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Dichromate Precipitation

We have a small passivation line setup to do QQ-P-35C (canceled) [link is to free spec at Defense Logistics Agency, dla.mil]-II and Type VI passivation of 303ss, 17-4Ph and 316ss parts.

My question concerns our first and second drag-out tanks.

Because we are using Sodium Dichromate, is it possible to somehow precipitate out the chrome, and any other chemicals out of these tanks in order to make the solutions easier to process for waste treatment?

We currently are running 3 drag-out de-ionized water tanks after the Nitric/Dichromate treatment in what so-far has been a self contained operation. We use the drag out as the basis or makeup for new Acid solution as needed.

Robert Prichard
Heat treat / Passivation Mgr. - Chadwicks, New York, USA
2004

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Good to see you recovering at least part of the solution as makeup. Unless you can add heat to a process tank to make room for the recovered rinse then it will eventually go to waste treatment. You have a choice of concentrating it even more and recovering some of the water with membranes (electrolytic or otherwise). The volume (gallons) of dichromate going to waste treatment would decrease but the concentration would increase. You might consider using the excess dragout as a dragin solution (ahead of the dichromate). This should improve the quality of the process and possibly extend its life. It will have some, but little, effect on the number of molecules going to waste treatment but will at least give you some benefit before it becomes waste.

Paul Morkovsky
- Shiner, Texas, USA
2004