Non-Chemical Question about pyrolysis/incineration

[bemate]

Hi all, back from an extended RL break that has involved moving to a small farmstead with my very own, quite sizeable workshop. I’m still figuring out how to build a proper fume hood with scrubber, but until then I have lots of other plans and projects.

For now, I was thinking about pyrolysis and incineration. I have a reasonable amount of IC chips and gold plated connectors if various types. It seems the first step would be to burn off the epoxy and plastic to expose the metal. I do, however, seem to recall someone claiming there could be some loss of gold due to evaporation at high temps.

I am planning to make an incineration ‘cell’ of a metal canister with a hole at the top connected to a metal tube that ends under the canister to burn the gases off and increase the temp.
Would it be a good idea the put some fine copper wire in this tube to allow any vaporized gold to cement onto the wire?

 

[kurtak]

You are NOT going to vaporize gold during the incineration process of chips or pins

in order to vaporize gold (the actual metal) there needs to be a "strong" oxidizer present (such as chlorine) in order to change the atomic/chemical structure of the gold to a gold plus state - gold plus chlorine goes to gold chloride which will vaporize at higher temps (above 600 degrees F if memory serves me right)

on the other hand - gold chloride will reduce (opposite of oxidize) at lower temps meaning that at lower temps the chlorine burns off reducing the gold chloride back to gold

so for example - if you have gold in a filter from filtering an AR solution (from filtering the gold out "after" dropping the gold) & you don't wash all the AR out & then incinerate the filter to recover the gold trapped in the filter it "may" vaporize some of the gold if the incineration temp is to high due to all the AR (chlorides) not being washed out

on the other hand - if you filter an AR solution "before" dropping the gold & you don't get all the AR washed out of the filter - you can incinerate the filter at a lower temp to "reduce" the gold chloride back to gold which can then be recovered (by leaching or smelting)

so temp control is important when incinerating filters that have had acids run though them (you never really get ALL the acid washed out)

but incinerating chips or pins (still in the plastic housing) is not an issue (as far as vaporizing it)

however - "ultra" fine particles of gold "may" get carried off as "fly ash" during incineration - but again that is not likely to happen with chips or pins but can be a problem when incinerating filters or bench sweeps where the gold can be "ultra" fine

Kurt

 

[snoman701]

I am planning to make an incineration ‘cell’ of a metal canister with a hole at the top connected to a metal tube that ends under the canister to burn the gases off and increase the temp.
Would it be a good idea the put some fine copper wire in this tube to allow any vaporized gold to cement onto the wire?

Just keep in mind what you have described is also known as a bomb in the right conditions.


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[g_axelsson]

I've said it before, if you are afraid that the gases released will mix with the oxygen in the pyrolysis chamber and explode, just add some water at the start. The steam will flush out the chamber at a relatively low temperature and create an inert atmosphere at the beginning for the pyrolysis.

Göran

 

[snoman701]

I've said it before, if you are afraid that the gases released will mix with the oxygen in the pyrolysis chamber and explode, just add some water at the start. The steam will flush out the chamber at a relatively low temperature and create an inert atmosphere at the beginning for the pyrolysis.

Göran

It’s not the heating stage I worry about. It’s unexpected cooling. If you don’t judge your end, or if you have to stop for some reason, you can end up having a sealed container suck back in oxygen to a fuel rich environment....then your wood fire shifts and heats back up.....there’s lots of scenarios.

Or a more likely one...your chamber cracks under heat.

There’s a reason flammable gas environment sealed furnaces cost $50,000+...it’s the safety interlocks they have in place.

Just design it so it’s not possible to build pressure. Stuffing copper wire or foil into the only exit, then passing high molecular weight compounds thru that opening, seems like a good way to make a bomb.

Especially when A stainless pan with a lid will provide a reducing environment without the possibility of explosion.

And as Kurt pointed out...it’s largely unnecessary anyway. Nobody should be tooling up to burn boards in a home workshop.





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[4metals]

It's only a "bomb" if the pressure cannot be vented easily.

Using a 5 gallon pail with the vent hole in the top of the lid and a connected pipe returning the volatiles to under the pail to be ignited by the fire below, you can successfully pyrolyze the material.

If you insist on clamping down the lid so the only possible vent of excess pressure is the hole then yes there is potential for trouble.

I prefer to just place the lid on and place a few firebricks on top to add a little weight. Then if the gasses build up beyond what the vent hole can handle they cause the lid to vent and they are not compressed beyond the resistance provided by the firebricks weight and vent without a boom.

Not everything has to be engineered like a spaceship to get the job done.

 

[snoman701]

And I have a feeling many many tons of material have been incinerated in those 5 gallon buckets....just wish they sold them at Home Depot!




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[bemate]

Thanks for replying, I think I might reassess my plan. I did a minor trial today with various connectors just to see how they behaved. I put them in an open pan above a fire to roast, which worked quite nicely, though I am left with a substantial amount of ash. Quite a bit of it is black, though, so I think it will need a second round to burn off all the carbon.

Once I get it properly burned off, I suppose it’s just a matter of washing off the ash and processing the metals according to metal type.

 

[g_axelsson]

Connectors should be easy to crush and separate the ash from the metal after a pyrolysis. There are no bond wires to be vary of. Then it doesn't matter if it was white or black. The white "ash" is mostly filler material, SiO₂, fine crushed sand. There could also be other filler materials used to give the plastic optimum properties... wait, not optimum, adequate properties at the cheapest price.

The metal will probably look like the gold has disappeared, the gold migrates (diffuses) at higher temperatures and alloys with the base metal while base metal could probably get to the surface and get a tarnish or oxidation layer. The gold is still there, just a bit harder to spot.
Elevated temperatures makes the gold move faster.

Göran