Viscous substance after react gold plated pin with HNO3

[DelayNoMore]

I cut the gold plated pin from cpu, then added HNO3 to dissolve the copper base in order try to filter the gold out.
However, after the reaction, semi-white color viscous substance is found sinked into the bottom and hard to filter.
My question is what is this substance and how to avoid it?
if present, how to remove it?
thank you very much.

 

[samuel-a]

My question is what is this substance

It's called metastannic acid H2SnO3, you are producing it while Tin is reacting to HNO3.

and how to avoid it?

Don't use Nitric acid where Tin is present.

if present, how to remove it?

With hot 40%-50% sulfuric acid, it's not going to dissolve easily though.


p.s. - we can read your words in the normal font size just as well.

 

[DelayNoMore]

Thank you Sam,

after you told me it is tin oxide, i search around the forum and found that it's call metastannic acid
and one method of removing it is to filter off the paste, incinerate the paste and wash with hot HCl
i will try and see the result.

 

[samuel-a]

it's call metastannic acid

Yes, you are correct, i'll edit the post to the right term.

Good luck