Metal finishing Q&As since 1989

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Disposal or inactivation of perchloric acid-ethanol and chromic-phosphoric acid mixtures

I am concerned about the proper neutralization or disposal procedures of perchloric acid-ethanol mixtures used in electropolishing. I am also concerned about the safe use and disposal or inactivation of chromic-phosphoric acid mixtures.

Thank you very much,

Felipe Caballero-Briones
Research - Altamira, Tamaulipas, Mexico
2003

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Perchloric acid is a super oxidizer which can be explosive. It is rarely used for electropolishing in the U.S., if at all, after a disastrous explosion in an electropolishing plant many decades ago. (See letter 9408). This should be handled only by a specialist because of its potentially explosive nature, so I would not suggest a treatment regimen.

The chromic-phosphoric acid is a toxic waste that must be disposed of by a licensed hauler but to my knowledge--and I hope someone will enlighten me if my knowledge is inadequate--it is not explosive. The solution would be neutralized if necessary to a mildly acidic condition (like pH 3.5) and a reducing agent such as sodium metabisulfite would be added. The hexavalent chromium would be reduced to trivalent while the solution is still acidic. Then the solution would be neutralized.

Ted Mooney, P.E.
Striving to live Aloha
finishing.com - Pine Beach, New Jersey
2003

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2003

Hi Felipe

Re neutralizing Perchloric, may I suggest you approach any Assay lab for their expertise ... in the Vancouver, B.C. area there's a Company called ANACHEMIA SCIENCE who certainly should be able to give you far better advice than me.

Freeman Newton [deceased]
(It is our sad duty to advise that Freeman passed away
April 21, 2012. R.I.P. old friend).