DETERMINATION OF COPPER IN MAGNESIA CUPEL

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robertova89

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Aug 16, 2017
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I have a problem to determine copper in a magnesia cupel, at the end of the cupellation the cupel blackens, it has a dark colour so I can’t determine if the cupel has copper in it. Could it be that the problem is the cupel or the flux that I'm using? Please help If anyone has ever had this problem before.

Thank you
 
robertova89,
I am unsure what the question actually is or what you are trying to do.

The cupel is made of a material made to absorb metal oxides (basically the rust of the metals).
Used with an oxidizing environment (air, oxygen from the torch, oxidizing flux...), copper will oxidize.

Copper like many metals can have several different oxidation states, depending on its oxidation state copper can have different colors, blue, green, black...
Many metals form black oxides.

Try asking the question again, giving us more details of what it is you are trying to accomplish.

Are you mining and looking to test for copper in the ore?
Do you have a copper ore and trying to recover it?
 
Hello there,
The problem is that I analyze various samples , and I know that after the finish of the cupellation the cupels that are dark green contain copper and the cupels that are of other colour not. So the cupels that are in dark green, it means that they have copper in it so in this way I analyze the samples that contain copper apart. But, nowadays after I finish the cupellation all the cupels are dark black so I can’t determine whether they have copper or not in it, so I have to analyze every sample apart to know if they contain copper, but this will be so expensive. The question is if I am working in the wrong way or that the magnesia cupels contain something that reacts in the cupellation and turns every cupel into dark black colour.

Thank you best regards
 
the cupels purpose is to oxidize the metals and suck them into its pores, why would you wish to find which ones have copper, or even care about it?
Lead now that is a totally different story.
The copper in the cupel (or most any metal it absorbed) would be useless to try and recover. you could go pick up a rock with much more copper and be less trouble to recover copper from it.

Are you doing something else? what are you trying to do? what are you using the cupels for? are you using a cupel when what you need is another dish or crucible to melt metals in?

Whats up doc? I still do not understand.
 
Copper oxide is black, there must have been some reaction that turned the old cupels green.

Try add a couple of drops of HCl to a cupel with absorbed copper oxide and watch the color change over a week.
What I suspect would happen is this progression. (NOT a balanced chemical reaction)
Cu + O2 -> CuO (black) + HCl -> CuCl2 + CO2 + H2O -> Cu2(OH)2CO3 (green solid)

You could put a piece of copper beside the cupel and watch the process unfold. Most of the HCl will evaporate but it is reformed when carbon dioxide replaces it so it will work like a catalyst.

This is obviously not something I have tested myself so take it as an idea and not instructions.

Göran
 
the cupels purpose is to oxidize the metals and suck them into its pores, why would you wish to find which ones have copper, or even care about it?
Lead now that is a totally different story.
The copper in the cupel (or most any metal it absorbed) would be useless to try and recover. you could go pick up a rock with much more copper and be less trouble to recover copper from it.

Are you doing something else? what are you trying to do? what are you using the cupels for? are you using a cupel when what you need is another dish or crucible to melt metals in?

Whats up doc? I still do not understand.
It's a matter of copper pattern , He/She would have put copper into some cupels inorder to identify the trays or check whether there is a mix up of samples after the fusion and cupellation
 
"at the end of the cupellation the cupel blackens"
It could also be a loss of silver. If cupellation takes longer than necessary, part of the silver in the precious bead starts oxidizing due to overheating and melting into a black spot around the bead.
 
It could also be a loss of silver. If cupellation takes longer than necessary, part of the silver in the precious bead starts oxidizing due to overheating and melting into a black spot around the bead.
I would just add that loss of silver is also in form of vapors. Sometimes quite measurable. Part of the PbO evaporates in the process, and take some silver with it. But deposits of nanoparticles of silver definitely aren´t coloured black (surroundings and edges of crucible/cupel) - most of the times, it has yellowish hue.
 
This may depend on the quality of the batch of magnesia cupels. We have had a couple of issues with circular deposits of oxidized silver around the bead after the sample was overexposed in the furnace, which is why I wrote about it.
 
I have a problem to determine copper in a magnesia cupel, at the end of the cupellation the cupel blackens, it has a dark colour so I can’t determine if the cupel has copper in it. Could it be that the problem is the cupel or the flux that I'm using? Please help If anyone has ever had this problem before.

Thank you
When you state "could it be the flux I am using", I am a little confused. Cupeling should involve putting a well hammered and cleaned bead or prill, into the cupel. Any remaining flux on the bead of alloy, will sink to the bottom in the cupel cup. This in turn can hamper the ability of the cupel to absorb the oxide metals. And leaves a glassy surface to the cupel, which could be any color of the slag composition you started with. Start with a flux free bead.
 
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