Microwave suspension roasting for efficient vanadium extraction from fine-grained shale: a dual mechanism of sintering suppression and oxidation enhancement

Abstract

Microwave roasting (MR) is an efficient and eco-friendly method for processing vanadium-bearing shale (VBS). However, when applied to fine-grained VBS, it often induces severe sintering, hindering vanadium (V) extraction. To address this limitation, this paper proposes a novel microwave suspension roasting (MSR) process that couples microwave heating with gas fluidization, simultaneously suppressing sintering and enhancing V oxidation. Under optimized conditions (600 °C, 10 min, 500 W, 600 mL min⁻¹ airflow), followed by leaching with 30 wt% H₂SO₄ (L/S = 1.8 : 1 mL g⁻¹, 5 wt% CaF₂, 95 °C, 6 h), the V leaching efficiency reached 90.06%. Compared with conventional MR, MSR improved leaching efficiency by 4.56%, while reducing the roasting temperature by 200 °C and the duration by 5 min. Multi-scale analysis and COMSOL simulations confirmed that fluidization homogenized heating, reduced hotspots, preserved porosity, and promoted V(III) to V(V) oxidation and pyrite desulfurization. MSR thus offers a sustainable, energy-efficient route for fine-grained vanadium resource utilization.