A study on volatilization of antimony and bismuth by heating with ammonium iodide—A method for separation and determination of trace antimony and bismuth in geological samples

A decomposition apparatus was established consisting of a reaction tube and a long air-cooling condenser for the separation of antimony and bismuth through volatilization. It is demonstrated that the reaction Sb₂O₃+6NH₄I=2SbI₃+6NH₃+3H₂O starts at 300°C and completes at 380°C in 8 min. In comparison, the reaction Bi₂O₃+6NH₄I=2BiI₃+6NH₈+3H₂O will not take place below 450°C and will complete at 550°C. The differences in volatilizing temperature between antimony and bismuth iodide are large enough to make them separate at different temperatures. Experimental data show that antimony iodide was sublimated at 380°C without any loss of bismuth, and upon the completion of SbI₈ volatilization the long condenser tube can be substituted for by a clean one to collect volatilizing bismuth iodide at the temperature of 550°C. Results are in good agreement with those obtained from thermodifferential-thermogravimetric analyses. Determination of antimony was done using extraction spectrophotometric method with the reagent 5Br-PADAP, and that of bismuth using spectrophotometric method with Xylenol Orange. The method is simple, rapid, accurate and suitable for rock and other geological samples containing antimony and bismuth in the range of X-X · 10² ppm.