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topic 59178

High Chrome Levels in Zinc Phosphate Sludge

February 26, 2013

Q. I am new to the Zinc Phosphate world, we run a dip cycle at about 140 °F for about 15 minutes. We are cleaning and pickling all parts before phosphating. The issue we are having is that upon sampling our phosphate "Sludge" during tank cleaning, there is Chromium present at hazardous levels.
Is this a common problem?

Adam Riggs
Assistant Supervisor - Evansville, Indiana, USA

March 1, 2013

A. Hello Adam,

It is not very rare to measure chromium content in phosphate sludge if you have some re-process (already phosphated parts that you pickle and phosphate again) and your sealer is chromium-based. But this content is not very high, and I doubt that it could be measured easily.

How are you testing for chromium? Are you testing for hexavalent or total chromium? And you are testing in the solution (lixiviation) or in the sludge?

I think that with these answers I could help you understand that high level chromium result.


Daniel Montanes
- Canuelas, Buenos Aires, Argentina

March 5, 2013

Q. We have conducted TCLP's on our sludge alone. The TCLP tells us that we are getting around 46 ppm(parts per million) of Chromium and about 1.5 ppm of Cadmium. The hazardous limits are 5 ppm for Chrome and 1 ppm for Cadmium. The sludge is the only question as we do not waste our solution. Never thought about the replating process, we do replate upon occasion.

Thank you for your response

Adam Riggs
- Evansville, Indiana, USA

March 14, 2013

A. Hello Adam,

TCLP is the correct procedure for sludge. If you test for cadmium, and the sludge does contain some cadmium (1.5 ppm is not very high, but it is something), there is some problem that I am not aware of...

Do you cadmium plate? Do you phosphate over cadmium plate? If the answer is no, there is no possibility that you can have cadmium in your sludge or lixiviate (TCLP test). I have worked some time with phosphate baths and the major problem is zinc or nickel, not chromium and not cadmium.

If the test was carried by a reliable laboratory, I would redo the test... And look for possible cross contamination from some cadmium or chromium plating bath. If the test was done in your laboratory or in an unknown source, I would take another laboratory, maybe some lab that some colleague trusts, and have the test done there. Here in Argentina we see sometimes strange results, so we have the same test done in two or more laboratories to check them.

Hope some ideas I gave you can help you with this issue. Good luck!

Daniel Montanes
- Canuelas, Buenos Aires, Argentina

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