Help with Ore Processing

Gold Refining Forum

Help Support Gold Refining Forum:

This site may earn a commission from merchant affiliate links, including eBay, Amazon, and others.

Aeon13

Well-known member
Joined
Nov 17, 2015
Messages
91
Location
Philippines
Good day to all! I am new to gold refining and other gold processing techniques. Thanks to this forum and members I have learned a lot already with just a short time. I would like to show you guys the processing of gold ores used by my uncle. They extract these ores from the mountains, grind it then leach it with cyanide. This is how they do it. They put these ground ore into the first stage (leaching) and wait for the liquid going to the second stage which contains the liquid gold. This second stage is then pumped to a container but first they will mix zinc powder prior to it.Then a filter is placed on the container to recover the powder which has gold in it . The liquid at the container is then pumped back to the first stage. They do this process for about 6-7 cycles. Then they get the filtered material for smelting.
Do you guys have any opinion on how to improve this system that they use? My uncle and his colleagues are small scale miners. It breaks my heart to see the things they do to get these ores. Specially the way they go inside the portal with just a blower used to supply oxygen inside. There has been death related to oxygen depletion while inside these portals . These portals range from 100-500 meters as of today. They also don't have any support placed in these portals. They know the risk yet they do it to live. I want to help them by maximizing the amount of gold that they may recover. This is the reason for me joining and posting here. I know that people here are kind and helpful. I read many topics already here by the way. I just did't find a complete process which looks like my uncle's set up. I will post the actual pictures once I have the time to visit them again.
Thanks in advance. More power and Godbless.
 
The processing system as you have described it is a small scale version of how the large mines processed gold ore before carbon in pulp processing took over the industry.

It would probably not be warranted to try to change the processing route as a whole lot of new skills and equipment would be required.

This leaves the possibility of improving the efficiency of the existing plant.

The standard residence time of ore in a processing plant is around 24 hours.

If they are running multicycle processing it is an indication that either or both of the following is occurring.

If coarse gold is present in the ore then it will take longer to dissolve. Use a small jig or table to remove this coarse gold from the ore before leaching.

The coarse gold can be direct smelted if cleaned up enough, or treated by intensive cyanidation in a separate small circuit.

If the ore is not milled finely enough then it takes the cyanide solution a long time to penetrate the fissures in the ore particles to access the gold. Use finer milling to speed up the leaching.

Warning

If there is gold in sulfides then you can get a phenomenon called overmilling of sulfides where the recoverable grade of gold drops when very fine milling of the ore occurs.

Do some milling tests followed by leaching tests to establish the best grind size for your material.

Some sulfide ores require an extended leach time to dissolve the gold even at the optimal grind size, if this is so with your ore then there is very little that can be done to speed up the leach cycle.

I am not even remotely likely to comment on actual mining procedures, this is a legal minefield.

My experience is that most small scale miners who have been in operation for several years have a pretty good working knowledge of the practical side of the operation.

Generally they have developed methods which suit them and their site and at best only need small tweaks to their systems.

It may appear to someone unfamiliar with mining that they are working under unsafe conditions and using outdated techniques.

Usually the operators who are actually using unsafe methods have been culled from the mining business early on in the game.


Deano
 
Deano said:
The processing system as you have described it is a small scale version of how the large mines processed gold ore before carbon in pulp processing took over the industry.

It would probably not be warranted to try to change the processing route as a whole lot of new skills and equipment would be required.

This leaves the possibility of improving the efficiency of the existing plant.

The standard residence time of ore in a processing plant is around 24 hours.

If they are running multicycle processing it is an indication that either or both of the following is occurring.

If coarse gold is present in the ore then it will take longer to dissolve. Use a small jig or table to remove this coarse gold from the ore before leaching.

The coarse gold can be direct smelted if cleaned up enough, or treated by intensive cyanidation in a separate small circuit.

If the ore is not milled finely enough then it takes the cyanide solution a long time to penetrate the fissures in the ore particles to access the gold. Use finer milling to speed up the leaching.

Warning

If there is gold in sulfides then you can get a phenomenon called overmilling of sulfides where the recoverable grade of gold drops when very fine milling of the ore occurs.

Do some milling tests followed by leaching tests to establish the best grind size for your material.

Some sulfide ores require an extended leach time to dissolve the gold even at the optimal grind size, if this is so with your ore then there is very little that can be done to speed up the leach cycle.

I am not even remotely likely to comment on actual mining procedures, this is a legal minefield.

My experience is that most small scale miners who have been in operation for several years have a pretty good working knowledge of the practical side of the operation.

Generally they have developed methods which suit them and their site and at best only need small tweaks to their systems.

It may appear to someone unfamiliar with mining that they are working under unsafe conditions and using outdated techniques.

Usually the operators who are actually using unsafe methods have been culled from the mining business early on in the game.


Deano

Thank you Deano for your reply. Then I guess there will be no more improvement that can be done with the system. I have read a process of leaching using starch. Do you know anyone who used this method? I also read about purging air into the pulp would improve leaching. If this is true, would it be practical to do it with this set up?
I will continue to read here and I'm sure I will learn many things. Thank you again!

Mohammed
 
Leaching using starch is a method where the dissolved gold is collected on undissolved starch similarly to collecting the gold on activated carbon.

There are a great number of similar adsorbent systems none of which have been commercialised.

Most of them remain interesting research projects which did not advance the systems enough to become used industrially.

Air is usually introduced into the pulp by the agitation system used to keep the pulp mixed.

Extra air is generally only required when high organic or sulfide loads are part of the ore.

I would be very surprised if the operators had not carried out tests to see if this was needed.

Deano
 
Deano said:
Leaching using starch is a method where the dissolved gold is collected on undissolved starch similarly to collecting the gold on activated carbon.

There are a great number of similar adsorbent systems none of which have been commercialised.

Most of them remain interesting research projects which did not advance the systems enough to become used industrially.

Air is usually introduced into the pulp by the agitation system used to keep the pulp mixed.

Extra air is generally only required when high organic or sulfide loads are part of the ore.

I would be very surprised if the operators had not carried out tests to see if this was needed.

Deano
Thanks again for the fast reply Deano.
I think there no tests carried out. They are not really that informed about the elements present in these ores. They just get it then process it with this setup. I was surprised myself after talking to them. They don't even know how the "Karat" measurement of gold is done and its importance. The buyers here pay them in based on the specific gravity.They for a fact don't also know these numbers as specific gravity.They just know it as a measurement for the price. 19.2 is the highest and the lower the measurement the lower the price. I learned that the specific gravity of pure gold is 19.3. I want to explain these things to them but its hard with their situation and considering that I'm much younger than them makes my opinions less significant :mrgreen: . I want to ask your opinion though. Is it right to base the gold price on the specific gravity of gold or much better using gold test kits with acids?
Thanks again!
 
Please give us a better description of your uncle's process or we may make suggestions that do not apply or make no sense because we have only a vague understanding of what your uncle is doing.

How small does he crush the ore? Like fine sand?
Is the ore leached in a vat or in a heap piled up on a plastic sheet?
Are chemicals like lime added to stabilize the cyanide?
Is the leach solution de-aerated before it is exposed to the zinc?
Does he pre-treat the zinc with lead Nitrate?
Does he recover only gold or is there significant silver present also?
How does he filter out the zinc to capture it and make sure none is lost?
Does he test the gold solution to know when to add more zinc?
Does he test the ore to know when it is fully leached?
Does he melt the gold and pour a bar or sell the raw zinc-gold powder to the buyer?

The success of this process is in the details of operating it. If operated improperly it can be inefficient. If operated properly it can be very efficient.
If we do not know the details, it is tough to make useful suggestions.

Raw gold is best tested based on an assay of the raw dore bar. That is how it is done by most gold buyers/refiners in the US. Only smaller scale operators use scratch tests and touchstones with acids. The acid test kits are made for testing jewelry that is normally certain Karat purity like 14K or 18K. Assays give a more exact result. Many buyers that purchase gold at remote mine sites pay only a small percentage of the spot gold price. I don't know that this applies to your uncle, but it is common.
 
Reno Chris said:
Please give us a better description of your uncle's process or we may make suggestions that do not apply or make no sense because we have only a vague understanding of what your uncle is doing.

How small does he crush the ore? Like fine sand?
Is the ore leached in a vat or in a heap piled up on a plastic sheet?
Are chemicals like lime added to stabilize the cyanide?
Is the leach solution de-aerated before it is exposed to the zinc?
Does he pre-treat the zinc with lead Nitrate?
Does he recover only gold or is there significant silver present also?
How does he filter out the zinc to capture it and make sure none is lost?
Does he test the gold solution to know when to add more zinc?
Does he test the ore to know when it is fully leached?
Does he melt the gold and pour a bar or sell the raw zinc-gold powder to the buyer?

The success of this process is in the details of operating it. If operated improperly it can be inefficient. If operated properly it can be very efficient.
If we do not know the details, it is tough to make useful suggestions.

Raw gold is best tested based on an assay of the raw dore bar. That is how it is done by most gold buyers/refiners in the US. Only smaller scale operators use scratch tests and touchstones with acids. The acid test kits are made for testing jewelry that is normally certain Karat purity like 14K or 18K. Assays give a more exact result. Many buyers that purchase gold at remote mine sites pay only a small percentage of the spot gold price. I don't know that this applies to your uncle, but it is common.


Thanks for the reply sir Reno. I apologize for giving such vague information. I am new to this thing and is continuously learning from you guys. Yes I know how these buyers are most of the times abusing small scale miners like my uncle and his colleagues. This is one reason I want to learn this field and help them make the most out of it. Besides, they do the hard and dangerous work. I think assay testing is not accessible here in our place. The buyers pay them based on the specific gravity of the end product.

About your questions.

How small does he crush the ore? Like fine sand?- the size is like sand (not fine)
Is the ore leached in a vat or in a heap piled up on a plastic sheet? they use heap leaching
Are chemicals like lime added to stabilize the cyanide? yes they add lime
Is the leach solution de-aerated before it is exposed to the zinc? He does not do this. How is this process done?
Does he pre-treat the zinc with lead Nitrate? no, He just add the zinc dust.
Does he recover only gold or is there significant silver present also? silver is also present and he is able to recover also.
How does he filter out the zinc to capture it and make sure none is lost? This I have to verify. I was not able to see the filtering inside the container. What would you prefer for him to use in this stage?
Does he test the gold solution to know when to add more zinc? No, I guess he based this on his experience and these are things that I want to help them. Maybe he is not doing it efficiently.
Does he test the ore to know when it is fully leached? This is also not done. But he repeats the cycle six times to ensure that all gold is recovered. In what way can we test the ore?I want to help him by making a stannous chloride solution for the pregnant solution.
Does he melt the gold and pour a bar or sell the raw zinc-gold powder to the buyer? He melts the gold using coal. This process makes the end product a bit dirty. I watched guys melt gold using OXYACETYLENE and the result is much better.

I cannot express enough my gratitude with the help you are giving me. Please know that your not only helping me but also the small scale miners that I will be sharing what will I learn from your knowledge. These miners are humble, caring and hardworking people. In behalf of them. Thank you very much.


Mohammed
 
Mohammed:
I can give you many thoughts and suggestions as I have set up an run an operation like this in the USA (Nevada). I have written mining magazine articles on how to do this.
Before I give you my thoughts and suggestions, I have a few more questions based on your last answers.

How does he put the ore onto the heap pad? (what equipment does he use?)
How deep is the ore piled onto the pad?
When he believes the gold is leached out, does he push the old ore off the heap leach pad and add more on; or is he able to build the pad further and keep adding more ore on top?
Does he have enough space to enlarge the pad?
How long does he put the cyanide leach waters on the pad?
In the 6 or 7 times, does he put all the cyanide liquid on, wait a couple days as it drains out, and then after processing to collect the gold out of the liquid, then re-apply the liquid?
How long does one "leaching cycle" take?
How does he apply the cyanide solution to the heap? Sprinklers? Drip lines? Some other way?
What sort of pump does he use?
How much silver is present? More silver than gold by weight or only a little silver, mostly gold. Is the final bar gold colored or silver?
Is there any visible gold that can be panned out of the ore before it is processed on the heap pad?
Is there any pyrite or sulfide minerals in the ores put on the pad?

If you will provide me these further details, I promise to give you an extensive answer with many possible suggestions to improve his process.
 
This looks like it could become another one of those meat & potatoes threads filled with lots of good info - maybe even end up in the library 8)

Mohammed - you have come to the right place to ask questions & learn & you have two of the best helping you so far (Deano & Chris) when it comes to the mining & processing of ore

There are others here that are "world class" in their knowledge of PM (Precious Metal) recovery & refining that can help with improving your families operation including but not limited to things such as doing actual assays, melting/smelting & alternate methods of processing &/or recovery

I look forward to seeing this thread progress

Kurt
 
Reno Chris said:
Mohammed:
I can give you many thoughts and suggestions as I have set up an run an operation like this in the USA (Nevada). I have written mining magazine articles on how to do this.
Before I give you my thoughts and suggestions, I have a few more questions based on your last answers.

How does he put the ore onto the heap pad? (what equipment does he use?)
How deep is the ore piled onto the pad?
When he believes the gold is leached out, does he push the old ore off the heap leach pad and add more on; or is he able to build the pad further and keep adding more ore on top?
Does he have enough space to enlarge the pad?
How long does he put the cyanide leach waters on the pad?
In the 6 or 7 times, does he put all the cyanide liquid on, wait a couple days as it drains out, and then after processing to collect the gold out of the liquid, then re-apply the liquid?
How long does one "leaching cycle" take?
How does he apply the cyanide solution to the heap? Sprinklers? Drip lines? Some other way?
What sort of pump does he use?
How much silver is present? More silver than gold by weight or only a little silver, mostly gold. Is the final bar gold colored or silver?
Is there any visible gold that can be panned out of the ore before it is processed on the heap pad?
Is there any pyrite or sulfide minerals in the ores put on the pad?

If you will provide me these further details, I promise to give you an extensive answer with many possible suggestions to improve his process.

Wow! Its an honor sir Reno Chris. I really came at the right place this time. And to have information from such a professional in the mining field. I am grateful.

About your questions, I have to go back there at mines and ask again for me to have accurate answers. I will also take pictures of the system employed. By this, I hope I can show you the exact process being done.

Thank you so much sir Reno Chris and every one here in the forum. I will post here as soon as I get the information.

Mohammed
 
kurtak said:
This looks like it could become another one of those meat & potatoes threads filled with lots of good info - maybe even end up in the library 8)

Mohammed - you have come to the right place to ask questions & learn & you have two of the best helping you so far (Deano & Chris) when it comes to the mining & processing of ore

There are others here that are "world class" in their knowledge of PM (Precious Metal) recovery & refining that can help with improving your families operation including but not limited to things such as doing actual assays, melting/smelting & alternate methods of processing &/or recovery

I look forward to seeing this thread progress

Kurt

Hi Kurt! Yeah I really came at the right place. You guys here in the forum are really very helpful. I learned so much already with just less than 10 posts that I made(But a lot to read here). This thread was made for the sole purpose to help these miners in our place. I saw their situation and how they get ores and its is really a very hard and risky job. That's why I want to help them improve and maximize their profit.Also, everyone having the same concern will benefit reading these thread because such "world class" individuals are contributing with priceless knowledge that they have. I am humbled by people of great experience and knowledge that share these with inexperienced people that they don't even know personally. I am grateful (I am always repeating these words because I can't really express how grateful I am,please forgive me if it annoys some).

Thanks for the reply Kurt.

Mohammed
 
"world class" may be a bit much, but I am competent and experienced to help with getting the best recovery that is possible in a practical way for a small scale operation. I'll keep an eye on this thread for future answers.
 
Heap leaching was developed as a low cost technique for extracting gold and silver from lean and low grade ores. Heap leaching is very inexpensive on a cost per ton basis. Most mines will put anything that grades .01 oz/ton or better on the heap. All the heap consists of is a large area covered with a heavy duty, thick plastic sheet, graded to drain to a central point. Gold bearing rock is stacked in a big heap on the sheet up to 50 or even 100 feet deep and then sprinkled with a weak solution of cyanide. Millions of ounces of gold are recovered annually from this type of operation all over the world. It is very common in my home state of Nevada. The cyanide solution dissolves gold and silver and the liquid drains down to a central point where it is pumped through a recovery plant and the gold and silver are extracted. Additional cyanide is added to the solution as necessary, and it is then recycled and put back onto the heap to dissolve more precious metals. Heap leaching is not really rocket science. Basically all you are doing is irrigating piles of rock.

How does he put the ore onto the heap pad? (what equipment does he use?)
One of the common problems in constructing a heap to be leached is that when materials are put onto the pad they tend to form channels. The coarse material forms a shell around the outside and the liquid will flow through these channels and miss the interior part. I have attached an image to show the concept of what this channel segregation looks like. The more fine material like clay which is present in the ore, the greater the tendency is for this channeling. This means that solution will flow through certain channels within the heap, avoiding other areas, so that these isolated spots do not receive sufficient solution and therefore the gold and silver within them is not recovered. If there are dry spots within the heap when it is removed after leaching is completed, those dry spots did not get processed and the gold within them still remains in the ore.

How long does he put the cyanide leach waters on the pad?
The gold and silver take a long time to be removed by the heap leach process. The majority will come out within a few weeks, but smaller amounts will continue to come out for months and even years. It is normal for heap leach operations in Nevada, USA and to spend years processing the material on the heaps. For small operator there is a point of limited return when you are not getting enough out of the pile to make it worth your time, but your uncle may not be leaching his rock long enough to get the gold that is possible out of the rock. When I was running a small scale heap leach operation, we would leach the ore for about six weeks to two months before we pushed it off and loaded new material on.

How does he apply the cyanide solution to the heap? Sprinklers? Drip lines? Some other way?
Once the heap is built, the solution has to be applied to the heap in the most efficient manner. Early heaps commonly used various types of sprinklers to apply the solution. In time it was realized that there were problems with losses created by the over spray from sprinklers or splashing. Sprinkler heads also sometimes fouled with the solutions when they dry. In constructing the facility, only plastic or black iron pipe can be used for handling cyanide solutions, as zinc, copper and brass are all dissolved by the cyanide solution. The best method of applying the solution to the heap is by using plastic agricultural drip irrigation lines. Perforated plastic irrigation line is inexpensive, easy to lay out and offers few problems even after continued use. It also can be laid out to cover the sides of the heap pile better as often the sides do not get the full amount of solution needed to leach them. Multiple lines of perforated plastic line are laid out on top of the heap and manifolded to a pump and piping system.

Is there any visible gold that can be panned out of the ore before it is processed on the heap pad?
Cyanide will dissolve gold particles either large or small, but it takes a long, long time to dissolve large pieces. A piece of gold the size of a coin might take several hundred years to dissolve. In general, particles large enough to be recovered by panning or other gravity based methods should not go on the heap as they take too long to dissolve. It is very common that systems are constructed to process gold ores which have both a gravity circuit to capture the coarser gold particles, and a cyanide circuit to capture the fine dust sized particles and those too small to see without strong magnification.
 

Attachments

  • heap_segregation02.jpg
    heap_segregation02.jpg
    336.7 KB · Views: 597
Deano said:
If there is gold in sulfides then you can get a phenomenon called overmilling of sulfides where the recoverable grade of gold drops when very fine milling of the ore occurs

May i ask what would you describe as "very fine milling"? Would 100% -150 mesh for example be very fine?

This is so good thread, i mean that this kind of practical approach would be hard to find from literature.

Salud

Finn
 
Overmilling of sulfides is totally dependent on the ore sample. different mines will have different milling levels at which this phenomenon occurs.

The effect is related to the level of interferent species present in the ore, the more interferent present the coarser the grind at which overmilling occurs.

Generally the effect occurs with milling below 75 micron or 200 mesh.

I have seen it at 100 microns and I have seen one very clean ore where it was totally absent.

This is why I use the term "generally" in answers.

Deano
 
hello I'm back guys.
Sir Reno Chris I was able to go down to the mines and ask your questions as well as take some pictures. I am a little hesitant about my answer if the process is using vat or heap leaching because I think I have a little understanding of the difference of the two. Please forgive me for this. I have attached the actual picture of the pad. About your questions.

Does he pre-treat the zinc with lead Nitrate? Yes he adds lead to the zinc dust.(I verified this and he said he is adding lead but did not use it while I was watching him last time)
How does he filter out the zinc to capture it and make sure none is lost? He filters the zinc with gold powder using satin fabric. 4 layers of satin is placed. I will put some pictures of this.
How does he put the ore onto the heap pad? (what equipment does he use?) They just put the ore manually. By the way they mix the ore with lime like mixing cement with sand before they put the mixture on the pad.
How deep is the ore piled onto the pad? About 3.3 feet. Just small space to full
When he believes the gold is leached out, does he push the old ore off the heap leach pad and add more on; or is he able to build the pad further and keep adding more ore on top? They remove the old ore and replace it. I helped them "pull out" the old ore while I was there. not easy, my hand got some calluses now :mrgreen: )
Does he have enough space to enlarge the pad? Yes he has enough space to enlarge
How long does he put the cyanide leach waters on the pad? 5 days before draining cycle.
In the 6 or 7 times, does he put all the cyanide liquid on, wait a couple days as it drains out, and then after processing to collect the gold out of the liquid, then re-apply the liquid? This is the complete process. After putting cyanide he will wait 5 days without draining. After 5 days he drains it. After draining, the solution from the blue tank will go back in the leach pad. This will take 5 hours again to drain. This cycle of draining is done 6-7 times.
How long does one "leaching cycle" take? It takes 5 days plus 30 hours of the draining cycle.
How does he apply the cyanide solution to the heap? Sprinklers? Drip lines? Some other way? This is done just by putting the cyanide solution into the pad in just one point.
What sort of pump does he use? I placed a picture of the pump
How much silver is present? More silver than gold by weight or only a little silver, mostly gold. Is the final bar gold colored or silver? He told me that there is more silver than gold. The final bar is colored gold.
Is there any visible gold that can be panned out of the ore before it is processed on the heap pad? He did saw this but it is very rare.
Is there any pyrite or sulfide minerals in the ores put on the pad? They don’t put pyrite. I saw some pyrites outside the portal. They remove this and don't mix it with the ore. As for the sulfide, we both don’t know physical appearance of this.
 

Attachments

  • leach pad.png
    leach pad.png
    25.9 KB · Views: 542
This is the actual leaching pad. The original level of the pad is the one with the lighter color of ore. My uncle is the one wearing black shirt.
 

Attachments

  • HPIM0010.JPG
    HPIM0010.JPG
    1.8 MB · Views: 538
Back
Top