Recycling of bismuth oxides

OBRABOTKAMETALLOV MATERIAL SCIENCE Vol. 23 No. 3 2021 After the charge melting and isothermal holding for 20 min; the crucible with the melt was removed from the furnace, covered with a graphite crucible and cooled in the air. Then, the product was weighted and assayed. It was expected that remelting of oxides would lead to separation of the melt into metallic and oxide phases, but the phase separation was not achieved (Experiment 1, Table 1). No separation was observed even when a carbon-bearing reducing agent was added to the charge (Experiment 2, Table 1). This agent was present in excess of stoichiometric quantity required for the reduction of lead and bismuth from oxides, due to the presence in the oxides of significant amounts of high melting point compounds (Zn x Pb 1- x O, CaPbO 3- x , etc.). Therefore, further smelting was carried out with addition of fluxes to the charge to form a high melting point slag. Na 2 CO 3 consumption was calculated based on the achieved ratio of the total mass of lead and bismuth to the mass of NaOH in the charge from 1 to 10, and SiO 2 consumption based on produced slag containing 38–50 % of SiO 2 . (Experiments 3 and 4, Table 1). Ta b l e 1 Composition of the charge for the production of bismuth lead Experiment Oxides, g Na 2 CO 3 , g SiO 2 , g Graphite, g 1 100 ‒ ‒ ‒ 2 100 ‒ ‒ 5 3 100 15 11 7 4 100 66 25 5 The samples of treated bismuth oxides produced in the refining cycle of rough lead at Non-ferrous Al - loys Production Branch of JSC “Uralelektromed”, and smelting products of the initial charge (Pb-Bi alloy, slag, dust) were analyzed by various physical and chemical methods. Size distribution was determined by screen analysis using a standard set of screens; bulk density – by weighing in a flask of known volume; true density – using a measuring flask; moisture – by drying. To study the elemental composition, the oxide sample was ground in a laboratory grinder to a particle size of less than 0.1 mm. The chemical composi- tion of the analyzed materials was determined by atomic emission spectrometry with inductively coupled plasma (Optima 4300 DV) and X-ray fluorescence spectrometry (S4 Explorer). The phase composition was estimated by X-ray diffraction analysis on an automated diffractometer DRON-2 in Cu Kα-radiation, the subsequent phase identification was carried out using the ICDD 2013 database. A JSM-59000LV scanning electron microscope with an OXFORD INCA Energy 200 energy dispersive X-ray spectrometer was used to determine the elemental composition of phases. Results and their discussion The results obtained (Table 2) confirm that the addition of fluxes and reducing agent to the charge leads to generation of three phases: metallic, accumulating bismuth and lead; slag, which receives the major amount of oxides; and dust and gas, concentrating elements and compounds with high elasticity of vapor. In experiments 3 and 4 (Table 2) the following products are reduced from initial oxides, %: 89.0–93.6 Bi; 99.5–99.7 Pb; 0.2–0.4 Zn; ~30 Sb; 7.2 Sn with a transition to lead bismuth of the following composition, %: 7.06–7.32 Bi; 80.6–81.6 Pb. According to X-ray phase analysis, the main phases of the Pb-Bi alloy (experiments 3 and 4) are el- emental lead and galena PbS (Fig. 1). An increase in flux consumption (Experience 4, Table 1, 2) leads to an increase in mass of released slag from 44.8 to 93.1 % of the amount of oxides. Silicate slags poor in target metals were obtained, %: 0.06–0.08 Bi; 1.23–1.81 Pb; 3.3–6.7 Zn; 0.6–1.2 Sb; 0.7–1.6 As; 0.5–1.2 Sn; 17.9–21.6 SiO 2 ; 22.5–36.7 Na 2 O;