# Leaching ore with Aqua Regia



## hokeypokey (Aug 25, 2014)

Please tell me if I understand this right or wrong. I fully understand that you cannot leach ore unless cyanide heap leaching is a possibility for you. It sounds simple to leach concentrate though. Say that one gravity concentrates a few tons of ore down to a few gallons of material. Next would be to split those few gallons into smaller batches for easier handling. The next and most important step would be to remove the base metals with nitric. I have read different formulas for this. Some call for 50% nitric and 50% distilled water to 10% nitric and 90% distilled water. I'm not sure the pre-leach formula is that strict. The way I understand it is when you remove the base metals the ore concentrate could be easily leached with Aqua Regia. No base metals to pull your gold from the leach back down into the cons your leaching. Would leaching ore concentrate with the base metals removed be the same as leaching gold shot mixed with sand?


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## Reno Chris (Aug 25, 2014)

Right. There have been dozens of threads on this topic. Take a look with a search and do some reading. Its almost never a good idea to leach hard rock ore with AR. Cheaper to just buy some gold. So what are you going to do with the base metals you leach out of the ore materials? Lead,iron and zinc are all common base metals in ores, and yes they can leach with AR. Normally most folks who ignore the advice against it end up with a gigantic mess and no gold.


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## hokeypokey (Aug 25, 2014)

Thanks for your response Reno Chris. To answer your question, I plan to do nothing with the base metals that are removed from the ore concentrate but dispose of them properly along with the nitric pre-leach. Please remember that I'm not removing the base metals from ore but removing base metals from the ore concentrate. There isn't going to be a lot of material involved in this process. I'm planning to take very careful steps on very small batches of concentrate so I'm not jumping into this head first.


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## Harold_V (Aug 26, 2014)

hokeypokey said:


> Please remember that I'm not removing the base metals from ore but removing base metals from the ore concentrate. There isn't going to be a lot of material involved in this process.


At least not until you start using acid, that is. I think you're in for a rather unpleasant surprise, although I could be wrong. 

If you digest with nitric alone, you won't remove everything that can be removed. That will complicate succeeding operations, perhaps yielding a solution that will be difficult, if not impossible, to filter, as the AR will digest those substances. 

If you insist on using acids (almost never acceptable for processing an ore), my advice to you is to roast the hell out of the ore before you start, to eliminate any possible sulfides. I would then process with HCl, to remove the vast majority of contamination, including, possibly, some of the gangue. I would then roast once again, then finish up with dilute nitric. At that point you may be pleasantly surprised to find you have only a few cups of material. Or not.

I processed about eight gallons of sulfides (concentrate) many years ago, with an abundance of finely divided visible gold. I did exactly as I described, with a recovery of several ounces. I ended up with about a quart of solids Had the yield not been what it was, it wouldn't have been worth the trouble. All of the operations are very demanding of time and energy, to say nothing of a large volume of acid. 

If your concentrate doesn't indicate several ounces per ton, you're spinning your wheels. 

It will work. The question is, is it worth the time and effort? 

Harold


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## hokeypokey (Aug 26, 2014)

Thank you for that process Harold. I know the advice you give here on this forum is as good as gold and I appreciate your giving it to me. I will test a small batch just the way you suggested. Roast, leach with HCL, roast again then leach with dilute nitric. Next the concentrate should be ready for the removal of precious metals with Aqua Regia. Got it. I do understand that this process is easier said than done. I also understand that there are dangers involved with the use of acids on ore concentrates. It's just that I believe if I do things the right way I can achieve success without contaminating myself and my environment. It may also turn out that this process will be used with smelting being the final recovery method instead of using AR. I'm still crawling with this ore but I will one day be walking then running with it all while keeping my health intact. This I am determined to do.


edited to add the last six sentences


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## Aristo (Aug 26, 2014)

The first thing you need to do is get an assay of your concentrate. Not just a fire assay, but a whole rock assay as well. 
This gives an indication of the nature of the cons as well as its constituent. Until you have the necessary information and an understanding of the concentrate, only then you should try to formulate the process chemistry.
Anything otherwise will be a shot in the dark and you may lose values or further complicate your concentrate.
Above all, be safe.


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## hokeypokey (Aug 26, 2014)

Thanks for that advise Aristo. I had several XRF assays performed on the ore over 10 years ago but no longer have those results on paper. I'm not very good at keeping up with things over long periods of time. I still remember what was in the ore but not the ppm of each except the AU. Never had one performed on the concentrate due to the fact that I didn't have the means to concentrate back then. I did have a fire assay performed two years ago that wasn't too far off from the XRF results. What would a whole rock assay of the cons tell someone like myself? I wouldn't have a clue on how to formulate the process chemistry based on an assay and I find that people with that knowledge consider it proprietary information and rarely are willing to share it without a hefty fee. I don't see this as unfair it's just that I'm not in a position to afford such fees. Shots in the dark are all I have for now but I'm fine with that since this is still just a hobby. I do respect the advise you have given me though.


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## FrugalRefiner (Aug 26, 2014)

hokeypokey said:


> Thanks for that advise Aristo. I had several XRF assays performed on the ore over 10 years ago but no longer have those results on paper. I'm not very good at keeping up with things over long periods of time. I still remember what was in the ore but not the ppm of each except the AU. Never had one performed on the concentrate due to the fact that I didn't have the means to concentrate back then. I did have a fire assay performed two years ago that wasn't too far off from the XRF results. What would a whole rock assay of the cons tell someone like myself?


Well, for one thing, it could tell you if there are any dangerous components in your material, like arsenates.



> I wouldn't have a clue on how to formulate the process chemistry based on an assay


And yet, lacking that information, you feel ready to start treating the material with acids.



> and I find that people with that knowledge consider it proprietary information and rarely are willing to share it without a hefty fee. I don't see this as unfair it's just that I'm not in a position to afford such fees. Shots in the dark are all I have for now but I'm fine with that since this is still just a hobby. I do respect the advise you have given me though.


Shots in the dark are a good way to kill people, even if you're just shooting as a hobby.

I'm sorry if my reply seems harsh. You've received some very good replies from some very knowledgeable people. You should follow their advice.

Dave


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## hokeypokey (Aug 26, 2014)

FrugalRefiner, I didn't think your reply was too harsh. I appreciate your concern. Your statement "And yet, lacking that information, you feel ready to start treating the material with acids". What would the forum expect one to do? Get a college degree in both chemistry and metallurgy before attempting this experiment? Please don't take this as me being a smart butt because that's not my intention. I'm not sitting in my garage with 5 gallon buckets full of acid and ore. I know its easy to imagine that because I'm sure that happens. I'm sure a lot worse than that happens. I have had XRF assays performed and I fully know what is in the ore. There shouldn't be anything in the concentrate that isn't present in the ore. Also I'm planning on testing Harold's process on a very small amount. No five gallon buckets full of acid or even 1000ml beakers for that matter. I'm working with very small samples in an outside area well away from any buildings or people. I admit I'm still crawling here but that doesn't mean I'm ignorant on the dangers of acids and ore roasting. I have used acids before and I have roasting experience. I'm not claiming to be at an expert level either. I didn't start this thread for people to agree with me but rather to see if I had the correct understanding of processing ore concentrate with AR. I appreciate every response I have received including yours.


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## butcher (Aug 26, 2014)

hokeypokey 

This is very hard to explain, but what the guys here are telling you is for your own good, ore is complicated and can be dangerous to try to manipulate, it can be a complete science of its own, and gold or other metal extraction from millions of different types of ore is another science in itself.

Ore can be many different compounds, if it contains free gold metal, the gold can be mechanically separated.

In fact since time began not much gold has been pulled from the earth, and what has been most all of it has been removed as free gold, not gold locked up in a chemical bond with ore and leached free from the grips of the chemical bonds.

If the gold is locked up chemically, say as a sulfide for example or one of the many other compounds (there are many), it will not be set free easily, sulfides are common but they are not the only type of ores, basically, to try and describe this somewhat, metals when dissolved with acids or acidic compounds, or basic compounds we get salts of the metals and the acids, ore can be many different metals and acids or compounds, salts of metals and acids, which form a type of salt or compound of these metals and acids, they can be formed from high temperatures or pressures in the earth, or in a volcano... for example with acidic sulfur compounds these can include metals or several combinations of metals, or metalloids, along with gangue materials like silicates or many other non metals, some of these can produce strong poisons when heated or treated chemically basically the chemistry make up of ores are very complex, not all ore is the same, even in one mountain there can be several different types of ore, and even ore of the mountain of the same mine can have become chemically changed by time or oxidation even changing the chemical makeup of that one type of ore... 

Many of the ores that do contain gold also contain deadly substances when roasted or chemically treated, can be very deadly to deal with.

Every ore is different, not every ore will react the same to the same pretreatment, or leach, or acid or base, or other processes, each has its own chemical make up and each will react differently when you try to treat it thermally or chemically.

Like in any chemistry to get results you need to understand the different chemicals or compounds you are mixing, example say I wish to make table salt, I have to know what chemicals I am using to make it, here in my example I choose Hydrochloric acid and sodium (metal) hydroxide and mix these to pH 7, but if I wanted to make table salt, and I use a known acid like HCl, and threw in an unknown compound like or no telling what, I would get no telling what, and the results would be no telling what, the reaction would be foolish at beat and very likely very dangerous, I would just be making a dangerous solution, and produce no telling what kinds of deadly gases from the reaction, I cannot expect to do chemistry with an unknown ore, and some known acids and produce gold from the ore, or do chemistry mixing things willy-nilly and expect some kind of outcome, at most I could hope to not kill myself, by the many different chemical concoctions I would be producing.

Trying this type of chemistry blindly would be fruitless and just plain stupid.

You need to know what kind of ore or concentrates you are dealing with, what they are composed of, and how they will react to different treatments, heat, acids or any of the many processes used...

You also need to study how others have found the best approach to dealing with that type of ore, or you may have to experiment to find the best approach, in your special case, education is where you will learn, you will need to educate your self about the ore you have, and how to best deal with it, educate yourself on the dangers, educate yourself on recovery methods used, or educate yourself on how to develop one that may work to free the gold in your case.

Mining free gold is one thing, breaking the chemical bonds of gold from ore and to recover that gold is a totally different thing.

I am sure sending man to the moon was simple (for the scientists who did it), shoot him up in a rocket at the right angle so he will hit the moon, mining is similar it is a simple thing, until you begin to learn more about It, and how complicated it actually is...

I am tired and can not explain this well, I hope you get the idea.

Listen to the advice, these guys have spent some time studying and know what they are talking about, and at least enough to help you, it is not as simple as you think it is, that is unless the gold in your ore is free gold, and your concentrate are fairly pure concentrated gold, then you just need to lean to concentrate it mechanically, if it needs leaching you will most likely need professional help or do a ton of study to learn to become a scientist and chemist in the art of gold ores...

Experimenting with acids and ores (especially unknown ore) without educating yourself makes as much sense and playing Russian roulette, and the outcome likely may not be too much different.

This is hard to explain, and I do not think it can be explained (at least by me) in one or a hundred posts, you really will need to educate your self, to understand what we are all trying to say, educate yourself on playing this Russian roulette before you load the gun and pull the trigger...


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## nedrah (Nov 15, 2015)

In the pre-leach process what is the best concentration of the dilute nitric ?


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## Reno Chris (Nov 16, 2015)

> *In the pre-leach process what is the best concentration of the dilute nitric ?*



So which part of "Its a bad idea" do you fail to understand?
Did you not bother to read the posts on this thread?


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## saadat68 (Jun 26, 2020)

Harold_V said:


> hokeypokey said:
> 
> 
> > Please remember that I'm not removing the base metals from ore but removing base metals from the ore concentrate. There isn't going to be a lot of material involved in this process.
> ...


When we roast ores, gold sulfide converts to gold oxide and when digest ores in HCl, gold dissolves in solution. Right?


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## butcher (Jun 26, 2020)

Gold will not oxidize in the roast.
Unless something is added to a roast like salt...

Arsenic along with the many other toxic and dangerous sulfide or other compounds which are a composition of the ore involved, proper assay's will give an idea of the composition and chemical make up of the ore, which will also give you the information to determine which toxic vapors would evolve from roasting the ore.

Most gold mined is free gold, it does not normally need roasting or leaching to recover the gold into a concentrate, it can be recovered using gravity separation for the most part.

Other ore the gold will be harder to recover, and may or may not need some type of pretreatment, floatation of sulfide ore, for example, roasting may or may not improve an ore before a recovery process, determining a leach will depend much on the composition of the ore.

Basically, without proper assays and a decent understanding of the composition of the ore, you do not have any clue of how to properly treat the ore for a decent recovery of the values, you also do not know what deadly gases it will form.

Gold does not dissolve in HCl.


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## saadat68 (Jun 27, 2020)

Thank you butcher
So how we should recovery gold from sulfide ores with aqua regia? Does gold sulfide dissolve in AR?


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## saadat68 (Jun 27, 2020)

butcher said:


> Gold will not oxidize in the roast.
> Unless something is added to a roast like salt...
> Gold does not dissolve in HCl.



Do you mean gold or gold sulfide? I mean gold sulfide in ores, Not free gold.


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## butcher (Jun 27, 2020)

It does not make much sense to me to be spending my time discussing leaching ore, for gold with aqua regia, free gold on quartz maybe but then we have better recovery methods.

Gold ores bound up in a sulfide matrix, while roasting can break the sulfide bond, to attempt leaching with aqua regia would be just a dangerous waste of time and acids.



Gold will not oxidize when bringing the temperature of finely ground ore up to a red hot heat and then holding that temperature for an hour while stirring or raking the ore to keep exposing the red hot mass to atmospheric air or a stream of oxygen.


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## saadat68 (Jun 27, 2020)

If we convert sulfide gold to oxides with roasting, Is there any chance for gold dissolving in HCl or nitric in this process:

Roasting sulfide ore > Digest in HCl > Roast again > Digest in nitric acid > Recovery gold with AR


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## butcher (Jun 27, 2020)

if I have a mountain of sulfide ore available to mine, with a mineral content that could be profitably mined roasting and aqua regia would be the last thing on my mind. 

Proper sampling and assays would be the first thing on my mind, then the work and logistics of planning on how to most cost-efficiently get that mountain of ore moved out of the ground and transported to where it can be ground up to a fine powder. 

The assays from this point will give me clues to the best choice of pretreatments that may be needed for any pretreatment or recovery process and before any leaching or attempt at the dissolution of the values, along with experimenting on the ore itself to find best recovery methods, as well as using the information on how that type of ore--from that part of the country in mines similar to yours is treated for the most effective recovery of metals for all of the labor equipment and other expenses involved...

Only after the gold was recovered would I begin thinking of using aqua regia to refine it.


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## butcher (Jun 27, 2020)

If the gold is bound up in sulfides, so are the other metals involved in the minerals composition, you would consume a heck of a lot of your acids leaching these other metals.

No mine in the world takes tons and tons of sulfide ore and cooks it red hot and leaches it with aqua regia, any miner attempting to do so would go broke soon, that is if he did not poison himself trying to get gold out of the rock first.


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## saadat68 (Jun 27, 2020)

I don't want recovery gold from ore but someone ask me this question. Here many peoples recovery gold from sulfide and oxide ores with aqua regia (here there is no free gold like north america). Of course the amount of gold in those ores is very high (for example 3 or 4 gram in one kilogram of ore) :shock:


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## butcher (Jun 27, 2020)

They should learn better recovery methods.


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## butcher (Jun 27, 2020)

saadat68,
How much do you know about the mining in your area, how the gold was recovered and processed historically, and how it is done today? 

Do you know of all of the processes involved with the ore before it sees aqua regia in the mining industry in your area?

I just cannot believe someone is mining a ton of rock of sulfide composition roasting it and attempting to dissolve the gold out of the ton of powdered ore with aqua regia for an ounce of gold.

Maybe for leaching of the other metals involved but not even then I cannot see anyone using aqua regia...

Now if the gold was recovered and concentrated through some other pretreatments and processes first, such as sulfide floatation and concentration of the values, and then we were discussing roasting and leaching those concentrates with aqua regia at these later stages I could understand.


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## saadat68 (Jun 27, 2020)

There are some gold mining industry in this area. They use cyanide method. But I speak about native peoples that steal ores from these mines and industries!
Some of them that have more ores, for example minimum 100 kg per day, use smelting method. and many that have less gold for example 5 kg per day, use aqua regia method (I am sure they use aqua regia without flotation and etc).
They grind and roast ores and then leach it in AR. Those ores are cheap or free with 1 to 7 gram in one kg ore! Also energy, acid and labor are cheap too. So I think these parameters make their work be profitable.
One of them asked me can I remove base metals from roasted ores with HCl and Nitric without dissolving gold, and I can't answer to him.


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## butcher (Jun 27, 2020)

If nitric is that cheap that they can just waste it and other acids by consuming it by leaching crushed rock. they may not need to roast the ore.
Nitric or H2O2 can be used to desulfurize the gold compound, similar to roasting it will release a slew of deadly compounds from the rock, the acids can also leach gold along with the many other base metals, making a toxic solution or mess that if they are lucky they may recover some of their stolen gold before they poison everyone around them by their methods of dealing with the waste.

Leaching sulfide ore with aqua regia in anything more than just doing testing on a small scale is just simply a stupid idea. waste of time and money and putting us all at risk from the environmental dangers.
Just like the open burning of tons of electronic scrap polluting the environment for a few pennies of metals.


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