# Alternative to bone ash cupel?



## goldshark (Jan 16, 2022)

Not being privy to a Scanning or transmitting electron microscope, does an alloy of metals consist of, for reference, 80% Pb/20%Ag, A fairly uniform distribution of Ag in the Pb, or are the Ag atoms clumped in bunches? if so, how many atoms per bunch? Where am I going with this? I read a post last night about what I understood, as aFine sand/Fine copper mixture, with flux, to pull tin or lead away from the PMs at a reduced temperature. Is this a tried and true method, or in the experimental stages? If it is tried and true, would somebody elaborate on it's parameters please. Also wondering if anybody has any knowledge about the use of an electrowinning cell in a metallic melt. IE, recovering silver from the previous alloy mentioned with electrowinning, in lieu of the Parkes process.


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## Yggdrasil (Jan 16, 2022)

I'm not sure which post you refer to, but recently there was a discussion relating to depopulation, 
where copper powder and sand bath was brought up.
That was to pull the solder from the PCB's and not any kind of separation.
Silver tin as you describe it is a proper alloy and will not be separated by such means.
Do NOT use nitric, but the tin can be dissolved in HCl, Silver do not dissolve in HCl.
How much are you talking about and in what form?


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## orvi (Jan 16, 2022)

goldshark said:


> Not being privy to a Scanning or transmitting electron microscope, does an alloy of metals consist of, for reference, 80% Pb/20%Ag, A fairly uniform distribution of Ag in the Pb, or are the Ag atoms clumped in bunches? if so, how many atoms per bunch? Where am I going with this? I read a post last night about what I understood, as aFine sand/Fine copper mixture, with flux, to pull tin or lead away from the PMs at a reduced temperature. Is this a tried and true method, or in the experimental stages? If it is tried and true, would somebody elaborate on it's parameters please. Also wondering if anybody has any knowledge about the use of an electrowinning cell in a metallic melt. IE, recovering silver from the previous alloy mentioned with electrowinning, in lieu of the Parkes process.


Question about "bunches of atoms" is very difficult to answer in general  If two metals alloy, they could form new solid phases, which could crystallize from the melts at lower temperatures. For most of the eutectic binary mixtures, grain size is relatively known thing. What could be said generally - if the cooling of the melt is prolonged and slow, bigger crystals of the separated phases could crystallize. 
You must study phase diagrams of certain alloys to recognize what will happen if certain composition undergo cooling. If it is in the area of solid solution - thus no separation and crystallization will occur. Or it isn´t and you could face grain formation of certain compositions, which you could identify and predict from phase diagrams.

This is for example the reason why after pouring a bar of metal alloy, there could be different XRF reading on the top and bottom side of the bar. Metal on the bottom cooled quicker than the top of the pour, resulting in varying composition at these two places. Very common with melts of metals which don´t mix well at lower temperatures, such as Pb-PGMs systems.


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## cosmetal (Jan 16, 2022)

Yggdrasil said:


> I'm not sure which post you refer to, but recently there was a discussion relating to depopulation,
> where copper powder and sand bath was brought up.
> That was to pull the solder from the PCB's and not any kind of separation.
> Silver tin as you describe it is a proper alloy and will not be separated by such means.
> ...


I tried the sand bath once and it was a total waste of time for me.

James


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## orvi (Jan 16, 2022)

goldshark said:


> Not being privy to a Scanning or transmitting electron microscope, does an alloy of metals consist of, for reference, 80% Pb/20%Ag, A fairly uniform distribution of Ag in the Pb, or are the Ag atoms clumped in bunches? if so, how many atoms per bunch? Where am I going with this? I read a post last night about what I understood, as aFine sand/Fine copper mixture, with flux, to pull tin or lead away from the PMs at a reduced temperature. Is this a tried and true method, or in the experimental stages? If it is tried and true, would somebody elaborate on it's parameters please. Also wondering if anybody has any knowledge about the use of an electrowinning cell in a metallic melt. IE, recovering silver from the previous alloy mentioned with electrowinning, in lieu of the Parkes process.


I have one-time experience with melt electrolysis of 3% Ag alloy in tin, using molten SnCl2 as electrolyte. Never again  but it worked to some extent, but not as great as we wanted. Keeping the electrolyte molten, fresh and fluid is one of the biggest issues with this type of process. Not to mention proper container for the molten bulk of the metal, suitable design of second electrode to contain the molten metal in - obviously graphite one, reliable heating of whole thing.

We then sticked to Parkes-like process with this material, but it wasn´t extremely efficient also due to tin as base metal for Ag extraction, not the lead. But much more doable than molten electrolysis.
Most funny part was filtering the 300 °C Ag-Zn suspension from the molten tin  not to pour the molten tin inside the heat gun...  good memories, I laugh a lot every time I think off this "operation"  

For silver/lead molten electrolysis I cannot imagine friendly/workable electrolyte right now. Lead chloride has melting point of 501°C, and as most of the similar metal chlorides such as ZnCl2, HgCl2, SnCl2 or AgCl, it vaporizes very easily. Nothing which I wanna experience - vaporized lead in my workplace, or even contamining whole fumehood. Big no. After experience with SnCl2 misting the whole hood (and SnCl2 isn´t that highly toxic as PbCl2)... Never.


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## goldshark (Jan 16, 2022)

Thanks all. Since I hadn't seen any posts about these thoughts I had, I just thought I'd ask. See if anybody else tried before experimenting.


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## goldshark (Jan 17, 2022)

Maybe you answered my question, but due to my lack of chemistry knowledge, let me ask in other terms. 
Is it possible to use an anode/ cathode system in a straight melt of the previously mentioned alloy, at say the minimum temperature requirement to get said alloy into a liquid state, to get an attraction to either the cathode or anode?


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## Yggdrasil (Jan 17, 2022)

goldshark said:


> Not being privy to a Scanning or transmitting electron microscope, does an alloy of metals consist of, for reference, 80% *Pb*/20%Ag, A fairly uniform distribution of Ag in the *Pb*, or are the Ag atoms clumped in bunches?





Yggdrasil said:


> Silver *tin* as you describe it is a proper alloy and will not be separated by such means.
> Do NOT use nitric, but the tin can be dissolved in HCl, Silver do not dissolve in HCl.



I have to bow my head in shame, I read it, but did not see that it was Lead not Tin.

It can be dissolved in either HCl or Nitric, but its salts are extremely toxic, even carcinogenic.
It may or may not be better to cupel it if it is not too much material and you can do it outside or in a scrubbed fume hood.
Or do a plain electrolysis with lead chloride as electrolyte.
You are not aiming for purity of lead and the silver will not dissolve in HCl.
Just an Idea.
Still, be safe and use caution around these substances.
Regards Per-Ove


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## goldshark (Jan 18, 2022)

Which leads me to the next question. In the above said alloy, would it be possible to do a continuous cupeling with a crucible size cupel. Since I haven't done much cupeling, does the cupel adsorb only so much lead, or will the lead eventually start leaking out the bottom if either left in heat too long, or an excess of lead for the cupel?


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## Yggdrasil (Jan 18, 2022)

No cupels can only absorb a set amount of litharge/lead so it is a batch operation.


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## goldshark (Jan 21, 2022)

Thanks, I thought so. However, I am still wondering if there is any kind of composition which could be configured to produce a molten bath filter to allow for a continuous filtration of molten metals such as in the Parkes process to eliminate the need for skimming. Even if you had to do a melt in a non porous crucible with the zinc, Then pour into the porous bottom crucible/filter, with a catch basin underneath. The ultimate objective is to eliminate any lead that may be unnecessarily recovered during skimming, making for a cleaner Silver/Zinc alloy.


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## orvi (Jan 27, 2022)

goldshark said:


> Thanks, I thought so. However, I am still wondering if there is any kind of composition which could be configured to produce a molten bath filter to allow for a continuous filtration of molten metals such as in the Parkes process to eliminate the need for skimming. Even if you had to do a melt in a non porous crucible with the zinc, Then pour into the porous bottom crucible/filter, with a catch basin underneath. The ultimate objective is to eliminate any lead that may be unnecessarily recovered during skimming, making for a cleaner Silver/Zinc alloy.


You can filter the molten metal using fiberglass filters, but the whole operation is tricky to perform. You need to pre-heat the filtering apparatus. Otherwise the metal solidify inside and you are stuck with lead brick inside.
I will personally stick to skimming, using some firm stainless steel mesh as "spoon" - molten lead will drip off it easily. 
You can then reheat the skimmed material in the crucible and pour the excess lead out - as mbmmllc shown in one of his videos about Parkes process with actual galena ore. You will be left with not that much afterwards.

Parkes process is quite nasty operation, lot of toxic stuff is produced and possibly inhaled. Not feasible if you do not have vast quantities of material to process. 20% Ag in lead is quite rich alloy, and with it, Parkes will be much easier than with raw ore.


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## goldshark (Jan 27, 2022)

Thank you Orvi, very informative. I was wondering what the filter media of choice was. Do you have any idea how the old timers did this on an industrial scale? Say in Leadville , Colo.during the 1880"s. I am a bit of a history buff, but can't find any particulars on the processes in vogue back then. Only drawings of the furnaces.


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