Foaming from chrome suppressant

A. Unfortunately, the additive is doing what it is intended to do, create a foam blanket. In the bath it keeps the mist down, which is good. But in your evaporation step, it slows the volume reduction, which is bad. That's a common problem with recycling and waste treatment operations - you're often trying to accomplish the reverse of what the process solution does while in service.

I can think of two things that might help. 1) Pass the rinse through a bed of a polymeric adsorbent, such as Amberlite XAD-4. This may remove the foaming agent. 2) Add a step where the rinse is downflowed through a tall, small diameter tank, and air sparged up through it. Then collect and remove the foam from the top, which will contain a much higher concentration of the foaming agent than the bulk solution. Then, pipe the rinse to evaporation.

I have never tried either of these treatments on a waste such as you describe, so you would have to do some bench scale tests to see if either would work.

Hope this is of some help. Good luck!

A. Firstly, why not try to recover more rinse waters before evaporation. That said,what do you do with the rinse water from the evaporator? If it is being concentrated for disposal, use a defoamer in the evaporator BUT do not do this if the water is being returned to the chrome tank. You may find it necessary to use a different type of evaporator,such as a "paddlewheel" instead of packing type.