Isotope exchange studies of the rate of dissociation of CO2 on liquid iron oxides and CaO-saturated calcium ferrites

Abstract

Measurements of the rates of dissociation of CO2 on liquid iron oxides and CaO-saturated liquid calcium ferrites have been made by the14CO2-CO isotope exchange technique. For temperatures up to about 1550 °C, the apparent first order rate constants for both melts are essentially inversely proportional to the equilibrium CO2/CO ratio over the range studied (≈0.4 to 12). Evidence is presented that the rate limiting step in the interfacial oxidation of these melts by CO2 is the dissociation of CO2- Rates of oxidation, in mol cm−2 s−1, in CO2-CO atmospheres are deduced to be given by the equations:v =( p CO 2 a o − 1 − p CO) exp(−15,900/T − 2.03) andv = (pCO2 α o -1 −pCO) exp(−3800/T − 6.93) for the iron oxides and CaO-saturated calcium ferrites, respectively, wherea 0 is the oxygen activity of the melt expressed as the equilibrium CO2/CO ratio and the pressures are in atmospheres. The strong dependence on the CO2/CO ratio is shown to be consistent with the need to transfer two charges to the adsorbing or dissociating CO2 molecule. Correlation with the existing surface tension data is inconclusive.