Hydrogen Reduction of Industrial Iron Ore Pellets. A multi-scale study from surface to core

The iron and steel industry is a major contributor to the global economy but also a significant source of carbon dioxide (CO₂) emissions, accounting for approximately 7% of global totals. Traditional steelmaking methods, primarily through blast furnace (BF) and basic oxygen furnace (BOF) routes, rely on coke for reduction, emitting around 1.9 metric tons of CO₂ per ton of steel. Although electric arc furnaces (EAF), using scrap and directly reduced iron (DRI), are cleaner, they still emit CO₂ when carbon monoxide is used as a reducing agent. This has led to growing interest in alternative, low-carbon technologies for ironmaking.

One of the most promising solutions is the use of **green hydrogen** as a reducing agent in place of carbon-based methods. Hydrogen can be introduced into steelmaking in three main ways: (1) injected into existing blast furnaces to partially replace coke, (2) used as the sole reducing agent in direct reduction (DR) processes such as shaft furnaces, and (3) applied in plasma hydrogen reduction where ore is melted and reduced simultaneously. Among these, **direct hydrogen reduction** is closest to industrial deployment, with several companies already designing commercial-scale plants. However, a complete and immediate shift away from blast furnaces is currently impractical, making hydrogen injection a viable short-term strategy.

This study focuses on an **in-depth investigation of hydrogen reduction kinetics**, especially on two types of industrial iron ore pellets with varying chemical and physical properties. The research aimed to bridge knowledge gaps by analyzing reduction behavior at both the **surface level** and within the **bulk** of the pellets. For surface-level reduction, ambient pressure X-ray photoelectron spectroscopy (APXPS) was employed, offering a novel look at the outermost layers of the pellets. Bulk reduction was studied using thermogravimetric analysis (TGA) under varying temperatures, providing insights into reduction rates and mechanisms.

A key highlight of the study was the **impact of water vapor**, an often-overlooked factor inherently present during hydrogen reduction. Its influence was systematically explored across a wide range of conditions (up to 30% water vapor), making the results highly relevant for industrial applications. By examining the process at microscopic, mesoscopic, and macroscopic levels, the research delivers comprehensive insights into diffusion rates, structural evolution, and interfacial reactions, laying the groundwork for future optimization of hydrogen-based ironmaking.