| An economically viable method for the removal of copper from iron, if available, could be used by steelmakers to turn high-copper-content scrap (above 0.1 wt.%) into useful products. Molten salt mixtures of charge-asymmetric cation species show a significant drop in the activity coefficient for monovalent cation species in the presence of trivalent or higher cation species. This phenomenon can be used to design a flux for the removal of copper as a cuprous species (monovalent) from iron-based metal.;Distribution coefficients of copper (i.e., the ratio of the weight percent copper in a matte to that in the metal) were determined between a sulfide flux (containing aluminum sulfide, ferrous sulfide, and dilute concentrations of either magnesium sulfide or calcium sulfide) and carbon-saturated iron at 1,638 K. A maximum distribution coefficient of 30 $pm$ 5 was found, and the copper level in the iron was reduced to as low as 0.07 wt.%. Magnesium sulfide and calcium sulfide both adversely affected the copper removal.;The activity coefficient of cuprous sulfide dropped from 2.9 with a pure FeS matte to 0.4 with a binary matte containing X$sb{rm FeS}$ = 0.18. The decrease with increasing concentrations of aluminum sulfide was due to the presence of the polyvalent aluminum cation in the flux.;A liquid-liquid miscibility gap above X$sb{rm FeS}$ = 0.43 was confirmed in the aluminum sulfide/ferrous sulfide pseudobinary system.;Because a sulfide matte would result in a large sulfur content in the treated metal, distribution coefficients were also determined between an oxide flux (consisting of alumina, silica, calcia, and ferrous oxide) and iron with various concentration of carbon at 1,923 K. A maximum distribution coefficient of 0.5 was found.;Finally, distribution coefficients were determined between a sulfide-modified oxide flux (consisting of alumina, silica, ferrous sulfide, and dilute amounts of calcia, magnesia, calcium sulfide, or magnesium sulfide) and iron with various concentrations of carbon at 1,823 K. A maximum distribution coefficient of 6.8 was found for iron with 0.1 wt.% carbon; distribution coefficients increased as carbon content decreased. Although the results are considered preliminary, further research with the mixed flux is strongly recommended because significantly higher distribution coefficients should be possible. |
