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ferric chloride use in waste treatment

Q. I began to use ferric chloride [on eBay or Amazon] in my waste water treatment process where I treat for zinc, nickel, copper, chrome, and cyanide. The ferric chloride[on eBay or Amazon]is used as settling agent. I been told that the ferric chloride[on eBay or Amazon]will interfere when testing for cyanide levels in the final discharge stream. Could this be true?

Karl Weyermann
- Winston-Salem, North Carolina
December 15, 2011

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It's really more of a coagulant. Whether it's the best thing to use depends on your waste. I always had better luck with ferrous sulphate ferrous sulphate [affil links].

FeCl3 addition will have no effect on the cyanide analysis, if it is being done properly.

Dave Wichern
Consultant - The Bronx, New York
December 16, 2011

Ferric should work but I prefer ferrous sulphate ferrous sulphate [affil links] and it has been used for years for cyanide destruction, but as mentioned earlier it depends on your water. I know that iron can give false chrome readings in some testing but I have never heard of this with cyanide. If this is a stream that has elevated chrome I would not rule it out.

Brian Wodetzki
- Valparaiso, Indiana, USA
December 24, 2011