Metal finishing Q&As since 1989
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Minimizing iron contamination in a hard chrome plating bath: HEEF? Reducing reverse etching times?
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Q. Joel did you manage to sort your high iron out -- if so, how, thanks.
I've got two tanks with very high contamination levels causing major headaches. We can't afford to dump the old chrome and start again so I've decided to keep topping my larger tank with solution from the smaller tank and add chrome to the small tank it will take time but hoping in the end I will be topping it up with good quality solution and it should lower iron level in both tanks without the expense. Do you think that would work thanks.
Regards steve
Shop manager - Uk
December 2, 2021
A. Hi Steve. We can try to alert Joel to your question but his visit was a long time ago so his e-mail probably won't work.
A porous pot will reduce iron contamination but you would need to find out if Hard chrome Plating Consultants in Cleveland, Ohio is still in business, or find another manufacturer and I've never heard of one. Trevor Crichton says he has used a regular ceramic flower pot as the diaphragm and it worked at least for the short term.
Alternately the iron can be removed by ion exchange. Hexavalent chromium, CrO4 -2 is an anion whereas metallic contaminants are cations. But chromic acid is a really aggressive oxidizer so you will need a specialized resin and system.
Full real name and town next time please -- it's been our way for 32 years now, and we believe it's one of the main factors in the site's longevity :-)
Luck & Regards,
Ted Mooney, P.E. RET
Striving to live Aloha
finishing.com - Pine Beach, New Jersey
December 2021
A. No matter how much you pour from one bath to another, sooner or later you will have to dispose of the entire volume of electrolyte from two baths. Membrane plants are expensive both in purchase and maintenance.
At the moment, an economically viable solution to the problem of iron in chromium plating electrolytes is the use of complexing agents that allow iron to bind, partially precipitated, and partially leave it in the electrolyte in a form that does not affect the course of the chromium plating process
- Nizhniy Novgorod, Russia
December 15, 2021
⇩ Related postings, oldest first ⇩
Q. Hi there,
As part of a grad course I have to help a local company produce a pollution prevention strategy for their hard chrome plating process. Their main difficulty is dealing with the iron contamination in the chromic acid baths; they've installed porous pot/ion exchange treatment systems in the past, and found the costs/trouble to outweigh the advantages. SO - does anyone have any experience in actually reducing iron buildup from the start, rather than removing what ends up in the bath? I've been looking into strategies such as using a HEEF (high efficiency, etching free) chrome source, or reducing the reverse etching time, or perhaps having them install a separate tank in which to do the R.E. - can anyone recommend/poke holes in these tactics? Any suggestions for things that have worked in your particular facility? FYI, here are some of the operating conditions of the current baths, if this helps: current = 1800A, voltage = 6-12V, temp = 65 °C, [Cr] ~ 125,000 mg/L, R.E. time = 10 seconds, tanks get refilled when [Fe] > 11g/L
Thanks!
Student, University of Guelph - Guelph, Ontario, Canada
2007
A. Yes, Joel, reverse etching in a separate fluoride-free chrome plating solution tank is a feasible alternative that is in practice in some shops.
Ted Mooney, P.E.
Striving to live Aloha
finishing.com - Pine Beach, New Jersey
2007
A. I ran HEEF 25 tanks with a porous pot and had no problem with iron. Since I do not know who made the pot and how well they followed instructions, I can not understand why they had "problems" with it. The inner pot does need to be emptied several time (every couple of days) when you start with a high iron content, but this only takes a few minutes. It is messy, but so is chrome plating. As the tank is cleaned up, the duty cycle can stretch out to over a week. A chrome tank cost too much to dump unless absolutely mandatory, so porous pot treatment is very cost effective.
James Watts- Navarre, Florida
2007
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