EP1006213B1 - Process for regenerating a processing solution - Google Patents

Abstract

Chemical reduction metal plating solution regeneration uses a weakly basic anion exchanger (T1) for hypophosphite ion recycle to the cathodic chamber (3) of a multi-chamber electrodialysis cell. An acid mixture, formed in the second chamber (6) by entry of protons from the anodic chamber (1), is supplied to a hypophosphite-loaded weakly basic anion exchanger with its outlet connected to the cathodic chamber. A chemical reduction metal plating solution, containing hypophosphite and ortho phosphite, is regenerated in a multi-chamber electrodialysis cell having two chambers separated from one another by an anion exchange membrane and which are located between a dilute acid-containing anodic chamber and a cathodic chamber, the first chamber being separated from the cathode chamber by an anion exchange membrane and the second chamber being separated from the anodic chamber by a cation exchange membrane. The solution is delivered to the first chamber for hypophosphite and orthophosphite ion transport from the solution to the second chamber and simultaneous hypophosphite ion transport from the cathodic chamber into the solution, the resulting regenerated solution being discharged for reuse. Preferred Features: Part of the solution, leaving the weakly basic anion exchanger (T1), may be passed over a plating metal ion-loaded, weakly acidic anion exchanger within the first chamber (5) of the cell (EZ). A regeneration circuit is formed by a connection (P1) between the cathodic chamber (3) and the second chamber (6). A further chamber may be provided between the anodic chamber (1) and the second chamber and separated from the second chamber by a cation exchange membrane, this further chamber receiving plating metal ions from the anodic chamber and being supplied with part or all of the process solution (PL) which is then transferred to the first chamber. Plating metal additions are made to the first chamber or to the anodic chamber. The anode (2) may be an insoluble anode, preferably of steel or platinized expanded titanium, or a soluble anode of the plating metal.

Description

The invention relates to a method for regenerating a process solution, the is used in the chemical-reductive deposition of metal layers and Contains hypophosphite and orthophosphite, in which the process solution at least four chambers having an electrodialysis cell, one anode chamber containing dilute acid with an anode therein, a Cathode chamber with a cathode inside and two more, through one Anion exchange membrane separated and between these two Has chambers arranged chambers, of which a first chamber through a Anion exchange membrane is separated from the cathode chamber while a second chamber through a cation exchange membrane from the anode chamber is separated, in which the process solution when performing the method of the first Chamber is abandoned, causing the hypophosphite ions and contained therein Orthophosphite ions electrodialytically into the second chamber and simultaneously Hypophosphite ions are transported from the cathode chamber into the process solution are, and at which regenerated process solution is removed and another Use is supplied (DE-A-4 310 366 and US-A-5 419 821).

Coating processes are increasingly being used in surface finishing those contained in an aqueous solution of non-ferrous metal ions by means of chemical Reduction on substrate surfaces made of metal or pretreated plastic as non-ferrous metals be deposited. Coating metals are, for example, copper, Nickel, silver and gold. Hypophosphite, for example, is used as the reducing agent used. As the chemical-reductive nickel deposition is a common in practice The procedure used is based on the following explanations - representative for all other usable metals - on nickel.

In the chemical-reductive deposition of nickel, the reducing agent hypophosphite (H ₂ PO ₂ ) is consumed. In contrast, the oxidized reducing agent orthophosphite (HPO ₃ ^2- ) formed as a reaction product accumulates in the process solution. Side reactions, such as the reduction of hypophosphite to elemental phosphorus, which is built into the deposited nickel layer, result in a consumption of about 3 mol hypophosphite per mol of deposited nickel. The consequence of this is that the hypophosphite concentration in the process solution decreases and has to be raised again by adding additional chemicals. The concentration of orthophosphite, however, increases.

With increasing concentration, the orthophosphite destabilizes the process solution. The leads to rough, uneven nickel deposition and precipitation in the Process solution. The process solution can therefore be used from a certain orthophosphite concentration (Interference limit concentration) no longer for electroless nickel plating be used. The process solution that can no longer be used is partly discarded and replaced by a fresh process solution. Processed solutions are currently being processed disposed of through complex neutralization precipitation or externally at high costs. There are procedures in the literature to extend the useful life of the process solution known in which only the disruptive components at least partially from the Process solution removed and the used components - nickel ions and Reducing agent - be replenished. Nevertheless, the process solutions are based on the Regeneration can only be used to a limited extent.

In the known method according to DE-A-4 310 366 mentioned at the outset, Regenerate the process solution used an electrodialysis cell. The reduction of Orthophosphite formed in the electroless metal deposition is said to be in the cathode compartment the electrodialysis cell. As practice has shown, the orthophosphite can with However, this method cannot be reduced cathodically to hypophosphite, since Orthophosphite continuously accumulates in the regeneration circuit until the Interference limit concentration of the process solution is reached. So no orthophosphite more can be removed from the processed process solution. Only after a discard the regeneration solution and the use of a fresh, orthophosphite-free Regeneration solution, this procedure would be brief - until the adjustment of the Balance - ready for use again.

According to US-A-5 419 821, which was also mentioned at the beginning, the Regeneration circuit to remove the orthophosphite magnesium or Calcium hydroxide added to the orthophosphite in the form of sparingly soluble salts to be removed from the regeneration circuit. The through the separation process Used chemicals (nickel ions and reducing agents) are said to be in the form of Nickel sulfate (addition to the process solution) and phosphinic acid (addition to the Catholytes) are supplied, the sulfate by adding barium hydroxide in the catholyte should be removed as barium sulfate. By the necessary discard of the regeneration solution or the precipitation of the orthophosphite in Forms of poorly soluble alkaline earth salts are described by the two Process causes a high chemical requirement and a high waste volume.

The invention is based on the object, the method described above to further develop that the disruptive orthophosphite from the Process solution can be removed, so that a longer service life of the same is achievable.

This object is achieved according to the invention in that the second Chamber formed by the entry of protons from the anode chamber mixture of acids a weakly basic in the hypophosphite load Anion exchanger is supplied with its outlet to the cathode chamber connected.

This process makes electrodialysis and ion exchange easier Combined operation, and so advantageous that the hypophosphite can be introduced stoichiometrically back into the process solution, whereby it remains fully functional. Electrodialysis will Orthophosphite transferred into a mineral acid solution, from which it is by means of weakly basic anion exchanger can be removed. The hypophosphite containing solution emerging from the ion exchanger is the cathode compartment Electrolysis cell abandoned, from where it is electrodialytic without interfering foreign ions is returned to the process solution through the anion exchanger membrane. The of Process solution depleted of orthophosphite can then be used directly for the process chemical-reductive deposition of nickel can be supplied. The stability and the Functionality of the regenerated process solution are due to equimolar exchange guaranteed by orthophosphite against hypophosphite.

Advantageous embodiments of the invention emerge from the subclaims.

The method according to the invention is described below with reference to the drawings in Exemplary embodiments explained.

Fig. 1 eine für das Verfahren nach der Erfindung verwendbare Anordnung in schematischer Darstellung.

Fig. 2 und 3 zwei unterschiedliche, gegenüber Fig. 1 ergänzte Ausführungsformen der Anordnung.

Fig. 4 bis 6 gegenüber Fig. 1 abgewandelte Ausführungsformen der Anordnung.

Show it:

Fig. 1 shows a usable for the method according to the invention arrangement in a schematic representation.

2 and 3 two different, compared to FIG. 1, supplemented embodiments of the arrangement.

4 to 6 compared to Fig. 1 modified embodiments of the arrangement.

The electrodialysis cell EZ shown in Fig. 1 consists of four chambers. These are an anode chamber (1) with the anode (2) therein, the cathode chamber (3) with the cathode (4) therein and two further chambers, a first Chamber (5) and a second chamber (6), which is between the anode chamber (1) and the cathode chamber (3). The anode (2) is insoluble For example made of steel or platinum-coated expanded titanium. The Anode chamber (1) contains a dilute acid, preferably sulfuric acid. The Cathode (4) consists, for example, of copper or steel.

The first chamber (5) is from the cathode compartment (3) through an anion exchange membrane (AM 1) and from the second chamber (6) through an anion exchange membrane (AM 2) separated. Between the second chamber (6) and the anode compartment (1) there is a cation exchange membrane (KM 1). To the second chamber (6) a weakly basic anion exchanger (T 1) is connected, which turns into The beginning of the procedure is wholly or partly in the hypophosphite loading. The The outlet of the anion exchanger (T 1) is connected to the cathode chamber (3).

The method according to the invention works with an arrangement according to FIG. 1 for example as follows:

The process solution (PL) to be regenerated is fed into the first chamber (5) of the electrodialysis cell (EZ). The hypophosphite and orthophosphite ions contained in the process solution (PL) pass through the anion exchange membrane (AM 2) and reach the second chamber (6), which goes from the cation exchange membrane (KM 1) to the anode (2) is limited and contains a dilute acid. Protons, which are formed by water decomposition on the anode (2), reach the second chamber (6) from the anode chamber (1). Together with the electrodialytically transported anions hypophosphite and orthophosphite, they form the free acids hypophosphoric acid (phosphinic acid, H ₃ PO ₂ ) and phosphorous acid (phosphonic acid, H ₃ PO ₃ ). These anions are prevented from passing into the anode chamber (1) containing a dilute acid by the cation exchanger membrane (KM 1). The acid mixture of phosphinic acid and phosphonic acid is passed through the weakly basic anion exchanger (T 1), which is located in the hypophosphite loading.

The anion exchanger (T 1) binds the orthophosphite ions and gives them Hypophosphite ions into the solution. Those still in solution Hypophosphite ions are not bound by the anion exchanger (T 1). The Drain of the anion exchanger (T 1) in the cathode chamber (3) Electrodialysis cell (EZ) directed. From there the hypophosphite ions electrodialytically through the anion exchange membrane (AM 1) into the process solution (PL) transported. As soon as the capacity of the anion exchanger (T 1) is exhausted, For example, it is regenerated with sodium hydroxide solution. The regenerate (R) of Anion exchanger (T 1) contains all of the orthophosphite, which during the Procedure was bound. For reuse, the Anion exchanger (T 1) transferred back to the hypophosphite loading.

Through a connection of the cathode chamber (3) indicated by the arrow (P 1) the second chamber (6) through the anion exchange membrane (AM 2) and Cation exchanger membrane (KM 1) is limited, a regeneration cycle be set up. During the course of the process, it is possible to replenish spent nickel, for example, nickel hypophosphite can be used, which according to the arrow (P 2) in the first chamber (5), ie in the process solution (PL).

The electrodialysis cell (EZ) can be supplemented by additional chambers to increase the throughput. According to FIG. 2, this can be three additional chambers (7, 8 and 9), which are arranged between the first chamber (5) and the cathode chamber (3). The chamber (7) has a combined function of anode chamber (1) on the one hand (delivery of protons) and cathode compartment (3) on the other hand (transport of hypophosphite into the process solution (PL)). It is separated from the first chamber (5) by an anion exchanger membrane (AM 3) and from the chamber (8) by a cation exchanger membrane (KM 2), which corresponds functionally to the second chamber (6). Similarly, the chamber (9) corresponds functionally to the first chamber (5). It is separated from the chamber (8) by an anion exchange membrane (AM 4) and from the cathode chamber (3) by the anion exchange membrane (AM 1).

The process solution (PL) becomes both the first chamber (5) and the chamber (9) given up. The acid mixture of the second chamber (6) and the chamber (8) enters the anion exchanger (T 1). The solution containing hypophosphite is added to the Cathode chamber (3) and passed into the chamber (7). Here too one can Regeneration circuit must be set up (arrow P 1) and nickel can be replenished (Arrows P 2).

In the embodiment of the arrangement according to FIG. 3 there is additionally a weakly acidic cation exchanger (T 2) which is connected at its inlet to the outlet of the anion exchanger (T 1) and opens at the outlet into the first chamber (5). In this embodiment, it is taken into account that the process solution (PL) to be regenerated is depleted of nickel, since nickel ions are consumed by the chemical-reductive deposition process. By using the cation exchanger (T 2), which is loaded with nickel, it is possible to introduce nickel into the process solution (PL) without disturbing foreign ions. The procedure of the arrangement according to FIG. 3 is basically the same as that of FIG. 1. Here, only a partial stream of the solution emerging from the anion exchanger (T 1) is branched off and passed over the cation exchanger (T 2). This partial flow of the solution discharges the cation exchanger (T 2) in the nickel form. It is fed directly into the process solution (PL). In this way, nickel ions are fed back into the process solution (PL) without an interfering anion. After the nickel has been completely removed from the cation exchanger (T 2), the latter is converted into the sodium form with sodium hydroxide solution and again loaded with nickel ions.

In the embodiments of the arrangement according to FIGS. 4 to 6 it is taken into account that The anode process can be used to remove electroless nickel replenish used nickel ions.

The electrodialysis cell (EZ) according to FIG. 4 is supplemented compared to that according to FIG. 1 by a further chamber (10) which is arranged between the anode chamber (1) and the second chamber (6). It is separated from the second chamber (6) by a cation exchange membrane (KM 3) which is only permeable to monovalent cations. A nickel anode is used here as the anode (2). During the process, nickel is dissolved anodically. It reaches the process solution (PL) electrodialytically. The process solution (PL) is introduced into the chamber (1) delimited by the cation exchange membrane (KM 1) and the cation exchange membrane (KM 3). The cation exchange membrane (KM 3), which is only permeable to monovalent cations, is necessary so that no nickel ions are transported into the regeneration circuit to remove the orthophophite.

Nickel ions migrate from the anode chamber (1) into the process solution (PL). she compensate for the deficit in nickel ions caused by electroless nickel deposition arose. At the same time, an equivalent amount of protons migrate through the Cation exchanger membrane (KM 3) from the chamber (10) into the second chamber 86). As a result, the one formed during the chemical-reductive nickel deposition Amount of acid removed from the process solution (PL). The one with nickel ions Enriched process solution (PL) is then in accordance with the arrow (P3) in the first chamber (5) passed by the anion exchange membrane (AM 2) and Anion exchange membrane (AM 1) is limited. Powered by the electric Field, the anions (hypophosphite and orthophosphite) migrate from the first chamber (5) into the second chamber (6) and form there together with the protons that were previously from the anode chamber (1) and the further chamber (10) into the electrodialytic second chamber (6) were transported, the corresponding free acids. The other The procedure corresponds to the procedure described for FIG. 1. The Nickel anode must be replaced here after the nickel has been used up.

5 , the anodic nickel dissolution can also take place externally. The nickel ions are then fed into the anode chamber (1). This is indicated by the arrow (P4). An anode (2) made, for example, of steel or of platinized titanium expanded metal can then be used, so that no anode change is required. The structure of the electrodialysis cell (EZ) according to FIG. 5 is otherwise identical to that of the electrodialysis cell (EZ) according to FIG. 4. This also applies to the procedure.

To improve the control of the nickel ion concentration and the pH of the process solution (PL), the same can be applied to the chamber (10) according to FIG. 6 only in a partial stream (TL). The nickel-enriched partial flow of the process solution (PL) emerging from the chamber (10) is combined with the process solution (PL) emerging from the first chamber (5) and to be used for further use.

Claims (11)

1. Process for regenerating a processing solution which is used in the chemical-reductive deposition of metal coatings and which contains hypophosphite and orthophosphite, whereby the processing solution is fed to an electrodialysis cell with at least four chambers which includes an anode chamber containing dilute acid and having an anode arranged in it, a cathode chamber having a cathode arranged in it and two other chambers arranged between the aforementioned chambers and separated from each other by an anion-exchange diaphragm with a first one of these chambers being separated from the cathode chamber by an anion-exchange diaphragm and a second one being separated from the anode chamber by a cation-exchange diaphragm, whereby the processing solution when the process is carried out is fed to the first chamber so that the hypophosphite ions and orthophosphite ions contained in the processing solution are electrodialytically transported into the second chamber and at the same time hypophosphite ions are transported from the cathode chamber into the processing solution and regenerated processing solution is taken out and put to another use characterized in that the acid mixture produced in the second chamber (6) by protons entering from the anode chamber (1) is fed to a weakly basic anion exchanger (T 1) which is arranged in the hypophosphite load and the outlet of which is connected to the cathode chamber (3).
2. Process to claim 1 characterized in that a portion of the solution leaving the weakly basic anion exchanger (T 1) is passed into the first chamber (5) of the electrodialysis cell (EZ) over a weakly basic cation exchanger (T 2) which is preloaded with ions of the coating metal.
3. Process to claim 1 or 2 characterized in that a regenerating circuit is created by means of a connection (P 1) of the cathode chamber (3) with the second chamber (6).
4. Process to any of the claims 1 to 3 characterized in that coating metal is fed to the first chamber (5) for making up.
5. Process to any of the claims 1 to 4 characterized in that between the anode chamber (1) and the second chamber (6), there is another chamber (10) separated from the second chamber (6) by a cation-exchange diaphragm (KM 3) into which ions of the coating metal which leave the anode chamber (1) are fed.
6. Process to claim 5 characterized in that the processing solution (PL) is fed to the other chamber (10) and passed from there to the first chamber (5).
7. Process to claim 5 characterized in that a split (TL) of the processing solution (PL) is passed through the other chamber (10).
8. Process to any of the claims 1 to 7 characterized in that an insoluble anode (2) is used which preferably consists of steel or platinized expanded titanium.
9. Process to any of the claims 1 to 8 characterized in that ions of the coating metal are fed to the anode chamber (2).
10. Process to any of the claims 1 to 7 characterized in that a soluble anode (2) consisting of the coating metal is used.
11. Process to any of the claims 1 to 10 characterized in that an electrodialysis cell (EZ) with a multiple arrangement of the chambers is used.

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