# Refining gold sulphide ore concentrate



## The Refiner49er (Feb 11, 2008)

I have several pounds of gold ore concentrate, the high sulphide type. I've read the thread from Paige, and would like a little more information.

The fire assay on the concentrate is 3,079 oz/ton gold and 1,025 oz/ton of silver.

I have an electric kiln and also a gas fired unit I fabricated that has an secondary "afterburner" above the pot to provide top heat. I am speculative about the afterburner possibly reducing emissions from the roasting process.

What temperture range would be proper to effectively eliminate the sulphides? Harold refers to refining with a furnace, I am interested in learning more of this methodology.

After roasting, immersion in water/nitric acid for how long? Should the nitric be done a second time to ensure all the base elements are stripped? Upon rinsing, Steve advises dissolving the gold, I assume this would be AR. But then, I never like to make assumptions. (You all know what it spells)

With a raw material like ore, would it be correct to process the gold twice by dissolution to obtain a high purity? I intend to refine a sample before attempting processing a significant amount. What size of sample can you recommend? (_so many questions_)

Thanks for your input!

Honemaster


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## aflacglobal (Feb 11, 2008)

honemaster said:


> I am speculative about the afterburner possibly reducing emissions from the roasting process.
> 
> What temperture range would be proper to effectively eliminate the sulphides? Harold refers to refining with a furnace, I am interested in learning more of this methodology.
> 
> ...



1950 deg F for 1.2 sec. That's the epa's guidlines here in the states if i remember correctly.


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## Anonymous (Feb 11, 2008)

I wouldn't leave to many tons of that laying around :lol:


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## Harold_V (Feb 12, 2008)

The closest I got to anything that you described was a quantity of pyrite, crushed fine, that had a lot of small gold particles dispersed within. The material was from a conveyer carrying concentrates, and had collected at the base of one of the support columns. 

For that particular lot, I roasted the material by placing it on a 1/8" thick stainless sheet on top of my small melting furnace. This was done under a large hood that was used for the melting furnaces, a necessary evil to control the SO2 that came from the roasting process. I roasted the material until there was no more sulfur being oxidized, then it was processed with HCl to dissolve and eliminate the iron. I recall having to give the resulting material a second roast to eliminate remaining sulfur. By the time that was accomplished, there was only a little gangue included, and the gold was then dissolved with AR for recovery. Your material may not lend itself to the same process, depending on how much gangue you have, and how much of the ore is pyrite, if any. 

The only other experience I had was refining a gold complex that assayed *only* 1/10 of your ore. The ore was primarily quartz, with streaks of iron pyrite, silver, gold and galena. The ore was crushed fine in a ball mill, then run with cyanide and bromine. Extraction was well over 99%, even without eliminating the sulfides. I tried a similar process with the pyrite (mentioned above), but got almost no recovery. The cyanide would dissolve the gold, but it self precipitated in the slurry. I attribute my success with the second ore to being relatively low in sulfides. 

I'm not sure what you interpreted as refining with a furnace. I used a furnace to recover values from wastes, but I don't recall talking about furnace refining. While it's possible (Miller chlorine process), it isn't something I've experienced. Perhaps you can point me to the post that alluded to what you said. Maybe I can clarify my intended message. 

Harold


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## The Refiner49er (Feb 12, 2008)

Ralph,

Thanks for the criteria for SO2 emission control standard. 
I haven't roasted any material as yet but I'm sure it will adequately reduce emissions. Don't want to meet the SO2 police, thank you.

I don't know about _tons_, but this concentrate works out to be 1.54 oz/lb on paper. It will be interesting to find out the net after refining.

Any pointers on final steps? I am open to suggestions.

Thank you!


Honemaster


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## The Refiner49er (Feb 12, 2008)

Harold-

I will look for the post tomorrow. I seem to recall a reference to the term " roast before you refine", or something to that effect. 
I am to some degree, overwhelmed by the volume and complexity of methods for refining. 
It is certainly not a cut and dried approach. 
A diversity of PM materials results in processing decisions requiring extensive experience.

Thanks for your input.


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## Harold_V (Feb 12, 2008)

honemaster said:


> Harold-
> 
> I will look for the post tomorrow. I seem to recall a reference to the term " roast before you refine", or something to that effect.



I may be able to save you a search. It's entirely possible you're referring to my constant preaching about incineration before refining. While there are times when ores may require the operation, my reference is to waste materials that are to be refined, particularly wastes from the jeweler's bench. Incineration removes oil and wax compounds that tend to be troublesome in refining, and in some instances can be the elimination of compounds that might be formed when the wrong ingredients are combined with nitric acid, some of which have the potential to be explosive. 

If I have it wrong, I welcome your input so I can evaluate what I may have said. 

Best of luck!

Harold


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## The Refiner49er (Feb 12, 2008)

I agree 100% on the incineration theory.

The process is required for high sulphide concentrates.

I would like some idea of temperature- hot enough but not too hot.

Steve made reference to a temp scale based on color (radiant).

I have a digital stat and can set cutout to any up to 2350 F.

Thanks again, Harold!


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## Harold_V (Feb 12, 2008)

honemaster said:


> I would like some idea of temperature- hot enough but not too hot.


I don't think you have to worry about getting the material too hot. You'll struggle to get it above a red heat considering it's done while exposed to the atmosphere. Fact is, I had to rabble it regularly to heat the portion that was on top. If memory serves, I had a layer that was les than 2" thick. It becomes obvious when you've achieved a functional temperature. Unless you can heat it beyond the melting point of silver, I don't think you have any worries. I stand to be corrected if I'm wrong. 

If you'd like to read a little about roasting of ores, you might consider finding a copy of Sir T.K. Rose's "The Metallurgy of Gold". From that book, along with a couple other references, I found enough information to process the gold ore of which I spoke, along with information on building a proper ball mill. I also combined styles of agitation tanks mentioned in the book, and came up with one that worked to my satisfaction. 

If you're not familiar with the book, I highly recommend it to you. I have a photo copy of the sixth edition, and I know it was printed at least one more time. I have no idea if the later editions are better. I recommend the book highly, along with Hoke's book Refining Precious Metal Wastes. Combined, they're a powerful force. 

One thing comes to mind. I don't think you'd want to perform this function in a furnace. If it's an electric, you're likely to do considerable damage to the elements, and possibly even the lining. Remember, regardless of how you heat the material, it's important that it have a fresh oxygen supply. 

Harold


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## jimdoc (Feb 12, 2008)

Here is a link to T.K Roses book on Google books;

http://books.google.com/books?vid=0X19knKCDiZJWGANoHe&id=4ikKAAAAIAAJ&dq=gold+dissolve&as_brr=1

And here is another book called The metalurgy of gold; A practical Treatise on the Metallurgical Treatment of Gold Bearing Ores;
http://books.google.com/books?id=v7BCAAAAIAAJ&printsec=frontcover&dq=The+metallurgy+of+gold&as_brr=1


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## Irons (Feb 12, 2008)

A number of years ago, someone gave me a washtub of similar ore. I used dilute Nitric Acid. The Suphides break down and give free sulfur in a finely dispersed form and the Gold and silicates are left untouched.
It's a handy technique for testing pyrites for Gold .


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## The Refiner49er (Feb 12, 2008)

Thank you for the references, I will definitely check it out.

As to the furnace, I will be using a gas fired unit, which is outside. The pot is suspended, and has a side shroud and a plenum over the top. The plenum has a gas burner and a vertical discharge stack. This was originally intended to reduce meltdown time by providing top heat.

The pot is made of steel (an old propane cylinder with the top cut off). Is the steel OK for this material? I know sulphur compounds can be corrosive; I'm not worried about the pot, they are cheap. Just don't want an adverse reaction with the gold bearing material.

When you say oxygen, do you mean air? Would it be beneficial to inject air into the material? The gas burners probably consume most of the oxygen around the pot.

Thanks you guys for your responses. 

John


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## allanwcoty (Feb 12, 2008)

Can you expand the definition of what you did when you treated your ore Irons? Does it build pressure or could I do a small sample in a sealed container in my house? Have a great day. allan


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## The Refiner49er (Feb 12, 2008)

Allan-

I would definitely NOT do nitric acid processes indoors unless you have a good fume hood/enclosure. Even then, outside is safer for exposure.
I am no expert, but have some experience with asbestos and hazardous materials.

Lower exposure to hazardous materials minimizes your health risks. And that should be a top priority.


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## Irons (Feb 12, 2008)

allanwcoty said:


> Can you expand the definition of what you did when you treated your ore Irons? Does it build pressure or could I do a small sample in a sealed container in my house? Have a great day. allan



It's something to do outdoors and you do have to neutralize the fumes, but the nice thing about it is it leaves the Gold intact. I was able to recover some beautiful specimen material that would have been ruined by roasting. The reaction is mild and usually takes a day or so to finish depending on the size of the material.
A gallon jug full of moist marble chips will absorb most of the fumes. Just run a tube to the bottom of the jug. I like the Wally World white play sand. It's like a fine gravel and mostly Calcium Carbonate and just a few bucks a bag.


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## The Refiner49er (Feb 12, 2008)

Hey Irons!

This may seem like a "no brainer" question, but until I clock some mileage at this refining game, I don't want to make presumptions.

When the term "dilute nitric acid" is used, is it the 50% material used straight, or is it diluted further? I suppose this process would also leach out most of the other metals as well.

Thanks!


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## Harold_V (Feb 12, 2008)

honemaster said:


> The pot is made of steel (an old propane cylinder with the top cut off). Is the steel OK for this material? I know sulphur compounds can be corrosive; I'm not worried about the pot, they are cheap. Just don't want an adverse reaction with the gold bearing material



Even stainless had a limited lifespan in my experience. As the metal degrades, some will be combined with the ore. Considering you are to do an acid treatment, it should dissolve and be carried away with the spent solution. Expect rapid deterioration of steel--even if only heating without the presence of sulfur. At red heat, it oxidizes rapidly. 



> When you say oxygen, do you mean air? Would it be beneficial to inject air into the material? The gas burners probably consume most of the oxygen around the pot.



Yes----I was making reference to air that does NOT have the oxygen consumed by combustion. 

As I've stated before, I'm not a chemist. Perhaps the sulfur will be eliminated by other means, but I assume that it normally combines with O2 to form SO2, the process by which it is eliminated from the ore. If the environment has little or no oxygen, I would assume that the sulfur would be difficult to eliminate. Perhaps Lou or Irons could enlighten me where this idea is concerned. 

Harold


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## The Refiner49er (Feb 12, 2008)

Sounds logical, Harold.

It won't be too much trouble to put a low pressure air feed inside the pot, probably preheated.

Still fishing for a temp range target setting.

Thanks!


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## aflacglobal (Feb 12, 2008)

honemaster said:


> I agree 100% on the incineration theory.



:arrow: http://www.banksengineering.com/TOgeneral.htm


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## allanwcoty (Feb 12, 2008)

Any info on how cold the dilute nitric will continue to dissolve the pyrite? allan


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## Lino1406 (Feb 15, 2008)

A piece of cake...


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## Irons (Feb 15, 2008)

allanwcoty said:


> Any info on how cold the dilute nitric will continue to dissolve the pyrite? allan



The rule of thumb for chemical reactions is that they double in rate for every 10 deg. C. rise in temperature, assuming other factors remain constant.

Don't take it as law because there are a lot of things that can affect reaction rates.

As for concentration of the Nitric, anything less than one Molar I consider dilute. If you see a lot of brown NO2 coming off, and the reaction seems greater then, say seltzer water bubbling, it's probably too concentrated. You can add Hydrogen peroxide to oxidize the Nitrogen Oxides back to Nitric Acid, assuming they haven't bubbled away.
Every ore is different. Start very dilute and work up. Use a small test sample first to try it out.

Patience is a virtue.

Here's some handy software for Windoze users:

http://home.c2i.net/astandne/help_htm/dwnload1.htm

Calculate your Moles the easy way....


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## allanwcoty (Feb 15, 2008)

Thanks for the link Irons,
I was wondering if you had any adverse reactions with any of the ores you ran with regards to lost gold values? I've got scheelite, pyrite and possible vanadiam for sure. Just want to make sure none of them will break down creating an acid mix that will dissolve the gold or other PM. I picked up a couple of beginner chemistry books and will get Hoke's when I can afford it. Have a great day. allan


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