The authoritative public forum
  for Metal Finishing since 1989
-----

Concentrated CYANIDE destruction

We are looking for a way to destruct high concentrations of spent plating baths with cyanide in our wastewater treatment system. Currently we are using 35% hydrogen peroxide, but it's very expensive. We cannot use the common methods of bleach, ozone, or Cl because of our very low Cl limit on the discharge permit, unless there's a low cost way to remove it.

Any help or suggestions would be appreciated.

George Koch
- Evansville, IN, USA
2002

---

You could destroy the majority of the cyanide by electrolysis. This would also plate out the metal. Electrolysis is very efficient for high cyanide concentrations, and environmentally sound, because it adds no additional chemicals. Unfortunately, it is also fairly slow.

Cyanide is converted to cyanate at a theoretical rate of 0.465 grams per ampere-hour. The cyanate can also be further odixized to carbonate and nitrogen, but this is also very slow.

If it is a small quantity of concentrate per week or per month, then electrolysis to destroy 90+% of the cyanide followed by the peroxide treatment to destroy the rest should work just fine.

Lyle Kirman
consultant - Cleveland Heights, Ohio
2002

Hot electrolysis is an inexpensive way of reducing cyanide to carbon dioxide and ammonia. The temperature has to be maintained at over 85 C. Simple D.C. current should be passed continuousley. In my works I use a small tank of 100 liters and pass about 10 ampers D.C. Current. Cyanide concentration level drops by about 3 times in 24 hours. Thus if I start with 10 gms./litre of cyanide on day 1 I have about 3.5 gms. per litre on day 2 and about 1.2 gms/litre on day 3 and so on. When the concentration is sufficientley low it can be finished off with chlorination.

Vishwas Deval
electroplaters - Pune, India
2002