Best and Easiest way to refine gold dust to get % purity
Oct 17, 2009· Decrease% of gold to < or = 25%, as low as possible by copper or silver. Then put in 35%40% HNO3. Wait 1 or 2 hr, filter solutions with filter paper. Rinse well with water. The black powder is gold. Dry it and melt it and you have % gold this way without the iron inside the metal.