# Melting cemented metals from AR



## guldspecialisten (Dec 22, 2020)

Dear Forum,
I have been a member here for some years and not posted very often as I have mostly been reading and learning. Maybe the information I am asking for is already here, but I have been unable to find any threads mentioning a case similar to mine. 
For seven years, I have been refining gold containing PGM’s, selling the fine gold, cementing out the metals from the barren AR solution with iron, and saving the cemented concentrate. The gold refined was dental gold, both the yellow and white palladium alloys; white gold alloys some with Pd and other probably with nickel.
I have some kilos of this concentrate mostly consisting of copper. I do not know the exact palladium content, but it could be everywhere between 10-40%. I have washed the first third of this concentrate 6-7 times and dried it. Some parts of this concentrate got greenish when drying. I imagine this could be from lumps of cemented metals, that did not permit the water to penetrate very well during washing.
I wanted to melt everything into a bar, take a drill sample, send it to a lab in order to know the content of PGM’s before selling to a refinery. I do not have experience melting this type of material and therefore I took a 200gr sample and melted it, just using borax as a first trial.
I have an induction furnace with a crucible large enough to melt 5 kg of silver. Melting this material generated a lot of smoke when the temperature got high (A bit yellowish as far as I remember). The furnace is placed under a hood. Unfortunately I am unsure how high the temperature was as I was too busy focusing on the melt I forgot to measure. However, from experience I am 100% certain it would have been more than enough to melt fine gold or copper.
When pouring, there was a lot of liquid/slag and the metal solidified before reaching the ingot. The weight of the metal was only 100 grams. Half of the sample taken. 
The solidified slag was very soluble in water, almost as pouring some paint into water. Water turn cloudy very fast.
I do not think this was a success  , and before wasting more time and maybe, even loosing PGM’s experimenting I was hoping someone more experienced could help me.
My next trial would have been mixing the dry metals cement with 50% silver powder in order to lower the melting point. 
But, I most likely need the right flux for the job (How much?) or maybe melting is not the way to go?
Any suggestions?

Wish you all a Merry Christmas


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## nickvc (Dec 22, 2020)

Chances are you will have some platinum and traces of gold in the mix there, my first thought would be to try and dissolve some of the copper using dilute hot sulphuric which should remove a fair amount of the copper but leave the values, try a small sample to see how effective this is. Another point to remember is that PGMs melt at a lot hotter temperature than gold and many induction furnaces are not built to reach their melting points.
Lou might be able to give you some better pointers than me if he has time and isn’t sharing trade secrets.


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## guldspecialisten (Dec 23, 2020)

Thanks for your reply Nick,
I am certain there is some Pt as well and traces of other precious metals. My primary goal was to melt it all together and sell the material as it is. If I remove the copper, I will increase the melting point even more as you mention. However, it could be interesting to take a sample and dissolve some of the copper using dilute hot sulphuric acid, in order to see what is left.
I hope someone can guide me with some suggestions on which type of flux should be used in case of melting this material. I have seen some suggestions for at flux 50/50 borax/soda ash, though I am uncertain if I will need a reducer in case of oxides.


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## nickvc (Dec 23, 2020)

I used potassium nitrate to thin my flux mixes and when melting dirty material stirred the material regularly and left it to cook for a long time to allow the metal beads to fuse together, I always smashed my flux afterwards to check for any beads which I added to any later melts.


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## guldspecialisten (Jan 12, 2021)

Made one more experiment melting 100gr of the dry copper cement with PGMs. This time I crushed the dry cement and mixed it with 12,5gr dry cemented silver, added 10gr Borax, 10gr Sodium Carbonate and 4 gr crushed carbon and mixed everything together.
The silver was added to lower the melting temperature.
This worked much better than the two previous attempts and I ended up with a nice-looking bar weighing 79,5gr. I did not get to take a picture of it as I melted it together with the bars and lumps obtained during my two previous failed experiments. This bar did not look as good as the first one.




Some of the slag was soluble in water. Does it look like iron oxide? or is it something else. Maybe someone can help enlighten me?




I took a drill sample to send to a lab




Next time I will try using more flux to see if it helps reducing the water soluble unknown in the slag. Any comments or suggestions are welcome.


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