Assessment of flotation process efficiency in producing DR concentrate from a low-grade iron ore

Abstract

The steel industry holds a pivotal position in modern society, widely acknowledged as the most significant basic industry globally. Nonetheless, its substantial energy consumption and carbon emissions present significant challenges, contributing notably to global warming and climate change. Consequently, the sector has been fervently pursuing greener steelmaking processes. Among the various options, hydrogen direct reduction technology stands out as the most promising. Thus, the quest for new sources of high-quality iron ore concentrates has intensified in recent years, aimed at supplying the necessary raw material for direct reduction processes. In this context, the Mont Reed iron deposit, located in Quebec, Canada, emerges as a promising asset. The deposit comprises both magnetite and hematite-rich ores, presenting an average iron grade of 30 % along with complex gangue minerals. The present study evaluates the implementation of a flotation process to enhance the quality of the concentrate generated through low-intensity magnetic separation in the Mont Reed flowsheet, targeting direct reduction (DR) levels. The research involved the assessment of various industrial reagents to concentrate the magnetite present in the ore, as well as the execution of a design of experiments conducted using the most effective combination of reagents and different parameters. Ether amine, ether diamine, amidoamine, and phosphoric ester were evaluated as collectors, while starch, dextrin, CMC, and humic acid were assessed as depressants. Bench-scale flotation experiments presented promising results, demonstrating the feasibility of reducing the silica grade of the concentrate by 75 % (from 6.90 % SiO₂ to 1.68 % SiO₂), while producing a high-grade product containing 70.04 % Fe. The addition of a desliming stage was mandatory to achieve these results, and a Design of Experiment (DoE) campaign determined optimal flotation conditions: 150 g t⁻¹ of collector, 400 g t⁻¹ of depressant, pH 10, and 30 wt.% solids in pulp, achieving the target concentrate quality with a yield of 23.9 % and an Fe recovery of 52.0 %. These findings enhance the value of the Mont Reed deposit, positioning it as a potential source of DR pellet feed for the global iron ore market. The study also offers insights for similar operations, highlighting flotation as a viable solution when magnetic separation alone cannot achieve the necessary silica levels for DR products.