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ferrous sulphate vs ferrous chloride for CN treatment

We treat our waste water effluent in our coking process for cyanide and fluoride. We use ferrous sulfate ⇦ this on eBay or Amazon [affil links] for the CN phase of the treatment. Could we use ferrous chloride (waste pickle liquor)? Is there a ratio of ferrous sulfate ⇦ this on eBay or Amazon [affil links] needed for coagulation.

David Hoffman
operator - Hamilton, Ontario
June 3, 2011

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June 13, 2011

Is this cyanide amenable to chlorination, or non-amenable, or both?

If it is only amenable, you should treat with alkaline chlorination rather than iron.

If both types of cyanide are present, chlorinate first, neutralize excess chlorine with sodium metabisulfite, then precipitate with iron at pH 2 - 3. It is better to use zinc or manganese for non-amenable CN, however. After neutralization of excess chlorine, add either Zn or Mn at a pH of about 6.

If only non-amenable CN is present, omit the chlorination.

In any case, it is necessary to allow the cyanide bearing solids to settle and to remove them before elevating the pH of the remaining water for metals removal. Otherwise, the CN will simply redissolve.

And, if you wish to use iron in this process, it makes no difference whether you use ferrous chloride or sulphate.

Good luck, let us know how it works out.

Dave Wichern
Consultant - The Bronx, New York