WO1995024518A1

WO1995024518A1 - Electrolysis process for regenerating a ferric chloride or sulphate solution, in particular for spray etching steel

Info

Publication number: WO1995024518A1
Application number: PCT/DE1995/000294
Authority: WO
Inventors: Uwe Landau; Sigrid Herrmann
Original assignee: Mib Metallurgie Und Oberflächentechnik Und Innovation In Berlin Gmbh & Co.
Priority date: 1994-03-07
Filing date: 1995-03-06
Publication date: 1995-09-14
Also published as: DE19532784A1; DE59504691D1; EP0748396B1; DE19532784C2; EP0748396A1

Abstract

An electrolysis process for regenerating a ferric chloride or sulphate solution (etchant), in particular for spray etching steel, is disclosed. The etchant to be regenerated continuously flows through the anode chamber (17) of an electrolytic cell (10) whose cathode chamber (14) is filled with a diluted conductive acid. Anode and cathode chambers (12 and 14) are separated by a cation exchange membrane (16) through which Fe(II) ions, excess Fe(III) and dissolved non-ferrous metals, in particular nickel and chromium ions, reach the cathode chamber (14), while Fe(II) ions are oxidised into FE(III) ions at the anode. The metals accumulated in the catholyte preferably precipitate as a powder in the cathode chamber (14) or are electrolytically precipitated in a subsequent electrolytic cell whose cathode and anode chambers are separated by an anion exchange membrane. This process allows the etchant to be continuously regenerated in a closed circuit, ensures the depletion of non-ferrous metals and excess iron, as well as the electrolytic precipitation of the depleted metal ions.

Description

Electrolysis process for the regeneration of an Exsen III chloride or iron III sulfate solution, in particular for spraying steel

description

The invention relates to an electrolysis process for regenerating an iron (III) chloride or iron (III) sulfate solution (pickling), in particular for spraying steel, according to the preamble of claim 1.

When spraying or pickling steel or nickel-based materials using an iron (III) chloride solution (pickling), mainly nickel chloride is formed in addition to iron (II) chloride, which dissolves together with that from the steel or nickel-based materials

Enrich non-ferrous metals such as chrome, nickel, cobalt, manganese, vandium, copper, tin and lead in the pickling solution. For the

The etching speed and the sharpness of the contours of the structures to be etched are the content of iron (III) chloride, iron (II) chloride

Non-ferrous metals and free acid as well as the temperature, the pH value and the density of the pickling solution are decisive. To achieve optimal pickling results, it is necessary to keep the iron III chloride, non-metal content and density constant. The iron (II) chloride content must be below 1 g / l.

A number of chemical processes have been developed for the regeneration of iron (III) chloride pickling, but they have certain disadvantages. For example, oxidation using NaClO ₃ leads to salting of the stain, while oxidation using Cl ₃ or O _{3 is associated} with a high safety risk and poses a high risk to the operator and the environment. In addition, an excess of iron (III) chloride arises in these processes must be disposed of by known methods, which are very expensive.

For the regeneration of stains have been in recent years

electrolytic processes have been developed which are inexpensive, a metal deposition or a metal deposition and one

allow extensive recycling of the pickling acid.

Diaphragm-free cells for the electrolysis of solutions containing nickel salt operate at a pH of "1". A current efficiency of 40-60% is achieved by adding buffer substances. The processed electrolyte must be disposed of conventionally (US Pat. No. 4,087,338).

The situation is similar with the electrolytic processing of iron stains. These bisulfate-forming salts are added to bind the free acid (DE-PS 24 56 058). The electrolyzed acid must also be disposed of. Since problems arise during the electrolytic processing of chloride-containing solutions due to the development of chlorine (jerk oxidation, harmful gas), cells were developed which allow the anode and cathode spaces to be separated.

Electrolyte-permeable diaphragms (US-PS 4,073,709, DE-OS 25 39 137) are used. Diffusion of the anode into the

Cathode liquid is said to be high due to different levels

are prevented (US-PS 4,155,821). In the electrolysis of the hydrochloric acid pickling using these processes diffuses in the

Interruption of the electrolysis operation the chlorine-saturated

Anode fluid in the cathode compartment. The jerk oxidation of iron II compounds to iron III compounds and the dissolution of fine metal particles cannot be avoided. A dilute, hydrochloric acid solution with a low content of heavy metals is obtained in all processes.

Electrolyte-permeable diaphragms are also used in the electrolysis of nickel and zinc from chloride-containing solutions. Sulfuric acid is added to the anode compartment to prevent the development of chlorine. Chloride ions that diffuse into the anode compartment are bound by the addition of silver sulfate (DE-OS 25 39 137). The addition of silver salts requires the processing of the resulting Silver chloride, which means that the process cannot be operated economically.

The use of a hydrogen diffusion electrode prevents the development of chlorine according to DD-PS 283 164. The cathode and anode compartments are separated by an acid-resistant fabric or the hydrogen diffusion electrode is to be covered with a diaphragm in order to restrict the access of hydrogen ions to the cathode. The working pressure is 6.7 kPa. A dilute ferrous hydrochloric acid is obtained, which has to be evaporated for pickling.

Buffer substances are added for the deposition of iron-chromium-nickel and iron-chromium. The hydrochloric acid formed cannot be used for pickling.

Another disadvantage of this method is the investment for the hydrogen station and the additional costs for the

Hydrogen.

The installation of ion exchange membranes for the separation of cathode and

Anode compartment. By combining extraction and

Electrolysis processes with ion exchange membranes are said to remove iron from sulfuric and hydrochloric acid stains (GB-PS 1 576 280). With this method, due to the use of extraction and electrolysis, the chemical and plant costs are unusually high. A very long payback period must be expected.

For the regeneration of old stains according to DE-PS 41 31 793

Electrolysis cells with cation exchange membranes used.

Sulfuric or hydrochloric acid stains containing iron and zinc are regenerated. Sulfuric acid is used as the anolyte. in the

Iron and zinc are to be separated from iron / zinc solutions containing 20 g / l hydrochloric acid or 50 g / l sulfuric acid, thereby obtaining a hydrochloric acid with a content of 150 g / l. These acids can be used again for pickling. This The method must work with very low current yields, since according to GB-PS 1 576 280 with a hydrochloric acid content of 100 g / l and one

Sulfuric acid content of 150 g / l the current yield goes to zero. A continuous process for the treatment of hydrochloric acids

Metal pickling solutions are described in DE-OS 26 27 088. The anode compartment, which is separated by a cation exchange membrane, is charged with sulfuric acid in order to prevent the development of chlorine

avoid. The pickling agent is fed into a central space and cathode space, both of which are separated by an anion exchange membrane. In this plant, metal separation and acid recycling are to be achieved. Acids can only be obtained with very low concentrations, since otherwise only very little metal deposition is achieved.

However, these methods essentially only serve the purpose of

Recovery of the metals from the stain, resulting in a dilute hydrochloric acid partially contaminated with metals, which must be disposed of. In addition, the costs for the plants and the chemicals required are relatively high, so that these processes for a

economic regeneration of spent iron (III) chloride pickling with the aim of extracting iron (III) chloride is unsuitable for quality pickling of steel.

Iron III chloride pickling can be regenerated if you remove the

spent pickling into the cathode compartment of an electrolytic cell, in which the cathode compartment and the anode compartment are separated by an anion exchange membrane, and the nickel contained in the pickling agent is electrolytically deposited together with portions of the iron. The demetallized pickle is then fed into the anode compartment and the iron (II) chloride is oxidized to iron (III) chloride. The process has an efficiency of 95% (power utilization), but has the disadvantage that together with the nickel, too much of the iron (80%) is deposited metallically and the pickle

then new ferric chloride must be added. The demetallized solution must be subjected to very fine filtration before being introduced into the anode compartment in order to be carried along by To prevent iron particles in the anode compartment and in the etching system (DE-PS 39 43 142).

You get a more effective regeneration of the stain in one

Electrolysis plant, in the cathode and anode space through a

Anion exchange membrane are separated, the anode compartment being filled with a FeCl ₂ / FeCl ₃ solution and the cathode compartment being filled with a NaCl / HCl solution. Iron II ions are oxidized to iron III ions at the anode. The missing chloride ion is delivered from the cathode compartment by transfer. The electrolytic regeneration takes place at redox potentials which are below the chlorine development. In this regeneration process, the solution, when used for pickling steel, is increasingly enriched with nickel, chromium and other impurities over time, so that the process cannot be repeated as often as required. In addition, 5 l of excess iron (III) chloride solution are produced per kg of etched steel, which then has to be disposed of (Galvanotechnik 84/1993, 10, p. 3276-32).

Another method is similar (DD-PS 257 361), which separates the anode and cathode compartments by means of a diaphragm. Iron II ions are oxidized to iron III ions in the anode compartment. Missing chloride ions are transferred to the anode compartment from the cathode compartment, which is filled with dilute hydrochloric acid, by means of positive pressure. The regenerated pickling solution is enriched with nickel and cobalt. The aim is to increase the service life of the pickling solution and improve it

Obtain recovery options for nickel and cobalt.

The present invention is therefore an object of the invention to provide a method which allows an iron (III) chloride or iron (III) sulfate solution to be regenerated in such a way that after the

Regeneration in compliance with the desired parameters can be used for the spray etching of nickel alloy steel. This process should be ecologically sustainable and should not pose an increased safety risk for people and the environment. The addition of iron III chloride to the stain should be largely avoided and chemical additives should be kept to a minimum be reduced. In addition, the excess iron in the stain should be depleted together with the non-ferrous metals and a concentration of the stain with nickel, chromium and other metallic and non-metallic impurities should be avoided, so that a continuous

Operation in a closed circuit is made possible.

This object is achieved in a method according to the preamble of claim 1 in that a cation exchange membrane is used as the ion exchange membrane, through which iron II ions, an iron III excess and dissolved non-ferrous metals, such as in particular nickel and chromium, into the cathode compartment are transferred, the pickling solution in addition to iron III and preferably iron II and nickel ions being depleted.

The transfer of the iron II, iron III, nickel and others

Non-ferrous metal ions are preferred when the solution moves past the membrane and the mass transfer is thereby improved. In addition, the transfer of the metal ions at higher temperatures is favored. The latter is made easier because the stain is used at 40-80ºC.

High current yields for the transfer of non-ferrous metals are obtained if these are present in the pickle in higher concentrations. Since non-ferrous metal impurities in the pickle up to a content of 40 g / l do not negatively influence the pickling process, it is advantageous to use such a pickle for continuous regeneration. In addition to the depletion of the Fe ⁺⁺ , Fe ⁺⁺⁺ and non-ferrous metal ions, an oxidation of iron II ions to iron III ions takes place at the anode and, if the potential for chlorine formation is reached, the oxidation of the chloride ions to chlorine instead of. At the cathode Fe ^{+++ is} reduced to Fe ⁺⁺ , hydrogen and metal is deposited at low acid concentrations.

When working outside the chlorine development area, since the iron II, nickel II, non-ferrous metal and portions of the iron III ions formed during the etching are transferred, no additional ones are transferred Chemicals (hydrochloric acid) required. The density of the stain must be adjusted by adding water because the ion transfer leads to a water transfer.

If the pickling is regenerated in the chlorine development area, hydrochloric acid must be added to replace the chloride depleted by the chlorine development.

It also shows that high current yields for the

Transfer occurs if the concentration of iron, nickel and other non-ferrous metals in the catholyte does not exceed 50 g / l. It is therefore also advantageous to continuously separate the metals accumulating in the catholyte. The metal deposition can be carried out in the electrolysis used to deplete the metals or in a second downstream electrolysis. The

The composition of the iron and nickel to be depleted can be influenced by the temperature, the current density, the acid concentration in the catholyte and the electrolyte movement. The electrolytic

Separation of iron and non-ferrous metals in the

Depletion electrolysis should preferably only be in the form of powder, e.g. in the limit current density range, because the

Deposition of solid metal there is a risk that the metal will grow through the membrane, destroy the membrane and short-circuit the cell.

Further details, advantages and features of the method according to the invention result not only from the claims, the features to be extracted from them - individually and / or in combination - but also from the following description of preferred embodiments shown in the figures.

Show it:

Fig. 1 is a schematic representation of an electrolytic cell

for the electrolysis process according to the invention;

Fig. 2 is a flow diagram of an embodiment of the

inventive electrolysis process for Regenerate an iron III chloride stain and

Fig. 3 is a flowchart of another exemplary embodiment

the inventive electrolysis process for

Regenerate an iron III chloride stain.

Fig. 1 shows an electrolyte cell 10, the anode space 12 and

Cathode compartment 14 is separated by a cation exchange membrane 16. In the anode compartment 12 is an iron III chloride pickling used for pickling steel with an iron content of 240 g / l and one

Nickel content of 46 g / l passed, while the cathode compartment 14 is filled with a 20% hydrochloric acid.

At a voltage of 5 V and a current density of 1 A / cm ² , the iron (II) ions in the anode compartment 12 are oxidized to iron (III) ions, while iron (II), iron (III), nickel and other non-ferrous metal ions the cation exchange membrane 16 are transferred into the cathode space 14. The transfer of iron and nickel into the cathode compartment 14 takes place here with a current efficiency of 27.5% (the calculation is based on the transfer of Fe ⁺⁺ and Ni ⁺⁺ .), The transferred iron and nickel ions having a composition of 59%. Iron and 41% nickel.

The pickling solutions processed as described above contain about 50-300 g / l iron in the form of Fe III chloride, less than about 1 g / l iron II, less than about 40 g / l non-ferrous metals and less than 1 g / l Acid and can thus be used immediately for a new pickling process.

If the electrolysis takes place at a current density of 50 mA / cm ² , iron and nickel with a current efficiency of 38% and one

Composition of 56% iron and 44% nickel transferred to the cathode compartment.

The optimal process parameters for the inventive

Regeneration processes can be found in the simplest case by trial and error and set accordingly. In the exemplary embodiment shown in FIG. 2, the iron (III) chloride pickling coming from the pickling system (not shown) is conveyed into the pickling bath overflow 18 and from there into the

Pickling bath reservoir 20.

For the depletion of nickel, non-ferrous metal, iron-II and excess iron-III-ions, this solution is worked up electrolytically in the subsequent regeneration electrolysis.

The regeneration electrolysis consists of individual cells 10 connected in parallel to one another, which are separated by cation exchange membranes 16 in cathode 14 and anode spaces 12. The pickling solution to be depleted is pumped through the anode spaces 12, and a dilute, highly conductive acid, such as hydrochloric acid or sulfuric acid, is pumped through the cathode spaces 14. In the anode compartment 12, the iron II ions are oxidized to iron III ions, iron II, iron III, nickel and others. Non-ferrous metal ions transferred into the cathode compartment 14.

When working in the potential range of the chlorine development, the chlorine formed in the anode compartment 12 is suctioned off and fed directly into the pickling plant.

To remove insoluble constituents, the regenerated anolyte is first passed through a filter 22 and then via a heat exchanger 24 into the anolyte 26 intermediate store. The metal content, pH value and temperature are checked here. Before being fed into the pickling tank, the parameters necessary for pickling, such as temperature, pH, density and the Fe-III and chloride concentration, are set in pickling bath buffer 28.

In the cathode compartment 14, the transferred iron III to iron II ions are reduced, and portions of the dissolved iron and non-ferrous metals are separated out as a powder. The conditions for electrolytic

Powder separation is known per se and z. BN Ibl, Chemie-Ingenieur-Technik 36, 6, (1964). In addition to the Powder separation leads to hydrogen evolution. To separate the powder, the catholyte solution is passed through a filter 30 and

Acid concentration sent over a Waremetauseher 32. The metal contents, the pH value and the temperature are checked and readjusted in the buffer store Katolyt 34.

Through the continuous regeneration of used pickling and the circulation of anolyte and catholyte, a control system can be set up that guarantees compliance with the pickling parameters of the iron III chloride pickling plant, which are within very limited limits. Any additions of chemicals required to adjust this are required to a much lesser extent than in previously known processes. The composition of the pickling and catholyte solution can be checked both electrochemically and analytically.

The electrolysis process according to the invention accordingly enables, in a surprisingly simple manner, continuous regeneration of an iron (III) chloride pickling in a closed circuit with simultaneous depletion of the non-ferrous metals and the excess iron, and electrolytic deposition of the depleted metal ions.

When using cells with very small electrode spacings (2-4 mm), it is more advantageous to use an at least 20%, highly conductive acid, such as hydrochloric and sulfuric acid, to prevent

Use metal deposits in the cathode compartment (14). In

Correspondence with this are shown in FIG. 3

Exemplary embodiment are those transferred in the cathode compartment

Metal ions are not deposited as powder in the cathode compartment 14 as in the first exemplary embodiment. The deposition takes place rather

electrolytically in a separate electrolytic cell 36, the

Cathode spaces 38 from the anode spaces 40 through

Anion exchange membrane 42 are separated. The demetallized electrolyte is concentrated and transferred to the buffer store Katolyt 34, then, after setting the necessary

Electrolysis parameters for the regeneration electrolysis by the Cathode spaces 12 of the electrolytic cells 10 passed. This structure has the advantage that the deposited metal can be drawn off continuously without interfering with the actual regeneration electrolysis.

In the exemplary embodiment shown, a pickle used for pickling nickel-alloyed steel with approximately 297 g / l iron and approximately 38 g / l nickel is placed in the anode compartments of the electrolytic cell 10. The content of sulfuric acid in the cathode spaces is 135 g / l. The solutions are pumped through intermediate containers at a speed of 1.0 l / min. At a voltage of 3 V and a current density of 0.4 A / cm ² , iron and nickel are transferred into the cathode compartment with a current efficiency of ≥ 90%. The composition of the transferred iron and nickel ions is 66% iron and 34% nickel.

The iron- and nickel-containing solution with about 12.4 g / l nickel, 24.9 g / l iron and 112.9 g / l sulfuric acid is led from the cathode spaces into the cathode space of the downstream electrolysis cell, which contains a sulfuric acid in its anode space Contains 50 g / l. The

Electrolysis voltage is 3 V at a current density of 0.5 A / cm ² and a temperature of 50 ° C. Iron and nickel are deposited as powder with a current efficiency of 76%. As already described, the solution depleted of metal is transferred into the cathode spaces of the cells 10.

In the above exemplary embodiments, the electrolysis process according to the invention was described using the regeneration of an iron II chloride pickling as an example. However, the present invention is equally advantageous for the regeneration of iron III sulfate pickling for spraying and pickling steel and

Nickel-based materials are used. The above statements apply equally to this type of stain.

Claims

claims

1. Electrolysis process for the regeneration of an iron (III) chloride or iron (III) sulfate solution (pickling), in particular for spraying steel, in which the anode compartment of an electrolytic cell, the anode and cathode compartments of which are separated by an ion exchange membrane, with the pickling agent to be regenerated as Anolyte and the cathode compartment of the cell are filled with a dilute acid as a catholyte, with Fe-II ions being oxidized to Fe-III ions at the anode, characterized in that as

Ion exchange membrane a cation exchange membrane (16) is used, through which Fe-II ions, an Fe-III ion excess and dissolved non-ferrous metals, such as in particular nickel and chromium, are transferred into the cathode compartment (14).

2. Electrolysis method according to claim 1, characterized in that the regeneration of the pickle takes place continuously, with anolyte and catholyte to improve the exchange of substances on the

Cation exchange membrane (16) are pumped past.

3. Electrolysis method according to claim 1 or 2, characterized

characterized in that the temperature of the stain to be regenerated is between about 40 ° C and 80 ° C.

4. Electrolysis process according to one of claims 1 to 3, characterized in that the content of iron, nickel and others

Non-ferrous metals in the catholyte are maintained at less than about 50 g / l.

5. Electrolysis method according to one of claims 1 to 4, characterized in that a highly conductive acid, such as hydrochloric or sulfuric acid, is used as the catholyte.

6. Electrolysis process according to one of claims 1 to 5, characterized in that at least about 20% acid is used as the catholyte with a small electrode spacing (2-4 mm).

7. Electrolysis method according to one of claims 1 to 5, characterized in that in the cathode compartment (14) the metals enriched in the catholyte are at least partially deposited.

8. The electrolysis process according to claim 7, characterized in that the metals enriched in the catholyte are deposited as a powder.

9. Electrolysis method according to one of claims 7 or 8, characterized in that the depleted metals are deposited as an alloy, the alloy composition being set via the deposition parameters.

10. Electrolysis method one of claims 1 to 9, characterized

characterized in that the metals enriched in the catholyte are electrolytically deposited in a downstream electrolytic cell 36, the cathode and anode space 40 of which is separated by an anion exchange membrane 42.

11. Electrolysis process according to one of claims 1 to 10, characterized in that the pH, the temperature and the

Non-ferrous metal concentration of the catholyte after

Electrolysis checked and reset if necessary.

12. Electrolysis method according to one of claims 1 to 11, characterized in that the anolyte and / or catholyte after

Electrolysis can be filtered.

13. Electrolysis method according to one of claims 1 to 12, characterized in that the content of non-ferrous metal impurities in the regenerated pickle is less than about 40 g / l.

14. Electrolysis process according to one of claims 1 to 13, characterized in that any excess chlorine from the

Aspirated and dried anode compartment (12) and directly into the

Pickling plant is fed.

15. Electrolysis method according to one of claims 1 to 14, characterized in that in the case of an electrolysis in

Chlorine development area is added as a replacement for the chloride depleted by the chlorine development hydrochloric acid.

16. Electrolysis method according to one of claims 1 to 15, characterized in that the parameters required for pickling, such as temperature, density, pH, Fe-III and Cl concentration, are readjusted before feeding the regenerated pickling into the pickling tank .

17. Electrolysis method according to one of claims 1 to 16,

characterized in that the regenerated stain for

Adjusting the density of water is added.

18. Electrolysis method according to one of claims 1 to 17, characterized in that the catholyte and / or the pickling are carried out in a circuit.

19. Electrolysis method according to one of claims 1 to 18,

characterized in that several electrolytic cells

can be connected in parallel or in series (bipolar electrodes).