Preparation of Sodium Cyanide

Catastrophe: Easy Cyanide Synth

In any General Chem book they always show some example of cyanide preparation. Here's what mine says:

BaO + 3C + N₂ - Δ -> Ba(CN)₂ + CO

Cyanides can be made by the action of carbon and nitrogen on metallic oxides. The mixture is heated to a red heat and is usually done in a stream of N₂. But this reaction really doesn't help us much, because we want Sodium/Potassium Cyanide, but we don't have the proper oxides, right? Well, what's that other metal oxide called Iron Oxide? That's right good old rust! Here's what you chould do:

First, here's some stuff you'll need:

Iron Oxide (rust)
Carbon (Charcoal!)
Sodium/Potassium Carbonate (Pool neutralizer)
Nitrogen (well the Earth's atmosphere is 70% N₂, so that should be fine)
Crucible (you should get one of these, but I guess you can use a tin can)
Bunsen burner (propane blowtorch)

Experimental

Here's how it works:

First we convert the carbonate to the ferrocyanide.
Then we convert the ferrocyanide into the cyanide.

Ferrocyanide:

Take 5 parts(by weight) of rust and 10 parts (by weight) of charcoal and 10 parts (by weight) of Sodium Carbonate (make sure they're powdered up real nice) and mix them together good. Fire up a crucible to red heat, then pour the mix in. Now everything should kinda fuse together and redden, and every once in awhile you'll see purplish flames shoot up from the mixture. Stir with a fork until the flaming stops. Turn everything off and let cool. Chip the mixture into a large amount of hot water and stir vigorously. Filter off the unreacted carbon and mostly unabsorbed iron. Evaporate water to leave the powdered ferrocyanide.

Cyanide:

The ferrocyanide is converted to the cyanide by mixing 8 parts of the ferrocyanide with 3 parts of the carbonate. Pour the mixture into the red hot crucible. The powder will melt and bubble and there will be a solid portion and a liquid portion. When the bubbling stops, pour the liquid portion onto a hard surface (marble countertop). It will solidfy on the surface and should be broken up and stored in a container. This will be your cyanide, and should be relatively pure.

It is a real good idea to have a supply of sodium thiosulphate or amyl/butyl nitrite handy as cyanide poisoning can occur easily. Oh and do it Outdoors! I don't think I need to tell you the fumes are toxic! Any cyanide-containing solutions should be destructed properly.

40% Aqueous sodium cyanide from potassium ferrocyanide(II)

Warning!
Sodium cyanide is highly toxic! Do not attempt this synthesis without adequate ventilation!

Experimental

Put 420 g of K₄[Fe(CN)₆]₃ (potassium ferrocyanide(II) trihydrate, FW 422) in a 2 L RB flask. In 1 L chemical glass pour 600 mL of cold water and carefully add 200 ml of conc H₂SO₄. Pour this hot soln to ferrocyanide, join to the neck of flask 40 cm glass tube (1.0-1.5 cm diameter) as deflegmator & condenser, attach silicon rubber hose and place the end (of hose, of course) in 181 mL 45% NaOH soln. After 10-min heating at boiling water bath, a strong gas evolution begins; be careful, do it only under good fume hood. From time to time stir NaOH soln in receiver flask (this soln may heated up to 80°C, this is doesn't matter - don't cool). After 1-1:10 reaction complete, no more gas evolution observed. Voila, you get near 260-280 mL 40% NaCN soln.

P.S.
Don't pour the residue into the sewer system; please destruct residual cyanide through oxidation.

Destruction of cyanide waste

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, as the formed cyanate is also moderately toxic (not by far as bad as cyanide, but still), I've read that you can decompose cyanate into NH₃ and CO₂ by adding a strong inorganic acid (acidiufying to pH=2). Now, 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. Are my concerns right?

You are correct about the first step: Adding bleach at a pH of greater than 10 will oxidize the cyanide to cyanate within minutes. If the solution contains a lot of cyanide you probably should dilute it along the way. A very easy test tool for the first treatment step is potassium iodide starch paper. As long as it turns dark blue there is excess bleach present and the amenable cyanide has been destroyed - once it has been oxidized to cyanate, it cannot revert to cyanide.

Summary: The most economical way to destruct cyanide 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.

Cyanide Destruction Methods: