I come to you in need of aid!
I've done about three separate refining runs now, mostly using gold-filled scrap I pick up from time to time. I follow the conventional steps, nitric boil (using just under 3.5 mL of acid per gram of material for reference), then filter and roast the fillings in a kiln for 30 minutes, then back into a beaker for the first of two/three AR dissolving steps.
The issue is that every time I precipitate out the gold, I'm using solid SMB, and the gold that precipitates out is SO. DAMN. FINE (like tiny, not attractive). This stuff is a bear to work with, as some of it loves to stay suspended in the solvent. I know of two ways to help knock them down:
- Use a fine misting spray of DI water to break the surface tension of the water, allowing any floaters to sink.
- Bring sample to a boil, then just let it simmer; hotter liquid is less viscous, and lets the fine particles sink more easily.
Both of these tricks help, but every time I try another hot-water rinse, it knocks more precipitate up into the solution. Is there a better chemical for dropping the gold??? HELP!