Coal-based reduction roasting and magnetic separation of low-grade Botswana iron ore for sustainable beneficiation

Abstract

This study demonstrates a novel pathway to beneficiate low-grade hematite-rich iron ore (56.1 % Fe) from Botswana’s Ikongwe deposit through coal-based magnetizing roasting and low-intensity magnetic separation (LIMS). Leveraging Botswana’s underutilized resources, Morupule non-coking coal (50.01 % fixed carbon, 21.13 % ash) was utilized as a sustainable reductant. A Taguchi L9 orthogonal array systematically optimized critical parameters: roasting temperature (700–900 °C), residence time (30–90 min), and coal dosage (25–50 %). Optimal conditions (800 °C, 60 min, 50 % coal dosage) yielded a magnetic concentrate grading 68.2 % Fe at 85.7 % recovery, representing a 21.6 % relative iron upgrade. Advanced characterization (XRD, SEM-EDS) confirmed efficient phase transformation from hematite to magnetite with concurrent gangue reduction. Kinetic modelling indicated a chemically controlled reaction mechanism, with activation energies ranging from 159.1 to 160.6  kJ/mol. Thermodynamic evaluation revealed negative Gibbs free energy values (ΔG), supporting the spontaneity of the reduction reactions across the tested temperatures. This integrated approach validates the technical and economic feasibility of utilizing Botswana’s local resources to valorise low-grade iron ore, offering a viable route for Botswana to enhance its mineral-based industrialization and to reduce reliance on imported ferrous materials.