Tredsaw12 said:
The silver chloride forms a crust on the surface of the karat gold and slows down the penetration of the aqua regia. If the silver content is high enough, the penetration of the acid completely stops. This problem is solved by inquarting with enough silver (preferably) or copper to reduce the gold content to 25%. Then, everything but the gold can be easily be dissolved in hot nitric acid. The remaining gold powder is then easily dissolved in aqua regia.
Hey Harold, I know you know what you're talking about so please help me with this. In the quote above, the last two lines read: "Then, everything but the gold can be easily be dissolved in hot nitric acid. The remaining gold powder is then easily dissolved in aqua regia."
We were wondering, if EVERYTHING but the gold can be dissolved, then why not just melt the remaining gold powder and be done, instead of dissolving in aqua regia.
Yeah, at a glance it sounds like you could avoid the AR step. I probably should have been more descriptive, or suggested that the gold is pure, relatively speaking. It rarely is. Problem lies in not being able to fully eliminate the base metals. There are many variables that interfere with the end results-----but in theory you could do exactly what you suggest, eliminate the AR process. Fire assayers do it all the time, but they also closely control their button, including eliminating base metals aside from silver, which is done in the cupel. They are absorbed as oxides, along with the litharge that is created in the cupellation process. The button is then inquarted properly, rolled thin (now called a coronet) so the silver can be properly eliminated with nitric and water. Rarely does a person refining expose their material to such exacting processes. They would be dreadfully slow, and not economical in large volumes.
Given ideal conditions, I have no doubt you could inquart properly, boil in nitric for an extended period of time, then rinse adequately to eliminate all traces of base metals and silver, but doing it routinely would be a tall order. It's far easier to get the gold as pure as you can with the preliminary washes and rinses, then to dissolve it so you can precipitate it and (hopefully) leave the trace contaminants behind. Even that doesn't guarantee 4 9's, and rarely does, if for no other reason, drag-down.
To be more specific, I was thinking that I have a jar of gold plated copper, I was going to just add nitric acid to the jar to dissolve the copper, now wouldn't I have pure gold solids left at the bottom of the jar. Then I could just melt them down into a nice little button.
You won't be the first to think it will work, and you damned sure won't be the last. Again, the problem is that while you've eliminated the vast majority of contaminants, you don't get them all.
I encourage you to try what you propose, so you'll get a firm understanding of what the end result will be, and what gold looks like when it's not quite pure. It will do no harm, and it's easy to re-process the gold to achieve a higher level of purity, although not quite as easy as dissolving those nice, well washed, foils.
I fully expect the gold that comes from this operation to be contaminated with traces of lead and tin, plus some copper and nickel. The surface of the gold will be somewhat mottled, and not brilliantly shiny as it can be. It also will likely not form the large, broad crystalline structure characteristic of pure gold----and is likely to form an oxide scale. Pure gold will melt without flux and cool with a bright surface without a trace of oxidation. Any contamination pretty much assures that will not be the case.
For the record, I refined all of my gold two times to eliminate traces of contaminants that hitched a ride through the first processing, even after washing well. Getting gold pure isn't easy, although GSP claims to have a process that pretty much assures it will be. I'm not privy to how it works, but he's talking about putting a book together that will include the process. Up to now, he's not been willing to share the information.
Harold
