using poor mans AR

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ItsaboutROI
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using poor mans AR

Post by ItsaboutROI » October 10th, 2019, 6:31 pm

Please forgive me if the answer to this question is somewhere in the forum. If it is maybe someone can tell me where to look?
question:
Reading hoke's book we are supposed to dissolve the base metals with nitric acid. If we are using poor mans AR how do we dissolve the base metals then? Since we have no nitric acid?

Refining Rick
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Re: using poor mans AR

Post by Refining Rick » October 10th, 2019, 6:44 pm

In basic terms. The nitrate you use (potassium/sodium) "creates" nitric in solution. This creates A/R and it dissolves most everything.
You can make nitric acid from your nitrate salt and sulfuric acid to use to remove base metals. Just search the forum for instructions.
"The time has come," the Walrus said,"To talk of many things. Of acids and chips and sulfamic. Of precipitants and PMGs. And why A/R is boiling hot. And whether nitric dioxide has wings."

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FrugalRefiner
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Re: using poor mans AR

Post by FrugalRefiner » October 10th, 2019, 7:08 pm

ItsaboutROI wrote:
October 10th, 2019, 6:31 pm
Reading hoke's book we are supposed to dissolve the base metals with nitric acid. If we are using poor mans AR how do we dissolve the base metals then? Since we have no nitric acid?
ROI, there is a way of using poor man's AR to dissolve base metals before dissolving our values.. sort of...

To make a very simple example, let's assume we have some "stuff". If we add a bucket full of AR we'll dissolve everything and have a mess.

But if we add a little AR, we'll dissolve a bit of everything, but as the acid is consumed, any values will cement out on any remaining metallic base metals. We can decant the spent acids, now saturated with base metals, and send them through our waste treatment circuit.

Now we can add more AR, and repeat the process as needed till we reach the point when the solution tests positive for values, indicating that there are no more base metals remaining. Then dissolve what's left and proceed as usual.

Dave
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ItsaboutROI
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Re: using poor mans AR

Post by ItsaboutROI » October 12th, 2019, 8:02 pm

Thank you for the responses. The forum books 1&2 say that acid peroxide will dissolve the base metals but i am not sure how well that will work with gold filled scrap. likely if its good scrap the gold layer is still covering all the base metals. FrugalRefiner, I think the method you mention in your post may work for dissolving the gold layer 1st only. However its highly likely i will still get some base metals dissolved..

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FrugalRefiner
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Re: using poor mans AR

Post by FrugalRefiner » October 12th, 2019, 9:15 pm

ItsaboutROI wrote:
October 12th, 2019, 8:02 pm
FrugalRefiner, I think the method you mention in your post may work for dissolving the gold layer 1st only. However its highly likely i will still get some base metals dissolved..
You've missed the point. The purpose of the method I've described is not to "dissolve the gold layer 1st only". Some of the gold will definitely dissolve, but as the acid is exhausted, any values will cement back out of solution on the remaining base metals. We decant the solution and repeat the process a couple of times, each time dissolving some values, but each time they cement back out on the remaining base metals. At the end, our goal is to have only a small amount of base metals with our values. It takes some experience, but it's a useful technique.

Dave
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ItsaboutROI
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Re: using poor mans AR

Post by ItsaboutROI » October 12th, 2019, 10:47 pm

FrugalRefiner wrote:
October 12th, 2019, 9:15 pm
ItsaboutROI wrote:
October 12th, 2019, 8:02 pm
FrugalRefiner, I think the method you mention in your post may work for dissolving the gold layer 1st only. However its highly likely i will still get some base metals dissolved..
You've missed the point. The purpose of the method I've described is not to "dissolve the gold layer 1st only". Some of the gold will definitely dissolve, but as the acid is exhausted, any values will cement back out of solution on the remaining base metals. We decant the solution and repeat the process a couple of times, each time dissolving some values, but each time they cement back out on the remaining base metals. At the end, our goal is to have only a small amount of base metals with our values. It takes some experience, but it's a useful technique.

Dave
OH OH OH LIGHT BULB HAS GONE ON!! CLICK THE IDEA HAS NOW MADE SENSE WOW!!! Thank you so much for taking the time and having the patience to help me understand. And just to confirm I understand it right Basically, I am dissolving the gold over and over and it's cementing back to the base metal until basically there is little to no base metal left and I can tell when I reach that point by testing the solution every time before I decant it and it should test negative each time , Then when it does finally test positive that means that so much base metal has been dissolved and decanted that there was not enough of it for the gold to cement back to you therefore some of the gold is now in solution and I have eliminated a lot of the base metals... Correct?

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Re: using poor mans AR

Post by anachronism » October 13th, 2019, 6:12 am

ItsaboutROI wrote:
October 12th, 2019, 10:47 pm

OH OH OH LIGHT BULB HAS GONE ON!! CLICK THE IDEA HAS NOW MADE SENSE WOW!!! Thank you so much for taking the time and having the patience to help me understand. And just to confirm I understand it right Basically, I am dissolving the gold over and over and it's cementing back to the base metal until basically there is little to no base metal left and I can tell when I reach that point by testing the solution every time before I decant it and it should test negative each time , Then when it does finally test positive that means that so much base metal has been dissolved and decanted that there was not enough of it for the gold to cement back to you therefore some of the gold is now in solution and I have eliminated a lot of the base metals... Correct?
Yep you nailed it :D

Jon
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FrugalRefiner
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Re: using poor mans AR

Post by FrugalRefiner » October 13th, 2019, 8:28 am

Correct!

Dave
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Re: using poor mans AR

Post by 608rogerm » October 14th, 2019, 6:40 am

Many gold filled objects have a sterling base metal.(or heavy base metal of whatever sort)
Have you thought about a sulfuric cell?

ItsaboutROI
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Re: using poor mans AR

Post by ItsaboutROI » October 14th, 2019, 11:58 pm

Yes i have used that before.. but i have powder now washed it with hcl & sulfuric and hot water.. little change

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Re: using poor mans AR

Post by KreAture » November 18th, 2019, 6:18 pm

Finally I found a thread here worth asking my question in.
I also believe I found the answer in this thread.

My question was basically when using HCl and H2O2 to dissolve base metals in gold plated boards, (gold fingers, other gold plated boards and what-nots of that kind without massive metal backings), why one does not just dissolve everything and percipitate it out again so one has a fine powder for the acids to work with instead of waiting for ages as the acid eats its way under all the gold foils. 2 stages like that would if I have read and understood things correctly (from quite a while lurking before registering - google custom search exposes entire forum by the way), one can make a mess on first etch and drop it to do a selective base metals etch after. This however appears to be avoided at all costs.

What my answer appears to be is that it would be very wasteful on the acids which then becomes waste in return, and all the time the process can actually be sped up by allowing it to attack the gold so it can get at the copper more easily. Once it gets at the copper, the gold will cement back out. I assume this takes practice to learn the levels needed to make this happen reliably and not end up taking forever, or make a mess.

Is this a correct conclusion for me to make?

To finish I'd just like to say this appears to be an awesome forum and I have indeed made my first run using 31% HCl and diluted down H2O2 (I had 12% available). The etching of bases and washing went fine, but I did have some issues with the dropping after using HCl + bleach for the foil dissolving. I fixed that as pr quides by heating solution a bit to drive off some Chlorine gas. This was done through labware and a Sodium Carbonate bubbler type scrubber with a reflux catcher to avoid any drop in heat resulting in a mess.
The process worked well enough for me to do a nice observable result with just a few sets of goldfingers and the massive losses this entailed. I made my own Stannous Chloride which worked nicely to verify the precence of gold even though I used too much acids in the small tests. I used Sodium Hydroxide (thinned) to neutralize the copper etch which left me with quite a lot of dry powder and evaporated the remainder to quite nice copper sulfate. As luck would have it I do have a local depot that can receive both of these.
This was a fun learning experience for me and I am not in this to make money. I am in it to learn and explore all possible avenues of prospecting and refining. (Electrochemistry seems like another area I will dig into.)

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Re: using poor mans AR

Post by kernels » November 18th, 2019, 7:21 pm

Answering your main question:
It is always nicer to remove base metals before bringing Gold into solution because the cleaner the Gold going into solution is, the cleaner the Gold will be that comes out during precipitation. It is also much easier to work with 400mL of solution that contains a few grams of Gold than 4L of dirty solution that contains the same amount of Gold.

Occasionally I do dissolve "everything", in which case I prefer to then cement the PMs out on a Copper bar, wash the cemented Gold out with water and then re-refine.

Also, you almost never want to use Cu(II)Cl (AP) on whole boards to recover any Gold, practically all visible Gold on boards other than fingers is ENIG, very thin, almost non-existent Gold. So you create a ton of waste acid for practically no Gold.

Spend your limited amount of time working with high-yield material.

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Re: using poor mans AR

Post by KreAture » November 19th, 2019, 11:37 am

Wow! Thank you so much. You read my mind and answered my next question as well.
I was unsure as to the amount of gold in enig vs the fingers. Do you know if this is a new approach or if selective plating was done on old memory as well? I ask because most of my stuff I have access to would have the large flatpack chips and I notice the unpopulated side of the boards that are not double sided are enig or gold plated. I have not yet run it through my set of tools for measuring the plating thickness, but I will.

Anyway, for now my conclusion seems to be to focus on the fingers, reduce acid use as much as possible and let it do the work of accessing the copper. Test to make sure I am not too aggressive and gold ends up in solution at end of base metal etch. Then collect fingers and process.

I am thinking I do not have to process the fingers before I have a suitable amount of them as I can just rinse them and store in filters. But, as long as the acid for the base metal etch is not spent I should be able to run multiple batches of fingers in it.

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Re: using poor mans AR

Post by g_axelsson » November 19th, 2019, 6:03 pm

A drop of nitric acid is a perfect way to assess plating thickness.

Successful engineer, ENIG vs plating
Hard Gold vs. ENIG - Be careful what you pay for!! https://www.youtube.com/watch?v=iav_KH0PEZY
Hard Gold vs. ENIG Part 2 https://www.youtube.com/watch?v=IRgEtH2MSeU
Hard Gold vs. ENIG Part 3 - Mobile Phones https://www.youtube.com/watch?v=gSDB-tJTAHo
Hard Gold vs. ENIG Part 4 - LCD monitor and P4 Processor https://www.youtube.com/watch?v=xPNdCWgEQDY

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Re: using poor mans AR

Post by kernels » November 19th, 2019, 6:39 pm

KreAture wrote:
November 19th, 2019, 11:37 am
Anyway, for now my conclusion seems to be to focus on the fingers, reduce acid use as much as possible and let it do the work of accessing the copper. Test to make sure I am not too aggressive and gold ends up in solution at end of base metal etch. Then collect fingers and process.
Sounds good, nice of you to come back and actually listen to advice!

With the Cu(II)Cl leach (AP), you only want to add a 'splash' of Peroxide right at the beginning to get the reaction going, after that, you should never have to add peroxide again and will have no risk of dissolving Gold. AP works best when you have an air bubbler bubbling through the solution and also works a lot better if you can keep the solution warm-ish. I use a aquarium air bubbler and aquarium heater set to 30 deg C in mine.

The AP can be re-used indefinitely, eventually it will become saturated with Copper and a white powder will precipitate, at this point you will need to add some more clean HCl. Never dilute your AP with water, only ever add HCl.

Under normal circumstances, it will take somewhere between a few days and a few weeks for a bucket of AP to fully consume the Copper on trimmed fingers, releasing all the Gold foils. It is not a fast process, but it is relatively safe and easy.

Make sure you also understand the waste treatment that will go along with creating the AP waste acid.

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Re: using poor mans AR

Post by KreAture » November 24th, 2019, 8:00 am

g_axelsson Unfortunately I can't get any nitric acid but I could make some. I just feel that I should not.

kernels My friend (a chemist) suggested I use Chaulk/Gypsum to neutralize the waste to avoid getting poorly settling like I would from Sodium Hydroxide. Luckally there was a supplier available of lab grade materials so I know all I would produce fume-wise is co2. I made a small test and indeed the settling was much quicker.
Seems nice for when I want to neutralize, not needing to wait ages for the settling.

I also picked up on the idea to simply drop any used filters from settled gold into the next round of AP instead of trying to rinse microscopic particles out of them in a video by Successful Engineer about using stannus chloride. That will reduce the waste a lot.

I am looking forward to my next run which will be much better with the insights learned here.

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