# Economical Seperation of Copper from Gold



## Higashi (Aug 15, 2010)

I have scraps comprised mainly of Copper and Gold, maybe some Nickel.

It's from PCBs, incinerated them. Filtered away all the ashes and debris.

Now all I have is the metals. Haven't done anything chemical yet to them.

I sat down, make some research on common copper and gold thickness on PCBs, played with data on Excel and find that Molality-wise there's way too much copper against gold in most configuration of copper/gold thickness.

I find that seperating copper from gold using HNO3 is quite costly. A kg of HNO3 70% cost more than 1kg of copper it self.

1kg of HNO3 costs me like US$12/kg.
1kg of Copper is valued at US$7/kg

0.5 ounce/ft2 PCB has USD1.05 worth of copper per m2. (0.156kg/m2, 2.467 mol/m2)
to seperate gold from that copper using HNO3 costs USD5.08 (4.92 mol/m2).

is there a cheaper way? I know the profit from gold will offset the cost of getting rid of the copper,but just to be safe i think it's best to keep every step in the procedure not inducing financial loss.

What if I use FeCl3 PCB etchant? Will the iron in it cause me trouble later?


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## qst42know (Aug 15, 2010)

Keep in mind your ash will contain values. You need large quantities to make it pay though.

As a hobby it can pay for itself (maybe plus a little), as a business you need large scale.


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## Barren Realms 007 (Aug 15, 2010)

Higashi said:


> I have scraps comprised mainly of Copper and Gold, maybe some Nickel.
> 
> It's from PCBs, incinerated them. Filtered away all the ashes and debris.
> 
> ...



You are possibly washing away values when you are washing your ashes away. If you are intent on processing this way I would consider putting the stuff in a all mill and then with some flux melt it up and shot it. Then process it in nitric. But that is a lot of work/expense for little return.


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## philddreamer (Aug 15, 2010)

How about AP?

Phil


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## Barren Realms 007 (Aug 15, 2010)

philddreamer said:


> How about AP?
> 
> Phil



For what he is trying to do it would create too much fluid to deal with. Run it in nitric. Clean and process your gold. And adjust the PH on your fluid to drop your your copper.


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## Lou (Aug 15, 2010)

Electroplate the copper out in a cupric sulfate/H2SO4 bath. Black-brown residue is your gold. Sulfuric is quite cheap.

If you've got all the time in the world, use HCl and sparge with air. Add a couple drops of nitric to initiate the reaction, and let it go for a couple days.

And I'm sure you've aware...you're overpaying for your nitric, it should be a dollar or so per kilogram for technical grade (if even).


Lou


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## Higashi (Aug 16, 2010)

Barren Realms 007 said:


> Higashi said:
> 
> 
> > I have scraps comprised mainly of Copper and Gold, maybe some Nickel.
> ...



The PCBs are still plastics... it's just laminates, one single layer of multi-layer PCBs, unpopulated. Looking at the chemical make up of mostly used polymers in PCB making, the ashes are just probably mostly carbon, silica stuffs, sulphurs, chlorines etc. sulphurs and chlorines i think are already gone as gases, i think.

i got loads of them. like, over a thousand cubic feet solid.


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## Higashi (Aug 16, 2010)

philddreamer said:


> How about AP?
> 
> Phil


for the last one month, i've been studying AR recipe only. I suppose that AP works on gold, right? I just need to dissolve the copper first, as cheap as possible. Using HCl also doesn't make sense because HCl cost about the same here.


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## Higashi (Aug 16, 2010)

Lou said:


> Electroplate the copper out in a cupric sulfate/H2SO4 bath. Black-brown residue is your gold. Sulfuric is quite cheap.
> 
> If you've got all the time in the world, use HCl and sparge with air. Add a couple drops of nitric to initiate the reaction, and let it go for a couple days.
> 
> ...



oh wow.. that's cheap. 
one supplier quoted me $8/kg, the other one $20/2.5L

the grades for both is EP (i think that stands for Extra Pure).

I'm in time constrain, I could go explore the electrolysis process on my own but it takes time before i could find a good tutorial. Can you, Sir, recommend a good source of readings?

I used to make a few power supply for use with diy cnc machines. i could make one for a electroplating tank i think. I need to understand the chemistry, so i can study the economy of it.


oh my, with $1/KG it really makes a lot of difference.


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## goldsilverpro (Aug 16, 2010)

Here's one thread. I'm sure there are others.
http://www.goldrefiningforum.com/phpBB3/viewtopic.php?f=37&t=6652&p=59443&hilit=copper+sulfate+sulfuric#p59443


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## Higashi (Aug 16, 2010)

goldsilverpro said:


> Here's one thread. I'm sure there are others.
> http://www.goldrefiningforum.com/phpBB3/viewtopic.php?f=37&t=6652&p=59443&hilit=copper+sulfate+sulfuric#p59443



thanks!


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## Higashi (Aug 16, 2010)

Question 1 : Stainless Steel Tray as Cathode and Stainless Steel Mesh to hold Anode

I read that it's okay to use Stainless Steel (passive) as cathode. If this is okay i'm thinking of getting Stainless Steel food tray rather than copper plate (1.5" wide is gettable, normally used as lightning conductor. could "borrow" from any building nearby, LOL). Now that gives a good surface area coverage... 

For the anode, is it okay to use Stainless Steel mesh/cage that wraps around the gold plated copper? I guess it's better not to melt the gold-plated-copper because i believe the plating will remain in it's original form (flakes) rather than powder/sponge hence more manageable. 

I don't see any sense in using copper mesh as part of the anode. It'll dissolve.

Question 2 : Molarity of Copper Sulphide

It's read that CuSO4 solution below 1.0M is safe, higher than that is not recommendable.
It's also read that at concentration of 2.0M the collection of copper around cathode increase greatly with the increase of voltage, less steep graph of collection vs. voltage is recorded with lower concentration 1/0M.

Do i understand it correctly?
Is it really that unsafe at at least 2.0M?

Question 3: What's the good voltage?

Most literature touch on the amperage. 10A-11A per square foot. 
Hard to get guides on the voltage level.
The higher the voltage the better?



thanks


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## Higashi (Aug 18, 2010)

Note to myself and other newbies...

One excellent primer course reading material : 

1. http://mech2006.vtk.be/downloads/mech2005/2e/materiaalkunde/5-b%20copper.pdf

will add more.


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