Potassium cyanide with hydrogen peroxide

[Ayham Hafez]

Hello All!

I'm willing to make a test on gold ore size less than 400 mesh, I read a lot about potassium cyanide, and I'm sure that it has higher gold recovery rate than sodium cyanide with less process time.

Cyanide in general need oxygen to dissolve gold, so that in gold heap/VAT leaching process,it take about month to dissolve most of the gold in the tank, but by using oxygen feeder, period will be less.

Since I'm making test on small scale, I wonder if I add peroxide to the cyanide solution will accelerate the gold dissolving without effecting the rest process.

My plan is to add about 6 grams of potassium cyanide per liter of water, then add 5% peroxide concentrate 3% per liter of water then adjust the PH to 12 using Sodium Hydroxide.


What's your thoughts?


Thanks in advance


Ayham

 

[Deano]

The most used cyanides commercially are potassium, sodium and calcium, for gold dissolution with the same concentration of cyanide complexes in solution there is no difference in leach performance between the three forms.
Commercial operators buy purely on price per unit of cyanide complexes.
Adding peroxide to a cyanide leach will speed up the leaching rate, it will also speed up to a greater degree the cyanide complex oxidation rate. This is not a good thing if you wish to run your process at a profit.
If you have milled your ore to minus 400 mesh the only way to leach all the gold is to run an agitated leach such as a stirred leach or a bottle roll or variations of such.
Any attempt to run leaches on this finely milled ore without direct agitation of the ore will fail due to insufficient
wetting of the ore particles.
If you are looking to run a heap leach you must have a much coarser grind of your ore in order to ensure complete wetting of the ore surfaces.
This coarser grind means that more of your gold will be encapsulated in the ore particles and not available for leaching.
You cannot compare leach results from two different grind sizes on the same ore purely because of the encapsulation effect.
Most commercial operations run around 1 gram of solid cyanide pellets per litre of water, this is also the cyanide level they test at.
Running 6 grams cyanide per litre is strictly reserved for use in a leach reactor treating concentrates, usually gravity cons.
People have been running cyanide leaches for over 100 years so the accumulated knowledge is vast.
If commercially the industry does not use a particular processing route there is always a practical or financial reason why not.
It is unlikely that you are going to spot a processing method which has been missed for all this time.
Deano

 

[Ayham Hafez]

The most used cyanides commercially are potassium, sodium and calcium, for gold dissolution with the same concentration of cyanide complexes in solution there is no difference in leach performance between the three forms.
Commercial operators buy purely on price per unit of cyanide complexes.
Adding peroxide to a cyanide leach will speed up the leaching rate, it will also speed up to a greater degree the cyanide complex oxidation rate. This is not a good thing if you wish to run your process at a profit.
If you have milled your ore to minus 400 mesh the only way to leach all the gold is to run an agitated leach such as a stirred leach or a bottle roll or variations of such.
Any attempt to run leaches on this finely milled ore without direct agitation of the ore will fail due to insufficient
wetting of the ore particles.
If you are looking to run a heap leach you must have a much coarser grind of your ore in order to ensure complete wetting of the ore surfaces.
This coarser grind means that more of your gold will be encapsulated in the ore particles and not available for leaching.
You cannot compare leach results from two different grind sizes on the same ore purely because of the encapsulation effect.
Most commercial operations run around 1 gram of solid cyanide pellets per litre of water, this is also the cyanide level they test at.
Running 6 grams cyanide per litre is strictly reserved for use in a leach reactor treating concentrates, usually gravity cons.
People have been running cyanide leaches for over 100 years so the accumulated knowledge is vast.
If commercially the industry does not use a particular processing route there is always a practical or financial reason why not.
It is unlikely that you are going to spot a processing method which has been missed for all this time.
Deano

Your response is really appreciated, I think you alright I have to decrease to 1 gram cyanide per liter.


Regard my experiment, will use peroxide because am not concern about the cost since I just want to test the gold grade in the ore in minimum time, so I think I can finish dissolution the gold within 48 hours with peroxide and without use agitated leach.


I wonder in commercial cyanide leaching how we can provide oxygen, is it enough to just bubble the surface of the solution since we can't bubble inside the ore at the bottom of the tank? In my area peroxide 3% cost about 0.15 USD, is it commercially specially that it will save a lot of time? And what is the best quantity of peroxide that we can add to cyanide leaching to reach the maximum speed process ?

 

[Ayham Hafez]

The most used cyanides commercially are potassium, sodium and calcium, for gold dissolution with the same concentration of cyanide complexes in solution there is no difference in leach performance between the three forms.
Commercial operators buy purely on price per unit of cyanide complexes.
Adding peroxide to a cyanide leach will speed up the leaching rate, it will also speed up to a greater degree the cyanide complex oxidation rate. This is not a good thing if you wish to run your process at a profit.
If you have milled your ore to minus 400 mesh the only way to leach all the gold is to run an agitated leach such as a stirred leach or a bottle roll or variations of such.
Any attempt to run leaches on this finely milled ore without direct agitation of the ore will fail due to insufficient
wetting of the ore particles.
If you are looking to run a heap leach you must have a much coarser grind of your ore in order to ensure complete wetting of the ore surfaces.
This coarser grind means that more of your gold will be encapsulated in the ore particles and not available for leaching.
You cannot compare leach results from two different grind sizes on the same ore purely because of the encapsulation effect.
Most commercial operations run around 1 gram of solid cyanide pellets per litre of water, this is also the cyanide level they test at.
Running 6 grams cyanide per litre is strictly reserved for use in a leach reactor treating concentrates, usually gravity cons.
People have been running cyanide leaches for over 100 years so the accumulated knowledge is vast.
If commercially the industry does not use a particular processing route there is always a practical or financial reason why not.
It is unlikely that you are going to spot a processing method which has been missed for all this time.
Deano

I have another question, I didn't try cyanide with PCB recovery, but I understand the process, my question is : since pcb has more metals rate than gold ore, do we need to increase the cyanide percentage in the solution, I mean 1 gram of cyanide per liter is enough with leaching PCB or we have to increase it?


What are the base metals that dissolved in cyanide solution?


Thanks in advance.

 

[nickvc]

Forget about speed if you are ore leeching and listen to Deano about the peroxide it will kill the cyanide if you add too much , cyanide is much more selective when run at low levels meaning it will not absorb as many base metals but and here’s the pay off it is a lot slower.
Yes you can strip e scrap in cyanide but again there is a cost between speed and recovery rates, in e scrap because there are other metals readily available to the cyanide to dissolve you need to run only one type of product at a time preferably exactly the same items or you may well strip one product but leave another barely touched because other metals have been exposed which the cyanide will preferentially dissolve, again low levels of cyanide negate this problem to a certain extent but again at the cost of speed, I think you get the idea, you can’t have speed and high recovery rates very easily.
Also be aware that using cyanide comes with great risk….
It does not give you second chances if you mess up with the chemistry , so do your homework before you start!

 

[Ayham Hafez]

Forget about speed if you are ore leeching and listen to Deano about the peroxide it will kill the cyanide if you add too much , cyanide is much more selective when run at low levels meaning it will not absorb as many base metals but and here’s the pay off it is a lot slower.
Yes you can strip e scrap in cyanide but again there is a cost between speed and recovery rates, in e scrap because there are other metals readily available to the cyanide to dissolve you need to run only one type of product at a time preferably exactly the same items or you may well strip one product but leave another barely touched because other metals have been exposed which the cyanide will preferentially dissolve, again low levels of cyanide negate this problem to a certain extent but again at the cost of speed, I think you get the idea, you can’t have speed and high recovery rates very easily.
Also be aware that using cyanide comes with great risk….
It does not give you second chances if you mess up with the chemistry , so do your homework before you start!

Really appreciated...


I will start a test on PCB after I depopulate all IC chips, so the only targeted material is gold plated pins, I will use 2 grams of cyanide per liter with adding air fish bubbler, without any addition of peroxide, I will use 10 Kg of PCB, please tell me if I need to adjust anything before starting my experiment and what is the approximate time for the experiment to dissolve the plated gold , thanks in advance

 

[Ultrax]

As I remember, standard oxidation order for KCN + H2O2: (1) cyanate -> (2) carbonate -> (3) nitrogen. Depends on concentration, conditions, etc.
Sometimes people use (1) cyanate as a safer and less aggressive alternative than cyanide.
But your condition is hard to control, so perhaps you will lose % of the available cyanide amount in the tank, and lose in whole reaction speed too.

 

[Ultrax]

P. S. And yes, 6 grams per liter is too much for your request. You will lose 95% of selectivity in your leaching process. Higher cyanide concentrations are intended for high-grade concentrates usually.

 

[Ayham Hafez]

I read this article

https://www.sciencedirect.com/science/article/abs/pii/S0892687515300558
They mentioned that if copper content is high in the materials, to make selective gold dissolution without consumption of the CN by copper is by increasing the PH to be higher than 12.5 and to use NaOH for PH modification.

Whats your thoughts about that, I have dedicated 10 Kg of pcb (laptops circuit boards)that have some gold plated pins and lot of copper for the experiment, willing to dissolve 40 grams of cyanide in 25 liter of water with adding some NaOH and adjust PH to 13, will not use any oxygen feeder, will leach for 48 hours then record results.

Kindly inform me if I have to modify any parameters before start the experiment.


Thanks...

 

[nickvc]

Really appreciated...


I will start a test on PCB after I depopulate all IC chips, so the only targeted material is gold plated pins, I will use 2 grams of cyanide per liter with adding air fish bubbler, without any addition of peroxide, I will use 10 Kg of PCB, please tell me if I need to adjust anything before starting my experiment and what is the approximate time for the experiment to dissolve the plated gold , thanks in advance

My suggestion would be to do small experiments using various amounts of cyanide but as I said any other metals present will hinder the dissolution of gold unless you use very low levels of cyanide, again as I said , and this comes from Deano , there is always a cost when using cyanide unless you are running exactly the same product, as to how long the simple answer is as long as it takes until you are happy with the result , one point to remember is that cyanide is not a perfect solution to gold recovery , you will rarely recover all the gold so it comes down to how much are you willing to sacrifice against the time it takes and that only you can answer.

 

[Ayham Hafez]

My suggestion would be to do small experiments using various amounts of cyanide but as I said any other metals present will hinder the dissolution of gold unless you use very low levels of cyanide, again as I said , and this comes from Deano , there is always a cost when using cyanide unless you are running exactly the same product, as to how long the simple answer is as long as it takes until you are happy with the result , one point to remember is that cyanide is not a perfect solution to gold recovery , you will rarely recover all the gold so it comes down to how much are you willing to sacrifice against the time it takes and that only you can answer.

My suggestion would be to do small experiments using various amounts of cyanide but as I said any other metals present will hinder the dissolution of gold unless you use very low levels of cyanide, again as I said , and this comes from Deano , there is always a cost when using cyanide unless you are running exactly the same product, as to how long the simple answer is as long as it takes until you are happy with the result , one point to remember is that cyanide is not a perfect solution to gold recovery , you will rarely recover all the gold so it comes down to how much are you willing to sacrifice against the time it takes and that only you can answer.

The reason of the experiment is I always run big pcb batches for gold recovering some times 1 ton per day, I don't care about other metals when I recovering gold from free IC chips PCB, I don't disassemble gold plated pins from pcb cause I can't have machines or labor, so recently I start the process by leaching pcb in HCl to git rid of tin then collect ic chips, then leach in AP to get gold foils, now I'm searching to shortcut the process by leaching the pcb in cyanide from the beginning, recovering 95% of gold is satisfying me since I believe that I loose more than 5% of gold in AP solution

 

[Ayham Hafez]

Second important reason is when using AP, a lot of gold foil stuck on pins and it took a lot of work to get them, and some pins made from steel not dissolution so can't get the gold foil plated on them by using AP.

 

[kurtak]

Whats your thoughts about that, I have dedicated 10 Kg of pcb (laptops circuit boards)that have some gold plated pins

I hope you do not mean that you intend to put whole circuit boards in a cyanide leach in order leach the gold plating off the pins on those boards

That is likely not going to work because at Ph 11.5 & above the leach solution is going to go to work at leaching metals like aluminum tin & lead thereby making the leach ineffective in leaching the gold plating

In other words - though raising the Ph to 13 will make the cyanide more selective to leaching the gold & less selective to leaching the copper --- at the same time Ph 13 will also make the cyanide leach more selective to leaching Aluminum tin & lead & less selective to leaching the gold (&/or copper)

Kurt

 

[Ayham Hafez]

I hope you do not mean that you intend to put whole circuit boards in a cyanide leach in order leach the gold plating off the pins on those boards

That is likely not going to work because at Ph 11.5 & above the leach solution is going to go to work at leaching metals like aluminum tin & lead thereby making the leach ineffective in leaching the gold plating

In other words - though raising the Ph to 13 will make the cyanide more selective to leaching the gold & less selective to leaching the copper --- at the same time Ph 13 will also make the cyanide leach more selective to leaching Aluminum tin & lead & less selective to leaching the gold (&/or copper)

Kurt

That's good, the PCB already leached in HCl so there is no tin or Aluminum, you encouraged me to make the experiment.

 

[Ayham Hafez]

I made the test, add 1 gram cyanide per liter of water with about 5 grams of NAOH ph was 14, material was gold plated pins, waited 48 hours in room temperature with fish air bubbler, after 48 hours I noticed that almost gold not effected, the only affected metal was copper, I increased the cyanide for 0.5 gram per liter then add 10 ml grams of peroxide 3% ,waited 2 hours , then noticed that all gold layer dissolved.

Complex of metals in pcb's make cyanide work less effective as it effected copper before gold even with using NAOH.

 

[Shark]

I hope you do not mean that you intend to put whole circuit boards in a cyanide leach in order leach the gold plating off the pins on those boards

That is likely not going to work because at Ph 11.5 & above the leach solution is going to go to work at leaching metals like aluminum tin & lead thereby making the leach ineffective in leaching the gold plating

In other words - though raising the Ph to 13 will make the cyanide more selective to leaching the gold & less selective to leaching the copper --- at the same time Ph 13 will also make the cyanide leach more selective to leaching Aluminum tin & lead & less selective to leaching the gold (&/or copper)

Kurt

Did you read this post from Kurtak? Did you understand it?

 

[nickvc]

I made the test, add 1 gram cyanide per liter of water with about 5 grams of NAOH ph was 14, material was gold plated pins, waited 48 hours in room temperature with fish air bubbler, after 48 hours I noticed that almost gold not effected, the only affected metal was copper, I increased the cyanide for 0.5 gram per liter then add 10 ml grams of peroxide 3% ,waited 2 hours , then noticed that all gold layer dissolved.

Complex of metals in pcb's make cyanide work less effective as it effected copper before gold even with using NAOH.

If you added more cyanide to the existing solution then the reason it worked is probably because all the base metals that could dissolve had done so, as I pointed out to make cyanide selective you need very low levels in solution and a lot of time there is no other method I know of.
Again cyanide isn’t the golden bullet for recovery in every circumstance.

 

[Ayham Hafez]

Did you read this post from Kurtak? Did you understand it?

Yes, but I read an article talking about adding NaOH will make cyanide very selective to gold since NaOH will immediately react with copper, which that not happen in my experiment.

 

[Yggdrasil]

Yes, but I read an article talking about adding NaOH will make cyanide very selective to gold since NaOH will immediately react with copper, which that not happen in my experiment.

You need to read more than one article stating something, before making up your mind,
there are millions of articles out there and not all are applicable in all conditions.
Many of which might not be trustworthy or targeting your specific situation.

Nest, are you sure you understood the article and all its ramifications?
This is an absolutely must, with regards to Cyanides even more so.

Pleas do not venture into new processes until you run it by us to get some feed back on its safety and viability.

 

[nickvc]

I always added a small amount of lye to my solutions which helps to allow the cyanide to be more aggressive and work slightly longer I believe but making the solution more aggressive will dissolve base metals just the same.
Working with cyanide is almost an art you have to adjust the amount of reagents used to achieve the desired reaction , every new product you have to recover the values from needs trial and error tests and careful examination, even the last time I processed using cyanide I had to adjust to achieve the desired yield and within an acceptable time.
To make it very plain working with cyanide is or can be highly complex and even more so if you are running mixed product that includes mixed boards which will have different metals on them.
I ran several tons of similar plated product over a few years and if memory serves me correctly the best yield we could get was around 90% , the rest was inaccessible as it was either covered or within the product and without dissolving the whole product or shredding it which would require very heavy equipment was recovered by the base metal refinery later.
If 100% recovery is what you need do not use cyanide , if you can accept 90% then it may be the process for you.