Thermodynamics of lead and bismuth in CaO–CaF 2 melts

In order to understand a new refining process for removing tramp elements from alloy steels under strongly reducing conditions, the authors previously reported the thermodynamic behaviour of P, Sn, Sb, As and Cu in CaO–CaF 2 melts. In this investigation, the thermodynamic behaviour of Pb and Bi in CaO–CaF 2 melts under oxygen partial pressures from 10 −16 to 10 −20 atm was studied at temperatures ranging from 1360 to 1550°C, using a similar technique. It was shown that Pb and Bi exist in slag mainly as Ca 2 Pb and Ca 1.5 Bi, respectively, under very low oxygen partial pressure although a part of Pb is soluble in slags as metal. The obtained results were extrapolated to lower oxygen partial pressures to investigate the possibility of removing these tramp elements from molten iron, causing Bi to be removed from molten iron below an oxygen partial pressure of 10 −23 atm, whereas Pb is removed under higher oxygen partial pressures.