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Ask the Expert Question-and-Answer Archive (Wastewater Treatment)

by Mike McGinness, EcoShield Environmental Systems, Inc.
January, 2002

Best Practices for Cyanide Treatment

Q. Where can I find the latest techinical information on current recommended best practices for cyanide treatment.

A. The EPA has only one recommended practice that I know of (the standard 2 stage pH adjustment and chlorination with sodium hypochlorite, which is called alkaline chlorination) but it requires ventilation, and can be dangerous (the second stage involves lowering the pH). I also have concerns about alkaline chlorination producing toxic THMs (TriHaloMethanes) that are carcinogenic or TTOs (regulated Metal Finishing Total Toxic Organics). AESF (American Electroplaters and Surface Finishers Society) has a Canadian Manufacturer member who makes a proprietary closed treatment system that uses high pressure and temperature (as I recall) to thermally convert CN into CO2 and N2 including iron cyanides that is specifically designed for Cyanides (I believe it was the result of an AESF R & D grant years ago, but not sure). Electrolysis (I think there is a company in Utah that advertises theirs for Cyanide destruction), ozone (converts it to cyanate), and a number of advanced oxidation processes will also destroy cyanide. (some more completely than others). The WEF (Water Environment Federation) has several member companies that market advance oxidation systems that can handle cyanide. In small concentrations (say 1 to 5 ppm) sodium and potassium cyanide reportedly is biodegradable. Silver and copper at even 1 ppm acts as a biocide however.

I have a fairly complete archive on this subject (and I have done some specialized work in the area) but it would take some time to put into more detail than the above (and pull the various parts out of my reference library) and therefore would involve consulting time if you need more than the above. The groups I listed above all have web sites, publications and suppliers lists that you can check out directly. One of the reference books I have is a 199x text on Cyanide treatment methods published by Noyes.



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