Cyanide destruction

I am looking for information on how to batch treat our rinse water from our almate zincate process before transferring to our evaporation system. I assume I need to destroy the cyanide component before mixing with the waste stream.

Rinse water contains sodium cyanide and caustic soda.

Can any-one point me in the right direction??

Thanx,
Bruce

Bruce O'Brien
- PHX, AZ

The most economical way is usually with sodium hypochlorite (industrial strength bleach). If you are batch-treating because you have very little such waste water, and you are looking for a minimal system, it can be done manually.

First, you raise the pH to at least 11.5, if necessary, with further additions of an alkali (with good mixing). Since you are already familiar with caustic soda, that could be a good choice for the alkali.

Second, you add the bleach, slowly, with mixing, until there remains an excess of chlorine as indicated by a dark blue to light purple color on potassium iodide starch paper [link is to product info at Amazon].

You have now converted the amenable cyanides to cyanates, and in many cases the waste can now be combined with your other flows for pH adjustment and precipitation. If the waste is to be evaporated and hauled, as I am inferring, this may be all you need to do for cyanide treatment.

You asked to be pointed in the right direction, so please consider this as such. You should have a competent consultant or laboratory person help you out and give you hands-on instruction, and you must verify that this idea meets the requirements of your operating permit.

Ted Mooney, P.E.
finishing.com
Brick, New Jersey

The most reliable method for treating cyanide is with an ORP (oxygen reduction potential) meter. Some portable pH meters have ORP capabilities. The pH works best between 11.0 and 11.5. The higher the pH, the more bleach it takes to reach the proper ORP reading. At the proper pH, add bleach until the ORP meter reads 450 mV. This will break the cyanide down to the cyanate. You might want to check your permits to make sure it is alright to release cyanates into your rinse water flow. Some regulations require the cyanide to be totally destructed before doing so. To finish the destruction, raise the pH to about 8.5. The ORP reading should be a minimum of 600 mV at this point. Excess bleach may need to be added to achieve this. Good Luck.

Phil Pace
- Tulsa, Oklahoma

Thu -

Thanks for the informative page, I'm chasing some more detailed information on destruction of NaCN in wastewater. I did see a book on the topic a number of years ago (~5 years)- It may have specifically dealt with its destruction in an artificial wetland. Any assistance greatly appreciated. Rob Catchpoole

Robert Catchpoole

Just a thought if your not aware, you can make sodium hypochlorite in house.You only need a vessel,tank, etc.(sized for your needs), and a electric variac with a anode and the tank for a cathode. Just add salt & water.

Mitchell Lee Shepard
- Gilbert, Arizona, U.S.A.

While that's true, Mitchell, the readers should know that the only thing causing the chlorine to go into solution as sodium hypochlorite versus evolving into the room as poisonous chlorine gas, is the limited solubility of chorine at a given pH. If they generate too much or fail to keep the solution sufficiently alkaline, they can soon have a roomful of poisonous chlorine.

Ted Mooney
finishing.com
Brick, New Jersey

+++

la destruction des cyanures de sodium ou de potassium se fait avec du pyroxyde d'hydrogene H2O2. vous pouvais également écrire la réaction qui va vous donnez de l'ammoniac.

Bouzar Essaidi Samir
AGNOR - Bouzareah, Alger

November 20, 2008

Can excessive bleach impaired the further reduction of cyanide?

Mark Z
- Santa Ana, CA