The tips you are talking about are very high in silver content. They are soldered onto the copper with silver bearing solder. I just use a propane torch. Hold the copper part with vise grips or pliers, heat the soldered joint until red, then lightly and carefully tap them onto a work bench, metal plate, cinder block, etc., the nice little silver square will come right off. They stay hotter longer than you think. Use caution when doing this. Safety glasses would be a good thing.
Save them until you get enough to mess with. There are several people here on T-NET that can recommended who to send them to. They will in turn melt them down to pure silver. Just remember, they need to make a little bit of money on their end of the deal too.
Bob