# Cyanide Destruction/Disposal



## kurtak (Feb 22, 2017)

OK - recently there has been a fair amount of discussion about cyanide leaching & the various methods of recovery of the gold from the leach solutions 

What has not really been discussed - at least not discussed in any detail is the destruction of the cyanide for safe disposal

As a result of more recent open discussions of working with cyanide there are now a number of member using &/or at least experimenting with cyanide leaching (including me) so it seems to me the prudent thing to do now is to discuss the destruction/disposal of our cyanide waste - we NEED to make this a priority discussion such that detailed instructions are made known & ALL safety precautions made know 

Based on my research - like most of what we do - there is more then one way to skin this cat as well --- so lets get this "important" discussion underway :!: :!: :!: 

This discussion needs to be such the it ends up in the forum library for easy reference/search in the future :!: 

On the forum 4metals made a good post about CN destruction - but - it was made back in 2010 & needs to be brought back to the forefront for current discussion - here is a link to what 4metals posted back in 2010

:arrow: http://goldrefiningforum.com/phpBB3/viewtopic.php?f=40&t=7627&p=70020&hilit=cyanide+orp#p70020

I will copy that post & re-post it here along with some questions after this post

Also Deano more recently posted info about doing it with the same flow through cell used for winning the gold from solution (which is also the cell Jon is working on & posted about) Deano's post about using it for cyanide destruction can be found here

:arrow: http://goldrefiningforum.com/phpBB3/viewtopic.php?f=37&t=21526&p=223805&hilit=cyanide+destruction#p223805

Back in May 6th, 2014, Lou posted the following comment in reply to a question about CN destruction

[/quote] You are best off to leave it to the professionals and have it disposed of responsibly. 


Bleach and peroxide both destroy free CN, but most large facilities use thermal hydrolysis to decompose it. [/quote] 

So we see two more methods for dealing with CN waste treatment (H2O2 - or thermal hydrolysis) - BUT - no details on the process &/or safety protocols --- soooo :?: :?: :?: 

Also - in my research outside the forum I found this :arrow: http://www.spartanwatertreatment.com/ozone-oxidation-cyanide.html

So ozone is yet another method of dealing with CN waste treatment

Then I also found this where they talk about the two step bleach/acid method - BUT - also another method using SO2 (Sulphur Dioxide)

So as we can see there are a lot of options here for dealing with our CN waste & we need to discuss all of them (in detail) so that members can choose the method that beast suits them - AND - then do it "safely"

I will next copy the old post by 4metals along with some questions about it - & then I have a question about the Eco-Goldex waste in particular due to the fact that ammonia is added to it in order to recover the gold by cementing with zinc or aluminum - I will post that question following re-post of 4metals old post

As a Note; - I posted this here rather then in chemical process because not all the methods are chemical

Kurt


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## anachronism (Feb 22, 2017)

The electrowin cell with the carbon felt cathode can have it's polarity reversed so the felt is now the anode and this completely destroys all organics that are passed through it. Organics such as Cyanide.


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## kurtak (Feb 22, 2017)

Back in July 31st, 2010 4metals posted the following

I am not going to have time right now to post my questions because I am having some problems with my dad - he is have an episode of being all confused - so its going to take some time to talking him down & gound him back to reality

Kurt



> I guess it would be helpful if I gave you the parameters.
> 
> Raise the pH of the solution with liquid sodium hydroxide and maintain the pH at 11.5 while adding the bleach.
> 
> ...


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## 4metals (Feb 22, 2017)

> The electrowin cell with the carbon felt cathode can have it's polarity reversed so the felt is now the anode and this completely destroys all organics that are passed through it. Organics such as Cyanide.



For the processing most members here are doing, this method is a 2 for 1 deal. The same machine that can extract your values from the leach can have it's poles reversed and destroy the very chemical we all are worrying about. Plus for what you would spend on a good pH ORP meter you will have your cell and your waste treatment. 

For simplicity, the thread already running on the cell should have all of the capabilities listed in one space. It was started here;http://www.goldrefiningforum.com/phpBB3/viewtopic.php?f=40&t=24899
and I would like to see that thread completed.


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## aga (Feb 22, 2017)

I have heard that CN is destroyed in sunlight, so a strong UV lamp might do the trick too.

The question with any method would be : "has all the CN gone yet ?"

In the same way that gold-bearing solutions are tested with SC, it appears that copperas (iron(II)sulphate) solution can be used to test for the presence of cyanide ions - it turns blue, Prussian Blue actually.

I'll test that out and see what sort of colours it gives for different CN concentrations.

Perhaps someone already knows a better way to test for CN ?


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## 4metals (Feb 22, 2017)

This paper is a very sensitive test for cyanide and it is semi quantitative, meaning if you were to make standards and test them under standard conditions the color is proportional to the concentration. It can detect levels as low as 0.2 ppm HCN with 15 minutes exposure. 

http://www.mn-net.com/Testpapers/Te...tesmo/tabid/10435/language/en-US/Default.aspx

And yes sunlight will break down cyanide.

Here are instructions for the paper's use

http://www.ctlscientificsupply.com/prodinsert/90604insert.pdf


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## Iggy-poo (Feb 23, 2017)

The body gets rid of it too, even in old cripples like me.:
https://www.ncbi.nlm.nih.gov/pubmed/3594853


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## g_axelsson (Mar 1, 2017)

By popular demand (Kurt asked me... :wink: ) I post some links I found. The third one lists a number of methods of cyanide destruction.

Young 1993, "CYANIDE REMEDIATION: CURRENT AND PAST TECHNOLOGIES" https://www.engg.ksu.edu/HSRC/95Proceed/young.pdf
Under Photolysis they discuss the splitting of ferric and ferrous hexacyanide complexes by light. In it they state that a wavelength of circa 420 nm or shorter is needed to split off CN- ions. With shorter wavelength free radicals can be created that destroys cyanide. Read the article for the details.

Another interesting article : "Sunlight-Induced Photochemistry of Aqueous Solutions of Hexacyanoferrate(II) and -(III) Ions", http://pubs.acs.org/doi/abs/10.1021/es00046a016

I found a third article that is a run through of a number of different methods to destroy cyanide waste. "CYANIDE DESTRUCTION" http://www.sgs.com/-/media/global/documents/flyers-and-leaflets/sgs-min-wa017-cyanide-destruction-en-11.pdf

Göran


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## upcyclist (Mar 1, 2017)

On the bleach/sodium hypochlorite method, I've also read (on finishing.com, for example) about using potassium iodide paper to check for free chlorine instead of using an ORP meter. The reasoning behind this is that (given sufficient stirring and reaction time) free chlorine won't build up until after it has reacted completely with the cyanide in stage 1, or the cyanate in stage 2.


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## Lino1406 (Mar 6, 2017)

Note
1.Body can get rid of cyanide absorption up to 1g only
2.In the course of cyanide oxidation some stinking gases may appear, CNCl, (CN)2, so performing under
a good hood or ventilation is a must
3.Cyanide identification: Add thiosulphate, this converts cyanide to thiocyanate; To this add Fe+++, this
will give a red color, Fe(CNS)3


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## Rougemillenial (Mar 20, 2017)

sodium dichloroisocyanurate, trichloroisocyanuric acid, electrolysis in the presence of NaCl, MnO2 from batteries, hydrothermal degradation, and acidic oxidants such as nitric acid also gets rid of cyanide. You might worry that HCN would be produced. HCN is extremely soluble in water so it wouldn't do anything funny unless it was really concentrated. HNO3 is in equilibrium with hydroxide and nitronium ions so this is the mechanism that gives it the oxidizing power. 9CN+2NO3+3H2O--------> 9CNO+2NH3. so cyanuric acid and ammonium cyanate will form


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## 4metals (Mar 20, 2017)

Rouge, 

You obviously have some background in chemistry but vague suggestions like you are putting in your posts need more of an explanation than you are giving. What you have suggested has the potential to do more harm than good. If you would please post a method which we can review, we can have a discussion. If not please stop posting vague technobabble because you are not impressing anyone.


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## aga (Mar 20, 2017)

Rougemillenial said:


> sodium dichloroisocyanurate, trichloroisocyanuric acid, electrolysis in the presence of NaCl, MnO2 from batteries, hydrothermal degradation, and acidic oxidants such as nitric acid also gets rid of cyanide. You might worry that HCN would be produced. HCN is extremely soluble in water so it wouldn't do anything funny unless it was really concentrated. HNO3 is in equilibrium with hydroxide and nitronium ions so this is the mechanism that gives it the oxidizing power. 9CN+2NO3+3H2O--------> 9CNO+2NH3. so cyanuric acid and ammonium cyanate will form


This is technobabble, certainly.

When anyone (in Chemistry) says something like "this happens" they either have Scientific Data from many experiments they have personally done/been involved with, or a Reference (that anyone can read) which is the detailed Scientific write-up of experiements that other people have done. Preferrably both.

Without one or the other, regard such pronouncements as utter garbage until the OP can provide the evidence.

Anyone can say "I made gold from shoe polish and 1 potato - look at my 10kg gold bar !"

All just Words without the evidence.

Edit:

Some things are Done that are un-Scientific that also work.

For example, a long-time refiner might say "stick in some shoe-polish and you get 4-nines"

That refiner will be able to Show you.


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## Rougemillenial (Mar 25, 2017)

Rougemillenial said:


> sodium dichloroisocyanurate, trichloroisocyanuric acid, electrolysis in the presence of NaCl, MnO2 from batteries, hydrothermal degradation, and acidic oxidants such as nitric acid also gets rid of cyanide. You might worry that HCN would be produced. HCN is extremely soluble in water so it wouldn't do anything funny unless it was really concentrated. HNO3 is in equilibrium with hydroxide and nitronium ions so this is the mechanism that gives it the oxidizing power. 9CN+2NO3+3H2O--------> 9CNO+2NH3. so cyanuric acid and ammonium cyanate will form



I apologize for the vagueness of this post.  . This is something I have been working on. Sometimes I do think I'm a bit too smart for my own good at times.  I never intended to cause confusion or liability to the forum. I do try to keep responses short by request from my doctor so people can stand to be around me, though I just realized that I made things too concise :| . I would suggest that If anyone decides to work with cyanide have ways of disposing of it. Also most of what I suggested could have easily been explained as oxidizing agents do a good job at destroying cyanide. Examples include pool chlorine/shock, electrolysis with a salt solution to make the chlorine in-situ, heating to 400C in a closed system to force it to decompose into carbon dioxide and ammonia, regular household bleach, and manganese black from pottery stores. Nitric acid or sulfuric acid can also be used but isn't recommended due to the potential release of hydrogen cyanide. Just add it directly to the solution and wait a few days for all cyanide to be destroyed.


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## Rougemillenial (Mar 25, 2017)

http://www.sgs.com/~/media/Global/D...s/SGS-MIN-WA017-Cyanide-Destruction-EN-11.pdf
http://www.srk.com/en/newsletter/metallurgy-mineral-processing/cyanide-destruction


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## CG_AG (Jun 2, 2017)

If your desired limit of detection is higher than 0.3 ppm, there's a simple and safe test for free cyanide that can help you obtain semi-quantitative results within 60 seconds.

https://www.cyanoguard.ch/technology

Hope this helps


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## 4metals (Jun 2, 2017)

> If your desired limit of detection is higher than 0.3 ppm, there's a simple and safe test for free cyanide that can help you obtain semi-quantitative results within 60 seconds.



Where is this kit available for purchase?


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## CG_AG (Jun 13, 2017)

4metals said:


> > If your desired limit of detection is higher than 0.3 ppm, there's a simple and safe test for free cyanide that can help you obtain semi-quantitative results within 60 seconds.
> 
> 
> 
> Where is this kit available for purchase?



The kit is available through:
https://www.cyanoguard.ch/contact

Hope this helps.


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## Topher_osAUrus (Jun 20, 2017)

I would like to bring this thread back to life, as I believe it was started with the best intentions, then derailed by babble. 

So I will post a couple questions I have regarding the destruction of cyanide.
(It seems to me though, that the electrowin cell is the winning deal, but, to cover all bases and have extra options, I would like to inquire about a couple of the other methods)

When doing the destruction via chlorination.
-*Loewen states that the CN concentration must be "fairly low (below 1%) to avoid creating an intermediate toxic material called cyanogen chloride. The toxicity of cyanogen chloride is equal to or exceeds that of hydrogen cyanide."
---Is this statement completely accurate? There are a few other things in his book that were pretty far off base (like doing AR on goldfilled..), so it made me wonder about the validity of that statement. Particularly the low concentration of cyanide variable. :?: 

Also, when doing chlorination, how much of an ill effect does the chlorine have on testing cyanide levels with the CN strips mentioned earlier? :?: 
-I suppose that is where the ORP meter comes in to save the day, eh?


And what happens to the zinc cyanide complex when the destruction of cyanide begins? Or aluminum for that matter (if it is used for reduction of gold)[supposedly aluminum does not form a CN complex, so that isnt as pertinent], but the zinc cyanide complex must be removed somehow before safe disposal.


Kurt also mentioned the SO2 method of destroying cyanide. All I could find on it, was, that it is a method developed by INCO, and the formula of it:
:arrow: CN + SO2 + O2 +H2O = CNO + H2SO4
*-"Their paper, (Devuyst), says that the metals and precious metals present are recovered as hydroxides by adjusting the pH to about 9-10"..."This could make it possible to simultaneously destroy cyanide snd recover precious metals. Further investigation and chemical tests are needed to see if this could be worthwhile"
--But, if its just forming cyanate and sulfuric acid, uh, isn't that going to try to murder you in the end as well???

Also mentioned in the same book, is the US bureau of mines has isolated bacteria that decomposes cyanide to non-toxic materials.
--I have yet to search for any literature on that. 

*(Loewen, pg 88)


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## FrugalRefiner (Jun 20, 2017)

Topher_osAUrus said:


> ---Is this statement completely accurate? There are a few other things in his book that were pretty far off base (like doing AR on goldfilled..), so it made me wonder about the validity of that statement. Particularly the low concentration of cyanide variable. :?:


I can't answer any of the cyanide questions as I don't have any first hand experience. 

When I read the AR on goldfilled idea, I was dubious too. But it has some merit. He processes it like some folks do processors. By adding the AR in small batches, and allowing it to run to exhaustion, any gold that dissolves cements back out on the remaining base metals. Decant off the barren solution and add some fresh AR. Of course, stannous test every step. The last batch of AR will dissolve the gold but most of the base metals will have been decanted off.

At least, I think that's what he described. Then again, I'm old, and that may have been someone else's idea.

It's actually a frugal approach 8) ; kind of an AP on steroids. It's cheaper to dissolve most of the base metals as chlorides, but it's slow. Nitric is faster, but more expensive. I expect the AR approach would cheaper than nitric but slower (waiting for each batch of AR to be exhausted), and more expensive but faster than AP.

Dave


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## Topher_osAUrus (Jun 20, 2017)

FrugalRefiner said:


> When I read the AR on goldfilled idea, I was dubious too. But it has some merit. He processes it like some folks do processors. By adding the AR in small batches, and allowing it to run to exhaustion, any gold that dissolves cements back out on the remaining base metals. Decant off the barren solution and add some fresh AR. Of course, stannous test every step. The last batch of AR will dissolve the gold but most of the base metals will have been decanted off.
> 
> At least, I think that's what he described. Then again, I'm old, and that may have been someone else's idea.
> 
> ...



He describes it as FASTER!
Heh
Cheaper, yes. Faster, no. Not when you are waiting overnight for it to cool and cement back out. Then having to do that multiple times/days. 

I can get a batch of goldfilled done pretty darn quick with nitric. Usually between 2-3 days, start to finish (unless its watchbands that I have to remove, painstakingly)
..Granted, he mentioned his lot being 50lbs, and that is a pretty good sized load, I would still prefer the nitric. Solely for the fact of -what happens to all of his silver from the pieces of vermeil?


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## saadat68 (Jun 13, 2021)

Hi
I have 100 millilitre solution with maximum one gram sodium cyanide. Can someone say to me how much bleach need to destruction of cyanide in this solution? 
Yes I know, I must use ORP meter or potassium iodide paper. 
In https://www.pfonline.com/articles/cyanide-destruction-a-new-look-at-an-age-old-problem I found approximately 23 gallons of 12.5% sodium hypochlorite solution destroy one ounce of cyanide. Is that true? 

I really need 3 or 4 liter bleach to destroy just one gram sodium cyanide in just 100 mill water?!
So this method produces a lot of sewage!!!


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## Lino1406 (Jun 13, 2021)

By theory for destroying 1 mole KCN, 2.5 mole NaOCl are needed. But you take an excess of course, and should study the process very well (it includes 2 stages).


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## saadat68 (Jun 15, 2021)

If I add 20 or 30 of millilitre 40% H2O2 to 100 millilitre cyanide solution with PH 11, Is it possible PH decrease under 9 and produce HCN gas? I ask this because PH of 40% H2O2 is about 4.5!


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## Lino1406 (Jun 15, 2021)

Cyanide is destroyed by H2O2 in presence of copper salt 
H2O2 + CN- → CNO- + H2O 
CNO- + H+ + H2O → CO2 + NH3
the 2nd stage seems to increase pH somewhat


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## saadat68 (Jun 16, 2021)

Thanks lino
What about first stage? Does it decrease pH? 
As you know second stage will not happen completely.


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## Lino1406 (Jun 16, 2021)

In 1st stage we do not see something to change pH significantly


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