# Platinum nuggets



## ps_jb (Jul 21, 2016)

Hi guys,

FInished panning platinum paydirt - got about 1g of small (~ 20# mesh) Pt nuggets. Also I have a lot of black sand - did my best but it's practically stays with Pt.

Question - can I remove black sand by HCl? HNO3? First calcine in air to 600C and then acids?

Magnet will not work because natural Pt is alloyed with Ni, so it is magnetic too

Thank you!


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## Lou (Jul 21, 2016)

Dilute sulfuric acid will do the trick. Some hydrogen peroxide will help. 

Beware of any sulfides...they make poisonous H2S upon acidification. Peroxide prevents this.


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## ps_jb (Jul 21, 2016)

Lou said:


> Dilute sulfuric acid will do the trick. Some hydrogen peroxide will help.
> 
> Beware of any sulfides...they make poisonous H2S upon acidification. Peroxide prevents this.



Got it. Diluted - 0.5M or 1M H2SO4?

Peroxide concentration as for piranha or just a noticeable amount to oxidize H2S to SO2?


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## Lou (Jul 21, 2016)

Perhaps 15% w/v H2SO4 is sufficient. I usually just covered it over with cold water, a bit of salt, and then put the sulfuric acid in (cautiously) until a good simmer was obtained. I did this in a hood because of the risk of hydrogen sulfide (or worse, selenide or arsine if sperrylite is present). 

I'd only use enough peroxide to keep the ORP high at first to ensure sulfides are destroyed as peroxide can sometimes passivate the iron oxide preventing the formation of ferric sulfate and the intended purpose, but if there's much FeS or Fe2S3... it's important to use at first to keep the stink down. The peroxide will decompose on its own.

Another oddity about removing iron...sometimes it's best to add large metallic iron pieces and stir to remove the iron oxides--ferrous sulfate is much more easily formed.


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## ps_jb (Jul 22, 2016)

Lou said:


> Perhaps 15% w/v H2SO4 is sufficient. I usually just covered it over with cold water, a bit of salt, and then put the sulfuric acid in (cautiously) until a good simmer was obtained. I did this in a hood because of the risk of hydrogen sulfide (or worse, selenide or arsine if sperrylite is present).
> 
> I'd only use enough peroxide to keep the ORP high at first to ensure sulfides are destroyed as peroxide can sometimes passivate the iron oxide preventing the formation of ferric sulfate and the intended purpose, but if there's much FeS or Fe2S3... it's important to use at first to keep the stink down. The peroxide will decompose on its own.
> 
> Another oddity about removing iron...sometimes it's best to add large metallic iron pieces and stir to remove the iron oxides--ferrous sulfate is much more easily formed.



Got it will try

I hope I will not de-alloy PtxFe nuggets, otherwise it will be a Pt-dust mud

Thank you - very useful comments


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## ps_jb (Jul 26, 2016)

Updates.

I used ~5M H2SO4 with ~ 10wy% H2O2. All black sand was intact. Some Pt flakes became shiner, but insignificantly

So basically method does not work for magnetite removal. Which is very strange - FexOy should be soluble in diluted sulfuric


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## Platdigger (Jul 26, 2016)

Haha, it is not stange. Do you know how many different oxides of iron there are? Not to mention all the other elements in their different forms, compounds, alloys, oxides and well, I am sure I still missed some.


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## Lou (Jul 27, 2016)

add a small amount of NaBr and see if that helps depassivate it.

Alternatively/additionally, put some metallic iron in there too. Oddly enough, reducing conditions sometimes help pull iron oxides into solution. 

Lou


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