Melting steel is a lot harder than melting gold and it would only alloy if you did. But melting with silver as a collector could dissolve the gold in the silver while the iron would not dissolve. Silver and iron doesn't alloy.
If the iron is washed in nitric acid any gold containing silver would be dissolved and gold as a fine mud could be filtered off.
When all the charms are processed and the gold is collected by the molten silver, the silver could be dissolved in nitric, leaving the gold behind as a fine mud.
Disclaimer, I have never tested this procedure, I have no access to your scrap and I don't have a furnace to even try melting scrap like this. What I wrote above is just what I would try if I had the scrap and equipment.
Another way might be via the sulfuric cell, 18k could be enough gold for it to work, especially if there is some silver in the alloy too. Same disclaimer here too, I don't know anything about your scrap and I haven't tried running 18k scrap in a sulfuric cell.
You really should do a lot of reading on the forum about any method you want to try, about safety and treatment of wastes. No disclaimer on that statement.
Göran