Abstract

JOFFRE ENCINAS, Juan Eduardo. Thermodynamic of the reduction smelting process of tin concentrates. Rev. Met. UTO [online]. 2015, n.37, pp. 3-17. ISSN 2078-5593.

Abstract A thermodynamic analysis of the most important reactions that occur in the reduction smelting process of tin concentrates is presented. It shows the influence of iron on the process. Tin reduction is limited by the equilibrium FeO -Fe and the process depends greatly on how the metallurgist proceeds to make it most effective. The first option is to perform a benign reduction of tin in the first smelting step, so the tin produced is practically free of iron, and then perform a more intense reduction of tin from liquid slag, to increase its recovery at the cost of obtaining metal with more content of iron (hard head). This liquid hard head, which remains inside the furnace, receives fresh tin concentrates to produce again clean tin, taking advantage of the iron content of the hard head as a reducing agent of fresh tin oxides in concentrates, and continuing the operations cycle. However, the consumption of carbon is excessive during the slag reduction stage because it also reduces iron in order to recover more tin units. The second option is to perform the same benign tin reduction in the stage of smelting, so the tin produced is practically free of iron, leaving from 4% to 8% Sn in slag. Then volatilize the tin from this liquid slag by either using sulfide or oxide fuming to discard a tin free slag with around 0.2% Sn. Then the SnO₂ fumes free of iron can be easily pelletized and recycled to the smelting stage. The systems Sn - Fe, Sn - Fe - C and Sn - Fe - slag are discussed and finally some comments are made with reference to furnaces used for tin reduction smelting, concluding that nowadays the Ausmelt furnace is the most capable operating unit for that purpose, taking into account its specific smelting capacity, based on the consumption of oxygen to support combustion. Tin fuming can be sulfurizing, adding pyrites to the liquid slag or can be neutral or oxidizing, in this cases tin volatilizes as SnO(_g). SnS fuming is much more intense and faster than SnO fuming. When fuming tin as oxide, temperature should be increases in order to attain discard slags.

Keywords : Thermodynamics; tin; smelting; hard head; fuming.