# Getting the gold out



## Twobrothers (Nov 28, 2017)

Hi everyone. I've been lurking and learning here on gold refining forum for about a year now. I've been prospecting and developing a few gold deposits and I am at a point where I have a good source of quartz based material with visible gold and some locked in sulfides. The gold is very fine. I haven't had success with physical recovery methods. Some success on a small scale with amalgamation. I've investigated chlorination, and cyanidation thoroughly. Done some experimentation with chlorine. Experienced some trouble keeping the ORP (>1000) and Ph(>7.5) in the right ranges. Chlorine is really nasty stuff. Caught a couple strong wiffs once or twice and called it quits. Not really willing to deal with cyanide. I am curious on people thoughts about thiourea. I know it exists but not much about the practical side of the process. Are there other processes that can be practically executed by the layperson with the necessary research, understanding, experimentation and access to resources? Are there people in the western united states who will smelt/ leach/ purify/ work with raw ores? Average grade by fire assay is about 1oz/ ton more or less depending on wall rock/ gangue dilution.
I crush the material to 1/8" minus then grind to powder (around 40 mesh). Could grind finer. Finding the gold is only half the work. Getting it to a marketable form takes respectable effort. So far been the funnest hobby I've ever had. Would like to see some gold for the effort. Thanks for sharing your knowledge and experience.


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## Twobrothers (Dec 30, 2017)

Still here with gold in rocks. Found pockets with abundant visible gold. No professional assays on that material yet. Beginning to learn how to do my own fire assays. Read Deanos posts. Man knows some stuff about chlorine leaching rocks.


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## Lou (Dec 30, 2017)

Grind it up and leach it!


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## cuchugold (Dec 31, 2017)

Sigue volando con tu hermanito "El Capitan". Dile que es mejor si compra una batea y empieza a caminar. Antes del siglo 23 seguro encuentran la mina que buscan. Mientras tanto, sigue nombrando ranas y vegetales... :G


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## g_axelsson (Dec 31, 2017)

Can you translate that, please.

I don't trust google translate is doing a good job on this...
"Keep flying with your little brother "El Capitan". Tell him it's better if he buys a punt and starts walking. Before the 23rd century they surely find the mine they are looking for. Meanwhile, he continues to name frogs and vegetables ..."

Göran


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## anachronism (Dec 31, 2017)

It's pretty safe to say he's not in Ireland as his profile states then. 8)


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## Lou (Dec 31, 2017)

From Ireland, sure...


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## Lou (Dec 31, 2017)

Oh and as to thiourea...works great very fine gold. Better than cyanide. Easily recovered with zinc or borohydride. Of course one can always work with base hydrolysis and redissolve the sulfide in aqua regia, kill nitric, dilute and chill, filter and precipitate the gold with hydrazine salt. Much more expensive

Pregnant solutions may crystallize and are very orange red.


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## Twobrothers (Jan 1, 2018)

Lou said:


> Grind it up and leach it!


 Easier said than done! 
Here's what I've tried so far: Into a five gallon bucket with a lid I added one gallon of 10% sodium hypochlorite solution, 1 cup of NaCl and twenty pounds of crushed ore (minus 20). I slowly added diluted hydrochloric acid stirred tested with litmus paper and added more acid until reading a Ph about 6. I checked on it hourly for the first 8 hours stirring and adding water and acid if necessary to keep the Ph at around 6 and sprinkling in a little calcium hypochlorite (from shock treatment MSDS for which listed 48%calcium hypochlorite and the remaining % NaCl) from time to time to maintain some chlorine scent in solution. Enough to smell wafting off the leach. After two days of maintaining the Ph best I could and adding fresh hypochlorite I let it settle out and I siphoned the liquid through a pvc column (1.5"x 16") filled with washed activated carbon. I burned the carbon to ashes and smelted about 25 grams of ashes with sodium carbonate borax litharge. Cupeled the lead and got about 2 milligrams of a silvery colored bead. 

The second time I basically did all of the above but when I filtered the liquid through the pvc column filled with activated carbon it started reacting strongly bubbling heating up and giving off chlorine gas.

I was very careful to exclude any sources of carbon in the leach. Probably be a lot better if I had an ORP/Ph meter but I didn't at the time (still don't).

I am at a stage where I am not at all committed to any one course of extraction method. It's all small scale experimental phase at this point. I've had some limited success with amalgamation. Whatever I decide to scale up to a production level I'm really wanting to keep it as simple as possible.

Cyanide-easy,simple,cheap, but if you get it wrong it's gonna break eggs. know what I'm saying?

Mercury- a little out dated this day in age. It has a place as long as the gold particle size isn't too large or too small. Potentially environmentally deleterious if it escapes its metallic phase and combines with something in the ore and goes water soluble organic compound mercury. 

Chlorine- it works but it tough to tailor/ pretreat the ore to a condition where that chlorine doesn't get used up eating all the iron and base metals in sight, that and maintaining Ph for a hypochlorous state where its active but not off gassing. 

Thiourea-short leach life. Don't know much about it really.

Iodine- not economically viable for treatment of raw ores 

Bromine- like chlorine but more expensive and potentially more dangerous 

That's where I am at. I feel kinda stuck. I don't know which direction to go on this.


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## Twobrothers (Jan 1, 2018)

Lou said:


> Oh and as to thiourea...works great very fine gold. Better than cyanide. Easily recovered with zinc or borohydride. Of course one can always work with base hydrolysis and redissolve the sulfide in aqua regia, kill nitric, dilute and chill, filter and precipitate the gold with hydrazine salt. Much more expensive
> 
> Pregnant solutions may crystallize and are very orange red.



So how does one go about using thiourea on a raw ore? Is it a matter of buying a chemical and sprinkle sprinkle a la a little lime a little cyanide a little water? Or do you have to generate it ad hoc for usage centrifuges, filter presses etc? I know very little about its practical application leaching ore only that it seems to be short lived thus lessening concerns for environmental impacts. 

I don't even know where to begin formulating a follow up question to the whole base hydrolysis. Way over my head. 

My impression is that raw ore treatment with AR is a no go. Especially for my application, too expensive and too messy with all the base metals present in my partially decomposed oxide/sulfide quartz ore


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## Lino1406 (Jan 2, 2018)

To negate fools' gold you need to do a sample with AR, at least once, even though the preferred process may be different


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## Lou (Jan 2, 2018)

Cyanide is more short-lived than thiourea. Short-lived is concentration and environment dependent anyway.
Chlorine in acidic conditions will not just oxidize sulfides but all 
I only use thiourea for concentrated products or a solvent extractant strip. I have done tests on Pd, Pt, Au powders and watched it out perform cyanide time and time again. 


Sounds to me that you really need to comminute, float, and then go after the concentrates if it's 1 opt. 

You could easily get an electric motor, gearbox or big big flywheel for momentum, some 1" steel, break it into half a hexagon hard face it with manganese and make a chain/hammer mill to get it to fine powder separate from oversize high grade gold and go after the froth concentrate. 

I have a 15 HP electric motor chain mill in production that's being made from AR400 steel. Want me to toll grind it? I also have a good size ball mill (think 12' long x 5.5' wide) and rod mill. 

You need to get it ground up.


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## Twobrothers (Jan 10, 2018)

Lou said:


> Cyanide is more short-lived than thiourea. Short-lived is concentration and environment dependent anyway.
> Chlorine in acidic conditions will not just oxidize sulfides but all
> I only use thiourea for concentrated products or a solvent extractant strip. I have done tests on Pd, Pt, Au powders and watched it out perform cyanide time and time again.
> 
> ...



Are you in Arizona? PM me? 

Preliminary plans are for a medium Jaw crusher (0.5 tons / hour) and a medium-small rod / ball mill (preferably rod) still working on raising the capital for that. 

Currently I can mill about 50lbs/ day to minus 20 mesh. Not production scale for the grade I am working. 

I've been developing a relationship with TCB Metals in Phoenix area http://tcbinter.com to see about some initial testing and processing. They do a thiourea leach with big filter presses, computer controlled feedback loop ORP-Ph, 1 ton per hour, able to take raw ores - They got it figured out. It's nice to have that option available. The cost of their service does come at a moderate expense. I would like to develop an in house recovery option. Like everything else figuring it out one piece at a time learning up on the options so when the time comes I can do it.


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## Twobrothers (Jan 10, 2018)

Lino1406 said:


> To negate fools' gold you need to do a sample with AR, at least once, even though the preferred process may be different



I don't understand what you mean by to negate fools gold?
Won't an AR leach dissolve all gold contained? Both free gold and gold locked up in sulfide matrices?


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## Twobrothers (Jan 11, 2018)

Lou said:


> Cyanide is more short-lived than thiourea. Short-lived is concentration and environment dependent anyway.
> Chlorine in acidic conditions will not just oxidize sulfides but all
> I only use thiourea for concentrated products or a solvent extractant strip. I have done tests on Pd, Pt, Au powders and watched it out perform cyanide time and time again.
> 
> ...



Understood on the Chlorine. At less than pH 5 or thereabouts it begins to exist as a predominantly gaseous product, not the hypochlorous state you want for precious metals leaching. Low pH conditions and it attacks base metals (most troublesome of which is iron). 

Froth flotation. I know it from industry. I've heard a lot of hobbyists/ small scale-er's talk about it. Know anyone who's done/ doing it? Something reasonably efficient for a small scale operator? 300-500lbs of raw material an hour?


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## Lou (Jan 11, 2018)

You need to get it finer than -20.

Once you've done that, probably send deano a PM.

There are various agents that can be tested out in a lab for frothing and I can even do so for you.


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## Lino1406 (Jan 11, 2018)

Sorry, I thought everyone knows what is fools' gold. Of course it does not contain gold, but glitters


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## Twobrothers (Jan 11, 2018)

I know what pyrites are. AR will digest pyrites. And most everything else except silica. Pyrites in the material I have are all oxidized away to geothite and limonite. I don't understand where you're heading. AR is almost never any good for extractive metallurgy of raw ores.


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## anachronism (Jan 11, 2018)

RenoChris made the single best post ever about fools gold. 

Hit it with a hammer and it shatters. Gold deforms.


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## aussie gold (Feb 11, 2018)

If you don't want to take risks with chemicals, you could try the method used by the ancients . 
Heat your rock in a barbecue to release any gold from sulfides, plunge it into bucket of cold water mixed with vinegar. The quartz will break up and can be turned to sand with your fingers. Then whizz it when dry in a food processor to separate the various metals by density. No harmful chemicals or intensive work involved.


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## Gold Priisk (Feb 14, 2018)

Twobrothers said:


> Lou said:
> 
> 
> > Grind it up and leach it!
> ...




Я не сторонник кучного выщелачивания, и предпочитаю работать с концентратами, когда содержание золота от 2г на килограмм материала. 
Для этого, тщательно измельчаю рудный/шлиховой материал, пропускаю через центробежный концентратор и только тогда подвергаю выщелачиванию хлором. 
Большая ошибка, работать с хлором, в открытой ёмкости, так как он при достижении концентрации в растворе, он становится летучим, и выщелачивание снижается, поэтому работаю в герметичных ёмкостях под давлением, где летучий хлор учавствует в постоянной рекурперации с образованием HOCl, HCl, Cl2.
Руду не обжигаю, так как при нагревании выше 300°, тонковкрапленное золото начинает окисляться продуктами распада, в основном это хлор из хлоритовых минералов, сера и мышьяк, и становится летучим.
К тому же, сам хлор хорошо разрушает сульфидные руды
Окисление пирита:
2FeS2+15Cl2+16Н2О=Fe2(SO4)3+H2SO4+30HCl
Окисление арсенопирита:
2FeAsS+14Cl2+16Н2О=2FeAsO4+2H2SO4+28HCl

Образовавшаяся свободная серная и соляная кислота, снова окисляет хлорную известь или дихлоризоцианурат натрия, для вырабатывания хлора и хоорноватистой кислоты.

Работу провожу в пластиковых бутылках 2л (2—2,5кг), а сейчас работаю над реактором в 50 литров, что позволит за раз, обрабатывать 65—70кг концентрата.


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## g_axelsson (Feb 14, 2018)

Translated into English (google).



Gold Priisk said:


> I'm not a supporter of heap leaching, and I prefer to work with concentrates, when the content of gold is from 2g per kilogram of material.
> To do this, I thoroughly crush the ore / schlich material, pass it through a centrifugal concentrator and then only leach it with chlorine.
> It's a big mistake to work with chlorine in an open tank, as it reaches the concentration in the solution, it becomes volatile, and the leaching is reduced, so I work in pressurized sealed containers where the volatile chlorine participates in a constant recurrence with the formation of HOC1, HCl, Cl2 .
> Ore is not fired, because when heated above 300 °, finely divided gold begins to be oxidized by decomposition products, mainly chlorine from chlorite minerals, sulfur and arsenic, and becomes volatile.
> ...


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## Liquidau (Apr 27, 2022)

Lou said:


> Oh and as to thiourea...works great very fine gold. Better than cyanide. Easily recovered with zinc or borohydride. Of course one can always work with base hydrolysis and redissolve the sulfide in aqua regia, kill nitric, dilute and chill, filter and precipitate the gold with hydrazine salt. Much more expensive
> 
> Pregnant solutions may crystallize and are very orange red.


Hi Lou---
Just came across this thread, and it's right in line with my latest experiment in the lab, regarding Thiourea. I came across a technical paper proposing a concentration of 10 grams/liter, pH=1.5, Ferric ions (Fe+3)=0.3%, and temperature 22-27C, with 2 hours of stirring.
This does dissolve whatever gold plating of pins and fingers I added to the beaker, although seems much slower on thicker gold surfaces of ceramic chips.
My question is: what's the best way to drop the gold? You mention zinc or borohydride; can you please elaborate? Can you just drop zinc into the solution as you would with PGM precipitation of catalytic converter solutions?
Cheers!
Len


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## Lou (Apr 27, 2022)

Well, I should mention that I was wrong. Gold thiourea complex seems to be colorless but Pd strongly colored. 

Zn and BH4- are the two reductants that will get the gold out of the solution. The ferric chloride might be annoying. Maybe something that won't form annoying hydroxide crap would be better, like ceric ammonium sulfate.


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## Stibnut (Apr 27, 2022)

I used H2O2 as my oxidant in a small-scale test since I'd seen this mentioned in the literature. It went well except that much of the thiourea eventually ended up as sulfur powder, but it wasn't too hard to filter.


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## Liquidau (Apr 29, 2022)

Stibnut said:


> I used H2O2 as my oxidant in a small-scale test since I'd seen this mentioned in the literature. It went well except that much of the thiourea eventually ended up as sulfur powder, but it wasn't too hard to filter.


Interesting. The zinc works fine by dropping black powder (maybe including Pd; I'll check on the XRF). 
When I added H2O2, nothing dropped but the solution turned orange-red clear (maybe Pd)?


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## Liquidau (May 2, 2022)

Lou said:


> Well, I should mention that I was wrong. Gold thiourea complex seems to be colorless but Pd strongly colored.
> 
> Zn and BH4- are the two reductants that will get the gold out of the solution. The ferric chloride might be annoying. Maybe something that won't form annoying hydroxide crap would be better, like ceric ammonium sulfate.


Lou, won’t tte zinc drop everything below it, including copper and iron? Maybe better to use copper instead to only drop gold? Or will copper not work in Thiourea?


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## Lou (May 2, 2022)

Doesn’t work very well. Thiourea tenaciously holds the gold.


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## Liquidau (May 2, 2022)

Lou said:


> Doesn’t work very well. Thiourea tenaciously holds the gold.


Ok, so does that mean everything drops with zinc (I.e. gold, silver, copper, etc.)? Which means each element needs to be removed/refined separately?


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## Lou (May 3, 2022)

Yep, it would go back to the front end. So thiourea is the recovery step then final refining.


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## Liquidau (Jun 26, 2022)

Update:
So for ferric ions, ferric sulfate looks to be a lot more effective than ferric chloride in leaching the gold. But a lot of solid white residue/precipitate is forming as well. This white material Dissolves when a little nitric acid was added, turning the solution light green. So ferric nitrate? Stannous test is positive for gold, so it’s there, but proving elusive to isolate. Since the source was fingers, there must be silver and copper also leached out? Or isn’t Thiourea selective for gold only? This is not in Hoke so flying blind here; only a few tech papers on the subject, though I’m convinced this might be a really good approach for many of us boutique extractors/refiners.
So any details the mod experts can provide on Thiourea would be greatly appreciated, and I’ll keep the updates on my progress coming.


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## Deano (Jun 26, 2022)

Most people who research thiourea leaching get to the part where they read that thiourea is a carcinogen and then they lose interest in using it.
If you make an informed decision that you want to use thiourea despite the known risks then that is your responsibility.
The chemistry of thiourea leaching is that thiourea itself will not leach gold, the thiourea must firstly be converted by oxidation to formamidine di sulfide, this is the active leaching agent.
The tricky part of the above is using an oxidising agent which has enough oxidising power to carry out the conversion but not so much oxidising power that it will keep oxidising the formamidine disulfide through to a mix of sulfates, nitrates and oxides which will just sit in solution without leaching gold.
The best practical oxidant used for bulk leaching is a ferric salt such as ferric sulfate, other oxidants work but not as well or as cheaply as ferric.
The above means that you have to keep a close check on the redox of the solution, a meter is essential. You also need to monitor pH in order to keep your ferric in solution but not to have the pH drop enough that the rate of oxidation of the formamidine disulfide is increased.
The biggest factor in deciding whether to use thiourea, apart from the OHSA aspect, is the cost of processing.
Firstly if you are using ferric as an oxidant you will have to have all wetted surfaces in your plant, including pumps and piping, made of non metallic material. This is because you will have to have the pH below 3 to keep the ferric in solution.
Gold thiourea complexes have very low loading levels on carbon and resin so you either have to get the gold in solution levels high enough for direct electrowinning or you have to filter and precipitate with zinc or other reducing agent.
Either way it will not be a cheap processing route for gold ores.
Thiourea has a role to play in working with concentrates where the high unit cost of leaching is balanced out by the high unit value of the recovered metal.
When you are looking at processes for leaching gold always start with what does the industry use. The answer is cyanide on a cost basis.
Next do some research on safe usage of cyanide, read lots of papers from pro and con advocates.
The fundamental safety aspects are pH and ventilation with a lot of care given to ecological concerns around dams and waterways etc.
You cannot always guard against stupidity but you can put in place working rules to minimise damage from stupidity.
Deano


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## kurtak (Jun 27, 2022)

Deano said:


> You cannot always guard against stupidity but you can put in place working rules to minimise damage from stupidity.


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## Biom (Jun 27, 2022)

Twobrothers said:


> Easier said than done!
> Here's what I've tried so far: Into a five gallon bucket with a lid I added one gallon of 10% sodium hypochlorite solution, 1 cup of NaCl and twenty pounds of crushed ore (minus 20). I slowly added diluted hydrochloric acid stirred tested with litmus paper and added more acid until reading a Ph about 6. I checked on it hourly for the first 8 hours stirring and adding water and acid if necessary to keep the Ph at around 6 and sprinkling in a little calcium hypochlorite (from shock treatment MSDS for which listed 48%calcium hypochlorite and the remaining % NaCl) from time to time to maintain some chlorine scent in solution. Enough to smell wafting off the leach. After two days of maintaining the Ph best I could and adding fresh hypochlorite I let it settle out and I siphoned the liquid through a pvc column (1.5"x 16") filled with washed activated carbon. I burned the carbon to ashes and smelted about 25 grams of ashes with sodium carbonate borax litharge. Cupeled the lead and got about 2 milligrams of a silvery colored bead.
> 
> The second time I basically did all of the above but when I filtered the liquid through the pvc column filled with activated carbon it started reacting strongly bubbling heating up and giving off chlorine gas.
> ...


Hello please you have to be very carefully with all chimicalls espacly cyanide any ore you find it's not easy to be done by small scall especially gold the best way if you find gold ore get it assayed and cleam the place and sale it to big company's to have big success is to be done by big scale they use for most part cyanide if you find high grade ore it will be easy to sale refining metal it's not that simple and it can be dengerous you can work with some electronic scrap at small scall but ores to compacted for small scall


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## kurtak (Jun 27, 2022)

Liquidau said:


> Since the source was fingers, *there must be silver* and copper also leached out?


Per the bold print (in above quote) - there is *NO silver* in/on the fingers from circuit boards

If they are clean cut fingers (no solder) you have a layer of copper - then there is a layer of nickel plated on top of the copper - then there is a layer of gold plated on top of the nickel plating 

If there is solder on the fingers - then besides the copper/nickel/gold - you have tin & antimony (in the solder) if the fingers are from new boards - &/or lead (in the solder) if the fingers come from OLD boards

If you are processing the "silvery looking" fingers - *they are more then likely* tin plating over the copper 

There are some very rare exceptions where fingers were plated with silver - *BUT - that is VERY RARE* - & will *most certainly never* be found in everyday common consumer electronics 

Kurt


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## Liquidau (Jun 29, 2022)

Thank you Lads. I do work in an industrial lab and always under a hood. The carcinogenic aspects of Thiourea are well noted and the material is being handled carefully. I won’t ever touch cyanide or use it in processing.

The fingers are well trimmed from 10-15 year old boards. So the white precipitate is likely to be some complex of nickel, copper, tin or lead, and can be filtered out. But no point in reinventing the wheel here—-AP is the proper way to process fingers. I am attempting to extract the gold from incinerated, washed, magnetically separated, milled and centrifugally separated blue bowl concentrate. This has been leached with HCl to remove tin, lead and nickel, then washed thoroughly, then leached in nitric acid to remove copper and silver. Only PGMs should remain, along with some silicon residue. It is here that I’m investigating Thiourea rather than AR. 
Opinions are welcome and eagerly awaited. Cheers.


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## madscientistatlarge (Aug 13, 2022)

Would that be formamadine di sulphide


Deano said:


> Most people who research thiourea leaching get to the part where they read that thiourea is a carcinogen and then they lose interest in using it.
> If you make an informed decision that you want to use thiourea despite the known risks then that is your responsibility.
> The chemistry of thiourea leaching is that thiourea itself will not leach gold, the thiourea must firstly be converted by oxidation to formamidine di sulfide, this is the active leaching agent.
> The tricky part of the above is using an oxidising agent which has enough oxidising power to carry out the conversion but not so much oxidising power that it will keep oxidising the formamidine disulfide through to a mix of sulfates, nitrates and oxides which will just sit in solution without leaching gold.
> ...


Would that be formamidine di sulfide dichloride or?


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## Deano (Aug 13, 2022)

Formamidine di sulfide can be purchased as a chloride salt, the exact form is dependent on the supplier. The chloride salt is only stable in solution at pH values <1. If an oxidant is not present in the solution then the chloride salt form can be reduced to thiourea. This reduction is not clean and substantial losses of thiourea occur. After all this you now have to add an oxidant to get the thiourea to formamidine disulphide.
Much cheaper and simpler to just run an oxidant with thiourea solution and form formamidine di sulfide in situ.
Apart from the health aspects there two main reasons not to use thiourea leaching.
Firstly the pH must be acid, usually between 2 and 3, this means that the leaching circuit must be made of non-metallic components.
Secondly the gold thiourea complex will load only poorly onto collectors such as carbon and resin. This means that you have to recover the gold directly from the leach solution. Not easily done if you want relatively clean gold.
Deano


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