# Collector metal - copper, silver or lead



## autumnwillow (Dec 23, 2016)

When such low grade material is to be smelted it is ideal to use a collector metal in order to concentrate the PMs further and lower the melting point of PMs.

Lead - melts at very low temp, vaporizes at high temperature. It will produce Pb fumes which is toxic. 
Copper - can be used for very low grade materials and the resulting metal run in a copper cell to collect PMs.
Silver - my preferred collector as I can easily digest the smelted material in nitric then proceed to AR or in a silver cell to concentrate PMs.

Though I still wonder why most refineries use copper as a collector metal because copper increases the melting point of PMs.
Silver seems the most expensive but its easier to recover.


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## upcyclist (Dec 23, 2016)

autumnwillow said:


> Though I still wonder why most refineries use copper as a collector metal because copper increases the melting point of PMs.
> Silver seems the most expensive but its easier to recover.


That's probably why--_expensive _carries more weight than _ease of recovery_. A ton (US) of copper is about $5,000. A ton of silver is about $460,000.


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## g_axelsson (Dec 23, 2016)

autumnwillow said:


> Though I still wonder why most refineries use copper as a collector metal because copper increases the melting point of PMs.


Copper has a higher melting point than silver but when alloyed with PM:s it lowers the combined melting point compared to the pure PM or copper. Both silver and copper have that effect.

http://www.saltlakemetals.com/MeltingPoints.htm

Göran


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## upcyclist (Dec 23, 2016)

g_axelsson said:


> autumnwillow said:
> 
> 
> > Though I still wonder why most refineries use copper as a collector metal because copper increases the melting point of PMs.
> ...



Duh. I wasn't even thinking of that. Note that the melting point of 14K red gold (where the other 10/24ths is all or mostly copper) is actually 50°F/28°C degrees *lower *than for 14K green gold (where the balance is all or mostly silver).


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## Topher_osAUrus (Dec 23, 2016)

Is copper how they smelt rhodium?

I remember Lou saying that silver and rhodium are immiscible...so I wonder if that too, is a deciding factor on collector metal.


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## g_axelsson (Dec 24, 2016)

As I understand it, few places makes any special concessions for rhodium. If they get it then it is a bonus but if they don't get it no one is going to lose sleep over it. The only place where rhodium is used in larger volumes is in industrial catalysts and in auto catalysts and those are recovered with special methods.

I'm sure Lou will correct me if I'm wrong.

Göran


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## anachronism (Dec 24, 2016)

g_axelsson said:


> autumnwillow said:
> 
> 
> > Though I still wonder why most refineries use copper as a collector metal because copper increases the melting point of PMs.
> ...



It's all a trade off. One metal has a benefit over another in one way however there's the downside as a counterpoint!

You never have a perfect "one stop" solution with no draw backs and it's about balancing.


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## nickvc (Dec 24, 2016)

As with most things in refining there are trade offs for any variation to a process, for the large recovery firms the cost of the copper is one point but so to is the fact that they do get paid for the copper by the refinery, for the small or home refiner silver is preferred because it can be easily reclaimed and used over and over and its value makes it worthwhile to recover which for many copper isn't unless they build a copper cell and the problem with cells is they do need attention and high grade feed stock to function well.


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## autumnwillow (Jul 21, 2017)

Back to this topic.

So I bought this high pressure stove for pyrolysis. I used a small aluminum pan with lid as the vessel to hold the high grade wastes and proceeded with the heating. As soon as the smoke started producing I ignited it until everything was almost smoke free then some parts of the pan itself melted. I know I should have used a steel pan, I didn't expect that high pressure stove would go above 600degC. So I stopped then collected the pyrolized material, sieved, removed the magnetics then mix with 1:1 ratio of flux.

Upon melting it didn't melt well. We removed it from the crucible and the material itself was crunchy. Probably due to some of the aluminum?
So then I still proceeded with inquarting with silver. It wont melt properly into a button. I stopped the heating then inspected the material. It alloyed to this lot that won't melt, it didn't even form a button. I tried again with more flux, no result. Then finally adding copper where it finally melted into a button.
The material processed was stone setter jewelry wastes.

What did copper do?
It was just at the back of the head that copper is a better collector than any other element. I forgot. I should start making notes.

edited: just wrong grammar, just re-read this today. and copper is the best collector due to its high affinity with most precious metals (except PGMS)


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