# Processing arsenopyrite gold ore



## SaltwaterServr (Feb 2, 2017)

Hello everyone!

I sent this to Deano directly yesterday, so forgive me if it sounds like I'm talking to one person. In hindsight, and after reading the forum more, I should've put it here for people like myself who will follow along.

A member here, Kurtak, told me I should get in touch with this forum for gold mining advice.

Myself and another gentleman here in Arizona are trying to set up a small-scale portable gold processing system for the small deposit refractory ores we have here. He actually still works in a facility in New Mexico and down in Tucson as well. He's got the mechanical aspect of it covered from run-of-mine, crushing, grinding, and floatation. 

One thing that he and I have noticed on our separate prospecting endeavor is that there are many mines, hundreds if not thousands, that didn't bother to process the arsenopyrite ores at all. One small pit I've claimed in the last month smells like a dang garlic festival once you dig down a half-meter into the filled-in dirt.

We're going to use bioxidation since it can lock the arsenic up, then go through processing the gold out. 

That's where I can use advice. As we build our equipment up, I'm processing small batches of ore using H2O2 and HCl with NaCl. 

As best as I can find, 12% H2O2 does nicely to oxidize the arsenopyrite. Then I hit it with 2 molar HCl with 200 grams per liter of NaCl based on research papers I've read and published books on the matter. I let that sit for 24 hours, double filter it, and then use zinc powder. 

Here's my first roadblock, how much hydrogen peroxide should I use on a volume basis compared to the amount of ore I have? Should I keep adding it until it no longer has any reaction? I made a batch here and added the HCl solution right after this:

https://www.youtube.com/watch?v=0Y-TkGSuFDI

I put an excess of zinc into the pregnant solution and I'm holding off on filtering it since I came down with a case of the shingles. 

Other than using carbon to pull the gold out of solution, do you have any suggestions? I'm pretty much sticking with HCl for now since my mining partner doesn't have a chemistry background and I don't want him messing with cyanide. 

Any help is greatly appreciated, or if you think I should post this to the main forums somewhere.

Respectfully,

Jeff F.


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## Deano (Feb 7, 2017)

The first point is that many arsenopyrite ores will leach with cyanide, no sulfide oxidation needed.

Other arsenopyrite ores will cyanide leach well in the original ore but will not leach when presented as a float concentrate.

This means that you need to do some basic testwork consisting of bottle roll cyanides and aqua regia assays.

The aqua regia assays will tell you what grade of gold exists in the sulfides, assuming that the free gold has already been cyanided out.

The bottle roll cyanides will tell you to what degree the sulfides can be leached without oxidising them.

The second main point is that oxidising the sulfides with oxidising agents is a fairly expensive way to go.

If you are wanting to run non-cyanide leaches you will also have the cost of all plant, including pumps and plumbing needing to be acid and/or chloride resistant.

There is a good reason why the mining industry uses cyanide for leaching in that it is a robust process which, unlike the common perception, is relatively safe if operated under the standard protocols.

It is no less safe than alternative leaching methods and it does have the one major advantage of being able to practice alkaline decomposition of sulfides rather than the chemically expensive methods.

As to the queries you have, you would add H2O2 until there is no further reaction as you said.

The major problem you have with an acid system is you will still need to get agitation into the pulp in order to have the chemistry able to attack the sulfides and metals.

Best of luck sorting that out with the systems available.

Generally you do anything possible to avoid large scale filtration, it is expensive and time consuming.

This is why the gold industry changed to CIP overnight when it was developed.

The only way to avoid filtration is either CIP or vat leaching with carbon column.

If you really want to go the filtration route then you can precipitate the gold from the leach solution with any of the standard methods provided that the oxidiser is removed.

The residual level of oxidiser in the liquor is measured with an ORP meter sometimes called an Eh meter or redox meter.

You generally want the reading to be <500mv to avoid consuming high levels of reductant.

Deano


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## kurtak (Feb 8, 2017)

Hi Jeff

Glad to see you have come to GRF - as I told you & MM (Mad Machinist) over on the TN forum when it come to the leaching of ores you can not find a better source of info then Deano --- He will definitely get you headed down the right path as to the best option(s) for the ore you are working with 



> Other than using carbon to pull the gold out of solution, do you have any suggestions? I'm pretty much sticking with HCl for now since my mining partner doesn't have a chemistry background and I don't want him messing with cyanide.



To which Deano replied



> There is a good reason why the mining industry uses cyanide for leaching in that it is a robust process which, unlike the common perception, is relatively safe if operated under the standard protocols.
> 
> It is no less safe than alternative leaching methods and it does have the one major advantage of being able to practice alkaline decomposition of sulfides rather than the chemically expensive methods.



I have to agree with Deano here - as long as your ore is cyanide leachable that is the way to go --- I understand the fears associated with cyanide leaching - which is why I took the time to post what I thought was some quite detailed info about leaching with CN over on the TN forum with special attention given to doing so in a safe manner 

I know I had promised to post more over on the TN forum - but then I got side tracked & just simply have not had time to get back over there  --- sorry about that :!: --- but if that has resulted in you coming over here to open a discussion with Deano that's a good thing because Deano really is your man when it comes to processing ores :mrgreen: 

Ore "IS" Deanos field of expertise - mine is more in the field of gold from electronic scrap & though there are many similarities that apply to processing both ores &/or E-scrap --- there are certainly issues concerning ores wherein Deano is "by far" a better source of info then I :!: 



> I sent this to Deano directly yesterday, so forgive me if it sounds like I'm talking to one person. In hindsight, and after reading the forum more, I should've put it here for people like myself who will follow along.



I want to personally "Thank You" for deciding to post your questions to the open forum :!: 

Its what this forum is all about - the open discussion of ALL aspects of the recovery & refining of gold (& other PMs) so that we can ALL benefit from the questions & answers of the open discussions in this field - regardless of the source the PMs are being recovered &/or refined from 8) 

There is nothing we enjoy more here then a good meat & potatoes discussion & I can see this becoming just such a discussion --- hopefully MM will join in the discussion as well - because as best as I can tell (from discussion on TN) it should/could result in some good discussion 8) 

Per the underlined in the last quote - not sure what you have read so far - but here are some links to threads you most certainly want to read

http://goldrefiningforum.com/phpBB3/viewtopic.php?f=37&t=21526&p=222607#p222215

http://goldrefiningforum.com/phpBB3/viewtopic.php?f=37&t=22978#p241077

http://goldrefiningforum.com/phpBB3/viewtopic.php?f=44&t=23120

http://goldrefiningforum.com/phpBB3/viewtopic.php?f=44&t=24682&p=261073#p261037

http://goldrefiningforum.com/phpBB3/viewtopic.php?f=40&t=24899#p263171 --- this one is about an electro winning cell - which besides being used to win your gold back from solution - can also be used to deal with cyanide waste to make it safe for disposal

http://goldrefiningforum.com/phpBB3/viewtopic.php?f=38&t=23680&hilit=smelting --- this is a good discussion about smelting

Kurt


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## kurtak (Feb 8, 2017)

Jeff

I see over on the TN forum you & MM have been looking at &/or talking about the Eco-goldex product - so I am going to add a couple more links (threads) for you to read

http://goldrefiningforum.com/phpBB3/viewtopic.php?f=37&t=23843

http://goldrefiningforum.com/phpBB3/viewtopic.php?f=37&t=25001&hilit=ammonia

Bottom line - you would/will be better served going with straight potassium ferrocyanide then with the goldex product

Also - to clarify - we are talking about ferro not ferri cyanide

Kurt


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## SaltwaterServr (Feb 9, 2017)

Deano said:


> The first point is that many arsenopyrite ores will leach with cyanide, no sulfide oxidation needed.
> 
> Other arsenopyrite ores will cyanide leach well in the original ore but will not leach when presented as a float concentrate.
> 
> ...



What we're kicking around right now is using a shaker table or a mineral jig to upgrade the concentrate rather than floatation. Our system ideally will be for small deposits, under 10K tons of ore in place, that will be on a pair of two or three axle trailers to be hauled on site for crushing, grinding, and upgrading.



> The second main point is that oxidising the sulfides with oxidising agents is a fairly expensive way to go.



We've been looking at BiOx for oxidation since we can lock up the arsenic at the same time as long as we have an excess of iron in the pulp. Once that's done, we'll move to cyanide. The thing now is that we're still getting assays of sites to see where our best first shot at this is located. 

Still have to go through some core drilling (small hand-held model) before we put together our paperwork for the BLM.



> As to the queries you have, you would add H2O2 until there is no further reaction as you said.
> 
> The major problem you have with an acid system is you will still need to get agitation into the pulp in order to have the chemistry able to attack the sulfides and metals.
> 
> Best of luck sorting that out with the systems available.



I'm using an air pump through perforated PVC to mix the pulp right now. Works okay. I pulled the idea from fluidized bed filters in ultra-high density aquaculture facilities. 



> Generally you do anything possible to avoid large scale filtration, it is expensive and time consuming.



Found that out in a hurry, even using a pump to put a vacuum on a Buchner funnel. No way that's scalable to any degree for even a small operation.



> This is why the gold industry changed to CIP overnight when it was developed.
> 
> The only way to avoid filtration is either CIP or vat leaching with carbon column.



I'm getting more comfortable with the CIP and using the Zadra elution method, from an academic standpoint. I had avoided going that route until I really read up on how stable cyanide is at ph 11. My minor in college was polymer chemistry, so using nasty stuff like phosgene and such isn't foreign to me. 



> The residual level of oxidiser in the liquor is measured with an ORP meter sometimes called an Eh meter or redox meter.
> 
> You generally want the reading to be <500mv to avoid consuming high levels of reductant.
> 
> Deano



I've got one in my cabinet. 

Thanks for your response and help on this. I'll no doubt be shooting you questions from time to time, if you don't mind. I also chat on occasion with folks over at 911metallurgist as well.


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## SaltwaterServr (Feb 9, 2017)

kurtak said:


> Hi Jeff
> 
> http://goldrefiningforum.com/phpBB3/viewtopic.php?f=37&t=21526&p=222607#p222215
> 
> ...



Howdy there Kurt,

I've got that first thread already read and bookmarked. 

The second one, wow. That needs to be published in a book. Or at least shoot it over to Marsden and House for their next edition of Chemistry of Gold Extraction. 

I haven't gotten to the third thread, I want to go back and take extensive notes on the second first!

I've read the goldex threads you put there already, good stuff and a great example of the knowledge of this board coming together to figure out that the ferrocyanide was really only dressed up.

I'll get to the smelting soon too.

Amazing resource here, really.


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## kurtak (Feb 10, 2017)

SaltwaterServr said:


> > The second main point is that oxidising the sulfides with oxidising agents is a fairly expensive way to go.
> 
> 
> 
> We've been looking at BiOx for oxidation since we can lock up the arsenic at the same time as long as we have an excess of iron in the pulp. Once that's done, we'll move to cyanide. The thing now is that we're still getting assays of sites to see where our best first shot at this is located.



Jeff

It might be a good idea to give Deano some more back ground/explanation on what you are talking about per the underlined above being as how this is something you & Mad Machinist have been discussing over on TN (TreasureNet) --- meaning being as how he has not been in the loop on that discussion he is not really aware of the what, how & why you guys are looking at incorporating this into your system/process 

He can't give you any feed back &/or suggest alternatives without some details about what you & MM are planning here in this part of your operation

So - I hope you don't mind if I post a bit (of my "limited") understanding of what you guys are looking at here - & then you can fill in any blanks &/or corrections to bring Deano up to speed

Deano - what Jeff & MM are working on - other then the problems associated with the recovery of the gold from arsenopyrite ore --- but "also" the problems associated with the arsenic in & of its self in order to meet EPA regulations for permitting purposes --- the EPA/BLM/USFS etc. is not going to permit any sizable operation for processing arsenopyrite ores unless the issue of the arsenic is first addressed in an "eco friendly" way

So what Jeff & MM are looking at is running a Bio pre-leach on the milled ore - the Bio leach process they are looking at is supposed to allow the arsenic to complex with the iron in the ore to become ferric arsenate effectively locking up the arsenic into a stable substance that is inert and nonhazardous --- as I understand it - the Bio leach is how the EPA actually deals with supper fund clean up of tailing piles from old - long abandoned mines with arsenic before the days of environmental concern &/or the EPA 

My (limited) understanding is that the Bio leach does not target (leach) the gold but rather addresses the arsenic problem (as well as deals with other base metal) so the Bio leach is then followed by leaching for the gold

Though I have been able to provide "some" help with the pros & cons of acid leaching vs cyanide leaching "of the gold" - the arsenic problem is beyond me - which is why I suggested they come here to pick your brain Deano - as this is certainly "far more" your field of expertise then mine

Jeff - I hope I didn't step out of line by posting this - my intent is/was to further open the discussion to not just address the question of leaching arsenopyrite ore "for the gold" - but also open it for questions concerning dealing with the arsenic as well

Kurt


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## SaltwaterServr (Feb 10, 2017)

kurtak said:


> Jeff - I hope I didn't step out of line by posting this - my intent is/was to further open the discussion to not just address the question of leaching arsenopyrite ore "for the gold" - but also open it for questions concerning dealing with the arsenic as well
> 
> Kurt



Don't mind a bit there hoss. Great synopsis.

I will only add that the biological leaching of the arsenic is done between pH of 1 and 2 at ambient temperatures. It uses 2 or 3 types of bacteria that can be purchased from biological supply stores at about $300-$400 per strain. Once you have the strain and you know biology, you should be able to keep that culture around forever.

The bacteria feed off of sulfur also, so sulfuric acid is the choice for pH adjustment. Extra iron can be added as necessary to complete the biological process to lock up the arsenic to the iron. Can't say off the top of my head what particular form of iron is added to the slurry. 

It can take anywhere from a few weeks to 90 days for the bacteria to acclimate to a particular mix/blend of concentrates so a lot of big operations blend their ore to keep the bacteria from going into chemical shock and losing a culture of bacteria. 

The bacteria like about a 20-30% solids slurry, need agitation that can be supplied in the way of an air lift pump for stirring, and do well up to about 40 degrees C. The complete leaching cycle take anywhere from 24 hours to 7 days depending on the conditions, most notably tied to temperature.


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## Deano (Feb 10, 2017)

Before you get too carried away with leaching the arsenic you might want to read the bureau of Mines Report of Investigation #8458 dated 1980.

This refers to the type of testwork you can do to see if your ores are amenable to straight cyanide leaching.

My experience has been that many arsenopyrite ores can be leached without oxidation of the arsenic, any ore tested should be run as both head ore and sulfide cons.

If you have a lot of different ores available then you should be able to find those which are leachable and operate on those.

Deano


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## Rougemillenial (Feb 12, 2017)

my opinion about arsenopyrite based ores is that you should heat it to 800C in a closed system to covaporize arsenic and sulfur which rises to the top of the vessel which forms crystals of arsenic sulfide which can be scraped off and bagged. then you can take it to a proper facility where they can turn it into something useful safely. Arsenic sublimates at room temperature giving off a garlic like aroma so it should be separated quickly w/o getting it into the atmosphere. the stuff that remains is mostly iron and the desired metals like gold, silver, PGM's, copper etc. this can then be processed chemically or by firing it down into a button in the presence of nitrate flux and running it through a parting cell to remove copper. Then aqua regia can be used to separate the PMs :G Some people roast the ore which really gets under my skin because arsenic gas is produced which can easily harm or kill the person doing it or others downwind :x. Chemically separating the arsenic is a very bad idea. heavy metals are far more dangerous when they are in solution and arsenic is no exception. also hydrogen sulfide forms when metal sulfides react with acids so you must use a scrubber if you wish to take the chemical path. good luck on processing your ore. hope to see a good yield


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## SaltwaterServr (Feb 13, 2017)

Rougemillenial said:


> my opinion about arsenopyrite based ores is that you should heat it to 800C in a closed system to covaporize arsenic and sulfur which rises to the top of the vessel which forms crystals of arsenic sulfide which can be scraped off and bagged. then you can take it to a proper facility where they can turn it into something useful safely.


. 

I'll take a look at that process. I can tell you from the pit I was working, there's a heavy amount of arsenic in the dirt already. Just digging in the loose soil that's accumulated in the pit smells like a garlic roasting contest. Same with another dry wash about a quarter mile downstream from the mine I found Saturday.



Deano said:


> Before you get too carried away with leaching the arsenic you might want to read the bureau of Mines Report of Investigation #8458 dated 1980.
> 
> This refers to the type of testwork you can do to see if your ores are amenable to straight cyanide leaching.
> 
> ...



I'm on that report like a hound on a June bug with July a coming. Appreciate it.

Deano, I found this mine this weekend, on the north end of my claim. There's a small tailings pile outside with a lot of arsenopyrite in it. Judging by the dynamite box we can nail the age of the mine down to being worked between 1894 and 1903. Considering the population in the area at that time was 100-500 people, this one might've gotten lost to history. The only mine listed in the federal registry is about a quarter mile to the south and is shown as a pit I've been excavating. I bet this is actually the mine itself.

I can trace the gossan I think the adit follows on Google Earth for certain for 800 feet, but it might extend out to 1300'. I won't know for sure until I get more boots on the ground next weekend.

The geology is a porphyry type deposit with the country rock either rhyolite or andesite. Guessing it is most likely under 70MYA, but I'd have to check. I didn't measure the dip, and I'll have to survey it next weekend to figure out the strike. 

https://www.youtube.com/watch?v=MKkazZaw88g


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