help

[Anonymous]

i have some difficulty when i use copperas to precipitating gold (when i add copperas the black cloud apears then disaspears ) is it normal ??

THANKS

 

[Harold_V]

If it truly disappears, you likely have an excess of nitric acid present. If, on the other hand, the cloud slowly settles to the bottom, that's how it behaves. The gold is precipitated in very tiny particles, especially from scantily concentrated solutions. It often takes as much as a full day for the atoms of gold to settle to the bottom.

Harold

 

[Anonymous]

so black cloud is very fine gold.

 

[Harold_V]

That would be my guess. I used ferrous sulfate early on in my refining experience, but I always evaporated and had no problems with the precipitated gold dissolving again. I also have no idea how introducing ferrous sulfate to a solution that has excessive nitric behaves. Just guessing, but you may be able to add enough ferrous sulfate to consume any free nitric, eventually precipitating the gold permanently. As I said, just guessing. I have not been through the process.

If you feel you have free nitric present, and you evaporate, you might try adding a button of pure gold to the solution when evaporating. Assuming you have an adequate amount of HCl included, any free nitric will be consumed by dissolving the gold button. It's an easy and fast way to eliminate nitric. If you wish to know how much gold you had prior to adding the gold button, weigh the button both before and after evaporation. Subtract the difference in weight from the yield.

Harold