Direct flame for cupellation

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alexxx

Well-known member
Joined
Nov 27, 2011
Messages
336
Location
Montreal / Quebec / Canada
I am posting here since the recovery method I use is pretty much the same as cupellation.

I have bought a few big bone ash cupels from Legend to recover PM from Pb - Ag alloyed pucks
The pucks contain approx the following
Pb 60%
Ag 30%
Au 7%
Pd 2%
Other base metals 1%

As I dont have a muffle furnace, I am curious to know if I can use a direct flame, in open air, to melt the alloy so the pb can be absorbed by the cupel. I have a propane torch and a oxy / acetylene torch.

I am aware of the dangers from the pb fumes.
What type of torch should I use ?
Any danger of damaging the cupel if using a torch?
Any chance I could lose values if heating too much ?
Anything am I missing ?
 
I have never seen it done with an open flame, cupellation requires controlling the oxygen levels, which a muffle furnace does nicely. A cupellation is started with a sealed muffle or restricted airflow until the charge is melted then air is introduced gently to flow over the pool of metal to do what is described as "driving the lead."

I have built cupellation furnaces in South America specifically for doing what you are talking about but they have always been in the form of a closed muffle. They were quite large and the bone ash was packed into trays with a trough in the center which was the base of the furnace but always enclosed.

You may achieve a similar effect by doing it inside a length of refractory pipe, which would also help you in directing the fume away from you.
 
Charles Butler taught a torch assay process that used a torch to cupel very small amounts. It would probably work with larger amounts but it would take a long time. Building a furnace would probably be better.

If you are interested, I did find a youtube video of the process but didn't get a chance to watch it fully yet. Butler labs still sell the books and videos of the process and offers private classes at their lab in Las Vegas. Their process is for quick DIY assays and NOT for actual production.

[youtube]http://www.youtube.com/watch?v=BA1gqIoxm9g[/youtube]

I have seen comments that some of the PM's might be vaporised from the intense heat of the torch.
 
Why do you want to use cupellation on such a nice high-grade alloy?
I associate that with the assay of lower grade ores and waste.
If it were me I would add more silver if it is not a weak enough alloy already, then part with nitric for the Ag, Pt, Pd, cement / silver cell and the residual into A.R. for selective precipitation.
 
I always need to think about how to prevent too much waste, so looking at it from my perspective:

dissolving in HNO3
cementing all PMs on lead
only Pb(NO3)2 in solution
crystallize
using Pb(NO3)2 to form PbO and nitric at >470°C (litharge and nitric can be reused)

Not tried, no proofs, only a thought.
 
alexxx said:
I am posting here since the recovery method I use is pretty much the same as cupellation.

I have bought a few big bone ash cupels from Legend to recover PM from Pb - Ag alloyed pucks
The pucks contain approx the following
Pb 60%
Ag 30%
Au 7%
Pd 2%
Other base metals 1%

As I dont have a muffle furnace, I am curious to know if I can use a direct flame, in open air, to melt the alloy so the pb can be absorbed by the cupel. I have a propane torch and a oxy / acetylene torch.

I am aware of the dangers from the pb fumes.
What type of torch should I use ?
Any danger of damaging the cupel if using a torch?
Any chance I could lose values if heating too much ?
Anything am I missing ?


You can use a big rose bud to do the job. Air is what's driving the lead, so run it lean and probably don't run it to completion.
Lou
 
My concern about doing this with a torch is that the cupel, which will absorb 90% of the lead in the process, may not be as likely to absorb as much lead if it isn't hot enough or evenly heated. Unless you can figure out how to evenly heat the cupel and at the same time play the flame on the charge, you will likely put even more of the lead into the atmosphere.
 
4metals said:
My concern about doing this with a torch is that the cupel, which will absorb 90% of the lead in the process, may not be as likely to absorb as much lead if it isn't hot enough or evenly heated. Unless you can figure out how to evenly heat the cupel and at the same time play the flame on the charge, you will likely put even more of the lead into the atmosphere.


If you had to play with such an alloy on a regular base, lets say 1 ton per month for 2 years. Would you get a muffle furnace to dedicate a fixed setup for this customer or would you go with Solar plasma strategy nitric bath, cementing on pb, evaporate, reuse pbo & hno3?

Or any other approach? We already received 400 lbs for the first "test run".
I am making a very reasonable profit out of it and this material will keep coming, I am ready to invest a bit to get the right setup for the right material.

Thanks again for all these replies.

Cheers,

Alex
 
Check out Ammen's book "Recovery and Refining of Precious Metals", he describes the operation of a cupellation furnace with the bone ash hearth. And he has a drawing of it as well.

I used something very similar daily in South America for a very long time with excellent results.


cupellation furnace.jpg








 
4metals said:
Check out Ammen's book "Recovery and Refining of Precious Metals", he describes the operation of a cupellation furnace with the bone ash hearth. And he has a drawing of it as well.

I used something very similar daily in South America for a very long time with excellent results.


cupellation furnace.jpg









Sir ,

Do you have pictures of the above furnace that you manufactured? We are planning to manufacture a muffle furnace for large scale cupellation.

Thanking you,
Gaurav
 
Thank you 4metals. I have a few questions on industrial cupellation. I shall probably start a new thread and post my queries there.

Regards,
Gaurav
 
Thank you sir for the link. I would be better of making my own cupel with di calcium phosphate and portland cement with 30:70 ratio. As the link to the cupel that you have provided will probably cost me double to get it shipped to India. At Least i have got the design in mind thanks to you! I will manufacture the same for minimal cost here!

Regards,
Gaurav
 
A place I worked had an old Johnson gas furnace with just a muffle plate - no enclosed muffle. The flame entered from both sides onto the plate. The first time I tried cupelling in it, the gas blew some on the molten lead out of the cupels, which ate some holes in the muffle plate and, of course, caused assay losses. I put some firebricks on both sides of the muffle plate to block the flame. By cracking the door open, I was able to properly oxidize the lead. Ended up with good assay repeatability.
 
You can cast into 10" round cardboard tubes used for casting concrete. The cardboard will burn off easily when you put it in the muffle furnace and they are easy to replace.

Make sure you ram it tight and dry out the mix before you go into the muffle. I made cupels in Ecuador in the '80's and they were dried in a small little glass house. (it probably was actually a greenhouse used just to dry out cupels) Sun near the equator made the time in the glass house relatively short.


Sent from my iPhone using Tapatalk
 
4metals said:
You can cast into 10" round cardboard tubes used for casting concrete. The cardboard will burn off easily when you put it in the muffle furnace and they are easy to replace

This is a Brilliant idea! Thank you once again Sir.

Since the thread is active I will post the details of the muffle furnace that I am planing to get manufactured. Any changes that need to be made are much appreciated before I proceed ahead.

So there are two type available, one where the door opens horizontally and one where it opens vertically. After reading multiple threads on cupellation and muffle furnaces I have decided to opt for the vertical type for much ease of use. The details are as follows:-

1)Item-Muffle furnace vertical type

2)Specifications-
Wattage-6Kw. 440v ,

Ceramic Heating box size- size-12" width X 12" height X 12"depth

Central hole of 20mm at both ends for air circulation with chimney fitting for removing fumes
outer shell made of Mild steel structure with cerawool thermal insulation

Maximum Temparature-1200 O c
Working Temparature-1100 O c
with digital temp control unit

I believe with this working space will the large cupel mentioned above fit in nicely?
 
I know you are in India so this may not be worth it for you but here in the US a lot of government institutions auction off their excess gear. A good website to find things is
http://www.Govdeals.com
Kilns are found in the Arts and Crafts section they usually have more than one kiln listed. They rarely sell for over $100.

Wouldn't you know it, I just checked and they only have 1 kiln active, figures. Anyway, this is it,https://www.govdeals.com/index.cfm?fa=Main.Item&itemid=63&acctid=5659#media

The price is low.
 
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