A novel technique to extract Bi from mechanochemically prepared Bi–Fe3O4 nanocomposite

The solid-state reduction of Bi2O3 to bismuth (Bi) nanoparticles by high-energy ball milling of raw materials (Bi2O3 and Fe) in air and argon atmospheres has been described. XRD results show that in addition to bismuth, a second phase of nanocrystalline magnetite is also formed. This is due to the formation of Fe2O3 and the subsequent change to Fe3O4 in the course of ball milling. Mean particle sizes of the obtained Bi and Fe3O4 particles were 22 and 18 nm, respectively, using Scherrer's formula. A saturation magnetization of 80 emu/g is achieved for magnetic phase (Fe3O4). As both Bi and magnetite were nanosized particles, it was not possible to separate these two phases by the magnetic separation technique. A novel technique based on different thermal expansions of the Bi and Fe3O4 was then used to extract metallic Bi from the as-milled powders.