must be adhered to as precisely as possible. This can be done according to the invention by z. B. determined by preliminary tests under which conditions the visible cloudiness occurs. The critical threshold value for the start of the still invisible precipitation must, however, be earlier when the precipitant is added, and the addition of the precipitant must stop there. When using complexes of the type described, from this critical moment onwards, without the addition of further precipitating agents, a long-lasting formation of a precipitate occurs, which usually results in a very sharp separation of neighboring elements. On the other hand, it is also possible to proceed in such a way that the addition of the precipitant is not ended until the separation of the element to be separated can be recognized by the onset of turbidity or the Tyndall effect. In this case, however, if without the addition of further precipitating agents, the precipitation intensifying changes, e.g. B. p _H -value or the concentration of ions or complexes occur, they go beyond the optimal threshold value changes in environmental conditions by the addition of an agent, eg. B. an acid, a base or a complexing agent, are compensated. A particularly effective effect is also shown if the crystal nuclei formed are dissolved again by increasing the temperature slightly or adding small amounts of an appropriate solvent and freshly prepared crystal nuclei of uniform substance are added and these are used as nuclei for the precipitation or crystallization of the desired fraction.

Various measures have proven to be particular for carrying out the method according to the invention proved suitable, of which the following are particularly indicated:

Complex compounds, for example, which are particularly advantageous in their formation, are found to be particularly advantageous Time, e.g. B. a few hours or several days, possibly up to 4 weeks. Since the decomposition of these complexes also takes place relatively slowly, it is possible to reduce the decomposition of the To make complexes so slow that this process is much slower than the exchange of substances in the Prandel's boundary layer, so that the ideal separation conditions can be implemented very well.

Preferably, the reaction medium is, before it is subjected to gradual decomposition according to the invention, adjusted by a rapid change in the environmental conditions to such values for temperature, _pH value, the concentration of ions or complex compounds, etc., that even a subsequently made

ίο constant further changes in very small amounts and the interruption of this change when the optimal threshold value is reached leads to the separation of the first fraction. Particular care must be taken when setting and maintaining homogeneous environmental conditions beforehand, as the threshold values for the fractions of the individual elements sometimes only differ very slightly, e.g. B. of only a few hundredths of p _H units.

According to an advantageous embodiment, is made so slowly in the separation by fractional precipitation and fractional crystallization of the change in the environmental conditions under continuous intensive mixing of the reaction medium, the temperature not more than a maximum of 0.1 ° C per minute, the _pH value (eg. as by adding a precipitating agent) by no more than at most 0.1 p _H units per hour changed and the concentration of the solution present in the ions and / or complex compounds is varied by more than 1% per hour. Appropriately, you can use this very dilute solutions that z. B. less than 50 g / l, expediently between 1 and 10 g / l of the elements to be separated, calculated as oxides, contain.

As far as the gradual decomposition of the complex compounds is concerned, this is also preferably carried out so slowly that the mass transfer at the boundary layers of the crystal nuclei takes place faster than the crystal growth itself. B. may comprise a few hours to about 4 weeks or even more. In an analogous manner, complexes which decompose particularly slowly can be used, so that during the decomposition the mixing of the reactants is in any case faster than the decomposition of the complex compounds.
The separation process can be designed particularly favorably if water can be used as the precipitant. This is the case with compounds that hydrolyze when diluted with water and thereby form an insoluble precipitate of the elements to be separated.

It has further been found advantageous to effect the gradual decomposition of the complexes by a particularly slow addition of such a precipitating agents, which only differ in their composition, concentration, _pH value and temperature slightly from the solution of the compounds to be separated. In this case, of course, particular attention should be paid to the fact that the quantitative separation of the respective fraction is a decided time reaction.

The invention can also be implemented in that the solution of the compounds to be separated and the precipitant in a certain ratio at the same time, but in different

Place a precipitation apparatus with intensive stirring in a medium provided. Here, temperature _pH value and concentration may vary only up to the optimum threshold value, also, what is characterized ensures preferably that the aforementioned numerical values for the variation of temperature, p _H -value and the concentration can be maintained in the time unit.

If desired, the deposition of the solid can be slowed down by simultaneously with the precipitant a complexing agent as a solvent for the corresponding precipitate adds. This measure is also important in the event that the threshold value is unintentional should have been exceeded or that after the precipitation of a precipitate for removal about occluded or entrained foreign substances solvents are supplied, wherein at most, the aforementioned numerical values for the change in environmental conditions can be taken into account will.

A particular embodiment, the is characterized in that at the critical point in time, which is shortly before the z. B. by preliminary tests determined point in time at which, in the event of a change in the environmental conditions, a (through beginning Cloudiness or first crystal nucleation (which can be determined by the Tyndall effect) would be expected, crystal nuclei on the nature of the compounds to be deposited, preferably only the substance to be deposited containing solutions produced crystal nuclei in the finest possible distribution, optionally can also be applied to inert materials with a large surface area.

For a better understanding of the fractional precipitation or fractional crystallization through Inoculation-induced processes must be noted that nucleation from a solution is it can only occur through precipitation or through crystallization, if a supersaturated one Condition exists. A certain state of supersaturation is necessary, which is considerably higher than that Equilibrium is so that the precipitation begins. Then, however, it sets in suddenly and immediately leads to the precipitation of such large amounts of substance that the principle of the particularly slow precipitation can no longer be achieved. Therefore you have to determine by preliminary tests when this state of saturation is reached, and must be added the germs at the right moment prevent a state of oversaturation at all can occur.

The advantages of the separation method according to the invention are briefly summarized, including the following: By working in the ideal homogeneous medium, a temporally and spatially uniform medium can be achieved Achieve separation in the entire reaction medium. Especially when adhering to higher Temperatures you get well-formed crystals and thereby avoid gelatinous precipitates occurring adsorption effects. The appearance of mixed crystals or real compounds is reduced to a minimum. The present method has for large-scale application Separation and separation of various elements that have recently become more important great value. This results in particular from the fact that instead of a frequently repeated separating operation only a single one needs to be carried out in order to achieve an excellent separation factor to get. The method is quite general for all types of fractional separations Precipitation or fractional crystallization can be used and in no way depends on their presence

ίο particularly stable complex compounds bound. From the variety of possible applications that working in the ideal homogeneous medium opens up, are in the following exemplary embodiments, without restricting the invention thereto, some typical process variants for fractional precipitation with and without the use of complex compounds as well as for fractional crystallization, also by seeding with crystal nuclei explained.

example 1

Separation of the lanthanum
from a cerite mixture by basic precipitation

In the present example, is used as the starting material a cerite mixture obtained by the known method of basic precipitation is used, that by five-fold precipitation of the mineral acid salts of rare earths with aqueous or gaseous ammonia and 95% lanthanum, about 3% neodymium and 2% praseodymium contains. The working conditions for the separation according to the method of the invention were in detail the following:

There were 101 uses a chloride solution of the rare earth oxide containing 20 g per liter of solution and a _pH value of 3.8 was obtained. As initially introduced medium, 10 1 used a 5% ammonium chloride solution which has been adjusted with dilute ammonium hydroxide solution to p _H 7.3. 5% ammonium hydroxide solution was used as the precipitant. The medium presented was constantly heated to a selected temperature between 70 and 80 ° C and now at the same time in equivalent amounts and while maintaining the stated temperature between 70 and 80 ° C, the cerite chloride solution and the dilute ammonium hydroxide, sprayed in fine drops, at two distant Place the precipitation vessel dripped into the presented medium, which was at the same time kept in lively turbulent motion by an intensive stirrer. The dropped amount was Ceriterdenchloridlösung ml per hour 2000th the dropped amount of ammonium hydroxide has been so dimensioned that the _pH value exceeded 7.3 in the medium presented in any case. The amount of 5% ammonium hydroxide used was about 21. The entire precipitation took a little more than 5 hours. An easily settable, easily filterable precipitate was formed, which was separated from the filtrate by decanting and filtration. The precipitate was then washed with 2 ° / cent ammonium hydroxide solution, which was adjusted to p _H 7.3. This precipitate contained 5.4 percent by weight of the rare earths contained in the starting material, which when burned gave a black-brown oxide with 34.9% praseodymium and 65.1% neodymium in the lanthanum

409 599/30

was undetectable. The filtrate contained 94.6 ^fl / o of the rare earth oxides with 99.5%> La, 0.5% Pr and no neodymium.

This lanthanum was made from the filtrate by adding more ammonia to it Temperature between 70 and 80 ° C and under lively

haftem stirring precipitated, had to the solution a _pH value of 9.0. The filtrate then no longer contains any rare earths. The precipitate can be separated off in the usual way.

These test results are compiled in the following table:

sample Oxides
G Oxide paint Atomic weight La Pr Nd After five precipitations of the usual type
New method:
Precipitation 100
4.5
95.5 White-gray
Black brown
White 142.36
139.06 94.6
0.0
99.5 1.8
34.9
0.5 3.6
65.1
0.0 Filtrate

Example 2

Separation of the rare earths by fractional
Precipitation with the help of complex compounds

a) Separation

with the help of aluminum oxalic acid complexes,
Erbium-lanthanum separation

The analysis of mixtures of rare earths is extremely difficult. It therefore became the Proof of the good separation effects that can be achieved with the method according to the invention is relative easily analyzable mixture of two rare earths used, consisting of erbium, the one has a very characteristic spectrum, and is made of lanthanum, which has no absorption in visible light shows.

A solution was prepared containing La ₂ O ₃ and Er ₂ O ₃ in a ratio of 82:18. Oxalates were precipitated from this solution with the help of oxalic acid in the heat. These contained 63.51 g of rare earth oxides. They were dissolved in half a liter of a 1 molar aqueous solution of aluminum oxalic acid under heat. This acid, which is also known as aloxalic acid, is a defined complex compound of the formula H ₆ [Al ₂ (C ₂ OJ ₆ ] · 3 H ₂ O), which is called "matured", that is, a complex that is formed by complete, but particularly slow complex formation Complex, can be obtained, and the solution proceeds smoothly and quickly, leaving no residue.

After the solution had been heated to 70 ° C., a total of 685 ml of distilled water, which had also been preheated to 70 ° C., was added at a rate of 5 ml per minute with vigorous stirring. At the end of the addition there was a slight cloudiness, whereupon the further addition of distilled water was immediately interrupted. After ^{stirring for 1} hour at the same temperature, a precipitate was separated off which consisted essentially of erbium oxalate and contained 15.52% of the oxides originally present. A second fraction was also obtained at 70 ° C. by further adding at the same rate 47 ml of 10% oxalic acid, which represented 2.53% of the original amount. The two fractions taken together made up 18.05% of the original amount. The spectral analysis showed that it was pure erbium oxide. The atomic weight was 167.0, which corresponds exactly to the atomic weight of erbium. The lanthanum, in which no erbium was detectable by spectral analysis, was precipitated from the filtrate due to excess ammonium oxalate. This separation is thus quantitative.

b) Separation of a mixture that contains all
contained rare earths

A preparation like the one obtained from the technical preparation of thorium and cerium from monazite sand after these two elements have been separated, was brought into solution. It is one very complicated mixture, the quantitative composition of which corresponds to the analytical methods known to date Methods cannot be precisely determined. There are spectral lines and absorption bands of all known rare earths, both cerite and ytter earths.

From a chloride solution containing 100 g of rare earths, calculated as oxides, containing, were precipitated by precipitation with ammonium oxalate solution at a _pH value 3-4 the total rare earths as oxalates. The freshly precipitated oxalates, thoroughly washed out with distilled water, were then dissolved in a 1.6 molar aluminum oxalic acid solution at room temperature. 1500 ml of aloxalic acid solution were required for complete dissolution, and 24 hours were required for complete clarification.

The resulting solution, which, based on oxides,

Contains about 6 to 8 percent by weight of rare earths, has an unlimited shelf life, the stability of the in the Solution contained aloxates of the rare earths is however not very large, so that only diluting with Water at a temperature of 70 to 80 ° C is sufficient to cause the complexes to decompose. It is particularly noteworthy that the stability of the aloxates of the individual rare earths is very high is finely differentiated. The degree of dilution at which the precipitation of the oxalates of the individual rare earths occurs is characteristic of each element. It is possible in this way to find the rare earths in the Order of their atomic numbers, starting from the higher ones, to be precipitated according to the lower ones. There the rare earths show an extraordinary chemical behavior among each other, but it is not possible to obtain fractions with a single separation run that are similar to the one described above Erbium-lanthanum separation each contain only a single highly enriched element. But you get fractions in each of which one or two rare earths are strongly enriched, next to it but still contain other earths. Since such mixtures are not easy to analyze, only the atomic weight of each fraction was determined, from which it can be concluded which one

of the fourteen rare earths is each particularly highly enriched.

The following table shows the determined atomic weights of five fractions. Next to it is the respective main component of the fraction is indicated, each of which is also detected by spectral analysis could be.

of rare earths with the following composition were used:

Lanthanum 50%

Neodymium 30%

Praseodymium 10%

Ytter earth 10%

A quantity of chloride corresponding to 100 g of oxide of this rare earth was dissolved in 1700 ml of water ίο dissolved and poured into 1500 ml of an imolar aluminum oxalic acid solution while stirring vigorously. The solution remains clear if the addition is made gradually rather than abruptly. The education of the oxalate chloride complex of aluminum and rare earths does not take place immediately, but gradually. The solution must be left to stand for at least 24 hours for the complex to form

The precipitation was carried out in such a way that it is complete. This solution can then be heated to 70 to 80 ° C. at a rate of decomposition without adding the water. You digkeit as in case a) at 70 ° C, but immediately 20 is interrupted at 70 ° C for the following separation operation, if an incipient cloudiness is used. With vigorous stirring it will very slowly become noticeable. The precipitate is then amplified and added dropwise a warmed to 70 ° C Amjeweils and the precipitates could easily moniumoxalatlösung which are separated approximately 48 g (NHY ₂ C ₂ O ₄ in the decantation contains the size of the five liters, and a p _H. - Value of about 5, fractions varied between 0.2 and 20 g. Ins-25 added.

a total of 30 g had precipitated in the five fractions. The dropwise addition of the precipitant

There were no more ytter earths in the filtrate - the complex solution will be instructed immediately. The rare earth oxides contained therein broke when a beginning cloudiness or consisted predominantly of lanthanum, praseodymium and showing a Tyndall effect. Adding it drop by drop Neodymium, which is made by further gradual dilution 30 at a rate of about 2 ml per with distilled water at 70 ° C from each other minute. The precipitation then intensifies

fraction lot
G Atomic weight Head
component 1
2
3
4th
5 0.4
3.1
6.5
0.2
19.8 161.42
158.27
155.70
146.92
145.86 Terbium
Erbium
Gadolinium
Europium
Samarium

can be separated.

Example 3

gradually, and after about 30 minutes of intensive mixing at constant temperature, the Precipitation of the first fraction ended. The precipitate is very easy to settle and can be removed by decanting separated and purified by filtering and washing with dilute ammonium oxalate solution will. The operation just described is repeated with the clear filtrate. It will

Separation of rare earths via complexes
with multiple components

The oxalates of rare earths are dissolved in concentrated solutions of aluminum compounds, with novel aluminum oxalic acid complexes with 40 built-in mineral acid ions which are again diluted at 70 ° C. with vigorous stirring. Another ammonium oxalate solution added and with beginfacher it is if one z. B. the addition of the precipitant acid nitrates or chlorides of rare earths to aluminum oxaline nender turbidity is interrupted. The precipitate increases again and both solutions in not too dilute, z. B. 1- ™ in the course of about 30 minutes, and the up to 2 molar solution is obtained in this way. The aluminum salt 45 second fraction. In this way, a total of or the aloxalic acid must always be ^{precipitated in excess of five} fractions. The result of this

be at hand. If the aluminum oxalic acid is made properly, i. H. had matured long enough no deposits of insoluble oxalates during this mixing.

From such solutions one can get the rare earths by adding oxalic acid and mineral acid gradually decompose, and precipitates are obtained which are strong in the individual fractions Enrichments of individual rare earths, from scandium and yttrium, starting with the elements with ordinal numbers 71 to 57. When using the most ideal homogeneous conditions possible according to the invention, very good separation effects can be achieved. Depending on the size of each Fractions while maintaining homogeneous conditions, very slow working method and more intensive By mixing, fractions can be obtained after only a single further reprecipitation contain individual rare earths in high purity.

A special example is given below in which chlorides are used as the starting material

suches are summarized in the following table.

Frac
tion lot
of
Precipitation
by means of
ml lot
the
fraction
Weight
percent composition 1
2
3
4th
5 623
1171
312
457
860 16.4
13.2
19.2
42.0
9.2 Samarium + ytter earth
with some neodymium and
Traces of praseodymium
Neodymium with about IVs%
Praseodymium, free from
Ytter earths
Praseodymium with traces of Nd
Lanthanum with about 0.5%
Praseodymium and traces
Nd
Pure lanthanum, at least
at least 99.99%, atom
weight 139.00 100.0

15 16

This separation is even more effective than that shown in the skin, and again in the crystallization vessel Basic precipitation described in Example 1. a rate of about 1 ° C per hour to

The process is extremely versatile, up to the onset of the first crystal nucleation, because besides oxalic acid also tartaric acid and this is cooled to 18 ° C, which produces praseo-citric acid and a whole range of other dymammon nitrates of about 92% purity receives,
and tribasic organic acids and, in addition to aluminum, fractional crystallization is carried out in the

minium also chromium, molybdenum, vanadium, uranium described above, but one etc. form similar complexes and because, in addition, the slow cooling when reaching a Temseltenen Ground practically all elements that interrupt the water temperature of 32 ° C and form fine-insoluble oxalates with 0.5 g, similar to the rare lanthanum ammonium nitrate germs that are ground with Earths can be separated. In this way some concentrated nitric acid has been made into a paste, z. B. the separation of calcium, strontium, barium, inoculated and then under for 12 to 18 hours Radium or of iron, cobalt, nickel, the platinum- intensive stirring at the temperature of 32 ° C metals that keep elements of the manganese group possible, the first fraction is 95 to 99% pure and on the other hand also the separation of zirconium, Haf-15 lanthanum ammonium nitrate. Further work-up on nium. Niobium, tantalum, gallium, indium, thallium etc. pure praseodymammon nitrate as the second fraction

takes place in the manner previously described.

Example 4 The separation of

Zirconium and hafnium through fractionated crystalline

Separation of the earths by fractional _{20 sation of the amrnom- um} . _or potassium double fluorides

Crystallization of solutions possible. While according to this in the literature

According to the principles of the ideal homogeneous written method, only after 70 to 100 times In the medium, practically all separations are recrystallized with a hafnium-free top fraction Chemically similar elements is obtained by fractionated, it succeeds already in the first Frak crystallization to improve significantly, especially 25 tion, to obtain crystals of the zirconium compound, the if you consider the selectivity of the crystal precipitates are almost free of hafnium. The prerequisite is all through Inoculating with the "right" germs, while doing the same thing as described above supports. In this way, z. B. from lanthanum way with hafnium-free zirconium ammonium fluoride-praseodymium-ammonium nitrate inoculated even in a single crystal.

Crystallization from aqueous solution of lanthanum up to 3 ° In a completely analogous manner, one can use the fractionated Gain 99% purity. Crystallization as "ideal" selective crystallization

A mixture of 100 g lanthanum ammonium nitrate and carry out, in the barium-radium separation the 100 g praseodymammon nitrate in 11 water bromides, in the niobium-tantalum separation with the and this solution on the water bath until the potassium double fluorides etc.
A honey-like consistency is obtained, 35
then with 100 cm ^{3 of} concentrated nitric acid Example 5

(d : = 1.41) dissolved and separated from elements of the platinum groups with water to 500 cm
thins. This solution is on the water bath so ⁶ _{,, u} . , _r .. ,, ^{6 1} ^

1 i_ j ,, λ .... ". ,. by basic precipitation

evaporated for a long time until an ^o

shows fine crystal skin. One now brings up against * ° A particular difficulty has caused up to now Heat emission well protected crystallization vessel technically the separation of the platinum and palladium and sets on a temperature group while stirring vigorously. You can now get through the chlorides temperature of 50 ° C. From this point on, basic precipitation becomes similar to the rare earths in very slowly, e.g. B. with no more than 1 ° C per a single, at most two levels, in the highest Cooled hour and this process can be maintained up to 45 purity. When adding reaching a temperature of 27 ° C, where caustic soda or ammonium hydroxide falls first the first visible nucleation occurs. Then palladium, then in turn the other becomes platinum For 3 to 4 hours with continued rest metal while the platinum is in ren held at this temperature, whereby the solution remains.

first fraction of lanthanum _{ammonium nitrate La (NO 3} ) ₃ 5o It was 11 of a chloride solution, which in the

• 2 NH ₄ NO .; · 4H ₂ O with a purity of 90 to chlorinating roast obtained from platinum waste

95% is eliminated. The crystal slurry is made at 27 ° C and contained 40 g of platinum metals per liter

filtered off and used by washing with 30 cm ³ concen- tration,

trated nitric acid of occluded praseodymium £ ^ _e Lö _sun g contained ·
ammonium nitrate exempt. Filtrate and Wash Liquid 55

are combined and in the crystallization vessel again 83% platinum = 33.20 g

while cooling with no more than 1 ° C per palladium 11.6% = 4.64 g

Gradually cooled from 25 to 20 ° C. for an hour, with rhodium 5 4% = 2 16 g
at what temperature the first nucleation can be determined. This gives a medium ^6o The _pH value was this chloride solution 5. As a preliminary fraction, the Laid of 30% and 70% lanthanum praseodymium medium 11 was a 2.5% strength sodium Consists. The crystal is used again boiled down to 25 ° C chloride solution, which was heated to 90 ° C and introduced, separated at this temperature and was adjusted with a _pH value of 7.0.
washed a little concentrated nitric acid. A 0.1N sodium from the combined filtrate and the washing liquid ⁶ 5 hydroxide solution was used as the precipitating agent. The weakly acidic solution obtained is concentrated on the one hand to precipitate praseo chloride solution and the basic sodium dymammonium nitrate on the water bath to 30 ° C hydroxide solution on the other hand, both to 90 ° C, until a fine one holds again when blowing, were simultaneously on two different ones

Was locations of the precipitation vessel is added dropwise under stirring busiest, wherein strictly ensured that the p _H -Wert7 has not been exceeded and entered no abrupt changes in the parameters. Around 150 ml of the chloride solution of the platinum metals were added dropwise per hour, so that the entire precipitation operation took about 6V2 hours. The amount of dropped aqueous sodium hydroxide solution was controlled not by rate measurement, but only by measurement of the p _H -value in the precipitation vessel. The precipitate formed was easy strip and could be washed out 7 by decantation followed by filtration and washing with 1 ° / cent sodium chloride solution at p _H. This precipitate contains the rhodium. The filtrate, which together accounted for with the washing water an amount of more than 21, was dropped again in a medium placed, which again consisted of 2.5 ° / cent sodium chloride solution and was adjusted with a little sodium hydroxide solution to p _H 8.5. The same sodium hydroxide solution was used as the precipitant as in the first precipitation. The precipitation temperature was again 90 ° C. There were about 300 cm ³ platinum-palladium chloride solution was dropped per hour and at the same time so much η 0.1 sodium hydroxide solution in that the p _H -Wert8,5 remained constant. The whole felling operation again took six and a half hours. It was re-obtain an easily filterable, easily deductible precipitate sodium by decanting and filtration and subsequent washing with 1% sodium chloride solution of p _H was purified 8.5. The filtrate contained practically all of the platinum, which in a known manner by reducing agents such. B. metallic tin, can be precipitated in elemental form. The result of this experiment is summarized in the following table.

Frac
tion p _H value lot
G composition 1
2
3 7.0
8.5 2.2
4.7
33.1 99.9% rhodium and about
0.1% palladium
99.96% palladium,
0.04% platinum and traces
Rhodium
99.97% platinum and traces
Rhodium 40.0

The separation of the iridium is just as effective and simple.

Also the extraordinary technical difficulties in the separation of the transuranic elements can just as with the rare earths by means of the described separation method of the »ideal homogeneous Medium «while achieving high separation factors and a high degree of purity. Closing Hch also arise in organic chemistry in all cases in which a fractional crystallization is used for the purification of certain substances by the method according to the invention significant improvements, e.g. B. in the separation of mixtures of carboxylic acids from crystallizable Sugars, amines, highly condensed aromatics and their derivatives, etc.

Example 6

Cobalt-nickel separation by diluting complex solutions

From a mixture of freshly precipitated, unaged cobalt and nickel oxalate in one composition corresponding to 42.3 g of nickel oxide and 47.7 g of cobalt oxide is obtained by dissolving in about 31 In a molar aluminum oxalic acid solution, a stable solution of complex cobalt-nickel aloxate can be obtained. By slowly adding water at room temperature while stirring vigorously, the Causes decomposition of the complex. The less stable nickel aloxate is formed first precipitated by nickel oxalate while the more stable cobalt aloxate remains in solution. At very slow speeds Working, constant stirring and careful dosing to achieve the optimal threshold value necessary amount of water, which is determined beforehand by preliminary tests, is the first fraction Composed of practically cobalt-free nickel oxalate. One obtains in this way after adding about 80 ml of water in 1 hour more than 90% of the nickel in the first fraction in a cobalt-free state.

The filtrate becomes noticeable by the slow addition of water until just before the onset of a noticeable Turbidity precipitated a second fraction, which accounts for all of the remaining nickel with a major proportion contains cobalt. The filtrate contains completely nickel-free cobalt, which is produced by oxalic acid is precipitated as cobalt oxalate. The results obtained are summarized in the following overview.

35

40

45 starting solution

50 VoNi + 50 VoCo

as sulfates

fraction

2 3

Precipitation in the ideal homogeneous

Medium amount

(Gram Vo Ni Vo Co

Oxide)

41.6

7.5

40.8

99.12

9.44

0.874 90.60 99.44

In contrast, according to the best currently known inorganic separation method,, and by precipitating cobalt as basic cobalt sulphate from a cobalt-nickel sulphate solution 50:50 with ammonia in the best case only after the third fraction a degree of purity of the precipitated Cobalts of 98%, while the nickel recovered from the filtrate is still 2 to 3% Contains cobalt.

Claims (3)

Patent claims: 1. A method for the separation of difficult to separate compounds by fractional precipitation or fractional crystallization, with the exception of the separation of niobium and tantalum by fractional precipitation via their oxalic acid complexes, characterized in that the changes in the milieu conditions serving to separate fractions, namely concentration of those involved components and / or _pH-value and / or temperature, in very small amounts and in temporal and spatial respect in continuously running, ie non-abrupt manner 409 599/30 & are effected and that these changes when the optimum threshold value is reached respective separation stage, the one immediately before the visible beginning of the first crystal nucleation the fraction to be separated is reached, can be interrupted until the separation of the separated fraction has been completed while maintaining the threshold value, after which the remaining medium to the eventual Obtaining further fractions is treated further in an analogous ίο manner. 2. The method according to claim 1, characterized in that the environmental conditions (concentration of the components involved and / or _pH-value and / or temperature) under permanent thorough mixing of the medium are changed in such a way to very small amounts, that the temperature at not more than a maximum of 0.1 ° C per minute, the _pH value (eg. as by adding a precipitating agent) by no more than at most 0.1 p _H units per hour and the concentration of the ions present in the solution and / or complex compounds is varied by a maximum of 1% per hour. 3. The method of claim 1 or 2, characterized in that the critical for the fractional precipitation or crystallization environmental conditions (concentration of the components involved and / or _pH-value and / or temperature), in particular the optimum threshold or the first Einritt Crystal nucleation, the rate of formation of the solids to be deposited, etc. can be determined by preliminary tests before the actual separation operation. 4. The method according to any one of claims 1 to 3, characterized in that is initially set by rapid and spatially uniform change in the environmental conditions to such values for the concentration of the components involved, the _pH value and the temperature before the fractional deposition, the medium in which the constant further change in very small amounts and the interruption of this change when the optimal threshold value is reached leads to the separation of the first fraction. 5. The method according to any one of claims 1 to 4, characterized in that the fractionated Precipitation from salt solutions is effected by ion reactions known per se, wherein the precipitant is gradually added either in very small amounts or by hydrolysis is generated in the solution itself. 6. The method according to any one of claims 1 to 4, characterized in that the fractionated Precipitation from solutions of such complex compounds is effected with steady Changing the environmental conditions in very small amounts are capable of either connections to split off the elements to be separated off directly or as a precipitant for the to split off effective connections and thereby precipitate the elements. 7. The method according to claim 6, characterized in that for fractional precipitation Salt solutions of the elements to be separated are used, which are initially created by means of a complexing agent, which may already be a complex compound itself, such as aluminum oxalic acid, in complex compounds with as different complex formation constants as possible be transferred, after which with constant change of the milieu conditions in whole small amounts cause gradual decomposition of the complex compounds. 8. The method according to claim 6 or 7, characterized in that the gradual decomposition the complex compounds extremely slowly, preferably while maintaining a decomposition time of z. B. a few hours up to four weeks. 9. The method according to claim 6 or 7, characterized in that particularly slowly decomposable Complex compounds of the elements to be separated with a decomposition time of z. B. a few hours to four weeks and mixing the reactants in any case faster than the decomposition of the complex compounds is carried out. 10. The method of claim 6 or 7, characterized in that the solution of the complex compounds are gradually added in very small aliquots precipitating agent, which in respect to composition, concentration, _pH value and temperature of the solution to be separated complex compounds only slightly differentiate. 11. The method according to any one of claims 1 to 4, characterized in that the fractionated Precipitation by gradually diluting the solution in very small amounts a hydrolyzable compound of the elements to be separated is effected. 12. The method according to any one of claims 1 to 11, characterized in that for the fractionated Precipitation uses very dilute solutions of compounds of the elements to be separated below 50 g / L, suitably between 1 and 10 g / l of the elements concerned, calculated as oxides. 13. The method according to any one of claims 1 to 12, characterized in that for the fractional precipitation the solution or the precipitant or both in the finest possible distribution, z. B. in the form of fine drops or in a sprayed state, are fed to each other. 14. The method according to any one of claims 1 to 13, characterized in that the solution and the precipitating agent are fed simultaneously, but at different points, into a presented medium with intensive mixing in such a ratio, expediently determined by preliminary tests, that the environmental conditions ( concentration, _pH value, temperature) only in very small amounts change. 15. The method according to any one of claims 1 to 14, characterized in that to increase the purity of the solid to be separated at the same time as the precipitant Complexing agent added or after as a solvent for the resulting precipitate successful precipitation of a precipitate to remove any occluded or entrained Foreign substances such a solvent is introduced. 16. The method according to any one of claims 1 to 15, characterized in that the additive of the precipitant is only ended when the separation of the fraction has already started Turbidity or a Tyndal effect can be seen and that without the addition of additional precipitant changes in the environment beyond the initial nucleation by adding an antidote, e.g. B. an acid, a base or a complexing agent, be compensated. 17. The method according to any one of claims 1 to 4, characterized in that the fractionated Crystallization from solutions or melts due to an extremely slow change in temperature or extraordinarily slow removal of the solvent and when reaching the optimal threshold is interrupted. 18. The method according to any one of claims 1 to 17, characterized in that shortly before the z. B. the occurrence of the first nucleation of the medium determined by preliminary tests Crystal nuclei of the type of compounds to be deposited, preferably finely as possible Distribution, to be added. Considered publications:
Riesenfeld, Inorganisches Chemisches Praktikum, 6th edition, 1925, p. 75; K. A. Hofmann and U. Hofmann, Inorganic Chemistry, 11th Edition, 1945, p. 266; Henglein, plan of technical chemistry, 1949, pp. 94 to 95; H ο ü en, methods of organic chemistry, 3rd edition, 1943, vol. 1, p. 548. 409 599/308 6.64 © Bundesdruckerei Berlin