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anonguest

Question About Melting Gold

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Can some of the resident more technically/scientifically knowledgeable here help out on this question......

My understanding is that an alloy is a simple mixture of different metals and that the constituent metals are not chemically bound to one another? (the subtle exception being mercury amalgams?)

Certainly in the case of gold alloys, such as 22 ct gold that makes up coins such as Sovereigns, it is literally just 22 parts gold and 2 parts copper? and they are simply intimately mixed and melted together?

Thus....IF one were to melt and keep it molten long enough would the much less dense copper separate out from the gold and rise to and float on the surface of the much more dense liquid gold?

The molten copper could then, presumably, be 'skimmed off' leaving just, or very nearly, the pure gold.

Bottom line, can or is gold actually refined/purified in this way? or is it done just by chemical means?

Thanks in advance

Edited by anonguest

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Can some of the resident more technically/scientifically knowledgeable here help out on this question......

My understanding is that an alloy is a simple mixture of different metals and that the constituent metals are not chemically bound to one another? (the subtle exception being mercury amalgams?)

Certainly in the case of gold alloys, such as 22 ct gold that makes up coins such as Sovereigns, it is literally just 22 parts gold and 2 parts copper? and they are simply intimately mixed and melted together?

Thus....IF one were to melt and keep it molten long enough would the much less dense copper separate out from the gold and rise to ad float on the surface of the much more dense liquid gold?

The molten copper could then be 'skimmed off' leaving just, or very nearly, the pure gold.

Bottom line, can or is gold actually refined/purified in this way? or is it done just by chemical means?

Thanks in advance

Someone just happen to come into possession of some Sovereigns then?

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Someone just happen to come into possession of some Sovereigns then?

I've had some for quite a while if you must know. The query is completely unrelated.

I was merely wondering about how the bullion trade refine/purify the tonnes of scrap they inevitably deal with and, for those wanting to do very small scale home jewelery work, etc etc, IF low purity gold (e.g 9ct) can be 'refined' by simple melting and separating out the non-precious metal component.

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I've had some for quite a while if you must know. The query is completely unrelated.

I was merely wondering about how the bullion trade refine/purify the tonnes of scrap they inevitably deal with and, for those wanting to do very small scale home jewelery work, etc etc, IF low purity gold (e.g 9ct) can be 'refined' by simple melting and separating out the non-precious metal component.

jem whatshisname shows you how to get it from scrap circuit boards

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I've had some for quite a while if you must know. The query is completely unrelated.

I was merely wondering about how the bullion trade refine/purify the tonnes of scrap they inevitably deal with and, for those wanting to do very small scale home jewelery work, etc etc, IF low purity gold (e.g 9ct) can be 'refined' by simple melting and separating out the non-precious metal component.

You add chemicals to the moltern alloy that react with the copper silver nickel etc. (borax is one of the chemicals used.) which then form a slag on top that can easily be skimmed (or removed when solidified). The slag is insoluble in gold (hence they separate like oil and water) unlike silver and copper which are 100% soluble in gold.

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You add chemicals to the moltern alloy that react with the copper silver nickel etc. (borax is one of the chemicals used.) which then form a slag on top that can easily be skimmed (or removed when solidified). The slag is insoluble in gold (hence they separate like oil and water) unlike silver and copper which are 100% soluble in gold.

BUT....is it strictly necessary to add chemicals? Presumably these just do what I described but faster? Would the lighter copper or silver separate out anyway (like oil or fat from water), if the alloy is left molten long enough?

If so then the secondary metals (i.e non-gold portion) can be extracted as the pure metal, rather than itself then need to be refined later.

Edited by anonguest

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BUT....is it strictly necessary to add chemicals? Presumably these just do what I described but faster? Would the lighter copper or silver separate out anyway (like oil or fat from water), if the alloy is left molten long enough?

If so then the secondary metals (i.e non-gold portion) can be extracted as the pure metal, rather than itself then need to be refined later.

Sorry just re-read that last sentence.....so partially negating my reply above.

So Copper and silver actaully 'dissolve' into gold? In another words 22ct gold is more like a mercury amalgam? rather than two or more metals mixed when liquid?

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Sorry just re-read that last sentence.....so partially negating my reply above.

So Copper and silver actually 'dissolve' into gold? In another words 22ct gold is more like a mercury amalgam? rather than two or more metals mixed when liquid?

Yes they dissolve better than virtually anything else in the galaxy...

Silver dissolves perfectly as both solid and liquid.

Copper dissolves perfectly as a liquid and as a solid within at least 500C of the melting point at all concentrations.

The silver will evaporate off into the air faster than Cu / Au due to its much lower melting range but there won't be much of a difference in evaporation rates between Cu/ Au. (only pure materials have melting point others (alloys etc) have melting ranges).

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Well, this is the first time a degree in Metallurgy has been half way useful in over 30 years.

The impurities in gold are completely dissolved and will not separate out, no matter how long it is held as a liquid. Imagine it being like dissolving sugar in tea - once in, it isn't going to come out easily. (Some low temeperature metal systems like tin/lead/zinc IIRC can "sweat" out one or more components, but not in the case of gold).

If you jack up the impurity levels stupidly high then you can get some microscopic separation on solidification, (which is the basis on which many alloys systems work), but the "gold" part would still have a lot of dissolved alloys metals in it.

Some contaminants can be oxidised out of molten gold, like silver as someone has already mentioned. You need to provide a lot of time or agitation or oxygen to do the job completely. Nothing "evaporates" out, but some metals wil oxidise first and then turn to vapour at the surface.

Other contaminants don't oxidise easily, but can be slagged off with alternative chemical reactions, It depends what's in there.

For most metal systems, oxidation reactions can be speeded up and made more efficient by lowering the partial pressure of oxygen in reaction - either by working in vacuum or by using a dlutant like nitrogen or argon. All this is regulated by thermodynamics/ thermochemistry and TBH I've never seen the relevant diagram for gold (an Ellingham diagram), so such sophistication might not be necessary for such a noble metal. But it might be of benefit to prevent losses of the gold itself.

If you want it laboratory grade pure then the best method is to use electolytic recovery - simple bucket chemistry will always leave a trace of something behind but will get you to good enough purity to satisfy gold bugs.

.

Edited by Stainless Sam

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Well, this is the first time a degree in Metallurgy has been half way useful in over 30 years.

The impurities in gold are completely dissolved and will not separate out, no matter how long it is held as a liquid. Imagine it being like dissolving sugar in tea - once in, it isn't going to come out easily. (Some low temeperature metal systems like tin/lead/zinc IIRC can "sweat" out one or more components, but not in the case of gold).

If you jack up the impurity levels stupidly high then you can get some microscopic separation on solidification, (which is the basis on which many alloys systems work), but the "gold" part would still have a lot of dissolved alloys metals in it.

Some contaminants can be oxidised out of molten gold, like silver as someone has already mentioned. You need to provide a lot of time or agitation or oxygen to do the job completely. Nothing "evaporates" out, but some metals wil oxidise first and then turn to vapour at the surface.

Other contaminants don't oxidise easily, but can be slagged off with alternative chemical reactions, It depends what's in there.

For most metal systems, oxidation reactions can be speeded up and made more efficient by lowering the partial pressure of oxygen in reaction - either by working in vacuum or by using a dlutant like nitrogen or argon. All this is regulated by thermodynamics/ thermochemistry and TBH I've never seen the relevant diagram for gold (an Ellingham diagram), so such sophistication might not be necessary for such a noble metal. But it might be of benefit to prevent losses of the gold itself.

If you want it laboratory grade pure then the best method is to use electolytic recovery - simple bucket chemistry will always leave a trace of something behind but will get you to good enough purity to satisfy gold bugs.

.

You just helped scratch a random intellectual 'itch'! For some reason I always thought that gold alloys were simply a 'mix' and that if held molten long enough they would separate out - but that this wasnt done cos of the added time/energy cost and that a chemical or electrolytic approach was quicker industrially. But now I know better. Many thanks indeed.

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