# How to eliminate copper from nitric solution with palladium



## LProcess (May 10, 2018)

Hi there, 

In this period I work on a scrap with 80% of copper, 12% of Silver and 8% of palladium.

The process is this:

- Nitric to dissolve the CU/AG/PD alloy
- Than i use HCL to precipitate Ag as AgCl

-*I'm looking for a solution to precipitate Cu without precipitate palladium*

- After this i will add Ammonia to the solutions and than i will dorp down the palladium as yellow salt with HCl at PH 3, and than i will reduce the yellow salt with formic acid.

Any ideas?

Thanks


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## FrugalRefiner (May 10, 2018)

Well, first, if you're digesting it with nitric, you're not using AR which is a combination of hydrochloric and nitric acids, so I'm going to edit the title of the thread.

After dropping the silver as AgCl, why not drop the palladium by cementation on copper as your second step?

Dave


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## LProcess (May 10, 2018)

Hi Dave, 
thanks for your reply.

But cementing palladium on copper is slow and is very difficult remove the palladium on the copper surface.

The best way is drop the copper like metal or salt, but i don't know how i do it.

Thanks


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## Lino1406 (May 10, 2018)

Watch selective etchants on chemical processes


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## LProcess (May 11, 2018)

Thanks Lino! 

The only chance at moment to eliminate copper is reduce palladium with NaOh and Formic acid after nitric digestion.

I think this because copper with formic doesn't react, it react with NaOh a little bit, then i refining again the palladium to increase the purity.

Any ideas are welcome! 

Thanks


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## Lino1406 (May 11, 2018)

If you looked at selective etchants you may have seen that ammoniak + H2O2 is assumed dissolving copper selectively.


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## LProcess (May 11, 2018)

Thank you Lino!

I'll try in this evening A/P!

I use Formic/NaOh on copper only this morning but the copper precipitate, this way is wrong, because copper 2+react with formic and soda too.


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## kurtak (May 11, 2018)

LProcess said:


> Hi Dave,
> thanks for your reply.
> 
> But cementing palladium on copper is slow and is very difficult remove the palladium on the copper surface.
> ...



LProcess

Hi & welcome to the forum

Per the underlined - my first question is - when trying to cement the Pd with copper are you just simply putting the copper in your solution & letting it sit there ? --- or are you adding some kind of agitation to the solution such as a bubbler or constant stirring of the solution ?

I ask because when cementing PGMs "without" agitation will cause the PGMs (Pd in your case) to "adhere" to the copper which then create a passivation layer on the surface of the copper

This passivation layer on the copper can/will cause the cementation process to slow down - even to the point of stopping the cementing thereby preventing full recovery of the PGMs from the solution --- & as you already pointed out - removing the passivation layer from the copper is difficult if not impossible

By providing "constant" agitation to the solution the solution is in constant motion with the surface of the copper & that constant motion does not allow time for the PGMs to adhere the surface of the copper but instead keeps them "washed off"

The more aggressive the agitation the better

You have two options when cementing with copper (along with agitation)

1) using "fine" copper powder - this needs "constant" stirring for the agitation in order to keep the fine copper powder in suspension during the cementing process

2) heave pieces of copper (like copper bus bars) "suspended" in the solution along with a bubbler for the agitation 

start you agitation "before" adding the copper other wise if you add the copper before starting the agitation the PGMs will "start" the cementing which will allow the passivation layer to get a head start

Here is a link to a "detailed" discussion about cementing PGMs with copper which details the problems & the solutions - the real discussion starts about 3 or 4 post down with my first post in the thread

:arrow: http://goldrefiningforum.com/phpBB3/viewtopic.php?f=49&t=21218&hilit=cementing

Kurt


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## LProcess (May 11, 2018)

Hi Kurt, 
thanks to welcoming me.

Your solution is good, but It's slow for my processes.
But I'll take it my mind! 

Lino I tried your way, but the best way is the nitric attack.


Thank you!


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## Owltech (May 12, 2018)

LProcess said:


> Thank you Lino!
> 
> I'll try in this evening A/P!
> 
> I use Formic/NaOh on copper only this morning but the copper precipitate, this way is wrong, because copper 2+react with formic and soda too.



copper hydroxide or carbonate (if Na2CO3 instead of NaOH is used) and formic acid should form a soluble product - cupric formate.

Do you have a picture of your "copper precipitate"?


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## anachronism (May 12, 2018)

OK so why not use Ascorbic acid to precipitate the Palladium?


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## Lino1406 (May 12, 2018)

Ascorbic acid precipitates copper as copper(I) oxide. In every case mentioned here you'll have copper traces with palladium


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## anachronism (May 13, 2018)

Lino1406 said:


> Ascorbic acid precipitates copper as copper(I) oxide. In every case mentioned here you'll have copper traces with palladium



As you say though in trace amounts of copper right? Leaving the vast majority in solution. The Pd is then metallic and doesn't need to be made into a toxic salt. Pretty much a win win.


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## Lino1406 (May 13, 2018)

What is your preferred way to separate palladium and copper(I) oxide? I do it with ammoniak


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## Platdigger (May 13, 2018)

What if this alloy was first ground to powder.
Then roasted in the presence of air or O2 to convert all the metals to their oxides.
First leached with ammonia to take up silver, rinsed.
Then leached with dilute sulfuric, leaving behind PDO.
?


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## Yggdrasil (May 13, 2018)

Well I did a test on PGM powders containing copper. My cementing went less then perfect.
It had quite an violent reaction, household ammoniahydroxide and appr 6-8 percent H2O2.
I guess the main reaction lasted less then 30 minutes, I even tried air bubbling but it was quite foamy.
How will one know if the reaction is complete? It still fizzes quite intense when the peroxide is added.
And the color is quite intense bluish purple, really a beautiful color.

To get some comparison I'll add a few pieces of PCB and try it as a caustic AP variety, just to see if it can hold up speed and durability. I'll try it after my Vacation I guess.
How does the ammoniaceroxide behave agaist Iron and Aluminum?


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## Lino1406 (May 13, 2018)

Of course the reaction is complete when no blue appears - but please inform if you have palladium traces in the ammonia digestion mix (especially in presence of PdO). Iron and aluminum complex with ammonia should not be expected


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## Yggdrasil (May 14, 2018)

In this specific instance it reacts violently due to fine copper powder and the color became opace indigo/blue almost immideately. I have now diluted with water rinses so its cleaning up.
I guess it is not possible to test these solutions with stannous so how would one test for palladium here? DMG? 
Anyways it should not contain PdO since it has been cemented out from solution in the first place.
Do you usually run a tight Ph regime on these leaches? I saw it was recommended with Ph 8.5.
I have just used straight 9 percent household Ammonia with no further adjustment.


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## Lino1406 (May 14, 2018)

DMG is fine (I refer to starting point with both metals, Cu and Pd)


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## LProcess (May 15, 2018)

Thanks to all!

I reduce palladium with Alluminium and it's not so bad. I check the end with SnCl2. 

Do you like this ways? 

I have much scrap, I need a way fast and clean!

Thanks Again!


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