Zinc Vs Activated carbon with GDA

[Sy-Spark]

Activated carbon in best conditions in gold dressing agents or cyanide solutions can absorb only 20 grams of gold per 1 KG of activated carbon, while zinc can precipitate gold more than half of its weight, so 1 gram of zinc can precipitate 0.5 gram of gold, so for small scale like using 200 liters barrels I think zinc commercially much better also take shorter time than activated carbon, but what about the gold recovery rate for both, which is better?

 

[nickvc]

For reasonably small runs I’d go with zinc dust and plenty of agitation , I’d add a small amount of lye to help the zinc dissolve, you can then use aluminium foil to scavenge any remaining gold.

 

[Yggdrasil]

I think one of the main reasons for the use of AC is it can in a circuit and when loaded the values can be "unloaded" and the AC put back into use again.
Besides that it do nothing to the liquid, just adjust and run.
While when using Zinc you more or less destroy the solution don't you?

 

[Yggdrasil]

The AC will get progressively weaker, but can be reactivated again,
at least a few times until it is deemed spent and ashed for the last remaining values.

 

[Sy-Spark]

The AC will get progressively weaker, but can be reactivated again,
at least a few times until it is deemed spent and ashed for the last remaining values.

I read about reusing AC, it gives you less than 80% of activity from the second use, with low grade ore maybe reusing AC is feasible but with high grade E-waste I don't think so, for example I have telecom plated equipment that gives 150 grams of gold only from plating gold, so reusing AC again not a good idea.

Since it a small scale, no mean for reusing the solution again, but in mines areas that have issues with water availability it worth

 

[Sy-Spark]

For reasonably small runs I’d go with zinc dust and plenty of agitation , I’d add a small amount of lye to help the zinc dissolve, you can then use aluminium foil to scavenge any remaining gold.

JinChan supplier which is well-known GDA supplier in China, mentioned to me that increasing PH more than 11 will make issue with cementing with zinc, so I don't think using caustic soda is a good idea, but don't have an idea about using aluminum foils, I think zinc much reactive than aluminum in cementing process

 

[Sy-Spark]

While when using Zinc you more or less destroy the solution don't you?

If adding zinc will destroy the solution, it will be a very good point, cause I don't know how we can stop the cyanide or GDA from redissolving precipitated gold again, hope someone have an idea about this.

 

[anachronism]

If adding zinc will destroy the solution, it will be a very good point, cause I don't know how we can stop the cyanide or GDA from redissolving precipitated gold again, hope someone have an idea about this.

Depending on the application you can electrowin the gold as part of a circuit.

 

[Yggdrasil]

If adding zinc will destroy the solution, it will be a very good point, cause I don't know how we can stop the cyanide or GDA from redissolving precipitated gold again, hope someone have an idea about this.

I do not think it is destroyed like that, but it will not be good for a second use.
These "Lurium" compounds are not on my list of sensible things to try.

Some of them have a degree of sense in mining.
If you are to selectively leach E-waste it is only going to be the plating and that is not where the majority of the values are.
Better use the pure chemicals for it then, Cyanide, Ferro/Ferri Cyanides, Iodide/Iodine leaches and so on.

Still that is just a small part of the values.

 

[Sy-Spark]

I do not think it is destroyed like that, but it will not be good for a second use.
These "Lurium" compounds are not on my list of sensible things to try.

Some of them have a degree of sense in mining.
If you are to selectively leach E-waste it is only going to be the plating and that is not where the majority of the values are.
Better use the pure chemicals for it then, Cyanide, Ferro/Ferri Cyanides, Iodide/Iodine leaches and so on.

Still that is just a small part of the values.

The material that I want to process has 64% of its gold in plating areas, unlike normal PCB's which has more than 90% of gold in IC's, also have material that only has plated pins without IC's so 100% of its gold is plated.

 

[nickvc]

JinChan supplier which is well-known GDA supplier in China, mentioned to me that increasing PH more than 11 will make issue with cementing with zinc, so I don't think using caustic soda is a good idea, but don't have an idea about using aluminum foils, I think zinc much reactive than aluminum in cementing process

I was assuming you were using proper cyanide leaching not one of the pain causing Chinese alternatives that may well strip the gold well but are really not good in letting it go again.
With a normal cyanide solution if you add aluminium foil and it changes color to a beige or brown it shows you still have gold in solution and simply adding it after you think you have all your gold will scavenge virtually all the gold left, it is also very easy to recover your gold , rinse foil carefully with water and dissolve in HCl .

 

[Sy-Spark]

This week I ran couple tests batches with cyanide leaching and gold dropping using zinc, I noticed that I can save the filtration time before adding zinc by using CIL method, but I wonder if AC have the same gold recovery rate like zinc?

My plan is to daily run 100 kg of high grade gold plated motherboards, by testing there is 0.14 of pure gold per 1 kg of plated material, so per 100 kg we have 14 grams of gold, to accelerate the process I'm willing to use a flat 90 liters plastic pool, with 60 liters of 1% cyanide solution, then add 4 fabric bags of AC in the pool corners, total weight of AC is 1 kg, cyanide solution temperature between 60c to 40c, then I will leach 10 kg of plated PCB's per batch till I finish the 100 kg, then keep the AC for more one hour before ash it and start gold recovering.

Will this method be effective enough to recover most of the gold? How I can make sure that 1% cyanide solution will not dissolve gold again from AC? I read that it should be heated more than 130 c degrees to make cyanide dissolve gold from AC but also noticed that @Deano mentioned that leaching AC in concentrated cyanide is enough to make gold dissolve again in cyanide.

 

[Deano]

Gold cyanide will start to elute from activated carbon at around 90C in the presence of dissolved caustic and cyanide.
It will not noticeably elute at lower temperatures, the entire elution process is thermally controlled.
The standard leach liquors for gold are 1 gram sodium, potassium or calcium cyanide per litre of leach liquor with pH 11 achieved by addition of caustic or saturated lime water.
Dissolved oxygen level in the leach liquor must be around 7 ppm, any lower will slow the leach rate noticeably.
Do not think that you can add peroxide to keep the DO level high, it will speed up the leach rate but will also destroy the cyanide.
DO levels are usually kept around 7 by plunging the leach liquor into the leach vat by the pump used to circulate the liquor into the leaching vat.
Keeping a constant flow of liquor through the vat will maximise the leaching rate and also the loading rate of gold onto the carbon.
Make sure that the carbon has been attrition and then washed before used in order to minimise gold losses on any carbon fines.
DO levels are usually measured using a hand held meter, buy by price as they are all of similar standards.
Deano

 

[Sy-Spark]

Gold cyanide will start to elute from activated carbon at around 90C in the presence of dissolved caustic and cyanide.
It will not noticeably elute at lower temperatures, the entire elution process is thermally controlled.
The standard leach liquors for gold are 1 gram sodium, potassium or calcium cyanide per litre of leach liquor with pH 11 achieved by addition of caustic or saturated lime water.
Dissolved oxygen level in the leach liquor must be around 7 ppm, any lower will slow the leach rate noticeably.
Do not think that you can add peroxide to keep the DO level high, it will speed up the leach rate but will also destroy the cyanide.
DO levels are usually kept around 7 by plunging the leach liquor into the leach vat by the pump used to circulate the liquor into the leaching vat.
Keeping a constant flow of liquor through the vat will maximise the leaching rate and also the loading rate of gold onto the carbon.
Make sure that the carbon has been attrition and then washed before used in order to minimise gold losses on any carbon fines.
DO levels are usually measured using a hand held meter, buy by price as they are all of similar standards.
Deano

Thanks Deano.

With leaching gold ore we usually use 1 to 1.5 grams of sodium cyanide per liter of water, and make water circulation into vat, usually leaching time be between 1 to 3 weeks depends on weather temperature, it's very hard to figure out if all gold dissolved or not, so if we are not in hurry we wait for 3 or maybe 4 weeks.


But with E-waste, we can notice the gold dissolving easily, usually gold plated on plated nickel so extra cyanide will not make issues and will not be consumed on copper, I didn't try the plan I supposed yet, but I think its more faster than using low concentrated cyanide with low dissolved oxygen, isn't it? Unless I didn't notice another issue.


7 ppm of DO is too low, I think DO in tap water is between 5 to 14 ppm, so little doses of peroxide will be more than enough, friend of mine advised me to add 0.36 ml of 35% peroxide per liter of water, you insured his advice.

One thing I want to make sure about, when using AC, gold ion's will be absorbed so CN will freed up and be available again to dissolve gold, isn't it?

Is 20 grams of AC with 6 hours in CIL design is enough to absorb most of the gold?

 

[Deano]

When gold cyanide complexes are adsorbed onto activated carbon the entire complex is adsorbed.
This means that you will have less cyanide in solution as the gold cyanide complexes are adsorbed.
Most operators use a handheld meter to check the free cyanide level during leaching, this lets them know how much make-up cyanide needs to be added over the time of the leach.
Cyanide losses will occur from volatilisation, adsorption onto carbon and formation of complexes with non-gold metals such as copper.
Cyanide will oxidise by reacting with dissolved oxygen in the leach liquor, the more free oxygen in the liquor the faster the rate of cyanide oxidation.
Yes you can speed up the leaching rate of gold by keeping the DO level high but you will also speed up the oxidation rate of the cyanide, there are no free rides.
This is why operators regularly check the DO and free cyanide levels in the leach.
Decades of experience have shown that the DO minimum level should be around 7ppm, lower levels will slow the leaching rate of the gold and much higher levels will speed up the oxidation rate of the cyanide more than the gold leaching rate.
Adsorption of gold cyanide onto activated carbon is a relatively slow process.
Most operators use a pump to circulate the leach liquor through the gold containing ore or gold bearing substrates in order to maintain high leaching rates.
This pumped liquor usually also passes through a packed column of carbon to give the fastest rate of gold adsorption onto the carbon.
Multiple columns in series are commonly run to speed up the gold adsorption rate.
The return liquor is plunged into the leaching vat in order to keep the DO level high.
Deano

 

[Sy-Spark]

When gold cyanide complexes are adsorbed onto activated carbon the entire complex is adsorbed.
This means that you will have less cyanide in solution as the gold cyanide complexes are adsorbed.
Most operators use a handheld meter to check the free cyanide level during leaching, this lets them know how much make-up cyanide needs to be added over the time of the leach.
Cyanide losses will occur from volatilisation, adsorption onto carbon and formation of complexes with non-gold metals such as copper.
Cyanide will oxidise by reacting with dissolved oxygen in the leach liquor, the more free oxygen in the liquor the faster the rate of cyanide oxidation.
Yes you can speed up the leaching rate of gold by keeping the DO level high but you will also speed up the oxidation rate of the cyanide, there are no free rides.
This is why operators regularly check the DO and free cyanide levels in the leach.
Decades of experience have shown that the DO minimum level should be around 7ppm, lower levels will slow the leaching rate of the gold and much higher levels will speed up the oxidation rate of the cyanide more than the gold leaching rate.
Adsorption of gold cyanide onto activated carbon is a relatively slow process.
Most operators use a pump to circulate the leach liquor through the gold containing ore or gold bearing substrates in order to maintain high leaching rates.
This pumped liquor usually also passes through a packed column of carbon to give the fastest rate of gold adsorption onto the carbon.
Multiple columns in series are commonly run to speed up the gold adsorption rate.
The return liquor is plunged into the leaching vat in order to keep the DO level high.
Deano

"AC will adsorb cyanide"I think this is why some gold miners don't make cyanide solution go again to the vat after it been contacted the AC. So they leach for one time after finishing they make the cyanide solution go throw AC pulps and never make it back to the leaching tank.

Yesterday I leached about 9 kg of high plated PCB's with 15 liters of cyanide solution as a test, after finished leaching I poured the washed AC (150 grams, expected gold is 1.4 grams)into a bucket with the cyanide solution, I only used small fish air bubbler, the distance between the AC at the bottom and the surface of the solution is about 40 cm, I did some manual stirring from time to time, will wait 12 hours before ash the AC, will that be enough or agitation is not enough?

 

[Deano]

Carbon levels in adsorption tanks where the carbon is agitated by gentle stirring or similar methods are usually around 5 to 7 grams per litre.
Stirring should be continuous otherwise the contact time is greatly increased and you will not know what the actual agitated contact time is.
What you are looking to find out is what contact time should apply for the carbon so that you can apply that as a standard method for extraction of the gold.
A bubbler will certainly work provided there is enough agitation supplied by the bubbles.
I cannot tell you what the contact time should be when I have no idea of what you consider to be suitable levels of agitation.
You can always check the adsorption level by removing the carbon after 12 hours, replacing it with an identical batch of fresh carbon and contacting under the same conditions for a further 12 hours.
The quantity of recovered gold from each cycle will tell you what contact time is required for that ratio of carbon to liquor containing that level of gold with that amount and type of agitation being used.
Deano