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Author: Subject: Liquid to solid Sodium Cyanide
GoldAlchemist
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[*] posted on 26-12-2014 at 22:07
Liquid to solid Sodium Cyanide


I'm looking for some advice on dehydrating liquid Sodium Cyanide to a dry powder state.
I plan on distilling off the water from 50 liters of 30% liquid (commercial grade) NaCN. I plan on using a heating mantle with a 5 liter rbf set up for distillation in order to remove H2O. This will take place in a fumehood with filtered fan extraction. I also have a proper rated respirator that will be used.
I don't plan to distill that liquid to a completely dry state as I think I will do this in a vacuum desiccator.
I'm aware that NaCN has a very high boiling point and I'll not get anywhere near that and NaCN should be kept away from metals.
My only concern is that I might be missing something by conducting this experiment.
Any advice would be appreciated.

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[*] posted on 26-12-2014 at 23:38


You don't even need to distill the water, just boil it off. When most of the water is gone from the mixture, put it on a steam bath and heat for a few hours. Actually, a shallow dish would be better, as it's very difficult to remove saltcakes from round-bottom flasks.

The only advantage of a distillation is that any mist from the boiling solution would be captured. This could be solved with a cotton or glass wool plug in the mouth of the open flask, if you plan to use one. In theory, the fiber should not be saturated with water (liquid water, that is) when it's temperature reaches that of the steam around it. But hopefully, you won't use a flask, so you don't have to deal with a saltcake INSIDE a tiny opening.

What does the suction hole look like on the fume hood? Is it a single opening, or is it baffled? If it's single, it'll be easy to put a cheap rag over it to catch any cyanide mists. Just dispose of it properly when you're done. If it's baffled, just use more cloth.

When heating, it's important not to heat the slurry too long, as this can cause it to spatter as it gets hot.

Judging by your username, and the fact that you have 50 L 30% NaCN, I'm certain that you'll handle your waste in the right way.




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GoldAlchemist
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[*] posted on 27-12-2014 at 03:38


Thanks for the response. I had thought about boiling off by using a erlenmeyer but I figured more of a closed system would be extra safe for myself and others.
The cheap rag sounds like a good idea as well as I have non baffled fume hood.
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cyanureeves
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[*] posted on 27-12-2014 at 07:35


ive always wondered if any hydrogen cyanide would be release along with steam if an aqueous cyanide solution was boiled.doesnt cyanide only bond with some metals though?so then cyanide acts like a salt in which it will not boil off after water is evaporated?i was scared to death when dealing with steam and wore a gas mask even when electroplating.some plating solutions work great when warmed and though i sort of doubted the steam was dangerous i began to wonder if cyanide could be released electrically with the anode.
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[*] posted on 27-12-2014 at 11:21


Thanks cyanureeves, I never considered that.

GoldAlchemist, if you're willing to sacrifice a little bit of purity, add a spatula-full of sodium hydroxide to the solution to be doubly certain that the CN- can't hold onto a proton.




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S.C. Wack
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[*] posted on 27-12-2014 at 11:49


Quote: Originally posted by Awesomeness  
You don't even need to distill the water, just boil it off.


If someone tried this on a large scale, they could die. Look up hydrolysis of cyanide. The addition of hydroxide is wise. If not added, it will be made...NaCN + H2O -> HCN + NaOH..also the CO2 in air will not help...




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[*] posted on 27-12-2014 at 12:18


Quote: Originally posted by S.C. Wack  
Quote: Originally posted by Awesomeness  
You don't even need to distill the water, just boil it off.


If someone tried this on a large scale, they could die. Look up hydrolysis of cyanide. The addition of hydroxide is wise. If not added, it will be made...NaCN + H2O -> HCN + NaOH..also the CO2 in air will not help...

Yes. I would NOT work with cyanide AT ALL due to its "deadly houdini" magic tricks.

The best way to deal with any sort of cyanide heating is in an anhydrous atmosphere away from acids or bases. If using any of those with cyanides, I would have a bubbler system leading into a beaker full of Sodium Hydroxide in case.
I believe that is what my companions in the inorganic community does when they work with hydrated cyanide ligands.
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[*] posted on 27-12-2014 at 12:22


Good point, SC.

Even with a distillation apparatus, the solubility of cyanide in water will limit how much can be trapped in the collection flask. A gas scrubber loaded with sodium hydroxide would be a good way to clean the gas stream, just remember that there'll be cyanide in this when the process is finished.

Hydrolysis and off-gassing of HCN would result in the terrible consequence of a decreased yield. Oh, maybe a little bit of death.




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[*] posted on 27-12-2014 at 13:56


Quote: Originally posted by Awesomeness  
Even with a distillation apparatus, the solubility of cyanide in water will limit how much can be trapped in the collection flask. A gas scrubber loaded with sodium hydroxide would be a good way to clean the gas stream, just remember that there'll be cyanide in this when the process is finished.


Add Hydrogen Peroxide to any and all glassware that has come in contact with cyanides. It oxidises it to cyanate that can actually be safely flushed down the drain. Better to bring it to your local disposal site but I believe a mixture of peroxide, hydroxide, and small amounts of cyanate is filtered out at the treatment plant.
Any leftover solution should be mixed with the peroxide as well.
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GoldAlchemist
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[*] posted on 28-12-2014 at 22:04


Thanks for everyones feedback. I was concerned about Hydrolysis and probably should have considered CO2 in atmosphere as a potential hazard.
The sodium hydroxide collection flask is a good addition to the setup that I had not thought about either but it makes sense as monitoring ph is not very feasible and is a good backstop.
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[*] posted on 28-12-2014 at 22:31


I expect that boiling that much solution down will require a long time. Be sure to use a flask that you aren't too attached to, as the NaOH, though dilute, might have time to etch the glass. Definitely teflon tape/grease your joints.



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[*] posted on 29-12-2014 at 02:22


Can't you just precipitate it with acetone, or something? With the amount of time and effort and money needed to distill 50 litres of water it may be cheaper to just buy 200 litres of acetone and precipitate it out. If not acetone then something else: I haven't looked into it.
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[*] posted on 29-12-2014 at 02:40


While lye can and will attack borosilicate glass it's not going to eat a hole in a beaker in a short time. I've boiled strong solutions of 75/25 NaOH/KNO3 (BP appr 140°C) many times, and while this proved too aggressive in the long term it took many hours of boiling and months of storage at room temperature before it became a real safety issue. Not something you'd want to subject precious glass ware to but it's not going to eat a hole in a couple of hours.
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