Studies on the rate-controlling step for the reduction of zinciferous coked briquettes. (1st report). The rate-controlling step for the reduction of Zinc oxide calcine briquetted by utilizing coking coal as a binder and a reducing agent.

The rate controlling step was examined for the reduction of zinc oxide in a coked briquette which was prepared from zinc calcine and coking coal by utilizing the latter as both a binder and a reducing agent. It has been found that the obtained data are best fitted by assuming the rate-controlling step for the reaction to be the diffusion of gases involved in the reaction through the gas film on the surface of a shrinking zinc oxide particle. From the temperature dependence of the reduction rate of zinc oxide, the apparent activation energy for the diffusion was found to be 35.5 kcal/mol. This apparent activation energy seems abnormally large for a diffusion process of gases through a gas film, and it is considered that the overall reaction might be affected by the carbon solution-loss reaction which gives a rather large activation energy. It is so far impossible, however, to evaluate the change of the surface area of carbon in the briquette in the course of the reaction, for the shape of the carbon is not particulate but a kind of matrix for zinc oxide particles because the briquette was pressed into shape while the coking coal was hot and fluid.