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topic 4801

Sulphates vs. Chlorides in plating solutions


(2000)

I have the strongly held belief it is easier to treat/purify sulphate effluents as opposed to chloride effluents. Now it looks like I might have to justify what I've said, so where can I find examples of the treatment processes for sulphates and chlorides? Ian

Ian Brooke
university - Glasgow, Scotland


First of two simultaneous responses-- (2000)

The question of sulfate vs. chloride depends on what you mean by easier. Sulfate will precipitate more when you are doing chemical treatment with lime, but is that better or worse? High buildup of chlorides will corrode metal more readily in pumps, evaporators, etc. Sulfate solutions also electrowin better than chlorides (ever tried to plate copper from a chloride solution?).

You need to define what you are treating for, and how you are going to do it.

bill vins
Bill Vins
microwave & cable assemblies
Mesa (what a place-a), Arizona 


Second of two simultaneous responses-- (2000)

Most people do not care about the anions.

If I remember correctly, most sulfates are less soluble than chlorides, particularly when lime (calcium) is used for the neutralizer/precipitator.

James Watts
- Navarre, Florida


(2000)

Thank you both for your responses.

The application is a ternary bath.

Tin Zinc and chromium, all can be plated from either sulphates or chlorides.

It's a cadmium replacement, and I want it to be as environmentally acceptable as possible, hence sulphates which as I said earlier I'm sure are easier to treat however I'm short on facts.

I know the anions are not important these days, but I want to get ahead of the game.

In some applications chlorides do have an edge in plating but not in my bath. Ian

Ian Brooke
university - Glasgow, Scotland


(2000)

Hello, Ian. Chlorides are corrosive, and more soluble in general, so I'd say go with sulphates if you have the choice. But a tin-zinc-chromium plating solution is something I'd like to see! How do you know you have metallic chromium in the deposit? Thanks!

Ted Mooney, finishing.com Teds signature
Ted Mooney, P.E. RET
finishing.com
Pine Beach, New Jersey


(2000)

I know the chromium is metallic as I analyse with an SEM, the only elements present are metal, if the metals were compounds then there'd be peaks for oxygen, carbon etc. I was looking for actual examples of how wastes are treated to remove chlorides and sulphates.

Ian Brooke
university - Glasgow, Scotland



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