Possible hot black oxide by-products

At our Co. we are currently hot black oxide treating parts for the nascar racing industry. Up until Oct. of 2003 our test results for last 7 years have never turned up any traces of cyanide. Since we installed the black oxide tanks(which includes a constant overflow rinse tank that goes into our sewer trap)there have been twice the acceptable levels of cyanide in the sewer trap samples we are required to have tested at our lab, and the City of Memphis labs. I was wondering if there is certain metals that could in the chemical reaction that produce any form of cyanide that is turning up in the samples. Some of our parts are titanium also. If cyanide as a by-product or boil off by-product is possible equipment/remedies to correct this problem will be welcome.

Cyanide is simply CN. I doubt that there is any way to create it from the metals you are processing. I'd say it's either in the black oxide process chemistry or the chemistry of a cleaning tank you installed.

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

First of two simultaneous responses --

Some parts require a copper plate as a heat treat stop, for example a soft washer on a case-hardened screw. This copper must be stripped before parts are sent to you for black oxide, most common strip is Sodium Cyanide. If these parts are not thoroughly rinsed, you end up with cyanide in your cleaner (or first tank the parts see).

Second of two simultaneous responses --

I'm assuming that you already checked the MSDS of the chemicals that you use to make sure there's no CN present. Is it possible that there is CN residue on the parts prior to black oxiding? If so, maybe you could test for this by soaking some of the incoming parts in distilled water and having the rinsate analyzed for CN. Have you called the independent lab that ran your CN tests to see if there's anything that can give a false positive?