Metal finishing Q&As since 1989

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TECHNICAL SUPPORT FOR CONVERSION OF HEXAVALENT CHROME AND CYANIDE TO NON-TOXICS IN SOIL

 

The Metal Finishing Assn. of Southern Calif. is preparing a position paper to be used to respond to negative comments re the metal finishing industry as related to soil contamination reported in the media.

One of our contentions is that hexavalent chrome (toxic) is reduced to trivalent chrome (non-toxic)in typical soil.

The second is that cyanide is also reduced to a non-toxic material (cyanate) in soil.

We are requesting references that could be used to support our statements.

BERT J. SHERWOOD
- Los Angeles, California, USA

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Good luck in finding that supporting data because it's not true--at least not to a substantial enough degree to matter. Yes, some soil has some limited ion-exchange and neutralization capability of theoretical interest, but much of it is reversible anyway. And the contamination of ground water with hexavalent chromium is pervasive and patently obvious, from New Jersey to Texas to California. And in some cases it is undebatable that the plating shop simply dumped chromium solutions on the ground and that this was the cause of the ground water contamination. If some chrome was trapped in the soil on the way down, that only broadens the problem rather than ameliorating it.

Ted Mooney, P.E.
Striving to live Aloha
finishing.com - Pine Beach, New Jersey
 

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There is no "half life" of hexavalent chromium in the natural environment. This is urban legend. It was a great line foisted upon the gullibly uninformed; great because it implies that after some certain amount of time, the chromium would essentially disappear.

There is no typical soil. There are thousands of soil types, each with different amounts of sand, silt, and clay, different types of clay minerals, different amounts and types of organic material and cation exchange capacity.

There is no progressive destruction of cyanide in the environment, at least none that doesn't involve the poisoning of entire ecosystems during the oxidation. And cyanate is still poisonous, Our own "Electroplating Engineering Handbook", (4th Edition, Lawrence Durney, Editor, Van Nostrand Reinhold) gives instruction for treating of cyanide in two stages to completely oxidize the cyanide to carbonate and nitrogen. I have never seen a treatment system (or jurisdiction) that only partially treated the cyanide, or that allowed the release of cyanate to the environment.

  
Tom Pullizzi
Falls Township, Pennsylvania