Non-Chemical Black Sand Beads not digesting Using 50% HNO3 and HCl

[MetAssayer]

Hi,

I have some black sand samples and after cupellation, I have tried to digest the beads using a 2 stage digestion technique. First stage is using 1ml of 50% HNO3 and after the silver has digested, I use 1ml of 100% HCl. Usually this will dissolve the beads, but these black sand beads will not digest.

Has anyone seen this before ? Any advice, should I use different acids?

Thanks

 

[Lou]

They're iron. Nitric is passivating them. Try 50/50 sulfuric acid with perhaps a small amount of HCl. That will solvate them.

 

[Westerngs]

You say they won't digest after cupellation.

Did you do a litharge fusion first to collect the precious metals?

Did you add enough inquart silver so that the silver to gold ratio is at least 3:1?

Some more details would help. Usually one would not cupel black sands directly without a fusion first.

 

[4metals]

I agree with Westerngs, a lead scorification or a fusion are in order before cupellation.