Electrochemistry Electrowinning cyanide solutions

[autumnwillow]

If I had a gold plating solution composed of 2.0g potassium gold cyanide with a pH >10.
Disodium phosphate and soda ash were used as the pH increaser.
This solution is known as a flash gold electroplating solution.

Can I simply take the 1.2g gold (noting that 1.0g of PGC is 68.3% gold) out of the solution by using an inert anode like graphite rod/platinized titanium and a copper or gold foil as the cathode?

Will the gold fully deposit at the cathode?

The reason I decided to go for electrowinning is to re-use the cyanide solution.
I have been using zinc dust before, but the solution becomes unusable after the zinc process.

I think it would be economical if I could just electrowin and re-use the cyanide solution.

Although time is at cost here and having a solution of cyanide left for days is also dangerous, I am still trying to find out whether an electrowinning cell will outweigh the zinc cementation process.

 

[goldsilverpro]

It's very unlikely you'll be able to plate out ALL of the gold. As the gold concentration in the solution gets lower and lower, the more the efficiency decreases and the slower and slower the gold deposits. Also, the lower the efficiency,I would think the more rapidly the cyanide decomposes at the electrode. I used to electrolyze strong cyanide solutions, using 2 stainless sheet electrodes, to destroy the bulk of the cyanide. After a couple of days, at least 90% of the cyanide was gone, proven by analysis.

 

[zachy]

You can use aluminum foil, you should chop it into small pieces, but it is good that you evaporate the solution as much as you can to lower the volume. Decomposes to cyanate and then you can put the aluminum

 

[kurtak]

You can use aluminum foil, you should chop it into small pieces, but it is good that you evaporate the solution as much as you can to lower the volume. Decomposes to cyanate and then you can put the aluminum

zachy

per the underlined - are you sure about that ??? - I ask because this is the first time I have heard that evaporating a cyanide solution decomposes the cyanide to cyanate - I am no chemist (so I don't know) but I have been doing a LOT of research on cyanide lately & no where have I heard of evaporating a cyanide solution to convert the cyanide to cyanate --- to my understanding cyanide is converted to cyanate by a chemical "reaction" --- seems to me - evaporation alone would not provide a chemical reaction - but instead would simply "concentrate" a dilute solution --- in other words - evaporation would simply make a dilute solution a more concentrated "cyanide" solution --- being cyanide - that (evaporation) sounds "dangerous" to me

"Warming" the solution "a bit" before adding the aluminum - would/will assist in speeding up &/or make the cementing more effective & is at most what I would suggest & when I say warm - I mean just warm NOT to the point steam evolves off the solution (which would then be evaporation - don't want that)

Here is some info from Wiki ------------

From the "cyanate" page

Cyanates are produced when cyanides are oxidized. Use of this fact is made in cyanide decontamination processes where oxidants such as permanganate and hydrogen peroxide are used to convert toxic cyanide to safer cyanate.

From the potassium "cyanate" page

in aqueoues solution by reacting with hypochlorites or hydrogen peroxide

On both these pages the conversion of cyanide to cyanate are done by a "chemical reaction" (its an oxidation reaction) --- NOTHING is said about evaporation

In this thread 4metals explains how to preform the reaction (using hypochlorite) to convert the cyanide to cyanate --- & then how to destroy the cyanate :arrow: http://goldrefiningforum.com/phpBB3/viewtopic.php?f=40&t=7627&p=69862&hilit=Cyanide+waste#p69862

I could provide more info (as a result of my research) the bottom line being - no where in my research did I see &/or hear where "evaporation" was used &/or recommended to convert cyanide to cyanate

So - could you please provide more info then simply saying "to evaporate" because I believe all evaporation is going to do is give you a more concentrated "cyanide" solution - which when talking about cyanide - would certainly make it more dangerous

Kurt

 

[kjavanb123]

Autumn,

Here is a video of someone who use electrowinning of gold cyanide solution. The actual cyanide solution electrowinning starts after 5 minutes to video.

Right before the electrowinning he adds a clear solution to cyanide solution that foams up, and changed color, my guess is hydrogen peroxide.

https://youtu.be/5Mi60UCv3UU

Regards
Kj

 

[aga]

'Oxidation' is indeed a chemical reaction requiring another element that can steal at least 1 electron from an atom. The reverse, where an atom gains at least 1 electron is called 'reduction'.

Oxygen isn't the only oxidiser, just that it was studied first, and the term 'oxidise' has stuck.
https://en.wikipedia.org/wiki/Oxidation_state

Potassium cyanide (KCN) exists in solution as K⁺ and CN^-, whereas the cyanate is K⁺ OCN^-.
That extra oxygen atom has ripped 2 electrons from the Carbon atom, giving it a +4 charge instead of +2.

It is possible that atmospheric oxygen reacts with the cyanide, which should happen faster at higher temperatures.

The key to knowing if that actually happens in real life would be to know the Rate of the reaction.

Somebody here probably knows the answer to that - does a potassium cyanide solution lose it's effectiveness if left unused for a long time ?

 

[anachronism]

Somebody here probably knows the answer to that - does a potassium cyanide solution lose it's effectiveness if left unused for a long time ?

If it has access to daylight (UV) then yes for sure. UV destroys CN.

 

[aga]

If it has access to daylight (UV) then yes for sure. UV destroys CN.

Thanks for that info.

So it does react with atomospheric oxygen at an appreciable rate - the mechanism with UV (i think) is that the O₂ gets split into two highly reactive Oxygen 'radicals', both hungry for 2 electrons each, i.e. a strong oxidiser.

Therefore boiling in air will (probably) oxidise cyanide to cyanate faster, although it'd be impossible to say how long it would take to oxidise all of it without some controlled experiments.

Sure ain't gonna be me boiling and titrating lethal toxic liquids !

 

[kurtak]

Sure ain't gonna be me boiling and titrating lethal toxic liquids !

My point exactly :!:

Kurt

 

[g_axelsson]

Here is some info from Wiki ------------

Nice to see the wiki referenced, but a bit of disclaimer is needed, it is so far only based on my writing and it can contain errors and it certainly contains omissions.

Just saying...

Göran

 

[goldandsilver123]

We are installing in a company electrolysis to remove gold from a cyanide, golpanol (Sodium 3-nitrobenzenesulphonate) solution.

From 1300 L we removed 99% with around 6 hours of electrolysis. We achieved 99,9% with longer runs.

Anode is the stainless steel tank, cathode is steel wool.

We know when it's almost finished when the solution is black, at this time most of the cyanide was already destroyed.