Pyrolysis, incineration and melting purpose

[autumnwillow]

It seems that I have forgotten the purpose of pyrolysis and incineration.
What was its purpose again?
Why not go to direct melt?

From my understanding, pyrolysis converts some materials to carbon, then incineration converts the carbon to ash.
Going for a direct melt will result in losses (a fact) but for what reason?

 

[autumnwillow]

Okay let me answer my own questions it was at the tip of my head. Heh

Pyrolize first in order to reduce toxic gases from evolving before proceeding with incineration. Pyrolizing converts some materials to carbon.
At incineration, little to no smoke will be produced if the material was completely pyrolized. An indicator for complete pyrolysis is the absence of smoke. At incineration we want to convert the carbon to ash.
At melting it is ideal to keep the material to be melted as a concentrate not doing so will tend to create complexes during the smelt, resulting in losses.

Following such steps will produce less toxic gasses and flue losses.

 

[nickvc]

You are learning even if you doubt yourself, which one has to say is a good thing, think twice do once!

 

[Gratilla]

The target of successful pyrolysis is to gasify, in an oxygen free environment, ALL hydrocarbons - particularly plastics. The resulting flammable gas can either be burnt off directly or distilled to produce various liquid (eg diesel, gasoline, etc) or solid (eg wax) products.

Pyrolysis should give a cleaner result than incineration.

 

[snoman701]

Well, I'm new and people will hopefully correct me if I'm wrong.

Pyrolosis serves a couple of purposes.

The most important is to burn off all of the organics (epoxies and other plastics) in a reducing environment to ensure that you are not releasing all of the nasty to breathe molecules into the air for you and your neighbors. By Burn off, I mean, heat until they gassify (ie, smoke) ...and yes, as was explained, you can either condense or combust this gas (smoke).

Another is to essentially incinerate (in the abscence of oxygen), so that you can then perform a more thorough sort. If you pyrolize prior to crushing, it will leave a nice brittle chip that crushes very easily, so that you can easily sort the magnetics from the non-magnetics. The magnetics will be easier to clean by themselves if you are going to go for an acid leach, and if you are strictly moving forward to a smelt, the magnetics should be removed anyway.

 

[FrugalRefiner]

Another is to essentially incinerate (in the abscence of oxygen), so that you can then perform a more thorough sort. If you pyrolize prior to crushing, it will leave a nice brittle chip that crushes very easily, so that you can easily sort the magnetics from the non-magnetics. The magnetics will be easier to clean by themselves if you are going to go for an acid leach, and if you are strictly moving forward to a smelt, the magnetics should be removed anyway.

You need to follow pyrolization with incineration. As has been said, pyrolization is done in an oxygen free environment. What is left is all the metals and carbon. Incineration needs oxygen to convert the carbon to ash. Once their thoroughly incinerated, i.e., all the carbon has been burned to ash, they will crush very easily. If you don't thoroughly incinerate ALL the carbon, it will steal some of your gold. :evil:

Dave

 

[snoman701]

Thanks for the feedback Dave!

I have read mention of retention time of a gas in reference to the afterburner...are you able to share any knowledge on that?

 

[FrugalRefiner]

I have read mention of retention time of a gas in reference to the afterburner...are you able to share any knowledge on that?

Only from what I've read. I believe some of the experts have said the outgas needs to be in the afterburner for at least 8 seconds, but I may just be having a senior moment on that. :|

Dave

 

[Grelko]

it will steal some of your gold. :evil:

Dave

Any idea why or how?

Besides this https://en.wikipedia.org/wiki/Electron_affinity

 

[g_axelsson]

According to this post a retention time of one second is enough.
http://goldrefiningforum.com/phpBB3/viewtopic.php?f=41&t=22746&p=239180&hilit=retention+time+incinerator#p239180
But it has to be at the right temperature and well mixed with enough oxygen to destroy any harmful substances.
I remember this topic being discussed quite a lot in the beginning of the forum. 4metals have written a number of posts about it.

Göran

 

[g_axelsson]

it will steal some of your gold. :evil:

Dave

Any idea why or how?

Besides this https://en.wikipedia.org/wiki/Electron_affinity

If you are panning the incinerated ash then it isn't a big problem, but if you have some carbon left when dissolving the gold some might be absorbed into the carbon. It's called preg-robbing.
http://goldrefiningwiki.com/mediawiki/index.php/Preg-robbing

Göran

 

[Grelko]

it will steal some of your gold. :evil:

Dave

Any idea why or how?

Besides this https://en.wikipedia.org/wiki/Electron_affinity

If you are panning the incinerated ash then it isn't a big problem, but if you have some carbon left when dissolving the gold some might be absorbed into the carbon. It's called preg-robbing.
http://goldrefiningwiki.com/mediawiki/index.php/Preg-robbing

Göran

Thank you, the links within that link explains a good bit. I was hoping that it would have gotten more in depth about the quantum physics aspect of it, but I'm sure it's online somewhere.

I thought it said "absorb", but it was actually "aDsorb" so the gold is getting stuck to the carbon like soap residue instead of being trapped inside of it.

Edit - Apparently it can do both, absorb and adsorb. Depends on what paper you're reading.

There doesn't seem to be an easy way to get the gold back after this happens for a home refiner. What about something like tetrachloroethylene (brake cleaner) to dissolve the carbon? (Besides smelting or cyanide)

This was interesting also. https://www.google.com/patents/US3920403

 

[g_axelsson]

You can still get adsorbed gold back from the carbon by incineration.

I don't think brake cleaner can dissolve carbon.

Göran

 

[Grelko]

You can still get adsorbed gold back from the carbon by incineration.

I don't think brake cleaner can dissolve carbon.

Göran

I wondered about the brake cleaner since it'll remove carbon buildup from engines. Reading more about it, it seems to break it down instead of actually dissolving it.

So the easiest way would be to re-incinerate it, or drop it in to molten iron "or other metals". A torch/small furnace could do both.

I figure it would be the same way to dissolve diamonds, but I wouldn't want to mess around with sodium hydroxide + sodium nitrate, or liquid oxygen.

 

[UncleBenBen]

Out of curiosity, would a slight excess of oxidizer stop or slow the adsorption rate of dissolved gold onto any carbon present in AR?

I would personally rather incinerate completely before the refine than take a chance at losing values. We all work too hard getting them to let any slip by.

I guess I'm just trying to get it straight in my head what is happening with it. Does the carbon trap gold by reducing it to metal on and in the pieces of carbon, or does it simply just suck the dissolved gold up like a sponge?

 

[autumnwillow]

Well just think of carbon as a sucker. It sucks most of the things around it like fumes, liquid, moisture, etc etc.

This is one reason why I always melt before I proceed with any wet chemistry.

Edit to add:

What I said about melting is only applicable to high grade stuff which is what I usually process.
Melting low grade material will result in slag losses. A collector such as silver/copper must be used in order to prevent such.

 

[UncleBenBen]

Thanks for the reply, autumnwillow. I think I've got it understood a bit better now. I definitely will try and avoid getting any "gold suckers" in my gold solutions!