Gold recovery through cyanidation with activated carbon

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sohwohn

Well-known member
Joined
Dec 25, 2017
Messages
50
I used 300g of sample (Gold grade: 27ppm) and 700cc tap water to perform the cyanidation process.

The process took 3 hours and I filtered the solution to separate liquid and sample powders.

I then put 15g of activated carbon into the filtered solution and stirred the mixture for about 90 minutes.

The carbon cubes were then taken out and put into a little furnace and burnt to ashes (around 0.3g).

I found the carbon had around 40% Cu and 0.3% Au with little amount of base metals like Fe, Pb, Zn, etc..

My goal is to repeat this process until I get enough Au and then I make a gold alloy.

My question is, how do I recover Au from the burnt ashes of activated carbon?

I tried my furnace and the temperature was almost about 1200 degree Celsius.

I did find a little bead at the bottom of the furnace cup but I couldn't remove it.

Then I added Cu2O with carbon powders into the furnace cup again hoping that it would make enough volume for the alloy mixture to flow out. But I messed up by putting too much Cu2O powders and now the outcome alloy looks like a mess and the X-ray spectrum only shows very very little reading of Au.

I'm wondering if there's better way to recover gold from the burnt ashes?

I looked up the Internet and it seems like I'm dealing with AuCN- but I have no idea what should I do next.
 
Also, I actually have another question. I read X-ray spectrum to determine the concentrations of elements in the carbon sample. The presence of Cu doesn't affect me at all but little Zinc can interfere Gold by very very much.

I found out that, after I put the activated carbon cubes into the solution, for first 10-15 mins, I can have a very very clear Au peaks as Zn is not disturbing. However, after 30 mins, there are more and more Zinc incoming and at some point the Au peaks are gone.

So I'm wondering (which I will be doing tomorrow) if I should put 20g of carbon and collect them after 20 mins and repeat the process until I don't see Au in the sample anymore. I know this sounds stupid and may cost me a lot of carbon powders but I'm not trying to refine the process. I just want to be 100% sure I'm getting Gold. If I get too much Zinc, I won't know even Au is there.
 
I also wonder..

I mixed Cu2O with carbon aiming to reduce Cu2O into Cu. Was it a correct concept?
 
First, a little math. You have 0.3 grams of ash and it has .3 % gold. This means you have (.3 x.003) or a little less than one thousandth of a gram of gold - roughly about 4 cents worth of gold. You could do this same procedure 500 times and have less than a half gram of gold even if everything went perfect. Its a whole lot of work for a tiny amount of gold.
Second, cyanide is a common treatment but it does not work directly with all ores. Some require special treatment prior to cyanide to allow the cyanide process to work - especially those with significant sulfides and some with certain base metal minerals. In order to use cyanide successfully, you need to know your chemistry well. You need to know your ores well. There are books, some of which are available for free download which explain the basics of cyanide treatment of gold ore. It seems like you may need to read a few of these.
Its way beyond the scope of a forum to teach the necessary chemistry and we cant guess what kind of ore you have either. The number of possible problems are huge and we dont have the info necessary about what you are doing to even give a guess.
 
Reno Chris said:
First, a little math. You have 0.3 grams of ash and it has .3 % gold. This means you have (.3 x.003) or a little less than one thousandth of a gram of gold - roughly about 4 cents worth of gold. You could do this same procedure 500 times and have less than a half gram of gold even if everything went perfect. Its a whole lot of work for a tiny amount of gold.
Second, cyanide is a common treatment but it does not work directly with all ores. Some require special treatment prior to cyanide to allow the cyanide process to work - especially those with significant sulfides and some with certain base metal minerals. In order to use cyanide successfully, you need to know your chemistry well. You need to know your ores well. There are books, some of which are available for free download which explain the basics of cyanide treatment of gold ore. It seems like you may need to read a few of these.
Its way beyond the scope of a forum to teach the necessary chemistry and we cant guess what kind of ore you have either. The number of possible problems are huge and we dont have the info necessary about what you are doing to even give a guess.
You're right..

Thank you for the reply.

The ore doesn't have much Sulfides but almost 35% Lead and Zinc Oxides. However, the cyanidation chemical I'm using doesn't absorb Pb, Zn, Fe out of the ore so it should be fine. Mainly the cyanidation chemical absorbs Cu and Au. The cyanidation process takes only 2 hours for 300g of ore, and it only takes 5 mins for the carbon to absorb the AuCN compounds. The Au grade in AC has increased but I have yet had an exact number. I have made another setup yesterday and I obtained some more AC which will be examined later.

For what I'm assuming: The cyanidation chemical absorbs Cu and Au first, given time it will start to absorb Pb, Zn and Fe. The AC works the same way.

Yesterday, I did an experiment, I picked up a carbon cube by every 5 mins and examined the Cu, Zn, Au concentrations. The Zn Au concentrations soon reach their peaks and they stop growing. The only thing keeps growing is the Cu peak. So I assume, the more Cu I get, the less Au I have after I burn the carbon into ashes. Also, I have found out that the longer I perform the cyanidation process, the more Zinc I get in the solution. However, gold grade in the solution didn't seem changing.
 
The thing which bothers me most and I can't find an answer online is that..

People say I can just smelt the ashes to get solid metal bead.

How much temperature? Anything else I need to add into the furnace cup?

I have spent a lot of time searching for an answer but it only comes up with 'desorbing the AC'..
 
You can make your leach more selective by reducing the amount of free cyanide you have.
Read Delano’s threads things that may be of interest to members and further things etc it may give you better guidance.
 
nickvc said:
You can make your leach more selective by reducing the amount of free cyanide you have.
Read Delano’s threads things that may be of interest to members and further things etc it may give you better guidance.
Are you suggesting if I add different amount of cyanidation chemicals it will be more Au favorable / Zn favorable?!

Oh my god! If that's true, I must make some tests to evaluate the best concentrations of cyanidation chemicals to enhance the Au grade in solution!!

I couldn't find member 'Delano' in this forum.. What's his member ID?

Thank you very much!!!!
 
FrugalRefiner said:
sohwohn said:
I couldn't find member 'Delano' in this forum.. What's his member ID?
His name is Deano.

Dave

Here are links to the threads suggested for reading

:arrow: http://goldrefiningforum.com/phpBB3/viewtopic.php?f=85&t=22668

:arrow: http://goldrefiningforum.com/phpBB3/viewtopic.php?f=37&t=22978

When it comes to the treatment of "ore" for gold recovery & refining you will have a hard time finding better &/or more complete info about it then what Deano has been so kind in taking his time to provide right here :!: :!: :!:

THANK YOU Deano :!: for providing this HUGE contribution to the forum :!: 8) 8)

sohwohn; - these are 2 very long threads - but - they are well worth taking the time to read "completely" --- as well as researching (& reading) other things Deano has posted in other threads

In fact - you will likely find that the info Deano has provided here (concerning the treatment of ore) is so vast - that its not just going to be a simple read --- in other words - I think you will find it to be a "study" --- meaning taking note & referring back to it in order to really grasp "all" the info Deano has been so kind to provide here

Kurt
 
kurtak said:
FrugalRefiner said:
sohwohn said:
I couldn't find member 'Delano' in this forum.. What's his member ID?
His name is Deano.

Dave

Here are links to the threads suggested for reading

:arrow: http://goldrefiningforum.com/phpBB3/viewtopic.php?f=85&t=22668

:arrow: http://goldrefiningforum.com/phpBB3/viewtopic.php?f=37&t=22978

When it comes to the treatment of "ore" for gold recovery & refining you will have a hard time finding better &/or more complete info about it then what Deano has been so kind in taking his time to provide right here :!: :!: :!:

THANK YOU Deano :!: for providing this HUGE contribution to the forum :!: 8) 8)

sohwohn; - these are 2 very long threads - but - they are well worth taking the time to read "completely" --- as well as researching (& reading) other things Deano has posted in other threads

In fact - you will likely find that the info Deano has provided here (concerning the treatment of ore) is so vast - that its not just going to be a simple read --- in other words - I think you will find it to be a "study" --- meaning taking note & referring back to it in order to really grasp "all" the info Deano has been so kind to provide here

Kurt
Yes. Thanks Deano.
 
You have two possibilities for adsorbing gold values onto activated carbon.

The first is where you are adsorbing from a clean liquor with no fine solids present.

In this case you can get very good gold recoveries by ashing the carbon and smelting the ash.

If you have fine ore particles present in the liquor you will get some of these particles caught in the carbon pores and they will be present in the ash no matter how diligently you wash the carbon before ashing.

These residual particles will cause gold losses of up to 50% of the gold if you smelt the ash.

The only way to get high recovery from such ashes is by leaching the gold with either cyanide or aqua regia.

Other gold leaches will also give high recoveries but are a pain to use apart from the pH7 hypochlorite leaches for which you need Eh/pH meters, the meter expense tends to put people off these leaches which is a shame as they are probably the safest leaches for both small and large operators provided basic safety precautions are taken.

Deano
 
Oh my god I'm so glad I found this forum as I had no one to talk to until now..

I had yet read Deano's threads but I definitely will. Before I could actually do so I can't believe Deano is actually replying my thread!! Thank you Deano and all of you who're helping me.

I came to China from Hong Kong about three months ago. Before I was living in Hong Kong and was an Interior Designer. My father is getting old and after considerations I decided to come helping him with his projects. Here has limited facilities and people. So basically I'm my own teacher. With the help from my friend purchasing VPN for me so that I can google, I started from nothing and learning little by little. I started with the X-ray spectrum assaying. I spent almost two and a half months to finally figure how to 'tune' the machine and make use of the standards and so to finally perform an semi-quantitative analysis on ore samples. Also now I can smelt ore samples on a Copper plate and hence provide ppm-level analysis on precious metals. However, I was only good at the software part (since I graduated in I.T. major), but not the hardware part.

Recently (among last 2-3 weeks) I had been doing acids/cyanidation/smelting by my own. I only have very very very very very very.. basic ideas of chemistry so I had a hard time. I studied Chemistry when I was secondary school but I picked Physics and Pure Mathematics for my high school subjects, and Information Engineering in University.. So I had been doing was googling and googling and googling..

Anyway, thank you very much for replying this thread and I guess I will first spend sometime on reading Deano's threads, before I make any updates.

Sohwohn
 
Deano said:
You have two possibilities for adsorbing gold values onto activated carbon.

The first is where you are adsorbing from a clean liquor with no fine solids present.

In this case you can get very good gold recoveries by ashing the carbon and smelting the ash.

If you have fine ore particles present in the liquor you will get some of these particles caught in the carbon pores and they will be present in the ash no matter how diligently you wash the carbon before ashing.

These residual particles will cause gold losses of up to 50% of the gold if you smelt the ash.

The only way to get high recovery from such ashes is by leaching the gold with either cyanide or aqua regia.

Other gold leaches will also give high recoveries but are a pain to use apart from the pH7 hypochlorite leaches for which you need Eh/pH meters, the meter expense tends to put people off these leaches which is a shame as they are probably the safest leaches for both small and large operators provided basic safety precautions are taken.

Deano
So, are you suggesting, if I filter the solution for like 2-3 more times, it will help induce the gold grade on AC?

I'm not sure I should ask questions now as I just woke up and yet read your threads (it's China and my morning should be your evening).

Also, I actually have some assumptions as I have run 4 experiments and I'm just guessing the factors. I assume (1) the longer the cyanidation takes place the more Cu, Zn I get into the solution (2) the longer time given to AC absorption the higher concentrations of Cu, Zn will be (3) the more AC I add one time the sooner the gold grade drops and hence higher risk

So, for what I'm assuming, I will run an experiment today, I will spend only 1 hour on cyanidation and 5 mins on each AC absorption run and maybe 3-4 runs would be enough. Also, I will filter the solution 3 times to reduce the fine particles as much as possible.

Reading Deano's threads and performing such experiment, is my today schedule.
 
Take your time reading Deanos threads and comments he gives a lot away but expects you to join the dots on many aspects he discusses, the clues are all there it’s up to you to make sense of them and follow his line of thought.
 
Activated carbon will basically adsorb all metallic ions from solution, the heavier the ions the more likely they are to displace lighter ions.

However the concentration of each ion species also plays a major part in that a high concentration of lighter ions can prevent or slow down adsorption of a low concentration of heavier ions.

The presence of ore solids will not greatly affect the adsorption of metal ions unless the ore particle sizes are such that they can enter the carbon pores and prevent metal ion access to these pores.

Adsorption onto activated carbon is a relatively slow process even if a clean liquor is pumped through a column of carbon, you pick up the high end of the gold values fairly quickly but once the outer surface of the carbon has been loaded the adsorption occurs in the pore structures and this is much slower.

Activated carbon is always used as a transfer medium, you are either loading it with values which are later to be desorbed in a more concentrated form or you are going to ash it and treat the ash to recover the values,

The only times that carbon is not used as a transfer medium are when it is loaded with pollutants and disposed of in a waste facility, even here the carbon has effectively transferred the pollutants to a safer environment in a more concentrated form.

Deano
 
Deano said:
Activated carbon will basically adsorb all metallic ions from solution, the heavier the ions the more likely they are to displace lighter ions.

However the concentration of each ion species also plays a major part in that a high concentration of lighter ions can prevent or slow down adsorption of a low concentration of heavier ions.

The presence of ore solids will not greatly affect the adsorption of metal ions unless the ore particle sizes are such that they can enter the carbon pores and prevent metal ion access to these pores.

Adsorption onto activated carbon is a relatively slow process even if a clean liquor is pumped through a column of carbon, you pick up the high end of the gold values fairly quickly but once the outer surface of the carbon has been loaded the adsorption occurs in the pore structures and this is much slower.

Activated carbon is always used as a transfer medium, you are either loading it with values which are later to be desorbed in a more concentrated form or you are going to ash it and treat the ash to recover the values,

The only times that carbon is not used as a transfer medium are when it is loaded with pollutants and disposed of in a waste facility, even here the carbon has effectively transferred the pollutants to a safer environment in a more concentrated form.

Deano
Sir Deano you are being really really helpful to me!!

I wonder, as you have said, 'or you are going to ash it and treat the ash to recover the values', we actually have an induction furnace (up to 1300 degree Celsius), what can I do to the ashes?

Ps. What I'm doing here is just to prove 'this ore can be done by cyanidation' and estimate the recovery rate. The large-scale process will be done by selling the AC in the end. People use ICP to determine the gold grade so even the AC has large scale of Zn it's not an issue. However, speaking of assaying, we here only have a XRS machine, which is great, for semi-quantitative analysis. Though we encounter an issue that if Au concentration is lower than 50ppm then it will not show X-ray spectrum peaks or it will be interfered (covered) by Zn-Kb peak.. You said..

Adsorption onto activated carbon is a relatively slow process even if a clean liquor is pumped through a column of carbon, you pick up the high end of the gold values fairly quickly but once the outer surface of the carbon has been loaded the adsorption occurs in the pore structures and this is much slower.

and I totally agree. The Au grade keeps climbing up but the issue is so are other elements. So your explanation has explained everything I observed. The problem I'm getting here is that I have dissolve too many other elements, which disturb me assaying Au grade. Or I can just put the AC there and stir for like a day or two to maximize the Au grade. Anyway, I'm still reading your threads and getting the picture clearer than ever. Thank you very much as I'm making significant progress on understanding 'what's happening behind the scene'.
 
I have read some of Deano's articles and replies, by filtering Deano's posts by keyword 'cyanide'. The posts are extremely helpful and I am taking time to connect the dots..

I have run out of sample powders and the sites are sending more samples to the lab. I'll have meetings tomorrow so I won't be able to carry out more experiments.

What I've discovered through my own tests/experiments:
1. It seems like the cyanidation chemical I'm using prefers to dissolve Cu then Fe/Mn then Zn/Pb at 2%. To make it more selective I guess it's to decrease the concentration to about 0.5% or even 0.1%.
2. The AC (coconut shell) I'm using absorbs Fe slowly but quite significantly on Cu. This is my guess and assumption because Ore-A (10% Fe, <1% Cu, Zn, Pb, 25ppm Au) is performing quite well (as described by Deano) the AC mostly absorbs Au and not much Fe and Mn, but almost no Cu, Zn and Pb. Ore-B (5% Pb, 3% Zn, 1% Cu, 50ppm Au) contains so much Cu and Zn in AC as I can observe the Au peak stops in certain level and Cu/Zn concentrations keep climbing and climbing. I guess it's due to the excess dissolve-rate of Cu and Zn.

I will make some time after tomorrow to make a relatively complete report on what ores I'm handling and what I've got from the experiment results.

Thanks everyone again as this is a perfect place for me to get and share ideas about what I'm doing.. My friends in Hong Kong support me but they don't understand the details so I basically had no one to discussed with and felt like I was fighting alone.
 
You are reading and studying so help and advice will keep coming, we try to stresss to all new members that they have to do their part and you certainly are and so will get help as and when we can advise.
 
The mining industry standard cyanide level is 0.1% sodium cyanide in solution, this is around 500ppm actual CN-.

You can play with lesser cyanide concentrations in order to minimise base metal dissolution and relatively enhance the gold dissolution.

High copper ores can be run with cyanide levels at 0.01% or even lower.

As the cyanide level is lowered the protective alkalinity will also lower so you will have to add lime or caustic for pH regulation.

Induction furnaces are not useful for carbon ashing, you need to have an air flow through the carbon with the temperature around 650C. Ashing needs to be complete. Get yourself an electric muffle furnace and some porcelain dishes for the ashing.

Usually you monitor the metals in solution values to see how the leach is going, get yourself a good second hand AAS unit to do this with.

Selling loaded carbon is usually an opportunity for dodgy assay methods to be used, much smarter to do your own stripping and then reuse the carbon, that way you maintain control over the gold.

Carbon in leach levels are usually around 5 grams per litre, much higher and attrition of the carbon becomes a major issue. Gentle agitation is needed.

Deano
 
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