Metal finishing Q&As since 1989

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Chromium and Electrocoagulation

2006

I'm about the embark on some lab-scale electrocoagulation tests on water contaminated with hexa-chrome, and I'm slightly concerned about the use of EC, with its off-gassing and whether chrome fumes would be given off.

I don't really know where else I could find this sort of very specific information, and was wondering if anybody else on the forum had used EC on chrome, and what sort of pre-cautions they took. Or, perhaps if people had any ideas or suggestions as to what they thought may happen, in terms of safety precautions and if a Chrome fume could be given off when I carried out the process?

Any ideas are gratefully welcomed.

Matthew Tondziel
- Bristol, United Kingdom

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I have been gun shy about EC because of the exotic claims of some sales reps, especially when they could not answer technical questions.
If no one else answers, I would run a lab scale in the hood first. As a person that heats cleaning chrome vapor residue, I would line the hood with tin foil which can be easily cleaned or put in a preapproved waste disposal container.

James Watts
- Navarre, Florida
2006

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There is no danger of chromium fumes from EC any more than from the static solution. No air is required (no agitation). The hex chrome is reduced immediately by the process. The only gas to expect is hydrogen in very small volume (not worth collecting) and possibly oxygen unless you use all steel plates. The chrome is removed when you see the color disappear and the pH is above 6.1. Test it. You should get clear water, but if you "over drive" the process it may contain excess iron (rusty color) below a pH of 8.1.

Paul Morkovsky
- Shiner, Texas, USA
2006

A middle-of-the-road safety approach is probably appropriate. Nobody can give an exact answer. Too many variables: wastewater concentrations and conductivity, pH, plate material and spacing, flow rate, voltage, etc.

The treatment doesn't give off any chrome fumes per se, but the mist created by hydrogen and oxygen bubbles carries everything in the wastewater. The Cr(+6) isn't exactly eliminated immediately, the unit I tested required 2 passes at a relatively slow flow rate. Strongly agree that over-voltage dissociates water and creates excessive misting.

I treated rinsewater with 750 ppm Cr, kept the voltage low and my face away from the bubbles. Decided that batch treatment using sodium hydrosulfite [on eBay or Amazon] was faster and less expensive.

Ken Vlach [deceased]
- Goleta, California
Finishing.com honored Ken for his countless carefully researched responses. He passed away May 14, 2015.
Rest in peace, Ken. Thank you for your hard work which the finishing world, and we at finishing.com, continue to benefit from.
2006