Letter 37092

Removing Chromium from rinse waters after ion tanks are regenerated [South Dakota] 

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I am looking for some help on a problem with our chromium rinse waters from regenerating our resins. In the past we have sent them out to a firm to be regenerated. They have merged with a larger company and have stopped working with small businesses. So I am going to regenerate them in house which we have the ability to do. My trouble is that I have to be within our permit limits to discharge into the waste stream. I need to find a way to drop the chromium out of or neutralize it so it can disposed of it properly.

Thank You for your help.

Steve Morris
Black Hills Gold Jewelry - Rapid City, SD, USA

The solution to your problem is very simple. You need a batch treatment system. But, before you try this you should get some help from someone who has done this before, and get more familiar with the chemicals and the process. These are strong chemicals and if the procedure is not done correctly it can generate a lot of noxious sulfur dioxide gas.

The classical treatment procedure is to reduce the pH to below 3, add a reducing agent such as sodium metabisulfite, then raise the pH to 8-9, add a flocculant and then settle and filter press the solids.

There are also other treatment chemicals that do not require as much pH adjustment.

Lyle Kirman
Kinetico Incorporated - Newbury, OH, USA

Can you clarify what you are treating? Are you treating the chromium rinse water with an ion resin unit, if you are , you should be able to treat the regeneration water also. I treat an acid rinse water laden with heavy metals with an ion unit, when the ion unit is spent and I regenerate it, I send the regeneration water back through the unit with no problems.

John Schwaller
- Buford, GA, USA

What water are you treating in the first place? If you're removing Chrome from wastewater in the first place, then having to treat the waste from the removal process it doesn't sound very efficient.

Not having much to go on I could be all wrong here, but it sounds to me like you may be better off treating the original waste stream without the ion-exchange step... by hydroxide precipitation for example, which is a very simple process, as described above...

Jeff Watson - Pearland, TX

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