Catalytic oxidation of cyanide using carbon

A. I've never heard of this at all and would appreciate hearing from you or from our readers about it. It doesn't seem to make sense to me, but apparently I'm missing something.

A. I'm guessing that the use of activated carbon to destroy cyanide will only work if an oxidizing agent such as hydrogen peroxide is mixed into the waste stream ahead of the carbon. The key is in the title: "catalytic" treatment of cyanide.

Activated carbon will remove some of the cyanide by itself through adsorption, but I doubt there will be any destruction without an oxidizer.

A. The articles I have seen are :

- Oxidation of Cyanides Adsorbed on Granular Activated Carbon
Author: HOFFMAN D C
PLATING Feb. 1973 pp157 to 162

- Decontamination of Cyanide Wastes by Methods of Catalytic Oxidation & Adsorption
Author: BUCKSTEEG, WILHELM
publication unknown.

These suggest that cyanide complexes are adsorbed onto the surface of carbon. However, the carbon also acts as a catalytic surface for oxidation of cyanides with oxygen adsorbed from water or air. In essence, no additional chemicals are needed.

We have performed laboratory scale experiments, where air was bubbled up through a bed of charcoal and static rinse solution from either cyanide zinc or copper plating. Cyanide level dropped from 500-1000 mg/L to virtually zero within 24 hours. A control without charcoal was unaltered. Metals were then precipitated as normal in alkaline conditions. In short, it appeared to have done what is claimed.

Whether this leads to practical application to batch or continuous treatment is now the question.

Hoffman's article refers to the following patents:-

D.G. Hager & J.L. Rizzo, U.S. Patent 3,650,949 (1972)
R.S. Joyce, U.S. Patent 3,222,277 (1965)
J.J. Hronas & J.L.Rizzo, U. S. Patent 3,276,136 (1966)
R.S. Joyse, U.S. Patent 3,192,156 (1965)
M. Manes & R.J. Grant, U.S. Patent 3,193,987 (1965)

Also, Rejuvenative catalytic oxidation of waste water, particularly for removal of cyanide and sulfur [affil links] compounds. by YAN T. (International Publication Number WO 95/28357) may have some relevance.

It seems that the general process would be public knowledge by now, but I am no expert on matters of Patent.

We are currently setting up a small batch trial using a diffused air supply feeding from the bottom of a 200 liter drum. Charcoal & zinc cyanide waste solution therein. With luck, it will be set up & going for the weekend. I'll give progress report early next week.

I have one concern with this method. We have not tested for toxic headspace gasses, which might be formed. Not much point if the system doesn't work first. I'm not anticipating any problems.

It might be worth waiting for results from trials at two of the plating shops here in Adelaide, before getting anyone else involved.

Hoffman cites two pilot scale installations - an Ohio Automotive parts zinc & copper plater and a New England electrical parts plater. It would be great to track down these people, to learn of their experiences with this treatment.

A. My dissertation: Adsorption and catalytic oxidation of cyanide of granular activated carbon Skopje 1989

Actual job Separation process : Bentonite Zeolite

A. Hartinger's Handbook of Effluent Treatment & Recycling for the Metal Finishing Industry [affil link on Amazon], does have a few details on this process and primary references.

Regards

A. Sir,

The topic is interesting. Activated carbon by virtue of its large surface area may be in a position to offer more reaction sites than otherwise and quicken the process of oxidation either by oxygen or chlorine. I think it should be a circulating stream of carbon particles rather than a fixed bed to improve the efficacy.