Selenium transfer to metal phase at Pd–Bi alloy/Se-containing borosilicate glass interface

During reductive heat-treatment of bismuth borosilicate glass with palladium and selenium, palladium is extracted along with bismuth as a liquid metal phase. Selenium may then be extracted from the oxide phase in a subsequent water-leaching step. However, selenium extraction can be hindered by partial transfer of the selenium to the metal. To suppress such selenium transport, the effect of varying bismuth and palladium proportions in the metal on selenium transfer was investigated. Thermodynamic equilibrium calculations predicted that bismuth, selenium, and palladium should coexist in all composition ranges. However, the experimental results demonstrated that the presence of palladium in the metal suppressed selenium transfer to the metal. Auger electron spectroscopy results indicated that the bismuth in the metal was more easily oxidized than palladium. At higher bismuth contents, the oxidized bismuth may enhance adhesion between the metal surface and the glass phase, leading to more selenium adsorption. For this reason, as heating time increased, the amount of selenium transfer also increased. Cross-sectional microscopy observations demonstrated that the selenium was present not only on the surface but also in the interior of the metal.