Sciencemadness Discussion Board

Cyanide destruction

Jor - 27-4-2013 at 12:43

Hello there, long time no see!

One year ago, I had decided to stop hobby chemistry, because my fume hood was broken, and was too busy with college.
Now, because our parents are moving away to another home, most of my stuff will follow to the new home, because I may want to continue this awesome hobby in the future.
However, I do not want to keep the very dangerous chemicals there. These include large amounts of acids and very toxic metal salts. One thing wich I decided to destroy, after I couldn't find any responsible buyers, is potassium cyanide. I have 50 grams of it. I know I'm breaking the hearts of people here for wanting to destroy, but I have already decided it will be done. I may keep 2 grams or so to do some experiments in the future on a very small scale, but the majority will be destroyed.

Acoording to most sources, it is best destroyed at pH 9-11 with bleach. However, without a fume hood, I'd like to add some NaOH to the solution for maximum safety. My question was, will the high pH (13+) be a problem? I don't see any problems, but I don't know how exothermic the reaction will be.
I'm thinking of doing the following outside, in a large bucket:
-add 3 liters of 4% chlorine bleach
-Dissolve a few grams (2-3) of sodium hydroxide in 250mL of water, and slowly add the cyanide to this (outside), and once dissolved, slowly add this to the hypochlorite solution.

I have moved most of my stuff, so I don't think i can test for remaining cyanide. The neutralisation is almost instantanous I recall?

Would this be safe?

I know many people will say that I should keep it, but I have really decided not to. I can still do thousands of experiments with the stuff I still have, so I just want to get rid of this dangerous chemical.

Mixell - 27-4-2013 at 13:46

Are you sure you don't want to give it away?
I would personally like to have some potassium cyanide for future experiments (although I'm too busy for it now).

Anyway, as long as it's properly sealed (not an issue when it comes to non-subliming solids) and labeled, it shouldn't pose a problem.

chemcam - 27-4-2013 at 14:05

I for one would be interested in it as well just a small amount <5 grams or so would be very cool to expirement with. I have planned on making my own but I recently broke my only still head. I have been waiting on my new one for a few weeks. Problem with the seller! Argh!!

Jor - 27-4-2013 at 15:08

Like I said, I am not selling it. First of all I would never ship potassium cyanide, especially not internationally. Second, I would only sell it to people I know well, and I would know they could handle it safely, e.g. some dutch home chemists .

I have proceeded in the destruction of the cyanide. I have dissolved about 43-44 grams KCN (I kept 6-7 grams) in 200mL of water with about 2 grams of KOH.
Next, outside, in a bucket was added almost 3 liters (I think it was more like 2,75L) of 4% household bleach and about the same volume of water (as a test reaction showed the reaction is somewhat exothermic). To this was also added about 7-8 grams of KOH.
I must say I have seen many scary things in home chemistry, mercury solutions, large amounts of toxic gasses, distillation of toxic solvents like nitrobenzene. But I must say that such an amount of KCN in solution in my hands scared me the most :o

Next the solution of KCN was poured in a bottle. It was slightly yellow. Now about 40mL of KCN solution at a time was added, each time holdling my breath (I know in theory no gasses can be released but this was such a large amount of cyanide that I was quite scared and I can hold my breath for long anyway), and stirred. The solution warmed up slightly.

Now all cyanide has been added and I left to the computer. Will leaving it for half an hour destroy ALL cyanide (at a pH of around 13)?
If yes, I will pour it down the drain, and rinse with at least 100 liters of water.

[Edited on 27-4-2013 by Jor]

Jor - 27-4-2013 at 15:30

Woelen's post:

It seems that cyanate further reacts with hypochlorite.
Then ofcourse I would not have enough total hypochlorite. I added a total of 3 liters now, wich is 4-5%. So worst case scenario, 120g active chlorine (1,66 moles Cl2 --> 1,66 moles hypochlorite).
Say I took 50 grams KCN worst case (because sometimes the bottle contains a little more than the label says it does). This is 0,76 mol KCN.
Now according to woelen's reaction:
2NaCN + 5NaOCl + 2NaOH ---> N2 + 2Na2CO3 + 5NaCl + H2O

There is not enough hypochlorite. But isn't the first intermediate (cyanide tot cyanate) much faster than the other reactions, and thus almost all cyanide will be destroyed?

Also, I added about 50 grams of KOH (see woelen's post again)

chemcam - 27-4-2013 at 17:11

Quote: Originally posted by Jor  
One thing wich I decided to destroy, after I couldn't find any responsible buyers, is potassium cyanide. I have 50 grams of it.

Even though you say destroy, that sure sounds like you were requesting people to make offers. If not, why bother writing that you couldn't find "responsible buyers" you're obviously going to get offers from that line. No need to be a dick here. It sounded to me like you were trying to be discrete and not just flat out offer to sell. Also, it seems as if you answered your own question about how to destroy it, were you just trying to get people riled up???

Jor - 27-4-2013 at 17:44

I'm sorry if I gave that impression, however this is not true. As I said, I did consider selling it, but only to
1) someone in the Netherlands, who could pick it up at my home, I'm not shipping that stuff
2) Someone responsible

I did post about the chemicals I wanted to dispose of on the Dutch forum, where most, if not all, Dutch home chemists also read. So I already knew I was not going to sell it and I was going to destroy it.

And how did I answer my own question? I still dont know how fast hypochlorite oxidises cyanide AND if all the cyanide will be oxidised in a 2:4 cyanide:hypochlorite ratio (wich is depends on the relative speed of the CN(-) oxidation and oxidation of cyanate to nitrogen.

I decided to leave it overnight, and decide what to do tomorrow, based any replies.

Magpie - 27-4-2013 at 18:03

Hello Jor, it's nice to hear from you again. I understand about how one can be too busy for home chemistry when in college. Some day you will have the time to devote to this hobby again.

During my experiments in making and using cyanide, contamination of my workspace and destruction of waste were major concerns. I found that the Prussian blue test was invaluable. Not only to detect workplace contamination but to verify successful destruction of waste. To put your mind at ease I recommend you that you do Prussian blue testing, even if you have to rustle up some chemicals to do it. ;)

chemcam - 27-4-2013 at 18:06

Oh okay I understand now. I actually read through all the disposal processes a few weeks ago because I was going to perform the synthesis. Let me look through my books as I forget which one it was in. I'll try to upload the entire page in a PDF file once I locate it.