The reduction of PbO-SiO2 melts by H2-N2 mixtures was investigated at 1173 K using a thermo-gravimetric arrangement. Some of the experiments were specially designed to assess the relative magnitudes of reaction rates at slag/gas, slag/refractory, and slag/metal interfaces. Analysis of the rate data revealed that the reaction rates at slag/gas and slag/refractory interfaces were comparable to each other. Reduction did not occur appreciably at the slag/metal interface. The concentration profiles of lead oxide in the partially reduced quenched slag samples were determined by electron microprobe. Significant concentration gradients of PbO existed at the slag/gas and slag/refractory interfaces. The diffusivity values of lead oxide in the slags were evaluated using the concentration profiles and the rate data. Additions of varied amounts of P2O5 to the slag were found to have a retarding effect on the reduction rate, which may be explained by a surface blockage mechanism.
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