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

[nickrpotts]

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.

 

[Yggdrasil]

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.

 

[orvi]

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.

 

[lanfear]

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.

 

[orvi]

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.

 

[J&D]

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.

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!

 

[J&D]

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.

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

 

[J&D]

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