US20020166772A1

US20020166772A1 - Maintenance of an electrolyte

Info

Publication number: US20020166772A1
Application number: US10/104,127
Authority: US
Inventors: Jan Hendriks; Josephus Weel
Original assignee: Enthone Inc
Current assignee: MacDermid Enthone Inc
Priority date: 2001-03-24
Filing date: 2002-03-22
Publication date: 2002-11-14
Also published as: SG111051A1; KR20020075825A; PL352752A1; CN1306072C; CN1382836A; EP1243673A1; JP2002322600A; RU2002107327A

Abstract

The present invention pertains to a method for the care and maintenance of an electrolyte, wherein the ion concentration and ion composition of the electrolyte are adjusted by means of an ion exchanger. Advantageously, the ion exchanger contains counterions that are contained in the electrolyte and that are relevant for the bath quality. For the exchange process, these counterions are exchanged with ions which negatively influence the bath quality from the electrolyte. Therefore, the composition of the electrolyte and the corresponding ion concentration are adjusted in an advantageous way. Therefore, e.g., the pH value of an electrolyte and its density can be held substantially constant, which considerably lengthens the lifetime of the electrolyte. By guaranteeing a substantially constant composition, the lifetime is no longer restricted. The extremely high effectiveness of the method according to the invention is dependent on these conditions.

Description

CROSS-REFERENCE TO RELATED APPLICATIONS

Pursuant to 35 U.S.C. § 119, this application claims the benefit of European Patent Application No. 01107350.9, filed Mar. 24, 2001.

BACKGROUND OF THE INVENTION

The invention pertains to a method for the care and maintenance of an electrolyte.

The control and maintenance of electrolytes is necessary in order to guarantee problem-free operation of an electrolytic process. In particular, tight control of electrolyte density, composition, pH , and temperature is desired. Here, the ion composition, in particular, is a determinative factor. Also, the electrolyte must be kept free from contaminants in order to guarantee problem-free operation. Thus, another goal is to prevent deposits and other essentially insoluble contaminants.

The care and maintenance of electrolytes is of particular importance in gold plating. For the most part, cyanide systems are used as the electrolyte in gold plating, wherein the gold is separated from anionic complexes. The stability of cyanide gold complexes is high, so that plating is typically performed in the acidic pH range.

Insoluble anodes are predominantly used in acidic gold electrolytes. Therefore, supplementation of the electrolyte with a gold salt is necessary. Such gold salts predominantly contain potassium as cations. In addition, it is typical for the flushing water to be fed back into the plating bath for the purpose of cost reduction. Thus, in the course of the bath operation, the concentration of potassium ions increases and leads to a large increase in the density of the bath, which results in a reduction of the bath operating time.

Further, the use of insoluble anodes results in problematic shifts in pH during operation. This also depresses cathode efficiency below 100%, so that hydrogen ions are reduced in addition to gold ions, thereby raising the pH. Because the deposition behavior is strongly influenced by the solution pH, acid is typically added to the electrolyte to control the pH to within certain limits. This can be, e.g., sulfuric acid or also an organic acid.

The addition of acids for the purpose of pH control can lead to the formation of deposits because potassium ions can form deposits with corresponding ions of the acids, resulting in the precipitation of, e.g., potassium sulfate. Such deposits are undesired and disadvantageous because the electrolyte is to be kept clean and, in particular, free from floating particles.

Therefore, the control and maintenance of the electrolyte has special significance, particularly for gold baths and, until now, has been very expensive. In addition to the control of the gold content, the concentration of other alloy metals must be monitored, the concentration of free potassium cyanide and potassium carbonate must be controlled, the density and the pH must be monitored, and drag-out losses must be supplemented. In spite of these expensive controls, the known baths have only a limited lifetime due to the circumstances mentioned above.

SUMMARY OF THE INVENTION

Thus, one object of the invention is based the provision of a simple method for maintaining an electrolyte, which is capable of lengthening the lifetime of the electrolyte in an electrolytic process by maintaining a substantially constant ion concentration and ion composition in the electrolyte. Another object of the invention is the provision of a method to maintain the pH of an electrolyte in an electrolytic process without the formation of precipitates. A related object of the invention is the provision of a method to maintain the pH of an electrolyte in an electrolytic process without wasteful addition of costly chemicals to the electrolyte.

Briefly then, the invention is directed to a method for maintenance of an electrolyte. The method is characterized in that at least one ion exchanger controls ion concentration and ion composition of the electrolyte. The invention is also directed to a method for the control of the composition of an electrolyte comprising alkali metal ions during a gold plating operation. According to this method, the electrolyte is circulated through an acidic cation exchanger to exchange the alkali metal cations of the electrolyte with acidic counterions from the exchanger, and the electrolyte is returned to the gold plating operation.

The invention is further directed to a device for care and maintenance of an electrolyte. The device comprises an ion exchanger for exchanging an ion of the electrolyte with a cation from the ion exchanger.

DETAILED DESCRIPTION OF THE INVENTION

The present invention proposes to adjust the ion composition and the ion concentration in the electrolyte by means of an ion exchanger. The electrolyte is guided through the ion exchanger and, during the exchange process, the counterions in the matrix of the ion exchanger are exchanged with ions from the electrolyte. Thus, the method according to the invention allows the ion composition of the electrolyte and the corresponding ion concentration to be controlled in an advantageous way. The method according to the invention is particularly advantageous in that, through the use of the ion exchanger, ions that negatively affect the bath quality can be exchanged with ions that are necessary to maintain a substantially constant bath quality. Thus, the composition of the electrolyte and the corresponding ion concentration can be adjusted in an advantageous way. [0012]
The method according to the invention provides an unexpected solution to the problem in the state of the art that the bath composition must be adjusted with an expensive process using additives, which, e.g., for gold baths, increases the risk of forming deposits as described above. The present invention discloses a method for the care and maintenance of electrolytes that is extremely advantageous because conventional means that negatively influence the lifetime of an electrolyte bath are avoided and, further, because environmental benefits are gained through reduced chemical usage. [0013]
Further, the method according to the invention is less expensive because processes that otherwise had to be controlled separately are now controlled by a single processing step, i.e., by guiding the electrolyte fluid through the ion exchanger. Also, with the method according to the invention, measurement and control steps can be eliminated because the bath composition no longer must to be monitored with expensive processes. Therefore, processing steps and costs can be eliminated. Further, the lifetime of an electrolyte is no longer limited by the problematic conditions described elsewhere herein because its composition can be kept substantially constant. The improved consistency in composition, and thus quality, of the electrolyte results in fewer quality defects for the deposited films. Furthermore, the feature according to the invention of using an ion exchanger for care and maintenance of an electrolyte is also advantageous due to the regenerability of the ion exchanger, so that the method has a low material expense and thus is also cost effective. [0014]
Therefore, the method according to the invention can be used for the maintenance of any electrolyte for which an ion composition and/or concentration can be adjusted by means of an ion exchanger. Preferably the ion exchanger exchanges undesired ions that negatively influence the quality of the electrolyte with ions that need to be replenished in the bath. The ion exchanger preferably contains counterions that are present in the electrolyte and that are needed to maintain bath quality. In this way, the ion exchanger can be advantageously regenerated after use. [0015]
In a preferred embodiment, the method according to the invention is used to maintain acidic gold electrolytes. As described above, the disadvantages for gold electrolytes during operations are the build up of potassium ions and the increase in electrolyte pH. The precise maintenance of the pH, and thus the hydrogen ion concentration, is a determinative factor, particularly for gold electrolytes. In an advantageous way, the present invention can reduce or eliminate the excessive addition of inorganic or organic acids for the purpose of pH control, by providing such control through the use of an ion exchanger. As these additives can be substantially eliminated, so too is the negative influence on bath quality from the undesired deposits that they cause. In this way, the principle of ion exchange is used with the present invention in an extremely advantageous way, wherein one type of ion can be easily exchanged with another, so that the ions negatively influencing the bath quality of the electrolyte, such as potassium ions for acidic gold baths, can be exchanged with counterions positively influencing the bath quality, such as hydrogen ions for acidic gold baths. [0016]
In this embodiment, a cation exchanger is preferably used for control. More preferably, an acidic cation exchanger is a used to perform the care and maintenance of an acidic gold electrolyte. The cations contained in the electrolyte can be exchanged with hydrogen ions of the cation exchanger. For the care of gold baths, the potassium ions that are disadvantageous for the operation of the bath are exchanged with hydrogen ions that are necessary in order to prevent an increase in the pH. Therefore, two essential problems in the operation of an electrolyte bath, particularly those of an acidic gold electrolyte, are solved in an uncomplicated way by means of the method according to the invention. By means of the ion exchanger, excess potassium ions, which produce a shortened lifetime for the bath due to an increase in density of the bath, are removed from the electrolyte. They are preferably exchanged with hydrogen ions that advantageously replace the hydrogen ions reduced by the electrolysis. This process acts against the tendency for the pH of an electrolyte to increase during operation. In this way, the addition of greater amounts of inorganic or organic acids can be substantially eliminated. This further prevents the otherwise occurring precipitation of potassium salt, e.g., potassium sulfate, according to the acids that are used. [0017]
Preferably, the ion exchanger is occasionally regenerated when the matrix becomes loaded with ions which are problematic to an electrolyte. After loading or exchange of the ions localized at anchor groups of an ion exchanger matrix, such as hydrogen ions in the case of the maintenance of an acidic electrolyte, with the problematic cations from the electrolyte, the ion exchanger becomes loaded with the problematic cations. Because ion exchange is a reversible process in which the problematic cations may be eluted out of a cation exchanger treatment with acid and water can transform a cation exchanger back to its original state loaded with hydrogen ions. Through this extremely advantageous property, the ion exchanger has a long service life and enjoys essentially unlimited use. This leads to a valuable cost reduction, especially in the operation of a gold bath. [0018]
Chemical decomposition of components of an electrolyte results in an unavoidable increase in electrolyte density. The density of an electrolyte on salt, alkali, and/or acid concentration. In an advantageous way, an ion exchanger can also adjust the electrolyte density within certain limits, which leads to an advantageous lengthening of the operating time of the electrolyte. The method according to the invention operates against a disadvantageous increase in density, because, e.g., in the case of acidic gold electrolyte, excess potassium ions are exchanged with hydrogen ions and because the addition of organic or inorganic acids, which contributes to increasing the density of the bath, can be largely eliminated. [0019]
Preferably, the composition of the electrolyte bath is held substantially constant, whereby the lifetime of the electrolyte bath is not limited. In the preferred embodiment, continuously determined amounts of electrolyte can be removed from the electrolyte bath by means of transport devices and guided through the appropriate ion exchanger. Electrolyte column effluent that is depleted of potassium ions, in the case of the maintenance of an acidic gold bath, and which has been enriched with an essentially equivalent amount of hydrogen ions can be fed back to the electrolyte bath. Flushing is preferably performed to regenerate an ion exchanger matrix loaded with potassium ions, wherein the ions captured from the electrolyte are eluted and, in turn, the matrix is loaded with hydrogen ions. Preferably, the column is alternately washed with diluted acid and water to elute the ions captured from the electrolyte. After flushing, the column is again ready for use. The means and steps are to be adapted to the ion exchanger that is used. [0020]
Due to the high cost of metals, gold is generally recovered from flushings that have settled out, from rejected electrolytes, and from defective tools. Because gold ions can also be captured in the matrix of an ion exchanger, an eluate may comprise gold ions can be fed into other flushing solutions, or the like, which perform a gold recovery. Gold recovery can be performed, e.g., by means of highly basic anionic exchanger resin or electrolysis cells. [0021]
In an advantageous way, the method according to the invention also allows the setting of additional fine adjustments. Thus, small pH value deviations that cannot be regulated by means of the ion exchanger are regulated by means that supplement the ion exchanger. According to an embodiment of the method according to the invention, the relevant process variables of the electrolyte are measured by means of measurement devices, compared with the desired target values, and appropriate means are automatically started. Thus, depending on the measurement values, the flow rate of the electrolyte fluid through the ion exchanger can be increased, a fine adjustment of pH, which cannot be done by the ion exchanger, can be performed by means of an inorganic or organic acid, and further, possible drag-out losses are supplemented. Further, measurement devices can determine the amount of floating particles, and, if necessary, filtration can be done by means of filter systems. [0022]
Relatedly, the invention proposes a device for the care and maintenance of an electrolyte, particularly an acidic gold electrolyte, which comprises measurement devices that measure the relevant process variables of the electrolyte to be maintained in the form of actual values, as well as storage devices that store the target values of the relevant process variables of the electrolyte to be maintained, as well as at least one calculation unit that compares the measured actual value with the stored target value and a control unit that controls the means in order to adjust the actual value of the electrolyte to the target value. Furthermore, the device may optionally comprise: an ion exchanger that exchanges the ions negatively influencing the bath quality from the electrolyte with its own counterions that are also present in the electrolyte and that are required for good electrolyte quality; transport devices that guide the electrolyte fluid to the ion exchanger as well as back into the electrolyte bath; and, flushing devices to regenerate a loaded ion exchanger. However, less complex devices that exhibit substantially constant operating parameters and that can function without measurement, storage, and calculation units are also included within the scope of the invention. [0023]
One skilled in the art will appreciate that the methods of the present invention can be adapted to a wide range of different electrolytes; they should neither be interpreted as being restricted to the care and maintenance of acidic gold baths nor to other processes in which pH would otherwise rise. For example, the methods according to the invention are also well-suited to maintaining a substantially constant composition and ion concentration of alkali electrolytes. Only the corresponding parameters, e.g., of the ion exchanger, which, e.g., can be a basic anionic exchanger, the flushing steps, and the regeneration, etc., must be adapted. These parameters can be adapted in an uncomplicated way and are obvious for someone skilled in the art from the combination of the appropriate ions to be removed from the electrolyte, the desired ions, and the ion exchanger with the corresponding counterions to be used, depending on the ions to be exchanged. Further, the corresponding matrices are subject to different requirements for the regeneration and the operation, which are indicated by the corresponding manufacturer of the ion exchanger to be used. [0024]

EXAMPLE

This non-restrictive example demonstrates the effectiveness of the method according to the invention for the maintenance of an acidic gold electrolyte. In this example, an aqueous electrolyte was used that contained as essential components citric acid/potassium citrate, a cobalt (II) citrate complex, formic acid/potassium formate, as well as a gold complex (potassium gold cyanide). Having a pH of 5.0 and a potassium ion concentration of 75 g/L, 500 mL of this electrolyte was led through a column with 75 g of exchanger resin, selected to exchange hydrogen ions with potassium ions. The ion exchanger reduced the potassium concentration from 75 g/L to 59 g/L and reduced the pH from 5.0 to 4.7. The stability of the gold cyanide complex was not negatively influenced. No other significant ions were observed to be retained in the matrix of the ion exchanger in subsequent tests. Thus, the selectivity is particularly advantageous in that no ions are removed from the electrolyte that must be replaced at great cost, such as gold ions. [0025]
The ion exchanger resin was regenerated with 5% sulfuric acid. Multiple repetitions of the test showed that the method functions consistently with good results, and, due to its regenerability, the ion exchanger showed essentially no aging effects. [0026]
In light of the detailed description of the invention and the example presented above, it can be appreciated that the several objects of the invention are achieved. [0027]
The explanations and illustrations presented herein are intended to acquaint others skilled in the art with the invention, its principles, and its practical application. Those skilled in the art may adapt and apply the invention in its numerous forms, as may be best suited to the requirements of a particular use. Accordingly, the specific embodiments of the present invention as set forth are not intended as being exhaustive or limiting of the invention. [0028]
When introducing elements of the present invention or the preferred embodiment(s) thereof, the articles “a”, “an”, “the”, and “said” are intended to mean that there are one or more of the elements. The terms “comprising”, “including”, and “having” are intended to be inclusive and mean that there may be additional elements other than the listed elements. [0029]

Claims

What is claimed is:

1. A method for maintenance of an electrolyte having an ion concentration and an ion composition, the method characterized in that the ion concentration and the ion composition are controlled by operation of at least one ion exchanger.

2. The method according to claim 1 further characterized in that the ion exchanger comprises a counterion, the counterion being identical in type to an ion present in the electrolyte.

3. The method according to claim 1 further characterized in that the electrolyte has a pH which is held substantially constant by operation of the ion exchanger.

4. The method according to claim 1 wherein the ion exchanger is a cation exchanger.

5. The method according to claim 1 wherein the ion exchanger is an acidic cation exchanger.

6. The method according to claim 1 wherein the electrolyte comprises a cation and the ion exchanger comprises a hydrogen ion, the method further characterized in that the cation in the electrolyte is exchanged with the hydrogen ion of the cation exchanger.

7. The method according to claim 1 wherein the cation in the electrolyte comprises a potassium ion and the ion exchanger comprises a hydrogen ion, the method further characterized in that the potassium ion in the electrolyte is exchanged with the hydrogen ion of the cation exchanger.

8. The method according to claim 1 further characterized in that the ion exchanger is regenerated.

9. The method according to claim 8 wherein an eluate is formed, the method further characterized in that the eluate is fed to a recovery processes.

10. The method according to claim 1, the electrolyte having a density, the method further characterized in that the density of the electrolyte is controlled at least partially by operation of the ion exchanger.

11. The method according to claim 1 characterized in that the electrolyte is led through the ion exchanger and then fed back into a bath by operation of a transport device.

12. The method according to claim 11 further characterized in that the electrolyte is led in a continuous cycle process through the ion exchanger, thereby achieving a substantially constant preparation of the electrolyte.

13. The method according to claim 11 further characterized in that the electrolyte is led through the ion exchanger at a selected rate.

14. The method according to claim 1 further characterized in that a measurement device compares an actual value of a process variable of the electrolyte with a target value for the process variable of the electrolyte and adjusts velocity and flow rate of the electrolyte through the ion exchanger.

15. A device for care and maintenance of an electrolyte, the device comprising an ion exchanger, the electrolyte comprising an ion, and the ion exchanger comprising a counterion, wherein the ion exchanger exchanges the ion from the electrolyte with the counterion from the ion exchanger.

16. The device according to claim 15 further comprising a collecting means that collects the electrolyte from the ion exchanger and a guidance means that feeds the collected electrolyte to a bath.

17. The device according to claim 15 further comprising:

a measurement device that measures an actual values of a process variable of the electrolyte;

a storage device that stores a target value for a process variable of the electrolyte;

at least one calculation unit that compares the measured value with a target value;

a control unit that controls a means to adjust the value of process variable of the electrolyte to the target value;

an ion exchanger;

a transport device that leads the electrolyte to the ion exchanger and back into an electrolyte bath; and

a flushing device that regenerates the ion exchanger.