Perpustakaan Digital ITB

The depletion of primary tin resources and the health risks associated with leadcontaining wastes have intensified the need for efficient processing of complex tin– lead secondary resources. However, conventional smelting of sulfate-bearing tin– lead secondary resources is limited by matte formation and uncontrolled slag evolution, resulting in poor alloy recovery and high energy consumption. In this study, a low-carbon recycling strategy based on stepwise fluxing and gradual reduction was proposed to regulate slag evolution and sulfate transformation. The proposed strategy was evaluated through a 150 gram smelting experiment using a pit-type electric furnace to assess the feasibility of the proposed strategy in an EAF. Samples of the intermediate slag and metal were taken to track the evolution of their composition and microstructure. Furthermore, a 5 gram scale experiment was conducted using an Al2O3 tube furnace with water quenching to investigate the sulfate transformation pathway, optimize desulfurization and smelting parameters. Conventional smelting produced a matte fraction of 25.8%, retaining 37.18% of Sn and 30.0% of Pb in matte, while delayed SnO2 reduction required 1300 °C with prolonged holding and resulted in only 11.98% alloy recovery. By employing a Fe2O3–SiO2-assisted slag system with controlled CaO addition, the slag trajectory was directed toward a low-melting fayalite-forming region rather than a highmelting dicalcium silicate region, enabling early slag liquefaction and SnO2 reduction at 1200 °C. Meanwhile, gradual reduction controlled the decomposition of CaSO4, PbSO4, and K2SO4 into oxide phases during weak reduction, followed by reduction into metallic phases during strong reduction, completely eliminating measurable matte formation. The combined strategy increased alloy recovery to 59.19% and lowered the temperature required to obtain homogeneous molten slag to 1233 °C. Further optimization parameter increased Sn recovery to 87.3% with 63.03% alloy recovery. These results demonstrate that integrated control of slag evolution and reduction atmosphere provides a promising low-carbon route for recovering valuable metals from complex tin–lead secondary resources.