substituting bismuth for lead in fire assays

[Eu_citzen]

I haven't run any more samples with bismuth since I first did the evaluations in the '90's. The cost is a big factor and no one in a declining (USA) refining market is looking to spend any more money than they have to.

It would be a good change for the assay industry but it needs to be driven by environmental regulations, in the US the majority of the refiners tend not to be the type to spend the substantial extra dollars just to be green. They would not be classified as "tree huggers!"

I hear ya. I got myself approx 1 Kg of bismuth from a fireworks shop, to try out.

My assaying is done for my own prospecting needs only, not much refining going on here.
Well, not yet anyway.

Pricing is second concern to health & disposal issues with lead, I won't be doing a whole lot of assaying.
So it makes a attractive alternative for me.

What were your findings in the 90's, if you remember? Any interesting observations?

Some preliminary testing I did (before the furnace broke!) indicated that it seems beneficial to add a bit extra bicarbonate as to improve results on assays containing silver. Otherwise I'd tend to get somewhat low results on that using bismuth.

Well, it'll be a week or two before the furnace is ready for action, so I'm reading all I can get my hands on.

 

[4metals]

The only thing I had issues with was replacing litharge with the bismuth oxide for sweeps assays when there was a high concentration of chromium in the sample. Back then I assayed a lot of jewelers sweeps and green rouge had high chromium. It was difficult to assay with a litharge flux and even more difficult with a bismuth oxide flux.

Checking old notebooks, my comment was if green (that's chromium) and an unacceptable spread between cups results with a green rouge specialty (litharge) flux, forget bismuth oxide, unacceptably low results.

 

[Eu_citzen]

4metals, Thanks! Curiously, chrome oxide is very rarely used for polishing jewelery these days, in Sweden.
I see more iron oxide based polishing compounds.

 

[4metals]

True but I'll wager money I'm a lot older than you! Green rouge was very popular in the '80's and '90's. Today not as popular. I believe it is used to polish Platinum though.

 

[Eu_citzen]

:lol: 4metals, Chances are you're right about that.

 

[goldrun]

Does bismuth require an exhaust? Is it imperative to use magnesium cupels?

 

[4metals]

I wouldn't do any cupellation without exhaust!

 

[goldrun]

Does bismuth require an exhaust?

Sorry for this one Even bismuth is less toxic than lead it is necessary to have axhaust :!: What about magnesia cupel? Someone :?:

 

[4metals]

Sorry all of my first hand experience with bismuth cupellation was with bone ash cupels

 

[Eu_citzen]

What ever you do, don't use pure cement cupels. (in case someone still makes cupels)
A 50/50 mixture of bone ash and cement gave good results, however. Bone ash cupels also worked.

Haven't tried magnesia cupels, don't have any at hand.

ALWAYS have an exhaust.

 

[Yggdrasil]

I am aware that this thread is old but since my question is on topic I hope its ok.
We have tried to cupel with Bismuth, but it failed.
The button had slags and was very brittle. It also had prills around it.
I was not there so I'm just relaying the information.
Are there some things not to do with Bismuth in stead of lead?
He was out of lead, but had Bismuth and gave it a try, it's for internal use no need for high precision.
Regard Per-Ove