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Release of free cyanide from cyanate

We are presently treating our waste water from cyanide with calcium hypochlorite. we would like to know at what conditions (pH, temperature) would the cyanate break off releasing free cyanide?

Oliver Adan
- Legaspi City, Philippines
2005

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2006

There are many good references on the subject of cyanide treatment, and you need to consult one.

Cyanide treatment with hypochlorite is done at a pH of 10.5 or greater, and the conversion of cyanide to cyanate is very fast at this pH. At lower pH values the reaction is slower, and cyanogen chloride, which is a very potent tear gas may be released. However, conversion of cyanate back to cyanide has never been reported to the best of my knowledge.

Lyle Kirman
consultant - Cleveland Heights, Ohio

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Once the conversion is made to cyanate, it becomes an inert substance. The cyanate will not "convert back" to free cyanide. BE SURE you have a chlorine residual after the cyanide destruct because if you do not then you may have free cyanide remaining in the solution.

PH above 10.5 (just go to 11) add hypochlorite until you have a chlorine residual (no specific level just free chlorine) and then you are set to go.

I always perform cyanide destructs at 11 because the hypochlorite has the potential to drop your PH..

Ryan Cook
Toccoa, Georgia
2006

Can you try Photo- Chemical oxidation for cyanide destruction. It is seen that UV light with oxidising agents reduce CN into carbon and nitrogen.

Aravind A Narayan
- Coimbatore, Tamilnadu, India
2006