Harold_V said:
I have discussed this cleaning procedure in the distant past. You may have success doing a search on cleaning melting dishes. There's a little more to the process but I am short of time and can't elaborate at the moment.
Harold
I looked up your posts..
By Harold (the Greatest- and humble too) (that comment by me- overdriv)
Borax absorbs oxides, yes, but when you reduce them with soda ash, they're put right back in your gold. You can see evidence of that by cleaning what you think is a dish that contains no metals, but is covered with dirty borax residue. Introduce soda ash and heat the dish well, until the soda ash starts dissolving borax. As it liquefies, you'll notice tiny beads start to appear everywhere. That's the oxides being reduced to their metals.
In order to clean melting dishes, you have to get them to red heat, and it helps to do a little stirring with a carbon rod to mix the molten soda ash with the old borax. You may even have to pour the entire mess off once and repeat the operation. It works, and works well. I've cleaned countless melting dishes that were beyond use without the cleaning operation. The cost of cleaning is well repaid by recovered values.
As for cupels, I don't have an opinion. They work very well for absorbing unwanted substances, but they're not generally the tool of choice for refining. They are used, primarily, to absorb lead from assays. Lead, introduced as litharge, oxidizes the charge, reducing the litharge to lead, which acts as a collector. the resulting button is then run in a muffle furnace on a cupel, where the lead is once again converted to litharge, and absorbed by the cupel, along with oxides. They have a capacity, which, once filled, renders them useless for their intended purpose. They may still be good melting dishes, but they will no longer absorb contaminants.
Without refining by some means, the gold extracted by these stripping systems will be of questionable quality. Melting in a cupel is one way to improve your gold, as Steve has so nicely demonstrated, but it's cumbersome when you get involved in large volumes of gold.
The material that comes from these cells is perfect for chemical refining. A boil in nitric to remove unwanted traces, followed by a boil in HCL, then dissolution with AR. The resulting gold should be of excellent quality, likely 9995 or better.
It seems like a long, hard way to go, but it is routine, and happens much quicker than you might imagine. As you progress in extracting, and find you're producing gold in larger and larger volumes, you might keep the process in mind.
Harold
