THERMODYNAMIC MODELING OF MINOR-ELEMENT BEHAVIOR IN IN-BATH COPPER SMELTING AND CONVERTING WITH CALCIUM FERRITE SLAG

Computer simulations were carried out to investigate the behaviour of minor elements in steady-state copper smelting (mattemaking) and conve rting as well as in batch-type converting with calcium ferrite slag (C aO.FeOx) containing 25 wt% CaO. The results were compared with those o btained with fayalite slag (2FeO.SiO2). Smelting (mattemaking) with ca lcium ferrite slag is predicted to proceed at somewhat lower p(SO2) th an with fayalite slag. Fayalite slag absorbs Pb and Bi better than cal cium ferrite slag, although their removal is predominantly by volatili zation. The degree of their volatilization is similar for the two slag s. Calcium ferrite is, however, much more efficient than fayalite slag for the slagging of Sb and As, and it greatly depresses the volatiliz ation of these elements, which would reduce the problem associated wit h dusts. When the overall process of smelting (mattemaking) followed b y converting is considered the predictions indicate that the eliminati on by slagging and volatilization occurs primarily in the smelting (ma ttemaking) step for both types of slag. There is little difference in the overall elimination of Pb and Bi whether one or the other slag is used in both steps. The overall elimination of Sb and As, however, is much lower with calcium ferrite slag, leaving large amounts of Sb and As in blister copper. When calcium ferrite slag is used only in the co nverting stage, with fayalite slag used in the smelting (mattemaking) stage-as in the Mitsubishi process-the contents of Sb and As in the bl ister copper can be kept at reasonable levels. This allows one to take advantage of the considerably higher iron oxide-holding capacity of c alcium ferrite slag than of fayalite slag at the high oxygen potential under the converting conditions, thus preventing the precipitation of magnetite. Satisfactory agreement was obtained between the predicted values and the observed data from a Mitsubishi converter.