I use cone mold then melt again and make shots.
I think sulphur is the best option to push base metals into slag, even we can reduce the copper content in the molten metal in case its very high, I did a test on different network coax gold plated connectors, they have very high content of copper and since I use nitric to part the copper I added 10% sulphur to the connectors, used small amount of soda ash,borax and fluoride since most of the connectors is metallic part, after pouring the cone I got 50% of the main connectors weights, I believe if I increased the content of sulphur to double will push all copper into slag, but in this case I have to add some silver to make sure I collect all gold beads, theory,if I want to recover the copper I can remelt the slag with adding some iron or I can just mill and roast the slags to get rid off sulphur.
Using sulphur from my test is much faster and cheaper than using copper electrolysis cell or nitric parting, I got same amount of gold that usually got from same type of connectors using hydrometallurgy process.
I want to get some advices before use sulphur in large batches, now I'm planning to first smelt pyrolized connectors without sulphur in the flux so I will have wide molten metals space into my flat crucible ( its a customized furnace), then I will add the sulphur to ic chips and mlcc's ash and feed them above the molten connectors, so I can make sure the molten connectors will collect the metallic parts of the ic chips, then the sulphur will start to sulphurize the base metals, then pour into the cone mold.
Sulphur makes the smelting and gold recovering very easy and controllable, this make me confused if I make something wrong, hope I will get some advices about it.