Sciencemadness Discussion Board

Purer KCN

xenevius - 16-3-2015 at 00:57

Hello,

I've posted here before but I lost my password due to computer problems, so I've had to make a new account. I found the people on this website extremely helpful and friendly before, which is why I've came back to ask for help in another matter.

I'm in need of some potassium cyanide as I plan to use it in the MacArthur-Forrest process to extract gold from ore and sell it for a profit. The materials I need are cheap and I feel like I could make a good bit of money this way, but the country I live in is not friendly to hobby chemists and there is absolutely no way to buy KCN here without a licence. That means I will have to make it myself.

The problem is, the method I have previously used to produce KCN (reducing cyanate to cyanide in the presence of carbon and high heat) always leaves a significant quantity of impurities which are hard to remove and make it unsuitable for use. That leaves me with one more option, which is treating ferrocyanide with a suitable acid and then distilling the generated HCN into alcoholic KOH. I've been purposefully trying to avoid this method for safety reasons, but it seems as if it is the only way I will be able to get a good grade of KCN.

I am confident in the strength of my equipment, but I'm not confident in my ability to not screw anything up in this process as I have never handled HCN before. I know there are people on here who have done this process before, so if someone could provide me with some helpful instructions on how to proceed, I'd be very grateful.

Thanks in advance.

woelen - 16-3-2015 at 03:09

If I read your post, then you give me the impression that you work at a large scale. How much ore do you want to process? How much KCN do you expect to need?

Making KCN from K4Fe(CN)6 and acid can be done on a small scale, but this is not something which can be done on a large scale, at least not without extreme precautions and certainly not in an amateur setting. You also will have to obtain all kinds of permits if you want to do this on a large(r) scale and you also will not be allowed to do this in a residential area.

I find your post somewhat contradictory. On one side you are writing about hobby chemistry, but your goal of extracting gold from ores and making money out of that process sounds like large scale or even industrial scale.

xenevius - 16-3-2015 at 03:22

Quote: Originally posted by woelen  
If I read your post, then you give me the impression that you work at a large scale. How much ore do you want to process? How much KCN do you expect to need?

Making KCN from K4Fe(CN)6 and acid can be done on a small scale, but this is not something which can be done on a large scale, at least not without extreme precautions and certainly not in an amateur setting. You also will have to obtain all kinds of permits if you want to do this on a large(r) scale and you also will not be allowed to do this in a residential area.

I find your post somewhat contradictory. On one side you are writing about hobby chemistry, but your goal of extracting gold from ores and making money out of that process sounds like large scale or even industrial scale.


No, this is not a large scale operation, which is why I don't need that much KCN (perhaps 100g at most). I'm processing small portions of ore that I can buy cheap on eBay. Where I live, Gold fetches a high price in small amounts (10g of 24c gold will pay in the hundreds) and I calculated that the potential gains outweigh the cost of the extraction and that it could be a profitable (if short-lived) venture.

careysub - 16-3-2015 at 04:17

I've never done this and so can't address your main question. But I am interested in the details of the your process/problem.

I imagine the contaminants in your cyanate reduction process would be carbon, and possibly unreacted cyanate.

Attached is a paper on cyanide loss during gold extraction. Some cyanide is oxidized to cyanate (a cyanide loss) during extraction anyway, so the presence of cyanate shouldn't affect extraction I would think. The presence of activated carbon however catalyzes this process and increases the loss rate. Is that the issue here?

Perhaps other process parameters could make your existing KCN work satisfactorily (high pH, exclude oxygen, etc.)? The South African paper gives information that might help.

Dan Vizine has posted information here about producing HCN for ferrocyanide, try searching for his comments.


Attachment: v090n02p037.pdf (680kB)
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[Edited on 16-3-2015 by careysub]

xenevius - 16-3-2015 at 04:31

Quote: Originally posted by careysub  
I've never done this and so can't address your main question. But I am interested in the details of the your process/problem.

I imagine the contaminants in your cyanate reduction process would be carbon, and possibly unreacted cyanate.

Attached is a paper on cyanide loss during gold extraction. Some cyanide is oxidized to cyanate (a cyanide loss) during extraction anyway, so the presence of cyanate shouldn't affect extraction I would think. The presence of activated carbon however catalyzes this process and increases the loss rate. Is that the issue here?

Perhaps other process parameters could make your existing KCN work satisfactorily (high pH, exclude oxygen, etc.)? The South African paper gives information that might help.

Dan Vizine has posted information here about producing HCN for ferrocyanide, try searching for his comments.




[Edited on 16-3-2015 by careysub]


Thanks for the paper, I'll give it a read later.

As to your other question, the main issue for me is shelf life. Obviously, KCN with significant impurities will deteriorate faster than if it was relatively pure (93-96% would be a satisfactory purity for me) and unless it's all used quickly it would be a waste of product.

And I'm aware of Dan Vizine's posts in the 'preparation of cyanides' thread; it's just that the thread is huge and I don't even know where to start, although I will check it out later. Thank you anyway.

careysub - 16-3-2015 at 04:44

I have read through this thread in the past, and one of Dan's findings was quite surprising: he found he could not distill the HCN directly into alkaline solution with creating a great deal of polymerization. The cause of this is mysterious, and difficult to explain when reading exactly how he does it (there is no obvious way for the alkali to get the HCN vapor where the polymerization occurs.

Consequently he distilled the HCN into a receiving flask, and then added alkali to make the salt afterward. This has the undesirable effect of building up a liquid HCN inventory, if only temporarily.

xenevius - 16-3-2015 at 04:53

Quote: Originally posted by careysub  
I have read through this thread in the past, and one of Dan's findings was quite surprising: he found he could not distill the HCN directly into alkaline solution with creating a great deal of polymerization. The cause of this is mysterious, and difficult to explain when reading exactly how he does it (there is no obvious way for the alkali to get the HCN vapor where the polymerization occurs.

Consequently he distilled the HCN into a receiving flask, and then added alkali to make the salt afterward. This has the undesirable effect of building up a liquid HCN inventory, if only temporarily.


Strange. Well, that's certainly going to complicate things.

And I really don't like the idea of holding on to HCN for any longer than I need to. I've heard it has the tendency to decompose explosively during storage, which doesn't sound fun.

What would be the best stabiliser to use for the HCN during the short time I need to hold onto it?

careysub - 16-3-2015 at 05:39

Phosphoric acid is the usual stabilizer, but sulfuric also works (both non-volatile). You want the pH to stay below 4 (not a hard goal).

So a little phosphoric acid in water would be in the collecting flask (which I would cool with ice to minimize cyanide volatility) . But I wouldn't store it at all, but immediately add KOH solution after collection to convert into the nonvolatile salt.

xenevius - 16-3-2015 at 05:41

Quote: Originally posted by careysub  
I have read through this thread in the past, and one of Dan's findings was quite surprising: he found he could not distill the HCN directly into alkaline solution with creating a great deal of polymerization. The cause of this is mysterious, and difficult to explain when reading exactly how he does it (there is no obvious way for the alkali to get the HCN vapor where the polymerization occurs.

Consequently he distilled the HCN into a receiving flask, and then added alkali to make the salt afterward. This has the undesirable effect of building up a liquid HCN inventory, if only temporarily.


Have you seen this video on YouTube?

https://www.youtube.com/watch?v=K5NuqpdYDhE

In it, the HCN is distilled directly into aqueous NaOH and no noticeable polymerization occurs, making the fact that Dan Vizine was having those problems even stranger. Could it have been related to the acid that he used to generate the HCN?

careysub - 16-3-2015 at 05:44

I inquired about possible causes, but nothing turned up. I cannot say why other people do not report this problem, just passing on the info for your consideration.

Polymerization (which is autocatalytic) during distillation is a known issue though, their are patents seeking to address it.

Bert - 16-3-2015 at 06:02
Quote:

I've posted here before but I lost my password due to computer problems, so I've had to make a new account.


PM a moderator with your old account name, password can be re-set.

xenevius - 16-3-2015 at 06:15

Quote: Originally posted by Bert  

Quote:

I've posted here before but I lost my password due to computer problems, so I've had to make a new account.


PM a moderator with your old account name, password can be re-set.


It won't work, though, because I closed the email address attached to my old account when I lost the password because I didn't need it anymore. It's completely lost.

Bert - 16-3-2015 at 06:42

It would work. All you need to do is tell me your old screen name, admin sends the new password via U2U and you log into the old account, edit whatever needs editing.

Only if the old screen name has a ban or other "issues", there might be a problem

xenevius - 16-3-2015 at 06:48

Quote: Originally posted by Bert  
It would work. All you need to do is tell me your old screen name, admin sends the new password via U2U and you log into the old account, edit whatever needs editing.

Only if the old screen name has a ban or other "issues", there might be a problem


Okay, then.

My old screen name was Riking.

Riking - 16-3-2015 at 08:20

I've done some research and I now have a good understanding of how this needs to be done and the precautions I need to take during the process. I'm confident that as long as I keep a level head and ensure my glassware is airtight, I shouldn't have anything to worry about from the HCN.

Thank you to everyone who contributed.

careysub - 16-3-2015 at 08:30

Do get a respirator with an acid gas cartridge though. This will protect you in the case of an accident.

Accidents happen.

Magpie - 16-3-2015 at 08:30

I have made a small amount of KCN without going the HCN route, ie, using a method that maintains a basic pH. This method is described by Engager on this forum. It's a somewhat finicky process and I had to try it several times before success. Purity was only ~65%, IIRC.

In reading up on gold processing I found that a local mining supplier carried KCN. I imagine that a license would be needed to buy it. I suggest that you get the license if possible.

morganbw - 16-3-2015 at 14:43

Quote: Originally posted by Magpie  
I have made a small amount of KCN without going the HCN route, ie, using a method that maintains a basic pH. This method is described by Engager on this forum. It's a somewhat finicky process and I had to try it several times before success. Purity was only ~65%, IIRC.

In reading up on gold processing I found that a local mining supplier carried KCN. I imagine that a license would be needed to buy it. I suggest that you get the license if possible.


Absolutely, get the license if required and I think, maybe, live longer. You need mad lab skills otherwise.

Boffis - 16-3-2015 at 20:41

You don't need potassium cyanide for the extraction of gold. I know, it my full time job!!

On this mine (I am currently on site on a gold mine high up in the Andes of south America) we use sodium cyanide (93-95%) that comes in briquettes about 6cm across. Lime is added to adjust the pH.

On other mines I have worked on we used "basic calcium cyanide" but this stuff assays only about 35% actual cyanide.

The easiest route to a simple cyanide for the amateur is via sodium ferrocyanide. I have already posted the preparation of this compound from commercial Prussian blue pigment. This give the decahydrate which is dried in the oven until anhydrous and then layered into a stainless steel pot (drinking "glasses" from the Pound Shop (UK only)) with a calculated quantity of sodium metal hammered into thin plates. The pot should be flushed with an inert gas while loading, I have found that propane works fine and is easily available but methane nitrogen argon etc can be used (but not CO2). The pot is filled with layers of dried and ground sodium ferrocyanide and hammered out sodium until about 90% full and then a "rammer" is used to compress the charge as much as possible. The pots I use hold about 190g per charge. The pot is covered with a heavy iron plate and heated until a reaction begins (quiet a low temperature circa the melting point of sodium) the pot becomes red hot but little gas escapes. You can either cool it in the pot and extract with water or I find rather better to let it stand until the liquid start to solidify and then pour onto a piece of old slate worktop. The sodium cyanide solidifies instantly and is easily removed with a scraper, roughly crushed and packed into a jar. If carried out carefully the product is white with only a few black iron specks and assays 88-93% NaCN. If rushed you tend to get more iron particles in the product but since these are insoluble they are not really a problem. The residue in the pot is leached with water and the cyanide solution used for some purpose immediately such as the precipitation of Cu+ or Zn2+ cyanides or precipitated with a mixture of ferric chloride and ferrous sulphate and recycling of the resulting Prussian blue.

You can run this reaction with alkalis in place of sodium but the product is much less pure or by heating a ferrocyanide (Na or K) alone but the yield and quality are even less. Potassium ferrocyanide can be used in place of the sodium salt but metallic potassium is too expensive so you end up with a mixed K+Na cyanide that require analysis to determine the effective cyanide content.

woelen - 17-3-2015 at 00:57

Another option for gold extraction may be the use of thiosulfate. I have read something about that, but more research from your side is needed. Maybe this solves your problem without the need of any cyanide at all.

Boffis - 17-3-2015 at 05:12

There are actually numerous alternatives to the simple-cyanide-carbon absorption process but they can be crudely divided into two groups. The "thio-ligands" and the complex cyanides. The former comprise thiosulphates, dithionites and thiourea and the latter potassium ferricyanide. The latter compound is interesting because it is less pH sensitive and more stable in solution but that said I have never come across a production scale plant that actually uses any of these processes.

I have vaguely heard of plants in the FSU that used chloride as the oxidising agent and ion exchange resins but never actually had first hand experience of such processes. The mining industry is rather conservative and so the well-known and understood cyanide route still prevails. One argument against thiourea was the greater difficulty in detoxifying the waste but the main one is cost.

I did once clean up some gold bearing iron oxide stained quartz with sodium dithionite; the following day most of the iron oxide had gone but so had the gold! So as a means of dissolution this clearly works but then the problem arises of recovering the gold from solution, though zinc precipitation would probably work here too.

There are many "patented" black box processes but the process outline is allows too vague and sketchy to make any useful assessment of them. If I could have a $100 for every time a black-box salesman had come through my office I'd have retired by now!

There is a great deal of literature out there on gold leaching, check it out, many of the older texts can be downloaded free and so can many of the patents.

[Edited on 17-3-2015 by Boffis]