Advances in Understanding of Direct Reduction using Hydrogen

Abstract

The hydrogen reduction of metal oxides presents a suitable substitute to traditional carbon-based reduction due to obvious reasons of eliminating carbon emissions. In this study, the advances in the understanding of the hydrogen reduction of a metal oxide, namely tellurium oxide, was investigated to determine the mechanism of the reaction. The investigation employed modelled and model free kinetic analysis of DTA-TG data of tellurium oxide under a hydrogen atmosphere at various heating rates. Further exploration of the process involved trial experiments in an oscillating kiln device at varying mass, time and temperature. Results from the study reveal a possible fit of the reduction process in more than one reaction model, indicating a multi-mechanistic reduction process. It was concluded from the kinetic analysis that the process could be a sequential or simultaneous overlapping of different rate limiting steps featuring diffusion, surface reaction and nucleation and growth of metal crystals. Reduction rates of the reduction process estimated from experimental trials demonstrate that the reaction is possible below the melting point of tellurium. Reduction rates of up to 100 % were achieved for experimental temperature of 600 ⁰C at different dwelling times. The experimental results also show that temperature variation significantly influences the reduction rate than variation in dwelling time and mass do. The study and its findings form part of the early explorations of the hydrogen reduction of tellurium oxide for future reference and comparison. Future studies should therefore verify the individual reaction regimes of the entire multi-step process suggested in the proposed reaction mechanism of the reduction process.