Process and apparatus for the electrochemical separation of metal mixtures and metal alloys

Abstract

The process for the electrochemical separation of metal mixtures and metal alloys comprises the steps of dissoloving the starting material in an electrolyte, substituting the metals dissolved in the electrolytic solution in succession in accordance with their electrochemical potential by electrochemically less noble metals in each case and depositing them. The electrolytic solution containing the dissolved metals is passed continuously through several cells, connected to each other, in which the electrolytic solution is brought into contact with said less noble metals. Several of the metals dissolved can be substituted simultaneously by one or more electrochemically less noble metals. Metals that are deposited simultaneously together are separated electrolytically from each other, and metals which have again gone into solution are again substituted outside the electrolysis cells by said less noble metals and deposited.

Description

FIELD OF THE INVENTION

The invention relates to a process for the electrochemical separation of metal mixtures and metal alloys, and also to an apparatus for carrying out said process in practice.

The invention is applicable, in particular, to the recovery of heavy metals from waste scrap, the metal constituents in which, in particular, can increasingly pollute and poison the environment.

PRIOR ART

Processes are known with which a few relatively valuable metal compounds are electrolytically deposited and recovered from waste scrap, for instance, from used electric batteries, but all the other constituents are discarded and deposited on disposal sites.

SUMMARY OF THE INVENTION

The object of the invention is to provide a possibility with which at least the heavy metals contained in waste scrap can be separated and recovered for reutilization in an economic manner, i.e. with the lowest expenditure in terms of equipment and energy and as completely as possible so that they no longer have to be deposited in disposal sites and endanger the environment at such sites.

This is achieved with a process according to Patent Claim 1, in which an apparatus according to the apparatus claims can be used in an advantageous manner.

Expedient possible embodiments emerge from the subclaims.

In the practical embodiment of the invention, the different electrochemical properties of the heavy metals concerned, in particular their different electrochemical normal potentials according to the so-called voltage series, are exploited in each case in a technically surprisingly simple manner and without special consumption of energy. As is known, this phenomenon states that any metal is substituted in its metal salt solution by a so-called "less noble" metal having a lower electrochemical potential and is deposited as a metal with the acceptance of electrons, the less noble metal going into solution as a cation with the donation of electrons, a process which proceeds without external supply of energy.

DESCRIPTION OF THE DRAWINGS

The accompanying drawing shows diagrammatically possible embodiments for carrying out the invention in practice, in which:

FIG. 1 shows a battery of deposition cells connected in series,

FIG. 2 shows a deposition cell in one embodiment and

FIG. 3 shows a deposition cell in another embodiment.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

According to the above, the apparatus in FIG. 1 comprises a battery of deposition cells 1 to 11 which are connected in series and an electrolytic cell 12 disposed at the outlet. Here the cells 1 to 12 are each equipped with an inlet 20 and an outlet 21 and the cells 1 to 11 with a discharge device 22 for deposited metal.

In the embodiment of the cells shown in FIG. 2, the latter contain a meal Me which is stationary and has a particular electrochemical potential which decreases from cell 1 to cell 11 in accordance with the so-called voltage series as is indicated in the upper row in FIG. 1 with the appropriate symbols.

Apart from mercury, these metals may, for example, be formed in the shape of spheres as shown. These spheres, with a diameter of, for example, 3 to 5 cm, are loosely arranged in layers with interstices in between, beside and on top of each other and make possible a flow of the electrolyte which flows round these spheres.

The manufacturing material of the cells and connecting pipes must obviously be resistant and insensitive towards the electrolyte solvent. For this purpose, in particular, certain plastics, such as polyethylene and polypropylene, have proved particularly advantageous. However, natural materials with a continuous rubber coating may also be suitable for this purpose.

The electrolyte is obtained by anodic dissolution of the starting mixtures or starting alloys to be separated, for example, of the metals from used electric batteries, electronic printed circuit boards and other electronic scrap, and also used ice boxes and automobiles, in tetrafluoboric acid (HBF.sub.4) in which almost all metals are soluble.

This electrolytic solution is fed through the cell inlet 20 into the first cell 1 and then flows in succession through the cells 1 to 11 where it comes into reactive contact with the metal contained in each case therein. During this process, for example, in the cell 1, which contains mercury, gold dissolved in the electrolyte is deposited as a metal while an equivalent quantity of mercury goes into solution as a cation. In the cell 2, which contains silver, the mercury, which is more noble with respect thereto, is deposited from the electrolytic solution and an equivalent quantity of "Less noble" silver goes into solution as a cation. This is then deposited in the cell 3 by means of copper which, in turn, is deposited in the cell 4 by lead, and so on, until the electrolytic solution emerging from the last cell 11 has a content of heavy metals of only an equivalent quantity of zinc cations which can then be deposited electrolytically as metallic zinc in the electrolysis cell 12. It is, however, also possible to work up the dissolved zinc chemically, for example, by precipitation as hydroxide and reduction to metallic zinc. In this case not even electrical energy has to be expended to separate the starting mixtures.

Still less noble metals having a still lower electrochemical potential cannot be deposited directly from the electrolytic solution and remain dissolved as fluoborates. This solution then emerges from the apparatus at outlet 21 of the last cell. They are essentially alkaline earth metals and alkali metals, such as aluminium, magnesium, sodium, potassium, lithium, which, however, usually occur in the starting materials in only very small quantities and are worked up again by known technologies.

If, as in the cell embodiment in FIG. 2, the depositing metal Me is used in the form of spheres loosely arranged in layers on top of each other, it may be expedient to provide a vibrating device or the like which is set in operation from time to time in order to free the spheres from metal deposited at their outer periphery and to create free surfaces. The spheres themselves gradually shrink with progressive solution of their metal which can result in complete solution. The deposited metal which sinks downwards in the cell is then usually drawn off in the form of a crystalline sludge at the discharge device 22.

The rate of reaction is naturally dependent on the ion exchange surface available for the reaction and on the reaction time and can be accelerated by heating.

The modified embodiment of the deposition cell in FIG. 3 is suitable in particular for use in binary systems, but it can likewise also be used for a continuous operation. It consists of a tubular housing with an inlet 20 and an outlet 21 for the electrolytic solution and is equipped with a device 23 for metered injection of the depositing metal behind the cell inlet in the flow direction. It furthermore also has a discharge device 22 for deposited metal and may, in addition, be provided with a filter 24 upstream of the cell outlet 21 and with a stirrer 25 at the injection device 23.

If, for example, lead is to be deposited by means of zinc in this cell, fine zinc powder is expediently injected in excess through the injection device 23 while stirring with the stirrer 25 into the electrolyte which contains lead in solution and flows through the cell, in a manner such that a suitable reaction temperature is reached and maintained, but spontaneous reaction and overheating is avoided. Consequently, by suitably metering the zinc powder addition, the possibility is in a way provided for making the reaction proceed as fast as is desired. The lead drawn off at the discharge device 22 as crystalline sludge is virtually pure and contains less than about 1% zinc, which is composed of unreacted zinc powder and can be leached out with tetrafluoboric acid, possibly while heating. The electrolyte emerging again from the cell outlet 21 no longer contains any lead, but, on the contrary, a quantity of zinc ions, equivalent to the deposited lead, which can then either be deposited electrolytically as metallic zinc or chemically precipitated and further processed.

The filter 24 is intended to prevent zinc powder, injected in excess, and deposited lead being entrained with the electrolyte.

In the direction of flow behind the filter 24 and before the cell outlet 21, an analytical device 26 may furthermore be provided which can operate continuously and can continuously monitor the stream of electrolyte passing through for metal ions which it contains, in the example described, for lead and zinc ions, so that the zinc injection can also be metered in accordance therewith, and can, for instance, be increased lead ions appear.

Under certain conditions, particularly also as a function of the nature of the starting material to be processed, it may be expedient not to deposit the metals to be separated individually in succession as was described in connection with FIG. 1, but in each case to deposit a group of metals, a multiplicity of metals having an electrochemical potential corresponding to each other being substituted by one or more electrochemically less noble metals composed with all these metals and deposited, and this group of metals deposited together then being separated electrolytically or by another known metallurgical process. The metals which then go back into solution because of their lower electrochemical potential may then be deposited again on a metal which is in each case electrochemically less noble. Thus, it is possible, for example, to deposit simultaneously electrochemically noble metals, such as gold, mercury, silver and copper, by means of lead in a first group and less noble metals, such as lead, tin, nickel, cobalt, cadmium, iron and chromium in a second group by means of zinc which can then be deposited with other metals still present as a third group directly on a cathode or chemically precipitated. The fourth group then contains only base metals which cannot be deposited directly from the solution, such as aluminium, magnesium, sodium, potassium, lithium.

Obviously, depending on requirements and expediency, this division into groups of the metals to be separated can also be carried out more widely or more narrowly by carrying out, for example, a finer division into groups containing at most three cations.

In any embodiment it is always possible with the process and an apparatus according to the invention to separate metal mixtures and metal alloys from each other on the basis of the different electrochemical potentials of their metallic constituents without expenditure of energy so that the individual metals can be supplied for a reutilization, as a result of which not only are serious environmental problems solved in a simple manner but a material benefit can also be achieved.

In addition, because a complete separation of metal mixtures and metal alloys and a recovery of all their constituents is made possible on using the process according to the invention, waste products which were hitherto regarded as more or less valueless are, moreover, again providing to be a valuable source of metallic raw materials which had otherwise only to be imported from third countries and were thrown away after processing and use. With the invention it is therefore possible to create and maintain a true cycle of available metals in which only small losses which are unavoidable due to process engineering have to be replaced or supplemented.

This "recycling" of the materials used can also take place in an advantageous manner in the case of the electrolytic solvent if, for example, if tetrafluoboric acid is used, the acid, which is again produced in an equivalent quantity in the electrolysis of the zinc in the electrolytic cell 12, is fed back, if necessary after suitable purification, to the electrolyte preparation.

Claims

1. A process for the electrochemical separation of metal mixtures and metal alloys, which comprises dissolving the starting material in an electrolyte and substituting the metals dissolved in the electrolytic solution in succession in accordance with their electrochemical potential with electrochemically less noble metals in each case and depositing them.

2. The process as claimed in claim 1, wherein several of the metals dissolved in the electrolytic solution are substituted simultaneously by one or more electrochemically less noble metals and deposited.

3. The process as claimed in claim 2, wherein metals deposited simultaneously together are separated electrolytically from each other, metals which have again gone into solution being again substituted outside the electrolysis cell by electrochemically less noble metals in each case and deposited.

4. The process as claimed in claim 3, wherein the substitution metals which are less noble in each case and have gone into solution are deposited electrolytically at a cathode.

5. The process as claimed in claim 3, wherein the substitution metals which are less noble in each case and have gone into solution are worked up chemically.

6. A process for the electrochemical separation of metal mixtures and metal alloys, which comprises dissolving the starting material in an electrolyte and substituting the metals dissolved in the electrolytic solution in succession in accordance with their electrochemical potential with electrochemically less noble metals in each case and depositing them;

wherein several of the metals dissolved in the electrolytic solution are substituted simultaneously by one or more electrochemically less noble metals and deposited;

and the metals deposited simultaneously together are separated electrolytically from each other, metals which have again gone into solution being again substituted outside the electrolysis cell by electrochemically less noble metals in each case and deposited; and the substitution metals which are less noble in each case and have gone into solution are deposited electrolytically at a cathode;

the substitution metals which are less noble in each case and have gone into solution are worked up chemically and are deposited as insoluble salts and reduced to the metal.

7. The process as claimed in claim 6 wherein an electrolytic solvent which dissolves at least three metal cations simultaneously is used.

8. The process as claimed in claim 6, wherein a distillation of volatile metals is carried out before the electrolysis of the metals deposited simultaneously together.

9. The process as claimed in claim 6, wherein the electrolysis is carried out in a so-called DIETZEL cell with roller-type cathodes.

10. A process for the electrochemical separation of metal mixtures and metal alloys, which comprises dissolving the starting material in an electrolyte and substituting the metals dissolved in the electrolytic solution in succession in accordance with their electrochemical potential with electrochemically less noble metals in each case and depositing them;

wherein several of the metals dissolved in the electrolytic solution are substituted simultaneously by one or more electrochemically less noble metals and deposited;

and the metals deposited simultaneously together are separated electrolytically from each other, metals which have again gone into solution being again substituted outside the electrolysis cell by electrochemically less noble metals in each case and deposited;

and the substitution metals which are less noble in each case and have gone into solution are deposited electrolytically at a cathode;

the substitution metals which are less noble in each case and have gone into solution are worked up chemically and are deposited as insoluble salts and reduced to the metal; and a solution of the metals in tetrafluoboric acid is used as electrolyte.

11. A process for the electrochemical separation of metal mixtures and metal alloys, which comprises dissolving the starting material in an electrolyte and substituting the metals dissolved in the electrolytic solution in succession in accordance with their electrochemical potential with electrochemically less noble metals in each case and depositing them;

wherein several of the metals dissolved in the electrolytic solution are substituted simultaneously by one or more electrochemically less noble metals and deposited;

and the metals deposited simultaneously together are separated electrolytically from each other, metals which have again gone into solution being again substituted outside the electrolysis cell by electrochemically less noble metals in each case and deposited;

and the substitution metals which are less noble in each case and have gone into solution are deposited electrolytically at a cathode;

the substitution metals which are less noble in each case and have gone into solution are worked up chemically and are deposited as insoluble salts and reduced to the metal,

12. A process for the electrochemical separation of metal mixtures and metal alloys, which comprises dissolving the starting material in an electrolyte and substituting the metals dissolved in the electrolytic solution in succession in accordance with their electrochemical potential with electrochemically less noble metals in each case and depositing them;

wherein several of the metals dissolved in the electrolytic solution are substituted simultaneously by one or more electrochemically less noble metals and deposited;

and the metals deposited simultaneously together are separated electrolytically from each other, metals which have again gone into solution being again substituted outside the electrolysis cell by electrochemically less noble metals in each case and deposited;

and the substitution metals which are less noble in each case and have gone into solution are deposited electrolytically at a cathode;

the substitution metals which are less noble in each case and have gone into solution are worked up chemically and are deposited as insoluble salts and reduced to the metal, wherein the acid used as electrolytic solvent and again produced in an equivalent quantity during the electrolysis is fed back to the electrolyte preparation.

13. An apparatus for carrying out the electrochemical separation of metal mixtures and metal alloys, wherein several cells (1 to 11) through which the electrolytic solution can flow continuously are provided with a flow inlet (20) and a flow outlet (21) and also with a discharge device (22) for deposited metal and are connected at their outlet with the inlet of the subsequent cell in the flow direction and contain in each case a metal (Me) which comes into contact with the electrolytic solution and has an electrochemical potential decreasing from cell to cell in the flow direction.

14. The apparatus as claimed in claim 13, wherein the last cell (12) is constructed as an electrolysis cell.

15. The apparatus as claimed in claim 13, wherein the metals (Me) contained in the cells (1 to 11) are arranged in spherical form beside and on top of each other.

16. The apparatus as claimed in claim 15, wherein the cells are equipped with an analytical device (26) which monitors the stream of electrolyte continuously for metal ions in front of their outlet (21).

17. The apparatus as claimed in claim 13, wherein the cells through which the electrolytic solution flows continuously are provided with a device (23) for the metered injection of a metal behind the cell inlet (20) in the flow direction and also, behind that in the flow direction, with a discharge device (22) for deposited metal, and with a filter (24) in front of the cell outlet (21) (FIG. 3).