Method and system for depositing zinc-nickel alloys onto substrates

Abstract

The present invention provides a method for depositing a zinc-nickel alloy onto a substrate, comprising the steps of: (a) providing a substrate; (b) providing an aqueous zinc-nickel deposition bath as a catholyte in the deposition compartment, wherein: the deposition compartment includes at least one anode with an anolyte; and the anolyte is separated from the catholyte by at least one membrane; and The catholyte is (i) nickel ions, (ii) at least one complexing agent for nickel ions, and (iii) Zinc ions the steps comprising: (c) contacting the substrate with the catholyte in the deposition compartment to electrolytically deposit a zinc-nickel alloy on the substrate, thereby obtaining a zinc-nickel coated substrate, wherein after step (c), nickel ions in the catholyte have a lower concentration than before step (c); (d) rinsing the zinc-nickel coated substrate in a rinse compartment containing water to obtain a rinsed zinc-nickel coated substrate and rinse water, wherein the rinse water contains a portion of the at least one complexing agent for the nickel ions and a portion of the nickel ions. Including, (i) treating at least a portion of the rinse water and / or at least a portion of the catholyte in a first processing compartment to separate the water from the at least one complexing agent for the nickel ions and the nickel ions; (ii) returning at least a portion of the at least one complexing agent separated from the water to the catholyte; and (iii) adding a source of nickel ions to said catholyte, provided that said source of nickel ions does not contain at least one complexing agent for said nickel ions or any other complexing agent for nickel ions; The present invention relates to the method, characterized in that:

Description

[Technical Field]

[0001] According to a first aspect, the present invention relates to a method for depositing a zinc-nickel alloy onto a substrate, in particular a method for electrolytically depositing a zinc-nickel alloy onto a substrate.

[0002] According to a second aspect, the present invention further relates to a system for depositing a zinc-nickel alloy onto a substrate, in particular a system for electrolytically depositing a zinc-nickel alloy onto a substrate. [Background technology]

[0003] Electrolytic deposition of metal alloys, sometimes referred to as coatings, onto other metals or metal-coated plastics, typically referred to as substrates, is a well-established technique for enhancing the corrosion resistance of such substrates. The deposition is usually carried out using the anode, the substrate as the cathode, and an electric current applied in the respective electrolytes.

[0004] In some cases, it is advantageous to separate the electrolyte by a semipermeable membrane into a catholyte compartment containing the electrolyte, catholyte, in the cathode space, and an anolyte compartment containing the electrolyte, anolyte, in the anode space. The anolyte is often different from the catholyte. Upon application of an electrical potential, current flows through the anolyte, through the membrane, and into the catholyte, initiating electrolytic deposition on the substrate.

[0005] In U.S. Patent Application Publication No. 2011 / 031127 A1, Hillebrand discloses that in such alkaline electroplating baths for plating zinc-nickel coatings having an anode and a cathode, the anode is separated from the alkaline electrolyte by an ion exchange membrane.

[0006] In US Patent Application Publication No. 2013 / 0264215 (US 2013 / 0264215 A1), Umicore discloses an anode system configured to be suitable for use in an electroplating cell for depositing an electrolyte coating as a result of simple immersion in catholyte, wherein after immersion in the catholyte, the catholyte is separated from the anode by a swollen polymer membrane that is permeable to cations or anions, and the polymer membrane is in direct contact with the anode and not with the cathode, wherein the membrane is fixed on the anode in a multi-layer structure by an electrolyte-permeable holder and clamping fixture, thereby ensuring good contact between the membrane and the anode.

[0007] German Utility Model Publication No. 202015002289 (DE 20 2015 002 289 U1) discloses an electrodialysis cell with anion and cation exchange membranes for use as an anode in alkaline zinc and zinc alloy electrolytes for electrolytic deposition in galvanic systems.

[0008] EP 1 533 399 A2 relates to a method for alkaline zinc-nickel plating with reduced wastewater.

[0009] Typically, zinc-nickel deposition baths are used continuously for extended periods of time, e.g., weeks or even months, to efficiently deposit zinc-nickel alloys on multiple different substrates. When zinc-nickel deposition baths are used for such extended periods, undesirable compounds (e.g., decomposition products of complexing agents, particularly organic compounds, e.g., cyanide-containing complexing agents) typically begin to accumulate in the zinc-nickel deposition bath over time. This often significantly impairs the deposition process after a certain time and can ultimately lead to the need to at least partially replace the zinc-nickel electrolytic deposition bath. In many cases, this is prevented by constantly removing (e.g., withdrawing) at least a portion of the deposition bath as wastewater.

[0010] However, because the wastewater contains nickel ions and often cyanides, extensive wastewater treatment is required before disposal. Therefore, there is a continuing need to further improve existing deposition methods, especially from an environmental perspective. With stricter legal restrictions worldwide, especially with regard to nickel ions, there is an urgent need for more sustainable methods for depositing zinc-nickel alloys onto substrates that produce less or no wastewater, or at least less contamination with dangerous metal ions. On the other hand, there remains a need for such methods that can be operated economically and do not impair the corrosion protection currently known. [Prior art documents] [Patent documents]

[0011] [Patent Document 1] US Patent Application Publication No. 2011 / 031127 [Patent Document 2] US Patent Application Publication No. 2013 / 0264215 [Patent Document 3] German Utility Model Publication No. 202015002289 [Patent Document 4] European Patent Application Publication No. 1533399 Summary of the Invention [Problem to be solved by the invention]

[0012] It is therefore an object of the present invention to provide a very environmentally friendly method and system for depositing zinc-nickel alloys onto substrates, which does not produce wastewater or at least minimizes contamination with hazardous metal ions, such as nickel ions and cyanide ions, and which can be operated economically over long periods of time. [Means for solving the problem]

[0013] Summary of the Invention The above problem is solved, according to a first aspect, by a method for depositing a zinc-nickel alloy on a substrate, the method comprising the steps of: (a) providing a substrate; (b) providing an aqueous zinc-nickel deposition bath as a catholyte in the deposition compartment, wherein: the deposition compartment includes at least one anode with an anolyte; and the anolyte is separated from the catholyte by at least one membrane; and The catholyte is (i) nickel ions, (ii) at least one complexing agent for nickel ions, and (iii) Zinc ions the steps comprising: (c) contacting the substrate with the catholyte in the deposition compartment to electrolytically deposit a zinc-nickel alloy on the substrate, thereby obtaining a zinc-nickel coated substrate, wherein after step (c), nickel ions in the catholyte have a lower concentration than before step (c); (d) rinsing the zinc-nickel coated substrate in a rinse compartment containing water to obtain a rinsed zinc-nickel coated substrate and rinse water, wherein the rinse water contains a portion of the at least one complexing agent for the nickel ions and a portion of the nickel ions. Including, (i) treating at least a portion (preferably all) of said rinse water and / or at least a portion of said catholyte in a first processing compartment to separate water from said at least one complexing agent for nickel ions and nickel ions; (ii) returning at least a portion (preferably all) of the at least one complexing agent separated from the water to the catholyte; and (iii) adding a source of nickel ions to said catholyte, provided that said source of nickel ions does not contain at least one complexing agent for said nickel ions or any other complexing agent for nickel ions; The above-mentioned problems are solved by the method,

[0014] The method of the present invention solves the above-defined problem very well, since it allows operation in a closed loop for a theoretically unlimited period, but at least for several weeks and in particular for one month, during which period the water is disposed of substantially free of nickel and cyanide ions (and therefore is not referred to as wastewater).

[0015] During closed-loop operation, preferably only the nickel and zinc ions that are deposited on the substrate during deposition have to be replenished; all other compounds contained in the deposition bath, preferably the catholyte, are recycled.

[0016] By returning (directly or indirectly) at least a portion (preferably all) of the at least one complexing agent separated from the water in the first processing compartment to the catholyte, the concentration of said at least one complexing agent for nickel ions in the catholyte is maintained at a constant concentration. As defined in the method of the present invention, the complexing agent does not need to be replenished or is nearly replenished. This is achieved by utilizing at least one anode equipped with at least one membrane. Such a membrane prevents anodic decomposition of organic compounds, such as the complexing agent. The complexing agent withdrawn to the rinse compartment is recycled by the first processing compartment. This allows nickel ions to be replenished without the complexing agent.

[0017] In particular, it is sufficient to provide an initial concentration of at least one complexing agent for said nickel ions when setting up the zinc-nickel aqueous deposition bath, preferably the catholyte, and no additional complexing agent needs to be added during the deposition method.

[0018] Furthermore, when the rinse water is treated in the first treatment section to separate the water, very pure water is typically obtained which can be reused.

[0019] The above object is further achieved, according to a second aspect, by providing a system for depositing a zinc-nickel alloy onto a substrate, the system comprising: (I) optionally a pre-rinse compartment for pre-rinsing the substrate; (II) a deposition compartment for electrolytically depositing a zinc-nickel alloy on a substrate in a catholyte to obtain a zinc-nickel coated substrate, said deposition compartment comprising at least one anode equipped with at least one membrane; (III) a rinsing section for rinsing the zinc-nickel coated substrate to obtain a rinsed zinc-nickel coated substrate and rinsing water; (IV) a first processing compartment for processing at least a portion of the rinse water and the catholyte to separate the water from nickel ions and a complexing agent for the nickel ions; and (V) optionally a second processing compartment for processing the catholyte to separate dissolved anions from the catholyte; Including, The first processing section comprises: the separated water is returned to the pre-rinse compartment and / or the rinse compartment, and The separated nickel ions and the complexing agent for the separated nickel ions are returned to the deposition compartment, preferably via a mixing compartment. The problem is solved by the system, which is adapted to [Brief explanation of the drawings]

[0020] [Figure 1] Figure 1 shows a schematic diagram of a system for depositing a zinc-nickel alloy onto a substrate, preferably for carrying out the method of the present invention. The system comprises various compartments, most of which are fluidly connected to one another. Further details are provided in the "Examples" section below. DETAILED DESCRIPTION OF THE INVENTION

[0021] Detailed Description of the Invention In the context of the present invention, the terms "at least one," "one or more," and / or "one or more" refer to (and are interchangeable with) "one, two, three, or more than three."

[0022] For purposes of the present invention, an anolyte is typically an electrolyte in direct contact with at least one anode, whereas a catholyte is the electrolyte, or at least a portion of the electrolyte, in direct contact with the cathode, i.e., the substrate, at least during the time that the catholyte is located in the deposition compartment.

[0023] As already mentioned above, the main advantage achieved by the method of the present invention is that no decomposition products are formed due to the anode equipped with at least one membrane. This means that preferably at least one anode and at least one membrane are adapted to form an anolyte that is separated from the catholyte, and selective permeation of ions between the catholyte and the anolyte is possible only through the at least one membrane. The at least one membrane is adapted not to allow at least one complexing agent to pass through the membrane (from catholyte to anolyte). This allows the closed-loop operation with constant recirculation of at least one complexing agent for the initial concentration of nickel ions. Most preferably, the at least one membrane only allows permeation of hydrogen ions (formed in the anolyte) into the catholyte.

[0024] Therefore, a method according to the invention is preferred, wherein said at least one complexing agent for nickel ions is not in contact with said at least one anode, most preferably not in contact with any of said at least one anode.

[0025] Furthermore, the method of the present invention is preferred, wherein the catholyte comprises only an initial concentration of at least one complexing agent for said nickel ions for at least one turnover of nickel ions, more preferably for at least two turnovers of nickel ions, even more preferably for at least three turnovers of nickel ions, and most preferably for the entire lifetime of the catholyte.

[0026] The at least one membrane preferably only allows the diffusion of protons between the anolyte and catholyte, which ensures efficient distribution of charge between the anolyte and catholyte.

[0027] During the process of the present invention, water is typically introduced into the catholyte, for example, by a nickel ion source to replenish the nickel ions. However, in the first treatment section, excess water is separated and subsequently removed from the process of the present invention so as to maintain an essentially constant volume of catholyte over time. If such excess water cannot be used in the process of the present invention, it is preferably easily disposed of, since it is essentially free of nickel ions, and preferably also free of zinc ions, and is essentially free of complexing agents.

[0028] In summary, the method of the present invention allows for economical and sustainable long-term continuous operation, for example for weeks or even months, during which no nickel-contaminated wastewater is produced and valuable metal ions and complexing agents are not lost through extraction. Essentially, only the amounts of nickel and zinc ions deposited have to be replenished by sources of the respective nickel and zinc ions.

[0029] For the method of the present invention, most preferably at least a portion (preferably all) of the rinse water and at least a portion of the catholyte are treated in the first treatment compartment to separate the water from the at least one complexing agent for nickel ions and the nickel ions. Treating a portion of the catholyte as well (in addition to the rinse water, preferably in addition to all of the rinse water) allows for maintaining an essentially constant volume of catholyte.

[0030] By separating the at least one complexing agent for nickel ions and the nickel ions from the water, the complexing agent and nickel ions so recycled have the desired concentration before they are returned to the catholyte.

[0031] The process of the present invention is preferred in which the complexing agent separated from the water is returned to the catholyte as a concentrated aqueous solution, more preferably the complexing agent separated from the water is returned to the catholyte as a concentrated aqueous solution directly or indirectly, most preferably the complexing agent separated from the water is returned to the catholyte as a concentrated aqueous solution indirectly via a mixing unit.

[0032] The mixing unit is preferably used to mix the separated complexing agent with, for example, a nickel ion source and / or a zinc ion source, and most preferably the mixing unit results in a freshly mixed zinc-nickel aqueous deposition bath ready for transfer to the deposition compartment to replenish the catholyte.

[0033] By returning the complexing agent and thereby maintaining an essentially constant concentration of the complexing agent, a constantly constant stabilization of nickel ions in the catholyte is achieved, which results in good stability of the catholyte. When the complexing agent is returned indirectly to the catholyte via a mixing unit, the complexing agent is preferably used to complex nickel ions newly introduced from the nickel ion source into the mixing unit (see FIG. 1).

[0034] Therefore, the method of the present invention is preferred, in which the source of nickel ions is added to the catholyte directly or indirectly, preferably indirectly via a mixing unit (preferably as described above).

[0035] Preferred is the process of the present invention, wherein a source of zinc ions is added to the catholyte directly or indirectly, preferably indirectly via a mixing unit (preferably as described above). More preferably, the zinc ions are obtained by dissolving metallic zinc in sodium hydroxide to obtain a zinc hydroxo complex, which allows efficient stabilization of the zinc ions in the catholyte.

[0036] Nickel and zinc ions are replenished by adding sources of nickel and zinc ions to the catholyte, preferably indirectly via a mixing unit to provide a thoroughly mixed composition prior to transfer to the deposition compartment.

[0037] Preferred is a method of the invention wherein the anolyte is water, preferably water containing sulfuric acid, most preferably water containing 5% to 40% by volume of sulfuric acid.

[0038] Preferably, the method of the present invention comprises the catholyte comprising more than 50% by volume of water, more preferably 75% by volume or more, even more preferably 85% by volume or more, and even more preferably 92% by volume or more of water, based on the total volume of the catholyte. Preferably, water is the only solvent in the catholyte.

[0039] The method of the present invention is preferred in which the source of nickel ions is an aqueous solution comprising water and a nickel salt dissolved therein. The method of the present invention is preferred in which the nickel salt is an inorganic salt. This preferably means that the nickel salt does not contain a carboxylate anion, more preferably does not contain an organic acid anion, and most preferably does not contain an organic anion.

[0040] The exclusion of organic anions, particularly carboxylate anions, prevents the buildup of potentially detrimental organic anions in the catholyte over time, and also essentially eliminates potential complexing agents for nickel ions.

[0041] The process of the present invention is preferred wherein said nickel salt comprises nickel sulfate, preferably nickel sulfate hexahydrate.

[0042] The process of the present invention is preferred in which the nickel salt does not include nickel chloride. By excluding nickel chloride, the concentration of chloride ions in the catholyte can be minimized, or most preferably even eliminated, thereby eliminating the need to remove excess chloride ions from the catholyte during the process of the present invention, which is typically difficult due to the high solubility of chloride salts.

[0043] The method of the present invention is preferred in which the nickel salt does not include nickel nitrate. The exclusion of nickel nitrate prevents the concentration of nitrate ions in the catholyte. In many cases, nitrates can interfere with the overall electrolyte deposition, which is highly undesirable.

[0044] The nickel ion source is most preferably an aqueous solution comprising water and nickel sulfate, preferably nickel sulfate hexahydrate, dissolved therein. Such a preferred nickel ion source is well suited for replenishing nickel ions. See the text below regarding sulfate anion accumulation.

[0045] The method of the present invention is preferred in which the nickel ion source has a concentration of nickel ions in the range of 70 g / L to 140 g / L, preferably 80 g / L to 120 g / L, more preferably 90 g / L to 110 g / L, and even more preferably 95 g / L to 105 g / L, relative to the total volume of the nickel ion source.

[0046] As mentioned above, the nickel ion source does not contain the at least one complexing agent for the nickel ions or any other complexing agent for nickel ions. This means that the at least one complexing agent for nickel ions is not replenished by the nickel ion source. Most preferably, the at least one complexing agent for nickel ions is not replenished at all. Furthermore, no complexing agent different from the at least one complexing agent for nickel ions, such as the complexing agent used to initially set up the zinc-nickel aqueous deposition bath, is added to the catholyte. Therefore, the method of the present invention is preferred in which the catholyte contains only one complexing agent for nickel ions (and therefore is not a mixture of two or more complexing agents). This helps to monitor the total amount of complexing agent in the catholyte over time.

[0047] The method of the present invention is preferred in which the nickel ion source is essentially free of or free of tetraethylenepentamine, preferably essentially free of or free of diamines, and most preferably essentially free of or free of amines. This is most preferred because such compounds are typically used as complexing agents for nickel ions in zinc-nickel aqueous deposition baths (see text below for further details on complexing agents). Therefore, such compounds are undesirable, especially in order to prevent their accumulation in the nickel ion source.

[0048] Preferred is the process of the present invention wherein said nickel ion source is essentially free or free of amines having one or more, preferably two, primary amine groups and one or more secondary amine groups.

[0049] In the method of the present invention, the catholyte contains at least one (preferably one) complexing agent for nickel ions.

[0050] In the present invention, the at least one complexing agent for nickel ions in the catholyte preferably comprises a chelating complexing agent, and preferably the chelating complexing agent is the only complexing agent for nickel ions in the catholyte. The use of a chelating complexing agent ensures efficient stabilization of nickel ions in the catholyte. In particular, the at least one complexing agent needs to be provided only once when initially setting up the zinc-nickel aqueous deposition bath, while there is no need to add additional complexing agent later.

[0051] The process of the present invention is preferred, wherein in the catholyte, the at least one complexing agent for nickel ions comprises an amine, preferably a diamine, most preferably tetraethylenepentamine. Amine, diamine and tetraethylenepentamine, respectively, as complexing agents for nickel ions, allow for excellent stabilization of nickel ions in the catholyte, especially at alkaline pH.

[0052] Preferred is the process of the present invention wherein an amine, preferably a diamine, most preferably tetraethylenepentamine, is the only complexing agent for nickel ions in the catholyte.

[0053] The process of the present invention is preferred wherein said diamine is selected from the group consisting of ethylenediamine, diethylenetriamine, triethylenetetramine, and tetraethylenepentamine.

[0054] Generally, the process of the present invention is preferred, wherein in the catholyte, at least one complexing agent for said nickel ions comprises an amine having one or more, preferably two, primary amine groups and one or more secondary amine groups.

[0055] Preferred is the process of the present invention wherein the amine having one or more, preferably two, primary amine groups and one or more secondary amine groups is the only complexing agent for nickel ions in the catholyte.

[0056] The method according to the invention is preferred, wherein the nickel ions of the nickel ion source added to the catholyte are not complexed prior to contact with an alkaline environment, preferably an environment having a pH in the range of 10.0 to 14.0, more preferably 11.0 to 13.3, even more preferably 11.5 to 13.0, still more preferably 12.0 to 12.9, and most preferably 12.3 to 12.8. In other words, the nickel ions of the nickel ion source added to the catholyte are preferably only complexed upon contact with an alkaline environment, preferably an environment having a pH as defined above, most preferably the catholyte.

[0057] Furthermore, the present disclosure relates to an alternative method for depositing a zinc-nickel alloy onto a substrate, the method comprising the steps of: (a) providing a substrate; (b) providing an alkaline zinc-nickel aqueous deposition bath as a catholyte in the deposition compartment, wherein: the deposition compartment includes at least one anode with an anolyte; and the anolyte is separated from the catholyte by at least one membrane; and The catholyte is (i) nickel ions, (ii) at least one complexing agent for nickel ions, and (iii) Zinc ions the steps comprising: (c) contacting the substrate with the catholyte in the deposition compartment to electrolytically deposit a zinc-nickel alloy on the substrate, thereby obtaining a zinc-nickel coated substrate, wherein after step (c), nickel ions in the catholyte have a lower concentration than before step (c); (d) rinsing the zinc-nickel coated substrate in a rinse compartment containing water to obtain a rinsed zinc-nickel coated substrate and rinse water, wherein the rinse water contains a portion of the at least one complexing agent for the nickel ions and a portion of the nickel ions. Including, (i) treating at least a portion of the rinse water and / or at least a portion of the catholyte in a first processing compartment to separate the water from the at least one complexing agent for the nickel ions and the nickel ions; (ii) returning at least a portion of the at least one complexing agent separated from the water to the catholyte; and (iii) adding nickel ions from a nickel ion source to the catholyte to replenish the nickel ions, wherein the nickel ions from the nickel ion source added to the catholyte are not complexed with a complexing agent prior to contact with an alkaline environment, preferably an environment having a pH in the range of 10.0 to 14.0, more preferably 11.0 to 13.3, even more preferably 11.5 to 13.0, still more preferably 12.0 to 12.9, and most preferably 12.3 to 12.8. The present invention relates to the method, characterized in that:

[0058] The features (including preferred features) of the method of the present invention defined throughout the text are preferably applicable (where technically applicable) to the alternative methods described above.

[0059] Prior to step (c), step (a) (a-1) pre-rinsing the substrate in a pre-rinse compartment containing water to obtain a pre-rinsed substrate and pre-rinse water; A method according to the invention comprising the steps of:

[0060] By pre-rinsing the substrate in the pre-rinse compartment, possible contamination on the substrate is removed before the substrate is transferred to the deposition compartment. Preferably, the pre-rinse compartment contains an aqueous solution of sodium hydroxide as a pre-rinse solution.

[0061] In the method of the present invention, in step (d), the zinc-nickel coated substrate is rinsed in a rinsing compartment.

[0062] A method according to the invention is preferred, wherein said rinsing compartment comprises 2 to 5 fluidly connected rinsing sub-compartments forming a cascade of rinses.

[0063] Such a rinse cascade is particularly efficient at rinsing because the concentration of ions rinsed from the zinc-nickel coated substrate is effectively reduced in stages, with the most downstream rinse sub-compartment containing a significantly lower concentration of ions than the most upstream rinse sub-compartment of the rinse cascade.

[0064] In the deposition compartment, there is at least one anode and at least one membrane, where the at least one membrane separates the anolyte from the catholyte. Most preferably, the at least one membrane is semipermeable, meaning that the at least one membrane is selectively permeable.

[0065] The process of the invention is preferred, wherein said at least one membrane is a cation exchange membrane, the use of which effectively prevents the adverse permeation of said at least one complexing agent from the catholyte to the anolyte.

[0066] The method of the present invention is preferred, wherein in said deposition compartment said at least one anode is an insoluble anode, preferably a mixed metal oxide insoluble anode, most preferably an insoluble anode of indium / tantalum oxide on titanium.

[0067] The method of the present invention is preferred, wherein the at least one anode has a distance to the at least one membrane in the range of 0.5 mm to 5.0 mm, preferably 0.75 mm to 4 mm, more preferably 1.0 mm to 3.0 mm, which advantageously allows the anolyte volume to be kept low, which results in a low amount of wastewater from the anolyte.

[0068] In the method of the present invention, at least a portion of the rinse water and / or at least a portion of the catholyte is treated in a first treatment compartment to separate the water from said at least one complexing agent for nickel ions and the nickel ions.

[0069] The method of the invention is preferred, wherein said first processing compartment comprises an evaporator, preferably a vacuum evaporator.

[0070] Preferred is the process according to the invention, wherein in said evaporator a vacuum is applied in the range of 1 mbar to 100 mbar, preferably 5 mbar to 70 mbar, more preferably 10 mbar to 50 mbar, most preferably 15 mbar to 35 mbar.

[0071] Preferred is the process of the invention, wherein in said first treatment section, preferably in an evaporator, most preferably in a vacuum evaporator, water is separated at a temperature in the range of 18°C ​​to 50°C, preferably 23°C to 46°C, more preferably 28°C to 42°C, most preferably 31°C to 40°C.

[0072] By using an evaporator, preferably a vacuum evaporator, efficient evaporation of water can be achieved, in particular by reducing the atmospheric pressure, which allows efficient separation of water from nickel ions and from said at least one complexing agent. Efficient separation of water is achieved because the boiling point of water is significantly lower than the boiling point of said at least one complexing agent, nickel and / or zinc ions.

[0073] By operating the vacuum evaporator at a temperature between 18°C ​​and 50°C, undesired heating or even thermal decomposition of the at least one complexing agent is prevented.

[0074] In a preferred method of the present invention, the vacuum evaporator is operated and controlled based on density measurements of the concentrated aqueous solution, preferably in a range of 1.08 kg / L to 1.30 kg / L, more preferably 1.10 kg / L to 1.26 kg / L, more preferably 1.15 kg / L to 1.24 kg / L, and most preferably 1.20 kg / L to 1.23 kg / L, relative to the total volume of the concentrated aqueous solution. Control based on density measurements is well suited for automatically operating the first processing section, preferably the evaporator, most preferably the vacuum evaporator. The aforementioned density ranges are most preferred. However, in some cases, higher maximum densities are acceptable as long as the concentrated aqueous solution does not form phase separation. This could include, for example, maximum densities of 1.28 kg / L, 1.30 kg / L, or even 1.32 kg / L. Phase separation typically depends on the total amount of, for example, sulfates, carbonates, and hydroxides (e.g., sodium and / or potassium), which may vary over time.

[0075] As defined above, the concentrated aqueous solution is aqueous. Therefore, the method of the present invention is preferred, in which the concentrated aqueous solution is homogeneous. This preferably means that the concentrated aqueous solution forms only a single phase, in other words, the concentrated aqueous solution preferably does not undergo phase separation. Most preferably, the concentrated aqueous solution does not contain an organic phase separated from the aqueous phase.

[0076] Therefore, even more preferred is the method of the present invention wherein said concentrated aqueous solution is entirely aqueous.

[0077] Phase separation is preferably prevented by not exceeding the above mentioned maximum density, most preferably 1.26 kg / L (or even higher as mentioned above).

[0078] The processing in the first processing compartment results in very pure water and a concentrated aqueous solution.

[0079] The method of the present invention is preferred, wherein at least a portion of the separated water obtained in the first treatment section is returned to the pre-rinse section and / or the rinse section, preferably to the rinse section, more preferably to the rinse sub-section of the rinse cascade.

[0080] By returning the very pure separated water, water is recycled and wastewater is avoided, since the separated water is essentially free of complexing agents, nickel and zinc ions. It is therefore very suitable for reuse in the pre-rinse and rinse compartments. With such a loop, fresh water is preferably not needed for rinsing over a relatively long period of time.

[0081] The method of the present invention is preferred in which the water is separated from the at least one complexing agent for nickel ions and from the nickel ions so that the catholyte has a substantially constant volume in the deposition compartment, preferably a constant volume. This is particularly achieved if at least a portion of the catholyte is further treated in the first treatment compartment in addition to the rinse water. Typically, more water is introduced into the catholyte (e.g., by adding a source of nickel ions and forming in the catholyte by hydrogen ions formed by the anode) than that separated from the rinse water.

[0082] In a preferred method of the present invention, at least a portion (preferably all) of the at least one complexing agent separated from the water and at least a portion (preferably all) of the nickel ions separated from the water are returned to the catholyte, preferably as a concentrated aqueous solution (preferably as described throughout the text). Preferably, said concentrated aqueous solution is returned directly or indirectly, preferably indirectly via a mixing unit.

[0083] Typically, the rinse water also contains zinc ions, and therefore the method of the present invention is preferred, in which the rinse water contains a proportion of zinc ions.

[0084] The method of the invention is preferred, wherein in said first treatment compartment water is separated from nickel ions, at least one complexing agent for said nickel ions and zinc ions.

[0085] Preferred is the process of the present invention, in which the nickel ions, zinc ions and at least one complexing agent for said nickel ions are returned together to the catholyte, preferably as a concentrated aqueous solution (preferably as described throughout the text).

[0086] As mentioned above, a preferred nickel ion source includes nickel sulfate. This means that sulfate anions are introduced into the catholyte, which typically accumulate over time. Furthermore, the catholyte typically has a tendency to form and accumulate carbonate anions. Both anions are usually well soluble in the catholyte. While certain concentrations can be tolerated, excessive accumulation of such anions should be prevented. Therefore, (e) treating at least a portion of the catholyte in a second treatment compartment to separate dissolved anions from said catholyte, preferably by precipitation and / or ion exchange, most preferably by precipitation. A method according to the invention comprising the steps of:

[0087] The process of the invention is preferred, wherein said dissolved anions comprise sulfate, carbonate and / or chloride, preferably at least sulfate and carbonate.

[0088] By applying step (e) in addition to steps (a) to (d), the concentration of dissolved anions in the catholyte is significantly reduced, avoiding excessive accumulation. As a result, the method of the present invention can be operated for a very long period of time. Preferably, step (e) is applied when the dissolved anions, individually or in total, reach an undesirable concentration. Preferably, step (e) comprises precipitation to remove one or more of such anions from the catholyte, most preferably by reducing the temperature of at least a portion of the catholyte in the second treatment section, thereby reducing the solubility of the corresponding salts.

[0089] Thus, preferably, the sulfate and carbonate anions are separated from the catholyte by precipitated salts containing sulfate and carbonate anions.

[0090] Most preferably, the treatment in step (e) forms a solid precipitate. If the solid precipitate further co-precipitates a cathode component, its replenishment is recommended (e.g., at least one complexing agent for nickel ions). In some cases, such co-precipitation appears unavoidable.

[0091] Less preferred are methods of the invention in which, in the second processing compartment, the dissolved anions are separated by ion exchange, which typically has insufficient specificity for said dissolved anions.

[0092] The method of the present invention is preferred, wherein the precipitation is carried out at a temperature in the range of -5°C to 11.0°C, preferably in the range of 0.5°C to 10.0°C, more preferably in the range of 1.0°C to 8.0°C, even more preferably in the range of 1.5°C to 6°C, and most preferably in the range of 2.0°C to 4.0°C. As mentioned above, by significantly lowering the temperature in the second treatment zone, a sparingly soluble anion-containing salt is typically formed, thereby at least partially removing said anion from the catholyte. Most preferably, the sparingly soluble anion-containing salt is a sodium salt. Alternatively, preferred temperatures are in the range of -3°C to 5°C, preferably -2.5°C to 4°C, and most preferably -2°C to 3°C.

[0093] Therefore, the process of the present invention is preferred, in which the dissolved anions comprise at least sulfate anions, and in which sulfate anions are preferably separated by precipitated sodium sulfate.

[0094] Furthermore, the method of the present invention is preferred, wherein said dissolved anions comprise at least sulfate and carbonate anions, and wherein the sulfate and carbonate anions are preferably separated by precipitated sodium sulfate and sodium carbonate, respectively.

[0095] Sodium salts are particularly preferred because sodium hydroxide is preferably used to maintain the pH of the catholyte. Because hydrogen ions are constantly formed by the anode (resulting in chemically formed water), the hydroxide must be constantly replenished, which also introduces significant amounts of sodium. Therefore, sodium is removed by treatment in the second treatment compartment.

[0096] The process according to the invention is preferred, wherein the catholyte is alkaline, preferably having a pH in the range of 10.0 to 14.0, more preferably 11.0 to 13.3, even more preferably 11.5 to 13.0, even more preferably 12.0 to 12.9, most preferably 12.3 to 12.8.

[0097] As mentioned above, the formation of decomposition products in the catholyte is essentially avoided due to the presence of at least one anode and at least one membrane separating the anolyte from the catholyte. This includes essentially eliminating the formation of undesirable cyanide in the catholyte. Accordingly, the method of the present invention is preferred in which the catholyte contains cyanide ions in the range of 0 mg / L to 2.5 mg / L, preferably 0 mg / L to 1.5 mg / L, more preferably 0 mg / L to 1 mg / L, and most preferably 0 mg / L to 0.5 mg / L, based on the total volume of the catholyte. Most preferably, the catholyte is essentially cyanide ion-free, i.e., 0.001 mg / L to 0.05 mg / L, and even more preferably, cyanide ions are free.

[0098] In a preferred embodiment of the present invention, the catholyte contains oxalate ions in the range of 0 mg / L to 2.5 mg / L, preferably 0 mg / L to 1.5 mg / L, more preferably 0 mg / L to 1 mg / L, and most preferably 0 mg / L to 0.5 mg / L, based on the total volume of the catholyte. Most preferably, the catholyte is essentially free of oxalate ions, i.e., 0.001 mg / L to 0.05 mg / L, and most preferably, is free of oxalate ions. Oxalate ions are also a typical decomposition product, which is essentially avoided in the present invention.

[0099] Since neither cyanide nor oxalate ions are formed in the catholyte, no specific wastewater treatment is required to deal with these ions.

[0100] As mentioned above, the zinc ions in the catholyte are replenished by a zinc ion source. In the preferred method of the present invention, the zinc ions are present in the catholyte as a hydroxo complex. Preferably, the zinc ion source comprises water, hydroxide ions (preferably sodium hydroxide), and metallic zinc. The hydroxo complex is preferably obtained when metallic zinc is dissolved under alkaline conditions.

[0101] The method of the present invention is preferred, wherein the zinc ions in the catholyte are not complexed with at least one complexing agent for said nickel ions, preferably not complexed with a diamine, more preferably not complexed with an organic complexing agent. Most preferably, the zinc ions in the catholyte are very stable as hydroxo complexes, and no complex formation between the zinc ions and at least one complexing agent for said nickel ions is observed under alkaline conditions.

[0102] Preferred is a process of the present invention wherein the zinc ions have a concentration in the catholyte of less than 10 g / L, preferably in the range of 5.0 g / L to 9.0 g / L, more preferably 5.2 g / L to 8.5 g / L, even more preferably 5.4 g / L to 8.0 g / L, even more preferably 5.7 g / L to 7.5 g / L, and most preferably 5.9 g / L to 7.3 g / L.

[0103] Preferred is a method of the present invention wherein the catholyte has a concentration of nickel ions less than 2.0 g / L, preferably in the range of 0.5 g / L to 1.9 g / L, more preferably 0.6 g / L to 1.7 g / L, even more preferably 0.7 g / L to 1.6 g / L, even more preferably 0.8 g / L to 1.5 g / L, and most preferably 0.9 g / L to 1.4 g / L.

[0104] Advantageously, in the process of the present invention, the concentrations defined above for nickel and zinc ions are typically lower than those prevalent in processes known in the art, and since the nickel ions and preferably the zinc ions are recycled in the process of the present invention, no significant amounts of nickel and zinc ions, respectively, are wasted.

[0105] As already mentioned above, the excess water (which is very pure) is separated and removed from the process of the invention.

[0106] Preferred is a method of the invention wherein at least a portion of the separated water obtained in said first treatment section is disposed of, and the disposed water contains nickel ions in a concentration range of 0 mg / L to 1.0 mg / L, preferably 0 mg / L to 0.5 mg / L, even more preferably 0.01 mg / L to 0.11 mg / L, and most preferably 0.01 mg / L to 0.1 mg / L relative to the total volume of disposed water.

[0107] Preferred is a method of the present invention wherein at least a portion of the separated water obtained in said first treatment section is disposed of, and the disposed water contains zinc ions in a concentration range of 0 mg / L to 1.0 mg / L, preferably 0 mg / L to 0.5 mg / L, more preferably 0.01 mg / L to 0.11 mg / L, and most preferably 0.01 mg / L to 0.1 mg / L relative to the total volume of disposed water.

[0108] Preferably, only a pH adjustment is required before the excess water is disposed of.

[0109] In other cases, it is highly preferred to use the discarded water (preferably excess water) in a pre-rinse, i.e., a rinse step that precedes steps (b) and (c). This preferably means that this water is discarded (or disposed of) in a pre-rinse compartment. This is most preferred. In this case, water is used as much as possible without being wasted.

[0110] Also preferred are methods of the invention wherein the discarded water (preferably excess water) is used in a further pretreatment step prior to steps (b) and (c), more preferably in a cleaning step, most preferably in one or more degreasing steps (e.g., a soak cleaning step, an electrolytic cleaning step, etc.).

[0111] Also preferred is a method of the invention, wherein the discarded water (preferably excess water) is used in one or more further post-treatment steps, preferably in a passivation step for passivating the zinc-nickel coated substrate.

[0112] By utilizing excess water in one or more of the above applications, water is used optimally and wastewater is reduced as much as possible.

[0113] According to a second aspect, the present invention provides a system for depositing a zinc-nickel alloy onto a substrate, comprising: (I) optionally a pre-rinse compartment for pre-rinsing the substrate; (II) a deposition compartment for electrolytically depositing a zinc-nickel alloy on a substrate in a catholyte to obtain a zinc-nickel coated substrate, said deposition compartment comprising at least one anode equipped with at least one membrane; (III) a rinsing section for rinsing the zinc-nickel coated substrate to obtain a rinsed zinc-nickel coated substrate and rinsing water; (IV) a first processing compartment for processing the rinse water and a portion of the catholyte to separate the water from nickel ions and a complexing agent for the nickel ions; and (V) optionally a second processing compartment for processing the catholyte to separate dissolved anions from the catholyte; Including, The first processing section comprises: the separated water is returned to the pre-rinse compartment and / or the rinse compartment, and The separated nickel ions and the complexing agent for the separated nickel ions are returned to the deposition compartment, preferably via a mixing compartment. The system is adapted to:

[0114] With respect to (I), (II), (III), (IV) and (V) of the system of the present invention, what has been said above in relation to the method of the present invention preferably also applies. Thus, preferably, what has been said above in relation to the method of the present invention, and preferably, what has been described as being preferred, also applies to the system of the present invention.

[0115] The present invention is further illustrated by the following non-limiting examples. [Example]

[0116] Test plating setup (according to the present invention) In a test plating setup according to the invention, a zinc-nickel deposition bath is set up as catholyte in the deposition compartment (about 20,000 L) in order to deposit a zinc-nickel alloy onto small metal parts (e.g. screws, loading of about 40 kg per barrel).

[0117] The catholyte initially contains 0.9 g / L to 1.4 g / L of nickel(II) ions, 5.9 g / L to 7.3 g / L of zinc(II) ions, and a diamine having at least one secondary amine group as a chelating complexing agent for the nickel ions. The pH is about 12.5, which is strongly alkaline, and is adjusted with sodium hydroxide.

[0118] The system utilizes multiple insoluble anodes of iridium / tantalum oxide on titanium with cation exchange membranes. For each anode, the distance between the anode and the respective membrane is less than 5 mm. Each anolyte, containing water and sulfuric acid, is separated from the catholyte by the membrane so that the complexing agent never comes into contact with the anode.

[0119] The metal member is contacted with the catholyte in the deposition compartment (at about 25° C.) and subjected to a current of 1 A / dm 2 A current density of less than 1000 kJ / cm was applied for a time period varying between 130 and 170 minutes.

[0120] The test plating setup was utilized for a period of four months and water consumption, compounds, and water disposal were closely monitored.

[0121] During the four-month process period, nickel ions are replenished by a nickel ion source, which is an aqueous solution containing dissolved nickel sulfate and no complexing agent for nickel ions, and has a nickel ion concentration of about 100 g / L. Zinc is replenished from dissolved metallic zinc under alkaline pH conditions. Due to the formation of zinc hydroxide under alkaline conditions, no additional complexing agent for zinc ions is used.

[0122] After deposition of the zinc-nickel alloy, the metal component is rinsed with water in a rinse compartment, which includes five fluidly connected rinse subcompartments forming a five-stage rinse cascade. A portion of the rinse water is repeatedly combined with a portion of the catholyte and transported to a vacuum evaporator (40°C, approximately 50 mbar, capacity: approximately 150 L / h) to separate the water from the complexing agent, nickel ions, and zinc ions, respectively. A portion of the separated water is returned to the rinse cascade. Excess water (nickel and zinc concentrations less than 0.1 mg / L) is used for disposal or other industrial purposes, particularly for the pre-rinse stage in this example. In each case, the separated water has a conductivity of less than 200 μS / cm. The nickel ions, zinc ions, and complexing agent are enriched as a concentrated aqueous solution (density 1.20 kg / L to 1.23 kg / L, completely aqueous without phase separation) and returned to the catholyte. During an operating time of about 4 months, less than about 500 L / week of excess water (<200 μS / cm) is disposed of, preferably for pre-rinsing.

[0123] Even after 4 months of operation, the catholyte is free of decomposition products such as cyanide and oxalate ions, confirming that the complexing agent is not decomposed in either the deposition compartment or the vacuum evaporator, which is the basis for repeated use of the water.

[0124] After about four months of operation, a portion of the catholyte was treated in a second treatment section (refrigeration unit) at temperatures between 2°C and 4°C or between -2°C and 2°C to precipitate at least a portion of the sulfate and carbonate anions. However, even after four months, critical concentrations of carbonate and sulfate had not yet been reached in the catholyte.

[0125] During the four-month run-time, no complexing agent was added to the catholyte. Instead, the concentration of complexing agent in the catholyte remained constant, with a variation of ±2.5% due to measurement error and catholyte deposition variations. Nickel and zinc ions were replenished so that their concentrations remained within the initial setting range. Furthermore, no nickel-contaminated water was produced for disposal.

[0126] Furthermore, the cathodic current efficiency (CCE) was approximately 15%-30% higher than in the comparative test plating setup (see below).

[0127] Comparative test plating setup (not according to the present invention) In a comparative test plating setup (not according to the present invention), a deposition bath was set up that was essentially identical (and similar in volume) to the catholyte used in the test plating setup according to the present invention. However, the anode was not separated by a membrane. Therefore, the complexing agent was at least partially decomposed at the anode and had to be replenished with nickel ions. Even though the rinse water (i.e., wastewater) was subjected to a vacuum evaporator to reduce the volume before disposal, the wastewater still contained significant amounts of decomposition products, including cyanide. This was costly and required specialized disposal. The (concentrated) wastewater volume amounted to approximately 1000 L / week and had a nickel concentration of at least 1 g / L, a zinc concentration of at least 8 g / L, a cyanide concentration of at least 0.1 g / L, and a significant amount of complexing agent. Thus, significant amounts of nickel and zinc were lost, which had to be replenished to the deposition bath. Furthermore, complexing agent had to be periodically added to the deposition bath.

[0128] In contrast, the process of the present invention (see the examples according to the present invention) not only reduces the amount of water to be disposed of; the disposed water is also substantially free of nickel and zinc ions. These ions transferred through the rinse are recycled back to the catholyte along with the complexing agent. As a result, the process of the present invention is very environmentally friendly and cost-effective, and represents a significant improvement over existing processes.

[0129] System for depositing zinc-nickel alloys onto a substrate (according to the present invention) In FIG. 1, a schematic diagram of a system 1 for depositing a zinc-nickel alloy onto a substrate is shown, in which an aqueous zinc-nickel deposition bath is provided as catholyte 3-1 in a deposition compartment 3.

[0130] The system 1 optionally comprises a pre-rinse compartment 2 for pre-rinsing the substrate. Since the substrate to be coated is often contaminated with undesired contaminants, it is generally recommended to pre-rinse the substrate with, for example, an alkaline pre-rinse solution in the pre-rinse compartment 2. However, if the substrate is already clean, the pre-rinse is preferably omitted.

[0131] The system 1 further includes a deposition compartment 3 for electrolytically depositing a nickel-zinc alloy on a substrate in a catholyte 3-1. The catholyte provided in the deposition compartment includes nickel ions, at least one complexing agent for the nickel ions, and zinc ions. The deposition compartment 3 includes at least one anode 3-2 with at least one membrane separating the catholyte from the anolyte. The volume of the anolyte is defined by the space formed by the at least one anode with at least one membrane.

[0132] When a substrate, preferably a pre-rinsed substrate, is transferred into the catholyte 3-1 in the deposition compartment 3 and an electric current is applied, a zinc-nickel alloy is electrolytically deposited onto the substrate to obtain a zinc-nickel coated substrate.

[0133] The system 1 further includes a rinse compartment 4 for rinsing the zinc-nickel coated substrate to obtain a rinsed zinc-nickel coated substrate and rinse water. By rinsing the zinc-nickel coated substrate, the remainder of the catholyte is removed, and the resulting rinse water contains a portion of the catholyte, which contains nickel ions, at least one complexing agent for the nickel ions, and zinc ions.

[0134] Rinse water is transferred (preferably by a pump) from the rinse compartment 4 by a rinse water line 4-1 to a first processing compartment 5 of the system 1 for treating the rinse water. Furthermore, a portion of the catholyte is transferred (preferably by a pump) from the deposition compartment 3 to the first processing compartment 5 by a catholyte removal line 3-3, the latter being required to maintain a constant volume of catholyte.

[0135] The treatment section 5 is preferably an evaporator, more preferably a vacuum evaporator, which allows efficient separation of water by evaporation.

[0136] At least a portion of the separated, preferably evaporated, water is returned from the first treatment section 5 to the rinse section 4 by a water return line 4-2. Additionally, and optionally, another portion of the water is returned to a pre-rinse section (not shown). Excess water is disposed of by a water disposal line 5-2 and is preferably used for other industrial purposes, since this water is very pure.

[0137] After separation of the nickel ions, the at least one complexing agent for the nickel ions, and the water from the zinc ions in the first processing compartment 5, the separated nickel ions, the at least one complexing agent for the separated nickel ions, and the separated zinc ions are returned as concentrated aqueous solutions to the deposition compartment 3 directly or, preferably indirectly, by transferring them from the first processing compartment 5 to an optional mixing unit 6 via a separation line 5-1 as shown in FIG. 1 .

[0138] Optional mixing unit 6 is fluidly connected to a nickel ion source 7-1, which is preferably an aqueous solution comprising water and nickel sulfate dissolved therein, and to a zinc ion source 7-2, preferably as described hereinabove in connection with the method of the present invention. In mixing unit 6, the replenished nickel and zinc ions are thoroughly mixed with the concentrated aqueous solution before being returned to deposition compartment 3 via return line 6-1, thereby closing the loop. Thus, nickel ions, zinc ions, and at least one complexing agent for nickel ions are maintained at essentially constant concentrations in the catholyte.

[0139] The system 1 further includes an optional second processing section 8 for treating the catholyte 3-1 to separate dissolved anions, such as sulfate and carbonate anions, from the catholyte 3-1. During long-term operation of the system, e.g., over several months, the concentration of dissolved anions may reach undesirable limits and such anions may be at least partially removed in the second processing section, preferably by precipitation. Such precipitated anions are removed via an anion disposal line 8-1. [Explanation of symbols]

[0140] 1. System for depositing zinc-nickel alloys onto substrates 2 Pre-rinse compartment 3. Sedimentary Section 3-1 Space for the catholyte 3-2 At least one anode with at least one membrane 3-3 Cathode liquid removal line 4. Rinse section 4-1 Rinse water line 4-2 Water return line 5. First treatment area 5-1 Separation line 5-2 Water disposal line 6 Mixing Unit 6-1 Return Line 7-1 Nickel ion source 7-2 Zinc ion source 8. Second treatment area 8-1 Anion disposal line

Claims

1. 1. A method for depositing a zinc-nickel alloy onto a substrate, comprising the steps of: (a) providing a substrate; (b) providing a zinc-nickel aqueous deposition bath as a catholyte in the deposition compartment, wherein: the deposition compartment includes at least one anode with an anolyte; and the anolyte is separated from the catholyte by at least one membrane; and The catholyte is (i) nickel ions; (ii) at least one complexing agent for nickel ions, and (iii) zinc ions the steps comprising: (c) contacting the substrate with the catholyte in the deposition compartment to electrolytically deposit a zinc-nickel alloy on the substrate, thereby obtaining a zinc-nickel coated substrate, wherein after step (c), nickel ions in the catholyte have a lower concentration than before step (c); (d) rinsing the zinc-nickel coated substrate in a rinse compartment containing water to obtain a rinsed zinc-nickel coated substrate and rinse water, wherein the rinse water contains a portion of the at least one complexing agent for the nickel ions and a portion of the nickel ions. Including, (i) treating at least a portion of the rinse water and / or at least a portion of the catholyte in a first processing compartment to separate the water from the at least one complexing agent for the nickel ions and the nickel ions; (ii) returning at least a portion of the at least one complexing agent separated from the water to the catholyte as a concentrated aqueous solution; and (iii) adding, directly or indirectly, a source of nickel ions to said catholyte, provided that said source of nickel ions does not include at least one complexing agent for said nickel ions or other complexing agents for nickel ions; The nickel ion source is an aqueous solution containing water and a nickel salt dissolved therein. The method, characterized by:

2. 10. The method of claim 1, wherein the at least one complexing agent for nickel ions is not in contact with the at least one anode.

3. 3. The method of claim 1 or 2, wherein the nickel ion source does not include tetraethylenepentamine.

4. 4. The method of claim 1, wherein the at least one complexing agent for the nickel ions in the catholyte comprises an amine.

5. Prior to step (c), step (a) (a-1) pre-rinsing the substrate in a pre-rinse compartment containing water to obtain a pre-rinsed substrate and pre-rinse water; 5. The method of claim 1, comprising:

6. 6. The method of any one of claims 1 to 5, wherein the at least one anode has a distance to the at least one membrane in the range of 0.5 mm to 5.0 mm.

7. 7. The method of claim 1, wherein the first processing compartment comprises an evaporator.

8. 8. The method according to any one of claims 1 to 7, wherein at least a portion of the separated water obtained in the first treatment section is returned to the pre-rinse section and / or the rinse section.

9. (e) treating at least a portion of the catholyte in a second treatment compartment to separate dissolved anions from said catholyte by precipitation.

9. The method of any one of claims 1 to 8, comprising:

10. 10. The method of claim 9, wherein the precipitation is carried out at a temperature in the range of -5°C to 11.0°C.

11. 11. The method of claim 9 or 10, wherein the dissolved anions include at least sulfate anions, and the sulfate anions are separated by precipitated sodium sulfate.

12. 12. The method of claim 1, wherein in the catholyte, zinc ions are present as hydroxo complexes.

13. 13. The method according to any one of claims 1 to 12, wherein at least a portion of the separated water obtained in the first treatment compartment is disposed of, the disposed of water comprising nickel ions in a concentration range of 0 mg / L to 1.0 mg / L relative to the total volume of disposed of water.

14. A system (1) for depositing a zinc-nickel alloy on a substrate for carrying out the method according to any one of claims 1 to 13, comprising: (II) a deposition compartment (3) for electrolytically depositing a zinc-nickel alloy on the substrate in a catholyte (3-1) to obtain a zinc-nickel coated substrate, the deposition compartment (3) comprising at least one anode (3-2) equipped with at least one membrane; (III) a rinsing section (4) for rinsing the zinc-nickel coated substrate to obtain a rinsed zinc-nickel coated substrate and rinsing water; and (IV) a first treatment compartment (5) for treating a portion of the rinse water and the catholyte (3-1) to separate the water from nickel ions and complexing agents for nickel ions; Including, The first processing section (5) comprises: the separated water is returned to said rinse compartment (4), and The separated nickel ions and the complexing agent for the separated nickel ions are returned to the deposition compartment (3) as a concentrated aqueous solution. The system (1) is adapted to:

15. (I) a pre-rinse compartment (2) for pre-rinsing said substrate, and / or (V) a second processing compartment (8) for processing the catholyte and separating dissolved anions from the catholyte; further comprising The first processing section (5) comprises: the separated water is returned to the pre-rinse compartment (2) and / or the rinse compartment (4), and The separated nickel ions and the complexing agent for the separated nickel ions are returned to the deposition compartment (3) as a concentrated aqueous solution. It is adapted to A system (1) according to claim 14.

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