# Gold-Selenide Separation



## Anonymous (Jun 10, 2010)

Hey everyone, just came across this forum by chance and joined and now I can't get off it!

OK, I have 60kg of black metal powder (obtained originally from a PM pregnant solution which was treated using SO2 with intention of selectively precipitating Gold, but too much was added and voila) which contains 27% Au, 51% Se, 16% Pd. 

I am currently working on the separation of the Gold and Palladium from Selenium, but am having trouble with the fact that the Se precipitates and dissolves with similar reagants to Gold, and I cannot seem to get rid of all of the selenium. There are of course pyromettallurgy processes which are possible, but my boss advises me to look for hydromettalurgical methods. Dissolving the solid isn't the problem, selectively separating the gold and palladium from selenium with the usual reagants (furrous sulfate, SO2, AR then Cl2, etc.) is however.

Any ideas guys? 

Thanks,


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## Irons (Jun 10, 2010)

amorrison5 said:


> Hey everyone, just came across this forum by chance and joined and now I can't get off it!
> 
> OK, I have 60kg of black metal powder (obtained originally from a PM pregnant solution which was treated using SO2 with intention of selectively precipitating Gold, but too much was added and voila) which contains 27% Au, 51% Se, 16% Pd.
> 
> ...



Distill off the Selenium as a Bromide using HBr. Be careful, Selenium is quite toxic.


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## lazersteve (Jun 10, 2010)

Don't know for sure if BDG (aka Dibutyl Carbitol or DBC ) is selective for gold verses Se, but it worth a shot. 

Steve


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## Platdigger (Jun 10, 2010)

What about first treating the powder with sulfuric acid to take up the selenium?
Would this effect some disolution of pd also?


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## Anonymous (Jun 10, 2010)

It doesn't matter if the Pd and Au end up together there will be no problem to separate them after, the problem is the Se. 

lazersteve: I thought about doing that (I'm going to try at least), but isn't DBC selective towards gold and not Pd? I'll have pure gold after treating it with oxalic acid but then the Pd is still stuck with Se in solution...

Irons: I'll let you know how that goes tomorrow

I'm currently using a method which involves precipitating the selenium in the form of MgSeO3 (Gold precipitates as well), but then I treat the solid with H2SO4 the majority of the Se dissolves. However in the process I still have leftovers everywhere of either Au and Se or Pd and Se. Attached is a quick diagram of what I'm talking about:




I've changed some of the ratios but the reagents remain pretty much the same. Currently my only problem is treating the "Blue Solution" without precipitating too much Se. I've been taking small samples and re-creating this but eventually I'll have 60kg to treat so just keep that in mind I guess...

Any Ideas? Suggestions? Comments?

Thanks for the ideas so far,
- A


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## Anonymous (Jun 10, 2010)

Platdigger said:


> What about first treating the powder with sulfuric acid to take up the selenium?
> Would this effect some disolution of pd also?



I tried that, a very minimal amount of Se was dissolved and maybe even none if you take into account the sytematic error on the machine I used to determine the make-up of the solid


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## Platdigger (Jun 10, 2010)

Have you tried H2SO4 with H2O2?


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## lazersteve (Jun 10, 2010)

Looking at your flow chart it seems like a very simple solution is to cement the Au and Pd with copper just after the first 'mix' block at the 'Au/Pd/Se dissolved in solution' block. 

Separating the cemented Pd and Au would be elementary (ie nitric acid) from that point on.

Steve


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## Harold_V (Jun 11, 2010)

Heh! If that was my problem, I'd likely use the same procedure I used when I encountered selenium rich slimes. Incinerate. It works. 
Roast the stuff in a pan, heating from below. You'll see the selenium coming off as a reddish brown fume. I did it in a fume hood. Probably a good idea. 

Harold


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## Lou (Jul 26, 2010)

Doing that in this day and age will get you fined out of existence if anyone got wind of it. 

I've had a bad, bad experience with Se once before and am now hypersensitive to it. 

Anyway, heat would be the way to get rid of it. 


I wonder if this fellow would entertain selling it all?

Lou


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## Harold_V (Jul 27, 2010)

Lou said:


> Doing that in this day and age will get you fined out of existence if anyone got wind of it.


Don't doubt that one bit, Lou. My experience was somethng like 25 years ago, although that certainly doesn't make it any more right. Likely not a good idea at all in today's world. 

Harold


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## Richard36 (Jul 27, 2010)

Can the Selenium gas produced by roasting be bubbled through some solution in order to capture it, thus creating a Selenium solution of some sort, similar to making Osmic Acid?

Just a thought, and an interesting question.


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## core (Nov 11, 2013)

Hey Guys,

Something is amiss here- If im reading this correctly then lazersteve and irons have submitted conflicting information.

Topic: Cementing with copper 

Platdigger wroteoes anyone know,
if there are any elements,
other than precious metals,
that if present in an acidic solution,
will cement out with copper?

such as rare earths, etcetera...?


In acid solution:
Hydrogen 0.00V +1>0
Sb .204V +3>0
As .240V +3>0
Bi .317V +3>0
Re .415V +7>0
Cu .520V +1>0
Se .740V +4>0
Rh .760V +3>0
Ag .799V +1>0
Hg .854V +2>0
Pd .915 +2>0
Ir .926V +4>0
Pt 1.19V +2>0
Au 1.52V +1>0

Just thought I would bring it to the attention of moderators, but now I still search for the total reactivity series that includes silicon.

Core


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## butcher (Nov 11, 2013)

I do not see the conflicting information you mention.

Laser Steve stated:
"cement the Au and Pd with copper"

the chart your referencing to is an electromotive series, or electrode potential series chart, these deal with electrode potentials with reference to hydrogen, usually used more in the electrolysis of metals and determining what metal will plate to which, or in figuring the voltages of the battery made with two dissimilar metals...

https://www.google.com/#q=electromotive+series
https://www.google.com/#q=electrode+potential+series

although very similar but a bit different when cementing metals I normally us e the reactivity series of metals as a reference.
https://www.google.com/#q=reactivity+series+series
Or the electrochemical series of metals.
https://www.google.com/#q=electrochemical+series+of+metals

example:
K
Na
Li
Ca
Mg
Al
Ti
Mn
Zn
Cr
Fe
Ni
Sn
Pb
Bi
Cu
W
Ag
Pd
Pt
Au

From above we see (in the reactivity series)where copper is above palladium and gold, so if any of these were dissolved in a solution they could be cemented out of solution with a piece of copper metal.

Where copper metal would give up electrons to the dissolved the ions of gold in solution, the atoms of gold now having a full shell of electrons would cement out of solution as a metal gold powder, copper atoms losing its electron would become a dissolved copper ion in solution, now if we removed the solution from the gold, and we could put a piece of iron metal in solution to replace the copper, cementing the copper out of solution as copper metal, leaving us with a solution containing iron ions, now if we put a piece of tin metal in solution, nothing would happen tin is less reactive than iron so tin will not replace iron from solution.


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## Platdigger (Nov 11, 2013)

Thing is Butcher, from my research at least, selenium as well as tellurium will both cement out to copper.
This is what core is referring to with regard to what Steve posted about using copper cementation as a means of separating gold and pd from se. It may not work unless there was a time factor involved.
In other words unless they cemented out sequentially and timing could some how be used.


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## butcher (Nov 11, 2013)

Platdigger, Ok I see now, what you and Core are saying, I do not think Steve studied the reactivity of selenium and tellurium with the relationship to copper.


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## Spiritfire (Dec 15, 2013)

If I may offer a suggest. I am currently working with a very high grade gold telluride and the cross solubility of tellurium was driving me crazy. And then I found that a warm solution of ammonium sulfate will dissolve the gold but not the tellurium. This gives a clear and colorless solution that produces beautiful small gold crystals on copper as a cementation agent/ This should also be true of gold selenide ores.

Randy in Gunnison


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## Reno Chris (Mar 9, 2014)

My thought was once the selenium was in solution in a strongly oxidizing environment, it would be found as a selenate, and one could just add Barium chloride and drop the selenium out as an insoluble barium selenate.


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## butcher (Mar 10, 2014)

Reno Chris,
It is great to see you back, I always love to read your posts on dealing with ore.
I always found so much valuable information in your discussions.

You were missed.


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## Irons (Mar 10, 2014)

Reno Chris said:


> My thought was once the selenium was in solution in a strongly oxidizing environment, it would be found as a selenate, and one could just add Barium chloride and drop the selenium out as an insoluble barium selenate.



Sounds good to me. Any Sulfates in the solution will also precipitate the Barium, so one would want to do this before adding Sulfuric to precipitate any Lead.
The solubility of Barium Selenate is 50mg/l at 20*C, so cooling down the solution would also help.

Barium Arsenate is also very insoluble, so one would precipitate that as well.


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## Reno Chris (Mar 11, 2014)

> You were missed.



Thanks. Just been busy. About to head for Africa to teach Africans about finding gold with a metal detector (for the second time in the last year).


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