Arc Smelting Precious Metal Ores Concentrates

[rusty]

Appears that the Australians invented the Sirosmelt a submerged lance used in precious metals smelting.

http://www.aussiethings.biz/sirosmelt_isasmelt.html

The Company: http://www.isasmelt.com/

Looks like a Thermo Lance used in demolition work, you would know it from the movies as a safe cracking device.
http://www.thermolance.com/Thermolance_Oxygen_Lance/thermolance_oxygen_lance.htm

 

[plasmasmelter]

Rusty,

That is pretty interesting. I can see how that would be useful
in smelting. I guess they run an oxidized bath to separate nobles
from bases. What are your thoughts about that? Any idea what temps
and types of ores they are working with?

PS

 

[depperl001]

Appears that the Austrians invented the Sirosmelt a submerged lance used in precious metals smelting.

http://www.aussiethings.biz/sirosmelt_isasmelt.html

The Company: http://www.isasmelt.com/

Looks like a Thermo Lance used in demolition work, you would know it from the movies as a safe cracking device.
http://www.thermolance.com/Thermolance_Oxygen_Lance/thermolance_oxygen_lance.htm[/quote

 

[rusty]

Hi,

Not the Austrians but Australians.

Regards,

Josef Vavryn

No offense Mate, at least I made a feeble attempt at using a spell check. I have made the correction to my post.

Now of you would do yours we would not perpetuate my error.

 

[plasmasmelter]

I'm glad that is settled. :lol:
Now can we get back to arc smelting? :mrgreen:

PS

 

[plasmasmelter]

Photos of a metal-slag separation.

 

[Harold_V]

Indications are you have a serious sulfide layer. It should be assayed for values. Should you find any, they can be recovered by melting and inserting scrap steel.

Harold

 

[plasmasmelter]

Harold,

We are supposed to get the assay back this friday. I'm hearing you say
that you think the button has sulfides in it and we should
reduce the sulfides with iron to get elemental metals.
What gave away the sulfides? The button's rainbow sheen?
How do we know how much scrap steel to use?

PS

 

[Harold_V]

What gave away the sulfides? The button's rainbow sheen?

That's what made me wonder, although my experience with sulfides dictates that the material will look like gray iron, with no colored sheen. Doesn't mean it can't have one, though.

How do we know how much scrap steel to use?

It tends to be self regulating. Insert an abundance, so reaction time is short. The lot will reach the point where there is no further dissolution of the inserted scrap. It's important that temperature is held below the melting point of steel. I did this process in a natural gas fired furnace, inserting lengths of rebar through the exhaust port. The inserted pieces can be easily removed to see your progress.

I hope I'm not forgetting anything. It's been many years since I performed this operation.

Harold

 

[Oz]

It's important that temperature is held below the melting point of steel

That is a key point, and I would think imposible in an arc furnace.

 

[Harold_V]

It's important that temperature is held below the melting point of steel

That is a key point, and I would think imposible in an arc furnace.

Oh, yeah! If memory serves, an electric arc yields something in the 10,000°F range. That's why I made mention of using a natural gas fired furnace. There are times when too much heat isn't in your best interest.

Harold

 

[qst42know]

I wonder if it would be prudent to have an assay done on the black crust that's building up on the face of your refractory.

You may be vaporising or simply blowing away elements of interest.

 

[plasmasmelter]

Bad news. The assay came back with no significant pm's. Small amounts of Ag and PGM's
showed up, but no Au. There was 85% Mn and 15% Fe leaving only traces of other metals.
I don't know if there were sulfides, since the ICP assay only reports back metals.

On friday I ordered an omega OS524E IR pyrometer


The temperature of the furnace can be controlled several ways in order to stay in a needed range.
Any PM volatization will be captured in the exhaust system or furnace wall.

The material shown in the earlier posted slag/button photos was supposed to be an orecons and we did
not get it assayed before processing it so we flew blind into it. Is it possible that there are pm's help
up in the slag? Or volatized off? There were after all traces of Ag in it. The boiling temp of Mn is 2061 C
and it seems that we would be boiling off that base metal instead of the PM's if any metals were in fact boiling off.
We were running a reduced furnace. Any ideas on where the PM's may have gone?

I ordered the book "Chemistry of Gold Extraction" by John O.Marsden
http://www.smenet.org/store/mining-books.cfm/Chemistry-of-Gold-Extraction,-Second-Edition/240-8

At this time we are faced with needing to be able to reduce the base metal content of our buttons in order
for the refiner to accept them. We are getting a 2.6% PM button with an orecon with a reduced furnace
extraction. We are considering approaching better concentration by running smelts in an oxidized
furnace to fuse as much base metals into the flux slag as possible and then use wet chemistry acid to
dissolve the base metals and collect the PM particles. I'm wondering what the technical issues will be
with getting the PM's to settle to the bottom of the crucible while we are oxidizing the base metals.
Is this where a getter metal like silver would be employed to wash the PM's out of suspension?

PS

 

[HAuCl4]

I still wonder what exact "edge" there is in having such high arc temperatures in smelting. The only angle I see is that the warmup period must be very short. Maybe someone can point the advantages of ultra high temperatures to me?. Many metal compounds just vaporize at those temperatures, including PM compounds.

 

[plasmasmelter]

HAuCL4,

The high heat that can volatize PM's is confined to the vicinity of the arc itself
and the temp quickly falls off a short distance from the arc.
The melt is theoretically not allowed to get beyond a certain temperature
to avoid pm losses to volatization. I think the flux material floating on top
shields the precious metals from volatization to a degree as well. I also think that
there is some volatization of pm's to a small degree resulting from direct impingement
of PM particles into the arc column.

So by controlling the temperature we can minimize PM losses.


PS