Letter 6852

Cyanide destruction problems

.

Dear Metal Finishing team,

our labs will be dealing with cyanides after Christmas for small scale stripping and plating baths and I have to write a security protocol to make sure that people know what to do if there is any accident with cyanide solutions.

I came up with a scenario where someone would spill a solution of cyanide into the sink drain. What do I do to neutralize cyanides?

As far as I know, you can neutralize cyanide with a Sodium Hypochlorite solution (Bleach) under basic conditions ( pH = 9-11 ) which will oxidize cyanides (CN-) ions into cyanates (CNO-) ions. However cyanate is also toxic ( not as much, but still), but I read that you can transform them into NH3 and CO2 by adding a strong inorganic acid to cyanates ( bringing to pH =2). However, my concern is that I'm afraid that by adding acid to the solution, the cyanate will be transformed back into cyanides and will produce HCN ( something that we don`t really want to happen). Are my concerns right?

Thanks for your help,

Daniel Picard, Chemist
Industrial Materials Institute - National Research Council of Canada - Boucherville, Quebec, Canada

You are correct about the first step: adding bleach at a pH of greater than 10 will oxidize the cyanide to cyanate within just a few minutes. If the spill has a lot of cyanide (if it's a stripper rather than a rinse) you probably should dilute it along the way. A very easy test tool for the first treatment step is potassium iodide starch paper [link is to product info at Amazon]. As long as it turns dark blue there is excess bleach present and the amenable cyanide has been destroyed.

Once the cyanide has been converted to cyanate this way, it cannot be reconverted to cyanide.

The chemistry behind your second step is only partially correct, however. First, I don't think you need to reduce the pH to anywhere near 2.0 -- more like 7.0-8.0 should be adequate. Second, you need to add a lot more bleach to complete the oxidation. This reaction is much slower, and you should allow at least an hour, even for treatment of dilute wastes.

I've been in the waste treatment industry from the time when single-stage cyanide treatment was acceptable. Although I'm not personally aware of any cases where acid was added to cyanide-bearing waste before it was inadequately chlorinated, it has almost surely happened, and I certainly share your concern about the inherent danger in prescribing a procedure that has the potential to go tragically wrong.

So be careful that have a reliable mixing mechanism and the cyanide waste is not somehow stratified away from the bleach.

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

 

Only one point to add. In my army days, we were taught that immediate first aid for cyanide poisoning was administration of amyl nitrite inhalant. Unfortunately, these can be hard to obtain.

James Totter, CEF - Tallahassee, Florida

In addition to the amyl nitrite, I would be sure that my local emergency room has a cyanide antidote kit. We actually have had one prescribed to us and keep it in our plating office to be sent to the hospital with emergency personnel. Many hospitals do not have a kit readily available so the best way is to have it on hand. Your company physician could help with this. Bill

William F. Morgan
- Saratoga Springs, N.Y. USA

At one time Eli Lilly offered a "cyanide antidote kit" which had the capsules, the intravenous solutions, and everything conveniently packaged. I understand that the kit is still available but is now known as the "Pasadena cyanide antidote kit". Your poison control center, emergency management response team, or anti-terrorism response team will know what you are talking about if your local pharmacist gives you a blank stare.

Ted Mooney finishing.com Brick, New Jersey

 

+ I've one other thing to add. If some one has passed out from cyanide gas, then don't give them the "kiss of life" or you too could be poisoned. There is a method for resuscitation, and I've seen it described in The Canning Handbook, I'd take it that other cyanide solution suppliers would give this information also. Ian Ian Brooke university - Glasgow, Scotland +++++++ Today, many companies are very careful of how to handle or store liquid for disposal, that contains "Cyanide". However, as mentioned before by Daniel Picard, and Ted Mooney, I will repeat it too in my post. For example: If you want to neutralize acid liquid with caustic liquid, first thing, a person takes a sample from the caustic tank, and use a kit that test for Cyanide. The kit stated that PH must be neutral, so, your first step is to neutralize your sample with acid, until you reach a neutral level. Note, Cyanide do release when the pH is low, so, know what you are doing in term of safety. Use your Cyanide kit to test for Cyanide. If there is, let say 1ppm or higher, than you want to find out how much it is needed to neutralize Cyanide. Add drops of Sodium Hypochlorite (blech), few drops, and check again. Find out how much you added. Use your potassium iodide (starch paper)as Ted Mooneyand said. When you know how much it takes to add bleach, than use that amount to neutralize your caustic in the tank. After neutralizing is complete, you will be able to neutralize your acid/caustic for disposal.... Shimun Ashurayah - Hamilton, Ontario, Canada