Gold inside chips (black, flatpacks - not CPU)

[patnor1011]

No need to put top piece to AP. If you split them carefully then there will be no plating there. Even if there will be same you will recover it after incineration.
But generally that do not bother me too much, plating there is so minuscule amount that if it will be lost along way I would not cry too much because of it. :mrgreen:

 

[Imran]

Patnor or someone else, what do you guys think about going straight with nitric and then AR after crushing chips (thus omitting panning)? I am kind of afraid I am losing values while panning.

 

[alvaschein]

Patnor or someone else, what do you guys think about going straight with nitric and then AR after crushing chips (thus omitting panning)? I am kind of afraid I am losing values while panning.

From my experience I can say following:
I do not pan. First I remove the magnetic parts, sieve the rest to remove the copper fragments and then simply flush repeatedly the incineration-dust in a beaker until I have very few "sand" in it. There may remain some little pieces of base metal. I remove them with nitic acid and flush again until I have removed all acid.
From this point I have the choice of three methods:
1. dissolve the gold with AR
2. panning
3. dry it for direct melting

I use method 1 when the risk is big to lose bond wires during panning or I have too much small silicon fragments, method 2 only when there are large bond wires and method 3 when I'm in a hurry.
You can, after having removed all base metals, go directly to the AR method. So you won't lose nothing or at least nothing on the "mechanical way".

Well, it depends on you.

Roy

 

[patnor1011]

Never tried that. I guess too much nitric spent. You need to reduce that ash somehow, hard to say how it will react with nitric. Also too much waste created.
Water is much much cheaper.
I do it pretty much like previous poster said, I use smaller bucket in bigger one and run water till it go off clear. Agitate from time to time. I pan only concentrate.

 

[Imran]

Thanks roy and pat. Gonna try your method patnor by using 2 buckets. It sounds awesome.

 

[patnor1011]

It is easy. Put all ash to smaller bucket. Put this smaller in bigger one. You can place everything in small thing used for baking cakes and everything in sink. Let water go to small bucket, when it fill it will carry mud and fine ash as dirty water in bigger bucket, from there in cake tray and from there into sink. If any value go for some reason from small bucket it will end up in bigger or cake tray. When water clears I then agitate material in smaller bucket again and wait till it clears. In this way I get rid of about 80% of material and only bigger pieces and gold will stay. You can pan this concentrate or maybe you can ground it bit more and wash again. If you are careful and slow there is poor chance anything will be lost.

 

[solar_plasma]

After removing ashes and base metals I am soaking my flatpacks since days if not weeks in HCl/clorox and still get no positive SnCl₂. Well, I have it outside at 15 deg C and only stirring trice a day, guess that's the problem. This is no crying for help, the gold cannot escape. Just one more example that the processes often sound much easier, than they are.

edit: another possibility is, that I hadn't washed enough after HCl and before incinerating and now the gold is hiding in the HNO₃ solution....this would be very stupid :lol:

 

[patnor1011]

Can you tell me what you did exactly and take a picture of what you have?

HCl/Cl is not recommended for this type of material. It is good on foils or powder, for wires AR is much better suited.

 

[solar_plasma]

HCl/Cl is not recommended for this type of material. It is good on foils or powder, for wires AR is much better suited.

It's a heavy fine sand that forms a concrete cake that is not easily stirred up, so the liquid has no good contact to the gold fibers. AR would have been my next choice.

Steps (every step got one or a few days):
incineration of 1,2 kg flatpacks, ramchips, ic, black tops of n/s-bridges (with small amounts of Sn, but mostly cut)
washing the light ashes off, always waiting some minutes before pouring off
trying to pan without success, after 4 hours I had more gold in a probe that wasn't panned - wisely I haven't thrown anything away
HCl, dissolving basemetals, especially Sn, solution got green like diluted CuCl₂
Washing by decanting and filtering till the filtrate looked clean
NaOH, possible AgCl should form AgOH, solution got blue like when Cu⁺⁺ react with NaOH forming soluble Cu complex
washing till no colour
incineration again
HNO₃, solution got slightly blue like Cu(NO₃)₂, some drops of HCl in a probe didn't form any AgCl (no white cloud)
washed til no colour
HCl/Cl

2 days ago I added about 10 pieces of cut ram fingers with only a little copper and assumed cemented gold on them from an old failed process, wanted to see, if it would dissolve or even cement.
The fingers are slowly dissolving and the solution got very slightly green. The fingers show no visible cementation. Since it still smelled of chlorine, I added more HCl today for about 8 hours ago. Now, it has got more green. I test SnCl₂ tomorrow. If still negative - after what you said, I expect it will be negative - I will pour off most of the liquid and add nitric for estimated 2g (max.5g) gold, unless I read other advices. Alternatively: wash first and start with clean AR (covering with HCl 33%, adding 1ml HNO₃ 65% in maybe 3 portions about every 30 min).

 

[patnor1011]

Hmmm.
It is maybe that you did not incinerate between HCl and HNO₃ washes.

Anyway, when I encounter this thick sand then what I do is that I dry it completely again and incinerate second time. That will help to reduce it to finer particles which are washed with water again. In that way you can reduce concentrate to half.
At this stage when you just take bigger pyrex dish and swirl material inside with water you must see gold wires and powder accumulated on bottom and on the middle.

 

[Geo]

I have been washing as much light ash out as I can with water and drain. I then run it through a bucket of AP solution letting the air stir the ash. Since the base metal is exposed on all sides, it only takes a day or two to remove whatever metal the magnet wouldn't pick up. It seems to be working good and making the dissolution a lot cleaner.

 

[patnor1011]

I remove all undesirable metal with sieve and magnet first, then rest is dissolved in HNO₃. I am talking about reducing that silt like heavy sand.
I just incinerate it again, ground up in mortar and pestle a bit and then wash with water again.
It can be repeated as many times as you want or till most of it is gone.
As you proceed you will see more and more gold being visible.

 

[g_axelsson]

The silicon die does NOT contain any precious metals inside.
The conductors are made of aluminum, copper and tungsten.

Bond pads on the die is usually made of aluminum.
From http://www.irf.com/technical-info/appnotes/an-1061.pdf page 7

In applications where the current carrying
requirement and hence heat generation is
relatively low, gold wire may be used for
connection to the aluminium bond pads.

Just because I didn't find any articles with gold plated dies doesn't mean there are none, but even if there is a surface treatment with gold on the landing pads for the bond wire, any such surface gold could easily be dissolved by washing it in aqua regia or similar solution. There could also be left over parts from the gold bonding wires so a quick wash is not wrong.

Göran

 

[patnor1011]

Correct. As we moved on on this topic I only treat them whole to remove traces of wires and plating from sides. I try to remove them whole. They are like glass shards when broken and damaging my plastic pan.

 

[chlaurite]

Not to resuscitate the horse just so I can kick it a bit more :wink: , but what about the EPROMs that show gold through the window? Perhaps they don't actually have any values (beyond the bonding wires) worth dealing with, but they at least appear to have a layer of gold on the die itself.

 

[patnor1011]

A lot of dies look golden colored.

 

[shmandi]

Here is a photo of CCD from mini DV camera. You can clearly see gold wires and gold solder

 

[patnor1011]

Just finished processing 1960g of mixed s/n (computer variety) yield was 10.2 g
Now, why I said computer variety? I just got my hands on kilogram of s/n harvested from TV, they are 2 types and are heavier than what you usually get from mobo or video card. Yield will be smaller, I will do that sample to confirm or compare yield with another member who already processed them. Stay tuned. :mrgreen:

 

[patnor1011]

I just spoke with Sucho, he confirmed what I suspected that it is essential to remove as much of burned carbon as possible prior leaching. That burned crap somehow absorb a lot of dissolved gold.
Hope he will chime in soon with more details, I can't explain it in my backyard terms.

 

[samuel-a]

Pat, your yield seems fine to me, assuming the N/S bridge were complete (fiber + molded resin).

As to Carbon, loose carbon powder has a lot of surface area. By nature, Carbon adsorb metal ions onto its surface, thus locking values in our case.
Several washes with plenty of hot water or dilute HCl and hard stirring will release most of the locked values. Or you can dry, incinerate and leach again.

Incinerated materials (i.e., no carbon, just oxides + ceramics) will absorb any solution, but is quick to release it due to larger particle size (and lower surface area) and morphology. This is also some of the reasons why it is almot always easier to filter ashes