# Cleaning the goldfingers



## Walcam (Jul 5, 2019)

I have read that most people use HCl + H2O2 to strip the foils of gold fingers but i would like to know if i can just use 62% Nitric Acid to do the same job?

And how would i precipritate the copper from the solution after? could i use ammoniumhydrogencarbonat?


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## rickbb (Jul 5, 2019)

Why complicate a rather simple, effective and cheap process?

If you just want to use some nitric, go straight to the AR process.


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## Walcam (Jul 5, 2019)

It was more if it is possible as i had run out of H2O2 and i wanted to strip some foils


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## FrugalRefiner (Jul 5, 2019)

Yes, you can use nitric, but I'd dilute it.

Dave


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## anachronism (Jul 5, 2019)

rickbb said:


> Why complicate a rather simple, effective and cheap process?
> 
> If you just want to use some nitric, go straight to the AR process.



Why say that Rick? I don't understand the logic because it's a perfectly viable way to do it.


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## kernels (Jul 6, 2019)

Also, you don't really NEED H2O2, it is really just to get the leach kick-started. You can also just burn some copper over a flame and place that in HCl until the HCl becomes discolored, then carry on as per usual. Then bubble air through with an aquarium air pump to keep the leach going.


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## Walcam (Jul 6, 2019)

thats great.
How do i proceed with the nitric waste then? is it possible to revigorate it? and since it now contain copper, can that be precipritated or will that destroy the solution for further use?

As i mentioned earlier i have some ammoniumhydrogencarbonat, but am unsure about the chemestry in regard to using that


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## kurtak (Jul 6, 2019)

Walcam

Yes you can use 62% nitric - but as frugalrefiner said you NEED to dilute it - with 62% nitric you will need to dilute it by 50% --- you should use distilled water --- the reason for that is that most tap water has been treated with chlorine & chlorine is an oxidizer for gold meaning that chlorine along with nitric has a potential to dissolve gold --- That said - you can eliminate the chlorine from tap water by filling a 5 gallon (20 liter) bucket with the tap water & let it sit out in the sun for a day before using it to dilute the nitric 

However - unless you get your nitric CHEAP - using nitric is an expensive way to go - it takes about 4 times more nitric to dissolve copper then it takes to dissolve silver or gold

Example - to dissolve "about' 1 gram of silver it takes about 1 ml of 67% -70% diluted with 1 ml of distilled water --- or to dissolve about 1 gram of gold it takes about 3 - 4 mill of HCl & about 1 ml of 67% - 70% nitric --- to dissolve 1 gram of copper it takes about 4 ml of 67% - 70% nitric diluted with 4 ml water


So - because it takes about 4 times more nitric to dissolve copper then it takes to dissolve silver or gold - unless you get your nitric "cheap" it could cost you more then the value of the gold foils you recover from using nitric to dissolve the copper in order to recover your gold foils --- that is why "most" people use the AP process (or actually the CuCl2 process) instead of using nitric

How much do you pay for your nitric ? 

As kernels said you don't "need" the H2O2 to do the AP (or CuCl2) process - you can do it with just an air bubbler in your HCl it just takes a little longer for it to start working - or - as kernels said - "You can also just burn some copper over a flame and place that in HCl until the HCl becomes discolored" 

To clarify - the AP process (acidic peroxide) is actually a copper 2 chloride (CuCl2) process --- the H2O2 being added to the HCL is the oxidizer to "kick start" the CuCl2 process by dissolving a small amount of copper which once that starts the CuCl2 continues dissolving more copper - adding an air bubble "helps" to keep the CuCl2 moving long (speeds the process up) as a result of oxygen from the air bubbler helping oxidize (dissolve) the copper --- so you actually need VERY LITTLE H2O2 to kick start the process
--- it is also why you can do it with out the H2O2 & do it with just an air bubbler - it just takes a little longer for it to get going because the oxygen from the air bubbler is not as strong an oxidizer as the H2O2 - but once the the oxygen "starts" dissolving copper - the CuCl2 takes over & continues dissolving copper


You should also be made aware the H2O2 is an oxidizer for gold - so you can use to much H2O2 in this process in which case you can end up dissolving both copper & gold where as oxygen from an air bubbler is not a strong enough oxidizer to dissolve gold but will continue to dissolve copper once the CuCl2 has started working --- many new members make the mistake of using to much H2O2 in the begainning - you only need a small amount of H2O2 to get the CuCl2 procss going --- which is why kernels told you you don't need H2O2 but that you can kick start it by burning some copper - which oxidizes the copper - then once the copper is oxidized the HCl will dissolve the oxidized copper which in turn kick starts the CuCl2 which in turn causes the CuCl2 to continue the process of dissolving the copper which in turn moves the process along by adding an air bubler to the process

Hope that all helped you understand the process

Kurt


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## kurtak (Jul 6, 2019)

Walcam

To answer your question about recovering the copper you dissolve - whether you dissolve the copper with nitric or with the CuCl2 process

this is done by a process we call cementing which is actually an ion exchange process & it works because of the "reactive series" of metals --- metals are ether more - or - less reactive depending on where they are in the reactive series

The more reactive they are the more potential they have to oxidize (dissolve) --- so - if you take a metal higher in the series & put it in a solution that has a metal lower in the series dissolved in a solution - the higher series metal will start dissolving there by putting those higher series metal ions into solution - this in turn "exchanges" the lower dissolved metal ions thereby causing them to drop out of the solution as there metal - or as we call it "cementing" the lower series metal out of the solution with a higher series metal

here is a link to the reactive series of metals

:arrow: https://en.wikipedia.org/wiki/Reactivity_series

As you will see in this series --- copper is above (higher) then silver, gold & PGMs --- therefore if you have silver or gold or PGMs (Platinum Group Metals) dissolved in solution you can "cement" the silver or the gold or the PGMs back out of solution by putting a piece of copper in the solution

What happens is that when you put the copper in the solution is that the acid goes to work dissolving the copper putting copper ions into solution because the copper is "more" reactive then the silver the gold &/or the PGMs --- as the copper ions go into solution it "displaces" the silver, gold or PGMs back out of solution as a result of the silver, gold or PGM ions being exchanges for/with the copper ions 

Now then - you will see that iron is higher in the series then copper --- therefore we use iron to cement copper back out of solutions that have copper dissolved in them

Here again - we use an air bubbler to help with the cementing process - the air bubbler is used to keep the solution in motion so that all the lower (dissolved) metal ions (copper) come in contact with the piece of higher series metal (iron) being used for the cementing process in order to insure that the cementing process works to completion -- in other words - if you don't use the air bubbler it will likely only cement the copper near the iron but not all the copper further away from the iron --- you want the solution in motion so that all the copper ions come in contact with the iron thereby allowing the iron to make the exchange with the copper ions forcing the copper to cement out of the solution 

Kurt


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## kurtak (Jul 6, 2019)

rickbb said:


> Why complicate a rather simple, effective and cheap process?
> 
> If you just want to use some nitric, go straight to the AR process.



Sorry rickbb but using nitric to dissolve the copper under the gold plating in order to recover the gold foils is NOT more complicated then the AP/CuCl2 process

In fact IMO (& I have been doing this for something like 10 - 11 years) using nitric is far less complicated then the AP/CuCl2 process & if nothing else - using nitric is faster - MUCH - faster

The only real questions here is cost &/or availability for the nitric --- most people here use the (IMO more complicated) AP/CuCl2 because they are ether paying a VERY high price for nitric or they can't even get it

By VERY high price for nitric - I have seen where people are paying from $40 - $60 for a liter of nitric & at those prices it will cost you more then the value of the recovered foils

on the other hand - I have NEVER used the AP/CuCl2 process for recovering gold plating (whether from finger or from pins) I have "always" used nitric & I have recovered MANY ozt. of gold from MANY pound of finger & pins 

Why do I use nitric instead of AP/CuCl2 ?


Because with nitric I can recover my foils in a matter of a "few" hours (2 -4 hour depending on batch size) compared to the days it can take with the AP/CuCl2 process --- & I buy my nitric for about $2.50 per GALLON - which is less then I pay for HCl

The only way I would every use the AP/CuCl2 process for gold foil recovery is if I could not get nitric &/or had to pay the high price for nitric that most member here have to pay

The "only" reason the Ap/CuCl2 became the go to method of foil recovery here on the forum over that of using nitric is because MOST members here ether can't get nitric or they have to pay a VERY high price for it --- it has NOTHING to do with nitric be more complicated - nitric is less complicated IMO

& for what its worth - going direct to AR is NOT the way to do it - recover you foils - then process the foils with AR

Kurt


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## Walcam (Jul 6, 2019)

Thank you so much, that was very helpful

Fortunately the tapwater in Denmark is of a high quality and is not treated with any chemicals at all so i am not worried about chlorine in the water.

I ran out of H2O2 quite fast on my first runs, so i guess i did the rookie mistake, and i have a huge amount of acid waste from very few foils, that i need to figure out what to do with, and as per your explaination now im worried if it contains gold also.
Also i guess i did something wrong as my AP solutions is pitch black and full of some muddy content at the bottom.
(my first run i just tossed fingers, pins, IC's and other stuff into the sollution so it is quite contaminated)

I managed today to find an airbubler for half the price of a small bottle of H2O2.
I read somewhere that i can restart my AP solution by letting air bubble through it, so i guess ill try that to see if i can bring it back to life.

Regarding your explaintaion about the reative metals, that makes good sence, however i have read that when it come to AR solutions you need to neutralise the AR before adding the SMB. Why is this nessesary? is that to minimize SMP usage? and what will happen tp the AR solution after? can it still be reused or will it turn to waste?

As Chemicals is a bit hard to come by in Denmark, i have added the chemicals i do have access to in a shortlist below so that you can tell me if some might be able to substiture others.
I am not sure if all is usefull for metal recovery and would appreciated if you could let me know which to not consider.

Nitric Acid 62%
HCl 30%
H2O2 10% (run out and very expensive to repurchase)
Chlorine
Potassiumpermanganate
Ammonium bicarbonate
ammoniawater 24%
sodium metabisulfite
i do not have access to urea


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## lanfear (Jul 7, 2019)

All you need is nitric acid, hydrocloric acid and SMB. Forget Urea. You should look for sulfamic acid (tile cleaner)(sulfamin syre). Its used to neutralize free nitric in solution. You could offcourse use an excess of smb to neutralize free nitric. But if you have alot of free nitric, you have to add alot smb, and you could end up with a big mess..
If you want to start a new batch of AP, just pour a few dl(metric) of old AP into the new batch.


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## kernels (Jul 7, 2019)

It sounds like you already have some AP solution from a prior run then ? Just add 200mL of that solution in with fresh HCL and run with air bubbler. Voila . . . fresh AP


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## rickbb (Jul 8, 2019)

kurtak said:


> rickbb said:
> 
> 
> > Why complicate a rather simple, effective and cheap process?
> ...



Too each their own. I'm glad you have success with nitric and can get it cheaply. I can't, even tried making my own, still not that cheap, or all that easy to do. 

I'm in no hurry to get the foils done so putting them in a bucket of AP and going off to do something else for a few days or weeks is not a big deal to me.

I do have to ask though, why put clean foils in AR? I use HCL and bleach, IMHO safer and all you need to do to dechlorinate is put it on low heat. I only use AR on alloys, like karat scrap, etc. And then it's poor mans AR. In fact I've almost quit using nitric, I only keep it around for any silver digestion needs that may come up.

I know nitric can and is being used safely all the time, but in a previous job I used it by the 55 gal drums. I never liked it, it was always a concern. Some of my employees were always letting it get out of hand and making a brown cloud. Once even had to evacuate the whole building and call hazmat in to get the reaction back under control. That guy got fired. Any time I can avoid nitric I will.


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## anachronism (Jul 8, 2019)

Don't ya love good debate? 8) 8)


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## kurtak (Jul 9, 2019)

anachronism said:


> Don't ya love good debate? 8) 8)



Don't have time right now - very busy for next couple day

Will get back to this thread to answer both rickbb & Walcam in a couple days

Kurt


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## rickbb (Jul 9, 2019)

Now worries, and not really a debate. We all use what works for us, just curious about it is all.


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