A novel method for efficient arsenic solidification and reduction from low-grade complex tin middling and its...

Low-grade complex tin(Sn) resources, with reserves exceeding 1 billion tons, are crucial for the sustainable development of the global Sn industry. However, arsenic(As) migration significantly reduces Sn dust quality and produces hazardous As-bearing sludge. This paper proposes a novel method for efficient As solidification, reduction and Sn recovery from low-grade complex Sn middling through roasting-magnetic separation. The migration and toxic mechanism of As were evaluated. At 823 K, FeAsS decomposed into As, which subsequently oxidized into the high-risk As₂O₃ through CO₂. Higher temperatures promoted the generation of unstable Fe_xAs_3-xO₄ through As₂O₃ doping into Fe₃O₄, resulting in an As leaching concentration of 68.1 mg/L. Fe_xAs_3-xO₄ was reduced to microfine-grained [Fe-As]_{Cu alloy} covered by Fe₃O₄ at 1023 K, with its particle size increasing to 110 µm with increasing temperature, thereby significantly increasing As environmental risks. SnO₂ was reduced to Fe_3-xSn_xO₄ and [Sn]_{alloy phase}, subsequently recovered in the form of SnS(g). Under optimal conditions, 85.94 % As solidification and 96.86 % Sn recovery were achieved, achieving superior qualities of Sn dust and Fe concentrate. The solidified As was separated and enriched from the roasted residue through magnetic separation, minimizing As pollution, and can be processed to obtain high-quality As₂O₃. This study may serve as a reference for the high-value utilization of low-grade complex Sn resources, including Sn-bearing tailings and Sn-bearing Fe ores.