Hey Phil:
Going to need some more info on what you have, and what you are trying to do before recommending any good flux for recovering platinum (Pt). Also, keep in mind the high melting point of Pt (1772C - 3222F), will require the flux mixture to have some sort of eutectic action (lowering the melting point) of the Pt if you are going to fire it in a regular furnace, and that is normally done by using some form of lead (Pb).
There are 4 basic types of fluxes; oxidizing, reducing, neutral and purifying. Depending on the matrix of ore or metal you are dealing with, determines the proper flux required to separate the gangue from the final metal.
You said the ore leaching is completed, and you are now ready to smelt. What minerals/metals are remaining (i.e. silica, feldspar, iron, nickel, cobalt), and how large of a charge are you trying to smelt at one time?
The normal procedure for handling Pt cons, sweeps and jewelry (unless you have a very high-temp furnace), is by wet chemistry. Any flux you use that contains lead as a collector, will require several additional steps to separate the lead and any other base or precious metal from the Pt by wet chemistry anyway.
I think that before you crank the old furnace up to 3200+ degrees for a Pt melting procedure, you might want to check out some easier wet chemistry procedures first. But if you do have a high-temp furnace on hand and want to try a general melting flux (a shot in the dark), then this one should work; (parts by volume) one part Pt ore, 5 parts soda ash, 4 parts calcined borax, and 2 parts lead-free flint glass. Without knowing the complete matrix condition of your ore, these flux results would be questionable.
Let me know what your next step, and I?ll check on any info that I have available. Good luck.
John
