Recycling of bismuth oxides

OBRABOTKAMETALLOV MATERIAL SCIENCE Vol. 23 No. 3 2021 The third melting product (24.1 % of oxides) is a dust-gas mixture. In general, with acceptable melting rates, such a ratio of fluxes transfers the imaging point of the slag composition (%: 23.1 Na 2 O, 63.0 SiO 2 , 13.9 CaO) to the region where the liquidus temperature reaches 1,200 ºС, as a result of which minor devia - tions from the specified flow rates for the dosage of fluxes, possible in the practical implementation of the process, will lead to disruption of its course. An increase in the consumption of Na 2 CO 3 to 33 % of the amount of oxides led to similar results when the share of SiO 2 was fixed at the level of 12.5 %. In this embodiment, the 55 % yield of the metal alloy of the following composition, %: 7.3 Bi; 80.2 Pb, had low extraction of bismuth (75 %) and lead (80 %). Slag yield amounted to 71 %, and contained, %: 0.8 Bi, 12.9 Pb, the imaging point of which on the Na 2 O-SiO 2 - CaO diagram, %: 68.4 Na 2 O, 21.7 SiO 2 , 9.9 CaO, was closely adjacent to the area in which no delamination had been observed earlier, and therefore to implement the process in practice, a high accuracy of dosage of fluxes is required. The output of dust and gas during smelting was 24.1 % of the oxide content. A change in the composition of the charge towards a simultaneous increase in the ratio of Na 2 CO 3 (66 %) and SiO 2 (25 %) also leads to the delamination of condensed phases. Lead-bismuth alloy with the yield of 62 % con - sists of 7.7 % Bi and 84.2 % Pb, while the target metals are quantitatively recovered in the alloy containing 89 % Bi and 94 % Pb. The slag yield expectedly rises (up to 103 % of the oxides amount). The content of bismuth and lead in the slag is low (%): 0.66 Bi; 11 Pb. It corresponds to the position of the imaging point on the diagram Na 2 O-SiO 2 -СаО, %: 23.7 Na 2 О, 62.1 SiO 2 , 14.2 СаО for the area with the liquidus temperature of 1,100–1,150 ºС. It was observed that the yield of the gas and dust mixture had increased up to 30.9 %. The reducing agent consumption of ~5 % is in line with the data on similar material treatment practice. The indi - cated consumption rate takes into account the surplus of reducing agent compared to the stoichiometrically necessary quantity for lead and bismuth recovery from oxides, and the change in the amount of the reducing agent does not significantly influence the melting results. Thus, the reduction smelting mode of bismuth oxides, %: 66 Na 2 CO 3 ; 25 SiO 2 ; 5–7 С, at the tempera - ture of 1,150 ºС, set during experiment 9 are optimum. Combined melting of bismuth oxides, Na 2 CO 3 , SiO 2, and carbon at the ratio of 100 : 15 : 26 : 5 and 100 : (33–66) : (13–26) : (5–7) allows splitting off the bismuth lead alloy with the yield of 61.8–74.0 % of the oxide content. The obtained bismuth lead alloy has the following composition (%): 7.1–8.0 Bi; 81.3–86.1 Pb; 0.08 Zn; 2.54 Sb; 0.76 As; 0.70 Sn; 0.99 Cu; 0.03 Ag. The ratio of metal recovery into alloy is the following (%): 95.6 Bi; 94.6 Pb; 0.8 Zn; ~71.3 Sb; 30.4 Sn; 67.5 Cu. According to the X-ray phase analysis findings the major phase of lead-bismuth alloy is elemental lead. Silicate slag with the yield of 73–103 % of the oxides was produced. Its composition was as follows, %: 0.03–1.20 Bi; 0.3–15.4 Pb; 5.9 Zn; 0.25 Sb; 0.99 As; 0.76 Sn; 0.02 Cu; 0.001 Ag; 24.0 SiO 2 ; 55.6 Na 2 O; 7.7 MgO; 6.9 CaO; 0.5 FeO. The following elements go into the silicate slag, %: 6.6 Bi; 7.7 Pb; 78.2 Zn; 8.7 Sb; 41 Sn; 4.8 Cu. Phase composition of the slag includes Na 2 CaSiO 4 , Na 4 Mg 2 Si 3 O 10 , MgO, Pb. The third product of the melting is dust and gas mixture (40 - 43 %), where some of the charge target compo - nents are concentrated, %: 21.0 Zn; 20.0 Sb; 22.1 As; 28.6 Sn; 27.7 Cu. Thus, the reduction smelting mode of bismuth oxides (100 %), recommended for further studies and calculations, was set: 66 Na 2 CO 3 ; 25 SiO 2 ; 5–7 C; process temperature is 1,150 ºC. The content of impurities in the obtained alloy is significantly higher than accepted in the practice of similar production processes. It might cause serious difficulties in the direct pyro-electrometallurgical pro - cessing of lead bismuth. This is confirmed by the results of a laboratory experiment on the electrolytic refin - ing of bismuth dross, %: 0.1–1.2 Bi; 0.6–12.0 Zn; 0.3 Sb; the rest percentage is Pb, obtained by Polymetal Production branch of JSC “Uralelektromed”. The electrolyte was a melt of an equimolar eutectic mixture of PbCl 2 and KCl, the process temperature was 823 K (550 °C). It was identified that besides bismuth (6.4–30 % Bi), significant amount of electrically positive antimony (16.5 % Sb) accumulates in anode prod - uct, which does not allow to obtain rough bismuth. Thus, it is required to include reagent treatment of the alloy (decoppering, alkaline softening), similar to refining of rough Pb, at minimum bismuth loss with Cu slurry and alkaline fusions. The reagent treated alloy can pass to pyrometallurgical stage.