Thermodynamic Stuby on the Removal of Copper in Steel Scrap by Sulfide Fluxes

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The tramp elements such as Cu, Sn, Sb etc. in steel scrap can not be removed by the traditional steelmaking process. Therefore, economical prcesses to remove these impurities have to be developed for the recycling of steel scrap. Present work dealt with the thermodmynamics on the removal of tramp elements, mainly Cu, in liquid iron by using sulfide flux. The present investigation consisted of following four parts.1) Phase equilibria in the basic system of Fe-S-C ternary melt were measured and thermodynamic properties of this system were evaluated by applying interstitial solution model.2) The activities of Cu, Sn, Sb in Fe-S-C_<sat>. Melts were experimentally determined.3) The distribution ratio of Cu, Sn, Sb Ni, Cr, Mn or Mo between FeS-Na_2S flux and Fe-C_<sat>. melt was measured at 1673K. The addition of Na_2S to FeS increased the distribution ratio of Cu, L_<Cu>=(mass%Cu)_<flux>/[mass%Cu]_<iron>, from 9 at X_<NaS_<0.5>>=0 to the maximum of L_<Cu>=24 at X_<Nas_<0.5>>=0.4. Na_2S also … More considerably lowered sulfur content in liquid iron. The activity coefficient of CuS_<0.5> in flux was evaluated to discuss the effect of Na_2S on L_<Cu>. It was founs that Na_2S decreased gamma CuS_<0.5>, so that L_<Cu> increased in spite of the significant decrease of sulfur potential. The distribution ratios of Sn, Sb, Ni, Cr and Mo were very low, while L_<Mn> was very high.4) Effect of alkaline or alkaline earth metal sulfides on L_<Cu> was studied. Similar to the effect of Na_2S, Li_2S, K_2S, SrS or BaS increased L_<Cu> and lowered sulfur content in liquid iron. The maximum of L_<Cu> in each flux were about 20 to 30. Thermodynamic consideration was made to discuss the removal limit of Cu from liquid iron by sulfide fluxes.It was concluded from the present work that Cu can be removed from liquid iron by sulfide flux. However, L_<Cu> was not high enough for the practical application. Therefore, we need more effort to develop the effective Cu removal process from remelted steel scrap. Less