Thermodynamics of Selenium and Tellurium in Calcium Ferrite Slags

New measurements have been made on the equilibrium distribution of selenium and tellurium between molten slag and metal phases under a controlled CO-CO2 atmosphere. Distribution coefficients of Se and Te between magnesia-saturated calcium ferrite slag and copper or silver alloy were measured at 1473 to 1673 K and oxygen patrial pressures of 10−11 to 10−0.68 atm. For the calcium ferrite slag, the highest distribution coefficients were recorded at the highest lime content, under strongly reducing conditions and at higher temperature. The selenide and telluride capacities were also calculated for each slag and were found to increase with increasing temperature and increasing lime activity. Activity coefficients of Se in the slag phase were found to be much lower than those of Te, and values for both minor elements decreased considerably with increasing activities of lime and ferrous oxide in the slag. Selenium showed strong negative deviation from the ideal behavior, while Te showed positive deviation up to 1573 K.