Rahul Bhaduri, PE

TC: Treatment Charge; RC: Refining charge; very simplistically, when you ship float cons (Cu, Au, etc) or spent catalyst for smelting/pyromet/hydromet to refining companies for metals recovery, these are the charges that are levied based on metals & impurity content in your product.

Check out the following entity web sites: Newmont, Barrick, Goldcorp, Kinross for starters...these are all Au producers.

Co or any metal gangue in slag are difficult constituents to extract based on inclusion in a silica matrix; what that means is fine grinding (<20-microns) or significant energy will be required to liberate the target metal(s)...once liberated, Co can be extracted under ammoniacal conditions w/T & P...ammonia is best suited for Ni, Co, Mo, V since it is selective to those metals...H+ will dissolve a host of unwanted contaminants which complicates separation. 

www.infomine.com & www.smenet.org might be applicable for starters!