Sciencemadness Discussion Board - Dissolving Mainboards in HCl :: Dangerous ?

Dissolving Mainboards in HCl :: Dangerous ?

chief - 27-9-2010 at 06:10

Having some Excess of HCl and a couple of mainboards as well as other circuitry ...
==> I might like to dissolve that in HCl ...

... the remains maybe in HNO3 ...

... just to look what can be found ...

Yesterday I already did this to an old Transistor (2N3055) ... ...

The solder is said to contain some silver ..., other parts are said to contain various precious metals ...

The gold of the contacts should collect at the bottom of the vessel ... (HCl will leave it alone, right ? As well the silver as dust ?) ...

Some Quartz-Crystals might appear ...
===============

But: What dangerous fumes might come out of the many resistors, capacitors etc. when those react with the acid ... ?

As long as _my_ HCl came at 1 EUR/liter (31 %) I might sacrifice a gallon of it to such an action

So: Any safety-concerns from anyone ? Any hints ? I'm mainly interested in the precious metals ... and maybe somethiong to look at with the microscope ... (processors are nice for that ...)

[Edited on 27-9-2010 by chief]

12AX7 - 27-9-2010 at 07:06

Epoxy doesn't really do anything in acid.

If you use concentrated HNO3 later, you'll probably start a fire (or worse), due to organics.

Typical precious metal recovery consists of pulverizing everything into teensy little bits, ashing it in a suitable furnace (hot enough to decompose toxic aromatics, dioxins, etc.), then fusing the ashes or leaching with chemicals.

Tim

blogfast25 - 27-9-2010 at 08:43

The amounts of precious metals you'll obtain are in fact extremely small using whole PCB's. Most of our computer garbage ends up in China where entire villages are currently poisoning themselves by extracting gram amounts of gold (and other stuff) from hundreds of PCBs using home made aqua regia (conc. HCl + conc. HNO3). And of course cavalierly burning the waste of the waste and dumping the ashes wherever... Unfortunately these poor souls often have no choice to make a bit of dough...

If you really want to have a stab at it, carefully separate the components that might contain anything useful and treat them separate and competently. It really isn't an easy gold rush at all...

[Edited on 27-9-2010 by blogfast25]

chief - 27-9-2010 at 11:05

Thats why I just go for the dissolving in HCl: Easiest way to separate the components ... ; all the contacts might liberate their part of gold as well ...
==> The reason why they do it in China might be that elsewhere it would be forbidden by environmental legislation ... ; eg. in Europe you wouldnt get anywhere when burning PCBs ... : A matter of a few hours at most till some control would arrive ...

In the moment I have 4 big triacs or Diodes in the HCl ... : It doesnt seem to get too quickly through the metal-housing ... which looked like Aluminum ...

The power-transistor revealed somewhat of what looks like silver, the contact-legs ... ; probably really silver, because of its high thermal conductivity ... ; looks like 100 mg per leg ...

HydroCarbon - 27-9-2010 at 16:04

Keep us posted on what happens. And as Tim said before don't add conc. nitric as that's likely to cause a violent reaction with the organics.

12AX7 - 27-9-2010 at 21:19

You will find somewhere between little and none on power devices. TO-3s are generally steel, sometimes tin plated. I don't know if new TO-3s are ever aluminum; some old ones were. Some really old ones were gold-plated, but you'd know that if you saw it.

AFAIK, all power devices are constructed on a copper backplane to which the die is bonded (usually with "die bond" epoxy, which I believe is silver-filled). You'll get very little reaction once the HCl gets to it. TO-220s are copper through and through (leadframe and tab); TO-3s have a "coin" inside to which the die is mounted.

Tim

metalresearcher - 28-9-2010 at 02:20

Simple calculation : 1 gram of gold costs about $45.
You'll have to extract hundreds of PCB's to get one gram. Plus the chemicals.
Go cheaper and go to a jewelry supply shop and spend $45000 for a kilo. To extract one kilo from boards you'll have to invest 100000s of dollars.
The only way to do this properly is how @blogfast25 tells it and that is only feasible for large scale (i.e. tens of kilos of gold extracting from mountains of PCB scrap).

1281371269 - 28-9-2010 at 02:41

If you spend a great deal of time pulling off all of the metal bits that looked like they might contain valuables, you'd have a higher change of achieving some sort of success.
I've collected about 60g of such bits, which at some point I will try to extract valuables from. I'll probably do something like heat them in sulfuric and then nitric to dissolve all the waste metals, decanting and keeping the nitric for silver extraction. I would then dissolve the last bit in aqua regia, again decanting the liquid and 'dropping' the gold. If I was very lucky, I might get between 0.1 and 0.5 grams.
Overall, it's undoubtedly for the fun, rather than the monetary, value.

blogfast25 - 28-9-2010 at 05:45

Quote: Originally posted by metalresearcher

The only way to do this properly is how @blogfast25 tells it and that is only feasible for large scale (i.e. tens of kilos of gold extracting from mountains of PCB scrap).

I actually watched a documentary about Chinese low-end-of-the-market 'computer recycling' and it was truly horrible... The gold extraction is kept to the very last, when they've extracted everything else from the PCBs. At that point they use home made aqua regia and large shallow plastic pans (about 1 m diameter) and this guy in wellies just kept ladling the acid over PCB after PCB, all in the open air with no more 'protection' than a paper dust mask and gloves!

At the end they evaporate the A.R. and get to the nugget of gold. Crazy! The rest is then dumped basically where they stand, turning their village into a toxic moonscape...

For silver, I'd recommend electroplated silver nickel (EPSN) goods: now more or less out of fashion, I've bought quite a bit of EPSN cutlery from junk shops, house clearance auctions and such like for very decent prices. Separating the Ag from the Ni is a doddle...

bquirky - 28-9-2010 at 06:53

yeah ive seen a simalar doco.. shocking stuff. kids sitting infront of hotplates pulling components off one by one breathing in clouds of solder vapor

I must admint that i find it supprising that the value of the acids and lpg etc used is less than the copper /tin/lead/silver/gold that is extractable.

but it whouldnt suprise me if they get there solvents as a waste product from some other process.

chief - 28-9-2010 at 12:57

My acids came at 1 EUR/l for HCl (31 %) and 68 ct (0.68 EUR) for HNO3 (53 %) ...; cheaper than good beer ...

; and they came in 35-liter-canisters ...

Anyhow: The mentioned power-diodes have lost their outer layer now ... and appear to be copper ... ; maybe as well that some copper plates out on them ... from the small PCB I put into it ...

==> The soldering goes away easily ... : Chips and other parts can be "unmounted" that way ... and the components of the solder should be in the solution ... : In times of lead-free solder ... this might be interesting ... ; even tin costs around 20 $/kg ..., let alone silver or indium ...

Now Antimony comes to my mind: Might it be contained in the solder ?
==> Antimony-Hydrogen (I believe SbH3 ??) is said to be even more poisonous than AsH3 or HCN ... ...

[Edited on 28-9-2010 by chief]

blogfast25 - 29-9-2010 at 06:16

Spill the beans chief: where did you buy the acids?

unionised - 29-9-2010 at 11:36

I don't know about Sb in the solder but I'd be wary of Ga As in LEDs etc.
Anyway, most of the wiring etc will be copper.
Copper doesn't dissolve in HCl.

chief - 29-9-2010 at 13:10

Where did I buy the acids ?
==> Busines supply ... ; these are standard-tools for many completely legitimate purposes ... : Just don't ask the chem-suppliers for their over-expensive 500 ml-bottles

...

The prices I mentioned are good in my area, but it might well still be even cheaper elsewhere ...

blogfast25 - 30-9-2010 at 06:12

Quote: Originally posted by chief

Where did I buy the acids ?
==> Busines supply ... ; these are standard-tools for many completely legitimate purposes ... : Just don't ask the chem-suppliers for their over-expensive 500 ml-bottles

...

The prices I mentioned are good in my area, but it might well still be even cheaper elsewhere ...

Sure, but they don't sell you 35 l canisters either. How many mountains of PCBs are you planning to chomp through? ;-)

chief - 30-9-2010 at 08:04

Yes, they do sell those canisters: The smallest available amount ; anyhow I had the acids for some other purpose ...
==> Though you can't pick the canisters up ... : They are beeing delivered ... , only to a reasonable adress (no home) for such things ... which I have ... as well as a legitimate busines ... .

In China the acids are probably much cheaper ...

=================

Meanwhile I find: Some copper plated all over the housing of the big diodes ... and prevents further dissolution ... ; the copper might have been from the "coin" of the 2N3055-Transistor ... which looked like some sort of brass (under the plating ...)

blogfast25 - 30-9-2010 at 08:22

I meant the chem-suppliers, of course: not everyone wants a 35 l cannister...

HydroCarbon - 30-9-2010 at 18:09

In china the acids used by the PCB recyclers are probably industrial waste.

peach - 4-10-2010 at 09:21

1 euro a litre! Darn!

My bottle's just emptied.

There are some clips from what may be China in this music video;

http://www.youtube.com/watch?v=4yKtcbJkZXo

They not only harvest the metals, but saw out the more expensive components as well. I do that too, to some extent. A lot of the electrical goods at the tip are shockingly close to new, and are full of big capacitors, rectifiers and transformers that are better than the ones I'd get from some places if I paid for them. Microwaves a positive haul of trash-ar as far as this pirate of the junk is concerned.

I think a lot about recycling, wind turbines, solar panels and how effective they truly are. We have the semi-enforced recycling thing in our area. The trucks have 'Recycle' written on them with a picture of a happy woman and a banana peel. The guy's jackets say recycle on them, and the tip has a big 'recycled this week' percentage sign.

Try taking stuff from there in front of the guys and see what happens. Because you'll likely be told to fuck off or be arrested if you keep doing it without a license. I did inquire with the council about getting such a thing. No reply, a few years later now.

And, I also discovered a vast quantity of the household waste was being shipped from the UK to the Netherlands, labeled as sorted and recyclable when it clearly was nothing of the sort. They weren't happy about that. That's what you get for trying to be nice.

zed - 7-10-2010 at 03:10

I live Portland, Oregon. Recycling is king.

But, don't figure we actually reuse our recycled stuff here.

Our recycle-able city garbage, goes straight to China. We don't even sort it very well.

Labor is pretty cheap in China. And, our garbage is considered a valuable resource.

Why China? Well, it's really quite near by. Just across the Pacific.

And, because of our massive trade imbalance, mountains of empty cargo containers accumulate here.

Might as well send 'em back to the East.....Filled with pseudo-garbage. It beats sending them back empty.

peach - 8-10-2010 at 00:03

Lots of derelict ships end up back around India and the East as well, graveyards full of them, where hundreds or thousands of guys set about them with oxy acetylene torches to strip them back and remelt the iron. Very cheap labour but, more importantly for some of them, no hazardous waste charges (or not a lot anyway).

[Edited on 8-10-2010 by peach]