NO126748B - - Google Patents

Description

Procedure for the separation of metal salt mixtures.

The present invention relates to a

method for separating metal salt mixtures in homogeneous solution in a dielectric under the influence of an electric field.

A widely used electrical separation method is electrophoresis. It is based on the fact that the migration speed of ions of different size or different charge in a solution of a certain viscosity in a given electric field is different. With prolonged exposure to the field, the electrophoresis results in an excellent separation of differently charged and large ions, such as e.g. the different egg white varieties. However, it is less suitable for the separation of simple metal ions.

It has now been found that the ions of different metals can be separated perfectly in solution, if not the migration speed of the ions but the stability of complex metal compounds is used as a separating agent.

This new method excels

in that the metals are separated in the room by applying an electric field which is rectified with the increase in concentration in the complex-forming base in a solution, where free convection is prevented, and where a drop in concentration is induced in a complex-forming base, which itself or with the help of an additional complexing base can form anionic complexes with at least one of the metal ions present.

The following facts are known and exploited

partly in analytical and technical chemistry: If a solution of different metal ions is successively added to

complex, the different metal-

ions are eventually transferred in complex compounds, and in the same order as the stability decreases in the resulting metal complexes. The relationship for a metal-complexer system is most simply characterized by the total analytical concentration of the complexer required at a certain pH, which is just sufficient to transfer 50 percent of the metal in the corresponding anionic complexes.

The inventive idea underlying the new method is based on the utilization of the spatially separated complex formation of the various metal ions in a spatially varying concentration of the complex former. Decisive for the utilization of this theory for the separation of metal salt mixtures is the practical realization that, under the influence of an electric field, it succeeds in leading the metal ions to the various complex-former-concentration sites in space that are characteristically assigned to them.

In order for a complexing molecule to be considered for the present separation method, it must be able to give off protons during complexation, i.e. it must be an acid. In the most common case, the formula HbB will therefore be suitable for a suitable complexing molecule, whereby HbB means a neutral molecule, which, during the release of a maximum of b protons, can pass into the complexing base B—<b> in the chosen solvent system .

According to the following equilibria, the molecule HbB in solution can emit resp. absorb protons

H;B<i->b + i S = B-b + i HS+ . A;.

Here means:

S the solute molecule

A; the equilibrium constant that is added

the reaction Ai = (B) (HS)1 (H;B)—<1>

in an integer that can assume the value 1,

2..b..b+n

n the number of protons that the complexing molecule can occupy in the chosen one

solvent system.

B—<b>the complex-forming base, which corresponds to a complex-forming molecular acid, and which is characterized by the fact that it no longer emits protons during the reaction with metal ions during the formation of complex ions, and which in the description and claims is only called complex-forming form the base.

The complexing base B—<b> is of great importance, as the degree of complexation with a metal is directly dependent on its concentration. It is the size at which there must be a drop in concentration for the present method. Hereby, it is indifferent whether the drop in concentration of the complexing base is achieved by variation in space of the complexing molecule's H,B concentration at constant pH or by a corresponding variation of the pH value or of the concentration of an auxiliary metal, which is suitable for complex formation, at constant concentration of the complexing molecule or by simultaneous variation in space of the three sizes.

If there are metal ions in this solution, where there is a concentration drop of a complexing agent, these will be present in the areas with low complexing agent concentration as simple or complex cations, and in the areas with high complexing agent concentration as metal-containing complex anions. If the metal ions are optionally added in the form of complex soluble compounds, complex rearrangements will occur. Under the conditions of the separation operation, the added complex compounds must thus not be more stable than the complexes to be formed. Under the influence of an electric field, which is applied in accordance with the increase in concentration, all areas of the solution with low complex former concentration will become poorer in metal, as the metal-containing cations originally present or newly formed during the process migrate in the direction of increasing complex former concentration. The total metal flow is thus aligned with the field in such areas. Conversely, the areas with a high complex-former concentration will become poorer in metal, as the originally present or newly formed complex anions during the process migrate in the direction of decreasing complex-former concentration. In such areas, the total metal flow thus has the opposite direction to the field. At the location where the metal is partly present as a cation and partly as a complex anion, the total metal flow is 0, so that the metal is enriched at this location. Since these places with complexing concentrations which are characteristic of the partial complexation of a metal, in the solution used according to the invention appear separately in the space for the different metals, the separation of the different metals is a given. It is therefore irrelevant where the metal ion mixture is introduced into the complex former's concentration drop.

In simpler separation operations, such as analytical separation of metal ions using paper strips in the device according to fig. 1, it will be appropriate to produce the drop in concentration in the complexing solution by the same electric field which causes the separation of the metals.

To enable respectively to facilitate certain at-separations, auxiliary complex formers can possibly be added in a constant or spatially variable concentration. This e.g. to prevent precipitation or to transfer uncharged complexes in anionic mixture complexes. Such auxiliary complex formers do not necessarily have to form anionic complexes with the metal ions to be separated.

The following list contains examples of complex formers or auxiliary complex formers, which can be used for the separation of metals according to the present method: Water, hydrohalic acids, rhodanic hydroic acids, hydrocyanic acid, carbonic acid, nitric acid, sulfuric acid, phosphoric acids such as trimetaphosphoric acid, tripolyphosphoric acid, saturated and unsaturated aliphatic, aromatic and hydroaromatic carbonic acids, f e.g. acetic acid, fluoroacetic acid, α-chloropropionic acid, oleic acid, succinic acid, sebacic acid, maleic acid, benzoic acid, toluic acid, naphthoic acid, cyclohexanecarboxylic acid, oxalic acid, hydroxycarboxylic acids of aliphatic, aromatic and hydroaromatic origin, e.g.

lactic acid, gluconic acid, tartaric acid, citric acid, sulfosalicylic acid, salicylic acid, 1-hydroxy-cyclohexanecarboxylic acid-1, aliphatic, aromatic and hydro-aromatic aminocarboxylic acids, such as e.g.

glycocol, (3-alanine, iminodiacetic acid, nitrilotriacetic acid, ethylenediaminotetraacetic acid, anilinideacetic acid, anthranilic acid, anthranilic acid-N-diacetic acid, 1,2-diamino-cyclohexanetetraacetic acid,

aliphatic, aromatic and hydro-aromatic aminohydroxycarboxylic acids, such as e.g.

Hydroxyethylenediaminetriacetic acid, Bis-((3-hydroxyethyl)-glycocol, N,N-Bis-((3-hydroxyethyl)-anthranilic acid, N-(2-hydroxycyclohexyl)-ethylenediaminetetraacetic acid,

ketocarboxylic acids, e.g.

pyruvic acid, levulinic acid,

phenol, e.g.

phenol, pyrocatechin, pyrocatechin disulfonic acid, chromotropic acid, dicarbonyl compounds, e.g.

acetylacetone, benzoylacetone, benzoyl-trifluoroacetone, 2-furyltrifluoroacetone, ditenoylmethane, trifluoroacetylacetone,

thenoyl trifluoroacetone,

hydroxyazo compounds, e.g.

nitrodiazoic acid >. |3-naphthol, nitrodiazo acid >■ a-naphthol, 0,0'-dihydroxyazo compounds, heterocyclic compounds, e.g.

8-hydroxyquinoline, 8-hydroxyquinoline-5-sulfonic acid, 2-(2-hydroxyphenol)-benzthiazole, 4-hydroxybenzimidazole, 2-methyl-4-hydroxybenzimidazole, proline, tryptophan, amino-barbituric acid-N,N-diacetic acid.

As only auxiliary complex formers, in addition to the above complex formers and auxiliary complex formers, e.g. a. The following should be discussed:

Ammonia

organic amines, e.g. methylamine, triethylamine, diisopropylamine,

ethylenediamine, triethylenediamine, cyclohexanediamine-1,2, pyridine, quinoline, ct-dipyridyl, imidazole.

The new method allows analytical separation of chemically very similar metals, e.g. of alkaline earth metals, trivalent light metals, the rare earth metals, the heavy metals, especially also the related heavy metals from the iron group, as well as their mutual mixtures or mixtures with other metals.

During the use of layers, which prevent free convection and form a separation in the room, such as e.g. diaphragms, the method can also be used for preparative separation of metals. This can possibly t. 0.

m. is performed continuously.

For the practical application of the principle according to the invention for the separation of metal salt mixtures, an apparatus is used, which comprises the following main components: anode compartment, cathode compartment and electrode space. The shape of these device parts is usually not critical and depends on whether stationary or continuous work is to be done. The construction material should consist of materials that are not attacked, e.g. glass, enamelled iron or aluminum coated with non-conductive synthetic resin.

In the simplest cases, e.g. for analytical purposes, the two electrode compartments consist of square shards of glass.

In the anode compartment A (fig. 1), the complex destroyer is introduced, which contains ions, which can enter into more stable compounds with the complex former bent for the separation than the metals to be separated. In practice, the following will come into play: solutions of mineral acids, such as HC1 and heavy metal salts, such as FeCU. The cathode compartment K contains the complexing solution (e.g. disodium hydrogen nitrilotriacetate) and possibly also an auxiliary complexing agent.

The most important part of this apparatus is the interelectrode space, as the separation of the metal salts takes place there. This includes a liquid volume, in which the metals in question (e.g. Cu, Ni, Ce etc.) are dissolved, as well as a fixed ion-permeable filler body, which at least prevents free convection of this solution parallel to the electric field, so that the drop in complexing base concentration that will later be induced (under the influence of the electric field) must last for a longer time. The interelectrode space is located in a cooling bath, which dissipates the heat generated by the flow of current.

In the simplest (and for qualitative analyses, most common) case, this "fixed filler body" is a strip of paper or PVC fabric, which is laid from bath A to bath B (see fig. 1). The solution of the metal salts to be separated is dripped onto this strip (moistened zone indicated in the drawing with striped reference lines). The paper is then allowed to fully absorb from both sides the cathode space or anoderm solution, until the entire strip is moist. The electric field is then switched on, whereby the complex-former-base concentration drop automatically adjusts. The electric field is allowed to work for a short time (approx. 1/2 tu approx. 10 min., depending on the field strength). If the metal ions to be separated are strongly colored, one can see how separate thin lines are formed on the paper across the electric field, which lines remain in the same place even with longer exposure to the electric field. These lines constitute the accumulation sites for the individual metals. The paper is then removed from the device and quickly dried. (The colored strips can afterwards be extracted individually and optionally worked up quantitatively.) If the ions to be separated are uncoloured or very weakly coloured, the separation process cannot be seen. The paper must therefore, after drying, be sprayed in a manner known per se with a solution which forms colored compounds with the metal ions to be separated. This can e.g. be solutions of the following substances: tetrapotassium hexacyanoferrate, rubeanic acid and their salts, etc. (The resulting colored strips can optionally be processed further quantitatively.)

For the preparative separation of metal ions, an electrode gap is advantageously used, comprising a volume of liquid, in which the metals are dissolved and which is prevented from free convection parallel to the electric field, so that the complexing-base concentration drop, which is subsequently induced, remains for a longer time under the influence of the electric fields. Perpendicular to the electric field, the liquid is free to move. In practice, this electrode gap consists of e.g. of a trough located in a cooling bath and which is divided into narrow chambers by ion-permeable partitions, which lie across the electric field and prevent free convection. As material for these partitions, e.g. cardboard strips, sintered and porous Teflon foils or "accumulator partitions" come to mind. The solution of the metal salt mixture, which is to be separated, is introduced into this electrode space. The drop in concentration of the complexing base, which is to be induced along the electric field, is preferably provided by the same electric field which also causes the separation of the metals. However, it can also be induced in another way, as the solution with the desired complexing base concentration, e.g. is filled individually in each chamber. Under the influence of the electric field, the metal ions will separate from the original mixture and within a short time collect separately in certain chambers, where they remain for a longer time. The solution can then only be taken out individually from the individual chambers and worked up quantitatively.

The separation of the metal salts can also be carried out continuously. In this way, solutions with a corresponding mutually graded complexing base concentration as well as solutions of the metals to be separated are allowed to flow slowly through the individual chambers mentioned above. Under the influence of the electric field, the metals will be separated and accumulated in specific chambers, where they are continuously flushed with the flowing liquid into collection vessels, and where they can be processed further. In this embodiment, the chambers must be particularly long so that the metals are only flushed out when they are completely separated.

(Lit. E. Schumacher, Helvetica Chimica Acta 41, 1572 (1958) Stability Constants of Metal-ion Complexes with Solubility Products of Inorganic Substances, complied by Jannik Bjerrum, Gerold Schwarzenbach and Lars Gunnar Sillén, Special Publica-tions. The Chem. Soc, London, 1958 No. 6 and 7.)

The following examples reproduce certain embodiments of the invention, although it is not limited to these.

Example 1.

In that in fig. 1 sketched apparatus is filled in the anode compartment (A) with 0.5 n hydrochloric acid and in the cathode compartment (K) with a solution consisting of 0.5 n caustic soda and 0.2 molar disodium-hydrogen-nitrilotriacetate. A drop (approx. 0.05 ml) of solution containing 0.001-0.005 molar amounts of each of the chlorides or nitrates of the metal ions Fe (III), NI (II), Zn (II), is applied to the tape (B). Al(III), U02(II), Co(II), Cr(III) and Mn(II), so that a 2-3 cm long moist zone is formed in the middle. One end of the strip is then dipped into the anode solution and the other end is dipped into the cathode solution. The middle part of the belt (B) is immersed in the cooling bath (C) below the surface of an inert coolant. A completely inert liquid is used as an aid, e.g. carbon tetrachloride. Tetrachlorethylene, solvent naphtha, o-dichlorobenzene, xylol, dibutyl phthalate etc. can also be used. As soon as the two solutions from the electrode spaces have united by capillarity with the applied zone on the tape (B), a voltage of

200 V on the electrodes (Ei and E2), whereby

a current of approx. 10 mA (at 2 cm bandwidth and filter paper Whatman No. 1). During the separation, the amperage will increase slowly and after 2-5 minutes optimal separation is achieved. The strip (B) is removed from the device and dried as quickly as possible with hot air. The individual separated ions

will, if they are colored or form colored

complexes, partially be visible as less than 0.2 mm wide sharp lines. For

accurate identification of the metals, the strip is appropriately cut lengthwise and sprayed on from the microchemistry

known reaction solutions (potassium ferrocyanide, dithizone, morin, rubean hydrogen, etc.). During weak leaching of the ion bands, the colors or fluorescences characteristic of the metals will thereby form in the order indicated above.

The main part of the strip can then be cut crosswise and the individual parts can be extracted with 1 N hydrochloric acid, whereby solutions of the pure metals, which were present in the original mixture, are obtained. Once the exact location of the metals has been determined, the tape can

(B) of course by further tests, as long as these are carried out accurately

the same experimental conditions, for quantitative isolation of the metals are cut directly into the individual segments containing the metals.

Example 2.

Using the same apparatus as in example 1, 1 n hydrochloric acid is filled into the anode compartment and a solution consisting of 0.5 n caustic soda and 0.1 m disodium dihydrogen-ethylenediaminetetraacetate. The tape (B), which can also in this case consist of a polyvinyl chloride substance, is applied with a drop of a solution of Nd (III) -, Pr (III) -, Ce (III) - and La(III) chloride. When the electric field is applied, the four metals are separated and the identification and isolation of the pure metals follows as indicated in example 1.

Example 3.

Using the same apparatus as in example 1, 1 n hydrochloric acid is filled in the anode compartment and 11.6 n hydrochloric acid in the cathode compartment. The tape (B), which can also in this case be made of a polyvinyl chloride weave, is applied with a drop of a solution containing the ions Fe(III), As(III), Co(II)) and Cu(II), optionally while adding a little wetting agent. With the construction of the electric field, a complete separation of the four types of ions succeeds here as well.

Example 4.

In the same apparatus as in example 1, 0.5 n hydrochloric acid is filled in the anode compartment and a solution consisting of 5 n acetic acid and 5 m sodium acetate in the cathode compartment. The tape (B) is applied to a solution containing the ions UCMII), Fe (III), Cr (III) and Co (II). When an electric field is applied, the four ions are separated and form sharply shaped zones in the specified order. Identification and isolation are carried out as in the above examples.

Example 5.

In the same apparatus as in example 1, there is 0.5 n nitric acid in the anode compartment and 0.1 m disodium calcium methylene diamine tetraacetate solution in the cathode compartment. With an analogous method as in the previous examples, the ions Hg (II) and Cu (II) can be separated very sharply. In this arrangement, Cu(III), Pb(II) and Cd(II) will lie close to each other in the order mentioned.

Example 6.

Cu(II)-, Ni(II)- and Co(II) ions can be separated completely, when 0.1 m ferric chloride is used in the anode compartment and 0.1 m disodium calcium methylene diamine tetraacetate in the cathode compartment for the same method as described above .

Example 7.

In the same apparatus as described in example 1, 0.5 m HC1 is filled in the anode compartment and a solution consisting of 0.2 m diammonium dihydrogenethylenediaminetetraacetate, 2 m sodium acetate and 2 m acetic acid in the cathode compartment. By an analogous procedure as in the preceding examples, UC-2(II) and Cr(III), which are focused together, can be separated from all alkaline earth, earth and rare earth metal ions as well as from Mn(II), Fe, Co(II) , Ni(II), Cu(II), Zu(II), Cd(II) and Hg (II).

Example 8.

By an analogous method as in the above examples, by using 0.25 m HC1 and 11.25 m HF in the anode compartment and 0.3 m diammonium hydrogennitrilotriacetate in the cathode compartment, it is possible to separate Tb (III), Y(III), La( III) and Sr(II).

Under the same conditions, it is also possible to separate Tm(III), Y(III) and Sr(III).

Example 9.

By an analogous method as in the above examples and using 0.3 m diammonium dihydrogen |3', (3"-diamino-diethyl ether tetraacetate in the cathode compartment and 0.5 m HC1 in the anode compartment and at a field strength of 150 V/cm can Y(III), La(III) and Ba(II) separate within 5 min.If Sr(II) is also present in the mixture, this occurs together with barium.

Claims (2)

1. Method for separating at least one metal ion from a metal ion mixture in a solution, which is prevented from free convection and in which an electric field is set up to separate the metal ions in the room, characterized in that in the ion solution a concentration rise is induced in a complexing base, which itself or with the help of another complexing base can form anionic complexes with at least one of the metal ions present, and that the electric field is rectified with the concentration rise of the complexing base. 2. Method as stated in claim 1, characterized in that the same electric field is used for producing the concentration gradient of the complexing base and for the separation of the metals in the room.