Letter 24126

Ni Stripping/Electrowinning  

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Hi
I am a chemist -- specialist in PM, but we need some expert advice here pls. We are looking at the plating of nickel onto nickel.

What is the most effective means of stripping Ni? Is it affected by Cr, and Fe presence?
Is there an effective electrowinning process?

As regards plating-- are we very limited using Electroless Ni plating -- in terms of pH, reducing agent, temp etc?
If so what is the most suitable sacrificial anode? and what operating voltage (current density) is best?

Thank you very much for your help

Bill O Leary
specialized metals refining - Dublin, Ireland

Lots of questions and very little information. If you are plating nickel onto nickel, why do you want to strip it? If you do strip it, what is the substrate?

You may not be restricted to electroless nickel, but that depends on what you want to put the nickel; if it is a conductor, you an use electrolytic nickel, but if it is an unmetallised plastic, you are limited to electroless nickel. If you use electroless nickel, sacrificial anodes are irrelevant as you won't need them. However, if you are using electrolytic nickel, that is a completely different story.

Can you please clarify what you are doing and what you need?

Trevor Crichton R&D practical scientist - UK

Thanks Trevor. We are hoping to strip Nickel from incoming material comprised of Nickel, Iron, and Cr. We then want to plate this material in bulk. So we need to know the most suitable means of stripping Ni . Is electroless better than using a bath containing the above solution and a sacrificial anode.

Thank you for your advice.

Regards,

Bill O Leary
- Dublin

Is the incoming material an homogeneous mixture of iron, chromium and nickel or is it iron plated with nickel and then chromium? If it is the latter, you can remove the chromium by anodic dissolution in a hot strong alkali. Nickel can be stripped from iron by anodic stripping in 3 parts sulphuric acid, 2 parts water and 50 g/l glycerol. This solution is aggressive and will start to attack the iron, so you must watch it. It can be done potentiostatically and you will see the potential change when the nickel dissolution ends and the iron starts.

If you have a homogeneous mixture, you will need to dissolve it all up in acid and then precipitate the different metals by increasing the pH. I suggest you keep the solution oxidising as this will keep the iron as ferrous hydroxide, which is more easy to handle than ferric hydroxide. Once the iron has been filtered off as hydroxide (say pH = ~4.5- 5), the nickel hydroxide will start to come down; filter this off and the remaining liquid should contain chromium. recovery of metals from the different aliqouts can be done electrolytically.

If you have only a very small amount, nickel reacts with dimethyl glyoxime and this is a specific reagent for nickel, so you could use that.

Trevor Crichton R&D practical scientist - UK