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Suitable membrane material for hexavalent chromium

April 11, 2011

We are in the planning stages of trialing a nano-membrane system to recover hex-chromium plating solution from the counter-current rinses after a decorative Chrome plating tank.The objective is to return as much as possible of the recovered concentrated solution back to the plating tank. If possible we would also like to reuse the permeate back into the rinses, depending on its quality.
We have had difficulty in finding a membrane which will stand up to Cr6/H+ and provide the separation required.
Anyone had successful experience in this area. Would appreciate any feedback.

Geoffrey Whitelaw
- Port Melbourne, Australia

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I've looked into this in the past, and haven't found anyone who would recommend their membranes for this application. But, I did also see a working system on the rinse after a small line.

The main problem with the use of a membrane in this application is the volume balance. There is very little evaporation from a decorative chromium plating tank relative to the volume of dragout. Complicating this is the very limited concentration that you could possibly achieve with a membrane. And, the more you concentrate it, the more likely the chromic acid will destroy the membrane. So, in order to reuse the recovered chromic acid, you would need to add supplemental evaporation.

For this reason, I usually recommend evaporation for Chromic Acid dragout recovery, with IX purification to remove cationic impurities.

Lyle Kirman
consultant - Cleveland Heights, Ohio
April 14, 2011

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May 8, 2011

You cannot use IX in a concentrated chromic solution. Therefor the resin (any resin) can be used only in the rinses. If you install cascade rinsing, all the chromium will go back to the chromium plating solution.
In this case you should connect the resin to the last rinse.

Most important - chromium in the plating solution or rinses exist in an anionic form, not cationic. That is why you need an anionic resin.

The resin can be backwashed and than you can recover the chromium

Sara Michaeli
Tel-Aviv-Yafo, Israel

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Dear Geoff,

prior of setting up the whole recycling system it's worth knowing what are the daily drag-outs regarding the geometry of the articles to be treated. Rinses however can be easy maintained over suitable ion exchange columns. The cleanest rinse as a spray rinse used as well for your chrome scrubber and returned into your "dirtiest" one. The dirtiest one runs over a weak basic anionic exchanger to recycle your CrO3 and use it for replenishing in your main process.
Since CrO3 acts as an anionic may you can try your luck with anionic permeable membranes process and/or electrodialysis process.

Kind regards,
Dominik

Dominik Michalek
- Melbourne, Australia
May 14, 2011