Recovery of strategic mineral resources such as iron and rare earth from solid waste stockpiled for years: Low-temperature fluidized reduction process and hydrogen substitution for carbon

Abstract

The development and utilization of low-grade iron-bearing solid waste resources have become increasingly urgent from both environmental and resource utilization perspectives. H₂, as a future energy carrier, is crucial to achieving carbon-free future. This study investigated the feasibility of low-temperature fluidized reduction of medium–low grade oxidized ore, which has been stockpiled for over half a century, by comparing H₂ and CO as reduction agents. Excellent technical indicators were achieved with all three reduction gas systems. Specifically, under the H₂ system, an iron concentrate with a TFe grade of 65.61 wt% and a recovery of 90.05 wt% was obtained, along with rare earth-rich tailings with an enrichment ratio of rare earth greater than 2. The reduction of hematite proceeded from the exterior to the interior, with the pores and cracks generated increasing the gas–solid reaction interface and promoting the reduction of internal hematite. Comparatively, the activation energy for CO reduction of hematite was lower than that for H₂. At low temperatures (450–500 °C), CO exhibited a faster reaction rate, while at medium–high temperatures (600 °C), H₂ was more advantageous. Replacing CO with H₂ as the reduction agent is entirely feasible, not only recycling long-stored waste resources but also achieving carbon-free reduction.