Evaporation Mechanism of Sn and SnS from Liquid Fe: Part III. Effect of C on Sn Removal

Abstract

To understand the effect of C on Sn evaporation from liquid iron in the view of ferrous scrap recycling, the evaporation of Sn from various liquid Fe-C-S-Sn alloys was experimentally investigated. A series of gas-liquid reactions was carried out at 1873 K (1600 degrees C) using an electromagnetic levitation melting technique, where mass transfers in gas phase and liquid phase did not significantly affect the reaction rate. It was found that CS2(g) is a major gas species evaporating from Fe-C-S alloy (initial S content [pct S](0): 0.028 to 0.502 mass pct), and Fe-C-S-Sn alloy ([pct S](0): 0.063 to 0.560 mass pct), thereby competing with SnS for S in the liquid alloy. A model equation for the evaporation rate of CS2(g) was established using the experimental data for the Fe-C-S alloys. The chemical reaction rate constant for the CS2(g) evaporation (k(CS2)(R)) was obtained as 4.24 x 10(-12) m(7) mol(-2) s(-1), and the residual rate constant (k(CS2)(r)) was 4.24 x 10(-16) m(7) mol(-2) s(-1), both at 1873 K (1600 degrees C). Roll of C on the evaporation of Sn in Fe-C-Sn alloy was confirmed to be the increase of activity coefficient of Sn. By taking into account (1) the evaporation of Sn(g), SnS(g), and CS2(g), and (2) the increasing activity coefficient of Sn and S by C, a comprehensive model for the evaporation rate of Sn and S in the Fe-C-Sn-S alloy was developed. The calculation results by the developed model in the present study showed good agreement with the experimental results. Some applications of the current model are presented in the view of increasing the Sn removal rate.