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In order to evaluate feasibility of Sn-containing ferrous scrap recycling by evaporation of Sn, a number of liquid-gas experiments were carried out using an electromagnetic levitation melting technique. Rate of decrease of Sn concentration in liquid steel droplets by evaporation in Ar-H 2 gas mixture was determined at 1873 K (1600°C). Evaporation rate of the Sn under various conditions (various flow rates of the gas mixture, initial S concentration, [pct Sn] 0 ) was examined using previously reported rate equations. Increasing flow rate increased the evaporation rate of Sn initially, but the rate became constant at higher flow rate, which indicates that the rate-controlling step is the chemical reaction at the liquid/gas interface. Increasing initial S concentration significantly increased the evaporation rate of Sn, which is in good agreement with previous understanding that Sn could be evaporated as SnS(g). It was found in the present study that neither a simple first-order reaction (rate proportional to [pct Sn]) nor a second-order reaction (rate proportional to [pct Sn] 9 [pct S]) could account for the Sn evaporation under a chemical-reaction-controlled regime. It is proposed in the present study that surface adsorption of S should be taken into account in order to interpret the evaporation rate of Sn in such a way that S blocks available sites for SnS evaporation on the liquid steel. The ideal Langmuir isotherm was applied in order to better represent evaporation rate constant k SnS as a function of [pct S] (0.06 < [pct S] 0 < 0.29). The obtained rate constant of a reaction Sn i + S i = SnS i (g), k R SnS , is 2.57 9 10 À8 m 4 mol À1 s À1 .

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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°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 CS 2 (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-SSn 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 CS 2 (g) was established using the experimental data for the Fe-C-S alloys. The chemical reaction rate constant for the CS 2 (g) evaporation (k R CS2 ) was obtained as 4.24 9 10 -12 m 7 mol -2 s -1 , and the residual rate constant (k r CS2 ) was 4.24 9 10 -16 m 7 mol -2 s -1 , both at 1873 K (1600°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 CS 2 (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.