Method and system for depositing a zinc-nickel alloy on a substrate

A method for depositing a zinc-nickel alloy on a substrate, the method comprising the steps:

• (a) providing the substrate,
• (b) providing an aqueous zinc-nickel deposition bath as a catholyte in a deposition compartment, wherein
• the deposition compartment comprises at least one anode with an anolyte, and
• the anolyte is separated from the catholyte by at least one membrane, and the catholyte comprises:
• (i) nickel ions,
• (ii) at least one complexing agent for nickel ions, and
• (iii) zinc ions,
• (c) contacting the substrate with the catholyte in the deposition compartment such that the zinc-nickel alloy is electrolytically deposited onto the substrate and thereby obtaining a zinc-nickel coated substrate, wherein
• after step (c) the nickel ions in the catholyte have a lower concentration than before step (c),
• (d) rinsing the zinc-nickel coated substrate in a rinsing compartment comprising water, such that a rinsed zinc-nickel coated substrate and rinse water is obtained, wherein
• the rinse water comprises a portion of the at least one complexing agent for nickel ions and a portion of the nickel ions,
• characterized in that:
• (i) at least a portion of the rinse water and/or at least a portion of the catholyte is treated in a first treatment compartment such that the water is separated from the at least one complexing agent for nickel ions and the nickel ions,
• (ii) at least a portion of the at least one complexing agent separated from the water is returned into the catholyte as a concentrated aqueous solution, and
• (iii) a nickel ion source is added to the catholyte, with the proviso that the nickel ion source does not comprise said at least one complexing agent for nickel ions or any other complexing agent for nickel ions,
• wherein the nickel ion source is an aqueous solution comprising water and a nickel salt dissolved therein.