Removal of Tin and Copper from Liquid Iron by Al₂O₃-Saturated Ca-CaCl₂ Slags at 1448 to 1648 K

Abstract

The removal of tin and copper from liquid iron by Al₂O₃-saturated Ca-CaCl₂ slags was carried out in separate alumina crucibles at 1448 to 1648 K that showed small partition ratios of less than 1. The tin content of the liquid iron typically decreased from its initial value of 50 to 40 wt pct and the (gross) copper content of the iron-copper mixture from 50 to 45 wt pct, at equilibrium. The small refining efficiencies (37 pct, maximum) of the slags, the initial composition of which were, in most cases, Ca-50 wt pct CaCl₂, may be attributed to the significant dissolution in them of alumina, up to 42.0 wt pct (29.6 mol pct), in experiments with Sn, and up to 54.4 wt pct (38.6 mol pct), in experiments with Cu. Treating Ca as the solvent, a number of interaction coefficients such as $\varepsilon_{{{\text{Al}}_{ 2} {\text{O}}_{ 3} }}^{{{\text{Al}}_{ 2} {\text{O}}_{ 3} }} ,\,\varepsilon_{{{\text{Al}}_{ 2} {\text{O}}_{ 3} }}^{{{\text{CaCl}}_{ 2} }} ,\,\varepsilon_{{{\text{Al}}_{ 2} {\text{O}}_{ 3} }}^{\text{Sn}} ,\,\varepsilon_{{{\text{CaCl}}_{ 2} }}^{{{\text{CaCl}}_{ 2} }} ,\,\varepsilon_{{{\text{CaCl}}_{ 2} }}^{\text{Sn}} ,$ and $\varepsilon_{\text{Sn}}^{\text{Sn}}$ as well as the activity coefficient $\gamma_{{{\text{Al}}_{ 2} {\text{O}}_{ 3} }}^{0}$ were all determined at 1448 K. The activity of Ca (relative to pure liquid Ca) was obtained as approximately 0.65 to 0.75 in the system. Further, the two partial molar mixing/excess properties of alumina $\bar{H}_{{{\text{Al}}_{ 2} {\text{O}}_{ 3} }}^{M}$ and $\bar{S}_{{{\text{Al}}_{ 2} {\text{O}}_{ 3} }}^{XS}$ in the alumina-saturated Ca-17 pct CaCl₂- ~37 pct Al₂O₃ (molar basis) slag were evaluated and found to be −118.3(±10.8) kJ/mol and −0.062(±0.007) kJ/K·mol, respectively, at 1448 to 1648 K. In addition, in view of the reported success of CaC₂ as a refining agent, some experiments were carried out with CaC₂-CaF₂ mixtures in alumina, magnesia, and graphite crucibles at 1873 K, to remove tin from liquid Fe-2 wt pct Sn. However, alumina and magnesia crucibles leaked owing to their dissolution in calcium fluoride; in graphite crucibles, only a small transfer of tin, 3 to 7 pct of its initial mass, to the slag phase took place.