# These metal Processor chips have me stumped! Over 18 lbs of them!



## J&amp;D (Oct 12, 2022)

Hi all. My name is Jason. Earlier this week I found about 18 lbs of manufacturer scrap processor chips. Still in strips of 4-6. Hundreds of strips of 4-6. They are beautiful. Packed with gold bonding wires and all, exposed already.
BUT the strips and the wafer the chips are on is made of aluminum.
I have never heard of aluminum wafers for a chip. I have no idea how best to process these!
I can recover the gold from printed circuit boards, ceramic chips, etc. But those materials are not on AL.....all of my acids will just work against me dealing with aluminum, right?
I am kind of stumped. I'm going to include some pics of this material. If anyone has an idea how best to process these, I would be very grateful to hear it. I have all of my acids, glassware, 10 years of experience, a proper workshop, fume hood, etc....I just wasn't expecting this curve ball!
Metal chips.....and so so many of them!
In the following pics, you can see a yardstick for reference to the scale of these. Its over a cubic yard of these buggers laid out, and there was probably 4 pounds left in a bin, I just got tired of making the cube there were so many


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## Yggdrasil (Oct 12, 2022)

J&D said:


> Hi all. My name is Jason. Earlier this week I found about 18 lbs of manufacturer scrap processor chips. Still in strips of 4-6. Hundreds of strips of 4-6. They are beautiful. Packed with gold bonding wires and all, exposed already.
> BUT the strips and the wafer the chips are on is made of aluminum.
> I have never heard of aluminum wafers for a chip. I have no idea how best to process these!
> I can recover the gold from printed circuit boards, ceramic chips, etc. But those materials are not on AL.....all of my acids will just work against me dealing with aluminum, right?
> ...


HCl eats Aluminum fast and efficient, but it can create a gooish slime that will lock up the foils.
Maybe a Sulfuric stripping cell will fix this?


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## MicheleM (Oct 12, 2022)

Is the chip side with the gold wires protected by some kind of plastic ?


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## J&amp;D (Oct 12, 2022)

Yggdrasil said:


> HCl eats Aluminum fast and efficient, but it can create a gooish slime that will lock up the foils.
> Maybe a Sulfuric stripping cell will fix this?


thx, yes I remember that about HCI. Would a sulfuric cell work on the tiny gold bonding wires?


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## J&amp;D (Oct 12, 2022)

MicheleM said:


> Is the chip side with the gold wires protected by some kind of plastic ?


On most of the chips, I can see plainly, there is no coating, as the bonding wires are exposed.
On some of the chips, like a small portion, the actual center of the chip has a glob of epoxy-kind of serving as a cap for the bonding wires and die in the center. On most, this epoxy glob is not present. As for the foils along the outside edges, so far as I can tell, there is no coating.


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## snoman701 (Oct 12, 2022)

These look like in process BGA chips without the epoxy added to protect the die and wires.

Can't you just remove the chips from their aluminum carrier?


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## rickbb (Oct 12, 2022)

What about a sodium hydroxide solution to dissolve the Al first?


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## J&amp;D (Oct 12, 2022)

hi, thx for the idea....the chips can be removed from their carrier, but the wafers themselves are also made of aluminum! So, they will be removed when I figure how to process them, just to eliminate the excess 5 or 10% AL


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## Lou (Oct 12, 2022)

I myself would just use 20% NaOH and be prepared for a lot of hydrogen and a very vigorous reaction. Sometimes those things catch on fire if they're not submerged and scrubbed properly.


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## J&amp;D (Oct 12, 2022)

I have not ever worked with sodium hydroxide.....
NaOh? is that lye? My concern with something like trying to dissolve away 18 pounds of aluminum is that I would think the weight of all these chips is 18 pounds, so 99.998 or so percent of that is not gold....I would hate to lose my .002% in all of that waste! What could attack just the gold? Ive imagined dilute nitric, Yggdrasil suggested sulfuric cell....


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## J&amp;D (Oct 12, 2022)

NaOh is relatively inexpensive yes? compared to sulfuric and nitric? And when you suggest a 20% solution, do you mean by diluting 5 to 1 with distilled water? I did look up some bottles of it, and it seems to come in a 99% conc.
I am up for a vigorous reaction, but I certainly wouldnt want any chemical fires going on! 
Small test run to start would be best I take it!


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## J&amp;D (Oct 12, 2022)

Lou said:


> I myself would just use 20% NaOH and be prepared for a lot of hydrogen and a very vigorous reaction. Sometimes those things catch on fire if they're not submerged and scrubbed properly.


Hi Lou, I just did a tiny amount of research on using NaOH (watched a Youtube video) It looks like the solution turns black with the dissolved aluminum....does that completely dissolve? Or just break down? If its totally dissolved, it would just work to filter and rinse the remaining gold?


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## J&amp;D (Oct 12, 2022)

snoman701 said:


> These look like in process BGA chips without the epoxy added to protect the die and wires.
> 
> Can't you just remove the chips from their aluminum carrier?


Can and willo, but the wafers themselves are made of AL too. Removing them would eliminate 5-10% of the weight, which I would do


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## J&amp;D (Oct 12, 2022)

rickbb said:


> What about a sodium hydroxide solution to dissolve the Al first?


I think I will try this. On a tiny amount


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## Yggdrasil (Oct 12, 2022)

J&D said:


> I have not ever worked with sodium hydroxide.....
> NaOh? is that lye? My concern with something like trying to dissolve away 18 pounds of aluminum is that I would think the weight of all these chips is 18 pounds, so 99.998 or so percent of that is not gold....I would hate to lose my .002% in all of that waste! What could attack just the gold? Ive imagined dilute nitric, Yggdrasil suggested sulfuric cell....


Nitric do not dissolve Gold or Aluminum.
I don't know what AR does to Aluminum though.
The Sodium Hydroxide route may be the cheapest.
Just add 200g of powder to 1L of water. this will give 17% or so solution.
Strip the majority of the Al from the items first, it will save time and cost.


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## J&amp;D (Oct 12, 2022)

I am ordering a bottle this morning of NaOH this morning. I will try on a test batch and post my results. Thank u for the suggestions


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## J&amp;D (Oct 12, 2022)

Yggdrasil said:


> Nitric do not dissolve Gold or Aluminum.
> I don't know what AR does to Aluminum though.
> The Sodium Hydroxide route may be the cheapest.
> Just add 200g of powder to 1L of water. this will give 17% or so solution.
> Strip the majority of the Al from the items first, it will save time and cost.


Does it need to be heated? Or does it produce it's own heat?


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## Yggdrasil (Oct 12, 2022)

J&D said:


> Does it need to be heated? Or does it produce it's own heat?


If you use powder, you need to be cautious. Mixing NaOH with water is exotermic. 
The bottles used for drain opening should be around 60-80ish%.
Mix it with about 3-4 times as much water, depending on concentration.
When you put in the Al it will bubble strongly and create Hydrogen gas and possibly heat, I really do not know since I have only used HCl for Al.


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## MicheleM (Oct 12, 2022)

First of all i would remove the bonding wires manually (using a appropriate container) , they are about 90 pct of all gold. After that I would break each single "square" and i would put them in HCl, in my opinion too much Al for NaOH


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## Yggdrasil (Oct 12, 2022)

MicheleM said:


> First of all i would remove the bonding wires manually (using a appropriate container) , they are about 90 pct of all gold


Is that even possible to do in a practical way?
They are usually way to small and thin.


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## MicheleM (Oct 12, 2022)

Yggdrasil said:


> Is that even possible to do in a practical way?
> They are usually way to small and thin.


Yes, I did exactly this with the gold bonding wires attached to CCD/CMOS inside cellphones and laptop, it's even more difficult because the smaller dimensions. For the gold plating HCl and HCl-Cl


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## J&amp;D (Oct 12, 2022)

MicheleM said:


> First of all i would remove the bonding wires manually (using a appropriate container) , they are about 90 pct of all gold. After that I would break each single "square" and i would put them in HCl, in my opinion too much Al for NaOH


Like scrape them off? Use a chisel or something? That makes sense, I would assume these are where my value is for the most part. Just scrape scrape scrape scrape


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## J&amp;D (Oct 12, 2022)

MicheleM said:


> First of all i would remove the bonding wires manually (using a appropriate container) , they are about 90 pct of all gold. After that I would break each single "square" and i would put them in HCl, in my opinion too much Al for NaOH


I see the benefit in this. Thank you for sharing that pic


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## J&amp;D (Oct 12, 2022)

MicheleM said:


> Yes, I did exactly this with the gold bonding wires attached to CCD/CMOS inside cellphones and laptop, it's even more difficult because the smaller dimensions. For the gold plating HCl and HCl-Cl


Here is the result of scraping two of these chips.....I guess I know what I'll be doing all week!
I think it is funny, I was looking for a complex solution, and just needed to be reminded, "you could just try scraping it off!" 
Thx for the tip, I think I'm gna go with this


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## MicheleM (Oct 12, 2022)

Great, absolutely beautiful. At the end do not forget to take look at each item with a good lens to be sure that no wire is left


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## BlackLabel (Oct 12, 2022)

Hi Jason,

First of all: Great haul - congrats!

I can't see it on your photos, but the round golden dots must be attached to a kind of epoxy board (they must be isolated from the aluminum part).
Did you try to split the epoxy from the aluminum by using a sharp cutter blade?


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## refam (Oct 12, 2022)

J&D said:


> Hi all. My name is Jason. Earlier this week I found about 18 lbs of manufacturer scrap processor chips. Still in strips of 4-6. Hundreds of strips of 4-6. They are beautiful. Packed with gold bonding wires and all, exposed already.
> BUT the strips and the wafer the chips are on is made of aluminum.
> I have never heard of aluminum wafers for a chip. I have no idea how best to process these!
> I can recover the gold from printed circuit boards, ceramic chips, etc. But those materials are not on AL.....all of my acids will just work against me dealing with aluminum, right?
> ...


There is a way to get around this using concentrated acetic acid which appears to only attack the gold. There is a link here to the article which is 6 years old. The green way to extract gold


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## J&amp;D (Oct 12, 2022)

BlackLabel said:


> Hi Jason,
> 
> First of all: Great haul - congrats!
> 
> ...


Hey there, when I was scraping at a couple of these, there is like a resin or epoxy stuff that comes off, a very thin coat of clear, didn't realize it was there. But it is over all of the bga dots, yes. Not sure what to do about that either!


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## J&amp;D (Oct 12, 2022)

refam said:


> There is a way to get around this using concentrated acetic acid which appears to only attack the gold. There is a link here to the article which is 6 years old. The green way to extract gold


Thank u yes I've also heard of acetic acid method. Never tried it. But I will check this link out and see if it applies to this material possibly. Thx for the suggestion


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## refam (Oct 12, 2022)

J&D said:


> Thank u yes I've also heard of acetic acid method. Never tried it. But I will check this link out and see if it applies to this material possibly. Thx for the suggestion


Many on here doubt this works, so I have emailed the person and asked if he would expand a little.


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## GoIdman (Oct 13, 2022)

J&D said:


> Hey there, when I was scraping at a couple of these, there is like a resin or epoxy stuff that comes off, a very thin coat of clear, didn't realize it was there. But it is over all of the bga dots, yes. Not sure what to do about that either!


Hi, 

The thin layer that you think is epoxy, is basically a thin layer of flux (alcohol mixed with pine resin and some chemical material) so when the pins or balls are soldered they stick better. You can wash that away with isopropyl alcohol ol plain sanitary alcohol. It will remove it almost instantly.

That is an amazing find, congrats and good luck.

Pete


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## nwinther (Oct 13, 2022)

Yggdrasil said:


> I don't know what AR does to Aluminum though.



I recently read an aside on a Danish website (can't find it now, though), that since AR doesn't attack aluminium it was once used to clean the insides of aluminium boilers at power plants or somesuch.

Other websites clearly state that AR does indeed attack aluminium.


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## Yggdrasil (Oct 13, 2022)

refam said:


> There is a way to get around this using concentrated acetic acid which appears to only attack the gold. There is a link here to the article which is 6 years old. The green way to extract gold


Acetic acid alone do not dissolve gold. Same with HCl or Nitric, but when you add Oxidizer it works and as one see here they use oxidizer.
Dissolved metal salts are toxic no matter how you dissolve them.
Lead acetate is very toxic and taste like sugar, hence the popular name "Lead sugar".


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## Yggdrasil (Oct 13, 2022)

nwinther said:


> I recently read an aside on a Danish website (can't find it now, though), that since AR doesn't attack aluminium it was once used to clean the insides of aluminium boilers at power plants or somesuch.
> 
> Other websites clearly state that AR does indeed attack aluminium.


Thanks nwinther, one can easy assume it has to do with alloy then. 
Edit to add:
On after thought, can they use Aluminum pressure tanks for boilers?
The flame side is highly corrosive due to flame oxidision, the boiler tank itself will have to withstand high pressure.
I’m not sure Aluminium is up to this kind if abuse.
I’d expect some kind of Titanium or special alloy for boilers.


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## J&amp;D (Oct 13, 2022)

GoIdman said:


> Hi,
> 
> The thin layer that you think is epoxy, is basically a thin layer of flux (alcohol mixed with pine resin and some chemical material) so when the pins or balls are soldered they stick better. You can wash that away with isopropyl alcohol ol plain sanitary alcohol. It will remove it almost instantly.
> 
> ...


Thx Pete, I will def do that. Good to know. Jason


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## orvi (Oct 13, 2022)

Yggdrasil said:


> Nitric do not dissolve Gold or Aluminum.
> I don't know what AR does to Aluminum though.
> The Sodium Hydroxide route may be the cheapest.
> Just add 200g of powder to 1L of water. this will give 17% or so solution.
> Strip the majority of the Al from the items first, it will save time and cost.


Aluminium dissappear in regular warm AR like nothing, evolving some funky nitrogen oxides as nitrous oxide. Very reactive and reaction is extremely exothermic, as practically all dissolutions of aluminium. Wasteful to use AR, HCL alone is more than sufficient.


J&D said:


> Does it need to be heated? Or does it produce it's own heat?


Sodium hydroxide dissolution in water is very exothermic - if you ever unclogged the drain by pouring the "drain cleaner white grains" according to manual and pour hot water onto it  
Prepare 20% solution by taking 4 parts of water, and add 1 part of NaOH (weight) slowly with stirring. Dissolution is quick, and you are left with warm solution ready to use. Wear thick rubber gloves also covering partly your forearms. Goggles or better face shield is A MUST - hot lye in the eye... I experienced that real life. Few seconds and you are blind for life. But as long as it does not get onto skin or worse eyes, you will be perfectly fine. Be also aware of "mist"  as you dissolve NaOH in water, and also reacting anything in NaOH - "mist" or aerosol, containing that NaOH is emitted from the vessel. Not severly bad, but it is annoyingly irritating to the nose and lungs, certainly not healthy and comfy to breath it 
Aluminium reaction with lye/hydroxide sometimes take few seconds or minutes to kickstart, but then, it become very very vigorous, and lots of heat is evolved during the process. Few dozens grams of Al reacting with lye can easily heat up the small bucket of solution to the boiling point. Be aware of this fact, and put them one by one to the solution and observe the reaction. 
Be careful and try it out on small scale before scaling up. There wouldn´t be any terribly toxic substances evolved during the process, but as with any caustics, great caution is a must  chemistry never do anything that it shouldn´t  only we are unprepared.


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## J&amp;D (Oct 13, 2022)

orvi said:


> Aluminium dissappear in regular warm AR like nothing, evolving some funky nitrogen oxides as nitrous oxide. Very reactive and reaction is extremely exothermic, as practically all dissolutions of aluminium. Wasteful to use AR, HCL alone is more than sufficient.
> 
> Sodium hydroxide dissolution in water is very exothermic - if you ever unclogged the drain by pouring the "drain cleaner white grains" according to manual and pour hot water onto it
> Prepare 20% solution by taking 4 parts of water, and add 1 part of NaOH (weight) slowly with stirring. Dissolution is quick, and you are left with warm solution ready to use. Wear thick rubber gloves also covering partly your forearms. Goggles or better face shield is A MUST - hot lye in the eye... I experienced that real life. Few seconds and you are blind for life. But as long as it does not get onto skin or worse eyes, you will be perfectly fine. Be also aware of "mist"  as you dissolve NaOH in water, and also reacting anything in NaOH - "mist" or aerosol, containing that NaOH is emitted from the vessel. Not severly bad, but it is annoyingly irritating to the nose and lungs, certainly not healthy and comfy to breath it
> ...


Wow, I will def take those precautions! I have a good full face mask and some elbow length rubbers I will put on. Thx for the tips. Currently waiting on my sodium hydroxide granules.....Chemistry never does anything it shouldnt, we only are unprepared! I like that! so true


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## J&amp;D (Oct 13, 2022)

J&D said:


> Wow, I will def take those precautions! I have a good full face mask and some elbow length rubbers I will put on. Thx for the tips. Currently waiting on my sodium hydroxide granules.....Chemistry never does anything it shouldnt, we only are unprepared! I like that! so true





orvi said:


> Aluminium dissappear in regular warm AR like nothing, evolving some funky nitrogen oxides as nitrous oxide. Very reactive and reaction is extremely exothermic, as practically all dissolutions of aluminium. Wasteful to use AR, HCL alone is more than sufficient.
> 
> Sodium hydroxide dissolution in water is very exothermic - if you ever unclogged the drain by pouring the "drain cleaner white grains" according to manual and pour hot water onto it
> Prepare 20% solution by taking 4 parts of water, and add 1 part of NaOH (weight) slowly with stirring. Dissolution is quick, and you are left with warm solution ready to use. Wear thick rubber gloves also covering partly your forearms. Goggles or better face shield is A MUST - hot lye in the eye... I experienced that real life. Few seconds and you are blind for life. But as long as it does not get onto skin or worse eyes, you will be perfectly fine. Be also aware of "mist"  as you dissolve NaOH in water, and also reacting anything in NaOH - "mist" or aerosol, containing that NaOH is emitted from the vessel. Not severly bad, but it is annoyingly irritating to the nose and lungs, certainly not healthy and comfy to breath it
> ...


with such a vigorous reaction, would you say the choice of vessel be a beaker or a flask?>I have large ones of each, just wondering, which best? thx


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## orvi (Oct 13, 2022)

J&D said:


> with such a vigorous reaction, would you say the choice of vessel be a beaker or a flask?>I have large ones of each, just wondering, which best? thx


Glass is fine, but as you scale up to the big lot, PP bucket will also serve good. For tests, definitely beakers. If you build up confidence, polypropylene bucket is also OK, as it is resistant to hydroxide.


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## BlackLabel (Oct 13, 2022)

orvi said:


> There wouldn´t be any terribly toxic substances evolved during the process, but as with any caustics, great caution is a must  chemistry never do anything that it shouldn´t  only we are unprepared.


Maybe "caution" comes from "caustic"…


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## nickrpotts (Oct 14, 2022)

I typically use dilute nitric acid 20% on nickel and gold plated aluminium parts, if there is any exposed edge the nitric finds it and dissolves the nickel and then leaves the gold floating in solution, but doesn't attack the aluminium. I normally then rinse and filter out the nitric solution. Then aqua regis the gold to ensure it is clean. As regards choice of vessel, either pyrex beakers or I use wine making buckets for larger volumes at about 20% of the volume filled. This needs doing in a fume cupboard. It works better heated but its not essential.
This isn't a quick process but I have found it gives me the best return. You could test a strip of chips in 100ml of nitric in a 1l beaker to prove or disprove the concept.


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## Yggdrasil (Oct 14, 2022)

nickrpotts said:


> I typically use dilute nitric acid 20% on nickel and gold plated aluminium parts, if there is any exposed edge the nitric finds it and dissolves the nickel and then leaves the gold floating in solution, but doesn't attack the aluminium. I normally then rinse and filter out the nitric solution. Then aqua regis the gold to ensure it is clean. As regards choice of vessel, either pyrex beakers or I use wine making buckets for larger volumes at about 20% of the volume filled. This needs doing in a fume cupboard. It works better heated but its not essential.
> This isn't a quick process but I have found it gives me the best return. You could test a strip of chips in 100ml of nitric in a 1l beaker to prove or disprove the concept.


That should be fine, but maybe try HCl/Peroxide, HCL/Pool Chlorine or HCl/bleach to dissolve the foils.
No need to denox if you overshoot the oxidizer then.
It is Aqua Regia by the way.


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## orvi (Oct 14, 2022)

nickrpotts said:


> I typically use dilute nitric acid 20% on nickel and gold plated aluminium parts, if there is any exposed edge the nitric finds it and dissolves the nickel and then leaves the gold floating in solution, but doesn't attack the aluminium. I normally then rinse and filter out the nitric solution. Then aqua regis the gold to ensure it is clean. As regards choice of vessel, either pyrex beakers or I use wine making buckets for larger volumes at about 20% of the volume filled. This needs doing in a fume cupboard. It works better heated but its not essential.
> This isn't a quick process but I have found it gives me the best return. You could test a strip of chips in 100ml of nitric in a 1l beaker to prove or disprove the concept.


If one has free access to tec grade nitric for fair bulk price around 1-1,5eur/L, it is very very convenient to use it practically on anything. As a person who does not have this privilege and must value it practically drop by drop - I use every alternative possible to replace nitric in all applications, where it is convenient.
If the struggle is only aluminium, hydroxide is logical substitute to nitric, as it only evolve harmless hydrogen, not noxious NOx gasses and N2O. Also, it is cheaper. That tidbit of nickel remained on the foils shouldn´t concern you too much, as it would be refined anyway.

If that material is on plastic, or there is too much gold stuck on plastic, I would consider incineration of the material. Leaching some plastics in HCL/Cl2 or AR can terribly etch them/create sludgy pasty goo - with another drawback - they tend to adsorb dissolved gold. Worst is fiberglass PCB.

When we processed fingers in bulk without nitric or AP (lots of "precious" nitric required, on the other hand, AP is slow for use to do it in good turnover time), we compared two few kg batches (same material). One we incinerated and smelted the ashes, other one we dumper in AR and leached as any other metallic material. Retention of dissolved gold in fiberglass with this specific batch was around 5-7 % (and it could be worse from my experience). Which is quite concerning number.


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## lanfear (Oct 14, 2022)

This has bin discussed on the forum before. The process is called revers AR. Because HCl will dissolve aluminium, you use only nitric. Then you add small increments of HCl. 
The trouble with this is the neutralizing. But with so much material you could start out small and then scale it up.


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## orvi (Oct 14, 2022)

lanfear said:


> This has bin discussed on the forum before. The process is called revers AR. Because HCl will dissolve aluminium, you use only nitric. Then you add small increments of HCl.
> The trouble with this is the neutralizing. But with so much material you could start out small and then scale it up.


As it could be done like this, in my opinion it would be very wasteful in terms of reagents. 

Really, take 20% NaOH, dissolve that aluminium (and all other things will stay practically untouched), decant off the saturated sodium aluminate solution, wash briefly with water and then continue with any acid process you intend to use. Less hassle with NOx outgas, no unnecessary de-noxing like in reverse AR... And if the platings are nickel based, you can conveniently etch the foils and wires with nitric or AP. Cheap.

Altough, with Al-plastic mixed material, I would prefer NaOH leach with consequent incineration and smelting the ashes. Because I work with larger volumes of material and smelting is usually quantitative, opposed to leaching - where adsorption of precious metals in plastic or fiberglass is very real issue, loosing 5% or even more % of Au on the substrate. 

High Au% metallic dore/ingot after smelting would be then dissolved and refined from much more concentrated solution => less acid, no wasteful de-noxing stage => less volume => less waste to process.


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## J&amp;D (Oct 16, 2022)

orvi said:


> As it could be done like this, in my opinion it would be very wasteful in terms of reagents.
> 
> Really, take 20% NaOH, dissolve that aluminium (and all other things will stay practically untouched), decant off the saturated sodium aluminate solution, wash briefly with water and then continue with any acid process you intend to use. Less hassle with NOx outgas, no unnecessary de-noxing like in reverse AR... And if the platings are nickel based, you can conveniently etch the foils and wires with nitric or AP. Cheap.
> 
> ...


Thx for your reply. I have just received my NaOH in the mail, and have 3 liters of nitric handy. I am going to begin testing both methods out tmrw. My concern with the NaOH method will be that I am trying to dissolve 99.999 percent of the material with it, and save the .001.....not much margin for error!


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## J&amp;D (Oct 16, 2022)

orvi said:


> If one has free access to tec grade nitric for fair bulk price around 1-1,5eur/L, it is very very convenient to use it practically on anything. As a person who does not have this privilege and must value it practically drop by drop - I use every alternative possible to replace nitric in all applications, where it is convenient.
> If the struggle is only aluminium, hydroxide is logical substitute to nitric, as it only evolve harmless hydrogen, not noxious NOx gasses and N2O. Also, it is cheaper. That tidbit of nickel remained on the foils shouldn´t concern you too much, as it would be refined anyway.
> 
> If that material is on plastic, or there is too much gold stuck on plastic, I would consider incineration of the material. Leaching some plastics in HCL/Cl2 or AR can terribly etch them/create sludgy pasty goo - with another drawback - they tend to adsorb dissolved gold. Worst is fiberglass PCB.
> ...


I have 3.5 litres on hand of some good nitric, and just got a bottle of NaOH in the mail today. Tmrw I am going to try each method on a small amount of material. My gut feeling is that the nitric will be best results, as it won't require the dissolving of 18 lbs of aluminum into solution. I appreciate ur replies thus far. I'll be sure to post my findings


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## J&amp;D (Oct 16, 2022)

nickrpotts said:


> I typically use dilute nitric acid 20% on nickel and gold plated aluminium parts, if there is any exposed edge the nitric finds it and dissolves the nickel and then leaves the gold floating in solution, but doesn't attack the aluminium. I normally then rinse and filter out the nitric solution. Then aqua regis the gold to ensure it is clean. As regards choice of vessel, either pyrex beakers or I use wine making buckets for larger volumes at about 20% of the volume filled. This needs doing in a fume cupboard. It works better heated but its not essential.
> This isn't a quick process but I have found it gives me the best return. You could test a strip of chips in 100ml of nitric in a 1l beaker to prove or disprove the concept.


I will be giving this a go tmrw. My feeling is that dilute nitric is best. But I'm going to use NaOH on a strip side by side with dilute nitric and see for myself. Thx for ur reply


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