A new approach for recycling arsenic and tin from low-grade tin middlings using a self-sulfurization roasting

Abstract

Massive amounts of low-grade tin middlings have been produced from tin tailings, in which arsenic and tin are worthy to be recycled. Owing to high sulfur content in these tin middlings, a novel self-sulfurization roasting was proposed to transform, separate and recover arsenic and tin in this research. There was no extra curing agent to be added, which decreased the formation of pollutant S-containing gas. The self-sulfurization process involved a two-stage roasting of reduction followed by sulfurization. First in reduction roasting, FeAsS decomposed to FeS and As and the As then transformed to As₄(g) and As₄S₄(g), via which the arsenic was separated and recovered. The arsenic content in the first residue could be decreased to 0.72 wt.%. Accompanied with it, the FeS was firstly oxidized to Fe_1−xS and then to SO₂(g) by the coexisted Fe₂O₃, and finally reduced and combined with the independent Fe₂O₃ to form Fe_1−xS. In the followed sulfurization roasting, the Fe_1−xS sulfurized SnO₂ to SnS(g), due to which tin could be recovered and its content in the second residue decreased to 0.01 wt.%. This study provided an efficient method to separate and recover arsenic and tin from low-grade tin middlings.

Keywords

low-grade tin middlings / continuous sulfur transformation / self-sulfurization / separation of arsenic and tin / recycling