A Laboratory Study of the Reduction of Iron Oxides by Hydrogen

TL;DR

This laboratory study investigates hydrogen-based reduction of hematite to produce direct reduced iron, revealing reaction kinetics, structural evolution, and the impact of sample type on reactivity, with implications for greener steel manufacturing.

Contribution

The study provides detailed insights into the reduction process of hematite by hydrogen, including reaction steps, structural changes, and effects of temperature and sample form, advancing understanding for sustainable steel production.

Findings

Reaction rate increases with temperature from 550 to 900°C.

Three distinct reduction steps through magnetite and wustite to iron.

Regular powder shows higher reactivity due to porosity despite larger grain size.

Abstract

To reduce the emission of greenhouse gases by the steel industry, particularly for ironmaking, the production of DRI (Direct Reduced Iron) using hydrogen as the reducing gas instead of carbon monoxide is being considered. In this context, the reduction of pure hematite by hydrogen was studied at the laboratory scale, varying the experimental conditions and observing the rate and the course of the reaction. All the reduction experiments were performed in a thermobalance and supplementary characterization methods were used like scanning and transmission electron microscopy, X-ray diffraction, and M\"ossbauer spectrometry. The influence of rising temperature in the range 550-900 degrees C is to accelerate the reaction; no slowing down was observed, contrary to some literature conclusions. A series of experiments consisted in interrupting the runs before complete conversion, thus enabling the characterization of partially reduced samples. Interpretation confirms the occurrence of three successive and rather separate reduction steps, through magnetite and wustite to iron, and illustrates a clear structural evolution of the samples. Finally, the influence of the sample type was revealed comparing a regular powder, a nanopowder and a sintered sample. The regular powder proved to be the most reactive despite its larger grain size, due to a more porous final structure.