I done this by the mystake. Once when I strips the silver plating from my scrap by the electrolysis using salt water and steinless stell cathode i find out that my silver scrap has a Rhodium plating lyer on top becouse it's left the dark yellow sediment before silver plating came off.
Rhodium plating will come off as very thin shiny flakes.
Then I remember the moment when I use Portland cement to remove impuritys from my beads (after smelting in oxidation flame) on Portland cement all of my Rh was dissapered but on the top of my used cement forms strenge shiny dark grey to black lyer. Then I realize it's make the reaction with the alcali metals from the cement becouse it's contein Mg and Ca minerals. So to the point, after read all liberary about Rh behavior, Rh catalitic proporties and all what I can get about it I came with a thing that Rh need the alcali metal as flux to melt. So if we get the rafined Rh from cementation on Zinc or other method like a hydrazine or formic acid we will go to the step where we melt it. Of corse if we have fine metalic powder and melt it in a vacum arc furence under presure of hydrogen and argon gas we can get success but the solvation for ouer problem has different path. So i take the risk and I add Portland cement to my solution of dissolved Rhodium Hydroxide at 60'C and magnetic stear, adding cement to solution with really small doeses, leave it over night to seatlle and after this wash it few Times with dem water. The XRF mesure on powder after drying showing only Mg and Ca but when I take the quartz+Zr/Al2O3 crucible and melt it with oxy/acetylen torch it's melting smoth and nice whitout taking reaction with crucible and carbon. So in my opinion rafined Rhodium need alcali metals at participation step and then need it at melting step. Remember Rhodium melts at almost 2000C so it would be hard to get it molten even with a OxyAcetylene torch. The missing Rh in the XRF could be a tell, since Rh and Ir are typical false positives.