# Research on the Mechanism of Hydrogen Plasma Heating and Reduction of Acidic Pellets

## TL;DR

This study explores hydrogen plasma heating for efficiently reducing iron ore, achieving high purity metallic iron and identifying the reaction mechanisms involved.

## Contribution

The paper introduces a non-transferred arc plasma heating system using Ar-H2 gas for high-efficiency iron ore reduction and derives a new reaction kinetics model.

## Key findings

- Hydrogen plasma heating achieved 99.89% conversion and 99.9% purity of metallic iron under specific conditions.
- A three-dimensional diffusion-controlled model accurately described the reduction process with a derived mechanism function.
- The apparent activation energy was found to be 21.9 kJ mol−1, and an empirical equation for the specific reduction rate was calculated.

## Abstract

Hydrogen plasma heating, a unique method for heating and reducing iron ore, is distinguished by its high heat, rapid reduction, and high efficiency, making it a promising technique in the metallurgy field. In this study, a non-transferred arc plasma heating system was used with Ar-H2 as the working gas and acidic pellets as the raw material. The microstructures and elemental distributions of the slag and iron phases during the reduction process were examined using electron microscopy and energy-dispersive X-ray. The variation patterns of Fe-containing phases in the reduction products were found using X-ray diffraction and full-spectrum fitting refinement. The conversion rate of the oxidized pellets and the deoxidation conversion rate per area were estimated for various gas flow rates and reduction times. A reaction kinetics model was also used to study the reaction controlling step. The results showed that during the reduction process, with an H2 flow rate of 4.5 L min−1 and a 40 min reduction, the conversion(α) reached 99.89% and the purity of the reduced metallic iron reached 99.9%, achieving the industrial-grade 3N standard. Si and Al in the melt bath generated fayalite (Fe2SiO4) and hercynite (FeAl2O4) with FexO. The deoxidation conversion rate per unit area was 1.11 g (cm2 min)−1. A three-dimensional diffusion-controlled model was used to describe the reduction process, and the mechanism function was 2/3(1 + α)3/2[(1 + α)1/3]−1. The values of the reduction reaction rate constant (K) were 12.6 × 10−2 s−1 and 12.8 × 10−2 s−1 when the flow rates of H2 gas were 3 and 4.5 L min−1, respectively. The apparent activation energy was 21.9 kJ mol−1. The empirical equation for the specific reduction rate was calculated as ln r = −2637.5/T − 0.407.