Extraction of Iron from Russian Red Mud by a Carbothermic Reduction and Magnetic Separation Process

Dmitry Zinoveev,Valery Dyubanov,Pavel Grudinsky,Alexander Petelin,Andrey Zakunov

doi:10.3390/iec2m-09247

Abstract

Red mud is a hazardous waste of alumina production. Currently, the total accumulated amount of red mud is over 4 billion tons. The promising method of red mud processing is a carbothermic reduction of iron at 1000–1400 °C into metallic form followed by magnetic separation. In this study, the mechanism of carbothermic solid-phase reduction of red mud was investigated. Based on the experimental data, the two-step mechanism of the first rapid stage of the process was proposed, which leads to almost full iron reduction. The estimated value of activation energy has indicated that solid-phase diffusion is a rate-controlling step for this stage. However, an almost full reduction is necessary, but insufficient factor for successful magnetic separation. The second crucial factor of the process is enlargement of iron grain size, which leads to gangue-grain release during grinding and increases efficiency of the magnetic separation. The prediction model of iron grain growth process during the carbothermic reduction process was suggested. The calculation of average size of iron grains formed during the reduction process that was performed according to the assumption of diffusion-controlled process showed their correlation with experimental data. Various methods were proposed to promote the process of iron grain growth during carbothermic reduction of red mud.

Highlights

This study focuses on a mechanism of the carbothermic solid-phase reduction of iron in red mud, as well as prediction model of iron grain growth process
It is clear that the contact of oxide-carbon surfaces in the powder mixture of red mud and solid carbon can be mostly pointwise, especially at the initial stage of the process, while diffusion sintering of the powder particles is not essential
The analysis of carbothermic solid-phase reduction of red mud has enabled to consider the stages that influence the degree of metallization of the total process

Summary

Introduction

Red mud is a waste of alumina production from the bauxite ore. The obtaining of 1 ton of alumina generates 0.8–1.5 tons of red mud [1]. Recycling or utilization of red mud is an important current task due to both environmental and economic reasons. Red mud occupies large areas and causes an adverse environmental impact [2]. Red mud is a valuable material for extractive metallurgy owing to significant contents of iron, aluminum, titanium, and rare-earth metals [3]. The typical content of Fe2O3 in red mud is in the range of 30–60% [4] that enables to consider its treatment to extract iron

Methods

Results

Conclusion