# Gold in Muratic acid and peroxide soultion



## 67eod (Jul 4, 2008)

I guess the way to test to see if there is gold in the solution used to strip the fingers is to use Stanis cloride. If there is how do you get it out,with SMB?


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## Smitty (Jul 4, 2008)

just add more smb until stannous test is clear of any more gold. If you find yourself adding too much smb and it still test positive then you might want to warm the solution up a little.


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## lazersteve (Jul 4, 2008)

Robert,

With AP, the amount of dissolved gold should be minimal. To save the cost of SMB you can keep using the AP on subsequent batches of fingers and as more copper is absorbed by the solution the gold will preciitate as a fien black powder. 

When adding SMB to AP the gold takes a very long time to settle and is difficult to filter out completey. 

I've tried both of the above mehtods and I prefer reusing the acid until the gold all precipitates out. You'll know the solution is saturated with copper when it changes to a chocolate milk color.

If you use SMB the gold can be reabsorbed if you let it sit in reactive AP too long.

Steve


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## cerise (Jul 10, 2008)

Steve
Im getting ready to put a 3rd batch of fingers into my AP solution.
So far i mixed 2000 ml of hcl and 1000 ml of h202 and put 900 g of fingers in and when they were done i filtered out and added 500 ml of hcl and 250 ml of h202 ,to spice it up a bit.Then i ran 500 g more fingers and i just filtered that and now my solution is turning amber brown.Can I keep going until the ap is muddy ,Also should i add any more hcl or h2o2.I want to run some more fingers.

Also Steve I have some 2inch round plates that are about a 1/16" thick, plated with gold.I think the plates are steal.If i run these through AR will the Iron affect my precipitant.I have some left over stuff from a place that i would rather not mention and Storm precipitant is what i am going to use to precipitate the gold.Im also using auqa regia from the same place.I hate to let that stuff go to waste.

Cerise


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## lazersteve (Jul 10, 2008)

You should *not* add any additional acid or peroxide unless the solution quits doing it's job. When you need to add always start with a little peroxide and give it some time to react. If the reaction doesn't pick up add a small amount of acid.

I posted some guidelines in another post about checking a sample of the acid peroxide with a few drops of water. You can find it with the search function.

The Shor Strom Precipitant is just SMB, use it the same way you use SMB.

The Sub-Zero is just sodium nitrate. Use it where you need NaNO3.

AR is *not* a good choice for steel objects plated with gold. I use hot HCl. This will free up the gold and then you can process the gold foils or powder in HCl-Cl or AR. Be sure you clean the resulting foils very well with HCl followed by lots of water before moving onto dissolving the gold.

Steve


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## cerise (Jul 10, 2008)

As always 
Thankyou
Cerise


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## Anonymous (Aug 12, 2008)

lazersteve said:


> With AP, the amount of dissolved gold should be minimal. To save the cost of SMB you can keep using the AP on subsequent batches of fingers and as more copper is absorbed by the solution the gold will preciitate as a fien black powder.
> 
> I've tried both of the above mehtods and I prefer reusing the acid until the gold all precipitates out. You'll know the solution is saturated with copper when it changes to a chocolate milk color.
> 
> ...



Out of sheer curiosity, I experimented by filtering some AP that we had used for several batches of depopulating boards. The color of the solution was a very dark green. I added some SMB to the filtered AP solution and saw a mild reaction. In letting it sit, the solution became very dark and deep red when held in direct light. Does anyone have any ideas what type of reaction I saw? At this point, I do not see any precipitate (or it's too fine to notice) so I think any gold is minimal, if any.


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## cmclean (Aug 14, 2008)

I have done three previous batches of fingers in AP and currently am processing the fourth batch, each with 500 grams of fingers.
The first batch was done with 2:1 HCL (31.45%) and H2O2 . I noticed on it quite a bit of black sediment. I was not able to obtain 3% H2O2 so I prepared it from 35% strength (86mls of 35% H2O2 and 914mls of water) to come up with 3% peroxide in 1 liter solution.
The subsequent two batches were done, in the same solution from the first batch, without adding anymore HCL or H2O2 but with continuous aeration from an air pump. Complete removal of gold fingers occured within 36 hours in both cases, as well as in the first one. 
I noticed in the second batch that the gold was composed of a rather large percentage of small/ very small particles and am still observing black sediment. The third batch had a lot less amount of small/very small particles, but still observed black sediment.
My questions;

From a previous post by Steve, I read that gold will not dissolve in the solution when you are using aeration instead of peroxide. I believe the black sediment observed be gold from the first run, or is it being also formed in the subsequent batches; or is it another material?

When gold is re-dissolved back into a reactive solution after adding SMB and not promptly removing it from the solution in , will it precipitate using SMB again?
What can be causing the formation of the small gold particles? The fingers were the same type in all cases. Nevertheless, these particles precipitate with SMB but a lot end up in the filters when you are washing and filtering.
Thanks


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## cerise (Aug 14, 2008)

The gold will precipitate when new gold fingers are added because of the copper in them.Copper will push the gold out in a black powder looking form.


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## cmclean (Aug 14, 2008)

Cerise: 

Thank you for your reply. 
As I understand the process, more copper will precipitate gold that is in solution; But my understanding from Steve's post is that with aeration, AP should not dissolve gold and therefore there should not be any precipitation from additional copper. Am I wrong?

Thanks
Carlos


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