Sustainable ironmaking from low-grade iron ores

Abstract

Decarbonization solutions enabling the use of low-grade iron ores are essential for a sustainable steel industry, reducing dependence on scarce high-grade ores and environmental impact. Current processes mainly require high-grade ores, highlighting the need for efficient methods to process lower-quality feedstocks. This study explores a hydro-pyrometallurgical approach for sustainable production. Dihydrate ferrous oxalate, obtained via oxalic acid extraction of iron oxide, was analyzed by thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC), with postmortem samples characterized by X-ray powder diffraction. Non-isothermal experiments were conducted from 25 to 800 °C at 2, 5, and 10 °C/min under inert (argon) and reducing (carbon monoxide and hydrogen) atmospheres. The curves show three main steps: dehydration, decomposition, and, under reducing conditions, reduction to metallic iron. In carbon monoxide, iron carbide formation and graphitic carbon deposition were also observed. DSC revealed endothermic peaks for dehydration and decomposition and in carbon monoxide, a strong exothermic peak, due to the reverse Boudouard reaction.Activation energies were calculated using the Kissinger method. Dehydration showed an activation energy of 62 kJ/mol in argon and carbon monoxide, and slightly lower in hydrogen (58 kJ/mol), likely due to faster diffusion. Decomposition appeared gas independent, with an activation energy of 90 kJ/mol. A mathematical model was developed to relate reaction conversion to time at a fixed heating rate. The model accurately fits the experimental data and remains valid even at higher heating rates, comparable to industrial conditions. This kinetic model supports simulation and scale-up of the iron oxalate reduction process.