DE10322120A1 - Methods and devices for extending the service life of a process solution for chemical-reductive metal coating - Google Patents

Abstract

The invention relates to a method and devices for extending the useful life of a process solution used in chemical-reductive metal deposition. In the process, the pH is adjusted and the ions of the coating metal are metered in without disturbing counterions by feeding the process solution, if appropriate after dilution, onto at least one weakly acidic cation exchanger loaded with ions of the coating metal. The reducing agent can be replenished either in an auxiliary circuit or in a dilute process solution. Interfering cations originating from the reducing agent are preferably separated off using a strongly acidic proton-loaded cation exchanger and interfering anions using a weakly basic anion exchanger. Interfering cations that accumulate in the process solution during metal deposition are preferably separated using a strongly acidic proton-loaded cation exchanger. DOLLAR A The process enables an almost constant composition of the process solution with low foreign matter content. This creates a special quality of the coating. DOLLAR A The extension of the service life of the process solution increases the economy and environmental compatibility of the chemical-reductive metal coating.

Description

The The invention relates to a method and devices for extension the service life of a process solution, used in chemical-reductive metal deposition. The chemical-reductive metal deposition is used to work with a metal coating (Cu, Ni, Ag or Au).

For the chemical-reductive metal deposition of non-ferrous metals (non-ferrous metals) on the surface of a base material (e.g. metal or pretreated plastic), the following, greatly simplified reaction equation can be set up for nickel deposition: 3NaH ₂ PO ₂ + 3H ₂ O + NiSO ₄ → 3NaH ₂ PO ₃ + H ₂ SO ₄ + Ni + 2H ₂ (Equation 1)

In the chemical-reductive metal deposition, reducing agents (here NaH ₂ PO ₂ ) and metal ions of the coating metal (here Ni ²⁺ ) are consumed and at the same time the oxidized reducing agent (here NaH ₂ PO ₃ ) and protons are formed as reaction products equivalent to the amount of metal deposited. whereby these lower the pH in the process solution.

conditioned through numerous side reactions for the deposition of one Mol of nickel requires about 3.3 mol of the reducing agent. It also becomes more elementary Phosphorus formed by side reactions from the reducing agent is alloyed into the resulting metal layer.

To In the prior art, the reducing agent is replenished and the metal ions of the coating metal by adding the corresponding salts and the adjustment of the pH by addition of alkalis in the process solution. Through the process of metal deposition, pH adjustment, the replenishment of the used components and by removal Foreign materials accumulate in the process solution from base material, that disrupt the process of metal deposition and the quality of the produced Negatively affect layers. To remove the foreign substances usually a partial disposal of the process solution, with its wastewater-technical Treatment is problematic because of the complex composition.

The common Unit of measurement for the Service life of the process solution is the metal throughput MTO (= "metal turn-over") 1 MTO spoken once the metal content of the process solution was implemented and is added again. According to the prior art, the compressive stress goes in the nickel-phosphorus layer disadvantageously after 2 to 4.5 MTO into a tension over and therefore the service life of the process solution is usually limited to 5 MTO.

In order to extend the useful life of a process solution for chemical-reductive nickel deposition, it is necessary to separate the foreign substances entered using suitable processes. Various methods are proposed for this:
Already in 1953 US 2,726,968 and US 2,726,969 Regeneration processes are described in which a weakly basic anion exchange material activated with phosphinic acid is used for the regeneration of process solutions for chemical-reductive nickel deposition. This is intended to separate orthophosphite from the process solution and to release hypophosphite into the process solution. The weakly basic anion exchange materials are directly loaded with process solution, which is why the pH value of the process solution must not exceed pH 5, otherwise the weakly basic anion exchange material from the hypophosphite loading is converted back into the form of the free base, which is not capable of ion exchange , Disruptive cations are not separated using this method. The metal ions are replenished by adding nickel salts US 2,726,969 by using basic nickel salts such as nickel hydroxide or nickel carbonate, a pH adjustment should be achieved at the same time without the use of further alkalis. However, the use of these poorly soluble compounds has the disadvantage that they contaminate the process solution with solids that can be built into the deposited metal layers and thus negatively influence their properties. These methods have not become established in practice, since in particular the use of phosphinic acid to activate the anion exchanger impairs their economic viability.

The Use of regeneration processes based on the principle of action of membrane electrolysis are proposed in a number of writings, whereby different cell configurations are used.

In the patent DE 43 10 366 proposes a membrane electrolysis cell with 4 chambers in which the reduction of the orthophosphite formed in the chemical-reductive nickel deposition is to take place in the cathode compartment of the electrolysis cell. Out DE 198 49 278 and in our own investigations it is known that the cathodic reduction of the orthophosphite to hypophosphite does not take place, so that by means of the in DE 43 10 366 described process no regeneration of the process solution can be achieved.

In the patent US 5,419,821 it is therefore proposed that the DE 43 10 366 membrane electrolysis cell described to add a precipitation step to remove the orthophosphite by adding magnesium or calcium hydroxide. The input materials consumed by the separation process (nickel ions and reducing agents) should be supplied in the form of nickel sulfate (addition to the process solution) and phosphinic acid (addition to the catholyte). The sulfate should be removed from the catholyte as barium sulfate by adding barium hydroxide. The risk of the membranes of the membrane electrolysis cell becoming blocked is very high in this process, since saturated solutions are present after filtration of the sparingly soluble salts.

In the patents DE 198 51 180 ( EP 1 006 213 ) the use of a membrane electrolysis cell is also described for the regeneration of a process solution for chemical-reductive metal deposition. In this method, the anions of the process solution are transferred electrodialytically in the membrane electrolysis cell into an acidic auxiliary circuit which is separated from the process solution by the membranes of the membrane electrolysis cell. In the auxiliary circuit, the anions are separated by a weakly basic anion exchanger, which was previously converted into the hypophosphite loading by using phosphinic acid. The use of phosphinic acid impairs the economics of the process.

In a special embodiment of the method according to DE 198 51 180 the use of a weakly acidic cation exchanger in combination with the membrane electrolysis cell and the weakly basic hypophosphite-loaded anion exchanger is also described. This weakly acidic cation exchanger is to be used for replenishing nickel ions: For this purpose, it is connected with its inlet to the weakly basic anion exchanger and with its outlet to a chamber of the membrane electrolysis cell that contains the process solution. Part of the acidic hypophoshite-containing solution of the auxiliary circuit is led over the weakly acidic cation exchanger, which is loaded with nickel ions. The effluent of the weakly acidic cation exchanger is fed to the process solution via the chamber of the membrane electrolysis cell. In order to avoid the entry of disruptive components, such as Na ⁺ ions, from the auxiliary circuit into the process solution, this arrangement requires the use of phosphinic acid as a source of hypophosphite, which has a negative impact on the economics of the process.

The required pH adjustment is made after DE 198 51 180 by adding lyes to the process solution and leads to an increasing salt content, which limits the service life of the process solution, as a result of the in DE 198 51 180 described processes no cationic foreign substances can be removed from the process solution. In addition, the use of phosphinic acid impairs the economics of the process.

In the patents DE 198 49 278 . EP 1 123 424 and EP 1 239 057 Two-stage electrodialysis processes are described, which are to handle the separation task required for the regeneration of the process solution. An auxiliary circuit is required to separate the anion mixture, in which the pH is raised to pH> 8. This is necessary so that orthophosphite is present as a divalent anion. By using a selective anion exchange membrane that only allows monovalent anions to pass through, the divalent anions (sulfate, orthophosphite) are to be retained and the monovalent anions are to be returned to the process solution. Practical experience has shown, however, that the selectivity of the available anion exchange membranes is not sufficient to achieve the required separation of orthophosphite and hypophosphite, so that the separated hypophosphite cannot be returned to the process solution. Therefore, the cleaning of the process solution is only possible through high material losses, the material losses being compensated for by adding fresh chemicals to the process solution. The contents of the auxiliary circuit are treated using wastewater technology, whereby compliance with the limit value for the parameter phosphorus requires considerable effort since the auxiliary circuit still contains considerable amounts of hypophosphite.

The The object of the invention is to specify methods and devices with which the service life of a process solution for chemical-reductive metal coating extended can be.

The Task is solved through an extension process the useful life of a process solution for the chemical-reductive metal deposition, in which the metal deposition used reducing agents and metal ions of the coating metal replenished and the pH in the process solution adjusted. The The metal ions are then metered in and the pH is adjusted according to the invention with the help at least one weakly acidic cation exchanger, the one with ions of the coating metal is loaded. This is done with process solution or one diluted process solution applied. The one prepared by the weakly acidic cation exchanger solution becomes the process solution fed again.

in the further text is one under the term ion exchanger Understand device which e.g. in the form of a column, column or filter chamber either partially or completely is filled with an ion exchange material. It will be organic or inorganic ion exchange materials used, wherein these have functional groups which are capable of ion exchange. The ion exchange materials can be solid or liquid. According to the structure of the functional groups of the ion exchange material used the ion exchanger can get closer be characterized, e.g. as strongly acidic or weakly acidic Cation exchanger or as weakly basic or strongly basic Anion exchanger. The substances bound by the ion exchanger can through Regeneration are removed again from the functional groups, regeneration is possible in cocurrent or countercurrent.

By rinsing the coated workpiece after the metal coating, ingredients of the process solution are dragged into the rinsing solution. As a result, foreign substances such as the oxidized reducing agent, the counterions of the reducing agent, as a rule Na ⁺ , and other disruptive ions also get into the rinsing solution. The rinsing solution is therefore a diluted process solution from which the foreign substances can be removed. In the further text, the term diluted process solution therefore includes the rinsing solution.

The Replenishment of the metal ions consumed in the metal deposition of the coating metal takes place according to the invention by abandoning the process solution or one diluted process solution on a weakly acidic cation exchanger that works with the cations of the coating metal is loaded. This gives in metal ions the process solution from. As a result, no interfering counterions are advantageously introduced into the process solution.

there becomes the process solution placed directly on the cation exchanger. That this has not been the case so far Tried, is probably that the professional world of it It is assumed that the process solution is brought into direct contact with Cation exchange materials lead to an undesirable metal deposition would lead to the ion exchange materials and thereby this quickly would become unusable.

Amazingly, let yourself the process solution but directly in contact with cation exchange materials, without this leading to a significant metal deposition on the Leads materials.

Surprisingly, it was found that with the aid of the weakly acidic cation exchanger, the pH of an acidic process solution can be adjusted in parallel with the subsequent metering in of the metal ions. This is achieved in that the weakly acidic cation exchanger, when it comes into contact with the process solution, binds the H ⁺ ions formed during the metal deposition.

Preferably will during part of the process solution or the diluted Process solution via the weakly acidic cation exchanger. When reaching the usable capacity the ion exchange column the ion exchange material can be replaced or the flow of the process solution be redirected to another cation exchanger.

By using the weakly acidic cation exchanger loaded with the cations of the coating metal, the addition of lye and metal salts to the process solution, which is necessary according to the prior art, is advantageously unnecessary in order to bind the H ⁺ ions and to replenish the used metal ions.

There with the help of the weakly acidic cation exchanger, which with process solution in Contacted, surprisingly also the pH in the process solution can be set, superfluous the addition of alkalis necessary according to the prior art to the process solution.

By replenishing the ions of the coating metal without interfering counterions and pH adjustment without addition of lye is considerably reduced by the inventive method with the weakly acidic cation exchanger compared to the prior art, the necessary salt input into the process solution. This simple method, in which a conventional system for chemical-reductive metal deposition only has to be supplemented with the weakly acidic cation exchanger according to the invention, can significantly extend the useful life of the process solution.

On a further part of the invention is a method for extension the useful life of a process solution for the chemical-reductive metal deposition, in which the metal deposition used reducing agents, as well as the metal ions of the coating metal metered in and the pH in the process solution adjusted an anion exchange for the separation of interfering anions in a membrane electrolysis cell with additional Auxiliary circuit between the process solution and the auxiliary circuit via anion exchange membranes he follows.

In this process, the reducing agent in the form of a salt, preferably NaH ₂ PO ₂ , or a salt solution is replenished into the auxiliary circuit, which contains a regeneration solution. The contact and exchange of anions between the regeneration solution and the process solution or a dilute process solution takes place via anion exchange membranes in the membrane electrolysis cell. In the auxiliary circuit, the interfering cations originating from the reducing agent are separated off via a strongly acidic cation exchanger loaded with protons, while interfering anions are removed from the regeneration solution using a weakly basic anion exchanger which is in its starting form as a free base.

The anion exchange membranes of the membrane electrolysis cell retain cations with the exception of protons and allow anions to pass between the process solution and the regeneration solution. The anions acting as reducing agents, preferably H ₂ PO ₂ ^- , can therefore pass through this membrane and migrate from the regeneration solution into the process solution. In contrast, the counterions of the reducing agent (Na ⁺ ions) are retained by the membranes and therefore cannot migrate from the regeneration solution into the process solution. A cation-free subsequent metering of the reducing agent, preferably H ₂ PO ₂ ^- , into the process solution is thus achieved. From the process solution, the used and oxidized reducing agent, preferably orthophosphite (H ₂ PO ₃ ^- ), as well as the counterions of the salt of the coating metal used for subsequent dosing can migrate through the anion exchange membrane into the regeneration solution. For this purpose, process and regeneration solution in a membrane electrolysis cell are brought into contact in separate chambers, the electrodialytic transport of the ions being brought about by an electric field which is induced by applying a voltage to the electrodes of the membrane electrolysis cell. The number of chambers in between determines the level of tension. A voltage drop of approx. 2 volts is to be expected per base unit of three cells, whereby the conductance of the solution in the chamber also influences the level of the voltage to be applied.

By The special arrangement of the membranes is achieved by the anions of the reducing agent and the foreign substances (oxidized reducing agent and possibly the counterions of the added salt of the coating metal) migrate through the membranes from the process solution into the regeneration solution, whereby the regeneration solution enriched with foreign substances.

In order to avoid salt formation in the regeneration solution, disruptive anions are separated by passing the regeneration solution over a weakly basic anion exchanger. After the redosing of the reducing agent in the form of a commercially available salt into the regeneration solution, the counterions of the reducing agent, such as, for. B. Na ⁺ , are separated. For this purpose, the regeneration solution is additionally passed through a strongly acidic cation exchanger which is loaded with H ⁺ ions. The strongly acidic cation exchanger removes sodium ions and replaces them with H ⁺ ions, so that an accumulation of sodium ions in the regeneration solution is prevented. The H ⁺ ions, on the other hand, are consumed by the cathodic electrode process or when the weakly basic anion exchanger is activated, and are thus removed from the regeneration solution.

As soon as the capacity the ion exchanger is exhausted the ion exchangers are regenerated. In the case of the weakly basic Anion exchanger this is done with sodium hydroxide solution, potassium hydroxide solution, sodium carbonate solution, potassium carbonate solution or Ammonia, in the case of the strongly acidic cation exchanger Regeneration with hydrochloric or sulfuric acid. The resulting Eluates are treated using wastewater technology.

By the use of the invention of the strongly acidic cation exchanger can surprisingly be found in the auxiliary circuit even on a separate activation of the weakly basic anion exchanger after its regeneration can be dispensed with, since the in the auxiliary circuit contained salts partially converted into the corresponding acids and be added to the active groups of the anion exchanger.

The volume flow of process solution V _P , which is passed over the membrane electrolysis cell to set the desired concentration c _{F, g} , can be calculated according to equation 2, which is valid for the steady state.

Its value is determined by the entry of foreign matter into the process solution (m _F ), the foreign matter concentrations in the inlet (c _{F, z} ) and in the outlet (c _{F, R} ) of the cleaning device and by the degree of recirculation of the components (γ _R ) that have been towed out. The mass flow of the foreign substance input can be determined from the deposited amount of nickel via the stoichiometry. The degree of recirculation depends on the proportion of the rinsing solution that is transferred to the coating container to compensate for evaporation losses, and can be between 0 and 1.

The Use of the combination according to the invention of strongly acidic cation exchanger and weakly basic anion exchanger in the auxiliary circuit of a membrane electrolysis cell with the one described below Arrangement of the chambers has the advantage that the reducing agent without annoying Cations in the process solution replenished and annoying Anions from the process solution can be separated, and there is no accumulation of interfering cations in the auxiliary circuit.

In a preferred embodiment the invention is the above-described dosing of the reducing agent and the separation more disruptive Anions in the auxiliary circuit with the pH setting described above and replenishment of the ions of the coating metal using the Weakly acidic cation exchanger loaded with ions of the coating metal combined. In this embodiment through the subsequent dosing according to the invention of the ions of the coating metal without a disturbing anion Quantity of foreign matter in the process solution entered. This means that the membrane electrolysis cell must also only a smaller amount of foreign matter can be separated.

In a further embodiment the invention is the above-described dosing of the reducing agent and the separation more disruptive Anions combined in the auxiliary circuit with a process in which disturbing Cations that accumulate in the process solution during metal deposition, separated using at least one strongly acidic cation exchanger that was previously loaded with protons.

Preferably this separation is the disruptive Cations temporarily in a special cleaning process if necessary carried out. This essentially serves to remove cations that are present in the the metal deposition from the base material into the process solution become. This is the process solution brought into contact with a strongly acidic cation exchanger, the was previously loaded with protons.

at this cleaning process also includes those contained in the process solution Ions of the metal to be deposited are removed and protons are added to the process solution. The cations of the coating metal must then be replenished and the protons entered when cleaning the process solution be removed again. To the cations of the coating metal to be able to use again becomes the eluate that is used to regenerate the strongly acidic cation exchanger accrues, after a pH adjustment for the loading of the weakly acidic cation exchanger with the cations of the coating metal used.

Preferably the ions of the coating metal are weakly acidic Cation exchanger with the corresponding cations of the coating metal is loaded, replenished. At the same time, it binds the protons, which were entered into the process solution by the cleaning process.

at low metal throughputs is the use of a membrane electrolysis cell with an auxiliary circuit however, involves relatively high costs.

Another component of the invention is therefore a method for extending the useful life a process solution for the chemical-reductive metal deposition, in which the reducing agent used in the metal deposition and the metal ions of the coating metal are replenished and the pH value in the process solution is adjusted, whereby disturbing cations and anions, which accumulate in the process solution during the metal deposition, are removed from the process solution or a dilute process solution with the aid of ion exchange processes. For the removal of interfering cations, at least one strongly acidic cation exchanger is used for this purpose, which was previously loaded with protons, while the weakly basic anion exchanger for the removal of the interfering anions is converted into the protonated form by protons. The protons which the strongly acidic cation exchanger releases as described above when it binds interfering cations are preferably used for this purpose.

In this process, the reducing agent is preferably replenished directly in the process solution or in a dilute process solution in the form of a water-soluble salt, preferably sodium hypophosphite (NaH ₂ PO ₂ ), or a corresponding solution.

The Separation of the disruptive Anions over the weakly basic anion exchanger and the interfering cations over the strongly acidic cation exchangers are preferably made from a dilute process solution.

Preferably become the disturbing cations by the strongly acidic cation exchanger and through the weakly basic anion exchanger the interfering anions from the flushing system separated. After by the strongly acidic cation exchanger next the cationic contaminants from base material but also the towed into the rinse solution Cations of the coating metal must be separated, the strongly acidic Cation exchangers more common be regenerated as if it were part of a separate auxiliary circuit the membrane electrolysis cell.

The cleaned rinsing solution to compensate for the evaporation losses that occur during metal deposition in the process solution recycled.

In a preferred embodiment The invention uses the separation method described above of distracting Anions or more disruptive Cations from a diluted process solution (or rinsing solution) with the pH setting described above and replenishment of the metal ions with the aid of the metal ion loaded weakly acidic cation exchanger combined.

Preferably the feed takes place the metal ions of the coating metal in the previously cleaned solution With the help of a weakly acidic cation exchanger, which had previously Metal ions of the coating metal was loaded. This will the pH in the returned solution is raised and there are those separated by the strongly acidic cation exchanger Metal ions of the coating metal are returned to the process solution. The Eluate of the strongly acidic cation exchanger can be after a pH adjustment for the loading of the weakly acidic cation exchanger with the metal ions of the coating metal can be used.

This Simplified process and plant technology also leads to a clear one Reduction of the foreign matter content in the process solution, but enables not the good use of materials with the membrane electrolysis cell described above can be achieved with auxiliary circuit.

Furthermore, the invention relates to a device for extending the useful life of a process solution for chemical-reductive metal deposition, consisting of at least one weakly acidic cation exchanger for use in adjusting the pH value and replenishing ions of the coating metal in a system for chemical-reductive metal deposition. The device has elements that connect the inlet and outlet of the weakly acidic cation exchanger ( 14 ) with at least one container containing process solution, diluted process solution, cooled process solution or pretreated process solution. Furthermore, the device contains associated peripherals, such as. B. pumps, valves, measuring devices for pH, conductivity, temperatures.

Preferably contains the cation exchanger is a weakly acidic cation exchanger material with carboxylic acid groups as functional groups.

For its use according to the invention, the weakly acidic cation exchanger is loaded with the cations of the coating metal. This is preferably done in two steps: First, the weakly acidic cation exchanger for conditioning, with an alkali, preferably with sodium hydroxide solution, into the salt transferred form. For loading, it is then brought into contact with a water-soluble salt of the coating metal in dissolved form. In the case of chemical-reductive nickel deposition, for example an aqueous solution of nickel sulfate or nickel chloride is chosen for loading with metal ions.

The Metal ion loading is preferably carried out in two stages differently concentrated metal salt solutions, with the second Level - preferably through a circuit - a full load with metal ions of the coating metal. Through this gradually The procedure is a complete transfer of the weakly acidic resin in the loading with ions of the coating metal and at the same time good use of the ions of the Coating metal guaranteed.

To the loading process is the ion exchanger with fully desalinated Washed water to remove the appropriate sodium salts from the ion exchanger to remove them so that they do not enter the process solution as foreign substances become.

at its use according to the invention the weakly acidic cation exchanger is charged with process solution and releases metal ions into them. At the same time, it binds protons. The maximum proton absorption capacity of the weakly acidic cation exchanger is at complete transfer in reached the salt form. The capacity is above the pH in its drain controlled. The pH value drops in the process Expiration of the weakly acidic cation exchanger when the discharge is complete was achieved by the metal ions.

at complete The weakly acidic cation exchanger is located in the discharge the H shape. For the renewed use according to the invention the weakly acidic cation exchanger must be reintroduced with an alkali the salt form is transferred and subsequently be loaded with ions of the coating metal. The so regenerated weakly acidic cation exchanger can be used again for pH adjustment, and the replenishment of metal ions can be used.

The weakly acidic cation exchanger has a high selectivity for protons, so that those formed during chemical-reductive metal deposition Protons are bound by this cation exchanger. In return are the metal ions previously bound to the cation exchanger in the process solution issued.

The for the Metal divalent cations are used by the metal deposition weakly acidic cation exchangers more strongly bound than monovalent ones Cations. Leaves advantageous the exchanger therefore in a simple manner with sodium hydroxide solution convert the salt form and subsequently loaded with the divalent cations of the coating metal. The column capacity of weak acid Cation exchanger is according to the desired service life and the amount of metal to be deposited.

It was surprisingly found that the weakly acidic cation exchanger was brought into direct contact with the process solution and not only did the ions of the coating metal be replenished, but the pH of the process solution could also be adjusted. This is achieved in that the weakly acidic cation exchanger, when it comes into contact with the process solution, binds the H ⁺ ions formed during the metal deposition.

By using the weakly acidic cation exchanger loaded with the cations of the coating metal, the addition of lye and metal salts to the process solution, which is necessary according to the prior art, is advantageously unnecessary in order to bind the H ⁺ ions and to replenish the used metal ions.

There with the help of the weakly acidic cation exchanger, which with process solution in Contacted, surprisingly also the pH in the process solution can be set, superfluous the addition of alkalis necessary according to the prior art to the process solution.

By the replenishment of the ions of the coating metal without interfering counterions and the pH adjustment without addition of alkali is achieved by the weak acid according to the invention Cation exchanger compared to the state of the art the necessary Salt entry in the process solution significantly reduced. Becomes a conventional chemical-reductive plant Metal deposition alone with the weakly acidic cation exchanger according to the invention added, the service life of the process solution can be significantly extended.

Another object of the invention is a device for extending the useful life of a process solution for chemical-reductive metal deposition, consisting of at least one strongly acidic cation exchanger for use in the removal of disruptive cations in a plant for chemical-reductive metal deposition. The device has elements that connect the strongly acidic cation exchanger ( 15 ) with at least one container containing process solution, diluted process solution, cooled process solution or pretreated process solution. Furthermore, the device contains associated peripherals, such as. B. pumps, valves, measuring devices for pH, conductivity, temperatures.

As strongly acidic cation exchange materials come to the compounds Use that carry sulfonic acid groups as functional groups Enables ion exchange are. These bind in dependence from the concentration ratios all cationic metal ions as well as ammonium ions stronger than Protons. This will remove these cations from the feed solution from Ion exchanger bound while at the same time an equivalent Amount of protons in the solution be delivered.

According to the invention, the strongly acidic cation exchanger is used to remove cations from the process solution, the diluted process solution, the rinsing solution or the regeneration solution, for which purpose the strongly acidic cation exchange material is converted into the H ⁺ form. This is done by placing an acid in the required concentration on the cation exchanger, with hydrochloric or sulfuric acid normally being used in practice.

The exhaustion the column capacity of the exchanger is about the measurement of conductivity determined in the inflow and outflow of the cation exchanger, a Decrease of the difference value of inflow and outflow to the exhaustion of the Column capacity of the strong acid Cation exchanger indicates.

To regenerate the loaded strongly acidic cation exchange material, it is converted back into its H ⁺ form by adding an excess of acid. The protons displace the bound cations from the functional groups of the exchanger. A larger excess of acid and possibly a higher acid concentration is required to remove polyvalent cations than to remove monovalent cations.

This device advantageously removes cationic foreign substances originating from the base material, such as Al ³⁺ , Sn ²⁺ , Zn ^2+, etc., as well as the disruptive cations of the replenished reducing agent, which can accumulate in the process solution.

The The invention also relates to the combination of the weak acid described above Cation exchanger with the strongly acidic cation exchanger described above in a device for use in a plant for the chemical-reductive Metal deposition to determine the useful life of a process solution for the chemical reductive Extend metal deposition. The device contains at least one strongly acidic cation exchanger for the removal disturbing Cations with at least one weakly acidic cation exchanger used for the pH adjustment and replenishment of ions of the coating metal in series or is connected in parallel. The device also has elements the combination of the weakly acidic cation exchanger and the strongly acidic cation exchanger with at least one container which Process solution diluted Process solution cooled process solution or pretreated process solution contains serve. Furthermore contains associated with the device Peripherals such. B. pumps, valves, measuring devices for pH, Conductivity, Temperatures.

Farther The invention relates to the combination of the strong acid described above Cation exchanger with a weakly basic anion exchanger in an extension device the useful life of a process solution for the chemical-reductive metal deposition. This device for use in a facility for the chemical-reductive metal deposition consists at least of a strongly acidic cation exchanger for the removal of interfering cations with at least one connected in series or parallel to this weakly basic anion exchanger for the removal of interfering anions, The device also has elements connected to the connection the strongly acidic cation exchanger and the weakly basic anion exchanger with at least one container, the process solution, diluted Process solution, cooled process solution or pretreated process solution contains serve. Furthermore contains associated with the device Peripherals such. B. pumps, valves, measuring devices for pH, Conductivity, Temperatures.

The weakly basic anion exchange materials used are preferably inorganic or organic materials with weakly basic functional groups, preferably with tertiary amines sentence. The weakly basic anion exchange material has specific selectivities and therefore binds sulfate, chloride and orthophosphite more strongly than hypophosphite. To use the weakly basic anion exchanger according to the invention, the functional groups of the weakly basic anion exchanger material have to be converted from the form of the free base into a protonated cationic form which is capable of ion exchange. This is done by taking up protons, for example by releasing acid. Due to the selectivity of the ion exchange material, certain anions, such as sulfate or orthophosphite, are preferably bound. These can also displace anions that are less firmly bound by the anion exchanger, such as hypophosphite, from the functional groups capable of ion exchange. This results in the separation of a given anion mixture. So that the exchanger is not converted from the cationic form into the free base form, which as an uncharged group is not capable of ion exchange, an acidic solution must always be applied to the weakly basic anion exchanger.

The strongly acidic cation exchanger and the weakly basic anion exchanger are preferably connected in series, so that the expiration of the strongly acidic Cation exchanger with the feed of the weakly basic anion exchanger connected is. The strongly acidic cation exchanger is added its use according to the invention Protons for the transfer of the functional groups of the weakly basic anion exchanger the shape of the free base into the protonated one capable of ion exchange Form can be used. The strong acid cation exchanger thus provides the pH of the solution applied to an acidic value for the use of the weakly basic anion exchanger is required is.

The The weakly basic anion exchanger is regenerated by the task of caustic soda, which makes the weakly basic anion exchanger is converted from the protonated form into the form of the free base. Wears in this form the functional group no longer has a charge and is therefore not for ion exchange capable. This allows all previously bound anions quantitatively from anion exchange material be removed. After a rinsing process the weakly basic anion exchanger can be used with deionized water again for the separation according to the invention disturbing Anions can be used.

By The weakly basic anion exchanger becomes the oxidized reducing agent and, if necessary, the counterions of the replenished coating metal and the annoying counterions through the strongly acidic cation exchanger separated from the replenished reducing agent. The replenishment of the reducing agent in the form of a salt or as a corresponding saline solution leads the use of the combination according to the invention of strongly acidic cation exchanger and weakly basic anion exchanger therefore advantageous not to salt the process solution. By the use according to the invention of the strongly acidic cation exchanger is an activation of the weakly basic Anion exchanger by phosphinic acid is not required.

In one embodiment of the invention the device in which, as described above, the strongly acidic cation exchanger can be combined with the weakly basic anion exchanger, additionally at least a weakly acidic cation exchanger as described above for the pH adjustment and replenishment of ions of the coating metal.

This Accordingly, the device has additional elements that the Connection of the weakly acidic cation exchanger with at least a container, the process solution, diluted Process solution, cooled process solution or pretreated process solution serve.

On Another object of the invention is a device for extension the useful life of a process solution for the chemical-reductive metal deposition for use in a plant for the chemical-reductive metal deposition, consisting of a membrane electrolysis cell with an auxiliary circuit.

This Includes device in the auxiliary circuit at least one weakly basic anion exchanger and at least one strong acid in series or parallel to this Cation exchanger.

At the Use of this device is carried out by the Metal deposition of used reducing agent in the form of a salt or a saline solution in the auxiliary circuit.

The Anion exchange membranes have functional surfaces Groups with positively charged fusions that cause anions can pass this membrane while Cations, with the exception of protons, do not overcome this barrier can.

The Membrane electrolysis cell consists of an anode (+) and a cathode (-) and at least four chambers arranged between the electrodes, the are separated from each other by ion-selective membranes.

The first chamber, the anode chamber 6 , contains the anode and a dilute acid. This chamber is through a cation exchange membrane from a second chamber, the enrichment chamber 7 containing the regeneration solution. In the direction of the cathode, this chamber is separated from the third chamber by an anion exchange membrane 8th separated, which contains the process solution. The fourth chamber, the replenishment chamber 12 , contains the cathode and is filled with regeneration solution. It is through an anion exchange membrane from the third chamber 8th which contains the process solution.

The second, third and fourth chambers 7 . 8th and 12 form a base unit that can be repeated several times to increase the membrane area used within the membrane electrolysis cell in order to be able to cope with a higher material throughput. When increasing the total membrane area by multiple arrangement of the chambers 7 . 8th and 12 however, only one anode chamber is used 6 and a cathode is required, the postdosing chamber 12 the base unit, which is furthest from the anode, contains a cathode.

Furthermore, the device contains elements which connect the third chamber 8th serve the membrane electrolysis cell with at least one container containing cooled process solution, diluted cooled process solution or pretreated cooled process solution, and preferably associated peripherals, such as. B. pumps, valves, measuring devices for pH, conductivity, temperatures.

The Anion exchange membrane carries on their surface functional groups with positively charged groups that cause that anions can pass through this membrane while cations except of protons cannot overcome this barrier.

By the task of the process solution into a chamber of the membrane electrolysis system, which consists of two anion exchange membranes is limited, and the over the anion exchange membranes are in contact with regeneration solution by the electrical field applied between the electrodes Migration of anions between process solution and regeneration solution achieved.

The anions are removed from the process solution through the anion exchange membrane into the second chamber, which functions as an enrichment chamber 7 transported to the fourth chamber via a weakly basic anion exchanger 12 connected is. In the fourth chamber 12 the reducing agent is metered in directly or indirectly into a buffer tank for the auxiliary circuit connected to this chamber and functioning as a metering tank 10 , The fourth chamber 12 is therefore to be regarded as a replenishment chamber.

By this combination according to the invention the strongly acidic cation exchanger with the weakly basic anion exchanger can surprisingly in the auxiliary circuit even on a separate activation of the weakly basic anion exchanger after its regeneration can be dispensed with, since the in the auxiliary circuit contained salts partially converted into the corresponding acids and be added to the active groups of the anion exchanger.

Prefers becomes the membrane electrolysis cell described above with an auxiliary circuit with the weakly acidic and strongly acidic cation exchangers described above combined. The device for extending the useful life of a process solution for the chemical-reductive metal deposition contains in addition to the membrane electrolysis cell with an auxiliary circuit with integrated strongly acidic cation exchanger and weakly basic anion exchanger at least one weakly acidic cation exchanger and / or at least another strongly acidic cation exchanger. The device also has elements with which the membrane electrolysis system with auxiliary circuit, the weakly acidic cation exchanger or the strongly acidic cation exchanger when used in a system for chemical-reductive metal deposition with a container, the process solution, diluted Process solution cooled process solution and / or pretreated process solution contains get connected.

The additional strongly acidic cation exchanger separates disruptive cations from the process solution. For this purpose, it is preferably charged with process solution, diluted process solution, cooled process solution or pretreated process solution if necessary. The strongly acidic cation exchanger in the auxiliary circuit is not able to do this because of the cell configuration in the membrane electrolysis system - no cationic foreign substances with the exception of H ⁺ can get into the auxiliary circuit from the process solution.

By the combination according to the invention the membrane electrolysis cell with the weakly acidic cation exchanger is achieved by replenishing the ions of the coating metal without annoying Anions introduced a smaller amount of foreign matter into the process solution. As a result, only a smaller one has to pass through the membrane electrolysis cell The amount of foreign matter is separated.

In a preferred embodiment of the invention, the above-mentioned ion exchangers are column exchangers, which with a solid, water-insoluble, ion exchange material filled are. The organic or inorganic ion exchange material contains functional groups that are capable of ion exchange. These column exchangers can be regenerated in cocurrent or countercurrent.

In an alternative embodiment of the invention are the above-mentioned ion exchange materials each part of a filter or membrane apparatus. This contains in each case a regenerable, organic or inorganic ion exchange material, which is preferably in a form capable of ion exchange is introduced into the filter or membrane apparatus.

In a further embodiment the invention are in at least one of the ion exchange materials used liquid Ion exchange materials used. The ion exchanger (s) exist in this embodiment one container each, the one with the process solution immiscible liquid contains in which an ion exchange material is distributed or dissolved. Preferably, the ion exchange material is in this embodiment from a reagent that is used for contains the functional groups required ion exchange action, such as they e.g. be used in the reactive extraction.

• • mindestens einem Beschichtungsbehälter,
• • einem Spülsystem,
• • und mindestens einer der oben beschriebenen Vorrichtungen zur Verlängerung der Nutzungsdauer einer Prozesslösung für die chemisch-reduktive Metallabscheidung.

Another object of the invention is a plant for chemical-reductive metal deposition consisting of:

• At least one coating container,
• • a flushing system,
• • and at least one of the devices described above for extending the service life of a process solution for chemical-reductive metal deposition.

Of contains further the system connecting lines between the individual components as well as the associated Peripherals, such as pumps, valves, measuring devices for pH value, Conductivity, Temperatures etc.

The coating tank contains the process solution, in which the workpiece to be coated is immersed.

In in its simplest form there is the system according to the invention from a coating container, a flushing system and a device as described above with a weakly acidic cation exchanger for pH adjustment and subsequent dosing of the metal to be deposited, which is connected to the coating tank with inlet and outlet.

In a second embodiment contains the system additionally a weakly basic anion exchanger for the separation of interfering anions. In this combination the introduction of the metal ions without interfering anions is a special efficient use of the weakly basic anion exchanger, because this essentially only contains the anions of the oxidized reducing agent, usually orthophosphite, of which the reducing agent, in usually hypophosphite, must separate.

In a further embodiment contains the system additionally a strongly acidic cation exchanger for the separation of interfering cations.

In one embodiment the system is the inflow and outflow of weakly acidic or of the strongly acidic cation exchanger directly connected to the coating container.

The process solution is preferably cooled before it is brought into contact with the sensitive components of the devices, in particular the ion exchange materials and the membranes. Cooling in particular reduces the risk of undesired metal deposition on these components. The process solution prepared by the device must be in the Be stratification tank is returned to the process temperature.

In a preferred embodiment of the system described above are the inflow and outflow of the weakly acidic or strongly acidic cation exchanger therefore via a heat exchangers with the coating container connected. Through the heat exchanger becomes the energy of the cooling process for the up process of cleaned process solution used.

In a preferred embodiment contains the system a device as described above with a weak acid Cation exchanger, a strongly acidic cation exchanger and a weakly basic Anion exchanger.

there sets the rinsing solution diluted process solution and can be added to the process solution to compensate for evaporation losses.

In an advantageous embodiment are the strongly acidic cation exchanger and the weakly basic one Anion exchanger in series or parallel connection with the flushing system connected. The feed of the weakly acidic cation exchanger is with the flushing system or the regeneration tank and the outlet of the weakly acidic cation exchanger is connected to the coating container.

In this embodiment the separation is more disruptive Cations and anions through the combination of strongly acidic described Cation exchanger and weakly basic anion exchanger from the Flushing system. It is preferably used to compensate for evaporation losses part of the processing rinse solution over the described, weakly acidic cation exchanger loaded with ions of the coating metal in the process solution fed. This allows In this system, both interfering cations and anions are advantageous are separated, metal ions are metered in and the pH is adjusted become. The function of this system depends on the height of the tow of process solution into the rinsing solution and the evaporation losses.

In a special embodiment of the system, the strongly acidic cation exchanger and the weakly basic anion exchanger are connected in series or in parallel with an additional regeneration tank connected to the flushing system 16 connected, which is filled with a mixture of rinsing solution and process solution.

In This system therefore separates interfering cations and anions and the repatriation of the purified solution from a mixture of rinsing solution Process solution. In this plant, the separation of Foreign substances and the replenishment of ions of the coating metal largely independent from the height the removal of process solutions in the rinsing solution. In addition can in the regeneration tank the pH value must be set to a value that is appropriate for the cleaning process best suitable is.

In Another preferred embodiment contains the system according to the invention as the centerpiece a membrane electrolysis cell with an auxiliary circuit, as above described in the process solution and auxiliary circuit through anion exchange membranes from each other are separated. The auxiliary circuit contains other components at least one weakly basic anion exchanger and one strongly acidic Cation exchanger.

The membrane electrolysis cell is preferably charged with process solution which has been cooled by the heat exchanger. For this is the third chamber 8th the membrane electrolysis cell with its inlet and outlet connected to the coating container via a heat exchanger. In a preferred embodiment, there is additionally a reservoir for the process solution to be cleaned between the heat exchanger and the membrane electrolysis cell 5 and a stacking container container for cleaned process solution 13 connected.

In the membrane electrolysis cell, anions from the process solution become electrodialytic transported into the auxiliary circuit. The separation of the anion mixture takes place through the weakly basic anion exchanger. Through this become the oxidized reducing agent and other disruptive anions (e.g. sulfate, chloride, orthophosphite) removed. In a preferred way embodiment are used to improve the separation performance and to increase the capacity several weakly basic anion exchangers in succession in the auxiliary circuit connected in series.

The reducing agent is replenished in the auxiliary circuit, with transport of the opposites ions of the reducing agent, preferably Na ⁺ ions, are prevented in the process solution by the anion exchange membranes. The setting of the acidic process conditions in the auxiliary circuit and the removal of the counterions of the reducing agent, preferably Na ⁺ ions, is carried out by means of a strongly acidic cation exchanger in the H ⁺ form. By contacting the process solution with the auxiliary circuit in the membrane electrolysis cell, the reducing agent is introduced into the process solution in a cation-free manner.

Advantageous can by separating process solution and auxiliary circuit in the auxiliary circuit for the separation of the anions required process parameters can be set. without that at the same time the composition of the process solution changed must become.

The Plant with membrane electrolysis cell and auxiliary circuit preferably contains at least one weakly acidic cation exchanger as described above for adjusting the pH value and for replenishing ions of the coating metal. In one embodiment, the is weak acid Cation exchanger connected to the coating container and is directly with process solution applied.

to Separation from disruptive Cations from the process solution contains the system with a membrane electrolysis cell with auxiliary circuit in addition to the strongly acidic cation exchanger in the auxiliary circuit, preferably at least one strongly acidic cation exchanger as described above, the one with process solution or a diluted one process solution is applied.

In one embodiment the system with auxiliary circuit is the strongly acidic cation exchanger with the coating container connected. In this embodiment it becomes direct with process solution applied.

In a further embodiment of the system with membrane electrolysis cell and auxiliary circuit, the strongly acidic cation exchanger, with its inlet with the rinsing system and with its outlet, is provided with a reservoir for the process solution to be cleaned 5 connected. This storage container is between the coating container and the third chamber 8th the membrane electrolysis cell switched.

In this embodiment part of the rinsing solution frees the strongly acidic cation exchanger from interfering cations, whereby an equivalent Amount of protons is released. The preparation of these pretreated and diluted process solution is preferably carried out in a membrane electrolysis cell with an auxiliary circuit.

In a further embodiment The system with a membrane electrolysis cell with an auxiliary circuit is weak acid Cation exchanger in a regeneration circuit with inlet and outlet with the additional stacking container that contains process solution prepared by the membrane electrolysis cell.

In a plant with a membrane electrolysis cell with an auxiliary circuit, the weakly acidic cation exchanger is connected in another preferred embodiment with its inlet to the third chamber of the membrane electrolysis cell and with its outlet via the heat exchanger to the coating container. A stack container for cleaned process solution is preferably located between the inlet of the weakly acidic cation exchanger and the third chamber of the membrane electrolysis cell ( 13 ) switched.

Of the invention further relates to the use of weakly acidic Cation exchange material or weakly acidic cation exchangers for the pH adjustment and replenishment of ions of the coating metal for extension the useful life of a process solution for the chemical-reductive metal deposition.

object the invention is also the use of strongly acidic cation exchange material or strongly acidic cation exchangers for the removal of interfering cations for extension the useful life of a process solution for the chemical-reductive metal deposition.

• a.) schwachbasischem Anionenaustauschermaterial oder schwachbasischen Anionenaustauschern für die Entfernung störender Anionen und
• b.) starksaurem Kationenaustauschermaterial oder starksauren Kationenaustauschern für die Entfernung störender Kationen zur Verlängerung der Nutzungsdauer einer Prozesslösung für die chemisch-reduktive Metallabscheidung.

Another object of the invention is the use of a combination of

• a.) weakly basic anion exchange material or weakly basic anion exchangers for the removal of interfering anions and
• b.) strongly acidic cation exchange material or strongly acidic cation exchangers for the removal of interfering cations to extend the useful life of a process solution for chemical-reductive metal deposition.

• a.) schwachsaurem Kationenaustauschermaterial oder schwachsauren Kationenaustauschern für die pH-Wert-Einstellung und Nachdosierung von Ionen des Beschichtungsmetalls und
• b.) starksaurem Kationenaustauschermaterial oder starksauren Kationenaustauschern (15) für die Entfernung störender Kationen zur Verlängerung der Nutzungsdauer einer Prozesslösung für die chemisch-reduktive Metallabscheidung.

The invention further relates to the use of a combination of

• a.) Weakly acidic cation exchange material or weakly acidic cation exchangers for pH adjustment and replenishment of ions of the coating metal and
• b.) strongly acidic cation exchange material or strongly acidic cation exchangers ( 15 ) for the removal of interfering cations to extend the useful life of a process solution for chemical-reductive metal deposition.

Compared to the State of the art can the useful life of a Process solution for the chemical-reductive Metal coating can be extended significantly. Advantageously results considerable savings in feed materials. simultaneously reduce the disposal costs, which according to the state of the art, are not insignificant.

Of others are almost advantageous by the invention constant process conditions in chemical-reductive metal coating and thus a particularly uniform separation of the Metal reached on the workpiece to be coated. Due to the low Foreign matter content of the process solution, that in the plant according to the invention can be achieved Nickel-phosphorus layers are deposited in the compressive stress range lie what is particularly the quality of the coating of the deposition causes.

Based The following drawings are exemplary embodiments of the invention shown and described schematically. Show:

1 Plant with weakly acidic cation exchanger for pH adjustment and replenishment of ions of the coating metal

2 : Plant with heat exchanger and weakly acidic cation exchanger for pH adjustment and replenishment of ions of the coating metal

3 : System with weakly acidic cation exchanger for pH adjustment and replenishment of ions of the coating metal as well as weakly basic anion exchanger and strongly acidic cation exchanger for the separation of interfering ions from the rinsing solution

4 : Plant for pH adjustment and replenishment of ions of the coating metal as well as separation of interfering ions from a diluted process solution

5 : Device for replenishing the reducing agent and for separating interfering anions in a membrane electrolysis cell with auxiliary circuit

6 : Extended device for replenishing the reducing agent and for separating disruptive anions in a membrane electrolysis cell with auxiliary circuit

7 : System with membrane electrolysis cell with auxiliary circuit

8th : System with membrane electrolysis cell with auxiliary circuit and weakly acidic cation exchanger for pH adjustment and replenishment of ions of the coating metal

9 : System with membrane electrolysis cell with auxiliary circuit, weakly acidic cation exchanger for pH adjustment and replenishment of ions of the coating metal and strongly acidic cation exchanger for regeneration of the process solution

10 : System with membrane electrolysis cell with auxiliary circuit, a weakly acidic cation exchanger connected to the stacking container for pH adjustment and replenishment of ions of the coating metal and strongly acidic cation exchanger for regeneration of the process solution

11 : System with membrane electrolysis cell with auxiliary circuit and indirect regeneration of the process solution via the rinsing system, pH adjustment and replenishment of ions of the coating metal by means of a weakly acidic cation exchanger connected between the stacking container and the coating container

1 shows a diagram of a plant for chemical-reductive metal coating, in which by means of a weakly acidic cation exchanger loaded with ions of the coating metal 14 the required ions of the coating metal are replenished without disturbing anions and at the same time the pH value of the process solution is adjusted and the service life of the process solution can thus be extended.

The plant after 1 consists of a coating container 1 , a multi-stage flushing system 3 in a cascade connection and a weakly acidic cation exchanger 14 , as well as connecting lines and associated peripherals, such as pumps, valves, measuring devices for pH value, conductivity, temperatures etc. The coating container 1 contains process solution in which a workpiece to be coated 2 is immersed. The workpiece to be coated 2 has a steel surface.

The multi-stage flushing system 3 consists of three cascaded containers that contain an aqueous rinsing solution. Between the left and right rinse tanks 3 is as in by the broken line 1 indicated, but not shown, another rinsing container lined up. The left rinse tank 3 contains an inlet for fresh water. The right rinse tank 3 is with the coating container 1 connected.

The weakly acidic cation exchanger 14 is with its inlet and outlet with the coating container 1 connected so that a certain volume flow of the process solution can be passed through it.

The weakly acidic cation exchanger consists of an ion exchange column 14 , which is filled with the weakly acidic cation exchange polymer Lewatit CNP 80 from Bayer AG, Leverkusen, Germany. However, comparable weakly acidic cation exchange polymers from other manufacturers, such as C 104 from Purolite, Ratingen, Germany, can also be used.

This weakly acidic cation exchange polymer is loaded with ions of the coating metal before use. For this purpose, the ion exchanger is first converted into the salt form with sodium hydroxide solution and then loaded with ions of the coating metal by applying a metal salt solution. In the case of chemical-reductive nickel plating, the weakly acidic cation exchange polymer is loaded with nickel ions, for which purpose a NiSO ₄ solution is passed over the ion exchange column. This loading takes place in two steps with nickel salt solutions of different concentrations, with a deficit of nickel ions being applied to the ion exchanger in the first loading step. Due to the selectivity of the cation exchanger, an almost complete removal of the nickel ions from the feed solution is achieved, which is discarded after loading and treated with waste water. In the second loading step, by using an excess of nickel ions when loading the ion exchanger and circulating the feed solution, the weakly acidic cation exchanger is fully loaded with nickel.

To The weakly acidic cation exchanger becomes the loading process with nickel washed with deionized water to remove unwanted ions from the polymer layer remove. Through this rinsing process becomes the surplus of nickel ions removed from the polymer bulk layer. The sequence the second fraction of the loading process is together with the first fraction of the rinse water interposed and in the subsequent loading of weak acid Cation exchanger used as the first loading fraction.

The process solution is composed in a known manner. When newly prepared, the ions of the coating metal in the form of nickel sulfate (6.0 g Ni ²⁺ / l) are added to it. The reducing agent is added in the form of sodium hypophosphite (17.0 g H ₂ PO ₂ ^- / l). The solution is buffered in the pH 4 to pH 5 range by the organic acids contained in the process solution.

For the deposition of nickel-phosphorus alloys on the steel surface of a workpiece to be coated 2 is with the in 1 proceed as follows:
The temperature of the process solution, which is the workpiece to be coated 2 surrounds, is adjusted to 85 ° C. Metal ions separate on the steel surface of the workpiece to be coated 2 from. During the deposition, elemental phosphorus, which is formed from the reducing agent by side reactions, is also alloyed into the resulting metal layer, which results in a nickel-phosphorus alloy. The redox process of chemical-reductive metal deposition oxidizes the reducing agent sodium hypophosphite to sodium orthophosphite. This consumption of reducing agent is compensated for by adding sodium hypophosphite to the process solution.

Due to the metal deposition, the pH value and the nickel content in the process solution also decrease. The pH value in the process solution is therefore monitored. If the pH value of the process solution drops below a specified value, for example from pH 4.5 to pH 4.2, then a partial flow of the process solution is circulated through the weakly acidic cation exchanger at a flow rate <5 m / h 14 directed. This results in the weak acid cation exchanger 14 an increase in the nickel content from 5 g / l to 8 g / l and an increase in the pH value from 4.2 to pH values> 5.

By checking the pH in the outlet of the weakly acidic cation exchanger 14 the functionality of the weakly acidic cation exchanger is monitored. As the metal release increases, the weakly acidic cation exchanger is converted into the H ⁺ form, which is why the pH value in the process of the cation exchanger drops. If the pH value in the outlet of the weakly acidic cation exchanger approaches the pH value of the process solution (in this case pH 4.5), the cation exchanger is transferred back to the nickel loading for reuse, as described at the beginning.

In the case of metal coating, the high treatment temperatures result in evaporation losses in the process solution. These evaporation losses are compensated for in the flushing solution from the flushing system 3 through which in 1 line represented by an arrow is fed from the right rinsing bath into the process solution, since the concentration of the rinsing water constituents is highest in this container. listed, which were obtained in the comparative test described.

In the comparative experiment (see right column of the table), the salt content in the process solution rises to high values after a metal throughput of 5.5 MTO due to the foreign substances introduced or formed (in particular Na ⁺ , SO ₄ ^2– , H ₂ PO ₃ ^- ) so that at this point the deposition rate at 90 ° C drops to values <5 μm / h and the properties of the deposited layers no longer meet the requirements.

When using the weakly acidic cation exchanger according to the invention 14 (see the two middle columns in the table), however, the SO ₄ ^2– content of the process solution does not increase with increasing metal throughput, since the nickel ions are introduced into the process solution without disturbing SO ₄ ^2– . In contrast to the comparative experiment, the Na ⁺ content increases considerably more slowly here, since the pH is adjusted without adding NaOH to the process solution. By using the weakly acidic cation exchanger 14 the process solution can be used due to the slower increase in the foreign matter content up to a metal throughput of approx. 8 MTO. The service life of the process solution is determined by the use of the weakly acidic cation exchanger 14 almost doubled.

2 shows a diagram of a plant for chemical-reductive metal coating with a weakly acidic cation exchanger 14 that has a heat exchanger 4 with the coating container 1 connected is. Regarding the coating container 1 and the flushing system 3 this system is made according to the system 1 built up. This system contains a storage tank as additional components 5 and a stacking container 13 , each via the heat exchanger 4 with the coating container 1 are connected.

The weakly acidic cation exchanger 14 corresponds in structure to that of 1 , In contrast to 1 However, in this system it is not directly with the coating container 1 connected, but with its inlet to the storage container 5 and with its drain with the stacking container 13 ,

In principle, how to coat the metal in this system 1 described, proceed. The weakly acidic cation exchanger 14 however, it is loaded with cooled process solution. For this purpose, a volume flow of the process solution through the heat exchanger 4 passed and cooled in this from the treatment temperature of 85 ° C to temperatures <50 ° C. This cooled solution is in the storage container 5 collected, and from this over the weakly acidic cation exchanger 14 directed. Through the weakly acidic cation exchanger 14 takes place in analogy to 1 , an enrichment of the treated solution with nickel ions and an increase in the pH value. The treated solution is in the stacking container 13 collected and over the heat exchanger 4 back to the coating tank 1 fed.

By using the heat exchanger 4 becomes the weakly acidic cation exchanger 14 with a cooled process solution, which significantly reduces the risk of chemical-reductive metal deposition on the cation exchange polymer.

3 shows a schematic of a plant for chemical-reductive metal coating, in which the service life of the process solution can be extended, with a weakly acidic cation exchanger 14 for replenishing the metal ions and adjusting the pH, as well as a strongly acidic cation exchanger 15 and a weakly basic anion exchanger 9 for the separation of interfering ions from the rinsing solution. The structure of the system corresponds with regard to the coating container 1 and the flushing system 3 the in 1 shown plant.

The weakly acidic cation exchanger 14 corresponds in structure to that 1 described cation exchanger. In contrast to 1 is here on the weakly acidic cation exchanger 14 however rinsing solution abandoned. Hence the weakly acidic cation exchanger 14 in contrast to 1 with its inlet with the right tank of the flushing system 3 connected, in which the rinsing solution with the highest concentration of carried out components of the process solution is located. The course of the weakly acidic cation exchanger 14 is with the coating container 1 connected.

This system contains a strongly acidic cation exchanger as further components 15 and a weakly basic anion exchanger 9 in a regeneration circuit with the right tank of the flushing system 3 are connected. Here is the inflow of the strongly acidic cation exchanger 15 with the right rinse tank 3 and its sequence with the addition of the weakly basic anion exchanger 9 connected. The process of the weakly basic anion exchanger 9 is again with the right rinse tank 3 connected.

The strongly acidic cation exchanger 15 consists of an ion exchange column which is filled with the strongly acidic, macroporous cation exchange polymer, Lewatit SP 112 from Bayer AG, Leverkusen, Germany, in the H ⁺ loading. Comparable strongly acidic polymers from other manufacturers, such as the strongly acidic cation exchange polymer C 150 from Purolite, Ratingen, Germany, can also be used. The strongly acidic cation exchanger is used before use 15 charged with hydrochloric acid and thereby loaded with protons.

The weakly basic anion exchanger 9 consists of a column filled with the weakly basic, macroporous anion exchange polymer, Lewatit MP 62 from Bayer AG, Leverkusen, Germany. Comparable weakly basic anion exchange polymers from other manufacturers, such as the weakly basic anion exchange polymer A 100 from Purolite, Ratingen, Germany, can also be used. The weakly basic anion exchanger is used before use 9 charged with sodium hydroxide solution and thereby the anion exchange polymer is converted into the form of the free base.

The column capacity of the ion exchange column filled with cation exchange material in the H ⁺ form 15 is higher than the column capacity of the ion exchange column filled with weakly basic anion exchange material 9 ,

The metal coating in this system is carried out in the same way as for the procedure 1 described was, however, the rinsing solution used to compensate for evaporation losses in the coating tank 1 is supplied with the ion exchangers 9 . 14 . 15 edited. The workpiece is used for the chemical-reductive deposition of nickel on steel surfaces 2 in the coating container 1 treated at a process solution temperature of approx. 85 ° C. The process solution has a pH of 4.5 and a nickel content of 6.0 g / l at the start of the process. The metal deposition reduces the pH value and the nickel content in the process solution.

After coating, the coated workpiece 2 in the rinsing container of the rinsing system 3 immersed. With the workpiece, part of the process solution is dragged into the rinsing solution of the rinsing system. A certain mass flow of components, including the foreign substances formed, is transferred from the process solution to the rinsing solution via the electrolyte extraction, which achieves a cleaning effect in the process solution. This means that some of the protons and other ions that are formed by the chemical-reductive nickel deposition get from the process solution into the rinsing solution. The rinsing solution is therefore a diluted process solution.

To compensate for evaporation losses in the process solution, the rinsing solution is poured over the weakly acidic nickel-loaded cation exchanger 14 , led who like to 1 described is constructed and loaded. This releases nickel ions into the solution and binds protons. Thus, the process solution with the supplied rinsing solution is simultaneously supplied with ions of the coating metal, and the consumption caused by the metal deposition is compensated. At the same time, the weakly acidic cation exchanger 14 Protons withdrawn from the supplied solution: With the supplied rinsing solution, the pH in the process solution is also adjusted. Checking the capacity of the weakly acidic cation exchanger 14 done how to 1 described about the measurement of the pH in its sequence.

The Subsequent metering of the used reducing agent is carried out here Add sodium hypophosphite to the process solution.

To prepare the rinsing solution, a volume flow is generated via the strongly acidic cation exchanger 15 headed in the H ⁺ load. The strongly acidic cation exchanger 15 binds interfering cations, which come mainly from the reducing agent and the base material of the workpiece to be coated, and releases protons into the solution. However, nickel ions are also removed from the rinsing solution.

The strongly acidic cation exchanger binds according to its selectivity 15 cations in solution until it reaches its capacity limit and releases an equivalent amount of protons into the solution. In addition to the cations of the reducing agent and the alkali used to adjust the pH, the cations of the coating metal and the cations originating from the base material are also removed, polyvalent cations preferably being bound.

Exhaustion of the capacity of the cation exchanger 15 is, as is customary in the prior art, by measuring the conductivity in the inlet and outlet of the cation exchanger 15 controlled. As soon as the difference in the leading values in the inlet and outlet of the cation exchanger 15 has fallen below a set value, the strongly acidic cation exchanger 15 regenerated.

to It is regenerated in a known manner by adding hydrochloric acid at a concentration of 70 g / l to 100 g / l again loaded with protons and can after a rinse with deionized water again to extend the service life of the process solution be used.

The through the strongly acidic cation exchanger 15 acidified rinsing solution is now over the weakly basic anion exchanger 9 passed, which is in the form of the free base. This binds disruptive anions, such as. B. the anions of the oxidized reducing agent orthosphoshite, in which the first by the strongly acidic cation exchanger 15 formed acids are attached to the functional groups. The tertiary amines, the functional groups of the ion exchange polymer, are protonated by the acid and thereby converted into the ammonium form. Only the ammonium form is capable of anion exchange. Due to the selectivity of the ion exchange polymer, certain anions, such as, for example, sulfate or orthophosphite, are preferably bound and can also displace anions which are less firmly bound by the anion exchanger, such as, for example, hypophosphite, from the functional groups capable of ion exchange. This separates the anion mixture. So that the anion exchange polymer does not convert from the ammonium form into the form of the free base, which as an uncharged group is not capable of ion exchange, the weakly basic anion exchanger is used 9 always given an acidic solution.

The regeneration of the weakly basic anion exchanger 9 takes place through the application of sodium hydroxide solution, whereby the weakly basic anion exchanger 9 is converted from the ammonium form into the form of the free base. In this form, the functional group has no charge and is therefore not capable of ion exchange. This allows all of the previously bound anions to be removed quantitatively from the anion exchange polymer. After rinsing with deionized water, the weakly basic anion exchanger can be used 9 can be used again for the removal of interfering anions.

The through the weakly basic anion exchanger 9 Purified rinsing solution is returned to the rinsing system, where, as described above, it compensates for evaporation losses in the process solution via the weakly acidic cation exchanger 14 the coating container 1 is fed. This preparation of the rinsing solution by the strongly acidic cation exchanger 15 and the weakly basic anion exchanger 9 takes place in batch operation. Through the strongly acidic cation exchanger 15 In this system, ions of the coating metal that have entered the rinsing solution from the process solution are also separated. However, these are caused by the weakly acidic cation exchanger 14 replenished again.

The regeneration of the strongly acidic cation exchanger 15 the resulting eluate is adjusted again after loading the pH value with sodium hydroxide solution to pH> 4.5 for loading the weakly acidic cation exchanger 14 used, whereby the separated metal ions of the coating metal are not lost. However, the eluate is only used as long as it does not contain the metal ions of the base material from the workpieces to be coated 2 that are foreign substances is contaminated.

Indirect cleaning of the process solution via the rinsing system 3 has the advantage that the concentration of the reducing agent and the metal ions of the coating metal in the rinsing solution are lower than in the process solution. This reduces the risk of sensitive components of the cleaning device, such as ion exchange materials, being inadvertently chemically and reductively metallized.

The separation of disruptive anions from the rinsing solution described in this embodiment and the replenishment of nickel ions via a weakly acidic cation exchanger loaded with nickel ions 14 If the drag-out and evaporation losses are sufficiently high, the service life of the process solution can be extended. The amount of drag required to clean the process solution is determined using equation 2. In the present example, the following parameters were determined in the process solution with a specific drag-out of 300 ml / m ² after 6 MTO and 12 MTO throughput.

When this system is used according to the invention, the SO ₄ ^2- content of the process solution does not increase with the metal throughput, since the nickel ions with the aid of the weakly acidic cation exchanger 14 can be introduced into the process solution without an annoying anion (SO ₄ ^2– ). In comparison to the prior art, the concentration of sodium ions increases considerably more slowly because the pH is adjusted by the weakly acidic cation exchanger 14 takes place and not, as is customary in the prior art, by adding sodium hydroxide solution to the process solution. Compared to the facility 1 there is an additional one Reduction of the concentration of sodium ions and oxidized reducing agent (H ₂ PO ₃ ^- ), since with the help of the strongly acidic cation exchanger 15 Sodium ions and with the help of the weakly basic anion exchanger 9 H ₂ PO ₃ ^- ions are separated. As a result, the service life of the process solution can be extended from approximately 5.5 MTO to approximately 12 MTO.

In order to be able to stabilize the orthophosphite content at a value <120 g / l via the electrolyte extraction into the rinsing solution, an electrolyte extraction> 4 l / m ² would be required with a deposition of 10 μm nickel.

4 shows a schematic of a plant for chemical-reductive metal coating, in which the service life of the process solution can be extended, with a weakly acidic cation exchanger 14 for replenishing the metal ions and adjusting the pH, as well as a strongly acidic cation exchanger 15 and a weakly basic anion exchanger 9 for the separation of interfering ions from a diluted process solution.

The structure of the system corresponds with regard to the coating container 1 and the flushing system 3 the in 1 shown plant. The right rinse tank 3 is not in this system directly with the coating container 1 but with an additional regeneration container 16 connected. This connection allows the regeneration tank 16 Rinsing solution are supplied. Also from the coating container 1 connects to the regeneration tank 16 through which this process solution can be supplied. Through this connection, the coating container 1 the required amount of process solution can be removed, for the complete transfer of the foreign substances formed in the chemical-reductive metal deposition into the regeneration tank 16 is required.

The regeneration tank 16 is with a strongly acidic cation exchanger 15 and a weakly basic anion exchanger 9 connected, which are connected in series. Here is the inflow of the strongly acidic cation exchanger 15 with the regeneration tank 16 and its sequence with the addition of the weakly basic anion exchanger 9 connected. The process of the weakly basic anion exchanger 9 is again with the regeneration container 16 connected. In addition, the feed of the weakly basic anion exchanger 9 via an additional line directly to the regeneration tank 16 connected. This connection makes the weakly basic anion exchanger 9 If necessary, the diluted process solution can be applied directly. These two ion exchangers 9 . 15 correspond to those in their respective structure and in their functioning 3 ,

The feed of the weakly acidic cation exchanger 14 is with the regeneration tank 16 and the course of the weakly acidic cation exchanger 14 is with the coating container 1 connected. The weakly acidic cation exchanger corresponds in its structure and mode of operation 14 to that 1 described cation exchanger. The metal coating in this system is carried out in the same way as for the procedure 3 has been described, but here the rinsing solution before treatment with the ion exchangers 9 . 14 and 15 in a regeneration container 16 mixed with process solution. This allows the coating container 1 the required amount of process solution can be removed, for the complete transfer of the foreign substances formed in the chemical-reductive metal deposition into the regeneration tank 16 is required. In contrast to 3 In this system, the reducing agent is replenished into the regeneration tank 16 ,

The workpiece is used for the chemical-reductive deposition of nickel on steel surfaces 2 in the coating container 1 treated at a temperature of approx. 85 ° C. The process solution has a pH of 4.5 and a nickel content of 6.0 g / l at the start of the process. The metal deposition reduces the pH value and the nickel content in the process solution. The reducing agent NaH ₂ PO ₂ is subsequently metered into the regeneration tank in aqueous solution 16 ,

To prepare the process solution, a certain volume flow of the process solution from the coating container 1 is the regeneration container 16 fed and diluted there with rinsing solution. This diluted process solution is removed from the regeneration tank 16 in a partial flow over the strongly acidic cation exchanger 15 headed in the H ⁺ load. This binds disruptive cations, which come primarily from the reducing agent and the base material of the workpiece to be coated, and releases protons into the solution. However, nickel ions are also removed from the solution. The acidified solution is placed on a weakly basic anion exchanger 9 abandoned, which is in the form of the free base. By giving up the acidified solution, it is converted into the protonated form capable of anion exchange. Due to the selectivity of the anion exchange polymer, anions such as sulfate or orthophosphite are more strongly bound and anions that are less firmly bound by the exchange polymer can be returned by the exchanger 9 displace. This achieves the preferred binding of sulfate and orthophosphite, which removes these anions from the diluted process solution. The process of the weakly basic anion exchanger 9 is back in the regeneration container 16 recycled so that an efficient removal of the interfering ions is possible via the circuit.

The cleaned solution is from the regeneration tank 16 about the weakly acidic cation exchanger 14 in the coating container 1 led to compensate the evaporation losses. This ensures that the protons introduced during the cleaning process are removed again and that the ions of the coating metal are simultaneously introduced into the process solution without a disruptive anion.

Through the direct connection of the coating container 1 and regeneration tank 16 the required volume flow of process solution into the regeneration tank 16 transferred and passed from this over the ion exchanger. Can be advantageous in the plant 4 the volume flow of process solution passed through the ion exchanger, in contrast to the system 3 , irrespective of the value of the electrolyte extraction in the rinse water. The desired concentration of foreign substances in the process solution can be set by adjusting the volume flow of process solution. Its value is determined by the equation 2 calculated. By avoiding the accumulation of foreign substances, the service life of the process solution in the system described here can be extended 4 can be extended significantly above 20 MTO.

5 shows a diagram of a device for extending the service life of the process solution, in which the redosing of the reducing agent and the separation of disruptive anions takes place in an auxiliary circuit.

The core of this device is a membrane electrolysis cell. This consists of a cathode (-) and an anode (+) and one of the chambers 6 . 7 . 8th . 12 , which are arranged between the electrodes, these chambers forming a basic unit. To increase the capacity, the membrane electrolysis cell can be equipped with additional chambers 7 . 8th and 12 be expanded, this between the chambers 6 and 7 be classified.

The chambers 6 and 7 , as well as the chambers 12 and 7 are separated from each other by a cation exchange membrane K1. The separation of the chambers 7 and 8 each take place through an anion exchange membrane A1, the separation of the chambers 8th and 12 each takes place via an anion exchange membrane A2. Membranes of the Neosepta CMX type, from Tokuyama Soda, Tokuyama City, Japan, are used as the cation exchange membrane K1, and membranes of the Neosepta AMX type, Tokuyama Soda, Tokuyama City, Japan, are used as anion exchange membranes A1 and A2.

In addition to the membrane electrolysis cell, the device contains a weakly basic anion exchanger 9 to separate the anion mixture and a strongly acidic cation exchanger 11 for the removal of interfering cations. These are part of the auxiliary circuit of the membrane electrolysis cell. The strongly acidic cation exchanger 11 The structure and loading of the auxiliary circuit corresponds to that of the strongly acidic cation exchanger 15 out 3 , The weakly basic anion exchanger 9 corresponds to that in structure and loading 3 , The device also contains a buffer container 10 , in which the reducing agent to be added is added.

The feed of the weakly basic anion exchanger 9 is with chamber 7 and the drain with the buffer tank 10 connected. By connecting the buffer tank 10 with the chamber 12 an auxiliary circuit is established. The buffer tank 10 is in another small cycle with the inlet and outlet of the strongly acidic cation exchanger 11 connected. The loading of the two ion exchange columns 9 . 11 takes place in a known manner with the aid of pumps, in a DC mode. Alternatively, a countercurrent mode of operation is also possible.

Furthermore, the device contains a storage container 5 for the process solution to be prepared and a stacking container 13 for the prepared process solution. The storage container 5 is with the inlet and the stacking container 13 with the drain of the chamber 8th connected to the membrane electrolysis system.

The chambers 8th the membrane electrolysis system or the storage container 5 and stacking containers 13 which are filled with process solution are shown hatched. The chambers without hatching contain regeneration solution 7 . 12 or a dilute acid (chamber 6 ). The regeneration solution consists of an aq sodium hypophosphite solution (approx. 50 g / l) and is applied to the strongly acidic cation exchanger 15 partially converted to phosphinic acid. Due to the electrodialytic transport of the anions from the process solution, the regeneration solution also contains certain amounts of these anions, these amounts depending on the state of charge of the anion exchanger 9 is dependent.

To extend their useful life, the anions in this device are removed cation-free from a process solution that was used in the chemical-reductive metal deposition, and at the same time the reducing agent is replenished. For this purpose, as explained by way of example for the chemically reductive nickel coating, the procedure is as follows:
The storage container 5 is filled with processed, cooled process solution. From the storage container 5 the process solution in the chambers delimited by anion exchange membranes A1 and A2 8th the membrane electrolysis cell passed. The anions contained in the process solution (sulfate, chloride, hypophosphite, orthophosphite and in some cases also the anions of the organic acids contained in the process solution) migrate electrodialytically through the anion exchange membrane A1 and reach the chamber 7 which through the cation exchange membrane K1 to the anode (+) or to the chamber 12 is limited and in which there is a dilute acid. From the anode chamber 6 protons, which are formed by water decomposition at the anode (+), enter the chamber 7 and together with the electrodialytically transported anions form the corresponding free acids. Through the cation exchange membrane K1, the anions are transferred to the anode chamber 6 or in the chamber 12 prevented.

The acid mixture in chamber 7 is about the weakly basic anion exchanger 9 headed in the form of the free base. The weakly basic anion exchanger 9 binds in chamber until its capacity is fully used 7 acids formed. At the same time, it is converted from the form of the free base to the protonated form. He then preferentially binds sulfate, chloride and orthophosphite ions and releases an equivalent amount of previously bound hypophosphite ions.

The process of the anion exchanger 9 is in the buffer tank 10 of the auxiliary circuit. There, the reducing agent is added in the form of sodium hypophosphite. The regeneration solution is made from this buffer tank in a small circuit via a strongly acidic cation exchanger 11 passed, which is loaded with protons. Through this cation exchanger 11 the sodium ions which have entered the regeneration solution as sodium hypophosphite as a result of the subsequent addition of the reducing agent are removed again.

From the buffer tank 10 the regeneration solution is in the chamber 12 the membrane electrolysis cell passed, the terminal chamber 12 the membrane electrolysis cell contains the cathode (-). Out of the chamber 12 The hypophosphite ions migrate electrodialytically through the anion exchange membrane A2 into that in the chamber 8th process solution.

Since no cations are removed from the process solution by the regeneration process in the membrane electrolysis cell, the salt content in the prepared process solution does not change by the regeneration process. Only sulfate, chloride and orthophosphite ions are removed from the solution and replaced by an equivalent amount of hypophosphite ions. This enriches the process solution with reducing agents. The process solution prepared in this way is removed from the chamber 8th in the stacking container 13 passed and can be used again for chemical-reductive metal coating.

6 shows a diagram of a device for extending the useful life of the process solution, in which the redosing of the reducing agent and the removal of disruptive anions takes place in an auxiliary circuit of a membrane electrolysis cell. To increase the throughput, the membrane electrolysis cell is compared to 5 expanded by additional chambers. This membrane electrolysis system contains 40 units of the chambers 7 . 8th . 12 , In 6 are only three units of the chambers for the sake of simplicity 7 . 8th . 12 shown.

By the additional Chambers is for needed the ion transport Membrane area over which process and regeneration solution are in contact with each other, enlarged. This can be used in the preparation process the transport service required to separate a given freight of foreign substances is required.

In order to extend the useful life of a process solution that was used in the chemical-reductive metal deposition, the process solution used in this device is enriched with reducing agent and disruptive anions are simultaneously separated from it. The description is analogous to this exercise too 5 method. A voltage of 90 V is applied to the expanded membrane electrolysis cell with 40 units.

7 shows a schematic of a plant for chemical-reductive metal coating, in which the service life of the process solution is extended by the removal of disruptive anions and the subsequent dosing of the reducing agent in a membrane electrolysis cell with an auxiliary circuit. Regarding the coating container 1 , the flushing system 3 and the heat exchanger 4 this system is made according to the system 2 built up. As an additional component, the system contains a device for separating disruptive anions and for further metering of the reducing agent, in which the anion mixture is separated in an auxiliary circuit. The construction of the device corresponds to that of 6 and contains 40 units of the chambers 7 . 8th . 12 , In 7 are, however, only two units of the chambers for simpler illustration 7 . 8th . 12 shown. The storage container 5 and the stacking container 13 the device are as in 2 via the heat exchanger 4 with the coating container 1 connected.

The procedure for the chemical-reductive deposition of nickel on steel surfaces is as follows: The workpiece 2 is in the coating tank 1 at a temperature of approx. 85 ° C in analogy to the description 1 treated. The process solution has a pH of 4.5 and a nickel content of 6.0 g / l at the start of the process. The metal deposition reduces the pH value and the nickel content in the process solution. The used ions of the coating metal are subsequently metered in by adding nickel sulfate to the process solution. The pH is adjusted by adding sodium hydroxide solution to the process solution.

The metering of the reducing agent and the removal of interfering anions is carried out in an auxiliary circuit in this system as for 5 described. For this purpose, a certain volume flow of the process solution becomes the coating container 1 removed and, according to the description 2 , via the heat exchanger 4 cooled to temperatures <50 ° C, and in the storage container 5 collected. The required volume flow is calculated using equation (2). For cooling in the heat exchanger 4 prepared process solution is used, the stacking container for this purpose 13 is removed and fed into the process solution.

From the storage container 5 becomes the process solution how to 5 described, brought into contact with the auxiliary circuit in the membrane electrolysis cell. A voltage of 90 V is applied to the membrane electrolysis cell with 40 units. In the membrane electrolysis cell, interfering anions are separated from the process solution by contact with the auxiliary circuit and the applied voltage, and at the same time reducing agent is metered into the process solution without cation. The processed process solution is the stacking container 13 fed and via the heat exchanger 4 analogous to the description of 2 brought back to process temperature and in the coating container 1 recycled.

When using the system according to the invention, the following parameters for the process solution result depending on the metal throughput:

Through the separation of disruptive anions and the cation-free replenishment of the reducing agent A significant reduction in the increase in foreign matter is achieved in the auxiliary circuit. With the in 7 shown system, however, no cations can be removed from the process solution. The pH is adjusted by adding sodium hydroxide solution to the process solution, which means that cations have entered the process solution. Due to the resulting salting, this limits the service life of the process solution, which increases the hypophosphite concentration in the process solution.

By the separation more disruptive Anions in the auxiliary circuit and replenishment of the reducing agent without annoying Cations can be an extension the service life of the process solution can be achieved on at least 12 MTO, with the volume flow of process solution being via the Membrane electrolysis cell is passed, the orthophosphite concentration in the process solution discontinued and a sharp increase in hypophosphite concentration in the process solution is avoided. The volume flows are calculated according to equation 2.

8th shows a schematic of a plant for chemical-reductive metal coating, in which the service life of the process solution by a weakly acidic cation exchanger 14 to replenish the ions of the coating metal and adjust the pH and the removal of disruptive anions and the replenishment of the reducing agent in an auxiliary circuit is extended. The plant after 8th is analogous to that from 7 constructed and additionally contains a weakly acidic cation exchanger 14 how he too 1 and which was described in 1 with the coating container 1 connected is. So that come in exemplary embodiments 1 and 5 described devices in combination for use.

For the chemical-reductive deposition of nickel on steel surfaces in this system, the procedure is as follows: The workpiece 2 is in the coating tank 1 at a temperature of approx. 85 ° C analogous to the description 1 treated. The process solution has a pH of 4.5 and a nickel content of 6.0 g / l at the start of the process. The metal deposition reduces the pH value and the nickel content in the process solution. The metering of the used metal ions and the adjustment of the pH in the process solution is done as for 1 described with the help of the weakly acidic cation exchanger 14 , The metering of the reducing agent and the removal of disruptive anions is carried out in this system via an auxiliary circuit as for 5 described.

As by the use of the weakly acidic cation exchanger according to the invention 14 If no disturbing anions are introduced into the process solution when the metal ions are replenished, significantly smaller amounts of foreign matter must be separated from the process solution. Salting of the process solution is also avoided, since no sodium hydroxide solution and therefore no additional cations are introduced into the process solution to adjust the pH. This enables the extensive separation of orthophosphite without simultaneously increasing the hypophosphite content above the target value in the process solution.

By metering the ions of the coating metal and the reducing agent without interfering ions, separating interfering anions from the process solution and avoiding adding sodium hydroxide solution to the process solution to adjust the pH, the composition of the process solution is stabilized over a longer period of time and almost steady state with respect to pH, concentrations of sulfate, Na ⁺ , hypophosphite and orthophosphite reached. The composition of the process solution in the steady state is characterized by the following tabular parameters and corresponds to a bath age of approx. 1 MTO.

This steady state advantageously corresponds to a fresh process solution in the important parameters such as pH value, nickel content and deposition rate. Since the ions of the coating metal and reducing agent are replenished without disturbing counterions in this system, and thus the positive effects of the devices 1 and 5 complement each other, the useful life of the process solution is further extended. The service life of the process solution is in the system 8th however, limited by the introduction of other foreign substances, such as cations from the base material of the workpiece to be coated.

9 shows a diagram of a system with auxiliary circuit and weakly acidic cation exchanger 14 which is a strongly acidic cation exchanger 15 for separation from interfering cations from the process solution. The plant after 9 is analogous to 8th constructed and additionally contains a strongly acidic cation exchanger 15 , This strongly acidic cation exchanger 15 is with inlet and outlet with the coating tank 1 connected. The structure of the strongly acidic cation exchanger 15 corresponds to that 3 , This attachment contains how the attachment looks like 8th , a strongly acidic cation exchanger in the auxiliary circuit of the membrane electrolysis cell 11 , whose task it is to separate disruptive cations from the auxiliary circuit, which are introduced into the regeneration solution as sodium hypophosphite by the addition of the reducing agent. Since the auxiliary circuit and the process solution are separated from one another by the anion exchange membranes A1 and A2, cations are not transported from the process solution into the auxiliary circuit. With the help of the strongly acidic cation exchanger 11 this means that no interfering cations can be separated from the process solution.

The procedure for the chemical-reductive deposition of nickel on steel surfaces in the plant 9 corresponds to that of the plant 8th has been described.

During the chemical-reductive coating processes run secondary processes such as. Pickling processes that lead to an entry of foreign substances lead from the base material into the process solution, whereby the foreign substances in the process solution usually in cationic form. Limit these foreign substances the service life of the process solution especially when the devices described above Removal of other disruptive Substances or the reduced entry of disruptive substances, such as here in particular Sulfate and sodium ions, the service life of the process solution is extended.

By using the additional strongly acidic cation exchanger 15 In a cleaning process, an accumulation of interfering cationic foreign substances in the process solution is eliminated. For this purpose, a volume flow of process solution is added to the how to 3 described, proton-loaded cation exchanger 15 directed. The strongly acidic cation exchanger binds according to its selectivity 15 until the cations in the solution have reached their capacity limit, polyvalent cations preferably being bound, and releases an equivalent amount of protons into the solution. In particular, it binds cations that come from the base material and interfere with the process of chemical-reductive metal deposition, but also the cations of the coating metal.

The removal of the protons released during cleaning and the supply of those during cleaning with removed ions of the coating metal is done in that the process solution, such as 1 described, about the weakly acidic cation exchanger 14 is directed. The regeneration of the strongly acidic cation exchanger 15 done how to 3 described by rinsing the cation exchanger with hydrochloric acid. By separating the cationic foreign substances with the help of the strongly acidic cation exchanger 15 can further extend the useful life of the process solution.

10 shows a schematic of a membrane electrolysis cell with auxiliary circuit and weakly acidic cation exchanger 14 with the stacking bin 13 and which is a strongly acidic cation exchanger 15 contains for the removal of interfering cations from the process solution. The plant after 10 contains the same system components as 9 , however, the inflow and outflow of the weakly acidic cation exchanger 14 not with the coating container 1 but with the stacking container 13 connected.

The chemical-reductive deposition of nickel on steel surfaces in this system takes place in analogy to the description of 8th , The reducing agent is then metered in and interfering anions are separated off analogously to the description 5 in a membrane electrolysis cell with auxiliary circuit.

The coating tank 1 a certain volume flow of process solution is taken and via the heat exchanger 4 cooled to temperatures <50 ° C, and in the storage container 5 collected. Prepared process solution is used for cooling, the stacking container for this purpose 13 removed and into the coating container 1 is directed. The cleaning of the cooled solution by the removal of interfering anions and the subsequent dosing of reducing agent takes place through contact with the auxiliary circuit in the membrane electrolysis cell, as is the case with 5 has been described.

The difference to the plant 8th consists of the cooled and prepared process solution from the stacking container in the system described here 13 for replenishing the used ions of the coating metal and for adjusting the pH value over the weakly acidic cation exchanger loaded with nickel ions 14 is directed. As in this embodiment of the plant, the process solution cooled on the weakly acidic cation exchanger 14 is given, the risk of unwanted nickel deposition on the ion exchange polymer is reduced.

This Procedure according to the invention is particularly useful when separating interfering anions with simultaneous replenishment of hypophosphite a very high one Concentration of hypophosphite in the cleaned process solution reached was because of the risk of unwanted reductive metal deposition with the concentration of the reducing agent increases.

The strongly acidic cation exchanger is used for the cleaning process to remove interfering cations 15 proceed like this too 9 has been described.

11 shows a schematic of a membrane electrolysis cell with auxiliary circuit, in which the inlet of the strongly acidic cation exchanger 15 for the purpose of indirect cleaning of the process solution to the rinsing system 3 connected. The plant after 11 contains the same components as the one after 9 , In contrast to the plant after 9 here is the inflow of the weakly acidic cation exchanger 14 not with the coating container 1 but with the stacking container 13 and its flow through the heat exchanger 4 with the coating container 1 connected. In another difference to the plant after 9 is the strongly acidic cation exchanger 15 with its inlet with the flushing system 3 and with its drain with the reservoir 5 connected. Through the heat exchanger 4 becomes the required cooling process when transferring process solution from the coating container 1 in the storage container 5 used for heating the prepared solution. A heat exchanger can be dispensed with, provided that only small volume flows of process solution for cleaning the process solution from the coating container 1 in the storage container 5 have to be transferred.

For the chemical-reductive deposition of nickel on steel surfaces in this system, the procedure is as follows: The workpiece 2 is in the coating tank 1 at a temperature of approx. 85 ° C analogous to the description 1 treated. The process solution has a pH of 4.5 and a nickel content of 6.0 g / l at the start of the process. The metal deposition reduces the pH value and the nickel content in the process solution. After coating, the coated workpiece 2 in the rinsing container of the rinsing system 3 immersed. With the workpiece, part of the process solution becomes the rinsing solution of the rinsing system 3 dragged out. Interfering cations and anions from the process solution also get into the rinsing system 3 , The pH value is adjusted and ions of the coating metal are replenished using the weakly acidic cation exchanger 14 between the stacking container 13 and coating container 1 is switched.

The metering of the reducing agent and the removal of interfering anions takes place in this system in a membrane electrolysis cell with an auxiliary circuit, such as 5 described, wherein a diluted process solution is applied to the membrane electrolysis cell. For this, rinsing solution from the rinsing system 3 about the strongly acidic cation exchanger 15 guided, whereby disturbing cations are removed from the rinsing solution. In order for the process solution to be adequately cleaned even without high specific electrolyte carry-overs, a certain volume flow of the process solution is removed from the coating container 1 via the heat exchanger 4 (optional) the storage container 5 fed. The volume flow required depends on the amount of metal deposited and is calculated using equation (2).

From the storage container 5 becomes the process solution how to 5 described, brought into contact with the auxiliary circuit in the membrane electrolysis cell. The voltage that is applied to the membrane electrolysis system is 90 V at 40 units. In the membrane electrolysis cell, disruptive anions are separated from the process solution by contact with the auxiliary circuit and reducing agents are added to the process solution without cation. The process solution prepared in this way becomes the stacking container 13 removed and for metering the used metal ions and for adjusting the pH via the weakly acidic cation exchanger loaded with nickel ions 14 directed. The course of the weakly acidic cation exchanger 14 becomes the coating tank 1 fed and used to compensate for evaporation losses.

Advantageous with this design of the process technology, that is the regeneration system a diluted one process solution is abandoned. Due to the lower concentration of ingredients (Ions of the coating metal, reducing agent) is reduced the danger of an unwanted Metal deposition on sensitive components of the cleaning device, such as. Membranes and ion exchange polymers.

The treatment of the process solution according to the invention achieves a steady state at a concentration level which corresponds to a bath age of approximately 1 MTO and is characterized by the following parameters of the process solution shown in table form:

Advantageous corresponds to this stationary Condition in the important parameters such as pH value, nickel content and deposition rate a fresh process solution. By varying the volume flows of process solution, the compositions can be brought into contact with the auxiliary circuit the process solution can be set that correspond to a bath age of 1 to 4 MTO.

1

coating tank

2

to coating workpiece

3

(Multi-stage) flushing system

4

heat exchangers

5

Storage container for to be cleaned process solution

6

anode chamber the membrane electrolysis cell

7

concentrating compartment the auxiliary circuit of the membrane electrolysis cell

8th

chamber the membrane electrolysis cell with the process solution to be cleaned

9

weakly Anion exchanger for the separation of the anions

mixture used

10

Buffer tank for the auxiliary circuit

11

strong acid Cation exchanger in the auxiliary circuit

12

regeneration chamber the auxiliary circuit of the membrane electrolysis cell

13

Stacking container for cleaned process solution

14

slightly acidic Cation exchanger for replenishing the

coating metal

15

strong acid Cation exchanger for cleaning the process solution

16

replenishment containers

+

anode

-

cathode

A1, A2

Anionaustauschermembranen

K1

cation

H ₂ O

fresh water

NaH ₂ PO ₂

reducing agent

Claims (26)

Process for extending the useful life of a process solution for chemical-reductive metal deposition, in which the reducing agent used in the metal deposition and ions of the coating metal are metered in and the pH of the process solution is adjusted, characterized in that the pH adjustment and the metering in the ions of the coating metal by placing the process solution or a diluted process solution on at least one weakly acidic cation exchanger loaded with ions of the coating metal ( 14 ) takes place and the solution prepared by the weakly acidic cation exchanger is returned to the process solution. Process for extending the service life of a process solution for chemical-reductive metal deposition, in which the reducing agent used in the metal deposition and ions of the coating metal are replenished and the pH in the process solution is adjusted, with anions in a membrane electrolysis cell with an additional auxiliary circuit between the process solution and the auxiliary circuit can be exchanged via the anion exchange membranes (A1, A2), characterized in that the reducing agent is subsequently metered into the auxiliary circuit in the form of a salt or a salt solution, with disruptive cations originating from the reducing agent using a strongly acidic proton-loaded cation exchanger ( 11 ) and disruptive anions with the help of a weakly basic anion exchanger ( 9 ) are separated from the auxiliary circuit. A method according to claim 2, characterized in that the pH adjustment and replenishment of the ions of the coating metal using at least one weakly acidic cation exchanger loaded with ions of the coating metal ( 14 ) he follows. A method according to claim 2 or 3, characterized in that during the metal deposition in the process solution accumulating interfering cations with the help of at least one strongly acidic proton-loaded cation exchanger ( 15 ) are separated. Process for extending the service life of a process solution for chemical-reductive metal deposition, in which the reducing agent used in the metal deposition and ions of the coating metal are replenished, and the pH of the process solution is adjusted, characterized in that the metal deposition in the process solution enriching interfering cations with the help of at least one strongly acidic proton-loaded cation exchanger ( 15 ) and in metal deposition enriching interfering anions with the help of at least one weakly basic anion exchanger ( 9 ) are separated from the process solution or a diluted process solution. A method according to claim 5, characterized in that the pH adjustment and the subsequent metering of the ions of the coating metal using at least one weakly acidic cation exchanger loaded with ions of the coating metal ( 14 ) he follows. Device for extending the service life of a process solution for chemical-reductive metal deposition, consisting of at least one weakly acidic cation exchanger ( 14 ) for use in adjusting the pH value and replenishing ions of the coating metal in a system for chemical-reductive metal deposition, the device elements for connecting the inlet and the outlet of the weakly acidic cation exchanger ( 14 ) with at least one container containing process solution, diluted process solution, cooled process solution and / or pretreated process solution. Device for extending the service life of a process solution for chemical-reductive metal deposition, consisting of at least one strongly acidic cation exchanger ( 15 ) for use in the removal of interfering cations in a plant for chemical-reductive metal deposition, the device elements for connecting the strongly acidic cation exchanger ( 15 ) with at least one container containing process solution, diluted process solution, cooled process solution and / or pretreated process solution. Device for extending the service life of a process solution for chemical-reductive metal deposition, consisting of at least one strongly acidic cation exchanger ( 15 ) for the removal of interfering cations and at least one weakly acidic cation exchanger connected in series or parallel to it ( 14 ) for use in adjusting the pH value and replenishing ions of the coating metal in a system for chemical-reductive metal deposition, the device elements for connecting the strongly acidic cation exchanger ( 15 ) and the weakly acidic cation exchanger ( 14 ) with at least one container containing process solution, diluted process solution, cooled process solution and / or pretreated process solution. Device for extending the service life of a process solution for chemical-reductive metal deposition, consisting of at least one strongly acidic cation exchanger ( 15 ) for the removal of interfering cations and at least one weakly basic anion exchanger connected in series or parallel to it ( 9 ) for the removal of interfering anions for use in a plant for chemical-reductive metal deposition, the device elements for connecting the weakly basic anion exchanger ( 9 ) and the strongly acidic cation exchanger ( 15 ) with at least one container containing process solution, diluted process solution, cooled process solution and / or pretreated process solution. Device for extending the service life of a process solution for chemical-reductive metal deposition according to claim 10, characterized in that it additionally has at least one weakly acidic cation exchanger ( 14 ) for pH adjustment and replenishment of ions of the coating metal and elements for connecting the weakly acidic cation exchanger ( 14 ) with at least one container containing process solution, diluted process solution, cooled process solution and / or pretreated process solution. Device for extending the service life of a process solution for chemical-reductive metal deposition for use in a system for chemical-reductive metal deposition, consisting of a membrane electrolysis cell with an auxiliary circuit that has at least one weakly basic anion exchanger ( 9 ) and at least one strongly acidic cation exchanger connected in series or parallel to this ( 11 ), where the membrane electrolysis cell consists of at least one anode +, a cathode -, and at least four chambers arranged in between, the anode in the first chamber, the anode chamber ( 6 ), the anode chamber ( 6 ) via a cation exchange membrane (K1) with the second, the enrichment chamber ( 7 ) is in contact, the third chamber ( 8th ) via anion exchange membranes (A1, A2) with the second, the enrichment chamber ( 7 ) and the fourth, the replenishment chamber ( 12 ), in contact with the enrichment chamber ( 7 ) and replenishment chamber ( 12 ) Are part of the auxiliary circuit and with the weakly basic anion exchanger ( 9 ) and the strongly acidic cation exchanger ( 11 ) are connected, whereby the contact between process solution and auxiliary circuit via the anion exchange membranes (A1, A2) in the third chamber ( 8th ) takes place, the chambers ( 7 ), ( 8th ) and ( 12 ) together one form a repeatable base unit within the membrane electrolysis cell and the device elements for connecting the third chamber ( 8th ) the membrane electrolysis cell with at least one container which contains cooled process solution, diluted cooled process solution, and / or pretreated cooled process solution. Device for extending the service life of a process solution for chemical-reductive metal deposition according to claim 12, characterized in that it additionally has at least one weakly acidic cation exchanger ( 14 ) for pH adjustment and replenishment of ions of the coating metal and / or strongly acidic cation exchanger ( 15 ) for the separation of interfering cations and elements for connecting the weakly acidic cation exchanger ( 14 ) and / or strongly acidic cation exchanger ( 15 ) with at least one container containing process solution, diluted process solution, cooled process solution and / or pretreated process solution. Device according to one of claims 7 to 13, characterized in that the ion exchanger (s) ( 9 . 11 . 14 . 15 ) Are column exchangers which contain at least one solid, water-insoluble, organic or inorganic ion exchange material and can be regenerated in cocurrent or countercurrent. Device according to one of claims 7 to 13, characterized in that the ion exchanger (s) ( 9 . 11 . 14 . 15 ) are each part of a filter or membrane apparatus which contains at least one regenerable, organic or inorganic ion exchange material. Device according to one of claims 7 to 13, characterized in that the ion exchanger (s) ( 9 . 11 . 14 . 15 ) each consists of a container that contains a liquid which is immiscible with the process solution and in which an ion exchange material is distributed. Plant for chemical-reductive metal deposition, consisting of at least one coating container ( 1 ), a flushing system ( 3 ) and associated peripherals, such as. B. pumps, valves, measuring devices for pH, conductivity, temperatures, characterized in that it contains at least one device for extending the useful life of a process solution for chemical-reductive metal deposition according to one of claims 7 to 16. Plant according to claim 17 with at least one device according to claim 11, characterized in that the strongly acidic cation exchanger ( 15 ) and the weakly basic anion exchanger ( 9 ) in series or parallel connection with the flushing system ( 3 ) or an additional one with the flushing system ( 3 ) connected, regeneration container ( 16 ) and the feed of the weakly acidic cation exchanger ( 14 ) with the flushing system ( 3 ) or the regeneration container ( 16 ) and the course of the weakly acidic cation exchanger ( 14 ) with the coating container ( 1 ) are connected. Plant according to claim 17, with at least one device according to claim 7 and / or 8, characterized in that the inlet and outlet of the weakly acidic cation exchanger ( 14 ) and / or the strongly acidic cation exchanger ( 15 ) directly or via a heat exchanger ( 4 ) with the coating container ( 1 ) are connected. Installation according to claim 17 with at least one device according to claim 12, characterized in that the third chamber ( 8th ) the membrane electrolysis cell via a heat exchanger ( 4 ) with the coating container ( 1 ) connected is. Installation according to claim 20 with at least one device according to claim 8, characterized in that the strongly acidic cation exchanger ( 15 ) with its inlet with the flushing system ( 3 ) and with its drain via an additional storage container ( 5 ) between the coating container ( 1 ) and the third chamber ( 8th ) the membrane electrolysis cell is connected, is connected. Plant according to claim 20 or 21 with at least one device according to claim 7, characterized in that the weakly acidic cation exchanger ( 14 ) with its inlet to the third chamber ( 8th ) connected to the membrane electrolysis cell and with its outlet via the heat exchanger ( 4 ) with the coating container ( 1 ) connected is. Use of weakly acidic cation exchange material or weakly acidic cation exchangers ( 14 ) for pH adjustment and replenishment of ions of the coating metal increase the useful life of a process solution for chemical-reductive metal deposition. Use of strongly acidic cation exchange material or strongly acidic cation exchangers ( 11 . 15 ) for the removal of interfering cations to extend the useful life of a process solution for chemical-reductive metal deposition. Use of a combination of a.) Weakly basic anion exchange material or weakly basic anion exchanger ( 9 ) for the removal of interfering anions and b) strongly acidic cation exchange material or strongly acidic cation exchangers ( 11 . 15 ) for the removal of interfering cations to extend the useful life of a process solution for chemical-reductive metal deposition. Use of a combination of a.) Weakly acidic cation exchange material or weakly acidic cation exchanger ( 14 ) for pH adjustment and replenishment of ions of the coating metal and b) strongly acidic cation exchange material or strongly acidic cation exchangers ( 15 ) for the removal of interfering cations to extend the useful life of a process solution for chemical-reductive metal deposition.